[Objective] The strength characteristics and underlying mechanical mechanisms of expansive soil treated with microbially induced calcite precipitation （MICP） remain insufficiently understood. Investigating the effect of varying calcium ion concentration on the strength of MICP-treated expansive soil can provide critical guidance for its engineering applications. [Methods] Sporosarcina pasteurii （CGMCC 1.3687） was selected for microbial solidification using the mixing method. This study systematically investigated the mechanism by which different calcium ion concentrations—the core variable—affect the strength characteristics of treated expansive soil. Through a series of consolidated quick shear tests， the relationship between calcium ion concentration and strength parameters was analyzed to elucidate the mechanism by which regulating calcium carbonate formation enhances soil strength. [Results] The results indicate that MICP treatment significantly enhances the shear strength of expansive soil， altering its mechanical behavior from the strain-hardening mode of untreated soil to a dual-mode response： strain-softening under low confining pressure and strain-hardening under high confining pressure. Soil treated with Ca²⁺ solution exhibited higher shear strength than the untreated control. Specifically， cohesion （c） and the internal friction angle （ϕ） followed a unimodal trend with increasing Ca²⁺ concentration， peaking at 1.5 mol/L （c=42.5 kPa， ϕ=18.4°）. This represents a 269.6% increase in cohesion and a 10.2% increase in the internal friction angle. A concentration of 1.5 mol/L was identified as optimal， maximizing calcium carbonate yield and cementation. Lower concentrations resulted in insufficient Ca²⁺， while higher concentrations inhibited bacterial activity； both scenarios reduced calcium carbonate production and soil strength. [Conclusions] This study confirms that MICP technology significantly improves the strength of expansive soil. The strengthening mechanism is attributed to a significant positive correlation between calcium carbonate content and strength indices.

[Objective] While the mechanical properties of rock-concrete composites and basalt fiber-reinforced concrete have been widely studied， research on their combined performance after high-temperature exposure remains limited. This study investigates the use of basalt fibers to enhance the high-temperature performance of granite-concrete composites， aiming to evaluate their efficacy in mitigating thermal damage. [Method] Granite， plain concrete， and granite-basalt fiber concrete （GBFC） composites with four fiber volume fractions （0%， 0.1%， 0.2%， and 0.3%） were tested. Following high-temperature treatments at ambient temperature and 200 ℃， 400 ℃， and 600 ℃， static uniaxial compression and splitting tensile tests were conducted to evaluate compressive strength， tensile strength， failure modes， and damage factors. Scanning electron microscopy （SEM） was also employed to analyze microstructural evolution. [Result] （1） The composites exhibited continuous medium mechanical behavior， characterized by plastic failure under uniaxial compression and brittle failure during splitting. Their compressive and tensile strengths fell between those of pure granite and concrete， trending closer toward the concrete values. （2） Basalt fiber incorporation improved both strength metrics and failure modes at elevated temperatures， with a 0.2% fiber content identified as optimal. （3） The damage factor increased progressively with temperature； specifically， the GBFC damage factors were 0.103 5 at 200 ℃， 0.339 1 at 400 ℃， and 0.702 7 at 600 ℃， indicating severe structural degradation at the highest temperature. （4） SEM analysis revealed that uniaxial compression primarily damaged the concrete matrix， while the interface and granite remained relatively intact. High-temperature treatment exacerbated concrete deterioration but had minimal impact on the interface and granite. Basalt fibers acted as bridging and crack-arresting agents within the concrete matrix， effectively mitigating crack initiation and propagation when added in appropriate amounts. [Conclusion] These findings provide valuable references for understanding composite mechanical properties， optimizing tunnel construction， and guiding post-fire evaluation and repair strategies for tunnel infrastructure.

