The strength of clay subject to drying-wetting cycles is influenced by multiple factors, rendering the prediction of its variation trend challenging. To investigate the variation in strength characteristics of cohesive soil subjected to drying-wetting cycles, silty clay was obtained from the Liangzhu archaeological site to prepare remolded soil sample. Subsequently, saturated consolidated undrained triaxial tests of control group, crack inhibition group, varied dry water content group and different overconsolidation ratio (OCR) group were carried out under different drying-wetting cycles. A thorough analysis of the test results reveals that the number of drying-wetting cycles does not affect the soil's critical state or phase transformation state. The strength of soil exposed to drying-wetting cycles is influenced by a combination of factors, including cracks formed during drying, overconsolidation, and hysteresis phenomenon. Specifically, cracks will destroy the integrity of the soil and thus reduce its strength, while overconsolidation and hysteresis contribute to an enhancement in soil strength. As the number of drying-wetting cycles increases, the prominence of cracks in the soil becomes more pronounced. Additionally, as the dry water content decreases, the deviatoric stress, excess pore water pressure, and effective stress path of soil continue to evolve in the direction of increasing OCR. This research enriches the study of the strength characteristics of clay under drying-wetting cycles, providing a foundation for the preventive protection of earthen sites in humid environments in geotechnical engineering.

Existing structures can deform and damage due to newly constructed underground structures, which induces surrounding soil deformation due to ground loss and stress relief. Compensation grouting is an active control method widely used in practice due to its advantages of using readily accessible material, a convenient construction process, and the ability to make real-time adjustments compared with passive control methods. However, in current studies, consolidation settlement is commonly considered the primary factor causing the gradual loss of the grouting effect. In this study, a numerical model exhibiting an elastic viscoplastic behavior was established using the finite-difference method to investigate the influence of creep on grout efficiency. The model parameters were first calibrated by comparing them with the measured and computed results of the grouting tests conducted in a consolidometer. Then, the model was used to perform parametric studies, to investigate the influences of initial overconsolidation ratio (OCR) and grout volume. The results show that the grout efficiency, defined as the ratio between total displacement and ideally anticipated heave displacement after grouting, is lower than that when only consolidation is considered. It can decrease up to 2.5 times over 3 years when the OCR is set to 1.00 and the grout volume is 1 mL. This implies that neglecting creep behavior may lead to a nonconservative design for compensation grouting in the long term. The creep control efficiency, defined as the ratio between the settlement induced by creep and that induced by consolidation, has been newly proposed to evaluate the influence of soil creep. It is found that the creep control efficiency of OCR = 1.00 serves as an upper limit under different OCRs because of the significant consolidation settlement in underconsolidated soil and the small creep settlement in overconsolidated soil. Therefore, the creep control efficiency value of OCR = 1.00 can be recommended for conservative design estimates when determining the final grout efficiency.

Partially saturated soils are ubiquitous in natural environments but still pose significant challenges for constitutive modeling. In this paper, a simple hypoplastic constitutive model incorporating a structural factor to describe the wetting-induced collapse behavior of unsaturated soils is proposed. The model features a straightforward formulation with robust prediction capacity using 10 material parameters, most of which can be calibrated through conventional laboratory tests. Comparison between numerical simulations of element tests and experimental results demonstrates that the proposed model is able to replicate the salient features of unsaturated soils, including shear dilatation, strain softening, and wetting collapse.

Natural soil layers often exhibit overconsolidation due to their deposition history, which significantly affects soil mechanical properties. However, traditional analytical methods for determining critical tunnel face pressure are ineffective in considering the overconsolidation effect. This study introduces a nonlinear Hvorslev surface as the strength criterion for overconsolidated soil. The equivalent Mohr-Coulomb strength parameters are derived using the tangent technique and then incorporated into the modified three-dimensional collapse analysis. A new model is established to predict the critical face pressure of tunnel faces in clay layers with varying over consolidation ratios (OCR). The model's validity is confirmed by comparing it with the existing model in its simplified form. The critical tunnel face pressure (sigma(c)) in overconsolidated soil is influenced by the over consolidation ratio (OCR), tunnel diameter (D), the ratio of the swelling line slope to the compression line slope (kappa*/lambda*), pore water pressure coefficient (ru), soil lateral pressure coefficient (K-0), tunnel depth-to-diameter ratio (C/D), and the stress ratio at critical state (M). The findings show that with increasing OCR, the collapse zone at the tunnel face shrinks, leading to a decrease in the critical tunnel face pressure (sigma(c)). When OCR is constant, sigma(c) positively correlates with D, kappa*/lambda*, and r(u), while negatively correlating with K-0, C/D, and M. The impact of kappa*/lambda* on K-c is significant at high OCR values, and C/D and K-0 have a high sensitivity at low OCR values. Therefore, to enhance the design of tunnel face pressure in overconsolidated soil, engineers should consider factors like stress history, OCR, tunnel dimensions, and depth.

