International Journal of Geomechanics

Abstract

Infrastructure development over quaternary unlithified, unconsolidated sediments is quite critical and poses geo-hydro-engineering challenges. The challenges are more perceptible near high groundwater table areas and increase with the depth of construction. In this study, long-duration (t ≤ 40 h) permeability experimentation on fine-grained soil sample is conducted under varying confining stress (σ₃) and fluid flow pressure (f_p) employing a flexible wall permeameter to simulate the behavior of fluid flow under the stress conditions equivalent to a depth of approximately 40 m below the earth's crust. The obtained result indicates a nonlinear relationship between discharge, q (m³/s), and time, t (s), there is a rapid reduction in q up to t (≤16 h), which becomes almost constant after attaining steady-state flow and complete saturation. The q linearly increases with an increase in f_p and follows Darcy’s law; however, q significantly decreases with an incremental change in σ₃. Further, a nonlinear relationship exists between k and σ_eff. The percentage variation in q_avg with changes in f_p (=40–80 kPa and 80–120 kPa) corresponding to σ₃ (=200 kPa) is about 50% and 70%. respectively. There is less change (5%) in q_avg, corresponding to incremental change in σ₃ from 100 to 200 kPa; however, the change is quite significant and rapid (about 28%) on an increase in σ₃ from 200 to 300 kPa. Further, slow or negligible change can be observed beyond σ₃ (=300 kPa). This research highlights the significance of σ₃ over f_p on the behavior of fluid flow through fine-grained soil and demarcates the flow boundaries, namely unsteady-state, critical-state, and steady-state flows, specific to unsaturated or partially saturated clayey–sandy–silty soil.

Practical Applications

The research provides quantitative assessment of the behavior of fluid flow through fine-grained soil under varying confining stress and fluid flow pressure conditions, which may be valuable in optimizing the design and construction of any civil or geoengineering projects especially where the depth of construction has significance. The research clearly highlights the flow boundaries, namely unsteady-state, critical-state, and steady-state flow boundaries, specific to unsaturated or partially saturated clayey–sandy–silty soil and provides the relationship among discharge, time, confining stress, and fluid flow pressure, which may assist in developing accurate predictive models to investigate fluid flow through fine-grained soil.

This study provides a solution for determining stress and displacement measurements of layered soil under the interaction of two adjacent strip footings by using conformal transformation methods (CTMs) in complex variable functions. Using the CTM, this research maps each layer of soil to a unit circle and calculates two single-valued analytic functions of each layer based on continuous conditions and boundary conditions to obtain the stress and displacement fields of the entire soil. The results were verified after being compared with the numerical solution of the Analysis Systems (ANSYS) finite-element software. In addition, this research uses two layers (as an example) to analyze influences of clear spacing of the footings and shear modulus of the soil on the interaction of two strip footings, as well as the influence of the center spacing of the footings and shear modulus of the bottom layer on differential settlements. The results indicate that an increase in the clear spacing of the footings and shear modulus of the soil sublayer greatly reduces the interaction between the two footings. Moreover, the differential settlement will increase with the center spacing, but will not vary with a changing shear modulus of the sublayer soil.

The development of high rockfill dams has imposed greater demands on the compaction quality of rockfill materials. However, because rockfill particles are subjected to crushing under the compaction of a high-powered roller, the rockfill compaction characteristics might be affected. In this paper, a 3D discrete element model of the rockfill compaction process under vibration force was established to investigate the compaction characteristics and the mesoscopic mechanism of rockfill, considering gradation, shape, and particle breakage. The results showed that the geometric accuracy of rockfill particles is well maintained with 30-surface polyhedrons based on SHAPE simplification. The rockfill material with larger aspect ratios showed a larger final cumulative settlement ratio, while those with larger d₅₀ showed a smaller ratio. Due to the combined effects of compaction and particle breakage, the porosity of the surface rockfill particles decreased more rapidly. As the settlement ratio increased and the porosity decreased, the coordination number of the rockfill material increased. In general, the average velocity of particle movement increased with decreasing particle size during compaction.

