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Plate anchors have great advantages that are useful in deep or ultradeep water mooring systems. The keying behaviors have a deep effect on the embedment loss and pullout capacity of strip plate anchors. In this paper, the effect of soil remolding on the keying behaviors of strip plate anchors is studied by large deformation finite-element (LDFE) analysis. First, the LDFE results are compared with centrifugal test results, theoretical solutions, and LDFE data from previous literature, showing good agreement. Then, a series of LDFE cases is studied to investigate the effects of the padeye offset, load eccentricity, soil sensitivity, and initial embedment depth on the embedment loss and pullout capacity of plate anchors during the keying process. The LDFE results show that different load eccentricity corresponds to different soil failure mechanisms, and both padeye offset and soil remolding will reduce the pullout capacity of plate anchors. Finally, an equivalent soil strength is introduced considering rate effect and soil remolding of clay. A combined factor and an equivalent ultimate pullout capacity are used to estimate the ultimate embedment loss and pullout capacity of strip plate anchors in uniform clay, respectively. [ABSTRACT FROM AUTHOR]

Stratum cavity collapse induced by water and sand leakage in a subway tunnel is a sudden urban geological disaster, which can cause serious casualties and economic losses. In response to the hazards of stratum cavity collapse induced by water and sand leakage around subway tunnels, a set of visual test devices with variable hole diameters were designed to simulate the stratum cavity collapse induced by water and sand leakage under comprehensive consideration of the size of the cavity diameter, clay thickness, clay strength, and so on. Based on pressure arch theory and unified strength theory, a critical calculation formula was established for stratum cavity collapse under two modes, of tensile shear and shear failure. Furthermore, the accuracy of the theoretical calculation formula was verified by experiment. The results show that the critical radius increases with the increase of clay strength and decreases with the increase of buried depth and friction angle. Clay soil is more prone to shear failure at the arch foot under the same conditions. The larger the soil sand mix ratio and the cavity diameter, the smaller the critical water pressure of soil collapse. The thicker the soil layer, the greater the critical water pressure. The theoretical analysis method has a clear physical meaning and the theoretical results agree well with the test results. The research results are of great significance for the warning of and prevention of such urban geological disasters. [ABSTRACT FROM AUTHOR]

In this paper, a constitutive model is presented to model the behavior of various soils (sand and clay) in different loading conditions and the minimum required parameters are obtained. Although some practical features (concepts) of the bounding surface framework and modified Cam-Clay have been employed in its formulations, the model is developed mainly based on the generalized plasticity framework. Moreover, some concepts such as dilatancy relation and loading history surface are redefined. Finally, the proposed constitutive model is evaluated using the experimental data related to two different sandy soils and three different clays under different loading conditions. Finally, it is concluded that the proposed constitutive model can easily be calibrated for various clayey and sandy soils. It can depict different behavioral aspects of these soils under different monotonic and cyclic loading conditions. [ABSTRACT FROM AUTHOR]

The deep soil mixing (DSM) method is used to improve the mechanical and/or hydraulic properties of soils. The DSM method refers to an in situ mixing of soil, water, and hydraulic binder without excavation. After describing the specific microstructure of DSM materials compared with soils or concrete, four porosity–permeability analytical models from literature and based on microstructural parameters (i.e., porosity and pore-size distribution derived from mercury intrusion porosimetry) were applied to predict the water permeability (K) of soil–cement mixtures. After comparing the estimated permeabilities (Kest) with the experimental measurements of such a parameter (Kexp) using a triaxial cell, an indicator parameter A (=Kest/Kexp) was proposed to evaluate the ability of each model to fit the water circulation in DSM material. By calculating the average ratio 〈A〉 from the 24 materials in the studied database, three of the four applied models satisfactorily estimated the water permeability of the studied DSM materials. To reach an 〈A〉 value closer to 1, an extension of the Aït-Mokhtar's model, initially developed for cementitious mortars, was proposed by considering the specificities of the DSM materials. If previous models used only the contribution of nanopores less than 100 nm to the water flow, the extended model considered the contribution of all pore populations in the permeability calculation. Such an approach resulted in a significant improvement in the matching between the calculated and measured permeabilities. [ABSTRACT FROM AUTHOR]

