With the large-scale exploitation and application of shallow geothermal energy, researches on ground-coupled heat pump and energy geostructures are gradually shifting from the individual, single-unit scale to the regional scale. Compared with the ground-coupled heat pump, energy geostructures have greater advantages in large-scale urban construction and underground space development due to their small area and low cost. This paper summarizes the existing research results on the theoretical potential of shallow geothermal energy in terms of thermal property parameters and subsurface urban heat island effect. It briefly describes the development forms of shallow geothermal energy and focuses on the systematic reviews of the adaptability evaluation of ground- coupled heat pump and energy geostructures at the regional scale. Additionally, a corresponding regional-scale energy geostructural evaluation system is established in terms of suitability zoning, heat exchange potential, and the effect of meeting building energy demand. This study presents an in-depth analysis of regional studies of ground-coupled heat pump in Linqu County, Shandong Province, China, Baden-Württemberg State, Germany, and energy piles in Xianlin Campus of Nanjing University, China, as case studies. It summarizes the problems in current research, and provides an outlook for future research on energy geostructures at the regional scale.

Identification of microcrack initiation, propagation and coalescence patterns is fundamental to the study of the development and evolution process of rock mass disasters. In order to explore the development process and mechanism of microcrack in fractured rock, the active ultrasonic measurement and digital image correlation technology (DIC) were used to simultaneously monitor the damage and fracture process of sandstone containing prefabricated fissure under uniaxial compression, and the surface strain field evolution and ultrasonic attenuation characteristics were analyzed. The results show that the local tensile stress concentration at the tip of the prefabricated fissure with a small inclination angle is conducive to earlier crack initiation. As the fissure inclination angle increases, the specimen containing prefabricated fissure changes from a relatively stable progressive rupture to a sudden failure, and its brittleness characteristics become more obvious. The surface strain field can track the initiation and propagation of crack in real time. The attenuation of P-wave velocity, amplitude spectrum and ultrasonic amplitude is closely related to the development of microcracks and the formation of macrocracks. The obvious attenuation of dominant frequency of ultrasonic waves can be regarded as direct evidence for the formation of macrocracks. The differences in P-wave velocity and amplitude attenuation in different ray paths are the results of anisotropy in the accumulation of damage induced by axial stress and prefabricated fissure. In addition, the improved spectral ratio method was used to analyze the time-lapse characteristics of ultrasonic attenuation, and it was found that the ultrasonic attenuation is more sensitive to the development of microcracks in rock media than P-wave velocity does. Further comparison found that the sensitivity of ultrasonic amplitude, surface strain, and P-wave velocity to rock damage identification decreased in order. The results of this study demonstrate that the active ultrasonic attenuation and DIC surface strain simultaneous monitoring are powerful tools for identifying and quantifying precursor information of rock damage and crack propagation.

The hot-drying method for strengthening slope of foundation pit in loess holds potential application value, and the scientific evaluation of high-temperature loess crack evolution is a key link to verify the feasibility of the hot-dry method for strengthening loess. In this paper, a self-made experimental device was used to conduct crack evolution experiments on unsaturated loess samples with different initial dry densities and initial water contents at different high temperatures, and the changes in water content and surface crack of the soil samples were observed. Cracking indicators such as crack rate r, total crack length L, fractal dimension D, and average crack width W were quantitatively analyzed through experimental image processing. The analysis results show that r, L, and D all increase as the high temperature level increases, while W does not change significantly; the increase of initial dry density significantly reduces r, L, and D and significantly increases W; the increase of initial water content significantly increases r, L, D, and W. High temperatures significantly altered the crack initiation pattern of the soils, and the initiation cracks of the soils appeared rapidly under the 100 ℃ critical temperature. This may be related to the inhomogeneous extrusion of high-pressure water vapor. The high temperature greatly accelerated the fracture evolution process, but after exceeding 100 ℃, the acceleration of the fracture evolution was not significant. The mechanical mechanism of loess cracking and extension under high temperature is analyzed from the perspective of fracture mechanics, revealing the mechanism of high-temperature loess crack evolution. Considering the significant influence of matrix suction on crack evolution, a formula considering high temperature and matrix suction is established, highlighting the significant influence of high temperature on matrix suction to a certain extent.