Rock masses have complex block-hierarchical structures involving various scale levels, which should be considered in dynamic and static conditions. Because the interlayer has weak mechanical properties, the deformation of rock masses is primarily concentrated at the interlayers, which provides the possibility of translation and rotation for rock blocks. In situ experimental data have shown that the blocky rock masses undergo significant angular deformation under a dynamic impact, and the rotation of blocks can significantly affect the wave propagation and dynamic behavior of rock masses. Consequently, to investigate the rotation of blocks, a two-dimensional dynamic model of blocky rock masses was established based on the accurate consideration of the rotation effect. This research revealed the mechanism of the rotation of blocks and determined the characteristics of energy transfer and the influence of block rotation on the inhomogeneous deformation of interlayers. The findings showed that the rotation of blocks is caused by the nonequilibrium shear between the interfaces in the absence of external torques, resulting in inhomogeneous deformation of interlayers. The blocky rock masses can produce additional tension and compression deformation caused by the rotation of blocks at local positions in addition to the deformation caused by the translation. The energy transfer and influence of the rotation of blocks under an external torque are inconsistent with those under a horizontal impact load. This study theoretically solves the problems of wave propagation in block media under arbitrary loads and torques and is helpful for the research of seismic wave propagation in block media with inhomogeneous complex structures.

The use of basalt fiber–reinforced polymer (BFRP) bolts has been investigated for their potential in improving the properties of anchorage systems in mixed soil environments, particularly for their lightweight, high strength, and durable characteristics. An experimental study was performed to examine the creep behavior of BFRP anchorage systems under pullout conditions in colluvial and deluvial mixed soil in Western Sichuan. The initial pullout force and the pullout force at creep failure were determined through the analysis of a theoretical model and creep tests. A power-hyperbolic creep empirical model was developed to describe the deceleration and stable creep stages of the BFRP bolt. The results of the study indicated that the improved generalized Burgers model was better suited to describe the accelerated creep process of BFRP bolts compared to the classical model. The findings of this study contribute to the understanding of the creep behavior of BFRP anchorage systems in mixed soil environments and have implications for the design and construction of infrastructure projects.

A rational method for estimating soil suction variations within the so-called moisture active zone or vadose zone is required. Within the unsaturated zone, a soil suction envelope is defined by the maximum and minimum suctions at the ground surface (i.e., the suction amplitude), equilibrium suction, and depth to the equilibrium (or constant) suction. This paper presents a mechanistic-numerical model for predicting equilibrium suction that takes into account the effects of the diffusion coefficient and makes use of surface field suction measurements. The rational attenuation function in this study represents the rate of suction change within the unsaturated zone. The model can predict the equilibrium suction in response to changes in the subgrade moisture regime. The geographic information system (GIS) platform was used to create contour maps of the mechanistic-numerical equilibrium suction values for Oklahoma. In addition, the paper presents a reliable statistical-based equilibrium suction prediction model based on readily available parameters such as Thornthwaite Moisture Index (TMI), clay content, and relative humidity.

The lateral earth pressure on a rigid retaining wall with different movement modes, of translation, rotation about the top with translation, and rotation about the base with translation, is investigated analytically in this study using a trigonometric model to describe the relation between lateral earth pressure and wall displacement. The piecewise sine function defining the passive and active earth pressures satisfies the actual major features of the lateral earth pressure–displacement curve. Validation work is carried out using the model tests results on the lateral earth pressures on the retaining wall. The simplified method generally predicts the passive and active earth pressures in good agreement with the test results; the main characteristics of lateral earth pressures under various wall modes can be reproduced. Parametric studies show that the characteristics of the lateral earth pressure are greatly influenced by the mode of wall movement, the ultimate wall displacement, and the rotation length ratio. The analytical approach can be used to estimate the displacement-dependent lateral earth pressure acting on a rigid retaining structure with sufficient accuracy and can thus be referred to in related experimental and numerical studies.

