Model tests and numerical simulation were conducted to study the effects of spandcan penetration and extraction on the motion behavior and lateral bearing capacity of adjacent suction caissons. Results indicate that during spudcan penetration, the suction caisson experiences a combination of rotational, horizontal, and vertical movements. The suction caisson moves horizontally away from the spandcan and vertically upwards during penetration, while it experiences horizontal movement away from the spandcan and vertical settlement during extraction. The maximum horizontal and vertical displacements of the suction caisson increase with increasing the spudcan penetration depth and spacing. In addition, the lateral bearing capacity of the suction caisson exhibits significant directional characteristics influenced by spandcan penetration and extraction. The lateral bearing capacity of the suction caisson after spandcan extraction varies in different directions as follows: along the direction of the line connecting the spandcan and the center of the suction caisson, toward the spandcan < away from the spandcan < perpendicular to the line connecting the spandcan and the suction caisson center. When the spacing between the spudcan and the suction caisson is 2.5 times the diameter of the suction caisson, the lateral bearing capacity in all directions remains unaffected. When the spandcan penetration and extraction area is behind the suction caisson loading direction, the soil deformation around suction caisson distributes symmetrically along the loading direction. When the spandcan penetration and extraction area is on both sides of the suction caisson loading direction, the soil deformation range no longer distributes symmetrically along the loading direction. The penetration and extraction of the spandcan reduces the range of the deformation of the soil under horizontal loading. Based on model tests and three-dimensional large deformation numerical simulation results, the impact of spudcan penetration and extraction on the lateral bearing capacity of suction caisson in different scales was studied. The correlation between model tests and prototype reality was established, enabling the test results to better guide engineering practice.

Damage deterioration of rock by freeze-thaw cycles seriously affects the long-term service performance of tunnel projects in cold regions. In order to obtain the fine-scale characteristics of freeze-thaw damage and post-freeze-thaw loading mechanical properties of fissured rocks, tests on the mechanical properties of water-filled fissured sandstones under different levels of freeze-thaw cycles were carried out. Equations were derived to describe the relationship between the volume increment of frozen water, recharge, and the number of freeze-thaw cycles throughout the freeze-thaw process. The particle flow method is used to construct a rock freeze-thaw deterioration model based on the theory of water ice phase transition volume expansion, and the reliability of the model is verified by indoor tests. It is shown that with the increase of the number of freeze-thaw cycles N, the mechanical properties of the specimens show linear attenuation, the degree of attenuation is positively correlated with N. And the mechanical properties of the specimens are the weakest when the fissure inclination angle is 30°. The degradation of fissure specimens due to freezing and thawing is more pronounced than in other parts of the sample. In addition to surface particle flaking, microcracks develop at the ends of the fissures. This results in freeze-thaw damage accumulating both on the surface layer and internally within the specimen. The fine microcracks produced by the freeze-thaw process of granular flow are mainly tensile cracks, and the number of cracks is positively correlated with N. The freeze-thaw microcracks are gradually extended and developed from the surface layer of the specimen to the inner layer, and the number of microcracks and their distribution characteristics affect the load damage morphology of the specimen, and they are mostly manifested as the secondary cracks distributed in the vicinity of the main rupture zone of the load damage rupture zone. This study provides new ideas and references for the damage degradation process of rock under freeze-thaw action, and also helps to promote the prediction of catastrophic changes and long-term service performance assessment of tunnel engineering in cold regions.

Particle gradation and morphology are key attributes that influence the mechanical behavior of sandy soils. Due to the intertwined characteristics of gradation and morphology in natural calcareous sand particles, current experimental research has not yet been able to provide insight into the influence of these factors individually. In this study, a mass production of calcareous sand particles with controllable morphology and size was realized based on X-ray computed tomography (X-CT) scanning technology, spherical harmonic analysis, and 3D printing technology. By conducting consolidated drained triaxial tests on simulated calcareous sand samples with different gradations, the influence of particle gradation, as a single variable, on the mechanical properties of calcareous sand was explored. The results show that the mechanical behavior of the simulated calcareous sand samples is highly consistent with the typical characteristics of natural sand. The fractal dimension only has a significant effect on the critical state stress ratio when it changes substantially, and the critical state of calcareous sand with different fractal dimensions can be described using the static unique line method. At the phase transformation state, the axial strain is positively correlated with both the fractal dimension and the effective confining pressure, while the stress ratio increases exponentially with the fractal dimension. The simulated calcareous sand exhibits apparent cohesion, with the peak apparent cohesion decreasing linearly with the increase in fractal dimension, while the residual apparent cohesion is largely unaffected by changes in fractal dimension. Both the peak and residual internal friction angles increase exponentially with the fractal dimension.

