This paper presents a rigorous, semi-analytical solution for the drained cylindrical cavity expansion in transversely isotropic sand. The constitutive model used for the sand is the SANISAND-F model, which is developed within the anisotropic critical state theory framework that can account for the essential fabric anisotropy of soils. By introducing an auxiliary variable, the governing equations of the cylindrical expansion problem are transformed into a system of ten first-order ordinary differential equations. Three of these correspond to the stress components, three are associated with the kinematic hardening tensor, three describe the fabric tensor, and the last one represents the specific volume. The solution is validated through comparison with finite element analysis, using Toyoura sand as the reference material. Parametric analyses and discussion on the impact of initial void ratio, initial mean stress level, at-rest earth pressure coefficient and initial fabric anisotropy intensity are presented. The results demonstrate that the fabric anisotropy of sand significantly influences the distribution of stress components and void ratio around the cavity. When fabric anisotropy is considered, the solution predicts lower values of radial, circumferential and vertical stresses near the cavity wall compared to those obtained without considering fabric anisotropy. The proposed solution is expected to enhance the accuracy of cavity expansion predictions in sand, which will have significant practical applications, including interpreting pressuremeter tests, predicting effects of driven pile installation, and improving the understanding of sand mechanics under complex loading scenarios.

At present, the theory of cavity expansion applied to pipe piles is mostly limited to the assumption of isotropic soil. However, the natural sedimentary site has strong anisotropy, which has an nonnegligible influence on the deformation and failure characteristics of stratum soil. (1) The proposed Von-Matsuoka-Lade(VML) strength criterion is used to describe the failure and yield characteristics of clay, sand and rock. (2) The fabric tensor is introduced to describe the anisotropic properties of clay, and the joint stress tensor is derived based on the isotropic representation of the anisotropic properties. The joint stress tensor Rij is used to represent the isotropic stress space. By mapping the VML criterion in the ordinary stress space to the Von-Mises criterion in the Rij space, the transformed stress method reflecting the anisotropy property can be established. (3) The Unified hardening (UH) model is generalized based on the above anisotropic transform stress method, and the corresponding constitutive equation is derived. (4) Based on the self-similar property of soil deformation around pipe pile in the formation, a new self-similar property solution is proposed and the corresponding radial strain and tangential strain are obtained according to the assumption of radial displacement during pipe pile pressing into the formation, and a new anisotropic soil stress analysis equation reflecting pipe pile static pressing into the formation is obtained by combining with the constitutive equation. The analysis and comparison with the experimental data show that the proposed method of soil stress analysis in anisotropic strata is reasonable and applicable.

This paper presents a novel analytical framework to predict short-term pile setup in natural structure clay, considering the influence of soil destructuration in installation and consolidation. Based on the cavity expansion method, a simulation of pile installation has been conducted, with an analytical solution formulated for cavity expansion under undrained conditions to capture soil destructuration effectively. The flow rate in the unit cell is determined by Darcy's law based on the soil mass volume change, leading to the consolidation equation, which is obtained in a fully analytical form for excess pore water pressure (EPWP) dissipation. The utilization of the average compression curve aimed to depict a partially disturbed state due to the effects of installation. Based on the rewritten effective stress method (beta method), which involves the time-dependent factor while properly incorporating the effects of relaxation and thixotropy by introducing the requisite parameters. Finally, the analytical framework for predicting short-term pile setup is established and validated through a comprehensive pile field test conducted at St-Alban. The close correspondence between the analytical results and the empirical data indicates the effectiveness of the proposed framework in forecasting short-term pile behaviour with reasonable accuracy.

This paper proposes a coupled hydro-mechanical constitutive model for unsaturated clay and sand (CASM-U) in a critical state framework. The mechanical behaviour of unsaturated soils is modelled by modifying the unified clay and sand model (CASM) with Bishop's effective stress, bounding surface concept and loading collapse (LC) yield surface. The hydraulic behaviour is described by a soil-water characteristic curve (SWCC) with nonlinear scanning law, considering the coupled effects of soil deformation and hysteresis. CASM-U is implemented into a commercial finite element software through the user-defined material subroutine (UMAT), and the implementation is benchmarked by a new semi-analytical cavity expansion solution adopting CASM-U. Finally, the performance of CASM-U in predicting hydro-mechanical behaviour of unsaturated clays and sands is examined by comparing with experimental data from tests along various loading paths, including isotropic compression, cyclic drying-wetting, triaxial shearing, and their combinations. It is shown that CASM-U can provide reasonable predictions for hydro-mechanical behaviour of unsaturated soils with a total of 15 material parameters.

