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Temperature is a critical factor affecting the matric suction of unsaturated soils. This study employed a simple and time-saving method to investigate the influences of temperature and moisture content on the temperature dependence of matric suction in loess and sand soils. Based on experimental data, the fitting performance of three data-fitting models-Brooks-Corey, van Genuchten, and Fredlund-Xing -was evaluated at temperatures above 0 °C. The results indicated that matric suction decreased as temperature increased. The variation of matric suction with temperature was categorized into the maximum value range (RMax), the highly temperature sensitive range (RTS) and the weak temperature sensitive range (RTW). Additionally, RMax and RTW were observed to decrease and increase, respectively, as moisture content increased. Above 0 °C, the sensitivity of matric suction to temperature decreased with increasing moisture content, while below 0 °C, temperature sensitivity increased as moisture content increased. Furthermore, the matric suction of loess showed greater sensitivity to temperature changes than that of sand. The van Genuchten model outperformed the other models at temperatures above 0 °C. This study provides experimental evidence for a deeper understanding of the impact of temperature changes on matric suction. [ABSTRACT FROM AUTHOR]

The stabilizing pile represents a promising solution for enhancing the seismic resilience of unsaturated slopes. This study introduces a novel analytical framework for assessing the stability of unsaturated slopes reinforced with piles, amalgamating the minimum potential energy approach with the pseudo-dynamic method. The formulation of the external potential energy arising from the self-weight of the landslide mass and seismic forces is derived. Furthermore, traditional plasticity theory is extended to unsaturated soil slopes to account for the augmenting influence of matric suction on the lateral pressure exerted by stabilizing piles. The efficacy of reinforcing unsaturated soil slopes with piles is gauged through the definition of the safety factor (SF), delineated as the ratio of resistance moment to sliding moment. Additionally, a fresh interpretation of the critical slip surface (CSS) for unsaturated soil slopes is proposed, alongside an original criterion for identifying CSS, introduced herein for the first time. The validity of the proposed methodology is substantiated through examination of three case studies, yielding results indicative of its efficacy and rationality. The analysis underscores the substantial fortifying impact of matric suction on the stability of unsaturated slopes, as well as the reinforcing influence of piles. Moreover, an exploration into the ramifications of seismic and pile-related parameters on slope performance and CSS is conducted. In conclusion, this approach serves as a valuable reference for the design of unsaturated slopes fortified with stabilizing piles. [ABSTRACT FROM AUTHOR]

As tunnel excavation technology matures and the demand for transportation infrastructure continues to grow, several high-temperature tunnels have successively emerged in high geothermal areas. The construction of tunnels in high-temperature regions is gradually becoming a new challenge encountered in the engineering field. This study aims to conduct a stability analysis of tunnel face excavation under different temperatures. In addition, soil is often considered to be unsaturated. A framework for assessing the stability of tunnel faces in unsaturated soils under fluctuating temperature conditions is proposed, with an analytical approach. The theoretical basis of this framework is established on the influence of temperature on the shear strength of unsaturated soil. The matric suction of unsaturated soil changes with temperature, thereby inducing variations in shear strength. The temperature-induced variation in apparent cohesion is quantified utilizing a temperature-sensitive effective stress model coupled with a soil–water characteristic curve. These models are subsequently incorporated into the stability assessment of tunnel faces in unsaturated soils under steady-state flow conditions. A three-dimensional logarithmic spiral model is utilized to ascertain the unsupported pressure on tunnel faces, with the safety factor (FS) being calculated through an iterative methodology. Subsequently, a comprehensive suite of parametric studies is undertaken to explore the influence of temperature on tunnel face stability under unsaturated seepage conditions, offering valuable insights for practical engineering endeavors. [ABSTRACT FROM AUTHOR]

Aeolian sand widespread in the arid and semi-arid regions has been taken use as the cost-optimal subgrade filling materials. Under the drought climate, the performance of the compacted aeolian sand subgrade is largely dependent on its unsaturated strength. In this work, the shear strength with respect to the matric suction of unsaturated aeolian sand was investigated. A series of triaxial tests were conducted on the compacted specimens with different matric suctions. Results showed that the shear strength of specimen firstly increased with matric suction and then dropped off to a certain value. The maximum shear strength was reached at the matric suction of 40 kPa, which locates in the residual zone on the soil-water characteristic curve (SWCC) of the tested soil. Such phenomena were analysed from the perspective of capillary pore distribution, as well as the internal tri-phase (air-water-solid) structure that identified by microfocus X-ray computed tomography (µCT) technique. According to the capillary pore size distribution of the specimen, pores with radius smaller than 21 μm are theoretically saturated with water at suction of 10 kPa. The identified delimiting pore radius was found to be comparable to that of 25 μm as identified by µCT. On this basis, the role of water bridges in unsaturated aeolian sand and the pore size-level that govern the mechanical properties were discussed. [ABSTRACT FROM AUTHOR]

