Compressed air energy storage (CAES) technology is a new type of physical energy storage and a kind of large-scale energy storage technology for power generation with broad development prospects. Large-scale CAES usually requires high-capacity underground gas storage devices. Among the existing types of underground compressed air storage reservior, the underground cavern with liner and air sealed layer has become a research hotspot in recent years because of its advantages such as easy site selection and minimal site constraints. Under the background of the urgent need for large-scale CAES technology in China, this paper comprehensively summarized and commented on the theoretical research results and technical development status of man-made cavern for gas storage, discussed the advantages and disadvantages of the existing stability analysis theory of underground gas storage cavern, sealing scheme of lined cavern and thermodynamic process analysis method. The key design points and critical issues that require attention in the development of the man-made underground lined caverns for air storaged project are also discussed. Finally, the challenges affecting the industry development of compressed air energy storage with lined rock caverns were put forward.

Salt cavern compressed air energy storage (CAES) is currently an important technique for grid peak regulation using renewable energy sources such as wind and solar power. However, daily gas injection and withdrawal result in high-frequency and high-amplitude fluctuations in the wet environment within the salt cavern. When the cavern temperature drops during gas withdrawal, the relative humidity can reach nearly 100%, causing the surrounding rock salt to deliquesce, which leads to lateral expansion of the cavern and affects its stability and tightness. This study involved exposing damaged rock salt to dry-wet cycles that mimic CAES operation conditions, and measuring the amount of deliquescence. The variation of the deliquescent rate on the salt surface with the deviation stress level was analyzed using the visual morphology, and their fitting relationship was established. A cell apoptosis method for FLAC^3D was developed, which was embedded in the numerical program simulating the long-term deformation of salt caverns. The subroutine calculates the deliquescent amount of the surrounding rock salt cells and induces their apoptosis at appropriate time, to characterize the macroscopic effect of deliquescence on the usability of salt caverns. The results show that after long-term operation, the cavern slightly extends outward due to the deliquescence of the surrounding rock, causing a slight deterioration in the displacements and the safety factor of the cavern wall, but still adequately satisfying the empirical safety criterion. However, deliquescent salt traps moisture in the air, which accumulates at the cavern bottom as brine, significantly reducing the cavern’s available volume. This change is more significant than creep shrinkage and requires control through the use of ground dehumidifiers and regular brine discharging.

Lined rock caverns (LRC) constitute a primary approach for constructing compressed air energy storage (CAES) power plants. Their mechanical capacity to withstand high internal pressures makes the stability of the overlying rock mass a crucial consideration in engineering design. For tunnel-type chambers, we establish a mechanical model of passive rock and soil pressure under the limit stress state of the overlying rock mass, based on the Mohr-Coulomb (M-C) strength criterion and the limit equilibrium concept. Stress boundary integration is applied to derive a system of three-moment equilibrium equations, and a rigorous method for calculating the safety factor of arbitrarily shaped failure surfaces is introduced. Parameter sensitivity analysis reveals that the safety factor is primarily influenced by burial depth, geostress coefficient, maximum air storage pressure, and chamber radius. The safety factor exhibits a nonlinear positive correlation with burial depth and a nonlinear negative correlation with both air storage pressure and chamber radius. For grade III rock mass, the permissible ranges of design parameters, such as burial depth, chamber radius, and maximum air storage pressure, that meet stability requirements are provided, offering valuable guidance for engineering design.

The cracking issue of reinforced concrete linings in compressed air energy storage (CAES) underground caverns poses a substantial challenge, which is difficult to fully mitigate. To control crack widths in the concrete lining, the reinforcement rate is frequently increased to high levels, making adequate reinforcement challenging. This results in increased construction costs and decreased pressure limits for the CAES system. A segmented lining structure is proposed as a solution for high-pressure air storage caverns to address this issue. This system utilizes pre-set seams to release circumferential tensile deformation, thereby reducing tensile stress on the lining. However, shear stresses between lining segments and initial support structures also induce tensile stresses on the lining. Although tensile stresses on lining steel bars are reduced near joints (within a 15º range), significant stresses persist at the distant ends. Therefore, a sliding layer is inserted between the lining and initial support to minimize frictional resistance. The shear stiffness of the sliding layer significantly affects the stress distribution of lining steel bars, with lower stiffness correlating with reduced stress levels. Despite the inability of the sliding layer to achieve complete smoothness, notable stress persists on lining steel bars under high internal pressures. To further alleviate tensile stresses within the lining structure, a stratified deformation release lining structure is proposed. This involves using pre-set joints in both the lining structure and initial support, with joint locations aligned between them. Computational analyses show that adopting a composite preset joint structure in high-pressure air storage caverns reduces relative shear deformations between the initial support and lining, thereby decreasing maximum crack widths in the lining. Therefore, in cases of elevated internal pressure, a segmented concrete lining structure with a sliding layer between the lining and initial support can be used. For exceptionally high internal pressures, a composite segmented lining structure with pre-set seams for both the initial support and lining can be used to facilitate layered deformation, thereby reducing tensile stress on the lining.

