In order to comprehensively utilize solid waste coal gangue, coal gangue concrete piles were prepared by replacing part of traditional fine aggregate. Laboratory model tests of coal gangue pile-net composite embankments under reinforced cushions of geocells and geogrids were conducted to analyze the differences in load-settlement relationships of the embankment top surface, load transfer capabilities of the reinforced cushions, and stress distributions within the piles. Additionally, a finite element calculation model was established to investigate the stress and deformation patterns of different reinforcing materials, revealing the mechanism of geocells applied in reinforced cushions. The results indicate that, in this test, compared to geogrids, the geocell reinforced cushion significantly reduced the settlement of the embankment top by approximately 29.71%. Under the geocell reinforced cushion, the attenuation of soil pressure at the top of the piles and between piles was approximately 61.51% and 56.35%, respectively, fully utilizing the raft effect and stress diffusion effect. When using a geocell reinforced bedding, the embankment load was more effectively transferred to the coal gangue piles, with the extreme values of pile stress at the center of the roadbed and along the cross-section of the roadbed being 1.78 and 1.80 times greater, respectively, than those using geogrid reinforced bedding. The stress distributions of geocells and geogrids exhibited "V"-shaped and "U"-shaped patterns, respectively, and the maximum stress value of geocells was greater than that of geogrids. The unique honeycomb structure of the geocell exerts lateral hoop and rib friction resistance on the embankment fill, effectively diffusing the embankment load through its own tension and deformation.

Aiming at the engineering problem of rock damage and failure caused by long-term dry-wet cycle conditions such as the hydro-fluctuation belt in the Three Gorges reservoir area, this paper investigates the challenging issue of the micro-macro mechanical properties of brittle rocks under the combined effects of dry-wet cycles and direct tensile loading. However, due to the challenges in conducting direct tensile tests under dry-wet cycles, there is a scarcity of macro-micro mechanical models that account for both dry-wet cycles and direct tensile loading. Based on the coupled method of the theory of fracture mechanics and the experiment of dry-wet cycle, a macro-micro mechanical model of direct tensile fracture of brittle rock under the influence of dry-wet cycle conditions is proposed. The model is developed by considering the combined effects of the number of dry-wet cycles (n) and water content (ω) on fracture toughness (K_IC) and initial damage (D₀). It is then integrated with a direct tensile microcrack propagation mechanical model that considers initial microcrack damage and crack fracture toughness in rocks. The theoretical results for tensile strength, wing crack limit length l_lim, elastic modulus, and rock deterioration damage are compared with experimental data to validate the reasonableness of the model. The influence of initial crack angle φ, material constant β, and other parameters on the variation of crack initiation stress and peak stress with the number of dry-wet cycles n is discussed. Furthermore, a comparative analysis is conducted to investigate the effects of dry-wet cycles and single water content conditions on the deterioration degree of rocks.

 To study the dynamic response characteristics and energy evolution of through-jointed granite under impact load, granite with different dip joints was selected as the research object. Using the theoretical model of damage mechanics for jointed rock masses with varying dip angles, a series of SHPB (split Hopkinson pressure bar) impact tests was conducted on granite samples under high strain rates. The dynamic mechanical properties and energy dissipation characteristics of the rock samples were obtained. The results indicate that: (1) based on the Druck-Prager criterion, the Weibull strength distribution criterion, and the theory of elastic waves, the stress-strain model of jointed rock mass with different dip angles is established. This model can effectively reflect the dynamic mechanical properties of granite as the joint dip angle changes and exhibits a strong dip effect. (2) As the dip angle of the joints increases, the energy reflection coefficient rises linearly, the energy transmission coefficient decreases linearly, and the peak stress of the rock samples gradually decreases. Under the same joint dip angle, as the impact load increases, the energy reflection coefficient first increases and then decreases, the energy transmission coefficient first decreases and then increases, and the energy absorption rate decreases with the increase of the joint dip angle. (3) When the impact load is the same, the fragmentation degree of intact rock samples and those with joint dip angles of 0° and 15° is greater, while the fragmentation degree of rock samples with joint dip angles of 30° and 45° is smaller. When the joint dip angle is the same, as the impact load increases and exceeds the maximum compressive strength of the rock samples, the failure mode gradually transitions from shear and tensile failure to crushing failure, and the degree of fragmentation also increases.

