[Objective] Current research on the damping ratio evolution of silty fine sand under varying saturation conditions remains relatively limited, and in particular, systematic investigations revealing the mechanisms by which saturation variations influence damping ratios within the framework of unsaturated soil mechanics are still insufficient. To address this gap, typical loose silty fine sand from the Hangzhou Bay area is selected as the research subject. Utilizing a self-improved unsaturated soil resonant column testing system, the damping ratio evolution characteristics and underlying mechanisms along the desaturation path are thoroughly investigated. The findings aim to provide a scientific basis for analyzing dynamic properties and engineering applications of unsaturated soils. [Methods] An improved unsaturated soil resonant column apparatus was employed to conduct small-strain dynamic property tests under controlled drainage paths and saturation conditions. Test specimens were initially prepared with varying saturation levels and stress states. A stepwise desaturation process under constant net stress conditions was then applied to establish a series of samples with different saturation states. Subsequently, shear modulus and damping ratio measurements were performed across varying saturation levels and net stress conditions via resonant column loading. By integrating theoretical analyses of soil-water characteristic curves (SWCC) and pore water distribution states, distinct stages of damping ratio evolution were identified, and damping mechanisms induced by saturation variations were elucidated. [Results] The experimental results indicated that: (1) under identical saturation conditions, the damping ratio of silty fine sand gradually decreased with increasing net stress. (2) During saturation evolution, the damping ratio exhibited distinct stage-wise variations: when the soil approached full saturation, the damping ratio remained relatively stable. As saturation declined, the damping ratio rapidly attenuated and reached a minimum near the optimal saturation Sr_opt. Further saturation reduction led to a slight rebound in the damping ratio. (3) Based on the SWCC and pore water morphology evolution, the saturation-dependent damping ratio variations were categorized into three stages: boundary effect stage, transition stage, and residual saturation stage. [Conclusion] This study elucidates the damping ratio evolution mechanism of loose silty fine sand along desaturation paths. It demonstrates that the damping ratio is influenced not only by net stress but also closely associated with pore water distribution states, and that its minimum damping ratio occurs at the optimal saturation Sr_opt. The results reveal that saturation-dependent damping ratio changes can be categorized into three stages, each corresponding to distinct pore water morphology evolution processes. By employing the improved unsaturated soil resonant column, the complete damping ratio evolution process with saturation variation is observed. The principle of minimum damping ratio under “optimal saturation” control is proposed, and the three-stage evolution mechanism is revealed through SWCC analysis. These findings provide a foundation for refining unsaturated soil dynamic models and enhancing the scientific rigor of related engineering designs.

[Objective] Large-scale excavation unloading above an existing subway tunnel, resulting from activities such as river dredging and widening or foundation pit excavation, induces unloading deformation of the soil mass, which threatens the stability of the tunnel structure. Therefore, measures are required to limit the soil deformation. Given the limited research on the impact of river dredging and excavation on existing tunnels, this paper, taking the Nanjing Jiuxiang River Widening Project as a case study, investigates the impact of the reinforcement project’s foundation pit excavation on the shield tunnel under different working conditions. It also predicts the effectiveness of the reinforcement structure in suppressing tunnel uplift, thereby providing a reference for subsequent construction. [Methods] A pressure slab structure, consisting of a slab, bored piles, and a diaphragm wall, was proposed to protect the tunnel, and the preliminary design parameters and construction plan for these components were determined. Based on this, the Finite Element Method (FEM) was employed to predict the impact of the reinforcement measures on the existing tunnel section. First, a three-dimensional finite element analysis model was established based on the fundamental assumption of compatibility between tunnel displacement and soil deformation. The parameters for the reinforcement zone and the structure were determined based on engineering experience and field-measured data. Then, a finite element analysis of the vertical displacement of the tunnel segments was conducted under various working conditions, and the contour maps of segment vertical displacement were obtained. Subsequently, the longitudinal deformation of the shield tunnel was analyzed using the calculation results from the most unfavorable working condition. A curve fitting regression analysis was performed using the Gaussian function on the tunnel segment deformation to establish its longitudinal distribution pattern. Finally, a verification calculation of the internal forces within the tunnel structure was performed. [Results] (1) Working Condition 5 was identified as the most unfavorable case, with a maximum uplift deformation of the tunnel segments of 17.8 mm. (2) The tunnel’s vertical displacement peaked near the intersection of the river and tunnel centerlines. This displacement decreased rapidly as the distance from the intersection increased, diminishing to nearly zero at a distance of approximately 90 m. (3) For Working Condition 5, the maximum negative bending moment per linear meter of the tunnel segment was 179.2 kN·m with a corresponding axial force of 724 kN, and the maximum positive bending moment was 161.3 kN·m with a corresponding axial force of 556 kN. The calculated crack widths were 0.170 mm and 0.187 mm, respectively. [Conclusions] (1) The pile-wall-slab structure is proven to be effective in restraining the tunnel’s uplift deformation. (2) The performance of the pile-wall-slab structure is closely related to the excavation method of the foundation pit. Adopting a strip excavation by sections can effectively control ground disturbance and, in turn, tunnel deformation. (3) Overall ground reinforcement is significantly effective in suppressing tunnel uplift deformation, whereas the effect of using counterweights inside the tunnel is relatively limited.

[Objective] This paper aims to investigate the mechanical properties and damage evolution law of lime-solidified saline soil under freeze-thaw cycles, with a focus on analyzing the effects of lime content, curing age, and the number of freeze-thaw cycles on its unconfined compressive strength (UCS). In addition, a damage constitutive model based on statistical distribution is established to predict the stress-strain response and performance degradation of solidified saline soil under freeze-thaw conditions. [Methods] Saline soil from Zhenlai County in western Jilin Province was selected as the research object. Lime was added at proportions of 3%, 6%, and 9% as the curing agent, and specimens were prepared under the optimum moisture content (20%) and a degree of compaction of 90%. The specimens were cured for 7 days and 28 days and subjected to 0-60 freeze-thaw cycles. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) analyses were conducted to examine the macroscopic mechanical properties and microstructural changes. Based on the Weibull distribution function, a damage evolution model was established using the experimental data. [Results] The optimum lime content was 6%, and the unconfined compressive strength reached 835.01 kPa after 28 days of curing, which was more than four times that of the untreated soil. Both untreated and solidified saline soils exhibited strain-softening behavior and brittle failure after freeze-thaw cycles. With the increase in freeze-thaw cycles, the strength of the solidified soil gradually decreased but still remained significantly higher than that of the untreated soil. SEM images showed that lime treatment effectively reduced crack development and improved the integrity of the microstructure. The established Weibull damage model accurately simulated the entire stress-strain process under different numbers of freeze-thaw cycles, and the fitting accuracy improved with an increasing number of cycles. [Conclusion] Lime solidification significantly enhances the strength and freeze-thaw resistance of saline soil, with the optimum effect achieved at a 6% lime content and 28 days of curing. The damage model based on the Weibull distribution can effectively characterize the mechanical behavior and damage evolution of solidified saline soil during freeze-thaw processes. The research findings provide theoretical and technical support for the solidification treatment of saline soil in cold regions. The innovation lies in correlating microstructural changes with macroscopic mechanical responses and establishing a statistical damage prediction model suitable for freeze-thaw conditions.

