Steeply dipping thin-layered ore bodies are prone to exhibit failure modes such as bending and breaking of the sidewall or bending and internal bulging caused by high tangential stress, which are closely related to the mechanical properties of the bedded rock mass. In order to investigate the deformation, strength properties, and failure characteristics of Sishanling layered iron ore during the shear failure process, conventional triaxial shear tests were conducted on layered rocks under various bedding dip angles and confining pressures. The test results show that the peak strength, axial displacement, circumferential deformation and failure mode of stratified iron ore samples are affected by confining pressure and layered joint angle. With an increase in the bedding angle, the shear strength of the specimen initially increases and then decreases, while the axial and circumferential deformations exhibit a ‘wave-like’ trend. Moreover, as the confining pressure increases, the peak shear strength of the specimen significantly improves, the axial shear displacement increases, and the circumferential deformation decreases. In addition, failure mode of bedding iron ore specimen is controlled by both the bedding dip angle and confining pressure. The study reveals that the failure mode is stress-controlled when the bedding dip angles are 0° and 30°. At a bedding dip angle of 45°, the specimens exhibit a stress-structure controlled failure mode, while for angles at 60° and 90°, the failure mode is predominantly controlled by the structure. Based on the test results, a failure criterion is proposed considering both the intermedium principle stress and the ore bedding angle. The test results could offer important technique support for the stope and blasting and also the ground support design.

The change of unfrozen water content in pores of rock during freeze-thaw process is one of the key factors affecting its mechanical properties. In this paper, the sandstone is taken as the research object, and the pore water content of rock during freeze-thaw process (20, 0, −2, −4, −6, −10, −15, −10, −6, −4, −2, 0, 20 ℃) is monitored by low-field nuclear magnetic resonance system (NMR), and the evolution law of unfrozen water content with temperature is analyzed. The influence of the evolution of unfrozen water content on the mechanical properties of rock during freeze-thaw process is also discussed. The research findings show that the pore water in rocks during the freezing-thawing process is significantly influenced by temperature, passing through five stages: supercooling, rapid freezing, slow freezing, slow melting, and accelerated melting. A distinct hysteresis phenomenon is observed in the rock during thawing. At identical temperatures, the unfrozen water content during freezing is notably higher than during thawing. Consequently, the peak intensity and elastic modulus during thawing are significantly greater than during freezing. The relationship between uniaxial compressive strength, rock elastic modulus, and unfrozen water content in freeze-thaw process can be expressed by exponential function. At the beginning of freezing, the change of rock mechanical parameters is mainly affected by the increase of pore ice content and the cementation effect of pore ice on rock particles. With the further decrease of temperature, the thickness of adsorbed water film decreases, and the adsorption capacity increases, so that the integrity between pore ice and rock particles is enhanced, and rock mechanical parameters further change.

A series of large-scale direct shear tests (DST) was conducted on sand-contaminated ballast (SCB) in order to address the paucity of research on subgrade fillers contaminated with sand. Wireless attitude sensors, known as SmartRock, were used to monitor the internal particle movement during the shear process of the SCB. The results show that the shear strength of the SCB decreases with an increase in the void contamination index (VCI), leading to changes in the shape of the shear stress-shear strain curve of the SCB. Additionally, the power function offers a more accurate fit for the peak shear strength envelope diagram of the SCB at various VCI levels. The volumetric strain exhibits a pattern of shear compression-dilation, and the power function better predicts the critical shear strain and peak volumetric strain in the shear compression-dilation process of the SCB specimens. The SmartRock sensor can capture the motion pattern of individual particles within the shear plane. The DST accurately reflects the behavior of the real ballast bed under train loading conditions. Moreover, the study shows that the motion pattern of particles within the ballast layer is multidimensional. The interaction forces between particles in the ballast bed, perpendicular to the train travel direction, can be described by unidirectional shear action.