In the literature, the influence of spatial variability of the undrained shear strength of foundation soils on the bearing capacity of footings is limited to footings seated directly on the foundation. This is an unlikely arrangement in practice. This paper revisits the footing problem by considering a thin granular layer between a strip footing and soft foundation soil using analytical and stochastic numerical modeling. The analyses are extended to the case of a geosynthetic-reinforced granular layer and to the idealized case of no granular layer. The study shows that the probability that the ultimate bearing capacity for the footing is smaller than the deterministic design value is greater for all three scenarios with randomly uniform clay soil than for the same soil with isotropic or anisotropic spatial variability of strength at practical levels of reliability index β (e.g., β≥3.09 for a permanent footing). The reason for this outcome, which may appear counterintuitive, is explained. Design charts are provided to estimate the deterministic design bearing capacity of a rigid strip footing required to meet a range of target reliability index for the three footing scenarios examined in this study. [ABSTRACT FROM AUTHOR]

In this paper, a modified/extended rotational hardening (RH) rule is applied to the nonassociated simple anisotropic constitutive model, SANICLAY-D, for clayey soils. In the proposed model, the destructuration mechanism, as well as zero and nonzero fabric anisotropy at critical state (CS), are considered. A detailed model formulation with the RH rule that yields a unique CS in the e-ln(p′) space is presented including an appropriate form of the relatively simple substepping integration algorithm. In addition, the model is implemented into ABAQUS finite-element software using a User-defined Material (UMAT) subroutine and used in the simulation of various experimental tests. The modified SANICLAY-D model (SANICLAY-MD) is meticulously calibrated step by step for Saint-Alban sensitive soft clay. Drained and undrained triaxial tests after various consolidation paths as well as the direct simple shear (DSS) test are simulated for Saint-Alban and Bothkennar clays as a boundary value problem. Simulation results approve the SANICLAY-MD model's performance in the prediction of the natural soil behavior. Results show that neglecting the effect of fabric anisotropy at CS and destructuration of natural clays can lead to inaccurate prediction in the constitutive modeling of intact soft soils. [ABSTRACT FROM AUTHOR]

The performance of the novel fish anchor has been assessed through field tests. The tests were carried out at three different locations in the Swan River, Perth. The water depths were 2.91–4.73 m. The riverbed soils consisted of clay (Location 1), silty clay (Location 2) and silt (Location 3). The anchor was installed in the riverbed by dropping first through an air column followed by a water column, and finally striking the riverbed at an impact velocity of 10.4 (Location 1), 11.43 (Location 2), 11.72 (Location 3) m/s. The anchor tip embedment depth in the riverbed was measured at 1–2.5 times the anchor length. For similar impact velocity, the tip embedment depth in clay was 1.56–1.68 and 2–2.1 times of that in silty clay and silt, respectively. The capacity was found to reduce with loading angle at the padeye to the horizontal. The ultimate capacity was 1.5–2.6 times the weight of the anchor submerged in water for loading angle 90°, which increased to 8.2–15.6 times the weight for θ0=∼16°. The fish anchor dove, as opposed to pull out of the riverbed, for loading angles ≤37–47° , resulting in nonelliptical failure envelopes, which have been expressed mathematically. [ABSTRACT FROM AUTHOR]

Clay–sand mixtures are deposited worldwide, such as naturally sedimentary soils and dredged clays in human activities. These mixtures usually have a fine fraction above the transitional fine content, and the compressibility is dominated by clay matrix and affected by sand fraction. In this paper, an explicit equivalent compression curve is proposed for clay–sand mixtures. This is done by directly incorporating the equivalent void ratio into the intrinsic compression model of the clay matrix. The roles of initial and evolving soil structure developed during the compression process are described by a structural variable, which can be directly computed from the experimental data. Experimental data compiled from various literature are used for evaluating the accuracy of the suggested model. They indicate that the proposed relationship of stress versus equivalent void ratio is simple yet effective to evaluate the compressibility of clay–sand mixtures with a wide spectrum of sand fraction. The model is also practically useful for estimating the compressibility of other gap-graded soils, such as clay–gravel mixtures. The proposed stress versus equivalent void-ratio equation is an elementary function and can be readily implemented into general elastoplastic models. [ABSTRACT FROM AUTHOR]