Compacted loess is a special collapsible unsaturated soil and is sensitive to hydraulic conditions. Understanding and modeling the coupled hydromechanical behavior of compacted loess during isotropic compression is essential for establishing a complete constitutive model for unsaturated soils, which is of significance for predicting the deformation of loess fills in engineering. In this research, a series of constant suction isotropic compression tests are conducted to study the behavior of compacted loess. The experimental results show that volume change and soil–water characteristics are mutually affected during compression and that the normal compression curves flatten out and shift downward with the decrease in suction. Based on the experimental observations, the normal compression surface is modified, and the loading–collapse yield curve is deduced for the compacted loess. An equation associated with the void ratio is used to describe the effect of the volume change on the soil–water characteristics. Furthermore, a coupled hydromechanical constitutive model for the compacted loess under isotropic compression conditions is proposed within the framework of the Barcelona basic model. Model predictions of the mechanical and hydraulic behaviors of the compacted loess for constant suction isotropic compression tests and wetting tests at constant net stresses are compared with experimental data to verify the performance and validation of the proposed model. The comparisons indicate that the proposed model can accurately reproduce the coupled hydromechanical behavior of the compacted loess under isotropic compression conditions.

Despite the widespread usage of the anchoring technique in geotechnical projects in Brazil, mainly in underground works and retaining walls, limited research has been carried out on the determination of load capacity in anchors. Ground anchored walls in Brazil are often dimensioned by methodologies that are not satisfactorily adapted to the reality of the national soil. In this context, this work proposes a simplified computational methodology for forecasting the load capacity of anchors in geotechnical projects. To this end, a fuzzy model is proposed using specific selected characteristics of the soils and geometry of tieback wall systems, whose measurements are easier to be obtained when compared with the load capacity measurement itself. For validation, calibration, and application of the model, the results of 40 performance tests (load tests) were used. Thirty-two samples were used to train the algorithm whereas eight were used to test the model. The results obtained using the proposed approach were close to the extrapolated values of the performance tests according to the existing empirical method, showing that the model is a viable alternative for the design of anchors. Finally, the methodology presented in this work seems to be a first step for the prediction of the anchor bearing capacity and therefore it will certainly benefit from the addition of new test databases of different locations around the world.

The technology of composite ground has been widely adopted in various engineering projects, and it presents the trend from a single column type to the combined use of multiple types. The combined use of long prefabricated vertical drains (PVDs) and short soil–cement columns (impervious columns) has been proposed and utilized in several ground improvement projects. The research for the consolidation behavior of combined composite ground could facilitate the design and calculation of it in practice. Nevertheless, almost no analytical theories for consolidating such a technique are available in the literature. To fill this gap, an analytical model including multiple long PVDs and short impervious columns is proposed to predict the coupled radial–vertical consolidation of the combined composite ground. The analytical solutions under instantaneously and multistage loading are obtained based on the assumption of equal strain and Darcy’s law. The average degree of consolidation calculated by the current study is then compared with several existing analytical models of composite ground. Furthermore, a parametric study is carried out to investigate the impacts of various factors on consolidation behavior. The results show that the increasing penetration ratio of the short impervious columns can accelerate the consolidation rate. Moreover, the distribution patterns of the construction site, the compression modulus ratio of impervious columns and soil, and the well resistance and smear effect of PVDs can also influence the consolidation behavior of the combined composite ground. Finally, the reasonability of the proposed analytical model is verified by comparing it with the measured test data reported in the literature.

Semianalytical solutions for circular tunnels under biaxial in situ stress fields are developed in this study. The surrounding rock is assumed to behave as an elastic–brittle–plastic model and is characterized by the unified strength criterion. For the stress analysis, the perturbation solutions for arbitrary-orders plastic radius for deep-buried tunnels are presented with a newly developed numerical iterative method. Furthermore, a stress renewal algorithm is provided for determining the stress function in elastic zones more accurately. In accordance with the small deformation assumption and nonassociated flow rule, the analytical expressions for radial and circumference displacement in a plastic zone are presented for the first time. Subsequently, the undetermined coefficients in plastic displacement can be solved numerically with the least square method. Based on the proposed semianalytical solutions for circular tunnels, an improved equivalent circular method is developed for estimating the plastic radius and convergence of tunnels with arbitrary shaped cross sections approximately. The reliabilities of the proposed semianalytical solutions and the improved equivalent circular method are verified by comparing with numerical simulation and field data. Meanwhile, the whole calculating process is illustrated in a flow chart for the convenience of programming. From the perspective of practicality, the provided solutions can be employed for predicting plastic radius and ground response curves in tunnel excavation, which can supply important references for the tunnel stability assessment and support design.