Coal is a porous medium structure. During the hydraulic fracturing process, fluids may escape along pre-existing pores and fractures, known as filtration effect, which reduces the effectiveness of hydraulic fracturing operations. Additionally, there is no established system for the relationship between pressure changes during coal seam hydraulic fracturing and fracture propagation, making it impossible to accurately assess the damage caused by hydraulic fracturing to coal. To address this issue, the Wudong Coal Mine is chosen as the research background, and theoretical analysis, laboratory experiments, and on-site tests are conducted. Firstly, the initiation mechanism of hydraulic fracturing under loss conditions is analyzed based on the stress analysis theory of surrounding rock in rock mechanics circular hole problems, coal seepage theory, and the theory of tensile fracture criterion induced by stress concentration on hole walls. Secondly, an experiment of hydraulic fracturing for steeply inclined top coal is conducted to determine the relationship between the pressure curve of steeply inclined top coal and the fracture of coal rock mass according to the crack propagation situation of the experimental coal sample. Thirdly, an on-site hydraulic fracturing test is carried out to further determine the relationship between the on-site pressure curve and the fracture of top coal. Finally, four types of pressure curve evolution patterns are summarized as a basis for judging the effectiveness of hydraulic fracturing in coal rock mass. The research results show that when the internal water injection pressure in the borehole reaches the tensile strength equal to that of the coal rock, the first crack appears at the borehole wall. During the hydraulic fracturing process, the water injection flow rate must be greater than the leakage rate, and the higher the water injection rate, the shorter the pressurization process duration. The pressure curves can be categorized into four types: (1) single initiation type, (2) fracture connection type, (3) fluid loss type, and (4) secondary initiation type. A smaller proportion of fluid loss type during the fracturing process indicates a better fracturing effect. These findings provide a basis for judging the damage effect of hydraulic fracturing on coal bodies on-site.

Liquefied landslide disasters induced by earthquake are serious, in order to solve the problem of support and management of slopes with liquefiable soil layer, a novel anti-slide pile to prevent liquefaction is proposed based on the concept of "combination of prevention and resistance", which integrates active drainage and passive anti-slip. To evaluate the effectiveness of the novel anti-slide pile in preventing liquefaction, a slope model was developed based on survey data from slopes with liquefiable soil layers in the upper Yellow River region. A large-scale shaking table model test was conducted to compare the novel anti-slide pile with conventional ones. The failure mode and dynamic response characteristics of excess pore water pressure in soil of the slope with liquefiable soil layer supported by different types of anti-slide piles under earthquake are obtained. The results indicate that the failure mode of slope with liquefied soil layer supported by anti-slide pile under earthquake is earthquake-induced-horizontal ejection of overlying soil layer on liquefied soil layer-bulging, shearing of slope surface at the bottom of liquefied soil layer-flowing and sliding accumulation of soil in front of anti-slide pile. In comparison to conventional anti-slide piles, the novel anti-slide pile for liquefaction prevention can rapidly and efficiently dissipate excess pore pressure in the surrounding soil. This mechanism effectively prevents liquefaction around the pile, achieving the goal of liquefaction prevention. The research findings confirm the reliability of the novel anti-slide pile for liquefaction prevention, providing valuable insights for mitigating seismic liquefaction landslide disasters.

Deep-buried tunnels in the central and western China pass through a large number of layered rock masses. Under the action of high in-situ stress, the layered rocks exhibit transversely isotropic properties and significant creep phenomena, which are highly likely to trigger engineering disasters such as tunnel face collapses and support structure failures. To accurately characterize the impact of bedding angles and time effects on the mechanical properties of layered rocks, based on the fractional calculus theory and the creep compliance substitution method, taking the component combination model as the foundation, this study established a transversely isotropic nonlinear creep model (T model) that takes into account damage and rock layer angles, and derived the one- dimensional and three-dimensional creep constitutive equations. The T model uses the fractional-order Kelvin model to describe the characteristics of the decelerating creep stage, the Abel dashpot for the steady-state creep stage, and connects the instantaneous plastic element and the fractional-order nonlinear damage dashpot in parallel to reflect the characteristics of the accelerating creep stage. Based on the creep test data of carbonaceous slate, the least square method was used to identify the parameters of the creep constitutive equations. Through the error analysis of RMSE (root mean square error), MAE (mean absolute error) and R² (coefficient of determination), as well as the comparison with the existing transversely isotropic creep models, the fitting effect of the constitutive equation of the T model was verified, which indicates that the T model can describe the characteristics of each creep stage of layered rocks more accurately. The research results provide a theoretical basis for the long-term stability analysis of the surrounding rock of layered rock tunnels.