Unsaturated soils exhibit distinct physical and mechanical characteristics compared to dry or saturated soils. Ignoring the influence of unsaturation (matric suction) and assuming either dry or saturated conditions can lead to unreliable predictions of pile behavior in unsaturated soils. In this study, the pullout capacity of different physical model piles driven in unsaturated Kaolinite-Bentonite matrices is investigated. A series of lab-scale pullout tests were carried out to examine the influence of matric suction, pile type, pile L/D ratio, and undrained cohesion (cu) of soil on the ultimate pullout capacity of model piles. Soil samples were prepared and compacted in a tank, and holes were created using a pile. Four model piles (solid and hollow stainless steel) were driven into the holes, ensuring proper spacing. Incremental loading was applied until the piles slipped out, with displacement measured by an LVDT. The pile pullout capacity increased with increased matric suction and undrained cohesion. The uplift capacity increased by 50% to 136% as matric suction increased by 157.97% as the compaction state was changed from 0.95γd(max) on the wet side of optimum moisture content (OMC) to 0.95γd(max) on the dry side of OMC of the compaction curve. However, for the compaction state of 0.90γd(max), the matric suction increased by 398.80%, leading to a 275% to 800 % increase in the uplift capacity. As the cohesion of the five samples increased from 17.84 kPa to 137.84 kPa, the uplift capacity of all the model piles increased. In Kaolinite-Bentonite mixes compacted on the dry side of OMC, hollow model piles resisted higher pull-out loads than solid model piles. The increase in uplift capacity was found to be in the range of 11.11% to 75% for different combinations of pile type and compaction density (matric suction). The results from the study imply a strong influence of matric suction, undrained cohesion, L/D ratio, and pile type on pullout capacity for piles driven in unsaturated Kaolinite-Bentonite mix. [ABSTRACT FROM AUTHOR]

The freezing strain characteristics of unsaturated soil are quite different from those of saturated soil. Besides the commonly observed frost heave, unsaturated soil may also experience frost shrinkage, causing uneven surface deformation and deterioration of soil properties. Matric suction and water–ice phase change are key factors affecting the freezing strain characteristics of soil. In this study, the freezing strain characteristics and underlying mechanisms of lean clay samples with different initial matric suctions at varying temperatures were investigated. A mathematical relationship between soil temperature and matric suction was established, enabling the estimation of variation trends in matric suction. The internal mechanisms of different freezing strain characteristics were analyzed based on the mesoscopic structures of frozen samples with low and high initial matric suctions. The results showed that samples with low initial matric suction and frozen at low negative temperatures are prone to frost heave. Frost heave occurs when the volume expansion of the soil caused by water–ice phase change exceeds the volume reduction due to increased matric suction; otherwise, frost shrinkage occurs. The morphology of pore ice in samples with different initial matric suctions varies, reflecting the degree of water–ice phase change in the soil. Using the Pearson correlation coefficient method, an empirical model for axial freezing strain applicable to unsaturated frozen lean clay was established, and the model's validity was confirmed with experimental data. [ABSTRACT FROM AUTHOR]

Adsorption and capillarity, in the order of high free energy to low, are the two soil–water interaction mechanisms controlling the hydro-mechanical behaviour of soils. Yet most of the poroelasticity theories of soil are based on capillarity only, leading to misrepresentations of hydro-mechanical behaviour in the low free energy regime beyond vaporisation. This inability is reasoned to be caused by two major limitations in the existing theories: missing interparticle attraction energy and incomplete definition of adsorption-induced pore-water pressure. A poroelasticity theory is formulated to incorporate the two soil–water interaction mechanisms, and the transition between them – that is, condensation/vaporisation, by expanding the classical three-phase mixture system to a four-phase mixture system with adsorptive water as an additional phase. An interparticle attractive stress is identified as one of the key sources for deformation and strength of soils induced by adsorption and is implemented in the poroelasticity theory. A recent breakthrough concept of soil sorptive potential is utilised to establish the physical link between adsorption-induced pore-water pressure and matric suction. The proposed poroelasticity theory can be reduced to several previous theories when interparticle attractive stress is ignored. The new theory is used to derive the effective stress equation for variably saturated soil by identifying energy-conjugated pairs. The derived effective stress equation leads to Zhang and Lu's unified effective stress equation, and can be reduced to Bishop's effective stress equation when only the capillary mechanism is considered and to Terzaghi's effective stress equation when a saturated condition is imposed. The derived effective stress equation is experimentally validated for a variety of soil in the full matric suction range, substantiating the validity and accuracy of the poroelasticity theory for soil under variably saturated conditions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study presents the effects of moisture variation and the influence of matric suction on the permanent deformation (PD) of three tropical soils with different geological-geotechnical characteristics used in road subgrades in southern Brazil. The experimental programme consisted in determining the soil-water characteristic curves and in dynamic triaxial tests to obtain the PD in different compaction and post-compaction moisture contents. The variation of compaction moisture content caused microstructural changes, influencing the plastic behaviour of soils: the higher the initial moisture content, the greater their accumulated permanent deformations. As expected, the post-compaction moisture variation (wetting process) tended to increase the plastic deformation of materials, evidencing the influence of the suction variation on the performance of the soils studied. In addition, matric suction proved to be the best variable to represent the effects of moisture variation on the plastic behaviour of soils subjected to cyclic loading. Thus, a PD prediction model for tropical soils with the inclusion of this parameter was proposed. The model proved to be highly predictive and may become an important tool to be incorporated into current mechanistic-empirical design methods. [ABSTRACT FROM AUTHOR]