[Objective] The identification and grouping of rock mass structural planes are essential prerequisites for conducting stability analysis. Existing clustering methods are highly sensitive to initial cluster centers, resulting in suboptimal grouping results and relatively low efficiency. To overcome these limitations, this study proposes a rock mass structural plane clustering method based on an improved sparrow search algorithm (KS-SSA). [Methods] First, SPM chaotic mapping was used to initialize the sparrow population, and then the step factor of the SSA was modified to improve the optimization speed. The improved SSA algorithm was used to optimize the initial cluster centers, achieving a global optimal solution. Subsequently, the K-medoids algorithm was applied for the final grouping of structural plane orientation data. Silhouette coefficient (SC) was used to evaluate the clustering performance. Four sets of artificial structural planes were generated using Monte Carlo simulation to validate the proposed algorithm, and comparative analyses were conducted with classical KPSO, FCM, spectral clustering, and traditional sparrow algorithms. [Results] The differences among different algorithms were primarily concentrated at the boundary points. The proposed algorithm could accurately identify all boundary data points, demonstrating good clustering performance with higher recognition accuracy and better clustering results. Using the silhouette coefficient, the structural planes could be accurately divided into four groups, which was consistent with the actual conditions. Furthermore, the sparrow population size and the number of iterations were identified as two key parameters for clustering analysis. Therefore, based on the artificial data, the optimal population size was determined to be 50 by analyzing the variation of fitness curves. Setting the number of iterations to 50 was appropriate while ensuring computational efficiency. The application of the proposed method to the publicly available Shanley dataset further validated its effectiveness. The new algorithm was applied to 201 structural plane data from a rock slope in the Nujiang River. By calculating the silhouette coefficients, three dominant structural plane groups were identified, which were generally consistent with the field investigation results. In addition, the KPSO algorithm was also employed in the field structural plane data analysis, and computational efficiency of the new method was discussed. The KS-SSA algorithm achieved stable clustering results within just 50 iterations, whereas the KPSO algorithm required 110 iterations for convergence. The runtime of the KS-SSA and KPSO algorithms was 45.97 s and 69.95 s, respectively, indicating that the new method had significantly higher computational efficiency. [Conclusion] The KS-SSA algorithm initializes the sparrow population based on SPM chaotic mapping, effectively preventing the clustering results from falling into local optima. Meanwhile, the step factor of the sparrow algorithm is modified, enabling the KS-SSA algorithm to dynamically adjust the step size and improve the optimization speed. Comparative analysis of three case studies demonstrates that compared with traditional algorithms, the proposed method exhibits superior performance in boundary data identification and improved robustness. This study discusses and clarifies the parameter selection and computational efficiency of the new method. The new method demonstrates promising application prospects and can be applied to large-scale data processing and analysis, providing a theoretical basis for the numerical simulation of three-dimensional networks of rock mass structural planes and rock mass stability analysis.

[Objective] During tunnel excavation, mining roadway development, or other underground construction processes, the rock mass of underground engineering is typically subjected to multi-stage permanent dynamic and repetitive stress disturbances. Moreover, cyclic stress amplitude is recognized as one of the primary factors influencing the occurrence of dynamic disasters in underground engineering. This study aims to investigate the influence of stress amplitude on the mechanical behavior and fracture modes of red sandstone under multi-stage constant-amplitude cyclic loading. [Methods] Utilizing an MTS-816 rock mechanics servo-testing system and real-time acoustic emission (AE) monitoring technology, the strength and deformation behaviors of red sandstone specimens during multi-stage cyclic loading were analyzed in detail. The evolution patterns of AE parameters under varying cyclic stress amplitudes and the final failure modes of the red sandstone specimens were elucidated. [Results] Lower cyclic stress amplitudes were found to impart a certain strengthening effect on red sandstone specimens, whereas higher stress amplitudes induced more severe deterioration. The increase in cyclic stress amplitude exhibited a hardening effect on the sandstone. Under multi-stage constant-amplitude cyclic loading, the elastic modulus and elastic strain energy of the red sandstone specimens were generally enhanced. Within a single fatigue loading stage, the AE signals gradually transitioned from active to stable with the increase in loading cycles. Under lower stress amplitude conditions, the red sandstone specimens exhibited a higher number of AE ring-count events during the loading process, and the cumulative AE curve showed only a sudden increase at the moment of failure. In contrast, for specimens under higher stress amplitudes, the AE activity remained relatively stable in the early loading stage but became more intense at the time of failure. An increase in stress amplitude led to the formation of larger axial primary cracks at specimen failure, and the secondary cracks and local spalling phenomena caused by crack coalescence became more severe. Specimens under high stress amplitudes were more prone to splitting failure dominated by overall tensile cracks. [Conclusion] The cyclic stress amplitude has a significant impact on the safety and stability of underground engineering. Therefore, the dynamic cyclic stress amplitude should be emphasized as a key factor during the operation and maintenance of underground engineering.