The propagation characteristics of seismic waves in soft soil are crucial for enhancing the seismic resilience of buildings. By analyzing the attenuation properties of dynamic peak acceleration (PGA) through centrifugal vibration table tests, we aim to enhance our understanding of the impact of soil properties on seismic wave propagation. To accomplish this, we adjust the obtained soil samples to moisture contents of 35%, 45%, and 55% and perform conventional physical tests. Subsequently, the cluster morphology and tangential stiffness of particle bonding within the model will be determined by macro-micro parameters, including friction factor, Poisson ratio, and other critical factors like the damping ratio. Additionally, both the mass damping β_n  and the stiffness damping k_n  will be meticulously examined as they regulate particle motion and collisions. According to the results of the conventional physical test of the different moisture contents, the effect of soft soil on the decay effect of PGA under different moisture content conditions are studied. The research results show that under different ground motion conditions, the peak acceleration in soft and hard layered soil at a depth of 30 m presents a change law of slow attenuation, sharp attenuation and then rebound rise. With the increase of water content, the attenuation ratio of peak acceleration in the depth of 30 m to 8 m increases in the range of 2.33 to 2.70. The corresponding magnification of 8−0 m depth strata decreases in the range of 1.60−1.23. The period of the response spectrum 0.2−1.1 seconds corresponds to the middle and low frequency range, and the acceleration value shows an increasing trend; the higher frequency range corresponds to the period 1.1−2.0 seconds, and the acceleration value generally shows a decreasing trend, which is consistent with the high-frequency attenuation effect. Through comparison and verification of numerical simulation and theoretical analysis, the law of ground motion propagation and amplification near the surface under different water contents is preliminatively verified, which provides a theoretical basis for assessing earthquake disaster risk and improving earthquake protection.

A self-designed water level control system was used to simulate the collapse of a red mud dam in a dry storage yard under varying water levels. The study unveiled the distribution patterns of seepage lines, pore water pressure, soil pressure, and crack evolution in red mud dams with varying slope ratios (1:2 and 1:1) under changing water levels. Experimental findings show that the rise of the infiltration line is initially rapid, then slows down, exhibiting a lag effect. The area with the highest pore water pressure beneath the infiltration line also experiences the highest horizontal soil pressure. Under different slope ratios, the reasons for the formation of main cracks are different. When the slope ratio is 1:2, under the combined action of gravity and hydraulic forces, slope cracks are generated due to the formation of a through channel extending from the interior of the red mud dam body to the slope surface. When the slope ratio is 1:1, cracks appear at the dam crest due to the traction effect of the sliding slope below the infiltration line on the upper slope. The stress and seepage fields of red mud dams with different slope ratios were analyzed using the finite element software ABAQUS, revealing the stress and displacement distribution patterns on the dam slope surface.

The soil-water retention curve is the basis for the study of the strength, deformation and seepage characteristics of unsaturated soils, but the direct measurement of the curve in laboratory is complicated and time-consuming. In order to quickly and accurately obtain the soil-water retention curve of granite residual soil, the resonant column tests were carried out on granite residual soil with different water contents, the small-strain shear modulus characteristics of unsaturated granite residual soil were also studied. The soil-water retention curve of granite residual soil was inverted on the basis of the double-stress-variable maximum shear modulus prediction model and the single-stress-variable maximum shear modulus prediction model for unsaturated soils, respectively. The results show that the water content has a significant effect on the small-strain shear modulus of granite residual soil, and the shear modulus decreases with the increase of water content and increases with the increase of confining pressure. The inversion result of the soil-water retention curve based on the double-stress-variable maximum shear modulus prediction model is more consistent with the pressure plate experimental data. The accuracy of this prediction model is verified by the experimental data, and its mechanical mechanism is discussed. The resonant column test can not only directly study the small-strain shear modulus characteristics of unsaturated granite residual soil, but also project the soil-water retention curve of granite residual soil by the inversion method, which provides a new method for obtaining the soil-water retention curve.

Given the insufficiency in research on the mechanism of fine particle impact on gravelly soil subgrade deterioration, a series of saturated gravelly soil consolidated drained triaxial shear tests was conducted using the GDS triaxial testing system under varying fines contents and effective confining pressures to investigate the effect of fine particle contamination on the static shear characteristics of gravelly soil. The results indicate that: (1) As the fines content increases, the stress-strain curve development pattern transitions from strain softening to strain hardening, with a critical threshold at a fines content of Fc=15%. (2) The addition of fine particles leads to a decrease in the principal stress ratio, brittleness index, peak strength, cohesion, and internal friction angle of the gravelly soil, while the degradation indices increase. The relationship between the degradation indices of peak strength and cohesion and fines content can be described by quadratic functions, and the degradation index of the internal friction angle by a cubic function. (3) With increasing fines content, critical state parameters decrease. The effective stress path shows retracing behavior, becomes shorter, and shifts to the left. (4) The addition of fine particles results in a decrease in the secant modulus, and the volumetric strain-axial strain curve changes from contractive-dilative to purely contractive.