Many geotechnical scenarios involve cavity unloading from a loaded state, particularly in pressuremeter tests, and the unloading data of pressuremeter tests has exceptional attraction as it is less disturbed by the insertion process. However, the analyses for continuous cavity loading and unloading (i.e., cavity initially experiences expansion and then contracts) in critical state soils are rarely studied. To this end, a novel semi-analytical solution based on the unified state parameter model for clay and sand (CASM) is proposed for the whole expansion-contraction of spherical and cylindrical cavities under undrained conditions. The problem assumes that the cavity is unloaded after a monotonic loading stage, leading to plastic regions during both loading and unloading periods. The cavity response for the whole expansion-contraction process is investigated, with the total pressure and stress paths at the cavity wall presented and validated against numerical simulation. The developed solution is successfully implemented to interpret both loading and unloading data of pressuremeter tests. The undrained shear strength, in situ effective horizontal stress and initial overconsolidation ratio are back analyzed by using a curve fitting method based on the proposed solution.

Cylindrical cavity exhibits non-self-similarity during contraction process following expansion. Previous studies solve this problem with total strain approach and simple constitutive models, but the approach is not applicable when using an advanced constitutive model. This paper presents a semi-analytical solution for a cylindrical cavity undergoing expansion-contraction in undrained soils with auxiliary variable approach, incorporating the Modified Cam-Clay (MCC) model. The stress states around the cavity are formed by the superposition of initial and superimposed stress states. By treating superimposed effective stresses as self-similar, a semi-analytical solution is derived for solving the cavity expansion-contraction problem. The elastoplastic stress-strain relationship is formulated as a set of first-order differential equations, which can be solved as an initial value problem though Runge-Kutta (RK) method. Then the stress distribution around the cavity during expansion-contraction process can be determined. To validate the proposed approach, a series of well-conduced self-boring pressuremeter (SBP) tests are used to verify the proposed approach, which shows good agreements. Additionally, a FEM simulation incorporating the MCC model is performed, and the simulation results are presented to carry out parametric studies on soil parameters. A significant influence on the range of the plastic and reverse plastic zones is shown for overconsolidation ratio, while the in-situ coefficient of the earth pressure only quantitatively affects the stress distribution.

The rate effect of cavity expansion is not only related to the drainage conditions of the soil surrounding the cavity, but also closely associated with the rate-dependent mechanical properties of the soil. Most existing cavity expansion theories primarily focus on the rate effect caused by partial drainage conditions, with little attention given to the combined influence of drainage conditions and the rate-dependent mechanical behavior of soil. By employing numerical analysis and utilizing the overstress elasto-viscoplastic (EVP) model, the study focuses on the partial drainage conditions during cylindrical cavity expansion. The analysis indicates that when only the effect of partial drainage conditions is considered, the total radial stress and shear stress decrease monotonically as the expansion velocity increases, and the expansion velocity ranging from 10(-4) to 10(-1) mm/s has a small impact on the total radial stress during the initial expansion stage. When the effect of partial drainage conditions and rate-dependent behavior is considered simultaneously, the total radial stress and shear stress gradually increase with the increase of expansion velocity during initial expansion stage, which is consistent with the results of in-situ self-boring pressuremeter tests conducted on the Burswood clay and Zhanjiang clay. With the cavity expansion, the radial total stress and shear stress show a pattern of first decreasing and then increasing with the increase of expansion velocity. Sensitivity analysis of the soil's viscoplastic parameters (gamma(vp) and n ) reveals that, for a given expansion velocity, the total radial stress, shear strength, and initial shear modulus gradually decrease as gamma(vp) or n increase, with the rate of decrease diminishing over time. The expansion velocity, permeability coefficient, and overconsolidation ratio of the soil significantly impact the drainage conditions at the cavity wall, while the influence of gamma(vp) and n is relatively minor. The drainage conditions of the soil can be assessed using a dimensionless velocity V , with values of V corresponding to partial drainage conditions ranging from 0.04 to 250. It is suggested that the time-dependent mechanical behavior should be considered when applying cylindrical cavity expansion theory to analyze geotechnical problems related to cohesive soils.