The deterioration of rocks on reservoir bank slopes under flowing water conditions can seriously compromise slope stability. Meticulously exploring the macro-mechanical properties and microstructures of rocks under dynamic water scouring conditions is of great significance for disaster prevention and control in reservoir areas. To simulate the water flow environment of reservoir bank slopes, a rock scour resistance test device was designed. Taking sandstone as the research object, three conditions namely, natural drying, hydrostatic immersion, and hydrodynamic scouring, , were considered. Combining with laboratory test results, digital image correlation techniques, scanning electron microscopy, and fractal theory, the influences of different water environments on the mechanical properties of rocks were systematically explored in terms of macro-mechanical parameters, distribution characteristics of strain fields, and microstructure. The results indicate that the softening coefficients of compressive strength and elastic modulus of hydrodynamically scoured specimens decrease by 0.07 and 0.06 units, respectively, compared to those of water-saturated specimens. The inflection point of the strain field differentiation rate-axial strain curve appears before the peak stress, associated with the localization of the fracture process zone, serving as a precursor signal for rock fracture. Compared to the effect of hydrostatic immersion, the precursor point P of hydrodynamically scoured specimens appears earlier, as hydrodynamic scouring aggravates the development of internal defects, thereby facilitating the earlier appearance of the precursor point. Furthermore, the loss of mineral particles and cementing materials within the sandstone increases significantly after hydrodynamically scouring, leading to a more pronounced degradation of its microstructure than that of water-saturated specimens. This change is confirmed by the fractal dimension calculations of scanning electron microscope images, indicating that the hydrodynamically scoured specimens exhibit the largest fractal dimension.

The high-precision gas steady-state method and the gas pulse decay method are widely used in the permeability measurement of tight porous media. However there is a lack of in-depth discussion and analysis of the gas periodic oscillation method (POM). The basic principle of POM is introduced, and three practical methods for simulating periodic pressure waves are proposed. Additionally, an experimental equipment scheme is recommended, which includes two adjustable gas storage containers on each side of the specimen. The theory proposed by Fischer regarding the periodic oscillation method is expanded in this study to include the scenario where the seepage medium is a compressible fluid, as opposed to only considering incompressible fluids. This extension allows for a wider range of applications for the periodic oscillation method. Additionally, the study examines the physical significance of this method and analyzes the relationships between different parameters involved. Based on the generic theoretical solution of POM, two special cases are analyzed and the treatment of some complex sub-terms is optimized. The calculation results of the theoretical and numerical solutions of POM are compared through a series of orthogonal cases, and the effects of permeability, porosity, downstream container volume, specimen diameter and length on the experimental process are discussed respectively. The numerical solutions are used to verify the accuracies and stabilities of the theoretical solutions, and to illustrate some shortages of the theoretical solutions. Based on the case study, a better design strategy of POM experiment is given.

An experimental study was conducted on shaking table tests of 1/4-scale back-to-back reinforced soil walls with full-height rigid facing. The reduced-scale model was designed according to the similitude relationships and excited using a series of sinusoidal input motions with increasing acceleration, to investigate the dynamic response of back-to-back reinforced soil walls with full-height rigid facing. The results indicate that the acceleration amplification factors on reinforced soil zone and retained soil zone increase significantly with increasing elevation and reach the maximum at the top of the wall. The maximum acceleration amplification factors under input motions with increasing acceleration amplitude can be divided into three stages, including stable stage, rising stage, and attenuation stage. The incremental maximum dynamic and residual facing displacements increase in a linear manner with elevation. For the input motion smaller than the critical acceleration, facing displacements are smaller, while facing displacements increase rapidly for the input motion exceeding the critical acceleration. In addition, the critical acceleration has an important influence on the deformation modes for back-to-back reinforced soil walls with full-height rigid facing. The incremental reinforcement tensile strains increase significantly with increasing input acceleration, and the incremental maximum strain in each reinforcement layer generally occurred near the connection in the lower layers and moved further inward along the height direction in the upper layers.

The breakage behavior of granular materials is prevalent across various fields and significantly impacts the mechanical properties of granular materials. A substantial amount of research on particle breakage behavior relies on reasonable calculation methods for breakage rate. This article proposes a calculation method for particle breakage rate based on particle volume as the fundamental parameter, addressing the current limitation of existing methods in accurately evaluating the breakage rate of irregular particles, exemplified by coral gravel. It improves upon the existing Hardin breakage rate calculation formula, which is based on particle size, to better assess the breakage rate of irregular particles. Breakage tests of coral gravel with different shapes were designed and conducted to conduct reliability validation of the aforementioned theoretical formulas, and the causes of errors generated by traditional methods were analyzed. Through experiments, the breakage rate values of particles with different shapes under different pressures and algorithms were obtained. Meanwhile, combining stress, deformation, and image observations from the experimental process, the fragmentation thresholds of coral gravel in three shapes—sheet, block, and rod—were determined, revealing the evolution characteristics of fragmentation modes exhibited by particles with different morphologies during the pressure change process.

