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Tensile strength is a crucial mechanical property that governs the initiation and propagation of soil tensile cracks. With the global prevalence of warming effects and extreme climatic events, the recurrent freeze-thaw (F-T) cycles intensify the complex evolutions of soil pore structure and tensile strength in regions with widespread seasonal freezing or permafrost active layers. This study investigates the combined influence of F-T cycles and desiccation on the tensile strength of clayey soils. Specimens with varying compaction water contents (14.5%, 16.5%, and 18.5%) and dry densities (1.5 Mg/m3, 1.6 Mg/m3, and 1.7 Mg/m3) were prepared and subjected to cyclic F-T actions. A direct tensile test apparatus was utilized to measure tensile strength (σ t) along the desiccation path. Additionally, the changes in void ratio (e) and suction (s) during F-T cycles were analyzed to understand the mechanism behind the changes in σ t. Experimental results reveal that as the number of F-T cycles (N) increases, water content (w) declines at a decreasing rate and eventually stabilizes. With increasing N , the tensile displacement at failure and σ t show a pattern of initially decreasing and subsequently rising, with the inflection point typically around 1.5%–2.0% lower than the compaction water content (w 0). Under a few F-T cycles, soils compacted at the optimum water content and on the wet side exhibit higher void ratio and lower suction and σ t compared with dry-side compacted soils. However, this trend reverses with further increasing N. In addition, σ t increases as compaction dry density (ρ d0) rises within all water content ranges, primarily attributed to the significant interparticle cohesion controlled by a dense pore structure. The variation of σ t under F-T and associated desiccation is linked with the microstructural evolution characterized by aggregates, interaggregate pores and water-bridges. It is recommended to compact soils both on the dry side of the optimum water content and at the maximum dry density to enhance the freeze-thaw resistance of earth-works in seasonally frozen regions. • Freeze-thaw cycles with desiccation influence compacted soils' tensile strength. • Variations in void ratio and suction during freeze-thaw cycles govern tensile strength. • Soils with higher compaction water content exhibit greater expansion and shrinkage potential. • Dry-side compacted soils resist freeze-thaw risks better. [ABSTRACT FROM AUTHOR]

The Kahramanmaraş Earthquakes that occurred on 6 February 2023 resulted in extensive structural failures, including damages caused by soil liquefaction. This study focused on investigating the excessive settlements observed in buildings along Ataturk Boulevard in the Golbasi district, with a primary emphasis on the toppling failure of the Kayı Apartment. Field exploration, laboratory testing, and bearing capacity analyses were conducted to understand the failure mechanism. Since the foundation soil of Kayı Apartment predominantly consisted of clay, soil liquefaction alone could not explain the observed failure. Instead, the cyclic softening of clayey soil underground shaking was identified as a significant factor contributing to the damage. As one of the rare case histories documenting a failure caused by cyclic softening, the results of the study also shed light on the excessive displacements observed in nearby buildings with fewer stories that managed to withstand the earthquake without experiencing complete bearing capacity failure. [ABSTRACT FROM AUTHOR]

The cracking of clayey soils in seasonally frozen regions is affected by cyclic drying-wetting and freezing-thawing. Understanding the mechanism governing soil cracking behavior is crucial for the construction and long-term operation of infrastructures and earthworks. In this study, a series of laboratory tests were conducted on clayey soils, including freezing-thawing tests and evaporation tests. The evaporation rate and surface cracks evolution were monitored. The cracking mechanism of soils were analyzed. Results show that both the initially unsaturated and oversaturated soils exhibit an increase in evaporation rate with increasing freeze-thaw (FT) cycles in the early stage. Under the same FT and drying conditions, initially unsaturated soils show a higher evaporation rate in the early stage than oversaturated soils, followed by a lower rate after entering the residual stage. In addition, cyclic FT accelerates the propagation of the number of crack segments, surface crack ratio, and total crack length, but weakens the propagation of average crack width. Moreover, it was found that for initially unsaturated soils, desiccation-induced matrix suction plays a leading role in producing wide, rough, and curved desiccation cracking patterns. While for initially oversaturated soils, freezing-induced ice pressure/cryogenic suction dominates, resulting in short, fine, and straight frost cracking patterns. • Soil desiccation cracking depends on freeze-thaw cycle. • The evaporation rate in the initial stage increases with the number of freeze-thaw cycles. • Initial water contents and the number of freeze-thaw cycles significantly influence the evaporation process. • Evaporation and cracking mechanisms of soil subjected to freeze-thaw and wetting-drying cycles were revealed. [ABSTRACT FROM AUTHOR]

Soil curling caused by drying is a common phenomenon in nature, and it can vary depending on different atmospheric effects. To investigate the coupled effects of temperature and relative humidity on soil curling, a sequence of desiccation experiments were performed by using elongated strip soil samples in the laboratory. The soil curling process is divided into five stages: vertical settlement stage, lateral contraction stage, concave-up curling stage, curling recovery stage and convex-up curling stage. In this study, the soil evaporation characteristic and curvature curves are obtained under different temperature and relative humidity conditions. The findings revealed that a lower relative humidity results in a higher evaporation rate and a smaller maximum concave-up curling curvature for soil samples. Additionally, as the temperature increased, the water content associated with concave curling decreased. The maximum concave-up curling curvature was determined by the transition from the appearance of concave-up curling to the maximum curvature of concave-up curling. Under the coupled effect of temperature and relative humidity, all the water content associated with the occurrence of concave-up curling, maximum concave-up and convex-up curling appearance are reduced with increasing temperature and decreasing relative humidity. As the temperature ranged from 20 °C to 40 °C, the maximum concave-up curling curvature initially decreased and then increased. Conversely, the maximum concave-up curling curvature increased within the relative humidity range of 30% to 45%. • The evolution of soil curlings under various temperature and RH was investigated. • Both concave-up and convex-up curling occur earlier with increasing temperature. • The curvature of the concave-up curling increases with increasing RH. • Water content at the start of curling decreases with temperature rise and RH drop. [ABSTRACT FROM AUTHOR]

This study investigates the cyclic freeze-thaw (F-T) effect on crack patterns in saline clayey soil. Samples with different NaCl concentrations (0 M, 1 M, 2 M, and 3 M) are prepared and subjected to cyclic F-T processes. Each cycle involves freezing the samples at a constant temperature of −20 °C for 24 h and thawing at room temperature (21 °C) for 24 h. Additionally, a parallel experiment is conducted to observe the effects of desiccation at room temperature. The weight and surface crack patterns of the samples are continuously monitored. The image processing technique quantifies crack morphology and determines crack area, surface crack ratio, crack width, crack length, and fractal dimension. The results reveal that as the salt concentration increases, the F-T and desiccation samples exhibit decreased crack area and width. This decrease is attributed to the reduced saturation vapor pressure caused by higher salt concentrations, which slows down water evaporation and delays crack formation. The final crack pattern in the F-T samples is closely linked to the initial pattern of ice crystal formation. Lower salt concentrations result in the formation of larger ice crystals, leading to larger cracks during thawing. In the experiment, where the temperature was above the NaCl eutectic point, only ice crystals were formed, and the salt remained isolated as the salt concentration increased in the unfrozen solution. Conversely, during the freezing process, samples with higher salt concentrations with higher unfrozen solution content experience upward movement of the solution due to temperature gradients and water evaporation. This study provides new insights into understanding the soil water and salt movement and the phenomenon of surface clay soil cracking during the freezing-thawing process. • Investigates the cyclic freeze-thaw (F-T) effect on crack patterns in saline clayey soil. • The image processing technique is applied to quantify soil cracks. • The evaporation rate decreased with increased salt content and delayed the appearance of cracks. • Ice crystal size and volume are significant at low salt concentrations. • The unfrozen water content of saline soil is related to the electric double layer. [ABSTRACT FROM AUTHOR]