The drying phenomenon in clays is a multiphysical process accompanied by alterations in the thermal, hydraulic, and mechanical states of the multiphase system. Reversible and irreversible characteristics of shrinkage deformation have been observed experimentally in clayey soils for different ranges of moisture contents. The kinematics of drying due to evaporation and drying-induced shrinkage can be studied by utilizing a coupled thermo-hydro-mechanical (THM) model. An accurate evaluation of drying-induced shrinkage is needed to investigate the thermal cracking and damage of geomaterials. In this study, we developed a thermoporoelastoplastic constitutive framework assuming a non-associative plastic flow rule that can accurately model the transversely isotropic behavior of stiff natural clays in unsaturated conditions. All material parameters used in the non-associative transversely isotropic constitutive model were calibrated based on experimental observations of Boom clay. Then, the capability of the model was assessed by analyzing the convective drying experiment on natural Boom clay. The comparison of the numerical and experimental results confirms the plausibility of the hypotheses made in this study. The results show that the first stage of evaporation ends rapidly and the falling rate period (second stage of evaporation) is the dominant evaporation mechanism due to the intrinsic hydraulic properties of Boom clay and the high evaporative demand of the environment. The developed model reasonably captures the anisotropic elastic and plastic deformations of the clayey soil during the transient drying process. Numerical results demonstrate that drying shrinkage induces a 30% reduction in porosity in which approximately 82% of the total volumetric deformation in drying-induced shrinkage is irrecoverable (i.e., plastic). Moreover, the results indicate that most of the plastic deformation occurs in the first couple of hours of the drying process, when the soil's unsaturated condition is in a funicular state (i.e., where capillary pressure is dominant). Finally, the last section of this paper is devoted to a sensitivity analysis of the THM behavior of Boom clay with respect to its elastic and plastic strength. The parametric study shows approximately 10% more reduction in the final surface shrinkage when the difference between the slopes of the drying-induced compression line and the swelling line (i.e., λ−κ) is doubled. [ABSTRACT FROM AUTHOR]

This paper examines the accuracy of a new elastic–thermoviscoplastic (E-TVP) constitutive model developed based on critical state soil mechanics. The model can be used for simulating the temperature-dependent and strain-rate-dependent behavior of clay soils. The study compares the E-TVP behavior of a single soil element with previously published thermo-mechanical experimental results performed on saturated clay specimens at different temperatures. Suggestions regarding unloading and reloading at constant temperatures as well as thermal consolidation under constant loads are presented. A modification for unloading–reloading adds a new criterion to the volumetric thermoviscoplastic strain rate formulation. A physics-based term is added to the current specific volume of the soil to include the viscous effect induced by temperature change. These modifications improve the convergence of laboratory data and simulated model responses. Comparisons of results from an earlier E-TVP model and the newly improved model provide evidence of improved predictive capabilities. [ABSTRACT FROM AUTHOR]

Time-dependent response of piled raft foundations (PRFs) in saturated, normally consolidated and moderately overconsolidated clayey soils under the single-drainage condition is investigated using three-dimensional, elastoplastic finite-element (FE) analysis with the modified cam clay (MCC) soil constitutive model. Four different types of clay (Boston Blue Clay, San Francisco Bay Mud, London Clay, and Shanghai Clay) with different values of overconsolidation ratio (OCR) (OCR=1 , 2, and 5) and 20 different configurations of rectangular PRFs are considered for the study. The settlement response and load sharing of PRFs are investigated. Regression analyses are performed with the FE analysis results to obtain fitted equations for immediate settlement, primary consolidation settlement, and degree of consolidation of PRFs. These equations are applicable to PRFs with cast in situ bored piles similar in size to those considered in this study. The proposed equations can be used to estimate time-dependent PRF settlement in normally consolidated and moderately overconsolidated clay as part of preliminary design calculations. [ABSTRACT FROM AUTHOR]

Efficient utilization of problematic soils such as soft clay by imparting additional strength using various stabilization techniques is done to improve soil properties. The application of nanomaterials in the area of soil stabilization has great potential to create a stiff skeleton, especially when blended with cementitious materials. Using the response surface method, this study focused on studying the effects of single and blended cementitious systems, comprising cement (0% to 20%), slag (0% to 20%), and nanosilica (0% to 2.4%), on the properties of soft clay in wet conditions [water-to-soil ratio (w/s) of 53% to 87%]. The mechanical [California bearing ratio (CBR), unconfined compressive strength up to 91 days] and durability (freezing-thawing durability factor) properties of stabilized clay were investigated, and the bulk trends were corroborated by thermogravimetry and microscopy analyses. Based on statistical analysis, incremental addition of cement, slag, and nanosilica led to the systematic increase in the properties of soft clay, albeit to different extents and with different mechanisms. At the low w/s (53%), superior mechanical and durability properties were obtained for soft clay stabilized with the ternary binder comprising cement, slag, and nanosilica. Numerical optimization showed that stabilizing this weak type of soft/expansive clay is possible, but the results (proportions, performance, cost) varied based on the target design criteria and application. [ABSTRACT FROM AUTHOR]