The two-phase displacement flow characteristics within complex porous rocks are pivotal to the recovery rates in unconventional oil and gas recovery as well as geothermal exploitation, garnering significant research interest. This study focuses on four types of porous media with both ordered and disordered structures, employing a self-constructed microfluidic experimental visualization setup to investigate the flow characteristics under five different flow rates and four distinct viscosities of the displaced fluid. The influence of capillary number, viscosity ratio, and the disorder of the porous structure on the two-phase displacement process is thoroughly analyzed. Findings indicate that the fractal dimension of the invading phase is correlated with the displacement pattern and positively associated with displacement efficiency, serving as a universal function of the invading phase's content. The distribution characteristics at displacement completion are intimately linked to the displacement mode. A transition from compact displacement to capillary fingering is marked by an increase in the quantity and standard deviation of the trapped phase. Conversely, the shift from capillary fingering to viscous fingering mirrors the transition from capillary fingering to ordered dendritic, characterized by a reduction in trapped phase quantity and an enlargement of standard deviation. Incorporating the impact of fluid viscosity ratios, a modified relationship between the capillary number and the displacement saturation of the invading phase is formulated, enabling the prediction of displacement efficiency that accounts for viscosity ratio effects.

There is currently a limited amount of research on mathematical models for seepage in enzyme-induced calcium carbonate precipitation (EICP) solidified sand. Existing seepage models neglect the influence of calcium carbonate crystals formed during the EICP mineralization process, thereby rendering them insufficient in predicting the permeability behavior of EICP-solidified sand. To address this issue, this study establishes a mathematical model for seepage in EICP-solidified sand based on the Kozeny-Carman (K-C) equation, incorporating the effects of calcium carbonate crystals on pore filling, tortuosity, and specific surface area. By comparing the theoretical results of the model with experimental data, the feasibility and rationality of the model are validated. Furthermore, the impact of porosity, mean particle size, calcium carbonate content, and specific surface area on the permeability coefficient of the samples is analyzed. The research findings indicate that: 1) The proposed mathematical seepage model can effectively represent the permeability coefficient of EICP-solidified sand under various particle size distributions and cementation degrees, demonstrating broad applicability. 2) The permeability coefficient (k) increases with the rise in porosity (n) and mean particle size (D₅₀), with k being more sensitive to changes in porosity than mean particle size. 3) The permeability coefficient decreases significantly with increasing calcium carbonate content and specific surface area. As calcium carbonate content increases, the sample porosity gradually decreases, tortuosity increases, and the water film adhering to the calcium carbonate crystals thickens, leading to a substantial drop in permeability coefficient. The results of this study provide a theoretical foundation for the engineering application of EICP-solidified sand.

Understanding the dynamic tensile behavior of rock is essential for studying the response of rock masses under blasting and seismic loading. Granite specimens were subjected to dynamic Brazilian splitting tests using a combination of ultra-high-speed camera and digital image correlation (DIC) techniques. Stress equilibrium and central crack initiation were assessed through strain gauge measurements and high-speed photography. The evolution of the deformation field on the microsecond timescale was analyzed using high-speed DIC, and the rate-dependent mechanisms at the crystal scale were investigated through polarizing microscopy. The results show that the tensile strength–strain rate relationship of granite can be divided into three regimes. In Regime II, the behavior conforms to the unified dynamic strength model, with a characteristic strain rate of 48.3 s^-1 and a dynamic increase factor of 0.97. Notably, the average fragment size remains nearly constant with increasing strain rate. The ratio of residual kinetic energy to total dissipated energy ranges from approximately 23% to 47%. At the crystal scale, meso-scale failure modes include transgranular cracking, crack deflection, crack clustering into bands, and grain pulverization. With increasing strain rate, the failure process transitions from central crack initiation to boundary-dominated failure. When the strain rate exceeds a critical threshold, stress equilibrium and central initiation conditions are no longer met, resulting in an apparent decrease in dynamic tensile strength. This indicates that test validity may be compromised under such conditions, and results must be interpreted with caution.