[Objective] In recent years, with frequent extreme climate events, the northwestern region of China has experienced large diurnal temperature difference in summer, with daytime high temperatures continuously rising and persisting for extended periods. The resulting water vapor migration significantly affects the subgrade moisture content, thereby influencing the engineering performance of the subgrade. Investigating the water vapor migration patterns in loess subgrades under sealed pavement structures subjected to high temperatures holds substantial practical significance and application value for scientifically predicting the engineering performance of loess subgrades and ensuring their long-term stability. [Methods] A self-developed one-dimensional soil column test apparatus was employed, with compacted loess columns from the suburbs of Xi’an as the study subjects. The MTD15 temperature and moisture sensors were utilized to monitor the temperature and moisture variations within the loess columns under a boundary heating condition of 55 ℃. The water vapor migration patterns in one-dimensional sealed soil columns were analyzed under two heating modes: diurnal temperature cycling and continuous heating. Furthermore, the effects of different heating modes on the temperature and moisture distribution characteristics of the soil columns were explored. [Results] Boundary heating caused the temperature of the soil columns to rise, with a faster increase in the upper part and a slower increase at the bottom. During the heating phase, the temperature distribution along the height exhibited an approximately linear pattern. Under the cyclic heating of diurnal temperature difference, the internal temperature of the soil columns dropped rapidly after the heating was stopped. The cooling rate in the upper part was significantly higher than that in the middle and lower parts. By 08:00 the next day, the soil column temperature ranged between 22-25 ℃, with the middle part slightly warmer than the two ends. At 20:00 each day and 8:00 the following day, the temperature distribution along the depth of the soil columns remained basically the same. Under continuous heating, the soil column temperature reached dynamic equilibrium after 10 days of heating, exhibiting a two-segment, piecewise linear distribution. The variation trends in the moisture content distribution curves of the soil columns under the two heating methods were basically the same—namely, a decrease in moisture content in the upper part, an increase in the middle, and a decrease in the lower part, with these trends becoming more pronounced as the experiment progressed. However, within the upper 22.5 cm of the soil columns, the moisture content under the cyclic heating of diurnal temperature difference was higher than that under continuous high-temperature heating. [Conclusion] Under boundary heating conditions, the moisture of sealed soil columns is primarily governed by the combined effects of liquid water vaporization and moisture migration within the pores, water vapor migration driven by vapor concentration gradients, and condensation of vapor in the pores when the vapor pressure exceeds the saturated vapor pressure. These mechanisms collectively result in an inverse “S”-shaped moisture distribution. For subgrades with cover layers, 30 days of cyclic heating of diurnal temperature difference during summer induces moisture at 5 cm depth to fluctuate between -2% and +2% of the initial moisture content. This cyclic fluctuation of the upper subgrade moisture induced by diurnal temperature difference will significantly affect the mechanical properties of the subgrade. Under extreme climate conditions characterized by continuously rising heating temperatures and prolonged duration, the moisture content variations in the subgrade become more pronounced. These significant variations in moisture will lead to dehydration, shrinkage, and cracking in the upper subgrade layers, thereby compromising the service performance and lifespan of the subgrade and pavement structures.

[Objective] Extensive red sandstone spoil generated from highway tunnel projects in central-southern China poses significant disposal challenges due to its high water content, susceptibility to slaking and disintegration, low strength, and high compressibility—characteristics that fail to meet subgrade material standards. To realise the goal of “treating waste with waste and turning waste into treasure”, we use quicklime, calcined coal gangue powder, fly ash and cinder powder as multi-source solid-waste curing agents to explore the optimal ratio and mechanism for co-curing red sandstone spoil, providing a basis for resource utilisation. [Methods] Red sandstone spoil was served as the base material, quicklime, calcined coal gangue powder, grade-III fly ash and cinder powder were selected as curing agents, with their chemical compositions determined by X-ray fluorescence spectroscopy. Single-mix tests were conducted to investigate the effect of each curing agent alone on the strength of the red sandstone spoil and to determine appropriate dosage ranges. Then orthogonal experimental design was employed, using 7-day unconfined compressive strength (UCS) as the index to obtain the optimal ratio. Based on the optimal mix ratio, the red sandstone spoil was modified with curing agent dosages of 8%,10%,12%,and 14%,and cured for 3,7,14,and 28 days respectively. Unconfined compressive strength (UCS) was tested. Water stability coefficients were measured through water immersion tests. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted to examine changes in microstructure and mineral phases before and after curing, revealing the stabilization mechanism. [Results] Optimal mix proportions and dosages:the optimal mass ratio was quicklime∶fly ash∶calcined coal gangue∶cinder powder=4∶8∶8∶7. The strength showed an initial increase followed by a decline with increasing total dosage, with 12% total dosage yielding the highest strength. Macro-scale performance improvement: at 12% dosage, 7-day UCS reached 1.659 MPa (16 times that of raw spoil) and 28-day UCS 2.255 MPa. Water stability was significantly improved, with the coefficient reaching 59.37% at 12% and 65.90% at 14%, with strength increasing over time, particularly rapidly between 3-14 days. Microscopic mechanism: XRD analysis showed that the contents of orthoclase and albite decreased in the improved red sandstone spoil, while the diffraction peaks of quartz and calcite were enhanced, indicating that ion exchange and pozzolanic reactions occurred, generating cementitious products such as calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). SEM observation revealed that the soil particles were loose and porous before improvement, while after improvement, the cementitious products bonded the particles to form a dense skeletal structure, which became more complete with curing age. [Conclusions] The optimal co-curing ratio is quicklime∶fly ash∶calcined coal gangue∶cinder powder=4∶8∶8∶7 at 12% dosage, delivering the best mechanical properties and water stability. The mechanism is a lime-centred synergistic reaction: lime hydration provides an alkaline environment and Ca²⁺, triggering ion exchange (soil particles changing from potassium/sodium type to calcium type) and pozzolanic reactions (forming cementitious products), while solid waste particles fill pores to reinforce the soil skeleton. This offers an economical and eco-friendly route for red sandstone spoil utilisation, with both engineering and ecological value.

[Objective] As a common form of underground structure in hydraulic geotechnical engineering, deep shafts have attracted widespread attention regarding their stress deformation and safety issues. This study takes a double-tube deep shaft near a reservoir in a water diversion project as the research subject, aiming to investigate its stress deformation characteristics and key influencing factors. [Methods] An integrated numerical modeling approach was employed, using multi-software platform interactive modeling to establish a 3D numerical model that accounted for complex geological conditions and reservoir proximity effects. Then, the influence patterns of key parameters, such as diaphragm wall segmentation, embedment depth, construction sequence, and segmented excavation height, were systematically analyzed. [Results] Diaphragm wall segmentation was identified as the most sensitive factor affecting the stress deformation of structures, with its segmentation scheme directly determining the distribution patterns of wall stress deformation. Embedment depth of the diaphragm wall ranked second in significance, while the construction sequence and segmented excavation height exhibited relatively minor effects on construction. [Conclusions] This study innovatively reveals the stress deformation mechanisms of double-tube shafts, providing crucial theoretical foundations and practical guidance for the safe construction of similar underground hydraulic engineering projects.