With the intensification of global warming, the increasing extreme drought climate has seriously threatened the stability of critical geotechnical infrastructure. This study proposes a novel, eco-friendly approach to improve soil resilience to drought climate. In order to verify the feasibility and durability of the proposed approach, a series of simulated climatic wetting-drying (W D) cycles were carried out using four sets of soil specimens treated with different W-OH (an eco-friendly polymer) concentrations. During this period, the water evaporation history, desiccation cracking process, W D cycle durability and microstructure evolution of soil specimens treated with different W-OH concentrations were investigated. The results reveal that the W-OH modification has a significant suppression effect on the whole process of soil evaporation, which can effectively prolong the soil evaporation time of constant rate stage and falling rate stage. The addition of W-OH not only significantly reduces crack ratio, total crack length, and average crack width, but also slows down the crack growth rate. Compared with untreated soil specimen, the treatment with low concentration of W-OH (2% and 4%) can effectively mitigate the formation of desiccation cracks, while the treatment of higher concentration of W-OH (6%) can directly prevent the occurrence of such cracks. The microstructure analysis results indicate that the W-OH can transform the soil structure into a denser state through two ways of bridging and encapsulation, which significantly increases the migration resistance of pore water and improves soil strength properties. This investigation is expected to improve fundamental understanding of soil-atmosphere interactions under eco-friendly polymer modification and provides insights into the potential application of eco-friendly polymer modification in enhancing soil resilience to extreme drought climate. • A novel eco-friendly approach is proposed to improve soil resilience to drought climate. • W-OH modification can significantly suppress the evaporation and crack formation of clayey soil. • This study reveals the fundamental mechanism of eco-friendly polymer for drought mitigation. [ABSTRACT FROM AUTHOR]

Different types of soil water, such as bound water and capillary water, have distinct effects on the physicochemical and engineering properties of soils, particularly unsaturated clayey soils. Therefore, it is crucial to develop an accurate and physically meaningful experimental method for identifying and quantifying these components. This study pioneers the use of a multi-step kinetic model to identify and quantify different soil water components across a wide range of relative humidity (RH) using thermogravimetric analysis (TGA) data. To validate the determined kinetic parameters (i.e., activation energy, preexponential factor, and reaction model) and the identification and quantification results of soil water components, TGA with multiple heating rates, nitrogen adsorption method, cation exchange capacity measurement, and nuclear magnetic resonance (NMR) were performed on kaolin samples equilibrated under various RH conditions. These experimental results cross-validate the superior performance of the kinetic model in determining soil water components and predicting the thermal desorption behaviors of soil water. Based on the cross-validation results, the soil water components obtained from the kinetic analysis are further identified as tightly-bound, loosely-bound, and capillary water, which exhibit variations consistent with empirical soil water isotherm models. The T 2 cutoff value between bound and capillary water is determined to be 1.79 ms based on TGA and NMR results. The determined thermal kinetic parameters of different soil water components can exhibit their distinct retention mechanisms. The method and results in this study provide a new perspective on identifying different soil water components, as well as understanding the mechanism of soil-water interactions in unsaturated soils. • A method based on thermogravimetric and kinetic analysis is developed to identify and quantify soil water components. • Kinetic model can detect tightly-bound, loosely-bound, and capillary water in kaolin. • Different soil water components exhibit distinct kinetic triplets. • Bound water content increases with humidity regardless of capillary condensation. • NMR T 2 cutoff value between bound and capillary water is 1.79 ms. [ABSTRACT FROM AUTHOR]

The thermal volumetric behaviour of soils plays a critical role in designing energy geostructures, withstanding temperature fluctuations. This study examined, for the first time, the thermal deformation of the partially saturated kaolin clay (matric suction of 0–300 kPa) within the operating temperature range of energy geostructures (8 °C to 45 °C), subjected to varying most recent stress histories (normal stress of 0–400 kPa). The thermal cycle has been applied to samples with identical hydro-mechanical stress histories initiated by heating or cooling from room temperature. Scanning electron microscopy (SEM) tests have been performed to investigate the impact of temperature on soil microstructure as a potential determining mechanism of thermal deformation. The volumetric deformation associated with thermal cycles is analysed, considering the concurrent role of the overconsolidation ratio and the most recent stress. Secondary thermal consolidation (i.e., particle rearrangement) mainly depends on the most recent stress history, occurring only in samples heated beyond the yield limit, with cooling preventing secondary thermal consolidation. A clear relationship between thermal volume change and matric suction was observed, with higher matric suction resulting in less pronounced particle rearrangement. Further SEM analysis revealed that heating beyond the yield limit alters the soil microstructure permanently, with cooling showing no impact. • Thermal behaviour is determined by the most recent stress history, suction, and OCR. • Clayey soils in the loading stage might experience plastic deformations upon heating. • Cooling leads to elastic deformations, regardless of OCR and most recent stress history. • In contrast to cooling, heating permanently changes soil microstructure. • The secondary compression index increases significantly with temperature. [ABSTRACT FROM AUTHOR]

The shrinkage potential of clayey soils dominates their volumetric deformation and microscopic cracking behavior during desiccation processes and has profound practical consequences. To investigate the evolution of desiccation crack network in the compacted clayey soil, we apply a noninvasive approach integrating X-ray computed tomography (CT) and digital image processing technique. Representative geometrical parameters including soil mass area, shrinkage strain, crack ratio, average crack width, total crack length, and crack segment number are acquired from image analysis results to quantify the morphological evolution of desiccation crack patterns. Experimental observations show that cracks initiate at surface, propagate both laterally and downward into the soil body, and transit into massive networks due to coalescence and bifurcation. Quantitative analyses reveal the strong dependence of geometrical parameters on water loss through evaporation. The shrinkage and cracking potential of the clayey soil specimen attenuate with the decreasing water content, which significantly reduces the growing trend of geometrical parameters during the posterior stage of desiccation. The spatial variation of crack network evolutions under drying results from intrinsic soil microstructural heterogeneity and suction capillary-induced local stress intensity. The proposed integrated approach is of great significance to characterize three-dimensional soil desiccation crack patterns and brings new perspectives into the study of the hydro-mechanical behavior of clayey soils. Unlabelled Image • CT was proposed to study soil 3D desiccation cracking with high efficiency • Spatiotemporal evolution of cracks inside soil was characterized by CT • 3D crack network was quantified by integrating CT and image processing technique • 3D crack characterization is significant for accurate evaluating soil properties [ABSTRACT FROM AUTHOR]

Abstract Tensile strength is one of the most important mechanical parameters controlling the development of cracks in soil. However, it is frequently neglected in conventional geotechnical practice, because its magnitude is small and difficult to measure relative to other soil strength parameters. In this paper, a newly designed direct tensile test apparatus was employed to measure the tensile strength of an unsaturated clayey soil. A digital image acquisition and analysis system was developed for tensile strain analysis with the help of Particle Image Velocimetry (PIV) and Digital Image Correlation (DIC) techniques. Six groups of samples were compacted at a dry density of 1.7 Mg/m3 and different water contents (6.5%, 8.5%, 10.5%, 12.5%, 16.5% and 20.5%). Test results show that the tensile strength characteristic curve (tensile strength versus water content) of the compacted unsaturated soil exhibits mono-peak feature. When water content is relatively low, the tensile strength increases with increasing water content and reaches the maximum value at a critical water content of about 9.3%. Then, it declines with further increase in water content. The evolution of tensile strength with water content depends on both suction and microstructure. Based on plotted tensile load-displacement curves, the tensile failure process can be divided into three typical stages which are: stress increasing stage (I), failure developing stage (II) and post-failure stage (III). It is found that the overall tensile failure process presents different patterns controlled by water content. Generally, the failure developing stage (II) lasts longer and the failure ductility is more pronounced when the sample is compacted at higher water content. Using PIV and DIC techniques, the development of displacement direction and strain concentration during tension can be well captured for appreciation of the soil failure mechanism. Based on the strain concentration information, the tensile fracture location and direction can be pre-determined for soil samples. Graphical abstract Unlabelled Image Highlights • New direct tensile test apparatus with image capture system is designed. • Tensile curve shows three typical stages which strongly depend on water content. • TSCC of compacted soil shows mono-peak feature related to both suction and fabric. • Tensile stiffness and failure brittleness decrease with increasing water content. • PIV/DIC is valuable to get deformation and strain concentration characteristics. [ABSTRACT FROM AUTHOR]

Abstract A correlation of creep index (C α) with high performance is highly recommended for soft clay engineering practice. Current empirical correlations are only acceptable for a few clays. This paper aims to propose a robust and effective evolutionary polynomial regression (EPR) model for C α of clay. First, a database covering various clays is formed, in which 120 data are randomly selected for training and the remaining data are used for testing. To avoid overfitting, a novel EPR procedure using a newly enhanced differential evolution (DE) algorithm is proposed with two enhancements: (1) a new fitness function is proposed using the structural risk minimization (SRM) with L 2 regularization that penalizes polynomial complexity, and (2) an adaptive process for selecting the combination of involved variables and size of polynomial terms is incorporated. By comparing the predictive ability, model complexity, robustness and monotonicity, the EPR formulation for C α involving clay content, plasticity index and void ratio with three terms is selected as the optimal model. A parametric study is then conducted to assess the importance of each input in the proposed model. All results demonstrate that the proposed model of C α is simple, robust, and reliable for applications in engineering practice. Highlights • A simple, robust, and reliable EPR model of C α using basic physical properties is proposed. • A fitness function with L 2 regularization and an adaptive selection process are incorporated in the proposed novel EPR. • Four criteria: predictive ability, model complexity, robustness and monotonicity are suggested to select the best model. [ABSTRACT FROM AUTHOR]