To estimate the cyclic shear-induced ground settlement of clay layers, cyclic simple shear tests were carried out on three normally consolidated clays with different plasticity. The pore water pressure accumulation during cyclic shear and the settlement at the postcyclic recompression stage were measured in tests with unidirectional and two-directional shearing, with different phase shifts between the shear strains applied in the two orthogonal directions and a wide range of shear strain amplitudes. All tests were performed with 200 cycles. In conclusion, firstly, the discrepancies of the pore water pressure accumulation and postcyclic settlement between unidirectional and two-directional cyclic shear were quantified, and the effects of cyclic shear direction on these properties were then described by the total length of strain path. Secondly, a method for estimating the cyclic shear-induced pore water pressure accumulation and postcyclic settlement of clayey soils with different plasticities was then developed considering the effect of cyclic shear direction. [ABSTRACT FROM AUTHOR]

Plastic clays in subgrade may cause major engineering defects such as excessive heave or settlement during the wet season that contribute to the formation of uneven geometry at the pavement surface. Soil stabilization is often a requisite to ameliorate the engineering properties of soft soils or reactive clays. This study investigates the application of nano-silica and nano-alumina to improve the California bearing ratio (CBR) of a local clay. The clay was treated with cement (2%–8%), with nano-additive (0.1%–1.5%) and with cement and nano-additive (3% cement + 0.1%–1.5% nano-additive). The compacted sample was cured for 7 days and subjected to soaked and unsoaked CBR tests. The soaked CBR of the nontreated clay increased by 49% and 27% for 1% nano-silica and 1% nano-alumina treated clay, respectively. Although 3% cement addition improved the CBR of the soaked clay by 28%, the combination of 3% cement with 1% nano-silica and nano-alumina resulted in 196% and 164% increase in the soaked CBR of the nontreated clay, respectively. The combination of nano-additives and cement yielded the same soaked CBR as if 6%–7% cement would have been used. Clay treated with 1% nano-silica and 3% cement achieved the highest CBR value within the tested samples and the sample treated with 1% nano-alumina and 3% cement achieved the lowest free swell potential. The scanning electron microscopy (SEM) micrographs of the treated clay showed the formation of uniform fabric with fewer pore spaces and calcium silicate hydrate (CSH)/calcium aluminate hydrate (CAH) products within the fabric of nano-additive treated clay. [ABSTRACT FROM AUTHOR]

Soft sensitive clays around a pile shaft experience destructuration during pile installation, excess pore pressure (u) dissipation, and creep after pile installation, but their influence on pile shaft resistance is difficult to assess quantitatively. This paper will present a semianalytical approach to evaluate the shaft resistance setup by considering soil destructuration, consolidation, and creep. Pile installation effects will be captured using the cavity expansion method. The dissipation of u will be modeled using linear radial consolidation theory, and the corresponding radial effective stress increase will be estimated by considering the stress relaxation effects. The changes in soil state after installation will be obtained by solving a system of ordinary differential equations with the initial conditions representing the pile installation effects. The limiting skin friction (τf,i) will be calculated by applying an interface reduction factor to the ultimate shear stress under simple shear conditions. Analysis of the results shows that the shaft resistance increases rapidly during the first few days after installation and continues to increase approximately linearly with the logarithm of time (t) after pore pressure equalization. The initial bonding (χ0) and overconsolidation ratio (OCR) have a marked influence on the time-dependent shaft resistance. [ABSTRACT FROM AUTHOR]

Soft marine deposits are widely distributed in the coastal region of China. The marine soft clays have high water content and high sensitivity, which shows high compressibility and low strength. The installation of precast piles for wind turbines over soft marine clay will generate high excess pore water pressure (EPWP) with very low dissipation rate, resulting in low bearing capacity and large postconstruction settlement, which will affect long-term stability. This study investigated the generation and dissipation of the EPWP correlated with the change in soil structure during the installation of pile foundations in a project of 100 MW wind-power generation in Lianyungang, Jiangsu, China. The results show that the marine soft clay soils feature strong natural structures based on the intrinsic compression concept. The EPWP decreases with increasing distance from the pile, whose influence reaches a distance of 6 m (about 10 times the pile side length). The structural strength of natural sedimentary clay has a remarkable impact on the generated EPWP. The dissipation rate of the EPWP is very slow in mucky clay with more than half the residual value after 30 days, which is mainly attributed to the sharp decline of consolidation coefficient induced by the disturbance of natural clay soils from pile driving. Moreover, hydraulic fracturing can well explain the dissipation characteristics of the EPWP in clay. This phenomenon is actually an ongoing process especially in marine soft clay soils with a strong cementation effect. [ABSTRACT FROM AUTHOR]

