Continental shale generally consists of layers with varying components, including clay, felsic minerals, and calcite. During hydraulic fracturing stimulation of shale fracture network structure, the interfacial transition zone (ITZ) forms, significantly influencing crack propagation direction and morphology. Currently, effective quantitative methods for determining the ITZ distribution range in shale layers are lacking. This study focuses on the discrete characteristics of shale micro-mechanical parameter curves and employs confidence ellipses to calibrate discrete data within the ITZ range. Linear fitting and the projection length of confidence ellipse intersections are introduced as a new method for quantifying the ITZ in shale layers. Scanning electron microscopy and a mineral quantitative evaluation system were used to obtain shale surface morphology and mineral distribution, analyzing mineral damage forms after scratch experiment. Nano scratch experiment results were used to determine mineral distribution lengths from various rock types via fracture toughness, compared with scanning electron microscopy findings. Results show that plastic minerals such as illite show a damage pattern of debris accumulation on both sides during the scratch test, while brittle minerals such as albite and quartz show jagged damage or point-like chipping. The presence of ITZ causes the distribution length of plastic minerals identified by scanning electron microscopy to exceed the quantitative results from fracture toughness curves. The friction coefficient method is affected by surface roughness, resulting in lower fitting confidence and higher quantitative results. Compared to the friction coefficient method, the fracture toughness method offers higher data continuity and fitting confidence, though it considers relatively fewer factors. Non-dimensional parameters comprehensively account for fracture toughness, hardness, friction coefficient, and scratch depth, reducing curve dispersion and fitting errors. Compared to traditional methods for identifying individual mechanical parameters, the accuracy of ITZ distribution range quantification based on dimensionless parameters is greatly enhanced.

To assess the engineering application potential of coral mud, a model test was conducted on cracking in the surface layers of polyvinyl alcohol (PVA) fiber-modified coral mud using particle image velocimetry (PIV) technology. The displacement and velocity fields of the coral mud surface layer were obtained, revealing the cracking and crack inhibition mechanisms from the perspective of multi-physical field interactions and energy dissipation. The interaction mechanisms between multi-physical fields and soil moisture evaporation, shrinkage, and cracking were discussed, providing a new perspective on crack dynamic behavior. The results indicate: (1) Under gravity, the trajectories of surface particle movement in the coral mud surface layer show a clockwise vortex-like contraction direction. Soil particles in the coral mud surface layer reach maximum velocity at crack locations. As cracks initiate, develop, and stabilize, particle velocity accelerates, peaks, and then decelerates. (2) Carbonate mineral components in the coral mud undergo chemical hardening, crystallization, and cementation. Cementation occurs between PVA fibers and coral mud particles and between coral mud particles, enhancing the strength of coral mud. Optimal performance occurs at a fiber content of 0.5%, with minimal cracks on the coral mud surface. (3) Coral mud cracking occurs in three forms: tensile failure, shear failure, and tensile-shear mixed failure. (4) From the perspective of multi-physical field interactions and energy dissipation, the mechanisms of cracking and crack inhibition in the coral mud surface layer are elucidated, offering new insights into the interaction between multi-physical fields and soil evaporation, shrinkage, and cracking are proposed. The interaction of moisture, displacement, velocity, and stress fields during soil cracking collectively influences the formation and development of soil cracks. These interactions form a complex system affecting soil stability and mechanical behavior.

The bottom-supported platform for offshore wind power, suitable for soft soil areas of the sea, has gained popularity with increasing total installed capacity of offshore wind power. The platform is anchored on a mat foundation through a supporting structure, which evenly distributes the concentrated load into the seabed foundation, providing essential support for the offshore wind installation platform. Due to long-term bottom-sitting, the soil beneath the foundation consolidates, increasing the difficulty of foundation recovery or relocation. Therefore, a new hollow square-shaped mat foundation structure is proposed. To investigate the vertical bearing capacity characteristics of this new type mat foundation in saturated soft clay, centrifuge vertical bearing capacity tests were conducted. Additionally, finite element numerical analysis was employed to study the effects of open porosity and normalized strength on vertical ultimate bearing capacity. The results indicate that the American Petroleum Institute (API) standards underestimate the vertical bearing capacity of foundations when the normalized strength of soil is less than 2, and overestimate it when it exceeds 2. Furthermore, the vertical ultimate bearing capacity gradually decreases as the open porosity increases. However, linearly reducing the effective area according to API standards is inappropriate. A formula considering the open porosity and normalized strength as variables is presented for calculating the vertical ultimate bearing capacity of hollow square-shaped mat foundation, serving as a reference for practical engineering.