With the rapid development of key projects in China, such as West-to-East Gas Transmission and South-to-North Water Diversion, buried pipelines will inevitably pass through the mountainous area and are affected by regional topography and landforms. However, the interaction mechanism between slope and pipelines is still relatively unclear. In this study, the model tests on sandy slope-pipe interaction under loading are carried out in laboratory based on distributed strain sensing (DSS) and particle image velocimetry (PIV) technologies. The factors influencing the bearing capacity of the foundation are investigated. The failure characteristics of the slope and the structural responses of the buried pipeline are also explored. The research results show that: (1) The slope foundation has undergone three stages: elastic compaction, local shear and overall destruction. The foundation shows asymmetrical wedge-shaped failure pattern. (2) With the increase in slope angle, the ultimate bearing capacity of the foundation decreases. Under the same slope angle, the presence of pipeline reduces the ultimate bearing capacity of the slope foundation. (3) With the increase in slope angle, the influence of the pipeline on the slope failure mechanism increases. (4) Under the loading of the slope, the circumferential strain in the cross-section of the buried pipe is “elliptically” distributed, and an ellipticity calculation formula and a simplified calculation model of the soil resistance around the pipe circumference are proposed. This study can provide a reference for the deformation control and structural design of buried pipelines in sandy slopes.

The southeast coast of China, particularly in Wenzhou, is characterized by soil strata comprising a thick layer of soft soil overlying an uneven pebble layer. In this region, post-grouting technique is frequently employed to enhance the bearing performance of bored piles. To assess the effectiveness of post-grouted piles in such strata, several model tests were carried out to analyze the impact of varying grouting volume on the bearing capacity of the piles. Subsequently, scanning electron microscope (SEM) tests were used to explore the distribution ranges of the grout in the pebble layer. Furthermore, the relationship between the diffusion range and the bearing capacity of piles was investigated. The results show that the grout effectively permeates the pebble around piles tip, and increasing the grouting volume expands the permeated range. The most significant improvement in pile bearing capacity occurs when the range is 3-4 times the pile diameter. An optimal grout volume level is identified, with the normalized value of the grout volume being approximately 2.8 for the model piles. The bearing capacity of the pile is no longer significantly increased once the normalized value of the grout volume is exceeded. Notably, the optimal grout volume closely aligns with the predicted result of Liu Jinli's formula[1]. The utilization of scanning electron microscopy proved instrumental in evaluating the effect of post-grouting in a soil layer characterized by a thick layer of soft soil overlying an inhomogeneous pebble layer.

In order to study the influence of confining pressure and pore pressure on the mechanical properties and deformation parameters during underground tunnel excavation, a gas-undrained triaxial compression test of layered phyllite was carried out with argon as the permeable medium. The study analyzed the evolution characteristics of stress-strain relationship, peak strength, deformation characteristics and failure modes of layered phyllite with bedding inclinations under varying confining pressure and pore pressure. Additionally, an anisotropy degree formula based on bedding inclinations was introduced to discuss the impacts of confining pressure and pore pressure on the anisotropy of layered phyllite. The results show that the peak strength of layered phyllite increases gradually as the pore pressure decreases or the confining pressure increases. The peak strength σ_c, elastic modulus and deformation modulus exhibit ‘U’ shaped changes with an increase in bedding inclinations. When the bedding inclination ranges between 30° and 60°, the layered phyllite has a low degree of hardness, and the predominant failure mode is shear slip along the bedding plane. Furthermore, the layered phyllite is greatly affected by confining pressure and pore pressure in the direction of parallel bedding, showing significant anisotropic characteristics.

Application of the drill-and-blast method generally leads to deterioration of rock properties in a disturbance-damaged region of rock tunnels. In this study, different mechanical models of disturbance-damaged rock tunnels were introduced according to the elastic-plastic states of both disturbance damaged rock and non-disturbance rock. Brittle-plastic solutions of stress, displacement, and plastic zone radius in disturbance-damaged rock tunnels were then presented by adopting the unified strength theory, the elastic-brittle-plastic model, and a non-associated flow rule. Furthermore, the study discussed the conversion paths and determinative approaches of the tunnel mechanical model and compared the results with those in the literature. Influences of various factors were analyzed, demonstrating that the obtained brittle-plastic solution of rock tunnels accounts reasonably for comprehensive effects of intermediate principal stress, tunnel disturbance range, rock post-peak strength, and dilatancy. Additionally, the solutions can be reduced to many traditional ones through combined parameter transformation, and its verification is demonstrated. As a result, it has important theoretical significance and application prospect. The determination of tunnel mechanical model is closely related to intermediate principal stress and rock disturbance range, which significantly affects distributions of tunnel stress and displacement as well as ground reaction curve. Support pressure and tunnel stable deformation increase obviously with the decrease of rock post-peak strength and the increase of dilatancy parameters.