A series of undrained triaxial shear tests, mercury intrusion porosimetry (MIP) tests, and scanning electron microscopy (SEM) tests were conducted on red mudstone fill material (RMF) at varying water contents to investigate its microstructure and stiffness degradation. Based on the principle of energy conservation, a relationship between the stiffness degradation of the fill material and the increment of elastoplastic strain energy was derived. The results show that the cohesion of RMF decreases with increased water content, while the internal friction angle initially increases and then decreases on the wet side. The evolution of strain energy leads to structural damage and subsequent stiffness degradation. The normalized stiffness ratio linearly decreases with the ratio of plastic strain energy to total strain energy and nonlinearly decreases with normalized shear stress. With optimal water content as the boundary, the RMF exhibits better load-bearing capacity on the dry side, while significantly lower on the wet side. The contours of damage stress and constant water content lines define a state boundary surface, whose upper and lower bounds follow logarithmic curves. The pore size distribution (PSD) of RMF on the dry side exhibits a uni-modal pattern with strong inter-aggregate contacts and good structural stability. On the wet side, however, a bi-modal structure is observed with weaker orientation of aggregates. It is recommended that the fill material be compacted on the dry side, with a target water content ranging from 5% to 7%.

The shear strength and stiffness characteristics of methane hydrate sediments in seabed reservoirs are crucial for the safe and efficient exploration and exploitation of hydrates. To investigate the impact of changes in occurrence environments on the shear strength characteristics of muddy hydrate-bearing sediments, a series of drained shear tests have been conducted on methane hydrate-bearing muddy silt sediments under varying conditions of saturation (water-saturated and gas-saturated) and confining pressure based on the improved triaxial shear tester for hydrate-bearing sediments. The experimental results show that changes in the occurrence environment in sediments have significant effects on the shear strength and stiffness characteristics of hydrate-bearing muddy silt sediments. Compared to gas-saturated sediments, the shear strength of hydrate-bearing sediments with the same hydrate saturation greatly reduces under water-saturated condition, with a maximum reduction ratio of 52.0%. Although the effect of occurrence environmental changes on the internal friction angle of sediment is limited, the effect on the cohesion of sediment is significant. Compared to the results from gas-saturated sediments, the reduction ratio of the effective cohesion for the water-saturated hydrate-bearing sediments can reach 68.1%. Furthermore, the exponential equation is developed for describing the relation between the effective cohesion and hydrate saturation. Under water-saturated conditions, the deformation modulus of hydrate-bearing sediments decreases significantly, with a maximum reduction ratio of 72.7% for E50. Additionally, the deformation modulus increases linearly with hydrate saturation under water-saturated conditions. Lastly, based on the stress analysis of the skeleton of hydrate-bearing sediments under gas-saturated and water-saturated conditions, the evolution mechanism of the mechanical properties of hydrate-bearing sediments under these two different occurrence environments is preliminarily revealed. The observations can offer fundamental data and methods for recovering the occurrence mechanism of methane hydrate-bearing sediments and assessing the stability of the reservoir.

Due to the influence of cycle water pressure permeation, the physical and mechanical properties of sandstone in the fluctuation zone deteriorate with time, which leads to a decrease in bank slope stability. Undrained triaxial compression tests were conducted on sandstone subjected to varying cycles of pore water pressure. The evolution of the deformation, strength, and brittleness index of sandstone were investigated, and the mechanisms of microstructural deterioration were discussed. The results show that the peak stress decreases with the increase of osmotic water pressure action cycle, and the strength degradation gradually decreases with the increase of confining pressure. With an increase in the number of cycles of pore water pressure, both cohesion and internal friction angle decrease exponentially and linearly, respectively, indicating that the decrease in cohesion is the primary cause of strength deterioration. The elastic modulus, failure strain and Tarasov brittleness index decrease gradually with the increase of pore water pressure action period, however there is a significant enhancement effect with increasing confining pressure. Moreover, the failure mode has evolved from single slope shear failure to conjugate shear failure, with the fracture angle decreasing from 67.2° to 62.05°. The stress concentration and stress fatigue caused by cyclical pore water pressure at the crack tip exacerbate the internal structural degradation of sandstone. Additionally, the increase in pore water pressure during undrained compression exacerbates the damage and degradation of the sandstone, while the confining pressure causes the closure of some seepage channels, reducing the seepage damage of sandstone.

The direction of inertial force under seismic conditions has a significant impact on the equilibrium state of combined structures, soil, and rock masses. To gain a deep understanding of the interaction characteristics between the pile-plate wall combined support structure and the bedrock and overburden layer slope, a series of large-scale shaking table model tests on the slope reinforced by combined structures under sinusoidal wave load were conducted, using a high steep slope at the tunnel portal in the southwestern region as a prototype. The analysis of the time-history characteristics of the pile-soil and the geogrid-anchor cable-slope under the direction of inertial force was considered. The results indicate: (1) Under the action of inertial force, the lattice anchor cable-soil interaction and pile-soil interaction show an approximate time-history consistency law, but the phase difference between the peak value of the inertial force of the slope reinforcement structure along the elevation cannot be ignored. (2) The interaction between the structure and the slope soil depends on the relative inertial motion, and the pile-bedrock interaction is determined by the deformation state of the cantilever section. (3) The inertial force reaches the peak value of the free surface, the dynamic soil pressure reaches the peak value, the pile-soil displacement difference reaches the positive peak value, the pile body shows an active failure state of camber, and the stress on the front side of the anchoring section increases due to camber, so the design using Coulomb active earth pressure should be revised based on the pile-soil conditions. (4) Under sinusoidal wave conditions, the inertial force and deformation of the slope are crucial factors affecting the force distribution characteristics of the combined retaining structure along the elevation. The design of the combined structure needs to focus on the stress concentration area at the foot of the slope and the inertial force amplification area at the top of the slope. This research can provide theoretical support for the seismic reinforcement design of combined structures.