The analytical calculations of unsaturated steady-state seepage in the widespread layered soils wewre relatively rare. Based on the Darcy seepage theorem and the continuity condition of soil layer interface, a mathematical model describing the steady seepage process of unsaturated layered soil was constructed. The analytical expressions of matric suction, effective saturation, and suction stress along the elevation for the same profile of layered soil were obtained by using the separation variable technique and mathematical induction. The analytical algorithm was validated based on the COMSOL numerical analysis platform, which enabled the analytical solution of the steady-state seepage process in unsaturated layered soils. Then, the influence of soil layer interface on seepage process was discussed and the sensitivity analysis of parameters was carried out. The analysis shows that: (1) Under the same infiltration conditions, the matric suction of sand at the same elevation is the highest, while that of clay is the lowest. The difference in surface seepage rate has the greatest impact on the distribution of effective saturation in the silt layer, while it has the smallest impact in the sand layer. (2) The suction stress in the clay layer increases almost linearly, while the suction stress in sand increases first and then decreases along the elevation. The presence of soil interface can affect the growth rate of matric suction along the elevation, leading to a sudden change in the distribution of effective saturation and suction stress along the elevation. (3) The smaller Gardner model parameter α, the greater the matric suction value at the same elevation, while the smaller the ks value of saturated soil, the slower the growth rate of matric suction. The smaller the values of ks and α, the slower the rate of effective saturation reduction. The smaller the value of α or the larger the value of ks, the greater the suction stress value at the surface. The research results can provide theoretical support for engineering geological problems such as slope stability.

Purpose – The experiments of this study investigated the effect of the subgrade degree of saturation on the value of the stresses generated on the surface and the middle (vertical and lateral stresses). The objectives of this study can be identified by studying the effect of subgrade layer degree of saturation variation, load amplitude and load frequency on the transmitted stresses through the ballast layer to the subgrade layer and the stress distribution inside it and investigating the excess pore water pressure development in the clay layer in the case of a fully saturated subgrade layer and the change in matric suction in the case of an unsaturated subgrade layer. Design/methodology/approach – Thirty-six laboratory experiments were conducted using approximately half-scale replicas of real railways, with an iron box measuring 1.5 x 1.0 × 1.0 m. Inside the box, a 0.5 m thick layer of clay soil representing the base layer was built. Above it is a 0.2 m thick ballast layer made of crushed stone, and on top of that is a 0.8 m long rail line supported by three 0.9 m (0.1 × 0.1 m) slipper beams. The subgrade layer has been built at the following various saturation levels: 100, 80, 70 and 60%. Experiments were conducted with various frequencies of 1, 2 and 4 Hz with load amplitudes of 15, 25 and 35 kN. Findings – The results of the study demonstrated that as the subgrade degree of saturation decreased from 100 to 60%, the ratio of stress in the lateral direction to stress in the vertical direction generated in the middle of the subgrade layer decreased as well. On average, this ratio changed from approximately 0.75 to approximately 0.65. Originality/value – The study discovered that as the test proceeded and the number of cycles increased, the value of negative water pressure (matric suction) in the case of unsaturated subgrade soils declined. The frequency of loads had no bearing on the ratio of decline in matric suction values, which was greater under a larger load amplitude than a lower one. As the test progressed (as the number of cycles increased), the matric suction dropped. For larger load amplitudes, there is a greater shift in matric suction. The change in matric suction is greater at higher saturation levels than it is at lower saturation levels. Furthermore, it is seen that the load frequency value has no bearing on how the matric suction changes. For all load frequencies and subgrade layer saturation levels, the track panel settlement rises with the load amplitude. Higher load frequency and saturation levels have a greater impact.

Sandy‐clay mixtures are commonly used in civil engineering projects, such as transportation and water resources, due to their unique construction properties. While the macromechanical characteristics of these mixtures under saturated conditions are well understood, their behavior in unsaturated states is still not fully elucidated. This study aims to investigate the mechanical behavior of sand–clay mixtures under unsaturated conditions by examining the influence of varying sand content and matric suction on their shear strength. The research includes unsaturated shear strength tests and nuclear magnetic resonance (NMR) experiments to analyze the pore characteristics within the mixtures at different sand content levels. The correlation between changes in pore structure and shear strength is systematically analyzed. The unsaturated shear strength of the mixtures is predicted using the Fredlund shear strength formula and compared with the measured values. The results indicate that the unsaturated shear strength of the mixture decreases as the sand content increases but stabilizes once the sand content reaches 20%. Below 20% sand content, the changes in micropore distribution are not significant with increasing sand content. However, beyond 20% sand content, there is a noticeable increase in the ratio of large pores and a decrease in the proportion of small pores. The sand content of 20% represents a critical threshold for the strength and porosity variations in the mixture. Under constant matric suction, the unsaturated shear strength of the mixture improves with the increase in sand content. However, the predictive accuracy of the Fredlund shear strength formula gradually diminishes as the sand content increases. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the behavior of enlarged base piles embedded within partially saturated soils under compression and uplift loading. This type of pile is rarely excavated and cast on-site. Accordingly, to construct an enlarged base pile model, an excavator was designed and manufactured to give appropriate shape through drilling and casting in the laboratory through the design and manufacture of an excavator to produce piles with a shaft of 35 mm in diameter, 500 mm in length, and a base of 80 mm in diameter inclined at an angle of 60 degrees. Three different partial saturation soils were achieved by lowering the water level below the soil surface 20, 40, and 60 cm and measuring the suction force of each stage using a Tensiometer. The average matrix suction results were 6.4, 7.6, and 9.1 kPa for each lower water level, respectively. The test results showed that the bearing capacity of the enlarged base piles under compression load in partially saturated soil was higher than that in the case of full saturation because of matrix suction, with an improvement rate of 2.5-4.5 times compared with the case of fully saturated soil. Additionally, test results showed that the enlarged base piles subjected to uplift loading in partially saturated soil were significantly improved compared with the fully saturated condition, with an improvement rate of 1.5 - 3 times. The reason for this is the apparent surface cohesion of the sandy soil, which increases the bearing capacity of the sandy soil. This study sheds light on the phenomenon of apparent surface cohesion of sandy soil and the extent of its effect on increasing the soil's resistance to the loads placed on it. [ABSTRACT FROM AUTHOR]