[Objective] This study aims to improve the reinforcement effect of electroosmosis and enhance its engineering practicability by applying an intermittent current to the electroosmosis-calcium chloride method. [Methods] Laboratory model tests were conducted on mucky clay reinforced by the electroosmosis-calcium chloride method under different intermittent current ratios, in order to reduce energy consumption and electrode corrosion, as the on/off time ratio is a key factor influencing reinforcement effectiveness. The effects of different on/off ratios on the reinforcement of mucky clay were analyzed, and the underlying reinforcement mechanisms were investigated. The off-time was fixed at 1 h, while the on-time was set at 8 h, 5 h, and 2 h. The concentration of the CaCl₂ solution was 10%. [Results] The addition of CaCl₂ increased the electrical conductivity of the soil, which enhanced the electroosmotic drainage by about 49.3%. At the same time, cementitious substances were generated at the cathode and the average shear strength of soil was enhanced by about 240%, which dramatically improved the strengthening effect of electroosmosis. Meanwhile, the anode corrosion and energy consumption increased by 6.6% and 12.0%, respectively, after adding CaCl₂. Applying intermittent current could reduce the anode corrosion and energy consumption induced by the addition of CaCl₂, but it also weakened the electrochemical reinforcement effect, which was related to the on/off duration. When the on-time was 2 h, part of the Ca²⁺ could not migrate to the cathode, the amount of cementitious products decreased, and water molecules at the cathode flowed back under the hydraulic gradient, resulting in a reduction in the electrochemical reinforcement effect. When the on-time was 8 h, the electrolysis at the anode and cathode produced more H⁺ and OH^-, which aggravated the dissolution and oxygen-evolution corrosion of the anode. Meanwhile, the generated metal oxides/hydroxides increased the surface film resistance of the electrode, leading to more heat production in the soil and unnecessary energy consumption. In addition, prolonged current caused gas accumulation at the cathode, resulting in detachment between the electrode plate and soil, an increase in interfacial resistance, and further increase in energy consumption. By comparison, the on/off time of 5 h/1 h showed the best reinforcement effect, which increased the drainage volume by 55.7% and increased the shear strength of cathodic soil by about 400%. The energy consumption per unit drainage decreased by 6.7%, and anode corrosion decreased by 4.7% compared with continuous current. [Conclusions] The electroosmosis-calcium chloride method under intermittent current can mitigate the drawbacks of conventional electroosmosis, namely limited strength improvement, severe electrode corrosion, and high energy consumption. It therefore provides an optimized approach for its practical engineering application.

[Objective] In response to the urgent need for preventing and controlling seepage disasters in shallow gassy sandy soil during major engineering construction projects in the Pearl River Estuary, this study aims to develop an efficient prediction method for unsaturated hydraulic properties based on physical mechanisms, thereby overcoming the technical bottlenecks of long testing cycles and high costs in traditional experiments. [Methods] Using typical gassy sandy soil from shallow gas reservoirs in the Pearl River Estuary, soil-water characteristic curve (SWCC) tests using a pressure plate apparatus and unsaturated permeability tests were conducted. According to the abstract conceptualization of the AP model, the soil internal structure was assumed to consist of a vast number of interconnected pore channels with different pore sizes. Based on the equivalent capillary tube model theory, under matric suction increasing from low to high, pore channels drained sequentially from larger to smaller sizes. Then, by assuming that the pore radius and matric suction satisfied the Young-Laplace equation, the relationships between sandy soil particle size distribution data, SWCC, and unsaturated permeability coefficient were established. Consequently, a prediction method for the SWCC and unsaturated permeability coefficient of sandy soil based on particle size distribution was proposed. [Results] Experimental results showed that the particle size distribution of the sandy soil was closely related to its water retention characteristics. Its air entry value (AEV) was generally below 10 kPa, and the residual volumetric water content was typically higher than that of pure quartz sand, approximately 8%. The residual matric suction corresponding to residual volumetric water content ranged from 10 to 20 kPa and was influenced by the fine particle content. The scaling factor α had a critical impact on the predictive performance of the AP model and showed a better correlation with the normalized volumetric water content (θ/θ_s). The optimal fitting equation was α=1.243 1+0.369 4exp(-4.9θ/θ_s). [Conclusions] The pore channels in the soil are categorized into n grades (r₁, r₂, r₃, …, r_n) from largest to smallest pore radius. Under unsaturated conditions, water in the larger pore channels is drained, and only channels from grades m to n (r_m, …, r_n, where m<n) remain water-filled, serving as the main pathways for unsaturated seepage. Based on the particle size distribution curves of sandy soil samples, the mass fraction of the i-th component (with a spherical particle radius of R_i) in the samples is w_i, from which the relative permeability coefficient of the sandy soil can be directly calculated without conversion via the SWCC. A comparison with a typical statistical model—the Jackson model—is conducted, which verifies that the method proposed in this study for predicting the unsaturated relative permeability coefficient of sandy soil based on the particle size distribution curve is reasonable and feasible.