Rock cavern compressed air energy storage (CAES) represents a promising solution for large-scale physical energy storage. Yet, it faces a critical challenge in ensuring the long-term airtightness of underground storage reservoirs. This paper introduces a composite sealing layer consisting of granular bentonite and a thin steel plate to address this issue. Granular bentonite is fabricated by compacting bentonite powder and subsequently crushing it into particles of varying sizes. Vibration tests and constant stiffness swelling tests were conducted on granular bentonite mixtures to evaluate its feasibility for constructing a sealing layer. Results indicated that, for granular bentonite mixtures, the packing dry density stabilizes after 210 seconds of vibration. For multi-size mixtures adhering to the Andreasen equation with a maximum granular size of 5 mm, the peak packing density is attained at n=0.5, corresponding to a value of 1.35 g/cm3. All binary-size mixtures achieved their peak packing densities at an optimal coarse content of 70%. This phenomenon can be explained by the theory of equal-size particle stacking states of granule. During vibration, granular bentonite tends to segregate, compromising its uniformity. However, upon hydration and subsequent expansion, bentonite compacts sufficiently to fill the interstitial voids between the original granules, thereby restoring overall uniformity. This process is crucial for ensuring uniform force distribution across the thin steel plate and the surrounding rock. Under constant stiffness constraints, the swelling deformation of bentonite partially releases its swelling potential, while the residual swelling potential manifests as residual swelling pressure. The relationship between residual swelling pressure and swelling deformation rate, under constant stiffness constraint, has been established. This relationship can serve as a design reference for constructing a composite sealing layer to prevent damage to the thin steel plate due to buckling deformation.

Fractures are critical factors causing the degradation of mechanical properties in rock mass. In this study, addressing the damage effects and crack propagation problems induced by open fracture on rock mass, an analytical solution for the elastoplastic boundary equation at the tips of open fracture was derived under the consideration of the T-stress effect, based on the Mohr-Coulomb strength criterion. Using the plastic core region at the fracture tips as the evaluation indicator, we analyzed the influences of stress environment and fracture inclination angle (α) on rock mass damage. Through discrete element numerical simulations, the mesoscopic crack propagation characteristics and damage evolution patterns of open fracture were investigated. The obtained results indicate that: (1) When the lateral pressure coefficient (λ) is less than 0.4, the expansion rate of the plastic core region within the range [π/2, π] exceeds that of other regions as λ decreases, resulting in its morphology exhibiting an uneven distribution on the fracture surface; (2) For λ < 0.7, with α = 45° as the critical threshold, the plastic core region area decreases gradually when α decreases below the threshold, while it increases rapidly when α exceeds this value; (3) As α increases, the plastic core region area exhibits an S-shaped growth curve characterized by “slow growth–rapid growth–stabilization”, with steeper curve transitions observed at lower λ values; (4) A negative correlation exists between the uniaxial compressive strength of open-fractured rock mass and the plastic core region area. Specifically, an increase in plastic core region area reduces the required stress increment for crack propagation, extends crack length, and consequently decreases the compressive strength of the rock mass. The study reveals the mechanical mechanisms of rock mass damage caused by open fracture and provides a theoretical basis for rock mass stability assessment.

Owing to the special composition and micro-fabric, the loess exhibits particular engineering mechanical behaviors, such as water sensitivity, structural strength, moistening deformation, etc. The Bishop’ effective stress and degree of saturation are taken as the direct driven variables of the model to consider the direct effects of degree of saturation on the structural strength and deformation behavior of intact loess. The structure of the intact unsaturated loess is divided into the intrinsic structure and degree of saturation dependent cemented structure. The evolution equations are developed for modeling the change of intrinsic structure with strain and the development of compressive behavior with degree of saturation. The load-collapse yield function is developed in the degree of saturation-Bishop effective stress space to represent the change of the structural yield behavior with the degree of saturation. By coupling the void ratio dependent soil-water characteristic curve via the volumetric deformation, a hydro-mechanical coupling elastoplastic constitutive model is developed for unsaturated intact loess. The model possesses 12 parameters, all of which can be determined by the unsaturated triaxial compression test and shear test. The model is validated by comparing the available results of loess in Xi’an, Iran, and Lanzhou from triaxial compression tests and shear tests under different hydraulic and stress paths. The results show that the proposed model is capable of predicting the structural yielding, moistening deformation, hydro-mechanical coupling behavior, and the effects of loading and wetting sequence on the deformation and hydraulic behaviours of the loess. The proposed model takes the degree of saturation instead of the suction as the direct stress variable, which can represent the direct relation between the hydro-mechanical behavior and the water content of the intact loess. The present study provides a new framework for developing constitutive models for unsaturated intact loess.