Stone columns are often subjected to shear deformations due to in-situ soil movement that ultimately leads to the shear failure of stone columns. This phenomenon is observed in both saturated and unsaturated soil conditions. For this reason, the objective of this study is to evaluate the behaviour of stone columns with and without geosynthetic encasement, subjected to shear loading conditions extending the mechanics of saturated and unsaturated soils. A series of large direct shear tests were conducted to account for the influence of matric suction on the shear strength of the soil reinforced with conventional and geosynthetic encased stone columns, using the soil–water characteristics curve as a tool. The study reveals that both matric suction and net normal stress play a pivotal role in the hardening–softening behaviour of the stone columns, contributing to their mechanical response and overall stability under shear forces. The shear strength of soil reinforced with stone columns, regardless of geosynthetic encasement, exhibited a direct relationship with matric suction until the primary transition zone of the soil–water characteristics curve. However, a further increase in matric suction reduced shear strength due to a decreased water-menisci area in contact. Geosynthetic encased stone columns exhibited distinctive behaviour compared to conventional stone columns, demonstrating a bending-type deformation without rupturing the encasement material. The interplay between matric suction, net normal stress, and mechanical behaviour highlights the importance of considering these factors for optimized stability and performance of geosynthetic encased stone columns. [ABSTRACT FROM AUTHOR]

This study evaluates the impact of compaction on the soil–water characteristic curve of unsaturated remodeled weakly expansive soils by assessing changes in soil pore structure resulting from variations in compaction. The remodeled weakly expansive soil in the Xinjiang Hami area is taken as the research subject to investigate how compaction affects microscopic pore structure using mercury intrusion testing. Subsequently, mercury intrusion porosimetry is employed to examine pore structure and distribution patterns at different dry densities. Based on the capillary principle and experimental methods (filter paper method and pressure plate method test), modified soil–water characteristic curves are obtained by fitting them with a three-parameter model law. The results indicate that higher dry density leads to an increased air intake value and significantly reduces the total volume of large pores within samples. Both the Fredlund and Xing model and the three-parameter model effectively capture the influence of initial dry density on the development pattern of the soil–water characteristic curve. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The matric suction of saline soil is the driving force that causes water migration, and it is of great significance for exploring the mechanism of water and salt migration in saline frozen soil. In order to investigate the effect of phase transition of soil pore solution induced by temperature on the matric suction of saline soil, the matric suction of different types of saline soils was measured by pF meter under different temperature conditions. The natural soil was first washed to obtain the desalinized soil, then different salt mass ratios of sodium chloride and sodium sulfate (0:6, 4:2, 2:4, 6:0) were added into the desalinized soil to model the composite saline soil, the salt content and water content were set to 6% and 20%, respectively. Subsequently, the remolded saline soil was compacted into the test chamber (0.37 m×0.25 m×0.22 m), and its dry density was controlled at 1.6 g/cm³. Hydra Probe II and pF meter were embedded at 11cm of the sample to measure the liquid water content and matric suction versus temperature. Freezing-thawing box (TMS 9 018-R30), produced by Zhejiang Tomos company, was employed to control the experimental temperature by step cooling method. The temperature range was from 30 to -24 °C, and the temperature interval was 3 °C. The data was collected by CR300 at an interval of 6 h. When the experiment was complete, the temperature effect of saline soil matric suction was analyzed and the effect of water/salt phase transition was explored. The experimental results reveal that the matric suction of saline soil increases almost linearly with the decrease of temperature when no phase transition occurs, which is caused by surface tension and wetting coefficient. Different types of saline soils have different effects on the phase transition process of pore solution, resulting in significant differences in the matric suction of different types of saline soils. The mirabilite crystallizes at 19 °C and the second phase transition occurs at -9 °C for the composite saline soil with 2% NaCl+4% Na2SO4, and the phase transition of composite saline soil with 4% NaCl+2% Na2SO4 occurs at 11 and -16 °C.Sodium chloride can inhibit the occurrence of ice formation, then the matric suction caused by ice formation is reduced, and the segregated frost heave caused by water migration is restrained indirectly. Besides, sodium sulfate is prone to crystallization at positive temperatures, and ice is also produced in the secondary phase transition process, both salt crystallization and ice formation increase the matric suction in sodium sulfate soil, and water and salt redistribute in this process, salt expansion and frost heave are induced. For composite saline soil, sodium sulfate mainly affects the salt crystallization of the soil at a positive temperature, while sodium chloride mainly affects the ice formation of the soil at a negative temperature. The different proportions of the two salts cause significant differences in the salt crystallization temperature and the secondary phase transition temperature, resulting in more complex phase transition laws in composite saline soil, and it is more difficult to predict the matric suction of composite saline soil. In addition, this paper further explores the contribution of ice and salt crystallization to the variation of matric suction, providing effective references for a deeper understanding of the relationship between phase transition processes and matric suction in saline soils. [ABSTRACT FROM AUTHOR]