[Objective] To address the engineering challenge of drainage efficiency reduction caused by filter membrane clogging in traditional plastic drainage bodies during vacuum preloading of dredged sludge, this paper innovatively proposes a fully biodegradable, non-filter membrane straw drainage body (NSD) technology. Model tests were conducted to verify the engineering applicability of the NSD, reveal its drainage consolidation mechanism, and provide sustainable solutions for the green treatment of dredged sludge. [Methods] A PVC cylinder with a height of 50 cm and a diameter of 30 cm was used as the test tank, filled with dredged sludge at a water content of 147.5% (approximately 2.5 ω_L). The sludge was collected from a disposal site in Wuhe County, Anhui Province, with a liquid limit of 59% and clay content of 21.7%. The control group used traditional plastic drainage bodies, consisting of rigid tubes wrapped with filter gauze and fabric. Two setups were tested: one with constant vacuum loading and another with staged vacuum loading. The experimental group employed NSDs, made of rigid tubes wrapped with straw ropes. Four setups were tested: (1) constant vacuum loading, (2) staged vacuum loading, (3) constant vacuum loading after installing a 2-5 mm self-filtering soil layer, and (4) staged vacuum loading with the pre-installed 2-5 mm self-filtering layer. During the testing period, the effluent discharge volume was recorded every 24 hours, and the solids content of the extracted tailwater was measured during each cycle. Upon completion of the vacuum preloading, the soil’s moisture content and particle gradation were determined. [Results] Drainage efficiency significantly improved, with the experimental group’s cumulative effluent volume 7.9%-22.1% higher than the control group, indicating that the three-dimensional pore structure of straw effectively alleviates the impact of clogging on drainage. Soil reinforcement was enhanced, with the experimental group’s average water content after vacuum preloading reduced by 6.8%-15.3% compared to the control group. Particle size distribution analysis revealed that when the self-filtering soil layer was pre-installed, the clay content (d<0.005 mm) increased by 5%-11.1%, confirming that the NSD, when combined with the pre-installed self-filtering layer, not only achieved effective soil filtration but also enhanced soil stabilization performance. [Conclusion] Technical innovation: The NSD achieves membrane-free drainage through its crisscrossing internal channels, overcoming the clogging bottlenecks of traditional plastic drains while increasing drainage efficiency by more than 15%. Mechanism breakthrough: A synergistic mechanism combining the NSD with the self-filtering soil layer has been proposed, demonstrating significantly enhanced drainage performance without compromising consolidation effectiveness. Application value: An efficient and eco-friendly dredged sludge treatment technology has been developed, providing a novel approach to vacuum preloading treatment of dredged sludge.

[Objectives] Numerous engineering practices and studies on foundation pits have shown that the bending moment and horizontal displacement of the support structure on the deep excavation side of asymmetric excavation foundation pits are significantly greater than those on the shallow excavation side, which is notably different from the situation where the support structures on both sides of symmetric excavation foundation pits deform inward uniformly. When using the current standard’s support fixed point adjustment coefficient method for calculation, there are shortcomings such as a wide range of values for the fixed point adjustment coefficient λ and difficulty in quantification, as well as significant discrepancies between the calculated results and actual conditions when asymmetric excavation causes the absence of displacement fixed points on the internal supports. [Methods] The hyperbolic model of earth pressure versus horizontal displacement (p-y) of the retaining structure was adopted. It was assumed that the curvature of the p-y curves for active and passive deformation at y = 0 are the same and calculated using the m-method, i.e., K_0a = K_0p = K₀ = mz·z. Calculation methods for active earth pressure, passive earth pressure, and net earth pressure on the retaining structure were proposed. Considering the excavation and support construction process of the foundation pit, the increment of earth pressure load on the retaining structure caused by excavation was first calculated, and then the increments of internal force and displacement were solved using the incremental method. An incremental iterative calculation procedure for the stress and deformation of the foundation pit retaining structure was established. Based on this incremental iterative calculation procedure and according to the force balance conditions and deformation compatibility at the left and right ends of the internal support retaining structure, a calculation method for the stress and deformation of internal support retaining structures under asymmetric excavation of foundation pits was proposed and numerically implemented on the MATLAB platform, overcoming the difficulty of quantifying the fixed point adjustment coefficient λ in current normative calculation methods. [Results] Calculation results of engineering cases showed that the horizontal displacement curves of the diaphragm walls on the deep and shallow excavation sides obtained by the incremental iterative calculation method were generally consistent with the distribution of the measured curves. The maximum horizontal displacement of the support structure on the deep excavation side was 23.15 mm, while the measured value was 25.83 mm, with a difference of 10.4%. The calculated maximum horizontal displacement of the support structure on the shallow excavation side was 8.75 mm, while the measured value was 8.99 mm, with a difference of only 2.67%. The maximum horizontal displacement of the support structure on the deep excavation side calculated by the traditional elastic fulcrum method was only 12.93 mm, differing from the measured value by 49.67%, thus underestimating the horizontal displacement of the deep excavation side. The maximum bending moments of the diaphragm walls on the deep and shallow excavation sides obtained by this method were 451.24 kN·m/m and 228.95 kN·m/m, respectively, differing by 49.3%. The axial force of the internal support obtained by this method was 204.56 kN/m, which lies between the internal support axial forces calculated by the traditional elastic fulcrum method for the deep and shallow excavation sides, avoiding the waste caused by designing solely based on the deep excavation side. [Conclusions] The study shows that the traditional elastic fulcrum method tends to overestimate the support stiffness and underestimate the horizontal displacement on the deep excavation side. The incremental iterative calculation method satisfies the force balance conditions and deformation compatibility at both ends of the internal supports. The horizontal displacement curves of the diaphragm walls on both sides obtained by this method are basically consistent with the distribution patterns and values of the measured engineering curves. It overcomes the difficulty of quantifying the fixed point adjustment coefficient λ in current normative calculation methods and can serve as a reference for the design and calculation of similar foundation pits.

[Objective] Geogrids are widely applied in high loess slopes engineering due to their advantages of strong overall durability, high tensile strength, and corrosion resistance. The interface friction coefficient between the reinforcement and soil is a crucial parameter for pull-out verification of reinforced soil slopes, and its value is influenced by multiple factors. [Method] This study employed an independently developed geosynthetic material tensile pull-out testing system to conduct a series of laboratory pull-out tests on steel-plastic geogrids and remolded loess under varying normal stresses, pull-out rates, and water contents, aiming to investigate the effects of these factors on the friction characteristics of the steel-plastic geogrid-loess interface. [Results] The peak pull-out force of the reinforcement increased with increasing normal stress and decreased with increasing water content, with a maximum value of 18.143 kN. Under different normal stresses, the relationship between pull-out force and displacement at the loading end was divided into four stages,such as linear increase, nonlinear increase, decay, and stabilization. The pull-out force increased with the pull-out rate, and higher pull-out rates corresponded to greater peak pull-out forces. Although the pull-out rate varied, the trend of the pull-out force versus loading end displacement curve remained similar; as the loading end displacement continuously increased, the pull-out force first increased, then decreased, and finally tended to stabilize. The maximum shear stress increased with normal stress and decreased with water content; the influence of normal stress on maximum shear stress weakened gradually as water content increased. The interface cohesion showed a trend of first increasing and then decreasing with rising water content, reaching a maximum of 11.043 kPa at the optimal water content. The apparent friction coefficient decreased with increasing water content and normal stress; when the normal stress was 105 kPa, the apparent friction coefficient was approximately 0.13, which was about one-third to one-half of the recommended standard value. [Conclusion] The pull-out characteristic tests indicate that engineering design should not be evaluated solely based on the apparent friction coefficient, but should also fully consider actual water content, overburden load, and other engineering conditions. The results of this study provide a reference for the structural design of high loess slopes.