Polymer mortar (PM) is recognized as a promising material for constructing the sealing layer of man-made caverns used in compressed air energy storage (CAES) systems, owing to its excellent airtightness, crack resistance, and deformation adaptability. This paper investigates the bonding properties and deformation adaptability of polyurethane polymer mortar (PPM) with lining concrete in man-made cavern gas storage, focusing on the effects of powder, polymer content, and mixture ratio variations on the PPM-concrete interface. Additionally, the failure characteristics and mechanisms of the interface are analyzed. The results indicate that the primary failure mode of the PPM-concrete interface is material separation on both sides. The relationship between interfacial shear stress and displacement exhibits two-stage approximate linear deformation characteristics prior to the stress peak, with a maximum shear strain of 11.05% during failure. Variations in powder and polymer content, as well as mixture ratio, significantly impact the interfacial bond strength. The maximum bond strength was about 1.21 MPa, while the lowest average bond strength was 0.237 MPa. The interfacial strength and deformability of the PPM-concrete interface satisfy the requirements for underground gas storage in CAES systems.

The compressed air method in shield tunneling exhibits significant advantages in underwater tunnel construction, yet it lacks a comprehensive theoretical analysis model. A theoretical model for the relationship between air pressure in the shield chamber and the inflow and outflow of compressed air is firstly established, based on the principles of mass conservation and the ideal gas law. A dynamic air pressure boundary at the tunnel face is used to integrate the theoretical model with a numerical model of the surrounding rock that considers gas-liquid two-phase flow. The model is validated through field data. Analysis of key factors affecting chamber pressure during shield shutdown reveals that chamber pressure initially increases, then decreases, and eventually stabilizes upon compressed air injection. Higher air injection rates lead to increased peak and stable chamber pressures. Compressed air within the chamber reduces the rate and amplitude of pressure fluctuations, with a larger volume of air amplifying this effect. The compressed air method is best suited for strata with low permeability. As the permeability coefficient of the stratum increases, the ability of stratum to contain compressed air decreases, leading to the formation of air discharge channels extending to the ground surface. In strata with higher permeability coefficients, abruptly halting air injection can cause a rapid drop in chamber pressure and groundwater influx, threatening construction safety.

High internal pressure can readily cause cracking in the underground cavern of compressed air energy storage (CAES), posing a significant threat to its stability and sealing. To effectively transfer internal pressure loads, enhance cavern deformation capacity, and leverage the bearing capacity of surrounding rock, we propose a flexible lining design using low-elastic modulus flexible concrete as the lining layer for CAES underground caverns. The mechanical properties of flexible concrete under various proportions are initially investigated through laboratory tests. Building on these findings, we propose a modified concrete damage-plasticity (CDP) constitutive model for flexible concrete and establish a mechanical calculation model for underground caverns utilizing flexible concrete. To demonstrate the feasibility of using flexible concrete in CAES underground caverns, this study compares the mechanical response of these caverns with different lining forms and varying flexible concrete ratios. This comparison is conducted within the context of an ongoing CAES underground cavern project. The results indicate that low-elastic modulus flexible concrete can effectively reduce tensile stress in the concrete lining of high-pressure CAES underground caverns. This stress reduction minimizes lining cracking, facilitates internal pressure load transfer, enhances cavern deformation capacity, and leverages the bearing capacity of surrounding rock.