Laying soft materials on the top of high-fill box culverts can greatly reduce the vertical earth pressure on the top of the culvert. However, it also leads to a significant increase in horizontal earth pressure and friction on the sidewall of the box culvert, which is likely to cause new structural diseases. In order to improve the stress state of high-fill box culvert, this paper studied the stress characteristics and load reduction effect of box culvert with laying soft materials on the top slab and sidewalls of the culvert through model test. The variation laws of earth pressure on the culvert top, sidewall, and the foundation contact pressure with the fill height were explored by considering two different soft materials (i.e., Sponge and expanded polystyrene (EPS) board). Moreover, the earth pressure coefficients were obtained by the dimensionless of the earth pressure data, which were compared with the existing representative research results of the culverts with laying soft materials on the culvert structures, and the load reduction effect of laying soft materials both on the top slab and sidewalls was proved. The research results show that laying soft materials on the top slab and sidewalls of the culvert can effectively improve the stress state of the box culvert. The soil arch effects generate on the culvert top and sidewalls, the vertical load on the culvert top is transferred to the outside fill of the culvert. Thus, it not only significantly alleviates the earth pressure concentration on the culvert top slab, but also effectively reduces the horizontal earth pressure on the sidewall and the foundation contact pressure.

Anchoring frame beams are at risk of anchor bolt fracturing or pulling out at joints, which can lead to overall failure under high-intensity seismic action. Based on the concept of flexible damping, buffer springs were installed at the external anchor heads of frame beam joints, and a shaking table model test was conducted on a shallow overburden-rock slope with a geometric scale of 12. The seismic responses, including slope acceleration and anchor bolt axial force, were compared with and without the flexible external anchor heads under high-intensity seismic ground motions (artificial seismic waves and Wenchuan earthquake wave). Specifically, the variation in the anchor bolt force reduction ratio with different buffer spring stiffnesses was analyzed, and the benefits of spring anchor heads on seismic energy response and vibration-induced cumulative damage in anchor bolts were explored. The research results indicated that installing flexible external anchor heads led to a reduction in the amplification factor of Arias intensity. As the stiffness of the buffer spring decreased, the reduction ratio of the anchor bolt dynamic axial force ranged from 72% to 89%, and post-earthquake prestress loss of the anchor bolts was effectively reduced. Spectral analysis of anchor rod dynamic axial forces and linear cumulative damage calculations at the anchoring interface demonstrated that the energy response in the mid-to-high-frequency range was significantly attenuated, which could lead to structural damage. Both the cumulative tensile fatigue damage of the anchor bolt and the cumulative shear fatigue damage at the grout-anchor interface were both significantly reduced. The adoption of flexible external anchor heads effectively controlled structural damage during high-intensity seismic events.

This study focuses on the freeze-thaw deformation of sandy soil under different freezing temperatures, examining the impact of water content and Alhagi sparsifolia root content, using typical sandy soil and the desert vegetation Alhagi sparsifolia root system from the northern slope of the Tianshan Mountains in Xinjiang as the research subject. Indoor unidirectional freezing experiments are conducted to simulate natural freeze-thaw conditions, and orthogonal experiments are used to determine the correlation and significance of various factors with the freeze-thaw deformation of sandy soil. The study analyzes the freeze-thaw deformation mechanism of sandy soil under varying water contents, freezing temperatures, and root contents, and proposes a fitting formula for the freeze-thaw deformation of sandy soil. The results show that the order of influence on the maximum deformation of freeze-thaw sandy soil is water content > freezing temperature > root content. The maximum deformation of freeze-thaw sandy soil is positively linearly correlated with water content, negatively linearly correlated with freezing temperature, and exhibits a quadratic function relationship with root content. Low water content bare sandy soil and root-containing sandy soil exhibit freeze shrinkage during the initial freezing stage and thaw expansion in the melting stage, while high water content bare sandy soil and root-containing sandy soil exhibit slow freeze expansion during the initial freezing stage and thaw settlement during the melting stage. A multi-factor regression model is developed based on this pattern, enabling accurate prediction of the maximum deformation of freeze-thaw sandy soil and offering guidance for the safety assessment of vegetation ecological slope protection in cold and arid regions.

Deep saline aquifers offer substantial CO₂ storage potential, and exploring the CO₂-water two-phase displacement mechanisms in tight sandstone is crucial for efficient and secure CO₂ storage in saline aquifers. CO₂-water two-phase displacement experiments were conducted on two low-permeability sandstones with distinct pore structures. Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques were employed to quantitatively and visually analyze the distribution of gas and water phases during the drainage and imbibition processes. The study examined the impact of core pore size distribution, heterogeneity, and permeability variations on the two-phase displacement characteristics. The research indicates that in the drainage processes, CO₂ is preferentially captured in larger pores, and cores with a larger proportion of large pores exhibit higher CO₂ saturation. However, during the imbibition processes, CO₂ captured in the cores with a higher proportion of micropores and lower permeability are less likely to be displaced by water, resulting in higher CO₂ storage efficiency. The local permeability changes of rock cores have a significant impact on the final residual gas distribution, and areas with lower permeability have higher final residual gas saturation and storage efficiency. This study can further improve the theoretical system of reservoir selection, efficient storage, and safety assessment in CO₂ saline aquifer storage projects.