Freeze-thaw (FT) deformation accumulates in rocks in cold regions under cyclic FT conditions, adversely affecting engineering stability. Currently, understanding of cumulative FT deformation and its potential hazards in rocks is insufficient. Therefore, this study investigates the cumulative FT deformation characteristics of sandstone over multiple cycles and examines the effects of factors such as freezing temperature, cooling rate, saturation, and porosity through cyclic FT experiments. Optical microscopy, scanning electron microscopy, and mercury intrusion methods are used to analyze the distribution of micro pores, cracks, and pore sizes in sandstone before and after FT action, revealing the microscopic mechanism underlying macroscopic FT deformation characteristics of sandstone. Results indicate that the cumulative frost heave strain and residual strain in sandstone are significantly greater than those observed in the first cycle. Significant risk exists in cold region engineering response analysis based on single-cycle FT strain. Thus, using cumulative FT deformation as a basis is more reasonable. As freezing temperature decreases, cooling rate increases, or porosity increases, both cumulative frost heave strain and residual strain in sandstone increase. During FT cycles, micro pores and cracks in sandstone gradually develop, and connections between particles loosen. The internal pore structure changes, with a significant increase in the number of pores within certain pore size ranges. The total pore volume increases, resulting in irreversible plastic deformation. Consequently, macroscopic cumulative frost heave strain and residual strain increase gradually with the number of FT cycles.

To explore the environmental effect of crack evolution characteristics of expansive soils, an environmental chamber was employed to perform desiccating tests on saturated undisturbed expansive soils in varying humidity environments. The soil crack network was extracted using computed tomography (CT) to obtain relevant characteristic indexes. The results show that crack evolution characteristics of expansive soils can be quantitatively characterized by characteristic indexes, which are closely related to desiccating rate. An increased desiccating rate reduces soil shrinkage strain and causes significant fluctuations in the two-dimensional longitudinal porosity. From a 3D perspective, water loss causes the gradual extension of micro-scale cracks. An increased desiccating rate results in greater connected porosity, pore-throat volume, and average coordination number, indicating enhanced connectivity between pores. Most cracks in expansive soil are distributed horizontally. As the desiccating rate increases, cracks exhibit a three-stage distribution pattern: (i) horizontal cracks progressively connect, and oblique cracks gradually increase; (ii) the connectivity of horizontal cracks reaches its maximum, and the proportion of oblique cracks peaks; (iii) oblique cracks gradually connect, and horizontal cracks re-emerge. The evolution pattern of crack distribution mainly depends on the initial distribution state of primary cracks, with the desiccating rate being an important factor affecting crack scale and connectivity degree.

The stability analysis of geosynthetic-encased stone column (GESC) composite foundations is a critical aspect of design calculations, but research in this area is still incomplete. This paper categorizes GESCs under embankments based on their distinct failure characteristics. Considering the compression and bending failures of columns, the stability analysis method for GESC composite foundations under embankments is studied. Initially, this paper proposes a method to calculate the theoretical critical bending moment of GESCs, considering their physical properties and using the quadratic approximation method for solving transcendental equations, by referring to the calculation method for the bending bearing capacity of reinforced concrete piles. Subsequently, the concepts of critical bending moment and equivalent shear strength are introduced to modify the traditional limit equilibrium method, and a stability analysis method based on bending failure of columns for GESC composite foundations under embankments is proposed. Finally, the results of the method, the traditional limit equilibrium method, and the numerical strength reduction method are compared using an example of laboratory model test, to verify the rationality and applicability of the method.