The physical and mechanical behavior of soil polymer composites tightly depends on the properties and structures of both soil and polymer. This study aims to investigate the effect of glass transition temperature as one of the most important characteristics of adhesive resins of acrylic polymers on the geotechnical behavior of soils that have not been fully covered by previous studies. To achieve that, three similar copolymers of methyl methacrylate-co-butyl acrylate with different glass-transition temperatures of 1°C, 33°C, and 51°C were synthesized, and two representative specimens of cohesive (kaolinite clay) and noncohesive (sand) soils were chosen to perform a full investigation of the consequential changes in the physical and mechanical behavior. A series of laboratory tests, including the Atterberg limits tests, the unconfined compressive strength tests, direct shear tests in soaked and unsoaked conditions, swelling tests, and odometer tests, were conducted on untreated and treated soils with synthesized polymers. The results showed a salient enhancement in the cohesion and the unconfined compressive strength value of both soils. However, the polymer with a glass-transition temperature near to ambient temperature led to a greater increase in the compressive and shear strength of stabilized soil among its peers. Samples treated with the polymer having the lowest glass transition temperature revealed a more compression index (i.e., obtained from odometer tests) and lower unconfined compressive strength. It is also observed that the swelling index and swelling pressure decreased marginally with increasing the glass transition temperature. [ABSTRACT FROM AUTHOR]

Many techniques, most notably soil stabilization, have been developed to enhance soil characteristics due to the growing trend of constructing structures on clayey soils. Therefore, it is imperative that researchers address clay-related issues utilizing geotechnical engineering achievements. This study evaluated the effect of volcanic ash (tuff) as a natural pozzolan on the improvement of cement performance in the clay stabilization. Various compositions of cement (0%–6% by dry mass) and tuff (0%–20% by dry mass) were added to clay and cured for 7 and 28 days. Then a set of tests, including modified Proctor, Atterberg limits, electrical conductivity (EC), pH, unconstrained compressive strength (UCS), California bearing ratio (CBR), wet-dry durability, and scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses, were performed on the untreated and treated samples. The secant modulus (E50) was measured to evaluate the stiffness of the specimens. The data showed that the incorporation of tuff into the studied cement-stabilized clay considerably enhanced the mixture mechanical properties and substantially reduced the plasticity index of the samples. After a 28-day period, the samples containing 6% cement and 15% tuff, as the optimum mixture, had increases of the UCS and CBR values of approximately twice those containing 6% cement. Moreover, the inclusion of tuff into the cement–soil blends increased the durability of the samples. According to the SEM and XRD analysis, the addition of tuff to the samples containing cement caused the formation of more cementitious compounds and fully changed the soil structure. The findings indicate that the use of tuff can lead to improved cement performance in the stabilization process. [ABSTRACT FROM AUTHOR]

A complete understanding of soil–water interactions and the corresponding mechanical behavior of unsaturated soils requires differentiating adsorptive and capillary components of water retention and dominant water uptake mechanisms. Water vapor sorption (WVS) isotherms have historically been used to quantify the water uptake behavior of clayey soils and to determine related mineral surface properties, such as specific surface area and cation exchange capacity. This paper introduces the WVS kinetics curve as a new measure for gaining additional insights into the WVS behavior of clays. The sorption rate calculated from WVS kinetics curves scales with the cation heat of hydration at low relative humidity (RH<10%), indicating that cation hydration is the first mechanism for water uptake by dry clays. Sorption rates up to 25% RH are related to monolayer adsorption and specific surface area (SSA). A distinct relationship is proposed to relate SSA to the sorption rate normalized with predominant cation valence. [ABSTRACT FROM AUTHOR]

Very often, geogrid layers are placed as reinforcement within pavement and railway roadbeds without careful consideration of their desirable location of placement. Although the clay subgrade soils utilized in this research paper and those in Saha Roy and Deb ([2]) were different and showed differing engineering characteristics, both provided useful information that is lacking in the published literature. Overall, the author's paper provides very useful practical information for enlightening the thoughts of geotechnical and civil engineer practitioners engaged in the design of both railway roadbed and highway pavement structures underlain by clay subgrades. [Extracted from the article]

Theoretical curves for different values of HT ht , 0.6, 0.8, and 1.0 are superimposed on the graph and can be seen to encapsulate the data. Yet, even without these separate curves, Wroth ([14]) noted that the parameter HT ht would track well with I ' i alone according to CSSM, and recommended the approximation HT ht (5) Graph: Fig. [Extracted from the article]