The solidification effect of contaminated soil degrades under wet-dry (W-D) cycles and acid rain. Acidic dry-wet cycle tests for Cr-contaminated soil solidified by alkali-activated granulated blast furnace slag (GGBS) are carried out. Toxic leaching test and accelerated leaching test are performed to study the leaching characteristic and mechanism. Scanning electron microscopy and energy spectrum analysis are used to investigate the microscopic mechanism. The long-term stability is evaluated through the apparent diffusion coefficient. The results show that a few W-D cycles at pH=7 will cause additional hydraulic reaction of GGBS and thus reduce the leaching concentration of total Cr and Cr(VI). Along with W-D cycles more AFt is generated. The expansion of AFt results in micro-fracture and thus more Cr leaching. In acidic W-D cycles, AFt dissolves first, releasing Cr immobilized by ion exchange. With the increasing acidity, C-S-H gels dissolve and more gypsum is generated, resulting in more micro-fractures. Consequently, the encapsulation effect weakens, resulting in more Cr leaching. However, the C-A-S-H gels remain stable. The slopes of the logarithmic curves of cumulative leached fraction versus time range from 0.373 to 0.675. The errors of fitting by a pure-diffusion analytical solution are mainly below 0.5%, indicating that diffusion is the dominant leaching mechanism. However, after 18 W-D cycles at pH=3, the effect of dissolution increases and the diffusion-dominated criteria are not satisfied. The mobility of Cr under neutral, weak acidic, and strong acidic W-D cycles is low, moderate, and high, respectively. It is necessary to take measures to reduce acid rain infiltration and W-D cycles when utilizing solidified soil. This research provides a reference for evaluating the long-term stability of solidified contaminated soil.

In recent years, extreme rainfall in the northwest region has led to frequent instability and landslides of loess subgrade slopes. To address these engineering accidents, a high-strength steel slag-coal gangue geopolymer (SC-GP) was developed to solidify loess, using steel slag (SS) and coal gangue (CG) as raw materials and water glass and desulfurization gypsum (DG) as activators. First, the optimal mix ratio of SC-GP was determined through unconfined compressive strength (UCS) tests after 28 days of curing. Then, solidified loess samples with different curing ages and SC-GP contents were prepared based on the optimal mix ratio of SC-GP. Macro- and micro-scale analyses were employed to investigate the influence of curing age and SC-GP content on the mechanical properties of the solidified loess, utilizing UCS, direct shear, disintegration, X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) tests. The results indicate that the optimal mix ratio of SC-GP is SS: CG: DG at 40:54:6, with a water glass modulus of 1.2 and a water glass content of 22%. SC-GP significantly enhances the mechanical properties of loess and effectively reduces the disintegration rate of solidified loess in water. After 28 days of curing, the UCS and cohesion of solidified loess with 20% SC-GP content are 359.09 kPa and 112.76 kPa, respectively, which are 3.45 and 2.3 times higher than those of remolded loess. Moreover, the solidified loess hardly disintegrates within 300 minutes in water, with a disintegration rate of less than 1%. Microscopic studies reveal numerous C-S-H (calcium silicate hydrated) and C-A-S-H (calcium aluminate silicate hydrated) gelling materials. The volume of large pores in the solidified loess decreased, while the volume of small pores increased relatively.

Dynamic triaxial tests were conducted to clarify the dynamic deformation characteristics of silty clay in flood irrigation areas under cyclic loading, using single-sample stepwise and multiple samples of constant amplitude. The effects of confining pressure, bias consolidation ratio, drainage conditions, dynamic load frequency, and cyclic stress ratio on the development law of cumulative plastic strain and residual dynamic pore pressure, the evolution characteristics of the hysteresis curve, and the change law of softening index of silty clay were studied. The results show that the development of cumulative plastic strain and residual dynamic pore pressure of soil under dynamic load is consistent. According to the stability theory, the dynamic behavior of samples under different test conditions can be divided into three typical cases: plastic stability, plastic creep and incremental failure. Under the basic conditions of this test, the boundary cyclic stress ratios of the three dynamic states of plastic stability, plastic creep, and incremental failure are around 0.30 and 0.40, respectively. The hysteresis characteristics of undrained specimens in the plastic stable state are obvious, and the hysteresis curve shows an S shape. With the progression of loading, soil experiences stiffness degradation. The cumulative plastic deformation of undrained specimens is smaller than that of drained specimens, and the softening index of soil under drained and undrained conditions remains stable at around 1.15 and 0.91, respectively, under lower cyclic stress ratios. Through grey relational analysis, it is found that the cyclic stress ratio has the greatest influence on the cumulative plastic strain and pore pressure ratio. The confining pressure exerts the greatest influence on the softening index. The parameters of the cumulative plastic strain model suitable for silty clay in flood irrigation areas have been determined, and the prediction effect is good.