Fault zones, prevalent in deep geological strata, are commonly filled with fault gouge, rock debris and other fillings, significantly impacting the stability of rock masses. The shear mechanical properties of filled joints within fault fractures are intricate and influenced by various factors, including rock type and its mechanical properties, joint roughness, the mineral composition and mechanical characteristics of the fillings, and as well as interactions, such as groundwater. This paper reviews the research trajectory of the shear mechanical behavior of filled rock joints and provides a systematic summary of the current research status on their shear mechanical properties. The key issues and research progress of shear mechanical properties of filled rock joints are analyzed from the aspects of laboratory shear experiment, numerical simulation, shear strength criterion and constitutive model theory. The existing problems and development trends of different research methods were also analyzed. Presently, filling degree, mineral composition and mechanical properties of fillings are recognized as the most critical distinctions from unfilled rock joints. Additionally, factors like fluid interactions, normal stress, and joint roughness significantly affect the mechanical properties of filled joints. However, the shear strength theories developed through macroscopic phenomenological approaches struggle to find precise application in engineering practices. Future research will primarily tackle the shear mechanical properties of multi-scale rock joints with fillings, focusing on the meso-mechanisms of shear failure within filled joints, the development of shear criteria for different types of filled joints, and the corresponding numerical simulation models and mesoscopic parameter determinations. Investigating the complex behavior of multi-scale filled joints under multi-field coupling conditions is poised to become a leading and pressing research area.

Hazardous gas migration in rock strata primarily occurs through fractured media, with the stress state of the rock mass significantly influencing its permeability. Generally, natural rock masses are in a triaxial state of unequal principal stresses. Studying rock mass deformation and seepage under various stress states is crucial for accurately predicting gas migration in rock strata. The deformation and permeability of rock mass under fluid-solid coupling were studied by triaxial test system considering different fracture angles and confining pressures. The results show that: (1) The precast fracture strain of rock mass initially decreases and then increases with the increase of axial stress. At confining pressures below 25 MPa, axial stress primarily causes volumetric expansion of the fracture, whereas at pressures above 25 MPa, it primarily leads to volumetric shrinkage. (2) Volumetric expansion of rock masses is primarily due to precast fractures at low confining pressures, and to newly formed fractures at high pressures. The change of rock permeability during compression of precast fractured rock mass is mainly determined by the deformation of precast fracture. (3) When the fracture angle is 90º, 80º, and 70º, the rock mass permeability at peak stress increases by 4% to −0.7%, 0.5% to −6.3%, and −0.2% to −15% compared with the initial stress, respectively, with the increase of confining pressure. The influence of the fracture angle on the permeability of rock mass under axial load is slightly higher than that confining pressure. (4) Considering the influence of different stress levels on fracture deformation, a calculation model for fracture permeability under triaxial state was established. It was found that the sensitivity of the lateral stress influence coefficient on normal deformation χ decreased with the increase of confining pressure and fracture angle

In order to master the creep deformation law of colluvial slope and the stress deformation characteristics of tunnel lining structure under rainfall, the response physical model test of seepage and stress deformation characteristics of tunnel slope parallel system is carried out by using earth pressure cells, strain gauges, dial indicators and hygrometers. The test results indicate that rainfall infiltration depth decreases with increasing slope height and distance from the slope surface. The existence of the tunnel will affect the seepage path of rainwater, accelerating infiltration and increasing peak moisture content on the slope above the tunnel, while decelerating infiltration and reducing peak moisture content on the slope below the tunnel. The slope deformation is positively correlated with the change rate of water content. Slope deformation is concentrated during rapid water content increase, with vertical displacements at the slope top, middle, and foot accounting for 89.6%, 96.4%, and 98.9% of the total, respectively. The earth pressure increment at the tunnel top due to slope deformation correlates positively with the tunnel’s buried depth in the accumulation body, with an average increase of 24% per 15 cm. The earth pressure increment at the bedrock end is approximately 2.4 times that at the entrance end, while the increment at the tunnel bottom is smaller than that at the top. The tunnel exhibits the following stress and deformation characteristics: compression at the top, tension at the bottom, overall sinking, local downward bending with the central position as the inflection point, and abrupt strain changes at the bedrock-accumulation layer junction due to shear stress. These characteristics resemble the stress mode of a beam structure with one end hinged and one end anchored. It is recommended to incorporate anti-seepage measures such as sprayed concrete, shallow grouting, or slope ecological protection on the upper slope of the tunnel during the design and construction of similar tunnels. Reinforcement treatment should be implemented in the tunnel entrance area, the middle section with significant deformation, and the rock-soil junction.