This study investigates the rheological properties of saturated soft clay surrounding a tunnel using the generalized Voigt viscoelastic model. The model incorporates linear semi-permeability boundary conditions to describe the behavior of the clay. Furthermore, two-dimensional rheological consolidation control equations are derived based on the Terzaghi-Rendulic theory, considering the excess pore water pressure as a variable. To solve the equations, conformal transformation and separation of variables methods are employed, resulting in two independent equations representing the excess pore pressure in terms of time and space variables. The Laplace transformation and partial fractional summation method are then utilized to obtain the solution for excess pore pressure dissipation in the time domain. The reliability of the solution is verified by comparing it with the existing four-element Burgers and five-element model, both of which are derived from the generalized Voigt model. Furthermore, the influence of liner permeability, Kelvin body number, independent Newtonian dashpot viscosity coefficient, and tunnel depth on the dissipation and distribution of excess pore pressure is analyzed based on the established solutions. The findings indicate that a higher relative permeability of the liner and soil leads to an earlier onset of excess pore pressure dissipation and a faster dissipation rate. Increasing the number of Kelvin bodies results in slower dissipation rate. Moreover, larger independent viscous coefficients lead to smaller viscous deformation and faster dissipation rates. Additionally, greater tunnel depth prolongs soil percolation path, slowing down the dissipation of excess pore pressure. When the relative permeability coefficient is 0.01, the excess pore pressure gradually decreases with distance from the outer wall of the tunnel. However, when the relative permeability coefficient is 1, the excess pore pressure initially increases and then decreases with distance. As the relative permeability coefficient increases, the influence of the number of Kelvin bodies on the dissipation of super pore pressure diminishes, the variation in super pore pressure dissipation caused by different independent Newtonian dashpot viscosity coefficients gradually decreases, and the role of tunnel liners as new permeable boundaries within the soil layer is becoming increasingly prominent.

In tunnel boring machine (TBM) tunnels, the pea gravel as a filling layer between the tunnel lining segments and surrounding rock is of significant importance for the load-bearing capacity and impermeability of the segments. Due to the poor flowability of cement slurry, it fails to adequately fill the backfill layer, resulting in defects such as voids behind the walls and inadequate grouting. Enzyme-induced calcium carbonate precipitation technology (EICP) has emerged as an environmentally friendly and efficient reinforcement method. The grouting material is liquid, exhibiting excellent fluidity and diffusivity, making it a promising solution for grouting in pea gravel backfill layers. To optimize the effectiveness of EICP grouting in pea gravel, an attempt was made to use standard sand and pea gravel as backfill aggregates. In order to quantitatively analyze the optimal mixing ratio, experiments were conducted with different ratios of pea gravel to sand (0.5, 0.75, 1.0, 1.25, 1.5) and varying grouting frequencies (9, 12, 15 times) in sand column solidification tests. Through unconfined compressive strength tests, permeability tests, determination of calcium carbonate content, ultrasonic velocity measurements, and scanning electron microscopy (SEM) microscopic analysis, the impact of different ratios of pea gravel to sand on the solidification effectiveness of EICP was analyzed from both macro and micro perspectives. The results indicate that the optimal ratio for EICP reinforcement of mixed pea gravel and sand is 1:1.5. After 15 grouting cycles, the uniaxial compressive strength of the specimens can reach up to 4.55 MPa, and the permeability coefficient is 1.72×10⁻⁵ m/s. Samples with a higher sand content exhibit a notable phenomenon where interparticle voids are readily filled and compacted by calcium carbonate crystals. This process results in a higher proportion of effective bonding among calcium carbonate crystals, consequently contributing to an elevated unconfined compressive strength of the stone body. The findings of this study can provide a theoretical basis for the engineering application of EICP technology in reinforcing TBM backfilled pea gravel.