In order to study the mechanical response characteristics of soil support of foundation pit under the combined action of different types of retaining piles. Based on the foundation pit project of Linjiazhuang Station, Line 4 of Jinan Rail Transit, and aiming at the composite support form of steel pipe pile and cast-in-place pile adopted for the first time on site, the analytical analysis model and calculation method of stratum support stress under the action of composite piles are proposed. The distribution characteristics of the maximum principal stress and the rule of arching effect under different formation depths and pile spacings are analyzed. On this basis, according to the relationship between the maximum principal stress support line and the soil arch axis between piles, an arch analysis model is put forward, in which the inner arch and the outer arch bear the lateral earth pressure together, the theoretical formulas of reasonable pile spacing S and load sharing coefficient λ  are derived, and the load-bearing capacity relationship between steel pipe pile and cast-in pile is discussed. Finally, the effectiveness of the soil arch analysis model is verified with concrete engineering examples, and the influence of different parameters such as internal friction angle, cohesion force, and pile diameter on reasonable pile spacing S and load sharing coefficient λ  is analyzed. The results show that the reasonable pile spacing S increases with the increase of internal friction angle, cohesion force, and pile diameter under the composite support design. The load sharing coefficient λ  increases with the increase of internal friction angle and cohesion, and the load bearing capacity of the outer arch gradually increases. When other parameters remain unchanged and the diameter of steel pipe pile increases, the load bearing capacity of outer arch will gradually decrease.

Energy piles are a new energy-saving technology for buildings that combines load-bearing performance and heat exchange performance. Most studies on energy piles are carried out under free and unconstrained conditions or rigid constraints, such as pile-cap/raft systems. However, the thermo-mechanical response characteristics of energy piles under the relatively flexible constraint state of a composite foundation remain unclear. Field tests were conducted at the BeSTDR Infrastructue Hospital in Pingyu County, Henan Province, as an ultra-low energy consumption green building project to assess how cushion layers affect the thermo-mechanical response characteristics of prestressed high-strength concrete (PHC) energy piles. The development patterns of temperature and strain along pile body were measured, and the changes in constraint stress, thermal-induced side friction resistance, axial displacement, pile-soil stress ratio, and the response characteristics of the adjacent pile were preliminarily explored. The results show that under the experimental conditions, the constraint capacity at the pile top (0.133L) is approximately 65% due to the influence of the cushion layer. After 96 hours of heating, the region between 0.133L and 0.333L from the pile top exhibited minimal negative skin friction, with the maximum upward axial displacement at the pile top (0.133L) reaching about 0.14% of the pile diameter. After 120 hours of heating, the pile-soil stress ratio at 0.133L from the pile top nearly tripled.

The non-uniformity and discrete nature of rock mass are among the most significant characteristics of rock mass. Jointed rock masses are complex block structure systems composed of different scales of rock masses. Different indexes and standards for the division of rock mass structure and integrity in various industries, along with qualitative descriptions, hinder the generalization of obtained data and conclusions. Using unweighted undirected graphs, the study achieved the rapid and batch construction of random joint network models. Employing algorithms such as connectivity domain detection and breadth-first search, the constructed simulation models were analyzed for block degree and equivalent sieving. With the original closed block area, the independent effective block, and the reconstruction of the effective block amplification area as a parameter source of the block degree deconstruction, a quantitative index for the degree of blockiness of jointed rock masses was defined (the rock block index, RBI_2D). Diverging from traditional rock mass quality assessment bases on structural planes, this study proposes a normalized treatment and quantitative evaluation method for the deconstruction of jointed rock mass blockiness. Simulations were conducted on jointed rock masses with varying degrees of integrity based on relevant industry standards and actual engineering site conditions, establishing a correlation between rock structure types and RBI_2D. The integrated development of a normalized processing evaluation system for jointed rock mass blockiness has been implemented and applied to the rock mass quality evaluation and surrounding rock classification of the Gandershan Tunnel on the Baotou-Yinchuan Railway, showing good consistency with onsite measurements. The research provides an alternative effective approach for obtaining integrity indices in surrounding rock grade evaluations.