To investigate the dynamic characteristics of the soil in seasonally frozen areas under intermittent cyclic loading, a series of dynamic triaxial tests on frozen–thawed aeolian soil were conducted by using the global digital system dynamic triaxial apparatus (GDS-DYNTTS). The dynamic elastic modulus and the dynamic damping ratio of freeze–thaw aeolian soil under different effective consolidation confining pressures, freeze–thaw cycles, dynamic stress amplitudes, and vibration frequencies were investigated. The results demonstrated a “step-type” dynamic elastic modulus curve for freeze–thaw aeolian soil under intermittent cyclic loading, and higher values were found compared to when the soil was under continuous vibration load. The developmental trend of the dynamic damping ratio was divided into accelerated growth and stable stages. The dynamic damping ratio under the intermittent condition was lower than that under continuous vibration load, which indicated that the intermittent stage reduced the internal energy consumption of soil samples and provided an improved buffering capacity against the vibration load. Overall, the fractional-order mathematical model based on the time-hardening approach exhibited good prediction skills for the freezing–thawing aeolian soil dynamic elastic modulus under intermittent cyclic loading. The results of this study will provide beneficial guidelines for engineering construction and disaster prevention practices in areas with seasonally frozen soils.

During rock joint shear tests, only some steep asperities on the shear surface participate in the shearing process. The existing peak shear displacement (PSD) models fail to reflect the role of steep asperities on the PSD fully. Therefore, this study proposes a new PSD model of rock joints to solve this problem. First, shear tests are carried out on red sandstone joint samples with the same morphology under different normal stress. The results show that the PSD increases with normal stress and decreases with joint surface roughness. A PSD model for rock joints considering the three-dimensional unevenness of the actual contact joint surface and normal stress is presented. The model reflects that the PSD increases with the normal stress because the increase of the normal stress leads to a decrease of the actual contact joint roughness, and the decrease of the roughness leads to an increase of the PSD of the joints. The new proposed model further shows that the roughness of the actual contact joint surface can well reflect the shear process. The test results of different studies describing the various types of joints verify the rationality of the proposed PSD model of rock joints, following which the adaptability and limitations of the model are discussed.

This study aims to comprehensively investigate the reinforcement mechanism of the tunnel support structure and its supporting characteristics in layered and weak rock tunnels. Uniaxial compressive tests were carried out to study the mechanical and deformation characteristics of anchored rock with the system anchor bolt and the steel floral pipe. Besides, a three-point bending test of the steel–concrete composite beam was conducted to investigate the bending capacity of the grilles and I-beams. The experiment showed the following results: (1) The anchor bolt achieved the anchoring effect by improving the stress state and the strength of the surrounding rock. The improvement of the anchorage strength to the surrounding rock was reflected by the effect of the compression zone of preload, the healing effect of the anchorage agent on the surrounding rock, and the reinforcement effect of the anchor bolt on the density and strength of the anchor bolt. (2) By the CT scanning of the anchored samples after the experiment, it was found that the crack was blunted and arrested within the anchorage zone, and the crack-arresting effect was related to the range of the anchorage zone. The larger the anchorage zones, the better the crack-arresting effect. (3) The steel arch could effectively improve the ability of concrete antideformation. Compared with the lattice girder, the coordination ability of steel arch and concrete deformation was relatively weak. Its coordinate deformation stage was shorter than that of the lattice girder and earlier into the debonding stage. However, the stiffness of the steel arch and concrete was greater than that of the lattice girder after debonding and showed a strong bearing capacity.