Liquid nitrogen cyclic fracturing is an environmentally friendly and efficient waterless fracturing technology that induces significant thermal stress in hot dry rock (HDR) through repeated liquid nitrogen cooling cycles, effectively enhancing fracturing and permeability in HDR reservoirs. To investigate how cyclic liquid nitrogen cooling affects the fracture characteristics and damage behavior of HDR, granite samples underwent high-temperature heating and liquid nitrogen cooling treatments with varying cycle numbers. The physical and mechanical properties, such as fracture toughness and behavior, were evaluated using three-point bending tests. Surface morphology and roughness of fracture surfaces generated during bending tests were quantitatively analyzed using three-dimensional laser scanning technology and fractal theory. Additionally, a numerical method was employed to reconstruct the heterogeneous granite matrix using a stochastic four-parameter generation approach. A thermo-mechanically coupled hybrid phase-field model was developed to simulate microcrack evolution and macroscopic fracture processes of high-temperature granite under different liquid nitrogen cycles, providing insight into the impact of cyclic cooling on macroscopic fracture behavior. Experimental and numerical results show that repeated high-temperature heating and liquid nitrogen cooling exacerbate granite damage, significantly reducing mechanical parameters such as fracture toughness. The fractal dimension of fracture surfaces and surface morphology parameters showed a significant positive correlation with cycle numbers. At higher cycle numbers, fracture surfaces displayed complex and tortuous crack propagation paths. The thermo-mechanical hybrid phase-field model accurately replicated the thermo-mechanical cracking behavior of granite under high-temperature heating and liquid nitrogen cooling. Thermal damage in granite was primarily concentrated in regions with the highest tensile strain energy. Microcracking observed in high-temperature granite during cyclic treatment was mainly driven by temperature gradients and differential thermal expansion between adjacent mineral particles. Ultimately, microcracks induced by liquid nitrogen cooling resulted in more intricate and convoluted mode I fracture propagation paths in granite.

During the improvement and reinforcement of peat foundation soils, cement hydration alters the pH of the subsurface water-soil ecosystem. This change negatively impacts humus acid, the main component of organic matter in peat soils, thereby deteriorating the engineering properties of peat foundations. Tests simulated the subsurface alkaline environment by using cement to treat peat soils in actual projects. The objective is to understand the dynamic processes of cement hydration affecting peat soil environments and to investigate the dissolution properties of humus acid in peat soil under alkaline environment during cement hydration. Results indicate that peat soil environment transforms into an alkaline environment under cement hydration, where humus acid in peat soil exhibits dissolution properties under alkaline environment. Humus acid undergoes dissolution and reacts in the alkaline environment. As the pH of the environment stabilizes, the dissolution of humus acid practically ceases. As humus acid dissolves, the pores inside peat soil expand, and the skeleton structure becomes less compact, reducing the soil’s compactness and connectedness, leading to significant strength loss. The dissolution of humus acid can significantly damage the peat soil structure. The study provides valuable insights into engineering issues arising from humus acid dissolution in peat soil under alkaline environment induced by cement hydration.

The stress-strain characteristics of over-consolidated clay exhibit complex mechanical characteristics with the evolution of the degree of over-consolidation. Developing a practical constitutive model can provide powerful tools for the numerical analysis of over-consolidated clay. Initially, variation of the dilatancy behavior of over-consolidated clay with degree of over-consolidation is analyzed. By introducing the over-consolidation parameters into the dilatancy relation, a simplified dilatancy equation for over-consolidated clay is established. The dilatancy equation can be integrated as a plastic potential surface. Subsequently, a practical bounding surface model is developed within the framework of bounding surface theory, utilizing the proposed dilatancy equation through a straightforward theoretical approach. Finally, the performance of the model is comprehensively validated through triaxial drained compression and extension tests at multiple levels of over-consolidation, along with undrained triaxial compression and extension tests and complex stress path tests. The results indicate that the model effectively describes the stress-strain characteristics of over-consolidated clay with the degree of over-consolidation and exhibits significant advantages in simulating volumetric deformation and pore water pressure.

Current research on deep-sea gas-bearing energy soils primarily focuses on soils with small air bubbles in a relatively stable state. Sinusoidal waves are commonly used in experiments to simulate seismic waves. Therefore, the authors propose a method to control bubble size and content, converting the acceleration time-history of seismic waves into stress time-history curves to replace sinusoidal waves. Dynamic triaxial tests are conducted to investigate the dynamic characteristics of various components of gas- bearing soils under seismic condition. The experiments show that under seismic loading, the failure modes of gas-bearing soils vary with confining pressure, including compression and tension failures. Different clay contents exhibit both strain failure and liquefaction failure. Higher clay content results in decreased stiffness and shear strength, but increased plastic deformation capacity of gas-bearing soils. Effective confining pressure significantly impacts gas-bearing soils. As saturation decreases, dynamic strength of soils diminishes, and the influence of effective confining pressure becomes more pronounced.