Coal serves as the primary energy source in China, playing a crucial role in maintaining national economic stability. Due to the characteristic of high thick-and-hard overburden strata, strong mine tremors occur frequently in Shilawusu coal mine in Inner Mongolia, which seriously restricts the safe mining of coal. The primary cause of strong mine tremors is the fracture of high thick-and-hard overburden strata, making it imperative to investigate the mechanical mechanism of such fractures under adverse geological conditions. The study is conducted using the 1206A and 1208 panels of the Shilawusu coal mine as the research context. On the basis of Reissner theory and considering the influence of gravity stress field, the analytical formulas of deflection, rotational angle, shear force, bending moment, and maximum tensile stress of the thick plate with fixed supports on four sides are derived. Considering the influence of horizontal ground stress field and its transfer, the breaking criterion of the high thick-and-hard overburden strata is established, and a MATLAB-based calculation program for determining the initial fracture step distance of such strata is developed. Finally, the program was used to systematically study the influence of the panel width, overburden strata thickness and overburden load on the initial fracture step distance of the thick-and-hard overburden strata.

The use of supplement piles is a common remedial measure in bridge construction. The resulting asymmetric pile foundation is calculated according to current highway specifications, which is not closed and unstable. A calculation method for asymmetric straight piles is proposed based on the m-method. Firstly, calculate the stiffness of a single pile and summarize the pile group stiffness at the base of the pile cap. Then establish a balance equation related to the longitudinal and transverse directions. The load at the base of the pile cap is recombined according to the asymmetric structure, and the displacement of the pile cap is determined by solving the equilibrium equation. Next, calculate the external force at the top of each pile in sequence. Then, carry out subsequent calculations according to the current specifications, and finally achieve the calculation of asymmetric pile foundation. It has been verified that this method is accurate, efficient, and easy to operate, making it suitable for inclusion in specifications. Practical engineering applications have demonstrated that the approach of using supplement piles around the bearing platform is structurally sound and straightforward to implement. In case of damage to a side pile, two symmetrically placed piles should be added adjacent to the affected side of the pile cap; for a corner pile damage, one pile should be added at each end of the pile cap; if the middle pile is damaged, one pile should be added to the closest side of the pile cap. To save costs, one pile can be damaged and replaced within a range of 1-2 times the diameter of the abandoned pile. However, as it does not meet the minimum pile spacing requirement, it should be used with caution.

Soft marine soils in southeastern coastal areas of China are widely distributed, with occluded gas bubbles that significantly impact soil compressibility. Finite volume (FV) method helps to develop consistent computation method of seabed dynamic response with fluid simulation, and then wave-seabed interaction can be simulated. Operator splitting technique can significantly enlarge time steps for stability of staggered algorithms, and such algorithms can easily be implemented on open-source FV calculation platform, OpenFOAM, thus they are efficient and versatile. Numerical cases indicate that the proposed staggered algorithm can reasonably reflect dynamic responses of highly saturated gassy soil. The existence of occluded bubbles can hugely lower transient responses and amplitudes of pore pressure of highly saturated gassy soil. Meanwhile, when considering gravity, decrease of saturation degree can lead to phase lag of dynamic pore pressure.

In order to study the fracture propagation morphology of hydraulic fracturing in heterogeneous rock, the random field theory of the center point method was applied to randomize the physical and mechanical parameters of rock. The surface of newly formed fractures was tracked in real time and pressure was applied to simulate the interaction between fracturing fluid and fracture wall. A numerical model for simulating the hydraulic fracturing process of rock was proposed based on the bond-based peridynamics. According to the compression test results of rock containing a prefabricated crack, the effectiveness of the proposed model was verified, the evolution of rock hydraulic fractures was explored considering the effect of the spatial variation direction of rock elastic modulus, fluctuation range of rock elastic modulus, and perforation spacing. When the distribution of rock elastic modulus is layered, the hydraulic fractures tend to propagate along the weak interfaces. When the parameter distribution is directionless, the expansion of hydraulic fractures exhibits strong randomness, and the fracture network tends to become more complex. When the parameter fluctuation range is small, the variability of rock elastic modulus is significant, which caused stress concentration locally, making it easy to form complex fracture structure. A larger parameter fluctuation range leads to homogenization of rock, and the expansion of hydraulic fractures is singular, resulting in a relatively low fracture propagation rate. Under the action of dual perforation, the expansion of fractures in homogeneous rock exhibits a symmetrical distribution. The perforation pressure suppresses the expansion of fractures between the perforations, leading to the main fractures tending to expand towards the boundaries on both sides. And there is a competitive relationship in the expansion of hydraulic fractures in heterogeneous rock. Under the combined effect of stress concentration and material heterogeneity, one hydraulic fracture preferentially expands and then inhibits the development of another one.