Loess is featured by a metastable structure, which results in its significant volumetric decrease under self-weight pressure when subjected to the increase in moisture. The prerequisite for analyzing such a unique deformation characteristic is to understand both water retention and thermo–hydro–mechanical (THM) behaviors of the loess. It has been well recognized that the water retention behavior of loess is related to its porosity and temperature. However, the influence of porosity and temperature-dependent water retention curve on the THM behavior of loess is still unclear and worthy of investigation. In this study, a coupled theoretical model for the THM behavior of loess was developed and then numerically solved using the finite-element method, in which the effects of changes in porosity and temperature on loess hydraulic properties are incorporated. Suction-controlled oedometer tests and pressure plate tests on loess specimens were conducted in the laboratory to calibrate the corresponding model parameters and validate the coupled model. The model was then adopted to investigate the coupled THM or deformation behavior of loess by simulating both the column tests and the field immersion tests. It was found that the predicted water saturation and void ratio increase with an increase in temperature. The results based on the van Genuchten model overestimated the water saturation and the void ratio, compared with that predicted using the Gallipoli model. The larger temperature during the field immersion test caused a larger volumetric strain rate and a larger surface settlement rate. The results of this study would contribute to the understanding of the coupled THM process for unsaturated loess and also enhance the importance of the effect of void ratio and temperature change on loess behavior.

Abstract

At present, the reliability analysis and design method of vertically loaded piles embedded in spatially variable soils is difficult to be applied in practical engineering due to the huge computation effort required. To improve computational efficiency, this paper proposes a new method called the FORM–KL–LTM, which integrates the advantages of the first-order reliability method (FORM), the Karhunen–Loève (KL) expansion method, and the load transfer method (LTM). The main framework of the FORM–KL–LTM is the FORM, which is used to perform reliability analysis for the pile. The KL expansion method is adopted to carry out random discretization to generate the discrete soil parameters required by each iterative computation of the reliability index using the FORM, and the LTM is employed to evaluate the nonlinear load–settlement behavior of the pile head and to compute the values of limit state functions required by the FORM. The proposed method is computationally efficient because the number of random variables is controlled by the limit number of KL expansion terms. Based on the FORM–KL–LTM, a reliability sensitivity analysis method is proposed, which can compute the sensitivity index for measuring the relative sensitivity of the reliability index with respect to soil properties. Furthermore, a procedure for the reliability-based design (RBD) of piles embedded in spatially variable soils is established for the design of pile geometry, and a design ratio is defined to select the controlling limit state in the RBD of pile for both the ultimate limit state and the serviceable limit state. The procedure, accuracy, and efficiency of the proposed methods are demonstrated by providing an example of the reliability analysis and design of a vertically load pile in spatially variable soils.

Practical Applications

The spatial variability of soil has been recognized as an important source of uncertainty of the bearing performance of the pile, and therefore, it should be considered in the reliability analysis and design of a pile foundation. However, the methods used in the current literature, such as the discretization of a random field, the calculation of load–displacement curves, and the reliability analysis of a pile foundation, require a huge computation effort. Low computational efficiency is highly disadvantageous to designers, which makes the reliability analysis and design method by considering a soil’s spatial variability difficult to be widely applied to practical engineering. Therefore, this study proposes a new method called the FORM–KL–LTM to perform the reliability analysis and design of vertically loaded piles in spatially variable soils. This method greatly reduces the number of random variables and simulations of the performance function, thus improving the computational efficiency. Based on the FORM–KL–LTM, a reliability sensitivity analysis method is proposed to carry out a sensitivity analysis of soil parameters on the reliability of a pile foundation. Moreover, this paper defines the design ratios for discussing which limit state mainly controls the failure state of the pile foundation under different soil properties and pile geometry.

At present, the research on retaining walls with relief shelves mainly focuses on translational displacement mode, and the research on RB mode is less. Using adaptive software, it is possible to obtain the grid distribution diagram and shear dissipation diagram of the filling soil by simulating the retaining wall’s rotation around its heel. The shear dissipation diagram was examined to determine the distribution of sliding surfaces in the active limit condition. The plastic region was meshed using the slip line technique. The slip line mesh distribution and the finite-element mesh distribution were compared to ensure that the two mesh distributions were consistent. Simultaneously, with the effect of retaining wall geometry, infill soil quality, and other elements on the grid distribution and earth pressure being investigated, by contrasting the computed normal earth pressure (σ_n) distribution with the finite-element findings, the correctness of the approach was demonstrated. It was discovered that increasing the relief shelf position and wall heel length will reduce the retaining wall’s earth pressure, while increasing the relief shelf length will have the reverse effect. In the active limit condition, the retaining wall earth pressure decreased with increasing filling strength, but changes in filling quality had little impact on grid distribution.

