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.

A novel thermo-hydro-mechanical-chemical (THMC) coupling model grounded in thermodynamic dissipation theory was established to unravel the intricate behavior of unsaturated sulfate-saline soils during cooling crystallization. The model quantifies energy transfer and dissipation during crystallization and introduces a method to calculate the amount of sulfate crystallization. It intricately captures the interdependencies between crystallization, pore water pressure, crystallization pressure and volumetric expansion, while also accounting for the dynamic feedback of latent heat from phase transitions on heat conduction. The reliability of the model was validated through experimental data. Numerical simulations explored the effects of cooling paths, thermal conductivity, initial salt content and initial porosity on the crystallization behavior and mechanical properties. The model provides theoretical support for optimizing the engineering design and facility maintenance of sulfatesaline soils.

The fundamental cause of frost heave and salt expansion of saline soil is the water condensation and salt crystallization during the freezing process. Therefore, controlling the water and salt content is crucial to inhibit the expansion behaviors of saline soil. Recently, electroosmosis has been demonstrated to accelerate soil dewatering by driving hydrated cations. However, its efficiency in mitigating the salt-induced freezing damages of saline soil requires further improvement. In this study, a series of comparative experiments were conducted to investigate the synergistic effects of electroosmosis and calcium chloride (CaCl2) on inhibiting the deformation of sodium sulfate saline soil. The results demonstrated that electroosmosis combined with CaCl2 dramatically increased the cumulative drainage volume by improving soil conductivity. Under the external electric field, excess Na+ and SO42- ions migrated towards the cathode and anode, respectively, with a portion being removed from the soil via electroosmotic flow. These processes collectively contributed to a significant reduction in the crystallization-induced deformation of saline soil. Additionally, abundant Ca2+ ions migrated to cathode under the electric force and reacted with OH- ions or soluble silicate to form cementing substances, significantly improving the mechanical strength and freeze-thaw resistance of the soil. Among all electrochemical treatment groups, the soil sample treated with 10 % CaCl2 exhibited optimal performance, with a 71 % increase in drainage volume, a 180 similar to 443 % enhancement in shear strength, and a 65.1 % reduction in freezing deformation. However, excessive addition of CaCl2 resulted in the degradation of soil strength, microstructure, and freeze-thaw resistance.

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 study investigates the freezing process and mechanical impact behavior of saturated soil to provide new insights into soil thermodynamic and improve its comprehensive investigation under a cryogenic engineering environment. The unfrozen water content is a major focus of study during soil freezing. Many studies have proposed models for calculating the unfrozen water content in frozen and unfrozen pores. However, they lack uniformity and consistency on a physical basis and mathematical derivation. An unified theoretical model was derived based on the principle of thermodynamic equilibrium. The main theoretical results indicated that the dimensionless total volume of the unfrozen water membrane in the frozen pores first increased and then decreased with increasing temperature, revealing the temperature effect on the unfrozen water content in frozen pores. By combining the theoretical model with the distinct element method (DEM), water freezing into ice in saturated soil was numerically simulated using two modes of particle expansion. One of the two modes proposed by the authors was to change the coefficient of expansion during saturated soil freezing to further consider the non-linear variation in unfrozen water content. Subsequently, the effects of the two modes on crack generation during saturated soil freezing were compared and analyzed. Finally, based on the dissipation energy produced in particle contacts, a method for calculating the rises in impact temperature in different particles was proposed for revealing the local and discrete changes in frozen saturated soil under impact loading. The main numerical results indicated that the proportion of the number of particles for different temperature rise ranges followed a Weibull distribution, and the average temperature rise of the particles near the incident end was higher than that of the particles near the transmission end.

To investigate the expansion deformation of predisintegrated shale as subgrade soil and develop a calculation model to describe its expansion characteristic, the nonloaded and loaded expansion tests as well as expansion force tests were conducted on the typical predisintegrated shale under varying conditions. The results show that the expansion rate of compacted predisintegrated shale is greatly affected by initial water content, dry density, and overburden load, and that its expansion characteristics can be divided into three stages. After compaction, the expansion force of predisintegrated shale has a strong correlation with the initial dry density and initial water content, and 1.45 gcm(-3) can be used as threshold density for the rate of expansion force growth. Moreover, a comprehensive calculation model for the expansion rate and expansion force considering the coupling effects of various factors was proposed. This study proposes an alternative subgrade material using shale, which can efficiently save land resources and reduce engineering costs.

The connection between subway stations and tunnels in subway systems is a critical consideration in the design of underground transportation systems. Expansion joints may be introduced between the station and tunnel to reduce the stress and deformation transmitted to the structure and mitigate the potential structural damage. However, adverse conditions such as large deformations in liquefiable sites and extreme earthquakes can severely impact the integrity of this connection. This study employs three-dimensional finite element numerical models of dynamic soil-structure interaction in liquefiable sites to investigate the seismic response of the subway station-tunnel connection structure under different distributions of liquefied soil layers and considering various structural connection methods. The results demonstrated that subway station-tunnel structure placed in liquefied interlayer sites experiences greater seismic damage compared to structures with their upper parts embedded in homogeneous liquefiable sites. In addition, using expansion joints between the station and tunnel can indeed reduce the seismic stresses and deformations transmitted to the structure, which can mitigate the extent and severity of its damage. However, the expansion joint can lead to misalignment between the subway station and the tunnel. The findings provide theoretical references for seismic design and disaster mitigation measures for subway structures in liquefiable sites.