Single-point mooring (SPM) system has been widely used in China’s offshore oil development due to its superiority in overcoming severe sea conditions. However, the research on the interaction mechanism between the anchor pile and soil in underwater single-point mooring systems remains inadequate, particularly with respect to the calculation method of horizontal bearing capacity that considers the depth of padeye depth. Utilizing the composite foundation reaction force method, the flexure control equation and boundary conditions of the anchor pile of the single-point mooring system under lateral load are established, and the calculation programs are compiled using iterative methods to obtain the anchor pile load-displacement curve and the distribution curve of pile displacement and bending moment along the pile shaft at different mooring point positions. The accuracy and reliability of results are validated through comparison with numerical simulation and existing centrifugal model test results. Furthermore, the parameter analysis is conducted to consider the impact of padeye depth on the horizontal bearing capacity of anchor piles and the reference range of the optimal padeye depth is provided. The findings indicate that increasing the padeye depth leads to a significant reduction in the lateral displacement and maximum bending moment of anchor piles, while also increasing the horizontal ultimate bearing capacity of the anchor pile.

The strength composite pile, as a novel pile foundation, holds significant practical significance in dynamic response analysis. This study, based on elastic dynamic theory and porous media model, investigated the longitudinal dynamic response of the strength composite pile in fractional viscoelastic unsaturated ground through theoretical derivation and parametric analysis. The research took into account the unique structure of the strength composite pile and the flow-independent viscosity of the soil skeleton. Firstly, the longitudinal vibration equation of the strength composite pile was established through mechanical equilibrium. The dynamic behavior of the soil around the pile was described using the existing governing equations for unsaturated soils, where the fractional standard linear solid (FSLS) model was utilized to characterize the frequency-dependent viscosity of the soil skeleton. Subsequently, the analytical solution of the dynamic impedance at pile head was deduced through a rigorous theoretical derivation. Finally, the study delved into the influence of pile and soil parameters on the dynamic impedance at the pile head through numerical calculations, parameter analysis, and mechanism discussion. The results reveal that an increase in both the cross-sectional proportion of cement-soil pile and the pile length enhances the dynamic impedance at pile head. An increase in the fractional order and the strain relaxation time, along with a reduction in the stress relaxation time, all improve the dynamic impedance at pile head. Additionally, increasing the soil saturation or decreasing its intrinsic permeability also elevates the dynamic impedance at pile head.

The material strength is directly affected by the random distribution of the size, shape, orientation and spatial location of internal microcracks. This study aims to investigate the statistical relationship of the strength of rockfill particles with respect to size and strain rate under quasi-static condition. The assumption is made both the size and spatial location of microcracks followed the power-law distribution. A rational link is established between the compound parameters, which consist of the cumulative damage probability and volume of the particles and the crushing strength within the framework of the weakest chain theory. From a microscopic perspective, the strength of microcracks in particles increases with the strain rate. The effect of strain rate leads to a reduction in the failure probability per unit volume. Simultaneously, the spatial location distribution of microcracks becomes sparse, and the size effect on particle strength weakens. The results of the single particle crushing tests show that as the loading rate increases, there exists a gradually decreasing power index of spatial location distribution, which allows the particle compound parameters to converge on the master curve determined by the weakest chain statistical model.

To investigate the effects of burden on rock crushing characteristics under lateral detonation of cylindrical charges, we analyzed the stress state at the free surface using the wave theory. Afterward, to simulate the cylindrical charge detonation, the physical experiment of lateral rock fragmentation was conducted using direct copper wire electro-explosion. The evolution process of surface crack network of the specimen was observed using ultra-high-speed camera technology. The impact of cylindrical charge detonation on rock properties was studied by combining the morphology, dimensions, and distribution characteristics of the blasting crater with different burdens. The results demonstrated that the burden is a crucial factor for controlling the fracture mode, morphology of failure zone, and fragment size during rock blasting. As the burden increased, the crack propagation velocity and density gradually decreased, while the range of crack network expanded, and the preferential propagation direction of cracks changed from transverse to circumferential. Furthermore, the experimental results indicated an increasing trend in the short axis of the fracture zone as the burden increased. Through analyzing the stress state at the free surface, the maximum tensile strain criterion was applied to justify this phenomenon. Finally, the relationship between fragment size and energy consumption was established. Our research findings provide a reference for optimizing the design of rock engineering blasting.