Implementation of the state‐of‐the‐art understanding of the mechanics of unsaturated soils into geotechnical engineering practice is partly limited due to the lack of quick, reliable, and economical techniques for matric suction measurement. Matric suction is one of the key stress state variables that significantly influences the hydro‐mechanical behavior of unsaturated soils. In this paper, to address this objective, two artificial intelligence (AI) models were developed for estimating matric suction in unsaturated soils based on the particle swarm optimization support vector regression (PSO‐SVR) and multivariate adaptive regression spline (MARS) algorithms. The results suggest that both these models can reasonably estimate matric suction. Compared to the MARS model, the PSO‐SVR model can achieve higher accuracy. Nonetheless, the MARS model facilitates the sensitivity analysis and the selection of essential inputs. A novel integrated framework is proposed and validated, leveraging the strengths, and alleviating the limitations of the PSO‐SVR and MARS algorithms for reliable and rapid estimation of matric suction in the range of 0–1500 kPa for low plastic soils (0 < Ip ≤ 7). Six inputs are required to use this model successfully; some can be measured using conventional laboratory tests, and others can be calculated from mass‐volume relationships. [ABSTRACT FROM AUTHOR]

Unsaturated soils are the major component of both natural and artificial earth structures, and they exhibit less predictable behavior than saturated soils. Presently, the world is experiencing pronounced impacts from climate change. Sudden heavy rainfalls and droughts both result in fluctuating soil moisture levels, meaning that soil responds differently to infrastructure loads. Accordingly, a better understanding is needed of failure causes in unsaturated soils. This research was conducted to investigate the coupled behavior of unsaturated soil with varying degrees of compaction and moisture change. Samples were prepared at 81% and 88% degrees of compaction with moisture content ranging from 10 to 25% on both sides of optimum moisture content for silty soil. Different parameters such as suction, porewater pressure, and deformation were carefully measured at every stage of the triaxial test, from sample placing to the shearing phase. The results show that there is more compressive soil behavior when there is a lower degree of compaction, i.e., 81%, along with moisture content of 15–25%. Where there is a higher degree of compaction at 88%, dilative behavior is more evident, which changes to compressive behavior as the moisture content increases. Any change in moisture content (increase or decrease) during the lifecycle of any earthen structure necessitates a long time to stabilize its suction value (decrease or increase) if it compacted to a degree that still exhibits a compressive response. This slow recovery of suction, specifically from the wetting to the drying cycle, is not favorable for soil stability upon loading. [ABSTRACT FROM AUTHOR]

When analysing the effect of negative temperature on overwintering pit constructions of unsaturated soil, using the mechanical parameter of saturated soil at room temperature leads to an inaccuracy in the research findings. The strength parameters are obtained through indoor experiments. The foundation pit model is created using FLAC3D numerical simulation software based on the indoor experimental data. The influence of different parameters on the stress and deformation of the overwintering deep foundation pit supporting structure is analysed. The numerical simulation results obtained are compared with the actual monitoring data. According to research, the matric suction of the silty clay in its natural state in the Changchun area is 70 kPa. As the temperature decreases, the total cohesion of the unsaturated soil increases, and the internal friction angle tends to decrease. The numerical simulation results are consistent with the actual monitoring data changes. With the excavation, the horizontal displacement of the supporting structure increases first and then decreases, reaching the maximum displacement at two-thirds of the foundation pit. Compared with room temperature, the deformation of the supporting structure is larger under a negative temperature condition. The deformation of the supporting structure simulated by the actual temperature mechanical parameters is larger than that under the condition of normal temperature mechanical parameters. The frost-heaving force increases with the overall excavation, and a surge occurs at the bottom of the pit. The frost-heaving force changes most significantly under the condition of freezing at −20°C for 30 days.

The study of slope instability includes a detailed study of environmental conditions and soil's geotechnical and hydrological parameters. In the present study, a thorough understanding of rainfall-induced slope instability is achieved by doing real-time monitoring on an unstable slope located in Shillong, Meghalaya, India. The area selected is prone to landslides due to heavy rainfall and because it is located in the wettest place on earth. The real-time monitoring involves observation of groundwater table variation, intensity of rainfall, soil suction, and their effects on the instability of an unsaturated slope. Boring data show that even if the area is in a hilly region, the groundwater table is very high. The effects of antecedent rain on the matric suction, which indirectly affected the stability of the unsaturated soil slope were noticed. The location of the irrometers helped us in assessing that the slope stability is affected by both the matric suction developed in the unsaturated shallow soil during rainfall and that developed due to the presence of high groundwater level. The displacements along the slope are independent of each other. The results of the numerical analysis show that the slope displacement is positively correlated with the principal strain and maximum shear stress, indicating that the infiltration of rainfall has a significant effect on the stress and strain associated with displacement. [ABSTRACT FROM AUTHOR]