To enhance national energy security, recent years have witnessed an increase in state investment directed towards the research and development of compressed air energy storage (CAES) technology. These initiatives are inherently more complex than traditional projects, as the stress relaxation characteristics of geological formations, particularly rocks, are influenced by a multitude of factors. According to the characteristics of CAES engineering, stress relaxation experiments of salt rock under barometric stress coupling were carried out from a new perspective to explore the stress relaxation characteristics of salt rock under different air pressures and axial starting stress conditions. The results show that: (1) The macroscopic behavior of stress relaxation in salt rock is independent of air pressure, and the process can be categorized into three distinct stages: rapid relaxation, decelerated relaxation, and stable relaxation. Notably, the rapid relaxation phase accounts for approximately 50% of the total relaxation, while the stable relaxation phase represents the predominant portion of the entire relaxation process. (2) The stress relaxation behavior of salt rock is significantly influenced by both axial starting stress and air pressure. Specifically, increased axial starting stress and air pressure correlate with heightened initial stress relaxation rates, greater relaxation rates, and an enhanced degree of stress relaxation during the stable relaxation phase. (3) Under cyclic pressure conditions, the stress relaxation of salt rock exhibits a cyclic relaxation pattern, with the relaxation curve being governed by the stress relaxation curve of salt rock at constant pressure, corresponding to its cyclic upper and lower limits. (4) Environmental scanning electron microscopy (ESEM) images of the relaxed salt rock reveal that the formation and propagation of micro-cracks constitute the primary mechanism of internal damage within the salt rock. Post-relaxation, the meso-structural damage observed in the salt rock includes grain debris, intragranular cracks, intergranular cracks, and trans-granular cracks. (5) The improved nonlinear two-element generalized Maxwell relaxation model can better describe the stress relaxation behavior of salt rock under different starting stresses and pressure conditions, and provide a certain reference for the stability assessment of salt cavern compressed air energy storage.

The 3D multi-horizontal wells hydraulic fracturing technology is the core technology to improve the production and recovery of unconventional oil and gas reservoirs. There is more complex interaction between adjacent fractures and adjacent horizontal wells, and the hydraulic fractures show complex morphology in the 3D space. This study conducted a 3D multi-well fracturing experiment. Using typical cases, the spatial distribution of the 3D fracturing network was investigated considering the interaction between fractures and wells. Under true triaxial conditions, multi-wellbore alternating, zipper fracturing was carried out, and the changes of pump injection pressure and pressure in the fracture were monitored. Through 3D reconstruction of the spatial morphology of 12 main fractures of three wells, it is found that the pre-fractured wells have an attractive effect on the hydraulic fractures of the subsequent fractured wells, and the fractures of the subsequent fractured wells show asymmetric expansion. The formation of branching fractures is related to the local stress field inversion induced by the main fractures, and the connectivity with the main fractures is good. Both of them are important components of the 3D fracture network. The statistical results of fracture density show that there is periodicity in the distribution of the interaction zone between main fractures, and the periodicity of the local fracture density, fracture geometry and corresponding breakdown pressure are formed. The above experimental results can provide a reference for the optimization of fracturing schemes.

The shear characteristics of continuously graded granular soils are closely related to their gradation characteristics. This paper aims to clarify the quantitative relationship between the apparent gradation of dense granular soils and their peak shear strength. Firstly, the influence of apparent gradation changes on the soil’s internal skeleton structure characteristics is investigated using a discrete element numerical model. Quantitative indices are introduced to characterize these structural characteristics. Subsequently, 16 continuous gradation granular soil samples are designed, and indoor direct shear tests are conducted to reveal the quantitative relationship between the skeleton structure characterization indices and the peak friction angle of the soils. The research results indicate that changes in the apparent gradation of granular soils can significantly alter the composition and network structure of the bearing skeleton. By using the dominant size of the skeleton structure (d_ed) and the coefficient of gradation non-uniformity (C_u) as characterization indices, a positive correlation is observed between these indices and the peak friction angle of continuously graded granular soils. An empirical shear strength model is established using d_ed and C_u as influencing factors, accurately fitting the peak friction angle results obtained from the direct shear tests. This model can be widely applied to various types of granular soils described in existing research. These findings provide a computational reference for predicting the strength of granular geomaterials in engineering practice.

Ring shear tests were conducted on the clayed sliding-zone soil of the Majiagou landslide to investigate the effects of water content and shear rate on its shear behavior. Furthermore, a statistical damage constitutive model was developed based on damage mechanics and statistical theory to describe strain-softening, revealing the relationship between sliding-zone soil damage evolution and reservoir-induced landslide development. The results show that the clayed sliding-zone soil exhibits distinct strain softening behavior. As water content increases, the shear strength and residual friction coefficient of the sliding-zone soil decrease. The shear rate has varying effects on the shear strength of the sliding-zone soil across different intervals. Within a shear rate range of 0.1−1.0 mm/min, shear strength shows minimal variation. However, when the shear rate exceeds 1.0 mm/min, shear strength decreases with increasing rate. The statistical damage constitutive model effectively captures the strain-softening characteristics of the sliding-zone soil, with the Weibull distribution parameters k and λ reflecting the soil’s elastic-plastic properties and degree of strain-softening, respectively. This study provides a theoretical basis for understanding the evolution mechanisms of reservoir-induced landslides and for developing effective mitigation strategies.