Cohesive soils in nature are created under anisotropic stress and have various stress histories. Embankments generate greater vertical loads underground. Moreover, associated excavation activities can exacerbate the extensional stress state. This study investigated the effects of induced anisotropy on the shear modulus in saturated and unsaturated cohesive soils. A triaxial testing apparatus, equipped with local small strain (LSS) measurement devices and bender elements (BEs), was used to measure the small strain shear modulus. Two series of tests were conducted: (1) LSS and BE tests used specimens normally consolidated under a constant mean effective stress of p' = 300 kPa or net mean stress p net = 300 kPa with different stress ratios to investigate the effects of anisotropic consolidation. The values of the applied stress ratios, represented as K = r ' h / r ' v for the saturated soil and K net = ( r h - u a )/( r v - u a ) for the unsaturated soil, were 0.35, 0.43, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, and 3.5. (2) BE tests used specimens consolidated under various mean effective stresses in the order of p' = 50, 100, 200, 300, 400, 500, and 600 kPa, and swollen in reverse order under K of 0.35, 0.43, 0.6, and 1.0, to elucidate p' and the effects of the overconsolidation ratio (OCR). The results demonstrated that K -consolidation under constant p' produces large differences in initial shear modulus G 0 in saturated cohesive soil, but K net produces only slight differences in unsaturated cohesive soil because of the influence of strong matric suction. Finally, G 0 was normalized successfully considering the effects of void ratio e , K , and OCR. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The interface resistance during installation is crucial for the stability and safety of suction caisson in offshore geotechnical engineering, which is strongly affected by the penetration rate and soil-structure interface mechanical properties. This research conducts a series of clay-structure interface shear tests using modified direct simple shear device to fully study the mechanical behavior of clay-suction caisson interface. The effect of shear rate, over consolidation ratios (OCRs), interface boundary conditions, stress levels, and interface roughness were considered. Results show that as the OCR increases, the strength of both the clay and interface increase but show distinct patterns under constant volume (CV) and constant normal load (CNL) boundary condition. It was found that the interface strength is positively related to interface roughness and shear rate impact both the clay and corresponding interface strength. Under CNL conditions, the strength of normally consolidated (NC) clay decreases with rising shear rate, while the over consolidated (OC) clay demonstrate a opposite trend. In contrast, the effect of shear rate on interface behavior gets complicated owing to the combination of roughness, stress levels, and OCRs. Under CV conditions, the shear strength of clay and interface exhibits a logarithmic growth relationship with shear rates. The result of this work can provide a basis for interface resistance evaluation for suction caisson installation in clay.

An advanced constitutive framework for unsaturated soils, the UTUH model, is proposed in this paper, which considers the joint effect of time, suction and overconsolidation within the framework of sub-loading surface plasticity. A reference line, namely the instantaneously normal compression line (INCLs) for unsaturated soils, is introduced from a conceptual framework drawn from constant rates of strain test results to determine creep time and overconsolidation states of unsaturated soils. Subsequently, an isotropic elasto-viscoplastic constitutive model for unsaturated soils is produced by combining viscous deformation with mechanical and hydraulic deformation through overconsolidation parameter. Net stress, suction and time are adopted as fundamental constitutive variables and time-dependent loading collapse yield surface is derived to characterize the relationship between yield stress, suction, and time. Then, an extension to a triaxial stress state is built in the space of mean effective stress, suction, deviator stress and time variable. The hardening of yield surface and sub-loading surface is controlled by viscoplastic volumetric strain and unified hardening parameter. The performance of the proposed UTUH model is addressed through four numerical studies, and the proposed model is validated against experimental data from the literature.

Based on the modified simple direct shear device which can directly measure the interface pore pressure and interface shear displacement, a series of interface shear tests and corresponding pure clay shear tests were conducted at an undrained state in constant normal load (CNL) boundary conditions or equivalent undrained state in constant volume (CV) boundary conditions. The clay-structure interfaces, consisting of seabed clay and Speswhite kaolin clay with overconsolidation ratios (OCR) of 1 and 3, were tested at three shear rates, respec-tively V1 = 0.0002 mm/s, V2 = 0.001 mm/s, and V3 = 0.01 mm/s. The results demonstrated that the shear strength of the clay-structure interface is lower than that of pure clay, and this difference is more pronounced under CV boundary conditions. In CNL condition, though the pure clay strength decreases with increasing shear rate at OCR = 1 and increases with increasing shear rate at OCR = 3, the shear rate effect on clay-structure interface strength is not obvious. In CV condition, the strength of the interface with the normally consolidated (NC) and over consolidated (OC) clay increases approximately linearly with the shear rate on the semi -logarithmic scale. the shear rate parameter p is used to describe the growth rate of pure clay or clay-structure interface shear strength with a tenfold increase in shear rate. As for normally consolidated clay, in CV condi-tion, the corresponding shear rate parameter satisfies that p (with R1 roughness)> p (pure clay)> p (with R2 roughness). The rate parameter corresponding to NC seabed clay is significantly higher than the rate parameter corresponding to NC Speswhite kaolin clay. For OC clay, the shear rate parameter for interface strength is higher than that for pure clay, meeting with the relationship that p (with R1 roughness)> p (with R2 roughness)> p (pure clay).