Ball penetrometers are particularly advantageous for predicting the undrained shear strength of clays in marine geotechnical investigations, due to their larger projection area compared to traditional cone penetrometers. However, if the ball penetrates silty clay or clayey silt, the surrounding soil may experience partially drained conditions, which can affect penetration resistance. Previous studies have focused on normally consolidated soils and have not been able to consider the coupling of partial drainage conditions with the overconsolidation ratio. A large deformation finite element method utilizing effective stress is utilized to model the deep penetration of the ball into overconsolidated soils. The reliability of the large deformation simulation was validated by comparing it with centrifuge tests and field measurements. A backbone curve of penetration resistance at the spherical probe is developed, establishing a relationship between penetration resistance and partial drainage conditions in overconsolidated soils. Based on extensive parametric analyses, a novel approach is proposed to predict the effective internal friction angle of overconsolidated soils using penetration resistance data from ball penetration tests. The normalized penetration rate can quantify the degree of partial drainage, eliminating the need to measure pore pressure during penetration.

A substantial number of geotechnical projects, including massive concrete structures, necessitate distributed crack monitoring, which can be accomplished through the implementation of fiber optic monitoring technology. In order to investigate the coupling performance of distributed optical fiber and mass concrete, a multifaceted approach was employed, encompassing theoretical analysis, numerical simulation, and indoor experimental studies. These investigations were applied to a mass concrete raft slab foundation. The findings indicate that the strain transfer model of optical fiber under compression, established based on shear-slip theory, can achieve precise quantification of the strain transfer efficiency of optical fiber. Numerical simulations are employed to verify the accuracy and reliability of the model. The coupling performance between optical fiber and concrete under different arrangement methods is studied by using different optical fiber arrangement methods for reinforced concrete beams and conducting three-point graded loading tests. The results show that the optical fiber laid along the vertical direction of the reinforcement has a better coupling effect with the concrete. The on-site fiber optic monitoring of mass concrete raft foundation demonstrates the efficacy of fiber optic sensors in coupling with the mass concrete structure, facilitating precise strain evolution process monitoring and key area law determination post-casting. The research findings establish a theoretical foundation and essential technology for distributed fiber optic technology in geotechnical engineering structure deformation monitoring.

Electrical resistivity tomography (ERT) has been gradually applied in the environmental geotechnical field, but its applicability for identifying organic pollution in soft soil areas lacks systematic validation and application examples. Through high-density electrical resistivity testing conducted at a chemical industry site in Shanghai, coupled with verification through borehole sampling and analysis of pollution characteristics, the pollution features of the site were effectively identified. Results indicate that contaminated areas exhibit localized high resistivity (above 70 Ω·m) and significant zones of encapsulation. Validation through borehole excavation confirmed the efficacy of high-density electrical resistivity tomography in discerning non-aqueous phase organic pollutants in soft soil areas. Analysis of longitudinal data revealed that point resistivity in polluted areas exhibits a trend of initial decrease, followed by an increase and subsequent decrease with depth. Based on pollution delineation results, a long-term monitoring system was established, proposing a quantitative evaluation method for continuous ERT monitoring information based on image grayscale correlation theory. By calculating image correlation coefficients throughout infiltration tests, rapid early warning of non-aqueous phase organic pollutants can be achieved, providing theoretical and technical references for rapid determination, monitoring, and early warning of pollution leaks in enterprises.

Acoustic emission (AE) monitoring technology is widely used in indoor mechanical test and concrete damage assessment, while microseismic monitoring technology is widely used in mine earthquake and rock burst disaster warning. P-wave arrival time picking is fundamental and crucial for both technologies. Processing and analyzing the P-wave arrival time picking data enables the determination of microsource locations and the retrieval of fracture mechanisms. The AR-AIC algorithm, based on the autoregressive model (AR model) and akaike information criterion (AIC), is presently the most commonly used method due to its high accuracy in picking. However, the double-sequence AR model restricts the overall efficiency of picking, and the picking performance under low signal-to-noise ratio and spike signals is also unstable. A more efficient, accurate and stable picking method, autoregressive model-variance surge phenomenon (AR-VSP) algorithm, is proposed by using the variance surge effect of single sequence AR model after signal arrival and introducing a reduction factor based on variance term. The accuracy rate of the AR-VSP algorithm is 96%, surpassing the 91% accuracy of the AR-AIC algorithm. Additionally, the picking speed has increased by 50.06%, and the algorithm exhibits enhanced anti-spike interference capabilities. The AR-VSP algorithm is more robust compared to the AR-AIC algorithm.