Based on the monitoring strains of distributed fiber optic sensors (DFOSs), an inversion method has been developed to predict the deformation behavior of shield tunnels. A curved Winkler beam-hinge model, which takes into account the joint rotational effect ignored in the existing related studies, is properly established and solved using the finite difference method (FDM). The inversed lining responses, including the deformation, internal force, external load and joint stiffness, are derived. Two types of lining damage, namely the voids behind the lining and stiffness reduction of joint, are identified in terms of the denoised strain increment and curvature profiles. The inversion accuracy is demonstrated to be hardly affected by the resistance of surrounding rock and noise interference. The assumption of dv/dφ=0 at the position of maximum strain yields high inversion precision, especially for a large lining deformation, where v represents the radial displacement, and φ represents the central angle of the node. An available inversion approach by fitting the bending moment of lining combining with few strain gauges is proposed for the case of single-sided layout of DFOSs. The influence of joint rotational stiffness on the deformation consistently lies within a range that remains almost unchanged for different surrounding stiffnesses, lining elastic modulus, and burial depths.

To address the limitations of the traditional Forchheimer equation in describing the nonlinear seepage behavior of single fracture rock mass under high confining pressure and water pressure coupling, the two-part Hooke’s model (TPHM) was used to describe the relationship between the hydraulic aperture and the effective normal stress of single fracture. Linear coefficient A and nonlinear coefficient B were both characterized as functions of the effective normal stress. A modified Forchheimer model, which accounts for the coupled effect of nonlinear seepage and normal stress in single fractures, was presented, and the validity of the model was verified through experimental data and numerical simulations. Furthermore, the variation of linear coefficient A and nonlinear coefficient B under normal stress and fracture water pressure was analyzed. The hydro-mechanical coupling effect is significant for a single fracture under high confining pressure and high water pressure. The pressure gradient-flow test data increasingly deviate from the traditional Forchheimer equation, while the modified Forchheimer model remains consistent with the experimental data. When the fracture water pressure p is zero, the modified model reduces to the traditional Forchheimer equation without considering water pressure effects. The coefficients A and B are sensitive to the effective normal stress, increasing nonlinearly with the normal stress, and decreasing nonlinearly with increasing fracture water pressure. Compared to simulations that do not account for hydraulic coupling, the numerical model that considers hydraulic coupling requires a smaller pressure gradient for the same flow rate, and the simulation results are accurately described by the modified model.

To explore the characteristics of the seepage grouting process of fractured rock, this study designed a set of rock fracture grouting experimental systems, including slurry supply, data monitoring, and grouting simulation sub-systems. Through the grouting experiment of single fracture sandstone under different grouting pressures (0.3, 0.4, 0.5 MPa), the variation of pipeline flow pressure, slurry flow rate, and slurry pressure were analyzed, and the influence of slurry parameters on flow characteristics was discussed by numerical simulation. The experimental results show that the pipeline flow pressure, slurry flow rate, and slurry pressure show a three-stage characteristic of rising-stabilizing-falling. In the stable stage, the three variables positively correlate with the grouting pressure, but the sensitivity to the change in grouting pressure is different. With the increase of grouting pressure, the slurry pressure increases, while the response of slurry flow to the change of grouting pressure gradually decreases (when the grouting pressure increases from 0.3 MPa to 0.5 MPa, the slurry flow increases by 15.3% and 8.1% respectively). When the grouting pressure reaches 0.3 MPa, the flow pressure in the pipeline remains unchanged. The numerical simulation results show that the slurry flow is related to its diffusion form in the fracture. When the diffusion is semi-circular, the slurry velocity decreases, and the flow rate increases. The slurry velocity increases when the diffusion form changes from semicircle to convex. When the diffusion form changes from convex to uniform diffusion, the parameters tend to be stable. The slurry flow rate and flow velocity are inversely proportional to the plastic viscosity of the slurry. The increase of the plastic viscosity enhances the effect, while the slurry yield stress has little effect on the flow rate and flow velocity.

To investigate the mechanisms of failure and instability in steep karst slopes with deep and large fissures due to mining activities, a comprehensive review of typical rock collapse and landslide cases in karst mountains with such fissures in southwestern China over the past 50 years was first conducted, and the basic characteristics of these collapses and landslides were analyzed. Subsequently, taking the collapse at Yaoyanjiao in Houchang Town as a case study and based on extensive field investigations, a thorough examination was carried out using similar physical model tests and theoretical analysis to explore the impact of underground mining on the deformation and failure of the steep karst slope with deep and large fissures. The controlling effect of these fissures on the mining-induced slope was discussed. The mechanism of slope collapse and instability was elucidated, and the stability variation of slope before and after collapse were obtained. Finally, the failure and instability modes of steep karst slopes with deep and large fissures under various geological conditions due to mining activities were discussed, revealing the formation mechanisms of different collapse and landslide modes. The results indicate that the deformation and failure of the slope adjust continuously with the progression of mining. Initially, the slope behind the deep and large fissure experiences settlement and outward deformation, ultimately transitioning into a failure mode of “cantilever collapse”. The dangerous rock mass undergoes initial backward inclination deformation followed by forward toppling as mining progresses. The deep and large fissures exert a segmentation effect on the deformation of the mining-disturbed slope, which is correlated with the mining process. Underground mining exerts a decisive influence on the deformation and failure of steep karst slopes with deep and large fissures. Although there are certain similarities in the mechanical responses of different mountains to underground mining, the modes and mechanisms of ultimate collapse of the slopes exhibit significant differences under varying engineering geological conditions.