The inner core of traditional stiffened deep mixed piles is typically a prestressed concrete cylinder, relying solely on friction and bonding between the inner and outer cores to transmit load. Field investigations reveal that the bonding force between the soil-cement pile and the tubular pile interface is minimal. When the design is carried out according to specifications, the shear strength of the inner interface is often significantly low. To address this issue, the inner core prestressed concrete cylinder is replaced with a steel pipe pile, and the shear strength of the interface between the inner core prestressed concrete pipe pile and the outer core cement-soil pile is investigated. Additionally, a steel pipe pile with spiral blades on its outer surface is proposed as a new type of inner core pile. Shear tests on the internal interface were conducted on pile section samples with inner cores of non-ribbed steel pipes and spiral blade steel pipes. The factors influencing the ultimate shear force of the internal interface were analyzed, and the quantitative data were characterized. The shear failure mode of the inner and outer cores of the new composite pile, along with the evolution law and calculation method of the shear strength parameters of the inner interface, were determined. The shear strength parameters of the inner interface in the bearing capacity calculation formula of the pile, as specified in the Technical specification for strength composite piles (JG/T 023－2007), were modified.

A series of water vapor cycle experiments was conducted to examine the evolution of strength, deformation, and damage characteristics of red mudstone. The experiments included uniaxial compression tests and Brazilian splitting tests, utilizing acoustic emission (AE) and three-dimensional digital image correlation (DIC-3D) technology. The study concentrated on the evolutions in strength, deformation, and damage characteristics of red mudstone following different water vapor cycles. Results indicated that as water vapor cycles increased, the water content and volume of the mudstone showed irreversible accumulation, and the time required to reach water vapor equilibrium extended. Water vapor cycles caused reductions in compressive strength, tensile strength, elastic modulus, and shear modulus of the mudstone, leading to the proposal of an exponential degradation model for red mudstone. During uniaxial loading after different water vapor cycles, the failure mode of mudstone transitioned from overall shear failure to localized development of dispersed cracks. The evolution characteristics included delayed closure points of fractures, earlier onset of initial and damage stresses, extended compaction processes, shortened linear elastic deformation stages, and reduced ability of the rock to resist deformation.

Analyzing the deformation behavior of underlying shield tunnels induced by foundation pit excavation is crucial for assessing their safety. However, existing studies usually treat underlying shield tunnels as homogeneous continuous beams, which makes it difficult to reflect the influence of segment joints. This study introduces a discontinuous foundation beam model that accounts for rotational deformation and longitudinal dislocation at segment joints to investigate the deformation behavior of underlying shield tunnel induced by foundation pit excavation. Firstly, a theoretical expression for calculating vertical additional stresses caused by the unloading effect of foundation pit excavation is derived using the Mindlin solution, and computation positions set along the longitudinal direction of underlying shield tunnel. Secondly, a governing differential equation for vertical displacement induced by additional vertical stresses is developed using the discontinuous foundation beam model, along with the derivation of continuity conditions for internal forces and deformation at segment joints. Finally, the finite difference method is employed to develop a theoretical solution and calculation approach for the vertical displacement and internal forces of the underlying shield tunnel. A case study is presented to verify the reliability of the develop solution and calculation method. The influences of rotational stiffness and shear stiffness of segment joints, foundation reaction coefficient, excavation depth, and horizontal spacing between foundation pit and shield tunnel are illustrated and discussed in detail. The results indicate that the calculated vertical displacements of the shield tunnel based on discontinuous foundation beam model align well with the measured data. The corresponding distribution curves are smooth within segments but change suddenly at joints, effectively reflecting rotational deformation and longitudinal dislocation at segment joints. As the rotational stiffness of segment joint increases, the rotational deformation decreases, while the longitudinal dislocation of segment joint increases. Greater shear stiffness of segment joint results in smaller vertical displacement of the shield tunnel and longitudinal dislocation of segment joint. The increase in foundation reaction coefficient, the increase in distance from foundation pit, and the decrease in excavation depth can reduce the vertical displacement and longitudinal dislocation of underlying tunnel, effectively controlling its bending moment and shear force.