Current theoretical researches on shield tunneling induced existing metro tunnels deformation generally simplify the existing tunnels as Euler-Bernoulli beams without joints, neglecting the tunnel shear deformation and the local stiffness reduction caused by joints. Additionally, the existing foundation model theory rarely incorporates the coordination between lining cross-section and soil deformation. The study utilizes the Loganathan and Polous method to establish the shield tunneling-induced soil greenfield. To account for the local stiffness reduction, the paper then treats the existing tunnel as a Timoshenko beam, with the tunnel stiffness function varying along the axis. By combining the energy principle and the Mindlin solution, the paper stablishes the tunnel displacement equation considering the coordinated constraint between tunnel and soil. The soil greenfield is applied to the tunnel, resulting in longitudinal deformation, which is solved by Fourier series. Finally, the Fourier energy variational solution is verified by three sets of engineering data, achieving good consistency. To conduct parameter analysis, the relative effects among factors such as bending stiffness, shear stiffness, joint action, soil parameters and space relationship are also adopted. Analysis results indicate that the theoretical solution considering the coordinated constraints of cross-section aligns more closely with the field data. Tunnel displacement results obtained without considering the coordination constraints tend to be larger. The local stiffness weakening effect of joint will cause significant sudden variations in tunnel bending moments along the axis. The increase in both bending and shear stiffness coefficients leads to a decrease in the bending moment of the tunnel structure. Changes in shear stiffness coefficient from low to high would result in a three-stage process of the tunnel deformation mode, which is from bending controlled stage to bending-shear mixed stage and then to shear controlled stage. As the tunnel deformation mode enters the shear-controlled stage, the effect of bending stiffness coefficients gradually weakens. An increase in the joint coefficient generally causes a decrease in the bending moment of the tunnel, but the impact is slight as the bending coefficient increases.

Most metal deposits with the steeply dipping geological structure are typically formed in structural fault zones, and caving mining often result in significant ground movement. In a study conducted at the Jinshandian Iron Mine in Huangshi, Hubei Province, a geological structure model is constructed based on the typical geological profile. The influence of steeply dipping geological structure on the ground movement law in caving mining was investigated by means of scaled-down physical model tests. The results show that, influenced by the steeply dipping geological structure, the ground movement in the goaf can be divided into three stages: slow growth, rapid growth and surface subsidence damage, in which the ground movement of the hanging wall is much larger than that of the footwall. Specifically, the hanging wall is primarily characterized by toppling deformation and failure, and the footwall is dominated by shear-slip failure. The roof strata in the goaf continuously collapse and fill the goaf to control the ground movement, forming a falling arch to resist the movement of the rock layer on the hanging wall and footwall towards the extraction area by its arch foot. However, when the roof falls to the surface, the supporting role of the caving arch diminishes, leading to toppling fracture collapses in the hanging wall near the goaf and shear-slip collapses in the footwall.

The accumulation body is extensively distributed in the valley area of major rivers in southwest China, and its stability directly impacts the safety and stability of dams during rainfall conditions. To study the geological evolution and disaster processes of landslides during rainfall events, a centrifugal model test system is designed to simulate heavy rainfall on the slope of a reservoir bank, with a focus on investigating the induced instability of the accumulation body at full storage capacity. Following the test results, additional numerical simulation is carried out to analyze the influence of rainfall intensity, reservoir level state and permeability of accumulation body on slope stability. The results indicate that during the reservoir storage stage, the slope front of the accumulation body experiences reduced resistance to sliding due to buoyancy and water softening. However, osmotic pressure exerted on the slope body also contributes to its strengthening. The cracks formed at the rear edge as a result of these two competing mechanisms significantly influence the development of slope deformation during the rainfall stage. Rainfall primarily leads to surface erosion and runoff on the slope, with a small portion infiltrating through cracks, resulting in shallow subsidence of the rear margin. If the slope is left untreated, it is likely to experience overall failure. Therefore, addressing the cracks at the rear edge of the bank slope is crucial for preventing and controlling geological hazards.

In complex geological environments, the use of simplified geometric bodies instead of real hidden karst caves for numerical analysis often fails to reflect real engineering characteristics. The naturally formed karst cave morphology lacks obvious geometric regularity, posing challenges in quantifying the characteristics of karst cave morphology. To address the lack of systematic research in the quantitative study of geometric features of hidden karst caves, this paper proposes a characterization and analysis method for hidden karst caves in borehole surrounding rock based on directional acoustic scanning. Initially, the paper utilizes borehole directional acoustic scanning technology to obtain basic data, and constructs the contour coordinate criteria for different hidden karst caves in the same borehole. Subsequently, the paper proposes horizontal and vertical structural characterization methods of hidden karst caves for quantitative characterization of the surrounding rock. The proposed methods achieve comprehensive quantitative characterization of hidden karst caves. For statistical analysis of hidden karst caves in the borehole surrounding rock, the paper introduces the horizontal omnidirectional proportion index, far-away proportion index, and depth proportion index, which can statistically analyze the distribution of hidden karst caves at different depths and surrounding locations from the borehole perspective. Finally, combined with practical engineering cases, a comprehensive analysis is carried out, which compared and validated with other methods. It can prove that the method described in this paper can provide more quantitative data for engineering investigation and numerical simulation in geological engineering in karst areas. It presents a new quantitative analysis method in the development and resource utilization technology of karst cave areas, with broad application prospects.