Compared to traditional small-diameter circular corrugated steel plate culverts, there have been few application and research on large-span pipe-arch steel corrugated plate culverts (PACSPCs) in subgrade engineering. Relying on a certain expressway project in Yan’an City, the field test scheme was elaborated in detail, and the mechanical characteristics of a rarely-seen PACSPC with a span of 9.5 m and a rise of 6.5 m during the embankment backfilling were tested. Numerical simulation was adopted to further study the influence of pipe parameters on its mechanical characteristics. The coefficient of soil arching effect Mf was introduced, combining orthogonal experiments and numerical simulations, and an earth pressure calculation model for large-span PACSPCs considering the soil arching effect was established. Finally, the accuracy of the calculation model was verified through the field test results. The results show that during the backfilling, the vertical deformation of the pipe is greater than the horizontal deformation. At the same position, the stress at the wave trough is greater than that at the wave crest. The existence of the soil arching effect makes the earth pressure on the top of the pipe and the settlement both show a V shape distribution. During the backfilling, the deformation at the top of the pipe is the largest, which is 36.1 mm. It meets the specification requirement that deformation should not exceed 2% of the span. However, the designers should pay particular attention to the stress design at the wave trough at 90° on both sides of the pipe. The bolt splicing positions of the pipe are recommended to be set near 30°, 180°, and 330° clockwise around the pipe. Increasing the corrugation size and the thickness of the steel plate can reduce the deformation and stress of the pipe to a certain extent, but the cost and material characteristics should be comprehensively considered in the design stage. The calculation results of the established theoretical model are in good agreement with the field test results, effectively reflecting the earth pressure distribution on the upper part of the large-span PACSPC. The research results can provide a reference for the design, construction, and theoretical analysis of large-span PACSPCs.

In order to find the slide-resistant capability of the subgrade steps in gravity-type anchorages of suspension bridges, the slip-line theory for plane strain problem of perfect plasticity is applied to derive the differential equations of the slip-lines for geotechnical materials satisfying Mohr-Coulomb failure criterion. Then, upper and lower limits of the slide-resistance of the subgrade step are developed by using the theorem of limit analysis, unlike the Rankine passive earth pressure, the proposed method takes account of the vertical pressure on the top face of the step, caused by the self-weight of the anchorage, and the friction between anchorage and the subgrade. Comparison with the finite element solutions shows that the actual slide-resistance lies between the lower and upper limits, and the resistance is greater than the lower limit by about 18%. At failure, the slip-band passes through the front end of the anchorage step; and the longer the horizontal length of the step, the higher the slide-resistance. Thus, the lower bound solution can be used to safely estimate the minimum slide-resistance of the subgrade step. The upper and lower limits of the slide-resistance of a multi-stepped subgrade can be expressed, respectively, as the summations of those values from constituent steps. However, due to the rigid rotation of the anchorage and the eccentric compression on the subgrade top, not all of the steps come into full play, and instead most slide-resistance comes from the first subgrade step. When it is near to the maximum load, the first subgrade step takes approximately 80% of the total slide-resistance, with remaining subgrade steps almost quitting work. It is shown that the lower limit of the slide-resistance of the multi-stepped anchorage is higher than maximum frictional force between anchorage and subgrade. Incorporation of the slide-resistance of the vertical step make the anti-slide stability factor of the anchorage increase by about 70%, and the actual slide-resistance of the entire multi-stepped subgrade is much greater than the horizontal component of the ultimate cable tension. In design stage, the slide-resistance of the multi-stepped subgrade can be estimated safely as the sum of those from the first and the second subgrades.