In this work, the effect of gas jets used in the deep vertical vibratory compaction technique are studied. Gas jets play a vital role in treating structured loess foundations by the pneumatic-vibratory probe compaction method. Utilizing the geotechnical particle finite-element method numerically, we estimate the limit gas injection pressure and delineate the injection-induced damage and plastic zones. The behavior of structured soil is described using an elastoplastic constitutive model considering its structure evolution. The analysis of structured loess under gas injection is based on the cavity expansion approach. Experimentally, we performed a scale model test of gas injection to investigate the mechanism of the gas jets on the surrounding soil and compared relevant results with numerical results. Numerical results show that the limit gas injection pressure for structured loess beyond a depth of 8.0 m ranges from 1,409.7 to 1,467.2 kPa, increasing with the increase of overburden depth while the current cavity expansion radius decreases. The radius of the plastic zone induced by cavity expansion is 2.0 to 3.0 times the current cavity radius within this depth range; for the damage zone, however, it ranges from 0.1 to 0.4 times. The horizontal pressure recorded during the model test is observed to be lower compared with the numerical simulation results. This discrepancy can be attributed to factors such as the neglect of gas leakage within the soil and the utilization of a uniform parameter. The gas jets expand soil in cyclic shear form. It goes through a process from destruction of soil structure to compression in the horizontal direction; then, its pressure gradually drops to zero in the expansion direction of the dominant channel in soil.

The paper introduces a semi-analytical approach for predicting the pile-soil response under cyclic lateral loads in sands, incorporating the cavity expansion/contraction theory with an anisotropy and non-associated constitutive model, Simple ANIsotropic SAND (SANISAND). The pile hole is regarded as a cylindrical cavity, and the cyclic loading process is reasonably treated as a cavity expansion/contraction problem. A superposition principle is introduced to determine the superimposed stress states around the cavity. The geometric relationship, quasistatic equation, and boundary conditions are integrated into a standardized solving procedure to obtain the stress-strain distribution surrounding the pile. Subsequently, the derived cyclic p-y curve is used in conjunction with the deflection equilibrium differential equation and finite-difference method to determine the pile-soil response under lateral cyclic load. The method's validity and capacity are further demonstrated through two well-examined centrifuge tests, which shows a good agreement with the experimental data. The cumulative deformation, hardening and ratcheting behaviors of pile-soil system can be captured in this study, which provides a novel approach to figure out the pile-soil response in sands under cyclic lateral loads.

Helical piles can be classified as partial displacement piles in terms of moderate advancement rate. However, its installation effect on surrounding soil is unclear. This study presented four field tests on the installation of helical piles with various dimensions in silty clay. The radial earth pressure and excess pore water pressure were measured during the installation processes. The installation effect of helical pile embedded in silty clay was comprehensively discussed and evaluated from multiple dimensions of time and space, based on the cavity expansion method (CEM) and Randolph and Wroth's elastic-plastic method verified by field data. The research reveals that as the length of the helical pile increases by 1.0 time, the maximum variations in radial earth pressure and pore water pressure by a remarkable 25.0 times and 7.8 times, respectively. Additionally, when the shaft diameter of the helical pile expands by 20%, the maximum alterations in radial earth pressure and pore water pressure swell by approximately 18.6 and 5.7%, respectively. Comparing the radial earth pressure at various embedment depths at the same penetration stage, it is found that the radial earth pressure induced by helices is slightly greater than that induced by pile shaft. The estimated radial earth pressure and pore water pressure agree with the measured maximum data, and the pore water pressure generated by the installation of helical pile completely dissipates after 10-12 days of installation in this work.