The large strain and nonlinear consolidation characteristics of soft soils with high compressibility have obvious effects on their consolidation, but few analytical solutions for large-strain nonlinear consolidation of soils with vertical drains have been reported in the literature. By considering the large deformation characteristics of soft soils with high compressibility during consolidation, a large-strain nonlinear consolidation model of soils with vertical drains is developed and an analytical solution for this consolidation model is obtained based on Gibson’s large deformation consolidation theory, in which a double logarithmic nonlinear compressibility and permeability model is adopted to describe the variation of the compressibility and permeability of soft soils. The proposed analytical solutions are compared with the numerical solutions of large-strain nonlinear consolidation of soils with vertical drains and the analytical solutions of small-strain linear consolidation under specific conditions to verify its reliability. On this basis, the nonlinear consolidation properties of soils with vertical drains under different conditions are analyzed by extensive calculations. The results show that the consolidation rate increases with decreasing the permeability parameter α , when the compression index I_c, keeps constant. The consolidation rate increases with decreasing the compression index I_c, when the permeability parameter α  remains constant. The consolidation rate of soils with vertical drains increases with an increase in external load, and decrease with an increase in the ratio of influential zone radius to vertical drain radius when the compressibility and permeability parameters remain constant. Finally, the proposed analytical solution is applied to the reclaimed foundation treatment project of Shenzhen Western Corridor boundary control point(BCP). The settlement curve calculated by proposed solutions is in good agreement with the measured curve, which further illustrates the engineering applicability of the proposed analytical solution.

In recent years, the northwest region has seen an increase in high embankment sites, leading to widespread use of pile foundations to mitigate uneven settlement of building foundations. However, in loess embankment sites, single piles experience significant deformation in the surrounding soil after loading, complicating the settlement mechanism of such single piles. As pile head settlement calculation is crucial for pile foundation design, this paper establishes a calculation model for pile head settlement of single piles in high embankment loess sites. The proposed model considers the interaction between piles and soil at the pile-soil interface and the shear deformation of the soil in the shear zone outside the pile-soil interface, based on the traditional load transfer method and shear displacement method. It classifies single pile types into friction piles and end-bearing friction piles based on the pile end boundary and establishes differential equations for pile body displacement control in both the elastic and plastic phases of the surrounding soil. Solving these equations with boundary conditions yields pile body displacement, axial force, and lateral friction resistance. Additionally, the model calculates the shear deformation of the soil in the pile-soil interface zone using elastoplastic theory and determines the total settlement at the pile head using the superposition principle. The ratio of pile length to the plastic development depth of the surrounding soil is defined as the pile bearing capacity safety factor, denoted as K. Results from case studies and comparisons with field test data demonstrate that the pile head total settlement calculated using the model proposed in this paper aligns closely with the field test results. When the pile head load is relatively small and the surrounding soil is in the elastic phase, the influences of the pile end boundary on pile body axial force, displacement, and lateral friction resistance are minimal. However, as the surrounding soil enters the plastic slip phase, the effect of the pile end boundary becomes more significant, and considering the bearing capacity of the pile end soil greatly enhances the ultimate bearing capacity of the single pile. This paper establishes a comprehensive calculation model that combines the load transfer method and the shear displacement method. It not only accounts for the relative slip at the pile-soil interface but also calculates the shear deformation of the soil in the zone outside the pile-soil interface. This leads to a more accurate calculation of the pile head total settlement and provides valuable insights for the analysis and control of single pile settlements in similar sites.