Functional filling of mine thermal storage has achieved the synergy of deep underground ore deposits and geothermal energy extraction. It is urgent to develop functional filling materials with suitable phase change parameters and excellent physicochemical properties. Aiming at the current situation that microencapsulated phase change materials (MicroPCM) lead to the decrease of compressive strength and thermal conductivity of the backfill, this study carries out pre-experiments to investigate the strength characteristics and thermal properties of the phase change backfill. After determining an optimal MicroPCM additive amount, the study further investigated the effects of various silicon carbide (SiC) additions (ranging from 0% to 8% by mass) on the compressive strength, thermal conductivity, and specific heat capacity of the phase change backfill. The density, water secretion rate, and fluidity of the backfill were also tested. At the same time, scanning electron microscope-energy dispersive spectrometer (SEM-EDS) was used to observe its micro-morphology, and energy spectrum analysis was carried out to explain the macro-experimental phenomena, to explore its thermal energy storage stability under alternating high and low temperature cycles. The following conclusions were obtained that the specific heat capacity of the phase change backfill reached a maximum of 1.75 MJ/(m³·K) at 5% MicroPCM addition. The maximum density of the backfill, 1.67 g/cm³, occurred at 2% SiC addition. As SiC content increases, both fluidity and water secretion of the backfill gradually rised. The compressive strength and thermal conductivity of the backfill increased continuously with the increase of SiC addition, and the increase was 10.1% and 21.7%, respectively, to 6.64 MPa and 1.12 W/(m·K) at 4% addition, and then the growth trend decelerated. The specific heat capacity of the phase change backfill exhibited a trend of initial growth followed by decay with increasing SiC addition. The fluctuation amplitude remained small. The maximum specific heat capacity of 2.32 MJ/(m³·K) is achieved at 4% SiC addition, making this the recommended SiC content. After 500 cycles of alternating high and low temperatures, the compressive strength of the phase change backfill increased, with a positive correlation to SiC content. Both the coefficient of thermal conductivity and specific heat capacity decreased, with the rate of decline gradually diminishing. This study offers data for reference in practical engineering applications of thermal storage filling.

To investigate the efficacy and strength properties of Fe²⁺-activated persulfate remediation for 1,2-dichlorobenzene-contaminated soil with varying persulfate concentrations, we conducted degradation, microscopic, particle size, liquid-plastic limit, unconfined compressive strength (UCS), and undrained shear tests. The results indicate that adding 15.0% Fe²⁺-activated persulfate achieves a 92.59% removal rate of 1,2-dichlorobenzene. Furthermore, the reaction produces sodium sulfate, calcium sulfate, and ferric hydroxide. Small amounts of sodium sulfate and calcium sulfate fill the pores between soil particles, leading to a denser soil structure. However, the expansive effect of excessive sodium sulfate crystals weakens the inter-particle cohesion, leading to soil loosening. After remediation, the clay content increases, while the silt and sand content decreases. The liquid limit, the plastic capacity and the plastic index increase, while the plastic limit decreases with the increase of the persulfate dosage. The UCS and the maximum shear stress decrease with the increase of the persulfate dosage. The UCS of the soil treated by 10.0% persulfate is 310.75 kPa, 20.34% higher than the strength of untreated soil. The maximum deviator stress at shear failure is 142.73 kPa.

Due to the extrusion shear action caused by long-term tectonic movement, fault zones are usually filled with fault gouge, significantly affecting the mechanical behavior of the rock mass and influencing the cementation effect of grouting. This study investigates the compression-shear behavior of grouted and non-grouted rock joints with sandy fillings, based on a tunnel passing through a fault zone in Yunnan Province, China. A series of direct shear tests was conducted on grouted and non-grouted rock joint samples with varying degrees of filling. The test results show that: 1) For both grouted and non-grouted specimens, sandy filling reduces the peak shear strength of joints. The former is because the sand weakens the contact between the joint walls, while the latter is because the sand affects the strength of cement stones and the thickness of the filled layer. 2) Grouting significantly improves the shear strength of rock joints with sandy fillings. The higher the filling degree, the greater the increase in shear strength after reinforcement. 3) Based on the joint roughness coefficient-joint compression strength (JRC-JCS) criterion, shear strength models for grouted and non-grouted rock joints with sandy fillings were established. The predicted values of these models were in good agreement with the test data. It is helpful to further understand the influence of fault gouge on grouting cementation of fractured rock mass.

In order to solve the collapsible difficulties of primary stope in subsequent stoping backfilling method, the idea of strengthening stratified structure in primary stoping backfill is put forward. The effect of strengthening stratified height, cement-to- tailings ratio and confining pressure on the mechanical properties and failure rules of cemented tailings backfill (CTB) is investigated by the triaxial compressive testing. The difference of deviational-stress-strain curves and failure modes between CTB and strengthening stratified CTB is investigated. The results show that the yield phase and peak strength of CTB are enhanced by the strengthening stratified structure in CTB. When the strengthening stratified thickness keeps constant, the strengthening effect is raised as the cement-to-tailings ratio in the main layer become lower. Moreover, the cement-to-tailings ratio in the main layer remains unchanged, the strengthening effect is advanced by the increase of strengthening stratified thickness as well. The peak strength of CTB is logarithmically increased with confining pressures, and the apparent cohesion and friction angle are linearly increased with cement-to-tailings ratio in the main layer and strengthening stratified thickness. The failure mode of CTB without strengthening stratified structure is mainly dominated by an oblique shear crack, and the strengthening stratified CTB presents three failure modes: shear, tensile and mixed. When the cement-to-tailings ratio in the main layer is low, tensile cracks run through the strengthening stratified structure. The feasibility of 1:7−0 backfill replaced by 1:20−2/5 is verified, and the backfill cost of 1:20−2/5 can be saved by 6.85% cement cost, where 1:20 is cement-to-tailings ratio, and 2/5 is the proportion of strengthening stratified. The results can provide theoretical references for saving backfill cost and improving operation safety.