A water conveyance open channel project in the northern Xinjiang region crosses a large area of collapsible loess. The mechanical properties of the collapsible loess have undergone severe degradation after years of exposure to rainfall, evaporation, and seasonal temperature fluctuations, making it highly susceptible to engineering phenomena such as channel foundation collapse and slope failure. To delve into the deterioration mechanism, direct shear, compression, and microscopic scanning tests were conducted on the collapsible loess under dry-wet & freeze-thaw cycles. The deterioration patterns of shear strength and compression properties, as well as their damage mechanisms, were analyzed at both macro and microscopic scales. The results of the study indicate (1) Straight shear test: with increasing the number of dry-wet-freeze-thaw cycles, the peak shear strength exhibits a three-stage trend: rapid decrease, decelerated rate of decrease, and eventual stabilization. The cohesion decreased exponentially, with the largest reduction occurring during the first cycle, and stabilizing after 5 cycles, reaching a degradation degree of 44.55%. The change in internal friction angle, which varied within 2.1°, was less affected by the wet-dry-freeze-thaw cycles, with a maximum degradation of 7.04%. (2) Compression test: the compression curve can be divided into two stages of elastic deformation and elastic-plastic deformation according to the consolidation yield stress σk, and σk shifts forward as the cycle times increase. The compression coefficient and compression index decreased exponentially or in a power function form with increasing cycle times, indicating reduced overall compressibility of the soil body. (3) Microstructure: through scanning electron microscope (SEM) analysis, under cycling, the number of large pores decreased while the number of medium and small pores increased, with the arrangement tending towards disorder. Large particles gradually transformed into medium and small particles, and their morphology tended to become rounded. Correlation analysis indicates that pore size and its angle are the main factors influencing shear strength. Pearson’s correlation coefficient reveals that particle morphology and pore size have the greatest influence on compression indices.

In order to study the shear strength characteristics of rock-like material joints in different loading control modes and unloading stress paths, the direct shear tests of rock-like material joints in two loading control modes and three unloading stress paths were carried out by means of RDS-200 rock joint shear test system. The results show that: (1) when the stress control mode is used for shear test, it can be found that the joint shear stress-time curve mostly has the instability drop, and the shear stress-displacement curve is mostly in the form of broken line after instability in each shear stress loading and unloading path. (2) Compared with the results of the joints that experiencing shear loading in a stress control mode, the instability shear strength is reduced when the rock-like material joints are sheared in the following control mode and unloading stress paths including loading shear stress in a displacement control mode, unloading the normal stress in a stress control mode while keeping the shear stress constant, unloading the normal stress while increasing the shear stress in stress control modes, unloading both the normal stress and the shear stress in stress control modes. The average decrease percentage of cohesion is 36.07 %, while the change range of internal friction angle is only 4.12 %. Therefore, the decrease of cohesion is the main reason for the decrease of the joint instability shear strength. (3) Based on Mohr-Coulomb formula for joints experiencing the shear loading in a stress control mode, the average relative error of the instability shear strength of joints experiencing a shear loading in the displacement control mode or experiencing loading and unloading in other stress paths in the stress control mode can reach up to 55.78 %. The maximum value of the average relative error can be reduced to 5.23 % after the cohesion correction coefficient k is introduced to modify the Mohr-Coulomb formula, which shows that the reduction correction of cohesion is necessary and feasible for engineering joints that may experiencing shear stress loading in the displacement control mode or may experiencing loading and unloading in other stress paths in the stress control mode. The research results have a certain reference value for accurately estimating the shear bearing capacity of rock mass joints in different loading control modes and unloading stress paths.

To address the issues of low early strength in cement-stabilized soft soil, as well as the high pollution, energy consumption, and costs associated with cement binder application, one-part geopolymer (OPG) is prepared by using solid sodium silicate (Na2O·SiO2, NS) to activate a mixture of binary precursors, namely fly ash (FA) and ground granulated blast furnace slag (GGBFS), along with water. The factors, including FA dosage, solid NS molarity, alkali molar concentration, and water-cement ratio, are considered for assessing the physical and mechanical properties of OPG. Based on this, optimized proportioning tests were conducted to determine the best mixing ratio of OPG for soft soil stabilization. The effects of the FA/GGBFS ratio in the precursor and curing ages on the unconfined compressive strength (UCS), porosity, and pore size distribution of OPG-stabilized soft soil were further investigated. Micro-analysis was performed using mercury intrusion porosimetry (MIP), scanning electron microscope-energy dispersive spectrometer (SEM-EDS) to reveal the stabilization mechanism. The results indicated that the OPG prepared with solid NS could effectively stabilize soft soil, with hydrated gels (N-A-S-H, C-A-H, C-S-H, and C-A-S-H) effectively bonding soil particles and contributing to the formation of a denser soil skeleton. The mixing proportion of FA/GGBFS of 0.1, water-cement ratio of 0.8, NS molarity of 1.0, and molar concentration of 3 mol/L was found to be optimal for soft soil stabilization. The corresponding OPG had good workability and achieved a UCS of 4.4 MPa. This study extends the application of solid sodium silicate-inspired one-step geopolymers in deep mixing techniques, providing guidance on the theoretical basis for the reinforcement treatment of soft ground foundations.