Two-phase flow and capillary trapping are crucial processes and key mechanisms in geological CO₂ storage within deep saline aquifers. Previous studies have extensively investigated the injection pattern and theoretical model in porous media, but research on two-phase flow characteristics and capillary trapping mechanism during cyclic injection is relatively limited. Through pore-scale water-oil two-phase cyclic injection visualization experiments, we investigated the effects of pore-scale disorder and cycle numbers on two-phase flow and capillary trapping characteristics. The experimental results show that cyclic injection disrupts the continuity of the non-wetting phase, breaking it into isolated “droplets” that are difficult to remobilize. After four cyclic injections, capillary trapping efficiency can reach up to 40%. As pore-scale disorder increases, the bypass mechanism significantly traps the non-wetting phase, with the capillary trapping efficiency in disordered porous media increasing by 32.5% compared to the homogeneous case. The experiments also reveal four typical types of capillary-trapped droplets during cyclic injection: bubble droplets, bridge droplets, ganglia droplets, and cluster droplets. Bubble droplets are the most numerous but contribute the least to trapping efficiency, whereas cluster droplets contribute the most. Our findings enhance the understanding of capillary trapping mechanisms during cyclic injection and provide theoretical support and practical insights for optimizing CO₂ storage efficiency in deep saline aquifers.

Saline soil, common in the western China, poses a significant threat to road engineering due to its salt swelling characteristics. Therefore, studying the water-salt migration patterns within saline soil subgrades and developing methods to interrupt this migration are crucial for road safety prevention and control. Based on the utilization of excavated waste soil, a new type of foamed lightweight soil based on saline soil is proposed as a subgrade separation fault in saline soil areas. Using self-developed equipment, we tested internal temperature changes, vertical displacements, and water and salt distribution after freeze-thaw cycles. The objective was to evaluate its salt insulation and swelling suppression capabilities and to explore the microstructure-based mechanisms underlying salt inhibition. Results indicate that under a temperature gradient, water and salt in the saline soil sample migrate upward, accumulating mainly in the middle and upper sections. Notably, the novel foamed lightweight soil separation fault effectively blocks water and salt migration, significantly suppressing salt swelling. Interestingly, a higher soil salt content results in a more pronounced anti-swelling effect. The porous structure of the foamed lightweight soil can not only store salt effectively, but also block salt migration, allowing salt crystallization within the soil, thereby reducing salt swelling damage.

This study investigates the strain development in saturated silty soil from Yellow River under varying initial consolidation inclination angles ξ by principle stress rotation tests. The results indicate that distinct patterns in axial, circumferential and torsional shear strains show the influence of ξ on the mechanical response of silty soil. Notably, the axial strain exhibits compressive behaviour at ξ =90° during the first cycle, while the circumferential strain displays tensile behaviour. Anisotropy initiates at around ξ =90° and ξ =60° for other ξ angles. Different values of ξ exhibit stabilization trends in strain fluctuations, with ξ =90° and ξ =75° showing intriguing similarities. The case of ξ =45° is distinctive, exhibiting the highest fluctuation and strain amplitude. Torsional shear strain similarities are observed among most ξ angles, except for ξ =90° and ξ =60°. Volumetric strain highlights the significant impact of consolidation angle inclination on anisotropic characteristics. As the initial solidification angle increases, the hysteresis curve shifts left, indicating cyclic creep characteristics, with negligible shear strain observed for ξ =60°. As the cycle period increases, the hysteresis loop contracts, indicating continuous strengthening and eventual stabilization of shear stiffness. This comprehensive study provides valuable insights into the complex behaviour of saturated silty soil under rotational stress conditions, highlighting the role of initial consolidation inclination angles in shaping its mechanical response.

In the loess mountainous area, many reinforced soil retaining walls are constructed with corners, unlike linear embankment fill retaining walls, due to new site developments. The upper sections of these walls are more prone to deformation and damage at the corners due to industrial plant (rectangular loads) or road (strip loads) construction, affecting their service life. To investigate the effects of rectangular and strip load types on the corners of folded-angle reinforced earth retaining walls, a physical model with both folded and vertical angles was established to explore soil pressure distribution and wall displacement deformation. The experimental results indicate: (1) A significant difference exists in soil pressure distribution in the transition section between the corner and the straight line of the retaining wall under the two load types. Under rectangular loads, maximum vertical soil pressure occurs at the corner, decreasing towards both ends. In contrast, the retaining wall under strip loads shows no significant fluctuation, only a gradual decrease along the top back of the wall. (2) The horizontal deformation of the reinforced soil retaining wall at the corner section under different loads shows a bulging shape, and the vertical deformation slows down as the load increases to 80 kPa. The macroscopic deformation cracks show a logarithmic spiral shape and are symmetrically distributed along the bisector of the corner angle. The research findings provide a theoretical basis for optimizing the design of reinforced soil retaining walls with similar folded angle structures.