Recent thermodynamics-based constitutive modeling has enabled robust formulations for complex coupled mechanical, hydraulic, thermal, and chemical interactions. Despite such advances, the constitutive modeling of fractured sorptive media with complex mechanical behavior has attracted less attention. We present a new sorptive poroviscoelastic model for fractured rocks that specifically integrates the rate-dependent viscous flow into the coupled fracture fluid flow and matrix gas desorption processes using the two-potential framework, mixture theory, and continuum mechanics. The proposed dissipative viscoelastic strain rate evolution law is governed by the applied stress variable and the amount of gas adsorbed in the matrix pores. The model is exemplified through the simulation of gas production from a sorptive shale formation. The numerical results show that poroviscoelasticity becomes dominant at late production times when the pore-pressure and desorption fronts have progressed significantly. It is revealed that time-dependent stress accumulation can reach high magnitudes which can cause fracture closure that risks impedance to further gas production. Neglecting viscoelastic multiphysics effects in the modeling of fractured sorptive rocks can reduce the accuracy of the predicted production data. In addition, the contribution of desorption-induced viscoelasticity to bulk rock deformation may be substantial in shales and other highly adsorbing rocks and may also be the key to explaining some of the complexities encountered during drilling or hydraulic fracturing operations.

The efficient assessment of tunneling effects on adjacent existing piles is significant for underground constructions. In this study, a new analytical approach was developed to rapidly assess lateral pile responses due to tunneling. A nonlinear Pasternak foundation model considering the unloading effect (NPFM-U), which took into account the nonlinearity of the pile–soil interaction and the attenuation of the soil resistance caused by tunneling, is proposed. Inspired by the minimum potential energy principle, an accurate and efficient artificial intelligence optimization algorithm––chaos radial movement optimization (CRO)––was developed to optimize the minimum value of the total potential energy of the tunnel–soil–pile system in which the proposed NPFM-U was utilized, and to obtain the lateral responses of the piles. The reliability of the proposed method was subsequently validated by comparing it with data from centrifuge and field tests. Parametric studies on the influence of the parameters of the CRO algorithm’s maximum iteration number, number of particle groups, tunnel diameter, pile modulus, pile diameter, pile length, soil undrained shear strength, reduction factor, and pile–soil horizontal distance were also performed.

Bored piles (drilled shafts) socketed in weathered rock mass are frequently used to transfer higher lateral loads from superstructures to competent underlying rock mass. A common method for analyzing the response of laterally loaded bored piles is to use nonlinear p–y curves to represent the rock mass resistance. This paper presents the development of a hyperbolic p–y criterion for flexible bored piles in weathered rock mass under static loading. The hyperbolic p–y criterion was derived based on the Hoek–Brown failure criterion. The ultimate resistance of the rock mass and the initial stiffness of the p–y curve were proposed based on mathematical and statistical analyses. The effectiveness of the proposed p–y criterion was verified with finite-element analysis and full-scale tests. Finally, recommendations for choosing the rock mass parameters to establish the p–y curve were provided.

A monopod bucket foundation supporting an offshore wind turbine structure is subjected to lateral loading on account of combined wind and wave action, in addition to vertical loading from the self-weight of the turbine structure. In this numerical study, the bearing behavior of the bucket foundation in medium dense and very dense sands is investigated for varying bucket geometries, superstructure loads, and lateral loading cases. The nonlinear stress–strain response of the sandy soil is incorporated. The results of the modeling are described and evaluated in terms of the variations of displacement and rotation responses, ultimate and allowable lateral load capacities, depths of rotation center, surrounding soil deformation, and failure mechanisms. Interaction diagrams between lateral load capacity and resisting moment capacity for various limit states are presented, and their differences are brought out. As the design is dominated by requirements resulting from serviceability limit state, predictive expressions are proposed for the depth of rotation center, initial stiffness, and allowable lateral load capacity to serve as preliminary design guidelines for a monopod bucket foundation in sandy soils. The expressions are suitable for interpolation within the range of realistic parameters considered in the study.