The rapid-setting two-component chemical grout needs to be achieved by static mixing, resulting in temporal and spatial variations in grout viscosity. We used poliurethane/water glass grout as the typical rapid-setting chemical grout. We studied the permeation grouting mechanism considering space-time variation in viscosity. We conducted the time-varying viscosity test of rapid-setting chemical grout. We derived equations for one-dimensional permeation grouting that describe the space-time distribution of viscosity, permeation motion, and the evolution of grouting pressure. We further derived equations for three-dimensional spherical and cylindrical permeation grouting that describe the space-time distribution of viscosity, permeation motion, and the evolution of grouting pressure. We established a theory of spherical and cylindrical permeation grouting, taking into account the space-time variation of viscosity. We compared the results of laboratory experiments and numerical simulations with the derived theoretical equations. According to the results, the viscosity of rapid-setting chemical grout increases exponentially with time. Compared with the traditional Karol permeation grouting theory, the permeation radius predicted by our grouting theory was closer to the experimental results. The described permeation grouting phenomenon aligned well with the numerical simulation results. The experimental and numerical data collectively validate the precision and accuracy of our proposed theory.

The primary objective of this study is to investigate the evolution mechanism of CO₂ breakthrough pressure in mudstone caprock under different effective stresses. This study specifically investigates the silty mudstone caprock in the Bohai Bay Basin, China, and conducted a series of experiments on breakthrough pressure and permeability under different effective stresses. Whereas, the evolution process of CO₂ breakthrough pressure in mudstone caprock was investigated, and the mechanism of pore water film affecting the breakthrough pressure was discussed. The results of this study illustrate that during the CO₂ injection process (reduction in effective stress on the caprock), the effective stress decreases from 27 MPa to 7 MPa, while the caprock permeability increases from 1.46×10⁻⁶ μm² to 1.81×10⁻⁶ μm². When the effective stress is 5.2 MPa, the minimum breakthrough pressure of caprock is 3 MPa, which exceeds the minimum sealing threshold of 2 MPa. The results of breakthrough pressure tests indicate that the caprock possesses effective sealing capability. The disjoining pressure and distribution characteristics of the pore water films are the main factors influencing the breakthrough pressure. The resistance of CO₂ transport increases with increasing the separation pressure of the water films, leading to high CO₂ breakthrough pressure. The pore throat radius of mudstone samples range from 0.1 nm to 2.5 nm in the Bohai Bay Basin, and the corresponding disjoining pressures of water films range from 5.2 MPa to 50 MPa. The water films has strong constraint ability on CO₂ migration.

The soil-water retention curve (SWRC) is one of the fundamental physical relationships for unsaturated soil. Experimental studies indicate that volume deformation not only alters the pore size distribution (PSD) of the soil but also significantly affects the heterogeneity (or non-uniformity) of pore structure. Based on the inherent relationship among the three phases of soil, a calculation formula considering the influence of volume deformation on soil saturation under constant suction is proposed. In terms of hydraulic hysteresis, the ink-bottle effect is employed to reveal the impact of volume deformation on the hysteresis characteristics of SWRC. Assuming that, given the initial void ratio, the increase in suction is mainly consumed in changing the soil saturation and overcoming the ink-bottle effect, a heterogeneity factor representing changes in pore structure is introduced into the VG model. This heterogeneity factor reflects the influence of volume deformation on the evolution of pore structure, thereby constructing a SWRC model that considers the coupling of hydraulic hysteresis and deformation effects. The proposed SWRC model not only captures the impact of volume deformation on SWRC but also explains the physical mechanism underlying the evolution of hysteresis loops with changing void ratio. Finally, the proposed model is validated using eleven sets of experimental data. The results indicate that the proposed model effectively describes the influence of soil deformation on SWRC boundary curves and hysteresis loop evolution.