The pull-pile support structure in a deep foundation pit is a three-dimensional spatial structure system composed of front-row piles, back-pull piles, a crown beam, and tie beams. Existing engineering cases demonstrate that the pull-pile support structure effectively resists overturning and controls horizontal deformation, yet lacks comprehensive theoretical support and systematic research. To thoroughly investigate the deformation behavior, internal force evolution, and working mechanism of the pull-pile support system during foundation pit excavation, an indoor scale test was conducted. Results indicate that the horizontal displacement curve of the front-row pile is convex, the bending moment curve is anti-S shaped, the axial force curve is shuttle-shaped, and the axial force on the pile body is compressive force. The bending moment curve of the back-pull pile is bow-shaped, and the axial force curve is spoon-shaped. The upper section of the back-pull pile experiences axial tension, while the lower section experiences axial compression. The horizontal lateral displacement curve of the crown beam presents sine function shape of the short crown beam, and the axial force curve presents an obvious M shape. The double peaks of the M shape correspond to the crown beam atop the front-row pile without back-pull support, marking a weak point for potential failure of the crown beam. The spatial characteristics of the pull-pile support structure allow for a stable tension-compression combined structure, forming a large triangle with two smaller triangles and a three-way door frame. The resulting back-pull pile effect and spatial deformation coordination can anchor the front-row pile and shield against earth pressure, as well as suppress differences in the top inclination angle of the supporting pile and excessive deformation of crown beam.

Inspired by big data, fully utilizing geotechnical data for precise characterization and modeling of geotechnical parameters is critical for the digitalization of geotechnical engineering. This study collected geotechnical investigation reports from 75 engineering projects in Shenzhen, established a database containing 8 geotechnical parameters of clay and weathered residual soil (SZ-SOIL/8/11369), and thoroughly analyzed the distribution characteristics of geotechnical parameter data in Shenzhen. Subsequently, a model for predicting geotechnical parameters was developed using this database and a generative adversarial network (GAN). The proposed method was applied to a project in Shenzhen, successfully predicting mechanical parameters from known physical parameters and accurately forecasting the geotechnical parameter distribution of the project site using small samples. The results indicate that the proposed method can make reasonable predictions for samples with missing parameters, achieving the goal of reducing the uncertainty in geotechnical parameters at local engineering sites through extensive regional survey data. This provides parameter assurance for the resilience design and risk assessment of geotechnical and underground engineering structures in Shenzhen.

Applying energy pile technology to support piles not only addresses structural safety issues, but also facilitates resource recovery and reuse. Based on the foundation pit support project of high-voltage line merging and reconstruction of a utility tunnel in Xinhe Business District of Jiaozuo City, thermal response tests of energy support piles were conducted before and after foundation pit excavation. Additionally, thermal response field tests of energy support piles under different interval ratios were performed once the excavation stabilized. The inlet/outlet water temperature, pile temperature, and strain change data were measured. Preliminary discussions covered heat transfer performance, thermal stress, and pile bending moments of energy support piles. Results indicate that under these test conditions, pit excavation enhances the heat transfer capacity of the energy support piles, while reducing additional temperature stress on the pile body. For energy support piles with different interval ratios, the heat transfer capacity improves as the interval ratio decreases. Additional temperature stress on the pile body increases with more cycles and decreases with depth. The bending moment of pile body caused by pit excavation is 128.98 kN·m at −8.0 m, decreasing towards both ends. As pile temperature increases, the bending moment initially decreases and then rises. For energy support piles with different interval ratios, the bending moment of pile body increases with the increase of interval ratio, reaching a maximum of 7.12 kN·m at −4.0 m when the interval ratio is 2.0.

The rapid development of renewable energy has become a global consensus, with offshore wind power as a key focus. The upper structures of offshore wind turbines are subjected to complex environmental loads, including wind, waves, and currents, ultimately supported by the anchoring foundation. Therefore, the bearing performance of the anchoring foundation plays a decisive role in ensuring the service stability of the entire system. The piggy-backed anchor is a novel hybrid anchor consisting of two or more traditional anchor plates, such as drag anchors or vertical load anchors. It offers advantages such as low installation cost, high anchoring efficiency, reusability, and high bearing capacity. The paper proposes an upper-bound solution for the plastic limit analysis of piggy-backed anchors to quickly predict their bearing capacity. This study found that the undrained shear strength gradient k does not affect the bearing capacity coefficient. Under the influence of coupled loads, the normal resistance of the piggy-backed anchor predominantly determines the bearing capacity, while the mechanisms of tangential loads and rotational torque are similar to those of a single anchor plate. During service, the piggy-backed anchor requires a larger displacement to mobilize its ultimate bearing capacity compared to a single anchor plate.