In this paper, a state-dependent, bounding surface plasticity model that simulates the behavior of unsaturated granular soils is presented. An unsaturated, soil mechanics-compatible elastoplastic response is adopted in which no part of the response occurs in a purely elastic fashion. To create an appropriate hydro-mechanical coupling, a newer generation stress framework, consisting of the Bishop-type effective stress and a second stress variable, is used in conjunction with a soil-water characteristic curve function. Details regarding the model development, parameter estimation, and assessment of the model's predictive capabilities are outlined. With a single set of parameter values, the model realistically simulates the main features that characterize the shear and volumetric behavior of unsaturated granular soils over a wide range of matric suction, density, and net confining pressure. [ABSTRACT FROM AUTHOR]

This paper presents the results of a geotechnical investigation regarding the slope stability in a pit lake, emphasizing the impact of water level variations. Advanced analysis techniques were utilized for this study. The research was performed by using fully coupled flow-deformation analyses. For the fully coupled approach, Bishop's effective-stress equation was used, and for the description of soil hydraulic behavior, the Van Genuchten's model was applied. The analysis of slope stability associated with reservoir water level changes revealed that the slope tended to become unstable as the water level decreased; the stability factor was negatively related to the rate of water level reduction. Concerning the water level fluctuations, the analyses revealed that the soil mass seemed to become less stable as the rate of water level change increased. Under a specific range of rates of water level variation, the safety factor became higher as the number of fluctuations increased. Additionally, the simulation results concerning the water level rising indicate that the pressure due to the external water level acts on the slope surface with a positive impact on the stability factor. The results obtained reflect the effects under a specific site condition, but they can be used as a reference for evaluating slope stability in a pit lake design. [ABSTRACT FROM AUTHOR]

There are relatively few experimental studies on the hydromechanical and critical state behaviours of unsaturated silty sand. In this paper, suction-controlled, consolidated, drained triaxial shear tests were conducted on silty sand under saturated (net confining pressures of 100, 200, 300 and 400 kPa) and unsaturated (suctions of 30, 100 and 200 kPa and net confining pressures of 100, 200 and 300 kPa) conditions. For unsaturated silty sand, the effects of dry density, matric suction and net confining pressure on the hydromechanical and critical state behaviour were investigated, and the critical state parameters were obtained. The main findings for unsaturated silty sand included shear shrinkage at low dry density (1·6 g/cm3) and dilatancy at higher density (1·96 g/cm3). The peak shear strength was positively correlated with dry density, matric suction and net confining pressure. The critical state volumetric strain and critical state degree of saturation were negatively correlated with dry density and matric suction but positively correlated with net confining pressure. A new dilatancy equation that includes the state parameter for unsaturated silty sand was established. A unique critical state line passes through the origin in the effective stress p ∗ –deviator q plane, and its slope is the saturated critical state stress ratio M s . In the lnp*–v plane ( v is the specific volume), the critical state lines corresponding to different matric suctions are parallel. [ABSTRACT FROM AUTHOR]

In karst regions, the occurrence of sinkholes is a common cause of roadway failures, leading to significant embankment deformation and instability. The advantages of geosynthetic reinforcement have been proven in practice in numerous countermeasures to lessen the impact of localized sinkholes, and associated design methodologies have been developed. However, some existing design methods assume there is no deformation in geosynthetics embedded in soils, and the effect of matric suction in soils is not considered either. This study suggested an analytical approach that took into account the strain in the geosynthetic reinforcements as well as the impact of matric suction. The developed design method was used to conduct parameter studies under various matric suction conditions. The method was validated against the experimental results, and the feasibility of the developed method was also compared with the existing design methods. The findings demonstrate that, in comparison to the method created here, existing design methodologies produce more conservative results. The strain and the deflection of the geosynthetic calculated using the suggested method are lower than those provided by the current design methodologies. [ABSTRACT FROM AUTHOR]

Upon infiltration, the mechanical behaviors of pile foundations in collapsible loess areas will deteriorate significantly due to the reduction of soil matric suction and collapsible deformation, which will lead to a series of engineering problems. In order to study the changes in the bearing behaviors of pile foundations in collapsible loess before and after infiltration, infiltration tests of model piles were carried out. The changes in the soil around the pile（including settlement, volumetric moisture content and matric suction） as well as the changes in the mechanical behaviors of pile foundations（including the pile head settlement, pile shaft friction and pile base resistance） were monitored. The changes in soil matric suction around the pile perimeter during infiltration were correlated with the changes in pile foundation bearing properties to elucidate the changes in pile foundation bearing properties before and after infiltration based on unsaturated soil mechanics. Research results show that the pile top settlement and pile end bearing capacity increase continuously during the infiltration process, and the pile axial force is roughly distributed in a “D” shape, with the maximum axial force appearing during the infiltration process. During the infiltration process, the matric suction of the loess around the pile decreases, resulting in collapsible deformation, which changes the magnitude and direction of the pile lateral frictional resistance, thus leading to changes in the bearing properties of the pile foundation. Based on the principle of unsaturated soil mechanics, the traditional shear displacement method is simplified and modified, and a single pile settlement prediction model is proposed to take into account the effect of collapsible deformation of the pile foundation. The theoretical model is validated with the experimental results. The research results help to further improve the design theory and engineering property evaluation of pile foundation in collapsible loess areas under complex environmental loads. [ABSTRACT FROM AUTHOR]