The study was conducted on a coarse-grained soil from a certain dam, and true triaxial tests were performed under complex stress paths. The expressions of tangent volume ratio and tangent modulus in the Shen’s elastoplastic model are modified in three dimensions by introducing the corner function, and the modified Shen’s elastoplastic model is applied to the deformation calculation of a high earth-rock dam. The results show that the proposed dilatancy equation has a good fitting effect under different confining pressures and different intermediate principal stresses, and improves the problem that the original model overestimates dilatancy under high confining pressure. The modified tangent modulus better reflects the law that the tangent modulus of coarse-grained soil decreases gradually with the increase of stress ratio and the change characteristics that the tangent modulus finally approaches zero after reaching the peak stress ratio. The modified Shen’s elastoplastic model was applied to deformation calculations for a specific high earth-rockfill dam. By comparing the calculated results with the field measured data, it is found that the settlement deformation results of the core wall dam calculated by the modified model are close to the measured results, which can be used for the deformation calculation of the existing high earth-rock dam.

This paper presents the findings on the horizontal bearing performance of prestressed reinforced concrete (PRC) pipe pile group. Using field horizontal static load tests, we conducted an analysis and comparison of the horizontal bearing capacity among single piles, single pile caps, and double pile caps, while also investigating the influence of pile caps on the horizontal bearing capacity of the pipe piles. We used the ABAQUS software to compare and analyze the effects of pile group with different pile cap thicknesses, numbers of piles, and pile spacings. The findings show that the horizontal critical load of a double pile cap is twice that of a single pile cap, while the horizontal ultimate load of a double pile cap is 3.095 times that of a single pile cap. An increase in cap thickness increases the bending moment at the pile top. Conversely, there is a slight decrease in the horizontal bearing capacity of the pile group. As the number of piles increases, the mutual influence between adjacent piles decreases, leading to an enhancement in the overall bearing capacity of the pile group. The horizontal bearing capacity of pile groups augments with greater pile spacing. The findings provide a theoretical foundation and serve as a reference for the application of PRC pipe piles in highway bridge engineering.

The traditional finite element method has certain limitations in modeling the dam-irregular foundation-reservoir system. Based on the ABAQUS secondary development interface, the scaled boundary finite element method (SBFEM) and the octree mesh are combined in this paper, and an automatic model generation method considering real terrain is established. The constructed octree SBFEM is used to numerically verify the seismic response of a gravity dam. Subsequently, the elastic and nonlinear dynamic response of the NG5 arch dam system was analyzed based on the flat foundation and the irregular foundation, respectively. The results show that, under seismic action, compared with the simplified flat foundation arch dam system, the transverse river relative displacement of the top and bottom and the peak of first principal stress of the undulating foundation arch dam system change greatly, increasing by 73.5% and 103.6% respectively. Considering the transverse joint and material nonlinearity of the arch dam, the relative displacement and velocity of the top and bottom of the arch dam increase by 43.9%, 32.0% and 56.6%, respectively. At the same time, the normal opening of the edge joint increases significantly, increasing by 388.9% and 381.8%, and the peak opening increases by 105%. In terms of stress and damage, the peak of first principal stress increases by 81.6%, and the area with damage also expands along the bottom of the dam.

The study of crack initiation, propagation, and connection mechanisms has important implications for the stability and safety of rock mass engineering. The Mohr-Coulomb criterion is first introduced into the classical phase field model, and a mixed crack driving force composed of pure tension, tension-shear, and compression-shear is established. Based on the Benzeggagh-Kenane fracture criterion, the equivalent I-II mixed-mode critical energy release rate is obtained to replace the mode-I critical energy release rate in the classical phase field model, and a modified phase field model is proposed to simulate the mixed-mode fracture of rock masses. In addition, a discrimination criterion is proposed based on the modified phase field model, which includes tensile crack, shear crack, and mixed tensile-shear crack. Finally, the uniaxial compression test of fissured specimens with different geometric defects is simulated and compared with experimental and numerical results, demonstrating that the proposed modified phase field model not only has the ability to simulate mixed fracture of fissured rock masses, but also can distinguish crack modes. The research results contribute to improving the understanding of the fracture mechanism of fissured rock masses.

To improve the prediction accuracy of soil settlement induced by shield tunneling excavation, a deep bidirectional recurrent neural network model based on self-attention mechanism (SAM-Bi-RNN) is proposed, which can capture spatiotemporal characteristics and vital information from settlement data. The SAM-Bi-RNN model utilizes time series data from multiple sensors as input and adopts the multi-layer bidirectional recurrent neural network architecture to capture the spatiotemporal correlations and long-distance dependencies in the settlement data. The self-attention layers are embedded between the adjacent recurrent layers to strengthen the model for the extraction of crucial data features and the capture of internal autocorrelations. The prediction effects of two variant models including bidirectional long short-term memory (Bi-LSTM) and bidirectional gated recurrent unit (Bi-GRU) on soil settlement before and after the introduction of self-attention mechanism are compared. The dataset collected from a tunnel project in Hangzhou is selected to verify the SAM-Bi-RNN model. The results exhibit that: compared with other models, the SAM- Bi-LSTM model has the best predictive performance at various monitoring points, with a total average absolute error of 0.036 6 mm and total average root mean square error of 0.034 8 mm. Furthermore, the mean absolute percentage error of SAM-Bi-LSTM model for each monitoring point in the dataset of a tunnel project in Suzhou is below 7.0%, indicating good generalization. Statistical analysis of the confidence interval shows that the results have 95% reliability. However, it is advisable to fine-tune hyperparameters according to the engineering needs to meet the prediction accuracy requirements in practical applications.