The loading inclination and mooring point position of a suction anchor are crucial design elements that can alter the failure posture of anchor body, thereby influencing the ultimate bearing capacity. In a centrifugal model test of tensioned suction anchor under displacement control in saturated soft clay foundation, different loading inclinations and mooring point positions were selected. The influence of these factors on the failure posture and ultimate bearing capacity was quantitatively analyzed using a six-degree-of-freedom magnetometer device. It was observed that when the mooring point position was at about 2/3 height of the anchor body, the suction anchor experienced translational failure. However, when the loading inclination angle changed from 35° to 20° at the same mooring point position, the suction anchor exhibited backward tilting failure and the normalized ultimate bearing capacity increased slightly. Even after reaching the ultimate bearing capacity, it still maintained a certain amount of load-bearing capacity margins. On the other hand, when the mooring point position was above 2/3 height of the anchor body, the suction anchor experienced forward tilting failure, leading to a decrease of about 25% in the normalized ultimate bearing capacity, and a significant reduction in the load capacity margin after failure. Regardless of the failure posture, no significant separation of the soil plug from the anchor was observed within the anchor.

Water and salt cycling is a significant factor contributing to the gradual deterioration of rammed earth sites. To investigate the impact of size on the distribution characteristics of water and salt transport in rammed earth, five groups of cubic rammed earth samples with 0.3% salt content and varying side lengths (50, 100, 200, 500 mm, and 900 mm) were prepared. These samples were subjected to a natural water loss test in an indoor environment with a temperature ranging from 10–27 ℃ and a relative humidity of 20%−50%. Throughout the water loss period, borehole sampling was conducted to measure the moisture content and salt distribution from the surface to the internal soil of the rammed earth samples. The analysis focused on the water and salt transport characteristics and the size effects of rammed earth of different sizes. The test results revealed that the water loss period and the salt enrichment of the surface soil increased with the size of the samples, while the water loss rate decreased with the sample size. The water loss period of rammed earth samples of different sizes was categorized into three stages: rapid water loss, slow water loss, and stable water loss, with water and salt transport predominantly occurring during the rapid water loss stage. Throughout the water loss process, salt was transported to the sample’s surface layer along with the water, resulting in an increase in the salt content of the surface soil and a decrease in the internal soil’s salt content. This led to the gradual concentration and enrichment of salt in the surface soil. This study provides valuable theoretical support for indoor small block experiments, full-size simulating experiments, and field observation experiments in rammed earth sites.

The development of deep water mooring system and its mooring foundation has become a key issue in the development of clean energy "offshore wind power" projects. The drag embedment anchor, owing to its high bearing capacity and ease of installation, presents promising prospects. A prediction model for the trajectory, pitch angle and capacity of the anchor in layered soil, considering the effect of shank, is established based on the upper limit analysis. Verification of the model using existing model tests demonstrates that the trajectory prediction error of the model, accounting for the shank effect is limited to 13.5%. Furthermore, compared with the model that does not consider the shank effect, the trajectory and angle prediction error are reduced by 78.32% and 36.9% respectively. The strength, thickness and depth of stiff layer jointly restrict the embedding capability of the anchor. The influence of strength is found to be the most significant, with a higher strength ratio leading to a shallower embedding depth until the stiff layer becomes impenetrable. Additionally, greater depth is associated with increased bearing capacity. When the stiff layer can be penetrated, depth has minimal impact on trajectory and angle. However, when the stiff layer cannot be penetrated, the greater depth will result in a deeper embedment depth and smaller final angle. Lastly, the thickness of the stiff layer is found to positively correlate with the bearing capacity during the embedding process.

Natural gas hydrates have significant economic and environmental potential, and their exploitation and utilization are of strategic significance for national energy security and realizing “dual carbon goals”of peak carbon and carbon neutrality. The majority of hydrates in China is distributed in the South China Sea. The complexity and concealment of the marine environment result in highly uncertainty of engineering measurement data, which affects drilling safety. However, there is a lack of reliability analysis for wellbore stability in hydrate reservoirs. Based on the analytical model of wellbore stability in hydrate reservoirs and the specific geological conditions of the Shenhu area in the South China Sea, the reliability analysis methods including the advanced first-order second-moment method and the response surface method are employed to quantitatively assess the probability of wellbore instability during drilling, and to analyze the sensitivity of the wellbore instability probability and safe drilling fluid pressure window to the mean and uncertainty of the main parameters. The research results indicate that: (1) If the measurement data are accurate enough, the drilling in hydrate reservoirs in the Shenhu area of the South China Sea is highly safe and the safe drilling fluid pressure window is also large. However, the increased uncertainty of measurement data can significantly increase the probability of wellbore instability and narrow the safe drilling fluid pressure window. (2) A lower drilling fluid temperature can slightly reduce the probability of wellbore instability and significantly increase the safe drilling fluid pressure window. (3) The mean and uncertainty of the five main parameters have the same order of influence on the probability of wellbore instability, that is: initial in situ stress > initial internal friction angle > elastic modulus ratio > initial cohesion > initial elastic modulus. Accurate measurement of initial in situ stress in practical engineering can significantly improve the wellbore stability in hydrate reservoirs.