In-situ tests for predicting geotechnical parameters related to shear strength, such as California Bearing Ratio (CBR), typically require drilling boreholes and manual cone driving, which can be timeconsuming, expensive, and labor-intensive. The Dynamic Cone Penetrometer Test (DCPT) has emerged as a simpler, faster, and less expensive alternative for predicting CBR and other geotechnical parameters. This systematic review uses Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to examine relevant literature on DCP testing for accurately predicting CBR and other geotechnical parameters. After trimming 111 relevant studies to 55, the review discusses various research questions, including the correlation between DCP and CBR, factors such as water content and seasonal variations, and recent advances in DCP testing. The review emphasizes the importance of considering unsaturated soil behavior, such as soil suction, in pavement subgrade design to ensure the longevity and quality of the pavement. The findings provide compelling evidence for the utilization of DCP testing as an essential tool for predicting geotechnical parameters and designing high-performance pavements. By demonstrating the DCPT's remarkable convenience, reliability, and cost-effectiveness in CBR and geotechnical parameter prediction, this study paves the way for significant advancements in pavement design efficiency and economic viability. [ABSTRACT FROM AUTHOR]

Collapsible soils are known as unsaturated soils that exhibit high strength when dry, while experiencing a drastic volume reduction when inundated. Due to the constant growth in construction and urban development, dealing with these types of soils has become unavoidable. Collapsible soils are exposed to water during deep excavations, rising the groundwater table, irrigation activities, heavy rainfalls, broken sewer pipes, etc., which results in excessive settlement of foundations, landslides, embankments or slope failures. In most of these structures, retaining walls and earth pressures dominate the design. Numerical models were developed to simulate the case of walls retaining over-consolidated, partially saturated collapsible soils. The models used the finite element technique and the commercial software "ABAQUS" to model walls subjected to at-rest or passive earth pressure. The theory of unsaturated soil mechanics was employed to evaluate the soil parameters at a given degree of saturation. It is of interest to report that for a given collapse potential, the coefficient of the at-rest earth pressure increases with the increase of the degree of saturation up to a maximum value for each over-consolidation ratio, beyond which it decreases with the increase of the degree of saturation, while the coefficient of passive earth pressure decrees with the increase of the degree of saturation. Design charts are presented to estimate the coefficients of at-rest and passive earth pressures for a given collapse potential, over-consolidation ratio, and degree of saturation. [ABSTRACT FROM AUTHOR]

Dispersive soils are highly sensitive to moisture content, and its particles are prone to hydraulic erosion and scouring. The objective of this study is to determine the impact of antecedent moisture content on the erosion of dispersive soils in the Zhenlai area and establish erosion characteristics. The soil samples were collected from the Zhenlai area in the western part of Jilin Province, China. The erodibility was assessed at five different antecedent moisture content levels (with a 2% increment) by simulating rainfall in a laboratory setting on small-scale slopes. The results indicate that there are significant differences in erosion characteristics among slopes with different antecedent moisture content levels. The sediment yield from slopes with antecedent moisture content above the optimum moisture content is 60% lower compared to slopes with moisture content below the optimum moisture content. The optimum moisture content was served as a clear erosion threshold. When introducing the soil parameter of matric suction, it was found that it effectively characterizes the sensitivity of dispersive soils in this area to variations in antecedent moisture content and their impact on slope erosion. [ABSTRACT FROM AUTHOR]

As tunnel excavation technology matures and the demand for transportation infrastructure continues to grow, several high-temperature tunnels have successively emerged in high geothermal areas. The construction of tunnels in high-temperature regions is gradually becoming a new challenge encountered in the engineering field. This study aims to conduct a stability analysis of tunnel face excavation under different temperatures. In addition, soil is often considered to be unsaturated. A framework for assessing the stability of tunnel faces in unsaturated soils under fluctuating temperature conditions is proposed, with an analytical approach. The theoretical basis of this framework is established on the influence of temperature on the shear strength of unsaturated soil. The matric suction of unsaturated soil changes with temperature, thereby inducing variations in shear strength. The temperature-induced variation in apparent cohesion is quantified utilizing a temperature-sensitive effective stress model coupled with a soil–water characteristic curve. These models are subsequently incorporated into the stability assessment of tunnel faces in unsaturated soils under steady-state flow conditions. A three-dimensional logarithmic spiral model is utilized to ascertain the unsupported pressure on tunnel faces, with the safety factor (FS) being calculated through an iterative methodology. Subsequently, a comprehensive suite of parametric studies is undertaken to explore the influence of temperature on tunnel face stability under unsaturated seepage conditions, offering valuable insights for practical engineering endeavors.

Earthquake-induced slope failures are common occurrences in engineering practice and pre-stressed anchor cables are an effective technique in maintaining slope stability, especially in areas that are prone to earthquakes. Furthermore, the soil at typical engineering sites also exhibit unsaturated features. Explicit considerations of these factors in slope stability estimations are crucial in producing accurate results. In this study, the seismic responses of expansive soil slopes stabilized by anchor cables is studied in the realm of kinematic limit analysis. A modified horizontal slice method is proposed to semi-analytically formulate the energy balance equation. An illustrative slope is studied to demonstrate the influences of suction, seismic excitations and anchor cables on the slope stability. The results indicate that the stabilizing effect of soil suction relates strongly to the seismic excitation and presents a sine shape as the seismic wave propagates. In higher and steeper slopes, the stabilizing effect of suction is more evident. The critical slip surface tends to be much more shallow as the seismic wave approaches the peak and vice versa. [ABSTRACT FROM AUTHOR]