Physiochemical forces of attraction and repulsion from clay mineralogy of an expansive soil during hydration contribute to the macro swell behavior of expansive soils. In this research, diffuse-double-layer (DDL) theory–related electrostatic forces from individual clay minerals of an expansive soil and their influence on soil swelling were studied. A fundamental approach for estimating swell potentials using the DDL model is proposed here for improved characterization of soil swelling potential. As a part of this research, 14 natural expansive clays were characterized and studied by performing basic soil characterization and clay mineralogy studies, followed by one-dimensional swell strain and swelling pressure tests. Clay mineralogy data were used to estimate total DDL thicknesses, which eventually transpire as adsorbed layers during the swelling process. Assumptions with respect to clay mineral crystalline alignment and orientation of clay particles were made in order to estimate adsorbed DDL thicknesses. Estimated DDL thicknesses were then converted to DDL strains, which were later correlated with the measured swell potentials of the present soils. Strong correlations between DDL-based strains and measured swell potentials are observed, indicating the importance of using DDL concepts in the estimation of swell properties. Further refinements of the modeling and model coefficients are to be conducted in the progressive studies for better prediction of the swell behavior of soils. [ABSTRACT FROM AUTHOR]

Inferences were also drawn from the results of tests done on normally consolidated Wenzhou soft clay ([1]), and Guo et al. ([2]) for comparison of the behavior of the two types of clay soil. In their paper, the authors have reported on the research findings of a stiff overconsolidated clay (Gault clay) from the UK subjected to undrained cyclic loading undertaken in a hollow cylindrical apparatus (HCA). For the Second Conclusion The test results for the stiff overconsolidated Gault clay were presented and discussed by the authors in relation to comparisons between the CT and CHCA test results, permanent strain accumulation, resilient stress-strain response, and pore pressure observations. [Extracted from the article]

The stress-dilatancy relationship is a key point to capture the evolution of both strains and excess pore pressure during an undrained creep of natural soft clay. This paper focuses on investigating the stress dilatancy of natural soft clay during an undrained creep. Undrained triaxial creep tests are performed on K0-consolidated and isotropically consolidated samples of a typical Chinese soft marine clay with different stress levels. A unique stress-dilatancy curve is obtained from all test results. Several typical stress-dilatancy relations for soils are discussed, comparing them with experimental results. A common modification method for the stress dilatancy of sand is adopted and discussed for clay. All comparisons demonstrate that modified dilatancy equations can describe the stress-dilatancy relationship during an undrained creep. The modified dilatancy equation with the inclination of a potential surface seems to better describe the whole trend, and is suitable for natural soft clay. [ABSTRACT FROM AUTHOR]

Full-scale testing can be an integral component of quality control/quality assurance for projects involving construction of deep foundations. Rapid load tests are being used in the deep foundation industry as a method for assessing the axial static behavior of deep foundations. Since rapid load tests involve dynamics, inertial and damping forces must be considered in analyzing measured pile response to estimate the static pile response. The unloading point method (UPM) is typically used for this purpose. Generally considered a consequence of load rate effects in clays, results from the UPM must be further modified by a reduction factor to obtain a reasonable estimate of the static pile response. A reduction factor of 0.65 applied to the UPM for clay soil sites has been recommended by others. However, a review and analysis of readily available literature reporting static and rapid pile load test results at sites predominantly consisting of clay soils indicate that an average reduction factor of 0.47 is more appropriate. Rapid load testing should be used judiciously. When using the UPM to estimate static pile capacity from rapid load tests in clay, static load tests should be performed to validate the reduction factor used to interpret rapid load tests. [ABSTRACT FROM AUTHOR]

This paper presents the results and analysis of a laboratory investigation of the behavior of lightly overconsolidated compressible Chicago glacial clays over a wide strain range. Each specimen was trimmed from high quality block samples taken from an excavation in Evanston, Illinois. Specimens were instrumented with three sets of bender elements and local LVDTs. After K0 consolidation to the in situ vertical effective stress of the block, drained stress probe tests were conducted. Results of bender elements tests obtained prior to stress probing show that compressible Chicago glacial clay initially is cross anisotropic. Propagation velocities measured by bender elements in axial direction after K0 reconsolidation and drained creep agrees well with the in situ shear wave velocity measured by seismic cone penetration tests. Results of drained stress probe tests are analyzed in terms of shear, volumetric and coupled stiffness, stiffness degradation, and direction of loading. The significant variability of shear, bulk and cross-coupling response depending on stress path direction and strain level provide experimental evidence that the Chicago clays are incrementally nonlinear at the strain levels investigated. [ABSTRACT FROM AUTHOR]