Large deformations in deep tunnels pose a significant challenge to safe and efficient mining. To control the stability of deep soft surrounding rock, a combined support method and its theoretical analysis model were proposed, based on the evolution of large deformation in deep tunnels. Results indicated that deep soft surrounding rock can be categorized into fracture deformation, damage and expansion deformation, and continuous deformation zones. Following the implementation of combined support measures, the ultimate bearing capacity increased linearly with the equivalent support forces of anchor rods and cables and exponentially with the grouting reinforcement coefficient. The parameters for pre-stressed bolts and cables should be determined based on bearing balance conditions when the grouting reinforcement coefficient is 1.0. Both the grouting reinforcement coefficient and the fracture zone radius of surrounding rock should be considered in the design of grouting support for deep and shallow holes. Collaborative support parameters for various support measures were determined by the ultimate bearing capacity balance conditions of the surrounding rock in the reinforced fracture zone. Numerical simulation and engineering application analysis demonstrated that the large deformation of deep soft surrounding rock can be controlled through the collaborative control of support structures. The combined support method can be widely applied in other tunnel engineering projects.

As mining depth increases, the large deformation of soft rock, such as roof fall, floor heave and two-side movement of the tunnel, poses a severe challenge to safe mining. Currently, continuous-discontinuous methods, combining advantages of both continuous and discontinuous methods, are rapidly developing. However, creep has not yet been introduced into these methods. Based on the experimental phenomenon that rock creep failure strain occurs in the post-peak region of the triaxial compression stress-strain curve, the viscoelasticity of the element is considered. A creep shear cracking model is developed to account for the viscoplasticity of the interface, and a criterion of creep shear cracking is introduced into the combined Lagrangian-discrete element method (a kind of continuous-discontinuous method) to simulate the creep shear cracking. The calculated creep curve under uniaxial compression aligns closely with experimental results. Once creep shear cracking begins, the specimen enters the accelerated creep stage. The proposed method has the potential to simulate accelerated creep. Results of the soft rock tunnel indicate that discrete blocks move into the tunnel due to the pushing of deep rock, sharply reducing tunnel size. Macroscopically, the tunnel exhibits a large deformation. The tunnel’s vertical shrinkage rate can reach 58.8%. The mechanisms of large deformation in the soft rock tunnel, attributed to the viscoelasticity of the element and the viscoplasticity of the interface (fictitious crack surface), result from a combination of small viscoelastic deformation of the medium, large block displacement, and viscoplastic deformation of the interface. It is unnecessary to describe the tunnel’s macroscopic large deformation using complex large deformation theories.

The traditional peridynamics method replaces partial differential equations in continuum mechanics with integral equations, resulting in more generalized equations without smoothness restrictions on the unknown function. This makes the methodology particularly suitable for simulating discontinuous problems, such as spontaneous crack initiation and propagation. However, the high computational cost often limits its practical engineering applications. This paper introduces a fast convolution-based method for peridynamics to enhance computational efficiency. This algorithm employs fast Fourier transformation to accomplish convolution calculations, facilitating the computation of integral terms in peridynamics equations, significantly reducing the computational cost of the peridynamics method. A preprocessing method suitable for this algorithm is proposed based on the computational process and numerical implementation characteristics of the fast convolution-based method for peridynamics. Its feasibility is verified through two tensile square plate examples with pre-existing cracks. Furthermore, a modeling method for predicting random crack propagation is proposed, offering a novel approach for research in predicting random crack propagation in geomaterials.

This study investigates the distribution of non-limit active earth pressure in sand under the rotation around the base and translation coupling (RBT) mode of rigid retaining wall. Three groups of position parameter of rotation center (n=0.5, 1.0, and 5.0) are selected for discrete element simulation study. The results indicate that the active earth pressure in RBT mode exhibits both concave distribution characteristics of the rotation around base (RB) mode and linear distribution characteristics of the translational (T) mode in rigid retaining walls. During failure, the wall-soil friction angle usually reaches its limit value before the internal friction angle. The slip surface behind the wall forms a curve, with a noticeable principal stress deflection at the soil slip surface. Based on the numerical simulation results, the relationship between the equivalent internal friction angle of the interlayer and the position parameter of rotation center n is derived using the middle symmetrical arc arch. The force equilibrium equation for the curved trapezoidal differential unit is established using the horizontal layer analysis method, and the numerical solution for non-limit active earth pressure in RBT mode is obtained using the finite difference method. Parameter analysis shows that displacement, internal friction angle and n significantly affect the active earth pressure. Comparison of numerical simulations and model tests verifies the rationality and reliability of the theory presented in this paper. The findings provide a valuable reference for calculating earth pressure in rigid retaining walls.