Abstract An earthflow/mudflow of a few thousand cubic metres occurred at the toe of the Pont-Bourquin Landslide (PBL, Swiss Alps) in late August 2010. This event was preceded by a drop of about 6% in surface wave velocity (dV/V) determined from ambient vibration records. A seismic monitoring system made of three pairs of sensors was re-installed across the transportation and accumulation zones of the landslide in October 2011, allowing daily relative changes in seismic velocity to be measured for a period of 4.5 years. No similar drop in dV/V was observed during this period, consistently with the lack of significant landslide acceleration or earthflow/mudflow events. However, the three dV/V time series showed periodic and reversible variations in a range − 2% to 2%, suggesting a probable influence of seasonal parameters. They were cross-correlated to daily environmental (temperature and rainfall) and surface displacement time series. In the long term (yearly scale), dV/V variations are mainly driven by the temperature with short delays (30 to 50 days) indicating that the shallow layer (first 2 m) controls the dV/V variations. In the short term, the landslide response to precipitations exhibits a small decrease in dV/V with a delay of 2 to 5 days, in contrast with the displacement rate that almost instantaneously responds to the rainfall. The continuous seismic monitoring of PBL using ambient vibrations has proved to be a robust method for getting information at depth, with no data gap even during winters. The seasonal reversible seismic velocity variations turned out to be in a range lower than the drop observed before the August 2010 earthflow/mudflow, highlighting the interest of incorporating the dV/V technique in monitoring systems. [ABSTRACT FROM AUTHOR]

Abstract The objective of this research was to investigate the effect of varying density and water content on the strength and deformation behavior of a low, a medium, and a high plasticity clay, as well as to determine the water content at which transition from brittle to plastic behavior occurs for each clay type. We used the standard Proctor test to compact six samples each of low, medium, and high plasticity clays to establish the compaction curves. We failed the compacted samples under unconfined compression and visually inspected their brittle versus plastic behavior during compression. Additionally, we performed direct shear tests on three samples of each type of clay that were compacted at different water contents. We used the stress-strain plots from both tests to determine the transition water content between brittle and plastic behavior for each type of clay. The results showed that unconfined compressive strength first increased and then decreased with increasing water content, with the change in trend occurring within 5% of OWC for each type of clay. The high plasticity clay had the highest cohesion while the low plasticity clay had the highest friction angle. The transition between brittle and plastic behavior for the low, medium, and high plasticity clays occurred between 19–20%, 27–29%, and 30–32% water contents, respectively. These results demonstrate that, in areas where clay embankments may be subject to cracking due to seismic activity or excessive differential settlement, they should be compacted on the wet side of the transition water content marking the boundary between brittle and plastic deformation. Highlights • We evaluated the effect of density and water content on the strength and deformation behavior for three different clays. • We defined the water content at which transition from brittle to plastic behavior occurs for clay soils. • We established the relationship between transition water content and plasticity index. • We propose designing clay structures on the wet side of transition water content for flexibility and integrity. [ABSTRACT FROM AUTHOR]

This paper presents the influence of temperature on the residual strength by analyzing shearing tests carried out in a temperature- and velocity-controlled ring shear apparatus. Temperature was applied in steps of cooling and heating ranging between 6 °C and 50 °C at a constant shearing velocity of 0.442 mm/min. Additional tests include the evaluation of the strength at 0.890 mm/min before and after the imposed temperature change. Six basic soil types characterized by different mineralogy, grain size and plasticity, as well as, mixture soils having different proportions of sand and clay, are evaluated and the results are interpreted in terms of their properties. The experimental results reveal that the temperature effect becomes relevant when fine particles and plasticity increase being negligible in the case of the sandy soil. Shear strength reacts immediately to temperature changes and a new residual strength establishes soon. The temperature effect is symmetric. An increase in temperature leads to a decrease in strength, and an equal and opposite trend is observed when temperature decreases. The magnitude of the strength variation is significant in clayey soils. For the case of high plasticity soils, the residual friction angle variation observed during cooling and heating (±50 °C) is around 2°. The strain rate effect evaluated in a smaller number of tests indicated a strain rate strengthening in all the materials tested except for the case of the sandy soil, which also was not reactive to temperature changes. The experiments are calibrated with a velocity, state, and temperature-dependent friction model. • Influence of temperature on residual shear strength have been characterized. • Heating leads to decrease in friction and cooling leads to an increase for high shearing rates. • Relevance of residual friction change with respect of temperature correlates with the soil plasticity. • No effect of temperature was measured for the clean sand tested. • The friction constitutive model developed by Chester (1994) can reproduce the tests performed. [ABSTRACT FROM AUTHOR]

Temperature has a significant effect on the bulk electrical conductivity (σ b) of soils because fluid properties, such as viscosity, which affect σ b , are functions of temperature. The governing mechanisms between pore water conduction (K w) and surface conduction (K s) in terms of temperature dependency are completely different. Thus, soils with a higher relevance of K s can exhibit a different temperature dependency of σ b when compared to K w -dominant soils. Therefore, in this study, we aim to determine the temperature compensation parameter (α) of σ b of soils as a function of the ratio of K s to σ b. Silica sand and kaolin clay were selected as the K w - and K s -dominant materials, respectively. The electrical conductivity of tested materials with varying initial porosities and pore fluid concentrations was measured as a function of temperature in the range of 10 °C to 50 °C. The results of this study showed that K w -dominant soils have an α value of approximately 2%/°C, whereas the α value of K s -dominant soils ranges from 1%/°C to 2%/°C as a function of porosity and pore water conductivity. The experimentally determined α value was compared with the α value calculated from the theoretical series–parallel model. Additionally, an empirical model to capture the α value of soils with varying magnitudes of K s and K w was suggested. Finally, the suggested model was verified using the results of Korean residual soil (i.e., clayey sand) and two other clayey soils (i.e., kaolin and ca-bentonite clays). • Electrical conductivity (EC) of sand and clay was measured according to temperature. • Experimental results were compared with the theoretical series-parallel model. • Surface conduction-dominant soils show different temperature dependency of EC. • A model for temperature compensation parameter is newly suggested. • The suggested model accuracy was verified using the data of other three soils. [ABSTRACT FROM AUTHOR]

A snowpack is known to affect landslide stability as the snow loading changes. Furthermore, the snowpack can have effects on the hydrological behavior in the landslide mass. To clarify the response of pore water pressure to snow loading, continuous field-based monitoring of hydraulic and meteorological factors in landslides was conducted for a deposit of extremely low-permeability “quick clay” in Mid-Norway. The pore water pressure increased during every snow-covered period. The pressure exhibited little response to meltwater and/or rain, but corresponded closely to changes in snow accumulation. The increase in pore water pressure during the snow-covered period was considered to be excess pore water pressure generated by undrained snow loading on the extremely low-permeability quick clay. The pore water pressure displayed a positive linear relation with the snow load, and the ratio of the increase in the pore water pressure to the snow load ( ru snow ) was 0.49–0.53. These values show that approximately half of the snow load contributed to the excess pore water pressure. Continuous field-based monitoring was also conducted for another landslide in relatively high-permeability deposits in Japan, where the pore water pressure showed a relatively low ru snow of about 0.15 and a different timing of the pressure peak. This comparative result indicates that the response characteristics of pore water pressure to the snow loading are strongly affected by the permeability of the landslide mass. Although the excess pore water pressure generated by the snow load theoretically had a negative effect on the slope stability, the value of excess pore water pressure at the monitored landslide was relatively too small to affect its stability. [ABSTRACT FROM AUTHOR]

Naturally deposited clays are generally K 0 consolidated. In some cases such as embankment construction and foundation pit excavation, the loading or unloading will lead to the re-consolidation of clays, which can be simulated by a simplified consolidation stress path with a certain ratio of vertical to horizontal consolidation stresses. In this study, a series of triaxial shear tests was conducted on a reconstituted Wenzhou clay, to investigate the effects of consolidation stress paths on the stress-strain, pore water pressure-strain, and effective stress path behaviors of overconsolidated samples. Based on the test results, the shear strength and pore water pressure coefficient at failure are found to grow and reduce linearly with the increase of the ratio of vertical to horizontal consolidation stresses, respectively. More strain softening and shear dilation are observed for the anisotropically consolidated samples compared to isotropically consolidated ones. The slope of failure line is approximately 1.25 for all specimens tested in this study. [ABSTRACT FROM AUTHOR]