Expansive soil, a commonly distributed clay, is unsuitable for direct engineering applications. This study proposes a method to produce foam lightweight soil from expansive soil, effectively mitigating its expansive properties. The physical and mechanical properties of expansive soil-based lightweight soil (E-LS) were systematically investigated under varying water-solid ratios, wet densities, and expansive soil contents, using tests for flow value test, drying shrinkage test, pH test, and compressive strength test. An orthogonal experiment was conducted to quantify the influence of these factors on unconfined compressive strength (q(u)), leading to the development of a strength determination method. The results show that the preparation of E-LS modifies the expansive soil structure, completely eliminating its expansiveness. Compressive strength of E-LS increases with both wet density and curing age. For expansive soil contents ranging from 30% to 60%, the unconfined compressive strength at 28 days (q(u-28 d)) varied from 0.21 MPa to 1.58 MPa. Specifically, for E-LS with 50% expansive soil content, a water-to-solid ratio of 0.8, and a wet density of 900 kg/m(3), the q(u-28 d) reached 0.92 MPa, meeting the requirements for embankment construction. The factors affecting compressive strength are ranked as expansive soil content wet density water-solid ratio, and a predictive model for E-LS strength was developed. E-LS exhibits the capability to fulfill diverse embankment filling requirements in engineering applications, while demonstrating distinct advantages including expansive property mitigation, compaction-free implementation, and construction efficiency, thereby presenting significant potential for practical engineering deployment.

Investigations of seismic response of underground structures often assume homogeneous or layered homogeneous sites. However, significant spatial variability in soil parameters may lead to vastly different underground structure performance from that obtained for homogeneous sites. Based on random field theory, this study models the spatial variability of the soil elastic modulus, cohesion, and friction angle using the Karhunen-Loe`ve (K-L) expansion method. Target acceleration response spectra are generated according to standards, and the trigonometric series method is employed to create artificial seismic waves of four different intensities. Nonlinear dynamic analyses of underground structures under deterministic and random field conditions are conducted using ABAQUS software. The study comprehensively analyzes the structural damage state, internal forces, interstory displacement, and drift ratio to evaluate the station structure's performance under different seismic intensities. Results show that the spatial variability of soil parameters significantly impacts the dynamic response of underground structures, especially for stronger earthquakes. The variability of soil stiffness and strength parameters leads to greater fluctuations and uncertainties in displacement and internal force responses, exacerbating structural damage. It is recommended that when the peak ground acceleration (PGA) reaches or exceeds 0.5 g, the spatial variability of soil parameters should be incorporated into the analysis to ensure a reliable assessment of the structural seismic performance.

Alpine treelines ecotones are critical ecological transition zones and are highly sensitive to global warming. However, the impact of climate on the distribution of treeline trees is not yet fully understood as this distribution may also be affected by other factors. Here, we used high-resolution satellite images with climatic and topographic variables to study changes in treeline tree distribution in the alpine treeline ecotone of the Changbai Mountain for the years 2002, 2010, 2017, and 2021. This study employed the Geodetector method to analyze how interactions between climatic and topographic factors influence the expansion of Betula ermanii on different aspect slopes. Over the past 20 years, B. ermanii, the only tree species in the Changbai Mountain tundra zone, had its highest expansion rate from 2017 to 2021 across all the years studied, approaching 2.38% per year. In 2021, B. ermanii reached its uppermost elevations of 2224 m on the western aspects and 2223 m on the northern aspects, which are the predominant aspects it occupies. We also observed a notable increase in the distribution of B. ermanii on steeper slopes (> 15 degrees) between 2002 and 2021. Moreover, we found that interactions between climate and topographic factors played a more significant role in B. ermanii's expansion than any single dominant factor. Our results suggest that the interaction between topographic wetness index and the coldest month precipitation (Pre(1)), contributing 91% of the observed variability, primarily drove the expansion on the southern aspect by maintaining soil moisture, providing snowpack thermal insulation which enhanced soil temperatures, decomposition, and nutrient release in harsh conditions. On the northern aspect, the interaction between elevation and mean temperature of the warmest month explained 80% of the expansion. Meanwhile, the interaction between Pre(1) and mean temperature of the growing season explained 73% of the expansion on the western aspect. This study revealed that dominant factors driving treeline upward movement vary across different mountain aspects. Climate and topography play significant roles in determining tree distribution in the alpine treeline ecotone. This knowledge helps better understand and forecast treeline dynamics in response to global climate change.