Accurate monitoring of the spatiotemporal distribution of soil moisture content is crucial for geotechnical engineering monitoring and geological disaster prevention and control. Given the limitations of passive distributed temperature sensing (PDTS) technology in monitoring soil moisture content, the Spearman correlation coefficient method was introduced to quantitatively analyze the correlations among radiation, air temperature, warming slope, soil temperature, salinity, and moisture content. By incorporating the back propagation (BP) neural network, a passive sensing model for soil moisture is proposed. The model considers the comprehensive effects of water, heat, and salt and can replace the complex numerical iterative algorithm in traditional PDTS technology. This model not only expands the application scope of PDTS technology, but also significantly improves the accuracy of moisture content prediction. Long-term observations on the Loess Plateau in China verified the effectiveness of the proposed model using in-situ data. The analysis results indicate a strong positive correlation between loess moisture content and salinity, temperature, which can complement each other in depth. The input variables maintain a shallow soil moisture content with a root mean square error below 0.006 8 m³·m⁻³. The model’s errors mainly arise from rainfall and soil freeze-thaw processes, which tend to be smaller in winter and larger in summer. This study provides important theoretical support and practical reference for applying PDTS technology to soil moisture content monitoring and reveals the water-salt migration mechanism in loess.

The application of digital image measurement technology to conventional geotechnical triaxial tests has successfully solved many issues in traditional deformation measurements, significantly enhancing measurement accuracy and efficiency. However, the diversity and gradient of gray level strata in high-pixel images complicate gradient iteration calculations. Additionally, multiple potential corner candidate locations near corner points directly affect sub-pixel corner point localization accuracy. To address the localization bias problem of the sub-pixel corner detection algorithm, a sub-pixel corner detection method based on corner correlation matching identification is proposed for the digital image measurement system developed for full-surface deformation of geotechnical triaxial test specimens. The method initially extracts whole-pixel corner coordinates from the original image using the Harris detection algorithm, then constructs fixed-size grayscale sub-areas centered on these corner points. Subpixel-level displacements of the initial whole-pixel corner points after deformation are obtained through an iterative process of correlation matching between subregions. In the simulated specimen affine deformation test, the improved algorithm has good affine invariance on the basis of inheriting the robust identification of corner features. The average absolute error is reduced by 80.5%, substantially improving the measurement accuracy of full-surface deformation of the specimen in triaxial test.

To investigate the quantitative relationship between drilling rig parameters and surrounding rock parameters, and to achieve the synchronization of rockburst pressure relief drilling and early warning evaluation, we independently developed an intelligent experimental platform for drilling and testing of rockburst prevention drilling rigs. The platform consists of an intelligent drilling and testing rig, a large-scale true triaxial stress loading system, a computer control system, and other auxiliary devices. The platform effectively reproduces the mechanical parameters and structural characteristics of rock masses in field environments, enabling real-time measurement and collection of parameters during drilling. This study utilizes the platform to conduct preliminary validation experiments. The results show that the true triaxial stress loading system controls the horizontal and vertical multi-point loading hydraulic cylinder through an electro-hydraulic servo system, achieving precise and uniform true triaxial loading of large-scale specimens, with a maximum pressure of 6 000 kN, and can accurately reproduce the stress state of the surrounding rock of a kilometer deep well. The intelligent drilling and test rig, based on a guide rail hydraulic drilling rig, incorporates a high-precision sensing device and signal transmission module to enable real-time measurement and transmission of drilling parameters near the drill bit during drilling process of drill rods under complex conditions. The computer control system has functions such as true three-axis loading, drilling control, and drilling parameter collection, achieving synchronization between drilling and data acquisition. The overall structure design of the platform is reasonable and user-friendly. The developed platform can conduct large-scale specimen drilling tests under true triaxial stress conditions, significantly contributing to the study and establishment of quantitative relationships between drilling parameters and surrounding rock parameters, the development of synchronous intelligent warning technology for impact hazards, and the achievement of stability evaluation and synchronous warning of surrounding rock.