Red mudstone fill material (RMF) exhibits high water sensitivity which indicates that the performance of the subgrade is dependent on the water content. A series of mechanical and microstructure tests including 41 cyclic triaxial tests, 5 mercury intrusion porosimetry (MIP) tests and 3 scanning electron microscope (SEM) tests were carried out to investigate the dynamic properties of RMF, with particular concentration on water content effects. Results show that the equivalent Young’s modulus and damping ratio are correlated to the strain amplitude, which can be modeled by Hardin-Drnevich’s hyperbolic equation. As the cyclic stress amplitude increases, a transition from stable to unstable permanent deformation is observed. The permanent deformation and critical cyclic stress vary with water content. Specifically, under the same cyclic stress amplitude, the permanent deformation of RMF on the dry side is less than that on the wet side. The number of loading cycles needed to achieve the target permanent deformation is higher for RMF on the dry side compared to the wet side. The critical cyclic stress is greater on the dry side and increases with initial suction, as characterized by the VG model. From the microstructural perspective, the pore size distribution changes from single peak mode to bi-modal structure as water content increases. The denser and more stable soil fabric is observed on the dry side, which results in the better performance of RMF on the dry side compared to that on the wet side. The ratio of critical cyclic stress to static shear strength ranges from 65% to 75%, indicating the overestimation of subgrade strength by the static strength design method. It is recommended to use RMF with a water content of 5.0% to 7.0% in the construction of red mudstone subgrades.

The rigid and fixed diaphragm wall (RFD) is a novel strut-free retaining wall system. This system needs a rigid connection between diaphragm panels. However, in Indonesia, constructing the rigid connection between diaphragm wall panels is scarce. The main objective of this study is to investigate the effectiveness of the RFD system on lateral wall deflection and excavation stability considering anisotropic factors due to joints in the diaphragm wall panels. First, the soil and structure parameters of the three-dimensional finite element model were validated through a well-documented braced excavation case history, which is located in Central Jakarta. Then, the RFD system was introduced to the 3D model. Some parametric studies were also conducted by varying several parameters to understand their influence on safety factors and wall deflections. The analysis results indicate that the implementation of the RFD system yields positive outcomes in controlling lateral deformations. The length of buttress walls and the use of cap slabs significantly affect excavation deformations and safety factors, while the depth of cross walls and buttress walls has a less significant impact. The presence of joints in the diaphragm wall panels causes the wall to be anisotropic, resulting in a reduction in wall stiffness. The reduction in wall stiffness leads to an increase in lateral wall deformations and a decrease in the excavation safety factor.

We conducted monitoring of peripheral rock deformation and performed discrete-continuous coupling numerical analysis on 11 typical inclined thin-layered carbonaceous slate tunnels of the Yunnan Shangri-la-Lijiang Expressway. This study investigated the large deformation characteristics and unloading failure mechanisms of peripheral rock in these tunnels, and proposed corresponding countermeasures. The results indicate that: (1) The peripheral rock deformation of inclined thin carbonaceous slate tunnels is significantly influenced by excavation unloading and construction disturbances. The deformation is characterized by large quantitative values, rapid rates, and long durations. Additionally, crown settlement is greater than horizontal convergence, indicating significant unloading deformation of the peripheral rock, which exhibits asymmetric spatial distribution characteristics. (2) Peripheral deformation failure further develops with the construction of each step. After excavating the upper step, bending failure occurs in the peripheral rock on the left shoulder of the tunnel, forming an initial unloading area with pronounced asymmetric characteristics. As construction progresses through the middle and lower steps, the bending failure of the left shoulder’s peripheral rock continues to develop, while shear-slip failures gradually occur in the crown and right shoulder, ultimately leading to an expansion of the overall unloading failure area. (3) Pre-reinforcement of the strata is the primary effective method for controlling the deformation of inclined thin-layered carbonaceous slate. This approach can be combined with strategies to reduce construction disturbances and optimize the timing and parameters of support for the comprehensive treatment of peripheral deformation.