It is of great significance to investigate the long-term performance of core disposal element of high-level radioactive waste under coupled thermo-hydro-mechanical condition, especially for the site experiments and repository conceptual design. In this work, a coupled thermo-hydro-mechanical model was proposed based on the core disposal element. The finite element numerical simulation software COMSOL Multiphysics was employed to conduct the 3D numerical simulation on the core disposal element under different disposal concepts. The simulation results indicate that the minimum disposal distance between deposition holes obtained by thermal transfer simulation is larger than that by coupled thermo-hydro-mechanical simulation, when disposing 1 canister, 2 canisters, and 3 canisters vertically in the deposition hole. That’s because the increase in water saturation of the buffer material is not considered in the thermal transfer simulation, resulting in a smaller thermal conductivity coefficient of the buffer material. However, the disposal spacing derived from thermal transfer simulation provides a more secure approach for disposal elements. It can be seen that as the number of canisters in the deposition hole increases, the average disposal area of the canisters slightly increases. The results of thermal transfer analysis indicate that it is optimal to allocate one canister per deposition hole in terms of disposal area conservation alone. For horizontally disposal, the overall heat transfer to the outside of the deposition hole deteriorates is slower than vertically disposal. The results of thermal transfer analysis indicate that it is optimal to disposal vertically.

Topography plays a crucial role in shaping the propagation paths and energy distribution of seismic waves. To investigate the modulation effect of topography on seismic wave propagation, the dynamic response of isosceles triangular mountain subjected to horizontal shear wave (SH wave) in a homogeneous semi-infinite medium was studied by the wave function expansion method. Based on the existing frequency-domain scattering solution, the topographic ground motion transfer factor was introduced, and the time-domain analytical solution of mountain displacement was obtained by combining Laplace and Fourier transform. The spatiotemporal and energy distribution characteristics of mountain ground motion under the interaction of SH wave and triangular topography were studied. This solution allows for a comprehensive study of the spatiotemporal and energy distribution characteristics of ground motion when SH waves interact with triangular topography. The results show that: (1) Under SH wave incidence, the surface points of the mountain exhibit significantly greater fluctuations compared to flat ground points, with a stronger influence from frequency components. At specific frequencies, notable amplification and attenuation effects are observed. The incident angle has a significant impact on the resonance frequency and the amplitude of the topographic ground motion transfer factor. (2) Seismic waves undergo multiple reflections and refractions at the mountain’s boundaries and apex, forming a complex interference wave field. Under vertical incidence, the displacement amplitude at the mountain apex reaches 2.65. As the incident angle increases, the maximum displacement amplitude decreases and shifts from the apex to the right slope, with a maximum value of 2.12 under horizontal incidence. (3) The interaction between the triangular mountain topography and seismic waves causes energy to focus on specific areas of the mountain. Under vertical incidence, energy is concentrated near the apex and slopes. Under oblique and horizontal incidence, energy tends to be distributed more on the right side of the mountain. The geometric focusing effect is more pronounced under oblique and horizontal incidence, leading to more significant energy convergence in localized areas.

Although elastic beam-spring models are commonly employed to predict wall deflections in deep excavations, most existing models neglect the stiffness hardening behavior of soil. Moreover, the determination of model parameters heavily relies on laboratory tests, along with the inevitable errors due to sampling disturbance. To address these limitations, this study introduces an enhanced elastic beam-spring model that incorporates non-limit state earth pressure and soil stiffness hardening. A novel CPTU-based analytical approach is then proposed to estimate wall deflections in deep excavations by correlating in-situ piezocone penetration test (CPTU) parameters with the model inputs. The validity and accuracy of the proposed approach are confirmed through comparison with previous centrifuge test data. The proposed approach is further applied to a deep excavation project in the soft soil deposits of Taihu Lake, where the CPTU-based predictions show good agreement with field measurements. In contrast, solutions derived from laboratory tests overestimate the wall deflections, likely due to underestimated soil stiffness caused by sampling disturbance. This discrepancy underscores the practical advantages of the proposed CPTU-based approach. Finally, the influence of excavation depth, Young’s modulus of soil, stiffness of retaining structures, and strut stiffness on maximum wall deflections is explored through the proposed approach.