[Objective] This study aims to investigate the water-salt migration and deformation characteristics of desert saline soil in southern Xinjiang under the combined effects of water-salt replenishment conditions and salt-freeze-thaw cycles. [Methods] According to the types of saline soil and the distribution characteristics of groundwater and salt in the Aral region of southern Xinjiang Autonomous Prefecture, we selected silty sand as the research subject and prepared synthetic sulfate saline soil specimens to conduct cyclic salt-freeze-thaw experiments under two different salt replenishment conditions to simulate secondary soil salinization, namely, groundwater (saline solution) replenishment and engineering replacement (underlying saline soil) replenishment. The water-salt migration features, phase changes, and deformation characteristics of silty sulfate saline soil under the two conditions were analyzed. [Results] Under saline solution replenishment condition, as the concentration of the replenishment solution increased, the migration height of water and salt decreased. The soil deformation characteristics exhibited initial salt-induced swelling followed by settlement, with the maximum salt-induced swelling deformation of 0.21 mm occurring at a 5% solution concentration. Under saline soil replenishment condition, as the sodium sulfate content in the soil increased, the reduction in water and salt content in the lower layer increased, and the soil deformation was characterized by settlement. The maximum settlement deformation of -1.37 mm occurred at a saline soil content of 1%. [Conclusion] Compared to saline solution replenishment, saline soil replenishment results in greater thermal sensitivity of the soil. Under saline solution replenishment condition, the migration of water and salt in soil pores and the trends of deformation and failure occur more rapidly than those under saline soil replenishment condition. Therefore, replacing the sulfate saline soil foundation with an overlying layer of salt-free silty sand can suppress the sulfate-induced frost heave. However, the thickness of the salt-free silty sand layer should exceed the critical depth of thermal influence. In engineering practice, when silty sand—a soil type prone to settlement deformation—is used as an overlying replacement layer to suppress salt-induced frost heave deformation of sulfate saline soil, attention should be paid to particle gradation and compaction of replacement soil, and the implementation of salt-blocking and drainage measures. This research provides a reference for the engineering prevention and control of secondary soil salinization in southern Xinjiang.

[Objective] A method for preparing solidified lightweight red sandstone soil using microbial-induced calcium carbonate precipitation (MICP) technology was proposed for the recycle use of red sandstone residual soil in engineering. A design study was conducted on bio-based solidified lightweight red sandstone soil to investigate the solidification mechanism of the modified material. The effects of expanded polystyrene (EPS) mass content and cementation solution concentration on the strength of the lightweight solidified soil are analyzed. Based on this, the compression failure characteristics of the solidified lightweight red sandstone soil are studied, and its cementation mechanism is validated through both strength analysis and failure characteristics. [Methods] Bacillus pasteurii was selected as the target strain, and cementation solutions with concentrations ranging from 0.5 to 2.0 mol/L were prepared. Solidified lightweight red sandstone soil samples with EPS contents ranging from 0% to 1.125% were prepared. The internal microstructure of the modified red sandstone residual soil was analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Additionally, its mechanical properties were evaluated through slow shear tests and uniaxial compression tests. [Results] After MICP treatment, a substantial amount of calcite-type CaCO₃ precipitates was generated within the red sandstone residual soil. These CaCO₃ crystals formed a continuous and dense cementation network between soil particles, serving as the primary contributor to the strength of the solidified lightweight red sandstone soil. In contrast, only sparse crystal clusters were observed on the surfaces of hydrophobic EPS particles. When the cementation solution concentration was 1.5 mol/L and the EPS content was 0.375%, the solidified lightweight red sandstone soil samples exhibited the optimal performance combination. The compressive strength reached 0.76 MPa, meeting the standard requirement (≥0.6 MPa) for foam lightweight soil. The bulk density was 14.3 kN/m³, representing a 13% reduction compared to the undisturbed soil. Additionally, the internal friction angle and cohesion increased by 39% and 17%, respectively. Failure mode analysis revealed that samples with low EPS content (≤0.375%) exhibited typical brittle shear failure, with cracks propagating in a “Y” shape. In contrast, samples with high EPS content (≥1.125%) showed bulging failure, accompanied by surface spalling and debris detachment. [Conclusions] The combination of microbial solidification technology and EPS lightweight foam soil technology has effectively solidified lightweight red sandstone soil, overcoming the high energy consumption limitations of traditional cement-based solidification methods. A quantitative relationship between “cementation solution concentration, EPS content, and mechanical properties” was established. The proposed optimal mix ratio (1.5 mol/L cementation solution + 0.375% EPS) combines both lightweight characteristics (bulk density of 14.3 kN/m³) and high strength (0.76 MPa). This study provides a low-carbon and environmentally friendly solution for the resource utilization of red sandstone residual soil, demonstrating significant application value in engineering fields such as subgrade filling.