Coral sand is widely used in island and reef reclamation projects, but its distinct physical and mechanical properties compared to land-based sand. To explore the deformation mechanism of hydraulic filled coral sand foundation, oedometer tests were conducted on coral sand, considering the combined effects of factors such as gradation, porosity, and loading methods. The initial particle size distribution of coral sand significantly impacts its compression deformation characteristics, with noticeable particle breakage. A larger initial void ratio in gravel sand results in greater compressibility. The deformation of coral sand primarily involves pore filling by particle movement, accompanied by minor particle breakage, all of which are irreversible plastic deformations. Consequently, the unloading index of coral sand is only 1/10 that of clay. Finally, a three-dimensional model of the aviation oil storage tank was created using Plaxis 3D software. Using mechanical parameters obtained from laboratory experiments, the deformation of the coral sand foundation in aviation oil storage tank engineering under cyclic loading and unloading was studied. The model’s accuracy was validated by comparing it with the monitoring results of the aviation fuel storage tank project at Maldives’ Ibrahim Nasir International Airport. At the maximum storage capacity of the aviation oil storage tank, the coral sand foundation reaches its peak deformation. At this load level, multiple loading and unloading cycles will not cause further deformation, providing valuable guidance for engineering safety control.

Based on the variational limit equilibrium method, the ultimate bearing capacity of composite foundation with vertical reinforcement is studied. Firstly, based on the static equilibrium equation of sliding soil in composite foundation with vertical reinforcement and combined with the variational principle, an isoperimetric constraint model for the functional extremum of the ultimate bearing capacity of foundation is established. On this basis, the control equations with potential sliding surface, normal stress on sliding surface, and Lagrange multiplier as basic unknowns are obtained using the Euler equation, and the movable boundary is transformed into a fixed boundary by introducing auxiliary variables. Finally, the shooting method is used to numerically solve the coupled two-point boundary value problem, obtaining an accurate solution and comparing it with the simplified equivalent strength index method in composite foundation design. Simultaneously, the numerical examples are used to analyze the effects of displacement rations, reinforcement cohesion, and internal friction angle on the ultimate bearing capacity of the foundation. The numerical results show that the simplified equivalent strength index method can effectively analyze the ultimate bearing capacity of composite foundation with vertical reinforcement.

Tunnel lining uplift frequently arises during shield tunneling excavation. To accurately characterize the dislocation between adjacent rings and joint openings induced by uplift pressure during shield tunneling, we propose a theoretical calculation method for uplift deformation of shield tunnels based on the short beam-spring model. Initially, we establish Euler-Bernoulli short beams and joint springs to simulate the longitudinal structure of shield tunnels, considering the arbitrary restraining effect of the shield tail through boundary springs. Subsequently, we apply the finite difference theory to derive the uplift deformation of shield tunnels under uplift forces during tunneling. Ultimately, we validate the correctness and effectiveness of the method through comparisons with engineering cases, numerical modeling results, and traditional equivalent beam calculations. We discuss the sensitivities of key parameters, analyzing the influence of the unconsolidated zone length, circumferential joint stiffness, and modulus of elasticity on the deformation pattern of tunnel uplift. The results indicate that, compared to conventional continuous beam models, our calculation method accurately reflects discontinuous deformation characteristics and reasonably captures the dislocation between adjacent rings and joint openings. Analysis of related parameters reveals that increasing the length of the unconsolidated zone significantly enhances both the maximum uplift deformation and its range of influence. Appropriately increasing the shear and rotational stiffness of circumferential joints can mitigate uplift displacement and reduce dislocation between adjacent rings and joint openings. The uplift deformation of shield tunnels in weak strata with low modulus of elasticity is more difficult to control.

The damage parameter is a variable used to describe the transition of geomaterials from a bonded state to an unbonded state. The correct expression of the damage evolution of structured soil is crucial in establishing constitutive models for structured soils. Currently, research on damage laws typically involves assuming expressions for damage parameters and then fitting these parameters using experimental results to establish the damage law. The rationality and applicability of these damage laws are yet to be validated. To derive a unified expression for the damage law of structured sands incorporating microscopic mechanisms, a prediction model based on symbolic regression is proposed. Firstly, using the definitions of damage parameters with microscopic physical significance, various damage databases are constructed using the distinct element method (DEM). Secondly, preliminary parameter screening is conducted on isotropic compression and constant p true triaxial compression stress paths using a method that combines input variables. p is the average effective stress. Combined with the genetic programming-based symbolic regression (GPSR), damage expressions with different complexities are derived. Finally, the best-performing expression is selected as the damage law for structured sand, namely the GPSR damage law, based on an analysis of prediction and generalization errors. The applicability of different expressions is compared using various DEM damage databases. The results show that the GPSR damage law represents damage parameters as functions of plastic deviatoric strain ε_s, normalized mean effective stress p/py and coefficient of intermediate principal stress b. It effectively reflects the transition from structured soil to remolded soil. The outstanding prediction ability of the GPSR damage law on different damage databases further demonstrates its applicability to various geomaterials. The research findings are valuable to establish constitutive models for structured sands.