With the increasing demand of transport construction in coastal areas, seabed instability around tunnels subjected to ocean waves and protection of the tunnels are becoming increasingly important. Current analytical solutions on the seepage field around subsea shield tunnels induced by waves are generally based on the impermeable lining, without considering the permeability. Furthermore, previous studies seldom take account of the influence of nonlinear wave loads under the sloping seabed terrain. For better tunnel stability, this paper presents a new set of analytical solutions for predicting Stokes wave-induced seepage pressure responses around a shield tunnel in a sloping seabed considering the influence of the permeable tunnel lining. The accuracy of the presented solutions is then verified by comparison with the numerical solution and experimental data, showing reasonable alignments. Moreover, parametric analyses are also performed to assess the influence of wave characteristics, seabed properties, and tunnel lining permeability on seepage pressure responses, in which the distribution of the excess pore pressure response outside the lining and excess pore pressure around the tunnel circumference is described in detail. In general, the analytical solutions provide an effective insight into the wave-induced seepage pressure response around a shield tunnel, which can serve as a credible theoretical basis in the preliminary design of tunnels.

This study examines the capacity of single piles subjected to cyclic axial tension or compression load in the loess area under in situ compaction degree and extruding conditions. Four cyclic tension and compression loading tests, and two conventional tension and compression tests on single piles were carried out at a typical loess site of the Loess Plateau region of Northwest China's Shaanxi Province. A series of pretest preparations, including site leveling, steel cage production, pile formation, and soil compaction, are performed. The axial displacement of pile top, pile axial force, and frictional force of the pile side of a single pile measured in the test process were analyzed. The cyclic tension or compression load–displacement curves of the piles in loess, under the in situ compaction degree condition, show the load results in an influence of the movement trend that cannot be ignored. There is no overlap between the compression-unloading curve and tension-unloading curve. This phenomenon indicates that the cyclic loading accelerates the destruction of the pile foundation. Under an extruding condition, the difference between the maximum deformation and the minimum deformation is 2.412 mm, which is 60% of the ultimate deformation of a conventional single pile. The lateral friction of the pile shows multipeak distribution along the pile body, and the attenuation range of lateral friction strength at the pile tip is more than 50% in the failure stage.

Cement stabilization is a widely applied technique in improving the workability and geotechnical properties of soft clay. This paper investigated the influence of cement stabilization on the soil–water characteristic curve (SWCC) and the deformation behavior of unsaturated cement–stabilized soft clay. The combined effect of cementation and partial saturation on the hydromechanical behavior of cement-stabilized soils was discussed. The SWCC of stabilized soil was measured in the full suction range under drying and wetting paths using the pressure plate method, the filter paper method, and the vapor equilibrium technique. The deformation behaviors of cement-stabilized soft soil were investigated by conducting suction-controlled oedometer tests. Furthermore, scanning electron microscope micrographs and mercury intrusion porosimetry tests were performed to investigate the effects of cement content on the evolution of soil pore structures. The test results showed that the water retention capacity of the stabilized soft clay increased with increasing cement content. The SWCC showed a significant hysteretic behavior in the boundary effect zone and transition zone, whereas the hysteretic effect was unapparent in the residual zone. The increased cement content had a more significant hysteretic effect on the SWCC. The deformation resistance capacity increased as the cement content and matric suction increased. However, the effect of matric suction on deformation resistance capacity decreased as the cement content increased. With the increase in cement content, the macropores were converted to small interaggregate pores, the pore spaces were distributed more uniformly, and the particle surface became rougher, resulting in higher water retention capacity and significant hysteresis of the SWCC.