[Objective] This study aims to break through traditional limitations by quantifying the influence mechanism of crack penetration rate on the strength characteristics of expansive soil through laboratory experiments. It seeks to establish a predictive model for shear strength based on penetration rate, providing a scientific basis for evaluating the stability of engineering slopes. [Methods] A novel method was employed to simulate cracks using geomembranes. Triaxial specimens with varying crack penetration rates (0%, 33.3%, 50.0%, 66.7%) were prepared and subjected to consolidated drained triaxial tests. During the tests, interface strength parameters between the geomembrane and the soil were obtained through direct shear interface friction tests. Combined with the Mohr-Coulomb strength criterion and strength calculation methods for cracked surfaces, a composite strength analysis framework for the “soil block-crack” structure was established. Compared to traditional crack simulation methods, this technique enables precise control of crack geometry, effectively reproducing the crack development process and providing robust data support. [Results] Crack penetration significantly affected the mechanical behavior of expansive soils. As penetration rate increased, the stress-strain curves of the specimens exhibited a transition from strain hardening to strain softening. When the penetration rate increased from 0% to 66.7%, a distinct peak appeared under high confining pressure (400 kPa), and the peak strength decreased by 60.73%, indicating a pronounced increase in brittle failure characteristics. Under low confining pressure, the specimens exhibited no obvious peak strength and were mainly subject to plastic failure, with the stress-strain curve displaying mild strain softening. The ultimate deviatoric stress at failure was influenced by both confining pressure and crack penetration. With increasing penetration rate, the soil’s resistance to shear failure diminished, and the ultimate deviatoric stress decreased accordingly. This decline became more pronounced as confining pressure increased. When cracks were introduced into the specimen, they altered the stress concentration zones, promoting shear failure along the cracks. Obvious shear cracks appeared along the shear plane, and the failure mode shifted from bulging failure to dislocation failure along the crack surface. Shear strength was a key mechanical property representing soil failure characteristics. In this study, the strength parameters of specimens with cracks were calculated using the cracked-surface strength method, yielding accurate shear strength indices. When the crack penetration rate was 0%, the shear strength indices represented intact soil, with cohesion and internal friction angle of 37.6 kPa and 22.0°, respectively. When the penetration rate increased to 33.3%, cohesion and internal friction angle decreased to 30.7 kPa and 20.1°, down by 18.4% and 8.6% compared to the 0% case. At 50.0% penetration rate, these values further dropped to 27.6 kPa and 16.4°, decreasing by 26.6% and 25.5%, respectively. As penetration rate increased, the actual contact area between soil particles and crack surfaces grew, reducing frictional resistance along the shear plane. When the penetration rate reached 66.7%, cohesion and internal friction angle declined to 21.8 kPa and 15.2°, down by 42.0% and 30.9% from the 0% condition, indicating that cracks exerted a greater control over shear strength. Therefore, with increasing penetration rate, the shear strength parameters of the soil-crack surface consistently decreased. To further illustrate that the variation in shear strength parameters under different penetration rates was the result of the combined effect of soil blocks and cracks, this study established a comprehensive calculation formula for shear strength along the failure surface. A comparative analysis of the calculated and predicted shear strength values under different penetration rates showed that the deviation of the internal friction angle prediction from the experimental value ranged from -2.5% to 6.7%, and that of cohesion ranged from -19.7% to -3.3%, all within the allowable experimental error. [Conclusion] This study uses a novel simulation material to quantitatively analyze the influence of cracks on the strength properties of expansive soil, investigating the effect of cracks on shear failure patterns and strength characteristics. A comprehensive strength calculation formula is proposed to validate the influence of the integrated behavior of soil along the shear surface. The findings enrich the theoretical system of expansive soil crack mechanics and provide a reference for slope stability analysis in similar hydraulic engineering projects.

[Objective] With the advancement of rainwater and sewage diversion projects in cities along the river, trenchless pipe jacking technology has been widely adopted due to its efficiency and environmental advantages. However, pipe jacking in the river-crossing sections faces challenges posed by complex hydrogeological conditions, which can cause riverbed surface displacement and even lead to engineering accidents such as water inrush or blowout. There is still a lack of systematic analysis of the mechanisms influencing surface displacement in the river-crossing sections during pipe jacking construction. Most existing studies are based on assumptions of semi-infinite elastic bodies or static stratum conditions, making it difficult to accurately reflect the disturbance patterns under dynamic changes of parameters such as bulk density, cohesion, and internal friction angle of geomaterials in river-crossing sections. This study focuses on a pipe jacking project in the river-crossing section of a city along the Yangtze River, investigating the displacement patterns of the riverbed surface under fluid-solid interaction. It aims to reveal the influence mechanisms of key parameters, thereby providing theoretical support for safe construction. [Methods] A combination of theoretical analysis, numerical simulation, and empirical formula comparison was adopted. First, the strength reduction method was applied to reflect the soil weakening effect under fluid-solid interaction by reducing the geotechnical mechanical parameters (cohesion c and internal friction angle φ). Then, a 3D numerical model was established using COMSOL Multiphysics. The model simulated actual operating conditions through roller supports and fixed boundary conditions. Considering soil elastoplasticity, the grouting layer, and hydrostatic pressure boundary conditions, this model simulated stress redistribution and surface deformation during the pipe jacking process. In addition, Peck’s empirical formula was introduced to predict settlement, and the results were compared with the numerical simulation to verify the reliability of the model. Finally, the single-factor analysis method was used to systematically study the influence patterns of pipe diameter, grouting pressure, and soil elastic modulus on riverbed surface displacement. [Results] (1) Characteristics of soil stress distribution: During the pipe jacking process, the stress in the soil around the pipe exhibited a near “M”-shaped distribution, with the minimum stress at the pipe axis and the stress on both sides increasing first and then decreasing. The closer to the pipe, the narrower the “M”-shaped trough became. At 38 meters of jacking distance, the maximum stress value increased by about 60% compared to the initial state, concentrated mainly at the pipe bottom and pipe crown. (2) Riverbed surface subsidence pattern: The surface subsidence trough followed a “U”-shaped normal distribution, with the maximum subsidence located directly above the pipe axis. At 38 meters of jacking, the maximum subsidence reached 1.352 mm, closely matching the prediction of 1.313 mm by the Peck formula. However, due to the influence of high water pressure and soil parameter weakening, the simulation result was slightly conservative. (3) Influence of parameters: Increasing pipe diameter from 1.8 m to 2.4 m raised the maximum settlement by approximately 40% and widened the subsidence trough by 23%, indicating that large pipe diameters significantly intensified soil disturbance. Raising grouting pressure from 0.1 MPa to 0.3 MPa reduced the maximum subsidence by 35%, and the support and lubrication effect of the slurry sleeve effectively inhibited soil loss. Increasing the soil elastic modulus from 7.2 MPa to 14.4 MPa reduced the maximum subsidence by 46%, indicating that hard soil had significantly stronger deformation resistance compared to soft soils. [Conclusion] Under the disturbance caused by pipe jacking construction, the soil stress redistribution exhibits an “M”-shaped pattern, and the surface subsidence trend is consistent with the predictions of the Peck empirical formula, validating the applicability of the numerical model. (1) Pipe diameter, grouting pressure, and soil elastic modulus are key parameters influencing surface displacement. In engineering practice, it is necessary to balance the selection of pipe diameter (large diameters improve jacking efficiency but increase subsidence risk), optimize grouting pressure (to suppress subsidence and avoid excessive uplift), and improve the disturbance resistance of soft soil through reinforcement (such as pre-grouting). (2) This study is the first to construct a 3D fluid-solid interaction model for pipe jacking in the river-crossing section, combining the strength reduction method and parameter sensitivity analysis to provide a theoretical basis for similar projects. Its limitation lies in the lack of field monitoring data for validation. In the future, site monitoring should be incorporated to further improve model accuracy. The findings can provide guidance for design optimization and risk control of pipe jacking projects along the Yangtze River Economic Belt and under similar hydrogeological conditions, contributing to the implementation of the “joint efforts for environmental protection” strategy.