Clogging areas often form around the prefabricated vertical drainage plates during the vacuum preloading of waste slurry. Accurate measurement and calculation of the permeability coefficient of mud in the clogging zone are critical for predicting the consolidation of waste slurry. Since the permeability coefficient of mud in the clogging zone is difficult to measure directly and there is a lack of theoretical derivation for it, a calculation method for the permeability coefficient and thickness of the clogging zone was proposed. A test device was established to investigate the formation of the clogging zone and validate the calculation method. The test proved the practicability and feasibility of the calculation method. It is concluded that when conducting vacuum preloading on waste slurry at construction sites, the vacuum degree should be controlled below 90 kPa, and the lower the vacuum degree used in the vacuum preloading between 60 kPa and 90 kPa, the slower the formation of the clogging zone is. The proposed permeability coefficient calculation method for the clogging zone can be used to predict the degree of mud consolidation during the vacuum preloading process.

Cementing loose coral sand to reduce the permeability of island reef formations is one of the key approaches to enhancing freshwater retention in ecological islands. To this end, a permeability test was conducted on zinc sulfate-bonded coral sand, analyzing the effects of varying immersion durations, zinc sulfate solution concentrations, and initial dry densities on its permeability. The durability was verified through dry-wet cycling tests, while the microscopic cementation mechanism was investigated using XRD(X-ray diffraction), SEM(scanning electron microscope), EDS(energy dispersive spectrometer) and CT(computed tomography) scanning. The test results show that: (1) the permeability coefficient of coral sand is reduced by 70.17% to 95.79% after cementation with zinc sulfate. (2) After undergoing 16 dry-wet cycles and 36 hours of cementation, the mass loss rate of the cemented coral sand samples does not exceed 4%, and the variation of permeability coefficient is less than 1.0×10⁻³ cm/s, indicating excellent durability of the samples. (3) Additionally, the reaction between coral sand and zinc sulfate produces dihydrate gypsum and smithsonite, filling the pores of the samples, resulting in a decrease in the average pore-throat radius and coordination number, and a significant reduction in pore connectivity. This technology holds significant engineering application value, as it can be applied to sand fixation and erosion prevention in the initial stage of island reef reclamation, improving foundation bearing capacity and reducing permeability to promote groundwater conservation and eco-island construction.

Studies show that adding carbon fiber to concrete to form a conductive network can make concrete feel its own stress, strain, cracks, and damage according to the change of conductive network, and improve the strength and durability of concrete. In view of the self-sensing characteristics of carbon fiber, carbon fiber reinforced cement-based composites are put forward as a new intelligent sensing material. Through unconfined compressive strength test, resistivity test, microscopic test, and model test, the influence of fiber volume fraction and fiber length on unconfined compressive strength and resistivity change rate of carbon fiber reinforced cement-based composites are studied. A carbon fiber reinforced cement-based composites "sensor" is made according to the optimal ratio, which is implanted into cement-based composites components to establish the functional relationship between the sensor resistivity change rate and the stress of cement-based composites components, so as to realize the stress monitoring of cement-based composites components by the sensor. The results show that, in the study of the strength of carbon fiber reinforced cement-based composites, the unconfined compressive strength of carbon fiber reinforced cement-based composites is affected by both carbon fiber volume fraction and carbon fiber length, and the compressive strength increases first and then decreases with the increase of both. In the test range, 2% is the optimal volume fraction and 6 mm is the optimal fiber length. In the study of the resistivity change rate of carbon fiber reinforced cement-based composites, when the carbon fiber volume fraction is 1% and the fiber length is 3 mm, the resistivity change rate of the specimen is the largest, and the self-sensing sensitivity of carbon fiber reinforced cement-based composites is the best. There is an obvious exponential relationship between the resistivity change rate of the sensor embedded in the component and the stress of the cement-based composites component. Through establishing a stress prediction formula based on resistivity change rate, the stress state monitoring of the cement-based composites structure can be realized.

A type of variable cross-section anchor is proposed for the binary layered foundation with upper soil and lower rock that is widely encountered in transmission line engineering. Its principle is to increase the cross-sectional area of the anchor in the overlying soil layer to fully utilize the bearing capacity of the soil and rock. To examine the performance of the proposed anchor, the load-bearing capacity improvement mechanism of the variable cross-section anchor is discussed through a combination of field tests and numerical simulations, and the effect of different factors on the bearing performance is investigated. The results indicated that compared with uniform section anchor, the uplift, downward, and horizontal bearing capacities of the variable cross-section anchor are increased, and the horizontal bearing performance is improved significantly. The thickness of covering soil on the sites has a significant impact on the uplift bearing capacity of the anchor, while the influence on the downward and horizontal bearing capacity is less. The terrain slope of site has a great influence on the horizontal load-bearing performance of the anchor, and the two are negatively correlated. Furthermore, under the “uplift + horizontal” loading, the group anchor foundation with variable cross-section anchor exhibits higher bearing capacity than the one with uniform section anchor and the traditional composite foundation, and also has the advantages of small excavation volume and more suitable for slope terrain. This study can provide technical support for the application of this new type of foundation.