Ground fissure is the most common geological catastrophe phenomenon in Xi’an, posing a major security threat to the currently developing urban cloud rail transit system. In this paper, a 3D-FEM calculation model is established to study the influence of the intersection angles between the hidden ground fissure and the cloud rail on the deformation and failure characteristics of the structure. The findings indicate that the pile foundation is under tension in the main deformation area of the hanging wall of the ground fissure, and the negative friction zone (NFZ) appears below the neutral point (buried depth 18 m for intersection angle 30°). The pile foundation is under compression in the footwall, and the pressure it bears is less than the tensile force sustained by the hanging wall pile, and the NFZ is above the middle point. The NFZ of the pile foundation in the hanging wall and footwall increases as the intersection angle decreases. The pile foundation mainly undergoes vertical settlement, and the horizontal displacement is relatively small. The 3D movement of the pile foundation results in settlement and inclination of the superstructure of the cloud rail simply supported beam bridge, such as the pier and track beam. Therefore, the cloud rail bridge should span the ground fissure at a large angle as far as possible, and 3D adjustable support should be adopted to adjust the offset of the track beam caused by the ground fissure.

When calculating the surface settlement caused by tunnel excavation, the conventional stochastic medium theory is complicated by integration. Particularly for tunnel undercrossing excavation, it shows large errors in calculating the surface settlement. In this paper, the conventional 2D stochastic medium theory is simplified by means of a nonuniform convergence. Based on the Sagaseta formula, the ground loss along the tunnel excavation direction is derived, and the 2D model is extended to calculate the 3D surface settlement. Furthermore, the effect of the existing tunnel is considered by the equivalent layered method, and the simplified 3D model is proposed for calculating the surface settlement induced by tunnel undercrossing excavation. The simulated and measured data are compared with the predicted results of the theoretical model, and the characteristics of the 3D surface settlement are investigated. The results show that compared with the surface settlement in the non-undercrossing section, the surface settlement in the undercrossing section has a larger lateral range. However, the maximum settlement value is significantly reduced, and the surface settlement trough curve is characterized as “wider and shallower.” The results of the proposed model are in better agreement with the simulated and measured data than those of the conventional stochastic medium theory and have higher correlation and broader applicability.

The present study addresses the characterization of long-term and durability properties for employment in road subgrade construction of geopolymer-treated sediments. Four mixtures are presently selected based on a previous study: untreated sediment, sediment treated with 2% hydraulic lime (L) and 7% ordinary Portland cement OPC, and two geopolymer-treated mixtures using 5% and 10% of ground granulated blast furnace slag/sodium silicate-based geopolymers. Long-term properties are investigated through unconfined compressive strength and tensile strength tests. The resistance of designed materials to weathering conditions is tested through freeze–thaw cycles, humidification–drying cycles, and immersion in water. Sediments treated using 10% geopolymer binder are resistant to weathering conditions and showed long-term properties superior to those of sediments treated using an L/OPC mixture.

Despite the convenience of tunnels for transportation in modern cities, ground movements induced by tunneling may cause pipeline deformations. One of the key challenges is the higher failure potential in the location of joints on jointed pipelines. This study presented a closed-form solution based on the Winkler model to explore the effects of joints on pipe–soil interaction due to tunneling-induced deformations. Finite-element simulations were used to verify the closed-form solutions and a design chart was proposed based on the governing equations to facilitate the estimation of pipeline responses to tunneling-induced ground movements. Generally, good agreements have been obtained between the results of the closed-form solution and the finite-element models. In addition, the findings suggested that the calculated tunneling-induced pipeline deformations may be significantly underestimated if the effect of joints is not considered.

A series of triaxial creep tests were carried out on red sandstone under the conditions of high temperature, high pore pressure, and high confining pressure, and the creep mechanism was analyzed in terms of the velocity and energy variations in the ultrasonic waves emitted during the creep test. Changes in porosity and pore distribution in the samples were investigated by nuclear magnetic resonance (NMR) for different creep stages, and the evolution of the internal microstructure of the samples was examined. The experimental results showed that shear microcracks were mainly initiated during the primary creep stage, these microcracks coalescing to form macroshear cracks in the accelerated creep stage. In addition, the changes in porosity exponentially increased with increased deviatoric stress, with small pores developing into medium pores, while the number of large pores was basically stable.