Using a ring shear apparatus, the variation in the residual strength characteristics of 21 groups of saturated clay soil samples were experimentally investigated, and the results are discussed in this paper. The clay soil samples had different plasticity indexes under 10 different consolidation conditions. The influences of shear rate, over-consolidation ratio, plasticity index, and multi-stage shear mode on the residual strength were investigated. New shear strength variation trend data and a corresponding equation for shear strength calculations as a function of plasticity index of soils under large deformation are presented. The experimental results indicate that 1) both the shear rate and over-consolidation ratio have a negligible influence on the residual strength; 2) the residual strength gradually decreases as the plasticity index increases; 3) the residual strength shows a significant nonlinearity with the normal stress when subjected to low- or high-levels of normal stress; 4) the internal friction angle of drained clay decreases as the plasticity index increases under large deformation. Finally, a formula is proposed to describe the relationship between the residual inner friction angle and plasticity index. [ABSTRACT FROM AUTHOR]

Under traffic loading, the soil elements in subgrade are subjected to a cyclic cardioid-shaped stress path in the 2 τ vh ~ ( σ v − σ h ) stress plane. This significantly differs from the conventional stress paths that have been simulated using the cyclic triaxial and simple shear apparatuses, as widely reported in the literature. To date, the influence of shear stress level on cyclic deformation behaviour of intact soft clay subjected to cyclic traffic loading were rarely considered in the existing experimental investigation. For this reason, a series of cyclic hollow cylinder experiments that mimic cardioid-shaped stress paths are carried out on intact samples of Wenzhou soft clay. A wide range of vertical stress levels combined with different shear stress levels (i.e., different cardioid-shaped stress paths) are simulated in the experiments. The results show that the shear stress level significantly influences the cyclic straining and exacerbates the potential of cyclic shear failure. The difference of cyclic tests with variable shear stress level increases as the vertical cyclic stress ratio value increases. Based on the test results, an allowable cyclic stress ratio is determined to be about 0.22, which may serve as the upper bound limit of cyclic traffic loadings on soft clayey deposit. For the hollow cylinder specimens used in this study, a resilient axial strain of 3% could be a proper failure criteria value. A simplified permanent strain model that considers shear stress is proposed for the deformation behaviour of soft clay under cyclic traffic loading. [ABSTRACT FROM AUTHOR]

The purpose of this study is to develop an easy procedure to diagnose the cyclic behavior of fine-grained soils, leading to liquefaction. There are approaches to this problem with reference to liquid limit (w L), plasticity index (PI), clay content, (C%), in-situ water content compared to the liquid limit (w n /w L), average grain size (D 50), and liquidity index (I L). Previous research has indicated that fine-grained soils defined as "sand-like" are prone to liquefaction. There is consensus that liquefiable silty soils have "sand like" characteristics. In the transition from sandy to clayey, it is generally accepted that it would be appropriate to make a judgment by making use of mechanical testing and that clayey soils do not liquefy. This paper presents the results of dynamic triaxial shear testing (CTX), where excess pore water pressures and axial strains are evaluated compared to the physical properties to reach the threshold for cyclic failure. Samples of undisturbed soil procured from different locations of the city of Adapazarı, Turkey, were subjected to CTX testing. The results were interpreted in the light of the physical properties to arrive at a judgment of cyclic failure. Being able to identify a liquefaction prone fine grained soil by merely measuring a few physical properties without resorting to arduous cyclic testing would be an advantage to the practising engineer. This however necessitates the elimination of the ' gray zone' for which most researchers recommended the use of cyclic testing. The main finding of this study is that samples reaching double strain amplitude (DSA) of <5% in the CTX test contain no sand and have a clay content of 20% or more. An attempt to establish a relationship between sensitivity to cyclic loading and physical properties is also made. • Seismic liquefaction in fine-grained fluvial soil. • Relationships between physical properties and cyclic triaxial test results of fine-grained soils. • Revision in the limit values of physical properties of soils for evaluation of liquefiability. [ABSTRACT FROM AUTHOR]

Shallow landslides are widespread in different geological contexts and generally occur as multiple events over large areas. When these phenomena involve fine-grained soils, they may cause serious consequences—in terms of environmental and property damages—and thus their spatial forecasting becomes a relevant issue for land use planning and design purposes. The existing literature provides several methods for landslide susceptibility assessment, categorized in qualitative and quantitative methods. When dealing with analyses at large scale (1:5000), quantitative methods are generally preferred. In this paper, landslide susceptibility maps are produced for a study area prone to shallow landsliding, located in Catanzaro (southern Italy). To this aim, two quantitative methods are implemented: the statistical “information value method” and the deterministic “TRIGRS model.” The two approaches are compared by means of two indicators of the grade of correctness of the landslide susceptibility maps: the area under curve of the ROC curve, AUC, and the overestimation index, OI. The results of the analyses in terms of AUC values demonstrate the effectiveness and consistency of both methods in performing the susceptibility mapping of the study area. When the OI values are considered, the results provided by the deterministic model are slightly better than the ones resulting from the statistical analysis. This does not come as a surprise for the case study at hand and it can be ascribed to the availability, within the study area, of: a reliable database of soil properties, and an in-depth knowledge of the behaviour of the considered landslides. [ABSTRACT FROM AUTHOR]

Cracks are ubiquitous in soils and can provide preferential pathways for rainfall infiltration and contaminant transport. The soil-water characteristic curve (SWCC) for a cracked soil is required when conducting seepage analysis. However, measuring SWCCs for cracked soils is difficult due to two reasons: (1) The presence of cracks leads to a significant change in the water content at extremely low suctions that cannot be controlled accurately; (2) The full development of cracks generally requires a large apparatus to accommodate the representative elementary volume of a crack network. This study aims to develop an experimental method to measure the SWCC for a silty clay with desiccation cracks. A large apparatus, 350 mm in diameter and 280 mm in height, was developed, which is capable of controlling extremely low suctions (< 0.01 kPa) at an accuracy of 0.005 kPa and accommodating a clay sample with fully developed crack networks. The crack development in the soil sample was observed, providing necessary parameters for the prediction of SWCCs based on a theoretical model for cracked soils. The drying and wetting SWCCs for a silty clay with desiccation cracks were measured in the suction range from 0.01 kPa to 300 kPa, and compared with the SWCCs predicted using the theoretical model. [ABSTRACT FROM AUTHOR]

Highly compressible clayey and peaty (soft) soils may expose structures (e.g. buildings) and infrastructures (e.g. roads and embankments) resting on them to absolute/differential settlements. These latter, with passing of time, can induce damages whose level of severity depends on several factors such as: the spatial distribution of the thickness pertaining to soft soil layers; the groundwater regime; the characteristics of the exposed structures and infrastructures along with their state of maintenance. The analysis of damages and the resulting management of the built-up environment usually require high costs due to the amount of data necessary for setting up reliable forecasting models as well as for defining the most suitable restoration works. This paper presents a multi-scale procedure tailored to analyze the settlement-induced building damage. The selected case study deals with an urban area in The Netherlands where, at medium scale, the role of soft soils in predisposing the occurrence of ground surface settlements is first investigated. Then, at large scale the relationship between cause (i.e. settlements) and effects (i.e. damage) is analyzed for building aggregates via the combination of high-resolution advanced differential interferometric synthetic aperture radar (DInSAR) and in-situ damage survey data. Finally, as main novelty of the proposed multi-scale procedure, both the above datasets are used to generate, at detailed scale, empirical fragility curves for single buildings that, once further validated, could be valuably adopted for damage forecasting purposes in similar urban areas. [ABSTRACT FROM AUTHOR]

It is of great significance to study the nonlinear evolution law of the small strain shear modulus of expansive soil for analyzing the deformation behavior of soil or geotechnical structure and the seismic site response. Existing studies rarely discuss the damage mechanism of the small strain shear modulus of expansive soil, and the corresponding damage model describing the small strain stiffness decay law is lacking. In this study, a series of resonance column tests were carried out to investigate the effects of mean effective stress, loading and unloading stress paths and vibration cycles on the nonlinear decay law of small strain shear modulus of expansive soil, and the damage mechanism was discussed in detail. Subsequently, a novel damage model describing the decay law of small strain shear modulus of expansive soil was proposed and verified by the results of resonant column tests. The results show that the decay process of the small strain shear modulus with the shear strain is essentially the damage of the soil structure, which can be characterized mathematically by damage model. The mean effective stress and the larger overconsolidation ratio caused by the unloading process can inhibit the damage, while the vibration cycles can cause small reduction in small strain shear modulus and promote the damage. The proposed damage model with clear physical meaning can well describe the evolution law of small strain shear modulus of expansive soil, and has higher accuracy than the traditional model. • The effects of various factors on the small strain shear modulus of expansive soil are investigated. • The damage mechanism of small strain shear modulus of expansive soil is analyzed. • A novel damage model describing the decay law of small strain shear modulus of expansive soil is proposed. [ABSTRACT FROM AUTHOR]