Soil reinforcement with discrete fibers is a viable technique to reduce desiccation cracking in compacted clay soils. The reduction in cracking is attributed to an increase in the tensile strength of the fiber-soil composite. A theoretical model is developed to describe the mechanism of the increased tensile strength due to fiber inclusion of soil undergoing desiccation. The model includes a distinctive effective stress combination acting on the fiber strings due to the generated matric suction by desiccation. Model formulation makes use of Mohr-Coulomb failure criterion at the interface area between fibers and the surrounding soil. The desiccation process of the soil generates matric suction within the soil mass, under given stress condition. The basic elements used in the model formulation include soil-water characteristic curve, Mohr-Coulomb parameters, and unsaturated soil parameters. Fiber inclusion increases significantly the tensile strength of the fiber-soil composite. This increase in tensile strength is expressed as a function of fiber content and soil-water content in this paper. Comparisons are made to published data regarding changes in tensile strength with variable water content. [ABSTRACT FROM AUTHOR]

It is well accepted that the quality of soft clay samples obtained using standard fixed piston samplers can be relatively poor and that block samples are necessary to yield very high quality samples. However, for many practical projects it is not economically viable or physically practical to obtain block samples. In this project, the quality of standard 54 mm composite piston samples of soft clay is examined by comparing six separate sets of 54 mm samples to parallel block sampling. Sampling and laboratory testing was carried out by three different organizations at a well characterized highly uniform soft clay site in Norway. As expected, the work showed that the block samples behaved significantly differently from those obtained using the 54 mm sampler and were of higher quality. Block sample-derived parameters were considerably different from those obtained from the 54 mm sample tests. However, significant differences were also found between the different sets of 54 mm samples. Although the differences are less than when compared with block samples, the consequences of poor quality 54 mm sampling will be significant in engineering design. It is concluded that the differences are due to small details in the sampling operation such as the need to keep the piston effectively stationary at all times, to avoid overcoring and to handle the recovered sample carefully. If a well trained driller follows good quality practice, then relatively good samples can be obtained by the fixed piston sampler, which are suitable for analysis and design of routine engineering works. [ABSTRACT FROM AUTHOR]

The purpose of this study is to evaluate the adequacy of the 100-year discharge along with the Froehlich bridge abutment scour equation adopted by the U.S. Federal Highway Administration (FHwA) in predicting abutment scour for bridge design purposes in South Carolina streams. The analysis utilized bridge properties, stream cross-sectional and hydraulic data, local flood frequency equations, a one-dimensional steady river flow computer model (WSPRO), and procedures recommended by the FHwA for predicting abutment scour. A method was developed to identify the single stream-discharge at each bridge that can cause the abutment scour that was observed at 73 bridge abutments. Analysis of the results revealed that for one-third of the abutments in the sandy soil region of South Carolina, the flow rates required to produce the observed scour depths had return periods greater than 100 years. Although for bridges in the region dominated by clay soil, the return periods were significantly smaller than 100 years. [ABSTRACT FROM AUTHOR]

Alibey Dam is located near Istanbul in Turkey on the Alibey Stream, 4.5 km north of its point of confluence with Golden Horn, an ancient submerged river mouth. It was constructed as an earthfill dam over 30-m-thick soft valley sediments. Before the construction of the dam, field and laboratory tests were performed to determine the geotechnical characteristics of the foundation soils. During the construction and many years after the construction of the earthfill embankments, including the cofferdams and the intermediate fills, the response of the foundation soils was monitored by extensive field instrumentation generating a unique long-term (over 25 years) database. With proper instrumentation and careful monitoring of the collected data, field construction rates could be adjusted and the earth dam was safely constructed on the thick soft deposits. Approaches to settlement prediction were evaluated in a historical context, starting with the simplified one-dimensional approach available at the time of construction to more sophisticated analyses including the employment of modern numerical methods, in terms of the recorded data. Standard subsurface exploration and field testing supplemented with conventional laboratory testing provided the relevant material parameters that were used in the finite element method. The only exception to this was the overall hydraulic conductivity of the deposit, which controlled the rate of consolidation. Early field observations were used to assign the appropriate hydraulic conductivity. An elastoplastic soil model in a coupled analysis of consolidation was employed in the analysis that yielded realistic predictions of field behavior in response to the complex construction history. The accurate prediction and monitoring of the behavior of soft and thick soil layers subjected to staged construction, as in the case of Alibey Dam, is very important for planning of the construction as well as the expected behavior after construction. [ABSTRACT FROM AUTHOR]

The laboratory and field test data on the response of piles under the combined action of vertical and lateral loads is rather limited. The current practice for design of piles is to consider the vertical and lateral loads independent of each other. This paper presents some results from three-dimensional finite-element analyses that show the significant influence of vertical loads on a pile’s lateral response. The analyses were performed in both homogeneous clayey soils and homogeneous sandy soils. The results have shown that the influence of vertical loads on the lateral response of piles is to significantly increase the capacity in sandy soils and marginally decrease the capacity in clayey soils. In general, it was found that the effect of vertical loads in sandy soils is significant even for long piles, which are as long as 30 times the pile width, while in the case of clayey soils, the effect is not significant for piles beyond a length of 15 times the width of the pile. The design bending moments in the laterally loaded piles were also found to be dependent on the level of vertical load on the piles. [ABSTRACT FROM AUTHOR]