Cone penetration test(CPT) has been widely used in offshore wind power projects due to its characteristics. Offshore wind power projects are located in areas prone to liquefaction. It is particularly important to study the applicability of CPT-based liquefaction evaluation methods. In this paper, four representative CPT liquefaction evaluation methods are introduced in detail. These include the method from the National Center for Earthquake Engineering Research (NCEER), the method from the Code for investigation of geotechnical engineering (GB 50021―2001), the method from the Specification for geotechnical investigation in soft clay area (JGJ 83―2011) and the method from the General rule for performance-based seismic design of buildings (CES 160: 2004). Through the analysis of the critical liquefaction lines of four methods and the test using the CPT liquefaction database, the applicability of the four methods was analyzed. The results indicate that the critical liquefaction line of National Center for Earthquake Engineering Research (NCEER) method turns back in the Ⅶ intensity site, the critical value increases too fast in the Ⅸ intensity site, and the evaluation is dangerous in the deep layers in the Ⅶ intensity site and obviously conservative in the deep layers in the Ⅸ intensity site. The NCEER method shows better evaluation results in the shallow layers of Ⅶ and Ⅸ intensity sites and in the Ⅷ intensity site. There is a problem in the critical liquefaction line of the Chinese investigation of geotechnical engineering code method. The critical value decreases with depth. The evaluation is dangerous in the shallow layers of the Ⅶ intensity site and more dangerous in the deeper layers, while in the Ⅷ and Ⅸ intensity sites, it tends to be conservative in the shallow layers and dangerous in the deeper layers. The critical liquefaction line of Chinese specification for geotechnical investigation in soft clay area method turns back at a buried depth of about 6 m, and the evaluation is dangerous in the deep layers. This method shows better evaluation results in the shallow layers of Ⅶ intensity site, while in the Ⅸ intensity site, it tends to be more conservative in the shallow layers. However, in various intensity sites, it consistently leans towards danger in the deeper layers. The Chinese general rule for performance-based seismic design of buildings method has a high and balanced discriminant success rate for different seismic intensities and buried depth of sand. The analytical results provide theoretical basis and support for the revision of relevant specification and engineering applications in China in the future.

The working behavior of transverse joints during earthquakes is critical to the stability of high arch dams. During the Luding Ms6.8 earthquake, the downstream peak ground acceleration (PGA) at the crest of Dagangshan arch dam reaches 586.63 cm/s², and the intensity scale of dam site reaches VIII. The Dagangshan arch dam, which is higher than 200 m, is the only one that has undergone a near-field strong earthquake and adopts dampers as aseismic measures. In this study, the working behavior of transverse joints and dampers after an earthquake is analyzed based on the macroscopic phenomena of dam transverse joints and dampers and the original monitoring data. The results show that the transverse joints undergo a process of opening and closing during the earthquake. Some transverse joints have residual opening after the earthquake, with an opening increment ranging from −0.05 mm to 0.43 mm. The opening increment at the downstream side is slightly larger than that at the upstream side, and the opening increment at the left bank is larger than that at the right bank. This is mainly due to the frequent opening and closing of the transverse joints, which leads to the partial stripping of the grouting material. The joint meter cannot be reset, and the arch dam remains in an elastic working state. The increment in displacement of the three sets of dampers on the top of the arch dam before and after the earthquake ranges from 0.32 mm to 1.06 mm, which represents tensile deformation, and the largest increment in displacement is observed at the transverse joint #16 near the arch crown beam. Combined with the preliminary analysis of the monitoring results of the joint meter, the damper has a certain effect on reducing the opening of the transverse joints in the local area during strong earthquakes, and there is no obvious action trace of the damper in the aftershocks. The research results can provide a reference for the post-earthquake dam safety assessment, as well as seismic design and research of high arch dams.