Landfill sites in China are characterized by high water levels and high air pressures. Despite the proposal of various stability evaluation indicators and grading standards in existing regulations and research, there remains a lack of systematic research on indicator weights and comprehensive risk assessment. Therefore, this study establishes a landfill instability risk assessment index system encompassing seven indicators across four categories: landfill geometric configuration, shear strength of waste soil, liquid and gas occurrence, and rainfall. Through parameter sensitivity analysis, a five-level classification (stable, relatively stable, basically stable, unstable, extremely unstable) is achieved, and set pair analysis is employed to construct the indicator correlation function. The comprehensive weights of the evaluation indicators are determined through the importance ranking of indicators, combined with parameter sensitivity analysis, engineering instability accidents, literature attention statistics, and game theory-based combination weighting. Subsequently, a comprehensive evaluation model for landfill instability risk is established by coupling the comprehensive weights of indicators with the indicator correlation function. This model is then applied to an actual landfill project, and the results are consistent with the actual monitoring data on site, thereby verifying the accuracy and effectiveness of the evaluation model.

Driven by human activities and global climate change, the climate on the Qinghai-Xizang Plateau is experiencing a warming and humidifying trend. It significantly impacts the thermal-moisture dynamics in the active layer of the permafrost, which in turn affects the ecological environment of cold regions and the stability of cold region engineering. While the effect of air temperature on permafrost thaw has been well quantified, the processes and mechanisms behind the thermal-moisture response of the permafrost under the combined influence of increased rainfall and rising air temperature remain contentious and largely unknown. A coupled model was applied to quantify the impacts of increased rainfall, rising air temperature, and their compound effects on the thermal-moisture dynamics in the active layer, considering the sensible heat of rainwater in the ground surface energy balance and water balance process. The results indicate that the compound effect of warming and humidifying resulted in a significant increase in surface net radiation and evaporation latent heat, a more significant decrease in surface sensible heat, and a smaller impact of rainfall sensible heat, leading to an increase in surface soil heat flux. The compound effect of warming and humidifying leads to a significant increase in the liquid water flux with temperature gradient. The increase in liquid water flux due to the temperature gradient is larger than that of warming alone but smaller than the effect of humidifying alone. Warming and humidifying result in a smaller increase in soil moisture content during the warm season compared to rainfall increases alone. The thermal conductivity heat flux in the active layer increases significantly during the cold season but less than the effect of warming alone. The convective heat flux of liquid water flux increases noticeably during the warm season but less than the effect of rainfall increases alone. Increased rainfall significantly cools the soil during the warm season, while both warming and humidifying lead to a more pronounced warming effect on the soil during the cold season than during the warm season. An increase in the average annual temperature by 1.0℃ leads to a downward shift of the permafrost table by 10 cm, while an increase in rainfall by 100 mm causes an upward shift of the permafrost table by 8 cm. The combined effect of warming and humidifying results in a downward shift of the permafrost table by 6 cm. Under the influence of climate warming and humidifying, the cooling effect of increased rainfall on permafrost is relatively small, and the warming effect of increased temperature still dominates.

With the frequent occurrence of heavy rainfall weather, the accidents of lining cracking, water leakage, and instability failure of in-service karst tunnels are becoming more prevalent. The accumulation of high water pressure behind the lining due to surface rainfall recharge is the primary cause of hydraulic disasters in karst tunnels. Monitoring and early warning for in-service karst tunnels are crucial methods to prevent such disasters. Taking the karst tunnel of Zhengzhou-Wanzhou railway as an example, similar model tests and seepage numerical simulations were conducted to investigate the water pressure distribution behind the lining and the uplift displacement of the lining under different karst morphologies. The research results provide a reference for the operational monitoring and early warning control standards of karst tunnels. The results indicate that when the recharge of surface rainfall exceeds the drainage capacity of the tunnel, a hydrodynamic pressure system of "surface recharge + tunnel drainage" will form behind the lining, making the bottom of the invert prone to accumulating high water pressure. When there are karst cavities and dissolution fracture zones in the strata, surface rainfall will lead to localized increases in water pressure on the lining, causing it to bear eccentric loads and further deteriorating the stress on the invert. Using the water pressure and uplift displacement at the invert center as the control basis, the monitoring and early warning levels for karst tunnel operation are classified into normal operation, temporary repair, speed limit rectification, and closure for rectification. The research findings can offer insights for the structural design optimization and monitoring and early warning of karst tunnels.