The thermal effects on geomaterials, especially on clayey soils are getting increasing concerns in many geotechnical applications. To study the effects of temperature on the stress-strain behaviour of Hong Kong marine deposits (HKMD), a series of temperature-controlled experiments were carried out. Oedometer and constant-rate-of-strain consolidation tests under temperatures from 10 °C to 60 °C were conducted on both intact and reconstituted HKMD considering different temperatures and stress paths. The effects of temperature history on the compression curves, thermally induced strain, and the characteristics of creep are revealed and discussed. The concept of virgin heating is proposed for interpreting the thermal plastic deformation. With increasing temperature, the creep coefficient is found to decrease while the creep strain rate increases. Consolidated undrained triaxial tests were performed on intact and reconstituted HKMD under different strain rates and temperature conditions. Under constant temperature, the undrained shear strength of HKMD is not significantly influenced by temperature. In triaxial tests subjected to step-changed temperature, the undrained heating causes a significant reduction of effective stress and rise of porewater pressure in HKMD. Finally, microscopic investigations with mercury intrusion porosimeter and scanning electron microscope are presented and discussed in this paper. It is found that the micropores of HKMD are evolutional with temperature. • Temperature and time dependent behaviour of HKMD is investigated. • Compression curves and shear strength are related to temperature conditions. • Thermal elastic visco-plastic correlations are developed from the test results. • Micro-pores are influenced by temperature according to SEM and MIP tests. • The study will be useful for understanding the thermal effects on clayey soils. [ABSTRACT FROM AUTHOR]

Desiccation cracks initiate and propagate during the drying process and healing occurs during the wetting process. However, most of the previous studies only paid attention to the drying-induced crack propagation and the wetting-induced healing behaviour was always neglected. In this paper, a series of wetting tests were conducted on cracked soils under different wetting rates. The crack pattern evolution during wetting was recorded and quantitatively analysed. The results show that the narrow and short secondary and tertiary cracks heal earlier than the long and wide primary cracks during wetting. With the elapsed wetting time, the surface crack ratio and average crack width decrease slowly at first, then rapidly decrease and eventually stabilise. However, at the early stage of wetting, the total crack length almost remains constant. The healing of desiccation cracks in clayey soils is mainly attributed by two factors: wetting-induced swelling and disintegration. Furthermore, the healing degree of desiccation cracks become higher with increasing wetting rate. The healing of desiccation cracks with a lower wetting rate is mainly due to the wetting-induced swelling of soils. However, that with a higher wetting rate is dominated by both swelling and disintegration. • The evolution of soil cracks subjected to various wetting rates was investigated. • The healing degree of desiccation cracks became higher with increasing wetting rate. • Wetting-induced crack healing at a low wetting rate is mainly due to soil swelling. • Both swelling and disintegration dominate the crack healing at a higher wetting rate. [ABSTRACT FROM AUTHOR]

In Niigata, Japan, many landslides have occurred in Tertiary rocks. Although most of these landslides were slow-moving, some underwent catastrophic failure, and different types of landslides sometimes occurred nearby under almost identical geological and hydrological conditions, but their mechanisms remain unclear. This study introduces a landslide triggered by Typhoon Hagibis in 2019 in an area in Niigata prone to landslide disasters. The landslide was small in scale, but the displaced materials were fluidized and deposited on a flat field at the toe of the slope after a long runout. To unravel this landslide's initiation and movement mechanisms, we conducted ring shear tests on the samples (clayey soils) taken from the landslide source area to examine their shear behaviors under both undrained and naturally drained conditions. Our results of undrained shear tests showed that shearing of the saturated landslide material can develop high pore-water pressure, lowering the shear resistance and elevating the mobility of the landslide. The results of shear tests under naturally drained conditions at different shear displacement rates (V) revealed that landslide materials behave rate-weakening at low and rate-strengthening at high rates, respectively. Further, it was found that during continuous shearing, a sudden change in V results in a sharp but temporal change in the mobilized shear strength. Different accelerations through which the shear rate was increased to a given V also result in different mobilized peak shear strengths. Our results indicate that the different landsliding phenomena occurring in the same area might be regulated by the diverse shear behaviors of the landslide materials involved in the sliding: contractive behavior may result in catastrophic failure, while the shear rate- and state-dependent shear behavior of the landslide material regulates the slow landsliding phenomena. Our results provide new insights for better understanding and predicting different landsliding phenomena within the same geological settings. • Kamoda landslide is a small fluidized one that occurred on clayey materials. • The landslide materials showed great reduction in shear resistance under undrained condition. • The residual shear strength of the landslide material exhibits diverse tendencies with shear rate. • These diverse shear behaviors provide insights toward understanding different landsliding phenomena in the same area. [ABSTRACT FROM AUTHOR]

This paper presents the results of a centrifuge study in which swell of an expansive clay profile was induced in the centrifuge. A factor which has previously hindered such research is the time required to induce significant swell in-flight, within a reasonable time frame. In this study the use of an artificially fissured fabric together with geotextile layers allowed for a significant magnitude of swell to be achieved within a matter of hours. Measurements of matric suction and water content throughout testing highlight the potential difficulties associated with such measurements in a fissured profile. The suction in clay along the interfaces of fissures can be significantly reduced almost instantaneously with the ingress of water. In contrast, elements closer to the centre of intact masses may take significantly longer to respond, illustrating the role of the dual processes (and hence dual scaling laws) of moisture ingress along fissures, followed by diffusion associated with swelling of the clay. A comparison of the magnitude of swell induced in this centrifuge model with that of conventional oedometer swell tests indicated gross overpredictions from the oedometer testing. In this comparison, the severe limitation of oedometer tests reducing a sample to a point of zero suction is emphasised. Finally, it is illustrated how an understanding of the rate of swell throughout an expansive profile can provide insights into the validity of the predictions from oedometer swell tests. • A centrifuge study of an artificially fissured expansive clay profile is presented. • A significant magnitude of swell was achieved in-flight in a short timeframe. • Suction, water content and penetration resistance were measured in-flight. • Swell in the model was compared with results of conventional oedometer tests. • Limitations of conventional oedometer testing are presented. [ABSTRACT FROM AUTHOR]

The influence of soil structure on the volume change behavior of clay soils has been often studied with reference to intrinsic properties and normalization of reconstituted clays. However, to date, there has been relatively little research conducted on the normalizing behavior of naturally and artificially structured clays. In this paper, the yielding modes and normalization, by introducing the void index, are clarified for the one-dimensional compression of natural Finnish clays. Based on 24 samples with different cement contents and curing times, two novel approaches are proposed to normalize the post-yielding range of artificially structured clays. Laboratory results show that approach I, i.e., linear extrapolation of the post-yielding line in a log-log graph, can normalize well the compression behavior of artificially structured clays. However, the normalized curves of the void index vs. the effective stress in the semi-log plot deviate from Burland's intrinsic compression line (ICL) at very high consolidation stresses. To address this issue, a novel formulation of the ICL is deduced from laboratory data for artificially structured clays. Approach II, i.e., redefinition of the constants of compressibility to modify the void index, results in closer convergence of the normalized compression curves. The normalized curves by the modified void index agree well with the proposed intrinsic compression line for artificially structured clays (SICL). Finally, the generalization of Burland's ICL can redefine the intrinsic formulations corresponding to different levels of the yielding stress by modifying the void index. [ABSTRACT FROM AUTHOR]