The conventional design of a piled foundation is based on a bearing capacity approach, and neglects the contribution of the raft. As a consequence, piled foundations are usually designed by overconservative criteria. With respect to the conventional approach, a more rational and economical solution could be obtained by accounting for the contribution of the raft toward the overall bearing capacity, but this potential is not exploited due to the lack of theoretical and experimental research on the behavior of piled rafts at failure. Based on both experimental evidence and three-dimensional finite element analyses, a simple criterion is proposed to evaluate the ultimate vertical load of a piled raft as a function of its component capacities, which can be simply evaluated by the conventional bearing capacity theories. The results presented in the paper thus provide a guide to assess the safety factor of a vertically loaded piled raft. [ABSTRACT FROM AUTHOR]

Tests for determining the water retention curve (WRC) can be time-consuming and tedious, especially with deformable soils for which volume change and water content have to be simultaneously monitored. In some cases, predictive models can become a practical alternative to obtain an estimate of the WRC. However, very few models are available to predict the WRC of deformable materials under increasing suction. In this paper, the modified Kovács (MK) model, developed initially for incompressible soils, is extended to describe and, in some cases, predict the WRC of deformable clayey soils. This generalization of the MK model is performed by introducing the volumetric shrinkage curve (VSC) in its formulation. A curvilinear equation is proposed to represent the void ratio-suction function e(ψ) corresponding to the VSC. This VSC model and the extended MK model (MKd) are validated using experimental data taken from the literature. Empirical relationships are developed for predictive purposes to estimate the parameters involved, using basic geotechnical properties. Applications show a good agreement between measured and calculated WRC. [ABSTRACT FROM AUTHOR]

This paper examines the validity of the plasticity index (PI) as a criterion for estimating the liquefaction potential of clayey soils under cyclic loading. The results of undrained cyclic stress-controlled ring-shear tests on artificial mixtures of sand with different clays saturated with water indicated that an increase in PI decreased the soil potential to liquefy, and soil with PI>15 seemed to be nonliquefiable, a finding that is in agreement with the results of other researchers. However, in this study some deviations from this relation were found when a bentonite–sand mixture was treated with solutions of different ions, thus bringing into question the effectiveness of PI as a measure of the liquefaction potential of clayey soil having a certain pore water chemistry. [ABSTRACT FROM AUTHOR]

The soil–water characteristic curve (SWCC) of fine-grained soils is usually determined experimentally. In the design of mine waste covers and landfill liners, the unsaturated hydraulic conductivity function, k(h), is often derived theoretically from the measured SWCC. Implicit in these derivations is the transformation of the SWCC to a pore-size distribution (PSD), typically assumed to be constant and monomodal. However, PSD measurements of a clayey till compacted at various water contents after compaction, after flexible-wall permeability testing and before and after SWCC tests show that the PSD of the same material varies significantly under the stated physical conditions. Predictions of the SWCCs using PSDs measured both before and after the SWCC tests significantly underpredicted the values measured. By applying a simple transformation to the PSD to account for the scaling effect from the porosimetry samples (approximately 1 g dry weight) to the SWCC test samples (approximately 200 g dry weight), the predicted SWCCs were found to envelop the measured values. A simple model that simulates the change in PSD during the SWCC test predicted water contents close (1% root mean square error) to the measured SWCCs. [ABSTRACT FROM AUTHOR]

The article presents a study on the singularities of geotechnical properties of complex soils in seismic regions by Ramon Verdugo. It notes that the study focuses on two highly unusual soil groups, such as the volcanic ash clays and diatomaceous soils. It also enumerates the significant findings from the trial embankments.

The article presents a commentary of the article "High-Modulus Columns for Liquefaction Mitigation," by James R. Martin II, C. Guney Olgun, James K. Mitchell, and H. Turan Durgunoglu. It aims to comment on the data and analysis for areas of the site where the stiff columns were not installed and where significant compression was observed in silt and clay layers. It stresses that data given by the researchers are insufficient enough which caused confusion on the issue that behavior of silts and clays at the Carrefour site was related to the "Chinese criteria," the criteria classifying silts and clay as being nonliquefiable if they exceed certain values of plasticity and if the percentage of clay size particles and their water contents are below certain specified values.