The accelerated construction of pumped storage power stations underscores the importance of reasonable arrangement in-situ stress testing and precise data acquisition for high-head pumped storage power stations. This study, taking a high-head pumped storage power station as an example, conducted comprehensive in-situ stress measurements across various survey stages, considering the topographic and in-situ stress characteristics. By integrating in-situ stress field inversion, we obtained the spatial three-dimensional in-situ stress field distribution and analyzed the anti-splitting properties of the surrounding rock. The comprehensive measurements revealed that the two-dimensional surface deep hole results vary with the buried depth gradient, exhibiting stress concentration in the middle and shallow regions, aligning with the in-situ stress distribution patterns of high-head pumped storage power stations. The maximum measured principal stress in the underground plant and high-pressure bifurcation pipe reached 20.9 MPa, while the minimum principal stress was 7.0 MPa, indicating that horizontal stress is the dominant stress in the rock mass. The maximum principal stress direction is concentrated towards the NEE orientation. The inversion of the initial in-situ stress field can be carried out by using the comprehensive measured results to strengthen the refinement of the model, which can better reflect the characteristics of the in-situ stress field of such projects, and is conducive to the anti-splitting analysis of the surrounding rock and the selection of subsequent lining schemes. This study demonstrates the feasibility of comprehensive in-situ stress testing for high-head pumped storage projects, providing a valuable reference for in-situ stress investigations in such power station projects.

Currently, earthquake liquefaction probability evaluation methods generally suffer from complex formula forms, inconsistent probability calculation values among multiple formulas, and insufficient significance of liquefaction probability at the site level. Based on these issues, after evaluating the consistency and discriminatory power of multiple probability formula methods, reasonable probability calculation values for existing measured historical samples were selected to calibrate the liquefaction probability levels of the samples. A preliminary liquefaction prediction model was established using the classification tree method and then optimized based on China's seismic design recommendations to develop a new method for liquefaction probability level evaluation. The new method is divided into two parts: single borehole and site liquefaction probability evaluation, which can provide a quantitative basis for liquefaction risk assessment in practical engineering. Compared with existing methods, the new method omits the traditional formula calculation process, making the evaluation process simpler and the results more intuitive. New Zealand earthquake liquefaction data and an actual engineering site were selected as test samples to validate the reliability and rationality of the new method at both the single borehole and site levels. The verification results show that the new method achieves a 93% accuracy rate for single borehole predictions and demonstrates better rationality in site evaluations compared to existing norms. The new method can provide methodological support for evaluating liquefaction probability at engineering sites and has practical engineering significance.

The micro-mechanisms of suction caisson-soil interaction under the action of inclined mooring lines remain unclear. In this study, a coupled discrete element method (DEM) and finite element method (FEM) was adopted to investigate this issue from macro- to micro-scales, with a focus on the influence of mooring depth. The sand particles were simulated by DEM, and the suction caisson was simulated by FEM. The mooring line tension was simulated by controlling the roller motion. The results revealed that the differences in the evolution of the force-displacement curves were attributed to the differences in the suction caisson motion modes at different mooring depths. The mooring depth differences caused significant differences in the vertical pull-out displacement, rotation angle, and deformation of the suction caisson. The critical reverse mooring depth point of suction caisson rotation direction and pull-out displacement is located near the depth of h = 66.7% from the top of the suction caisson (i.e., 2/3 of the suction caisson depth). Moreover, the deformation behavior of the soil was analyzed at the scale of particles, ultimately determining the failure mode of the interaction between the suction caisson and the particle soil. The study showed that neglecting the mooring depth of the mooring line may lead to a misjudgment of the bearing capacity of the suction caisson and the failure mode of the soil.

A method for precise localization of seismic sources in rock mechanics was proposed. The method combines accurate picking of P-wave arrival times with an analysis-based filtering of anomalous arrivals and a joint localization approach using genetic algorithms (GA). The method was applied to locate fracture surfaces in rock materials and in mining engineering. To mitigate the impact of sensor timing accuracy, traditional iterative methods, and the selection of initial iterative values on localization, an improved STA/LTA method based on time-frequency analysis was used to pick the P-wave arrival times. A logic probability density function of the analysis-based solutions for different sensor combinations was employed to filter out anomalous arrivals. Genetic algorithms were then used to locate the clear arrivals from filtered data. The method was validated through tests on lead breaking and layered coal-rock compression, as well as controlled blasting experiments. The results show that combining precise filtering using variational mode decomposition (VMD) after pre-bandpass filtering with the improved STA/LTA method significantly enhances the accuracy of P-wave arrival time picking. The combination of the analysis method for filtering the impact of anomalous arrivals on positioning accuracy and the genetic algorithm, which is globally applicable and not influenced by initial values, allows for more accurate localization of seismic sources in rock material testing and mining engineering. This method has greater practical engineering application value compared to traditional iterative methods and linear positioning methods.