The residual strength of sliding basal soils plays a pivotal role not only in the movement of bedding landslides controlled by clay-rich interlayers but also in remobilized granular deposits. Many studies have focused on better understanding the residual shear behaviors of clayey and granular soils under relatively low shear rates. However, the residual strength varies with various clay fractions for clayey soils and fine-size fractions for granular soils, as well as shear rates (especially in fast ranges) need further examined. In the present research, results of a low- to high-rate continuous ring shear test on a clayey soil and three granular soils at the shear rates ranging from 0.5 to 50.0 mm/s were reported. The clayey soil was remolded from the shear zone soil of a bedding landslide controlled by a clay-rich interlayer with main minerals of illite-smectite, and the granular soils included two silica sands and one mixture of silica sand with fine granite residual soil particles. The results show that saturated clayey soil has an obvious positive shear rate effect on its residual strength after a certain shear rate; the mechanism is the transformation of shear mode, i.e., from sliding shearing to turbulent shearing with the increasing of shear rate. The high clay fraction may promote this transformation of shear mode. In addition, the critical shear rate of the clayey soil that has a positive shear rate dependency of the residual strength (i.e., rate-strengthening) is related to the clay fraction, i.e., a smaller critical shear rate appears in the clayey soil with higher clay fraction. The residual strength of saturated granular soils with different fine-size fractions do not show any shear rate-dependent, while the fine-size fraction affects the residual strength both in drained and undrained conditions; that is, the higher the fine-size fraction is, the lower the residual strength is. Moreover, the neutral shear rate effect of granular soils in this study may be related to the low normal stress and low shear rate range. The authors believe that, results such as those obtained in this work, may be useful for developing a more suitable constitutive model to better understand the postfailure motion (or reactivation kinematics) of bedding landslides controlled by clay-rich interlayers, as well as rock avalanche deposits remobilized by heavy rainfall. • Shear rate effect on the residual strength of clayey soil rich in illite-smectite minerals has been investigated. • The critical shear rate of the clayey soil that shows rate strengthening is related to the clay fraction. • Neutral shear rate effect on the residual strength was found in granular soils with different fine-size fractions. • Shear rate effect on the residual strength can provide insights for better understanding landslide motion. [ABSTRACT FROM AUTHOR]

It is essential and important for engineering design and maintenance to systematically investigate the physical–mechanical properties of frozen soils. At present, a series of tests have been carried out on frozen silty clay based on improved testing techniques. The results indicate that brittle and plastic failures occur for frozen silty clay under low and high confining pressures, respectively, and strengthening and weakening effects from the water content and confining pressure on the frozen strength are also observed. With the increase in confining pressure or water content, the compressive strength first increases to a maximum and then begins to decrease, and at the same time, the pressure fracturing of pore ice is gradually aggravated. Under the combination of confining pressure and water content, the microstructure evolution of frozen silty clay includes the soil particles or cementing soil crushed and reclotted, the initial soil skeleton destroyed, the pore ice fractured and melted, and the growth of microcracks, which mainly depends on the amount of water content and axial and radial loads. The tearing of cementing soil or sliding of soil particles causes drum-shaped deformation of the sample. • Based on the improved testing techniques, a series of triaxial compression tests were carried out on frozen silty clay. • The mechanical behaviors are investigated for the typical range of water content. • Microstructure evolution is analyzed according to the X-ray CT scanning and Cryo-SEM images. [ABSTRACT FROM AUTHOR]

Many uncertainties exist in geotechnical engineering. Spatial variability is a type of uncertainty that has received more and more attention in recent years. Scale of fluctuation (SOF) is a parameter for measuring the spatial variability of soil properties. To investigate the proper method for computing the SOF of soil properties, two types of methods (auto-correlation function method (ACM), and variance reduction method (VRM)) are compared theoretically and numerically, and the influence factors, such as number of data points involved in curve fitting for the auto-correlation function (ACF) or variance reduction function (VRF) and sampling interval, on the SOFs are analyzed. To improve the accuracy of curve fitting for the ACF or VRF, a weighted least squares (WLS) method is proposed, in which the weight of each data point of sample function decreases with the increasing of lag distance between two points in a random field. Three types of soil parameters, including the CPT, the physical, and the hydraulic parameters, are tested by in-situ and laboratory tests, and the SOFs of these parameters are computed. Computation of the SOFs proves that the VRM combined with the suggested WLS is a good method for computing the SOFs of soil properties. Comparison of the SOFs shows that there are negligible differences among the three types of soil parameters of clay layers in Hefei, which is further proved by the Wilcoxon test from a statistical point of view. By using the VRM combine with WLS, the SOFs of clay are computed based on 509 sets of CPT data from 34 sites in Hefei. The statistics of SOFs can give a reference for the selection of SOF for reliability analysis or reliability-based design of geo-structures with spatial variability. • The auto-correlation function method and variance reduction function method (VRM) are compared thoroughly. • A weighted least squares method (WLS) is proposed in which the weight decreases with the lag distance. • The VRM combined with WLS is suggested to compute the SOFs of soil properties. • Spatial variability is an inherent property of clays. [ABSTRACT FROM AUTHOR]

Extensive research has been conducted to establish empirical equations between the resilient modulus ( M r ) and other testing parameters. Despite an increase in the correlation studies, less effort has been made in developing reliable correlations to predict the resilient modulus using cone penetration testing indices. In this research, an attempt has been made to propose new correlations between M r and the piezocone penetration test (CPTU) indices of clayey soils by using a multivariate normal distribution approach. A database collected from 16 different sites in Jiangsu province, China, was presented to achieve this study. The database contains 124 sets of resilient modulus ( M r ) values at the in-situ stress condition, cone tip resistance ( q c ), sleeve frictional resistance ( f s ), moisture ( w ) and dry density ( γ d ). Four major procedures including the data transformation, correlation analysis, Bayesian updating, and back transformation were applied to derive the correlations among M r and other indices in the framework of the multivariate normal distribution model. First, each individual parameter was converted to a standard normal variable using the Box-Cox transformation. Later, the correlation matrix of the multivariate normal distribution model was estimated using the product-moment (Pearson) correlation coefficients between all pairwise data. The uncertainties associated with the Box-Cox transformation parameters and the correlation coefficients were evaluated using a bootstrapping technique. Furthermore, the formulas for predicting the posterior mean, coefficient of variation (COV), median, and 95% confidence interval (CI) of M r conditional on different indices were derived using Bayesian updating combined with back transformation. A new approach based on the Taylor-series expansion was proposed to approximate these statistics in this study. Comparisons between the correlations derived from the multivariate model, the database of Jiangsu clay, and the data collected from the literature demonstrated that the model should be capable of the correlations among the five indices, but it might be slightly biased when applied in the global dataset. This research highlighted a new method to establish the reliable correlations to update M r using different testing indices. [ABSTRACT FROM AUTHOR]

Under extreme climate conditions, clayey soils experience not only seasonal drying and wetting but also frequent freezing and thawing. Cracking would also occur in clayey soils under freeze–thaw cycles, but now less academic attention has been paid on this issue. In this study, a series of laboratory tests were conducted on a clayey soil to investigate the cracking behaviors under freeze–thaw cycles. Water loss, surface crack initiation and propagation processes were monitored after each freeze–thaw cycle. By using the image processing technique, the crack patterns were described and then quantitatively analyzed on the basis of the fractal dimension concept. It was found that for the tested clayey soil subjected to freeze–thaw cycles, the surface crack pattern slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi-hexagonal one; and the water loss, closely related to the sample thickness, plays a significant role in the process of the clay cracking; Upon cyclic freezing–thawing, the fractal dimension is well correlated to the surface crack ratio in a logarithmic equation. Fractal dimension concept can offer a new perspective on the quantitative understanding of cracking initiation and propagation in clayey soils under freeze–thaw cycles. [ABSTRACT FROM AUTHOR]

The use of non-conventional additives in soil stabilisation has increased significantly in recent years. Nevertheless, the effectiveness of alternative additives, which can be determined by the impact promoted on the pH of the soils, could be limited due to insufficient time for the pozzolanic reaction (associated with a quick decrease of pH). Thereby, this paper focuses on the study of the efficacy of using different dosages of innovative industrial wastes in both clayey and marly soils. The additives studied were dolomitic lime (from residual quarry sludges), biomass fly ash, steel slag (from Electric Arc Furnace), and conventional lime which was used as a control. The effectiveness of these additives was evaluated by measuring the evolution of pH, carbonate content and particle size at 0, 7, 14 and 28 days. Results showed that residual dolomitic lime can be as effective as commercial lime in soil stabilisation, while the biomass ash used in this work was found to be the least effective additive. All additives used in this study led to greater changes in soil properties for clayey samples. [ABSTRACT FROM AUTHOR]