The filter paper (FP) method, a cost-effective, versatile, and convenient approach, has found extensive application in analyzing fine-grained soils, enabling the successful measurement of a broad spectrum of total and matric suctions. However, using the FP method in sand with a limited range of suction profiles has been notably underrepresented in the existing literature. Therefore, this study investigated the applicability of the contact FP method in establishing soil water retention curves (SWRCs) using five distinct FP calibration curves for 10 poorly graded sands. Among these calibration curves, the one presented by Chandler yielded the highest suction values, which were followed by those of ASTM. Furthermore, the FP results were subjected to fitting with a mathmatical model, which led to the observation that the overall trends in the obtained SWRCs displayed smooth sigmoidal shapes, resulting in a complete and coherent SWRCs. The SWRC results of five sand samples were assessed through validation against the hanging column technique (HCT) results, indicating a high degree of concordance and affirming the suitability of the FP method for sands characterized by a limited suction profile. Notably, the entire range of suction values fell within the 0.01–20 kPa range based on the calibration curves presented by Chandler and ASTM for all the examined sand samples, except sands 9 and 10. Furthermore, the suction values were unobtainable using the two aforementioned calibration curves within the ranges of 0.01–1.47 kPa and 0.01–0.172 kPa. [ABSTRACT FROM AUTHOR]

The uniaxial tensile strength (UTS) of soils is conventionally considered as a fraction of suction stress and suction stress is believed to be the product of matric suction and the kth power of effective saturation. The effective saturation is hard to be accurately determined while k, a parameter used to balance the surging matric suction as the soil dries, is rather ambiguous in its physical meaning. This study aims to develop an equation for describing the relationship among matric suction, unconfined compressive strength (UCS), and UTS. To this end, two stages of experiments involving unconfined compression test, uniaxial tensile test, and matric suction measurement test on expansive soils are performed on two batches of expansive soils. Results show that although no one-to-one relation could be found between UCS and UTS, there is a sound linear relationship between matric suction and the ratio of UCS to UTS. Based on this fact, a two-parameter equation correlating matric suction, UCS, and UTS, was established, and the physical meanings of both parameters are interpreted. [ABSTRACT FROM AUTHOR]

The shear strength of unsaturated soils exhibits significant nonlinearity, while previous studies often simplified it with linear strength models. The objective of this paper is to investigate the distinctions in the stability of three-dimensional (3D) tunnel faces when using linear and nonlinear strength models. A new 3D rotational failure mechanism and an extended form of the Mohr–Coulomb (M-C) failure criterion were integrated into the kinematically limited analysis (KLA) framework to describe the failure characteristics of tunnel faces. Subsequently, the factor of safety (FS) of the 3D tunnel faces was calculated using the strength reduction method (SRM). In the discussion section, the impacts of nonlinear shear strength, matric suction in the unsaturated soils, and the 3D geometric parameters of the tunnel on the stability of the tunnel face were analyzed. The outcomes indicate that, in unsaturated soil conditions, diverse nonlinear strength calculation models and soil types exert disparate influences on the FS of 3D tunnel faces. The main novelty of this study lies in establishing an effective method for assessing the stability of tunnel faces in unsaturated soils. [ABSTRACT FROM AUTHOR]

The main reason why horizontal freezing is different from vertical freezing is that the nonzero angle between the directions of matric suction and gravity changes dynamically. Current theories are mainly applicable to vertical freezing, but the interactions between driving force components during horizontal freezing are ignored. Based on soil water potential theory, the driving force of water migration in unsaturated silt during horizontal freezing is further investigated. First, the influence of different components of soil water potential on water migration is analysed, and the nonnegligibility of gravity in unsaturated silt is confirmed. Then, an experimental test is conducted to explore the particularity of horizontal freezing, and equations for calculating the nonzero angle are derived. Finally, the evolution of the nonzero angle during horizontal freezing and the influence of different factors are summarized based on theoretical analysis and numerical calculation. [ABSTRACT FROM AUTHOR]

Granite residual soil typically forms complex pore structures and exhibits high water sensitivity due to physical and chemical weathering processes. Changes in initial compaction conditions significantly affect the mechanical and hydraulic properties of in situ granite residual soil subgrades, with these variations fundamentally related to changes in pore structure and soil–water characteristics. This study investigates the pore structure and bimodal soil–water characteristic curve (SWCC) of a compacted granite residual soil through laboratory tests and mercury intrusion porosimetry tests. Nine initial conditions were selected based on potential in situ compaction conditions of subgrades, and their effects on the pore size distribution (PSD) and SWCC were thoroughly analyzed. The results show strong correlations between bimodal pore structure and SWCC. The size and volume of inter-aggregate pores exhibit noticeable changes with initial conditions, affecting SWCC within the low and middle suction range. Conversely, the intra-aggregate pores, which constitute over 60% of the pore structures, remain nearly intact across different initial conditions, resulting in similar SWCCs within the high suction range. As the compaction energy increases, the inter-aggregate pores are compressed and lead to a higher water retention capacity. In addition, as the compaction water content increases, the SWCC becomes less sensitive to compaction energy after the aggregates in the pore structure are fully saturated. Additionally, a three-dimensional bimodal SWCC equation is proposed and validated using test data with an R2 value above 0.98. These findings offer valuable insights for the design and quality control of granite residual soil subgrades. [ABSTRACT FROM AUTHOR]