Rolling resistance between particles significantly influences the mechanical properties of granular media, yet the underlying mechanisms remain incompletely understood. We conducted several drained triaxial shear tests on granular media using the three-dimensional discrete element method. The simulation results were quantitatively analyzed at macroscopic, microscopic, and mesoscopic scales, followed by a detailed correlation analysis. The study revealed the load transfer and deformation processes in dense granular media, and explored the internal mechanism of the influence of rolling resistance on the mechanical behavior of granular medium. The results show that in the strain hardening stage, the mechanical coordination number decreases, the fabric anisotropy increases, the number of chained particles increases, the force chains become longer, the number of force chains decreases, the average normal contact force increases, the number and volume proportion of small clusters decrease while the number and volume proportion of large clusters increase, and so dilatancy occurs immediately in the specimen after its initial elastic compaction. As the triaxial shear load increases, the contact force between particles in force chains becomes substantial, and the proportion of large clusters surrounding them rises significantly. Consequently, some force chains buckle or collapse, leading to decreased fabric anisotropy, a reduction in the number of chained particles, shortened force chains, and macroscopic strain softening. During the strain hardening stage, large rolling resistance effectively inhibits relative rolling between particles in force chains and reduces the deformability of surrounding large clusters, thereby enhancing force chain stability and increasing the shear strength of the granular medium. During the strain softening stage, rolling resistance prevents timely rearrangement of particles, causing deformation to concentrate in local areas where force chains have bent or collapsed. In these areas, particle rotation increases, leading to the formation of larger clusters. Consequently, the softening and dilatancy of the sample become more pronounced, resulting in the formation of a clear shear band. This study provides deep insights into the complex mechanical behavior of granular media and offers inspiration for the development of multi-scale constitutive theories.

Utilizing machine learning to predict the uplift of shield tunnel linings ahead of the cutterhead during construction enables timely adjustments of control parameters, mitigating lining uplift issues. Nevertheless, existing models exhibit limited performance in long sequence time-series forecasting (LSTF) and face challenges in accurately predicting the uplift of multiple lining rings ahead of the shield cutterhead. Considering the impact of shield control, attitude parameters, and geological condition, and utilizing the Boruta algorithm to determine model input features, a shield tunnel segment uplift prediction model based on LightGBM-Informer was proposed. This model incorporates a wavelet transform filter and a complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) method to eliminate noise in time series data. The accuracy and applicability of the proposed model were validated using the monitoring data from subway shield tunnel projects in Nanjing and Xiamen. The results demonstrate that the model exhibits enhanced prediction accuracy in comparison to other models, including recurrent neural network (RNN), long short-term memory (LSTM), gated recurrent unit (GRU), and Transformer. Additionally, it demonstrates robust generalization capabilities across diverse geological condition datasets. As the length of the prediction sequence increases, the performance advantages of the model become more pronounced, accurately predicting the uplift of 1−2 rings of linings ahead of the shield cutterhead. Feature importance analysis based on Shapley additive explanations (SHAP) method indicates that earth chamber pressure and vertical displacement at the shield head and tail have significant impacts on lining uplift. The model provides theoretical guidance for intelligent control of shield tunnel lining construction in complex, water-rich environments.

To investigate the three-dimensional dynamic response of a deeply buried storage and drainage tunnel in saturated soil subjected to water hammer, we propose a frequency-domain finite element method and boundary element method (FEM-BEM) coupling model for the fluid-lining-saturated soil system. The fluid is modeled as an inviscid and compressible fluid, the lining as an elastic medium conceptualized as a hollow cylinder of finite length, and the soil as a saturated poroelastic medium. Initially, the governing equations for the fluid and lining are solved using FEM in the frequency domain, while those for the soil are solved using BEM in the same domain. In the following, fluid, lining, and soil are coupled based on the conditions of deformation compatibility, force equilibrium, and impermeable boundary conditions at their interfaces. The presented model is verified through the comparison with the existing models. Finally, a case study of internal water pressure (water-hammer load) and the displacement and pore pressure of the saturated soil in a fluid-filled lined tunnel due to water hammer is presented. The results show that: (1) The dynamic response caused by the water hammer presents significant periodicity and attenuation. (2) The radial displacement of soil is significantly larger than that of axial displacement. (3) Modeling soil as a single-phase elastic medium inaccurately evaluates the dynamic response. (4) The water hammer makes an extensive impact on the ground surrounding the storage and drainage tunnel. (5) The peak values of internal fluid pressure, the soil displacement and pore pressure decrease with the decrease of soil permeability.