This paper reports on experimental results that show how variations in pore fluid composition can induce time dependent shear displacements in clay soils under constant effective stresses. The experimentation has been carried out on a bentonite, mainly composed of Na-montmorillonite. The clay, reconstituted with distilled water and with NaCl solutions at various concentrations, was first sheared to the residual state under constant displacement rate. The residual friction angle was found to increase greatly with the pore solution concentration. Then, the solution-saturated specimens were submitted to shear tests under constant driving shear stresses lower than the residual strength obtained with the salt solutions and higher than the residual strength obtained with distilled water. As a consequence, shear displacements with decreasing rate occurred. On the subsequent exposure to distilled water, the displacement rate increased progressively and the specimens re-experimented failure. The observed behaviour has been attributed to the loss of strength caused by the decrease in pore solution concentration following exposure to water. During this transient phase, shear strength and average pore ion concentration on the slip surface seemed to be related by the same relation as that evaluated in the absence of chemical gradients. [ABSTRACT FROM AUTHOR]

The overconsolidation ratio (OCR) was determined through three different series of consolidation tests on the samples, which were retrieved using an oil-operated fixed-piston sampler at two sites in a deltaic deposit. The constant rate of strain (CRS) consolidation test and the end-of-primary (IL EOP ) consolidation tests proved to be superior tests with higher quality of samples and produced close OCR values. The CRS and IL EOP tests provided OCR values close to those of the field measurements, whereas the conventional 1D consolidation (IL 24 ) test underestimates the values. The OCR values obtained from the CRS and IL EOP tests lie between the upper and lower bounds of existing empirical formulas, whereas those from the IL 24 test belong to the lower bound. Empirical formulas that were suited for both sites were newly developed through the correlations between the results of the two consolidation tests and three field tests. The empirical formulas, which have been developed based on the correlation coefficients, are appropriate for predicting the OCR values for a site where the great majority of data are given. This trend is more pronounced in the predictions obtained from the piezocone and the field vane tests than the predictions from the flat dilatometer test. [ABSTRACT FROM AUTHOR]

Boom Clay has been considered as a potential host-rock for the geological radioactive waste disposal in Belgium. In this context, it is important to well understand the thermo-hydro-mechanical behaviour of this clay around the disposal galleries. In this study, the effect of excavation damage on the thermo-hydro-mechanical properties of natural Boom Clay around the Connecting gallery (excavated in 2002) in the Mol underground Research Laboratory HADES (High-Activity Disposal Experimental Site) was investigated. Several samples taken from a horizontal borehole drilled in July 2012 were tested. The thermal conductivity in three different orientations (perpendicular, parallel, and 45° to the bedding plane) was measured using the needle probe method. The results show a cross-anisotropy of natural Boom Clay and an impact of the excavation damage on the thermal property of samples near the gallery. To further investigate the anisotropy behaviour, bender element tests were carried out under unconfined conditions to determine the small-strain shear modulus also in three different orientations. The obtained results confirm the anisotropic behaviour of Boom Clay. Moreover, the evolution of small-strain shear modulus with the distance from the gallery axis ( r ) was found to be similar to that of thermal conductivity: the values in the zone near the gallery are lower than those in the far field. From these experimental data, an extent of the excavation damaged zone (EDZ) of 4 m from the connecting gallery axis was determined. Further investigations on the microstructure of several samples taken at different distances r by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) methods were carried out. Macro-pores of diameter ≥ 5 μm were identified in the samples near the gallery. The identified macro-pores were related to the effect of excavation damage, and a damage variable was thus defined, allowing a damage model to be developed. The values of the two model parameters have been determined from the observed relationship between macro-porosity and thermal conductivity. Comparisons between the predicted and experimental results in terms of small strain shear modulus and hydraulic conductivity show a reasonable agreement. [ABSTRACT FROM AUTHOR]

This article presents results describing the in situ behavior of clay soils (Pleistocene Brach formation) regarding shrinkage and swelling; an experimental site was established. Different types of sensors were used to continuously measure the movements of the clay bed-rock and variations in the temperature and water content of the soil. These parameters were correlated with annual climatic variations as measured at an on-site meteorological station. The results obtained thus far represent five cycles of drought-rewetting, thus enabling a medium-term study of the shrinkage-swelling of a clay soil over time. A cumulative effect of shrinkage over several cycles was observed with non-negligible variations of water content to a depth of 3 m. Almost 1 cm of cumulative shrinkage occurred over the first three cycles of a 2-meter-thick clay layer. The last two cycles were marked by a stabilization of the swelling. By determining the accumulated soil hydric condition over time, we discovered a correlation between this parameter and the periods of shrinkage-swelling. The accumulated hydric condition, as defined in this article, is a good indicator of the behavior of soil under shrinkage and swelling. [ABSTRACT FROM AUTHOR]

A 31 m high excavation located at Niterói/RJ in residual soil from gneissmigmatite with high N SPT (> 40) was performed for a building construction. Two levels of anchored walls were considered in order to guarantee stability. When the construction of the upper wall was almost completed, a crack parallel to the direction of the wall formed in the hilltop. It was decided that the construction works would cease in order to perform additional studies. The presence of reasonably continuous soil layers of different colors (gray, white, and red), with thicknesses varying from a few millimeters to some centimeters, clearly observed in the face of the cut slope. The inclination of these soil layers varied along the length of the excavation, and they were in an orientation that was unfavorable for the stability of the cut. Laboratory tests were performed and the presence of high activity clay mineral and low shear resistance parameters was determined for the gray clayey sand soil. Those weakness planes, i.e., the thin layers of gray clayey sand, had not been properly detected in the previous studies that supported the design of those walls. Considering these new findings, the original project was reviewed, and it was decided that soil nailing would be used for accomplish the excavation to the original planned level. The upper wall was also reinforced with additional anchors. Load measurements in the nails indicated that the stress state in the soil mass corresponded to the active condition at the final level of excavation. Significant lateral movements were measured and varied according to the direction and inclination of the cited weakness planes. It was observed that the reliquiae planes were fundamentally important to the behavior of the excavation. [ABSTRACT FROM AUTHOR]

An experimental program was undertaken to investigate the effects of discrete polypropylene fibers and Class C fly ash on the stress–strain and shear strength behavior of clayey soil. Two types of fiber (fibrillated polypropylene fiber and multifilament polypropylene fiber) in two different lengths (6.0 mm and 19.0 mm) and two fiber dosages (i.e. 0.5% and 1.0% by dry weight of soil) were considered. At first, compaction characteristics of the untreated soil and seven different fly ash–soil mixtures (2.5%, 5.0%, 7.5%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were evaluated at standard compaction energy. Considering compaction characteristics, unconfined compression tests of untreated soil and five different fly ash–soil mixtures (5.0%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were carried out after 1-, 7-, 14-, 28- and 90-day curing periods. According to the obtained test results, untreated soil and two different fly ash–soil mixtures (i.e. 10.0, and 30.0% by dry weight of soil) were mixed with fibrillated polypropylene fiber and multifilament polypropylene fiber in two different lengths and in two different fiber dosages, separately. A total of 17 different fiber–fly ash–soil mixtures were composed, and their unconfined compression tests were carried out after 28-day curing period. According to unconfined compression test results, 6 different fiber–fly ash–soil mixtures were selected for UU triaxial tests at the end of 28-day curing period. The obtained test results indicated that the effect of fly ash content on the stress–strain behavior is superior to the effect of fibers. The post-peak strength behavior is strongly affected by fiber type, length and dosage. The magnitude of the effect increases as the fly ash content increases. Inclusion of fiber alone without fly ash decreases unconfined compressive strength (UCS) of the compacted fiber–clay mixtures. On the other hand, when combined with fly ash, fiber inclusion increases UCS depending on fiber type, length and dosage. Moreover, for both fiber types and fiber lengths, the higher the dosage of fiber, the higher the UCS is. The increase in UCS becomes as much as 218% for 30% fly ash content and 1.0% 19 mm long fibrillated polypropylene fiber. [ABSTRACT FROM AUTHOR]

Conflicting recommendations and opinions can be found in literature concerning the effects of a delayed compaction of lime-stabilized soils. This study was carried out to evaluate such effects on a clayey soil (CH) with 5% of quicklime and hydrated lime. One-dimensional consolidation and hydraulic conductivity tests were carried out on samples compacted soon after lime addition and after 48 h. Analysis of results, helped by scanning electron microscopy and mercury intrusion porosimetry, shows that, for the tested soil, delayed compaction causes a reduction of the dry unit weight up to 11% with hydrated lime and to 18% with quicklime and a greater compressibility of the mixtures at high pressures (at 800 kPa the compression index of samples compacted with delay is doubled relative to that of the immediately compacted ones). However, pozzolanic reaction was found to progress with curing time, even in the case of delayed compaction. The hydraulic conductivity is not significantly modified by a delayed compaction; it is strongly affected by the wetting conditions of curing in the case of hydrated lime. In general, a prompt compaction is always recommendable after addition of hydrated lime whereas the use of quicklime mitigates the influence of a delayed compaction. [ABSTRACT FROM AUTHOR]