[Objective] Under the influence of climate change and engineering activities, the thermodynamic stability of subgrade engineering in permafrost regions faces severe challenges. To investigate the influence of seasonal temperature boundary conditions on the thaw consolidation characteristics of frozen soil subgrade, this study modifies the three-dimensional nonlinear large-deformation melting-thaw consolidation theory. [Methods] By introducing seasonal temperature boundary conditions and using the Mohr-Coulomb criterion to describe the plastic settlement deformation of thawed soil, a three-dimensional nonlinear plastic thaw consolidation theory incorporating seasonal temperature effects was developed. The theoretical model was numerically implemented using the FLAC3D simulation platform. Taking a typical high ice-content frozen soil subgrade section of the Qinghai-Tibet Highway as the research object, the thaw consolidation evolution patterns under seasonal temperature boundary conditions were systematically analyzed. The validity of the theoretical model was verified through comparison with field-measured data. [Results] The results showed that the settlement deformation of the frozen soil subgrade exhibited a periodic variation pattern with seasonal surface temperature changes, representing the most significant characteristic of thaw consolidation under seasonal temperature boundary conditions. Due to self-weight of subgrade soil, the distribution scope of vertical effective stress expanded with time. The calculation model considering plastic deformation demonstrated higher prediction accuracy. As plastic deformation accumulated continuously during thaw consolidation, its effect could not be neglected in long-term deformation predictions for high-ice-content frozen soil engineering. Through the study of the pore water pressure distribution during the consolidation process, it was found that the pore water in the shallow thawed area of the subgrade dissipated during initial operation. In the subsequent long-term operation, the continuous development of the thaw and settlement of frozen soil subgrade primarily resulted from the dissipation of the newly thawed pore water at the thaw front. [Conclusion] The improved theoretical model proposed in this study can more reasonably describe the thaw consolidation characteristics of high-ice-content frozen soil subgrades under seasonal temperature boundary conditions, providing a critical theoretical basis for the design and maintenance of subgrade engineering in frozen soil regions.

[Objectives] Large-scale urban underground space development has led to numerous anti-floating problems. Groundwater level is a key parameter in the anti-floating design of underground structures, but it is inherently dynamic and influenced by various factors. This study aims to investigate how groundwater level in fractured rock layers dynamically responds to rainfall. [Methods] Field monitoring was conducted along a subway line, with seven groundwater level monitoring points and two meteorological monitoring points installed. Real-time data of groundwater level in fractured rock layers and rainfall at the site were collected. Based on these data, the annual variation patterns of groundwater level and rainfall were analyzed. Groundwater level increments under moderate to heavy rainfall conditions (daily rainfall ≥10.0 mm) were extracted, and a linear fit was performed between rainfall and groundwater level increments. [Results] Groundwater level variations were closely related to rainfall, rising during wet periods and falling during dry periods, with peak-to-valley amplitudes ranging from 3.34 to 17.55 meters. Additionally, the slope of the linear fitting between groundwater level increment and rainfall ranged from 0.006 to 0.025, indicating varying response speeds of groundwater level changes to rainfall. These differences were mainly influenced by rainfall intensity, site topography, surface water systems, and excavation activities. Based on the permeability of the rock layers, recommendations for anti-floating design were proposed: when the permeability coefficient of fractured rock exceeds 20 m/d, underground structures should strengthen passive anti-floating measures or increase active drainage and pressure relief measures; when the permeability coefficient ranges from 10 to 20 m/d, the anti-floating safety factor should be appropriately increased; when the coefficient is below 10 m/d, standard design practices are sufficient. [Conclusions] The study identifies the main factors influencing groundwater level fluctuations, quantifies the response of groundwater level to rainfall, and proposes an anti-floating design method that accounts for the permeability coefficient of rock layers. This approach addresses the limitations of traditional anti-floating designs that assume a uniform design water level and provides practical guidance for the anti-floating design of subway stations.

[Objective] Underground oil storage caverns are typically located in areas with hard crystalline rock, where the stability of surrounding rock mainly manifests as localized block instability. Traditional rock mass classification methods focus solely on analyzing and evaluating the overall stability of the surrounding rock, often neglecting the problem of block instability caused by unfavorable combinations of structural planes. [Methods] Block theory, utilizing geometric topological analysis to evaluate rock blocks formed by intersecting structural planes and their stability characteristics, serves as an effective approach for assessing the stability of underground caverns. Building on this block theory, this study utilized the whole-space stereographic projection method to identify removable blocks formed by the combinatorial intersection of various structural planes. The residual sliding force of these removable blocks was then used to determine whether they were key blocks requiring support. Subsequently, key blocks underwent maximum block morphology analysis to eliminate non-engineering-support blocks. Finally, positional block analysis was performed on blocks requiring support. [Results] This study developed a comprehensive flowchart for on-site block prediction analysis during engineering rock mass excavation. The specific analysis process was as follows. First, the development patterns of structural planes in the main cavern were analyzed and summarized based on geological mapping data obtained from preliminary surveys and the excavation of the main cavern’s top layer. Next, structural planes were combined, and the whole-space stereographic projection method was employed to identify potential removable blocks and key blocks that may form on the middle and lower sidewalls of the main cavern for each combination. Then, the geometric morphology of these key blocks was analyzed using their maximum block shape. Finally, blocks requiring support were identified based on their maximum block morphology, and corresponding support schemes were proposed. [Conclusion] The main conclusions are as follows: (1) through full-space stereographic projection analysis of various combinations of structural planes, the removable blocks and key blocks formed by these combinations on the left and right sidewalls were identified. (2) Based on the maximum block morphology of each key block, “shallow-buried” and “slender” types of non-support key blocks were eliminated, leaving only the “compact” type of blocks requiring support. (3) Support schemes were proposed based on the actual morphology of the identified “compact” blocks. The findings provide a theoretical foundation for the support design of cavern surrounding rock and hold significant value for broader applicability in rock underground engineering construction.