Clustering of rock discontinuities is crucial for evaluating rock mass stability. The conventional clustering methods often rely on the orientations of rock discontinuities, without considering the influence of physical characteristics on rock mass stability. To address the limitations of single-factor grouping, a stepwise clustering method of rock discontinuities dominated by multivariate parameters based on student-distributed stochastic neighbor embedding (t-SNE) is proposed. This method takes into account the effects of dip direction, dip angle, trace length, opening, filling state and roughness of rock discontinuities. Firstly, the t-SNE algorithm is used to reduce the dimensionality of discontinuity characteristics except for the orientations. Subsequently, the simulated annealing algorithm is employed to search for the global optimal initial values of the K-means algorithm, and the stepwise clustering idea is utilized to accomplish the clustering. The research shows that the proposed method addresses the sparsity issue of high-dimensional data while preserving the local and global structures of the data. Compared to the conventional methods, the proposed method achieves more accurate partitioning of physical characteristics within the spatial distribution similarity zone, resulting in higher grouping accuracy. Furthermore, the proposed method effectively distinguishes the differences between orientations and physical characteristic parameters on rock mass stability without the need for complex weight value calculations. Finally, the proposed method is applied to the measured data of rock discontinuities in an open-pit slope in Xinjiang, China. The grouping results are found to be reasonable and reliable, which further validates the effectiveness of the proposed method in practical engineering. This research provides a reference for stepwise clustering of multi-parameter rock discontinuities.

Studying the changes in site conditions before and after sand liquefaction is crucial for improving liquefaction discrimination methods. In a study utilizing the strong seismic observation data from the borehole array at the California Wildlife Park in the United States, we investigated the variation characteristics of the equivalent shear wave velocity and dominant frequency of the array site before and after liquefaction, triggered by the Brawley strong earthquake sequences. This analysis employed cross-correlation analysis and the Fourier spectral ratio method. The monitoring results of pore pressure under strong earthquake action indicate that the excess pore water pressure in the liquefied layer has reached the critical liquefaction state and rapidly dissipates after the earthquake, without any visible sand boil on the surface. The building up of excess pore water pressure causes a delay in the propagation time of shear waves among different observation positions of the borehole array. Furthermore, the dominant frequency of the array site evidently decreases during the sand liquefaction process. After the dissipation of pore pressure, the propagation time of shear waves and the dominant frequency of the site return to normal state within 4 days. This observed phenomenon holds significant reference value for establishing liquefaction criteria based on in-situ testing data at the site following liquefaction.

The Coriolis effect has gradually become one of the key challenges limiting the use of geotechnical centrifuges to handle high-speed debris avalanche disasters. In particular, there is still a lack of in-depth research on the Coriolis effect involved in the study of how volume affects the flowability of debris avalanche based on centrifugal testing. To tackle this issue, a series of centrifuge modeling tests and DEM simulation tests are conducted, and the influence of different initial volumes on the flowability of debris avalanche under various Coriolis conditions is analyzed. The results indicate that the Coriolis force changes the conversion efficiency from potential energy to kinetic energy of debris avalanche and the magnitude of the final transport distance being enhanced with increasing volume. The behavior of debris avalanche with different volumes under Coriolis conditions is controlled by the inertial flow mechanism and particle-agitation restraint mechanism as well as the transition between these two mechanisms. Considering the practicality, it is recommended to ensure that the flow direction is the same as the rotation direction of the centrifuge as much as possible in the physical centrifuge test, while a linear model can be used to calibrate the experimental results.

Disaster monitoring and prediction play significant roles in the fields of geology and geotechnical engineering. Distributed fiber optic sensing technology plays a significant role in long-distance, long-cycle, highly hidden, strong sudden disaster monitoring by virtue of its continuous, real-time, anti-interference, good stability and other advantages. However, effectively evaluating and addressing the coordination deformation issue between the sensing fiber optic cable and the measured rock and soil mass is crucial for different engineering problems. This coordination is essential for accurately analyzing deformation distribution and understanding the evolutionary patterns of rock and soil masses. In this paper, the development of a three-dimensional active deformation controllable confining pressure fiber-sand coupling test device is presented. The device aims to investigate the coordination between the metal base cable sensing fiber and the compression deformation of coarse sand medium under a confining pressure range of 0 to 4.0 MPa. Experimental results show that the metal base cable exhibits inadequate coordination with sand compression deformation at low confining pressures, displaying nonlinear deformation characteristics. However, as the confining pressure increases, the coupling effect between the sensor cable and the sand intensifies, resulting in linear deformation changes. Notably, when the confining pressure reaches 1.6 MPa, there is a significant enhancement in coordinated deformation, transitioning the deformation from nonlinear to linear behavior. Based on the aforementioned deformation characteristics, we propose a numerical model of confining surface projection. To predict the actual displacement of non-test data, we employ the spline interpolation algorithm with non-kink boundary conditions. The results demonstrate the reliability of the model. Furthermore, the experimental study highlights the higher accuracy of the metal base cable for sand deformation testing under high confining pressure conditions. The findings of this study serve as a scientific reference for the application of distributed optical fiber sensing technology in deep stratum deformation monitoring.