For the excavated clayey cover of a coal seam in open-pit mining, the shear strength is the most important issue after its deposition in landfills. For this purpose, an artificial lumpy material was investigated in this paper. A transition form between a reconstituted soil and natural lumpy soil governs the mechanics of the soils artificially deposited after the excavation. This paper presents triaxial and oedometer tests (including K 0 and isotropic consolidation tests conducted in triaxial cell) both on an artificial lumpy soil and its corresponding reconstituted form. Compression, permeability and strength of lumpy materials have been evaluated. When normalized by Hvorslev pressure, the shear strength of both lumpy materials and reconstituted soil lies on unique lines, with strength parameters of the lumpy materials lower than that of the reconstituted soil. Both the consolidation and triaxial test results indicate that the reconstituted soil, which exists in the inter-lump voids, plays a crucial role in the behaviour of lumpy materials. [ABSTRACT FROM AUTHOR]

The design and optimization of the dewatering scheme for deep foundation pits in a highly permeable heterogeneous layer are critical to protect water resources, control subsidence and mitigate environmental impacts. Numerical simulation is an important and sometimes the only tool in the design of dewatering schemes, especially when the dewatering projects are planned under complex hydrogeological conditions with limited data. The open excavation method was chosen for a project to drain a deep foundation pit (35–44 m) in an upland river valley landscape. Quaternary alluvial deposits (129.0 m thick) are generally distributed in the riverbed and the overburden consists mainly of alluvial-diluvial sandy gravel cobbles, clayey soils, sandy clay, and silty fine sand, making the study area very heterogeneous. There may be water inrush from foundation pit, uneven subsidence and deformation due to the uneven structure of the sand and slope stability. MODFLOW-USG (Unstructured Grid) and Subsidence and Aquifer-System Compaction (SUB) Package were used to create a coupled 3-D groundwater flow-subsidence numerical model for foundation pit dewatering. MODFLOW-USG provides greater flexibility in the design of the grid to achieve a high degree of accuracy in numerical simulation, while effectively reduces computational costs. A combination of waterproof curtain and a partial penetrating well was proposed for lowering the groundwater table. The optimized dewatering scheme with a curtain depth of 60 m and a hydraulic conductivity of 0.00518 m/d, and four rows of dewatering wells with an equal row spacing of 40 m, well depth of 50 m, and well spacing of 12.5 m in each row can meet the dewatering requirements with minimum groundwater discharge in the scenarios. The numerical simulation of this study provides a powerful and useful tool for dewatering and subsidence control of deep foundation pit under complex hydrogeological conditions. • Optimized schemes for deep foundation pit dewatering under complicated hydrogeological conditions is determined. • 3-D Coupled groundwater flow-subsidence numerical model is established considering construction of dewatering well and curtain. • MODFLOW-USG provides greater flexibility in grid design to achieve a high degree of accuracy in dewatering schemes simulation. [ABSTRACT FROM AUTHOR]

Desiccation crack is an important factor affecting engineering properties of clayey soils. In this study, the effects of compaction state and wetting-drying cycles on desiccation cracking behaviour of a clayey soil were investigated. Nine samples with various compaction water contents and dry densities were subjected to three wetting-drying cycles and the evolution of desiccation cracks was quantitatively described. The results reveal that both compaction water content and dry density play an important role in the development of desiccation cracks. Specifically, for the samples compacted on the dry side, desiccation cracks develop simultaneously. This phenomenon is also observed in samples compacted on the wet side with low densities. However, for the samples compacted on the wet side with high dry densities, desiccation cracks develop sequentially. Moreover, the higher the compaction water content, the faster development of desiccation cracks, and the smaller surface crack ratio, total crack length and average crack width. The higher the dry density, the slower development of desiccation cracks, and the smaller surface crack ratio and total crack length. Furthermore, the development of desiccation cracks can be divided into two stages according to the evolution of crack propagation velocity: (a) crack length extension, where total crack length increases rapidly with little changes in average crack width, and (b) crack width widening, where total crack length no longer changes and average crack width increases until it stabilizes. In addition, surface crack ratio, total crack length and average crack width all show an upward trend as wetting-drying cycles progresses. This tendency is more pronounced in the soil sample with a higher compaction water content and a larger dry density. • Effects of compaction state on soil cracking is investigated. • Three wetting-drying cycles are applied. • Larger compaction water content and dry density, smaller cracking degree. • Crack closure and rerouting during wetting-drying cycles are observed. [ABSTRACT FROM AUTHOR]

An experimental program was conducted to investigate the effect of pore fluid and stress history on the consolidation behavior of two clay soils with low and high plasticity. The soil samples were prepared by slurry method with water and different concentrations (10, 25 and 40%) of two organic fluids (glycerol and ethanol). Consolidation tests were performed on two types of samples (a-slurry samples, b- slurry samples compressed under a pre-defined load to represent the effect of stress history) in an odometer apparatus. The results show that the compression index Cc increases for both soils with increasing the concentration of ethanol but the variations are not considerable for glycerol. On the contrary in the case of samples with stress history there is a decrease in the compression index of soil samples. The preconsolidation pressure increases for the soil with low plasticity but for the soil with high plasticity there is no significant change in preconsolidation pressure. Furthermore the variation of compression index is dependent on the type of soil and chemical composition of pore fluid. [ABSTRACT FROM AUTHOR]

Abstract: Results from a comprehensive series of suction-controlled ring shear tests, conducted on statically compacted specimens of silty clayey sand and silty sand, are presented. The experiments were accomplished in a newly developed servo/suction-controlled ring shear apparatus suitable for testing unsaturated soils under large deformations and suction-controlled conditions via the axis-translation technique. The present work focuses primarily on two crucial aspects of compacted unsaturated soil behavior, namely, the behavior of silty clayey sand under suction-controlled ring shear testing, and the effects of pre-shearing and suction histories on unsaturated residual shear strength of compacted silty sand. Test results corroborate the important role played by matric suction on residual shear strength properties of unsaturated soils. For the range of net normal stresses and suction states investigated, the increase in residual shear strength with increasing suction was confirmed to be a linear trend for silty sand, but significantly nonlinear for silty clayey sand. Results from multi-stage ring shear tests confirmed that the residual shear strength of unsaturated soils is virtually independent of the pre-shearing and suction histories experienced by the soil. [Copyright &y& Elsevier]

Abstract: The void index is a relative quantity measuring the position of the current void ratio of a clay against the void ratios of the clay at two specific vertical effective stresses (i.e., σ v ′=100kPa and σ v ′=1000kPa). Based on this concept, a simple systematic tool is proposed for estimating the compression behaviour of reconstituted clays over a wide range of stresses and water contents. Following the practice of geotechnical engineering computation, the compression behaviour of clays is idealised as linear segments in the Iv ~lnp′ (or the void index and the mean effective stress) space. Considering the variation in the available data, there are three related but independent models for describing the compression behaviour of reconstituted clays. The accuracy of estimation increases with the level of available data. The proposed estimation is used to simulate the behaviour of a variety of reconstituted clays over a wide range of stresses and water contents. With different levels of available data, the estimation is evaluated on the basis of these simulations. The proposed estimation can take maximum use of available data and provide a simple yet practical tool for calculating the compression behaviour of reconstituted clays and a basic parameter for geotechnical engineering computations, the compression index. An empirical equation for the initial compression index is also suggested and verified. [Copyright &y& Elsevier]

Abstract: A type of clayey diatomaceous earth of Pliocene Mangbang Formation (N2 m) was encountered in highway projects in the Tengchong region of Yunnan Province, Southwest China. The Tengchong clayey diatomaceous earth is characterized using multiple test methods, such as granulometric analysis, chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, shrinkage and swelling tests, unconfined or uniaxial compression test, triaxial test and direct shear tests. The chemical and mineralogical compositions, physical and hydraulic properties and engineering properties of the clayey diatomaceous earth are presented in this paper. It is revealed that the Tengchong clayey diatomaceous earth is an unusual soil or rock which has characteristics of both typical diatomaceous earth and swelling clayey soil or soft clay rock. The diatoms in the earth enhance the connection between micro-structures, and improve the mechanical properties of diatomaceous earth. However, due to the existence of a significant amount of swelling clay minerals, the Tengchong clayey diatomaceous earth becomes swelling soft rock, and is prone to engineering problems or geohazards. Based on the test results, a number of issues regarding classification, discrimination and geohazard control related with the clayey diatomaceous earth are discussed to provide both some basic understanding and new insight into the characteristics of the clayey diatomaceous earth deposits. [Copyright &y& Elsevier]