[Objective] To address the stability issues of rock ridges during the blasting demolition of the large cofferdam for the unit expansion project at Wuqiangxi Hydropower Station， this study proposes an optimized blasting scheme， aiming to prevent the sliding instability of the remaining thin rock ridge after layered blasting under the influence of fracture seepage. [Method] A discrete fracture seepage-stress coupling model was employed to evaluate the excavation sequence， slope height-to-width ratios， and seepage stability of the downstream slope of the rock ridge. The stability of the rock ridge under various blasting schemes and slope height-to-width ratios was analyzed considering fracture seepage. By integrating safety factors and failure slip modes， the optimal blasting sequence and a reasonable downstream slope height-to-width ratio were determined， providing precursor information on potential failure modes of bedded rock masses under seepage conditions. [Result] （1） Based on the engineering characteristics and blasting challenges， a demolition design for the intake cofferdam was formulated： blasting the outer earth-rock cofferdam during the dry season， thinning the inner side of the cofferdam， removing the top concrete cofferdam， and blasting the remaining rock ridge in a single pass. This scheme prevents the instability of the remaining thin bedded rock ridge under fracture seepage while minimizing risks to existing structures. （2） At slope height-to-width ratios of 1∶0， 1∶0.3， and 1∶0.5， the failure mode was global， with failure boundaries comprising a composite slip surface of the concrete-rock interface， weak interlayers， and bedding planes. At ratios of 1∶0.7， 1∶0.9， 1∶1.1， and 1∶1.3， the failure mode transitioned to local bedding slip instability. As the ratio increased， the tensile failure boundary at the trailing edge moved further from the toe of the excavated slope， and the thickness of the unstable rock layer decreased， indicating an evolution toward shallow bedding slip failure. [Conclusion] Considering both the safety factor and the failure slip mode， a slope height-to-width ratio of 1∶0.7 was determined to be optimal for the downstream slope excavation， as the safety factor exceeded 1 and the failure mode transitioned from global to local. The proposed scheme effectively controls the deformation and instability risks of the reserved thin-walled rock ridge. These findings provide valuable references for the demolition of large cofferdams and the stability evaluation of rock ridges under fracture seepage conditions.

[Objective] Based on suction-controlled triaxial isotropic compression tests on compacted loess， this study establishes a soil-water characteristic curve （SWCC） and hydraulic conductivity prediction model that accounts for compression deformation. This work aims to provide an accurate and convenient method for predicting the SWCC and hydraulic conductivity of compacted loess under compressive deformation， facilitating seepage analysis in loess embankment engineering. [Method] This study takes the Q₂ compacted loess samples from the Phase I Project of mountain flattening and city construction in Yan’an New Area as the research object. Four sets of isotropic compression tests under different constant suctions （y=25， 37， 50， 100 kPa） were conducted by using a GDS unsaturated triaxial apparatus. Building upon the test findings， a power function related to the void ratio is introduced into the four-parameter Fredlund-Xing model to establish a SWCC model considering compressive deformation. The model has fewer parameters， requiring only 7 parameters； the tests are simple， as the model parameters can be obtained only through suction-controlled compression tests and saturated permeability tests； （3） the model also considers the influence of adsorbed water on the hydraulic conductivity. The proposed model is applied to predict the SWCC and hydraulic conductivity curve of Yan’an compacted loess within a wide suction range， and the predicted results are compared with measured test data. [Results] （1） Compressive deformation causes a significant mechanical wetting effect， specifically manifested as follows： a. during the constant suction loading process， the degree of saturation of the samples increases significantly with the development of compressive deformation； b. in the process of compressive deformation， the SWCC of the samples shifts overall to the right as the void ratio decreases， and the air entry value increases significantly. （2） The proposed model can accurately predict the SWCC and hydraulic conductivity of compacted loess under any void ratio within a wide suction range， and its prediction accuracy in the high suction range is significantly higher than that of the Gallipoli model and the CCG model. In addition， the proposed model is used to predict the influence of compressive deformation. During compressive deformation process， as void ratio decreases， the soil-water characteristic curve of compacted loess gradually shifts to the upper right， and the air entry value increases significantly. In the low suction range， the hydraulic conductivity of compacted loess decreases with the decrease of void ratio， while in the medium and high suction ranges， the hydraulic conductivity increases with the decrease of void ratio. The response of the hydraulic conductivity of compacted loess to compressive deformation is essentially caused by the change of the cross-sectional area of water flow and flow paths due to the change of micro-pores. [Conclusion] The proposed model provides a reliable tool for understanding the soil-water characteristics and permeability behavior of compacted loess under compressive deformation. It not only improves the accuracy of seepage analysis in loess filling projects but also provides a theoretical basis for evaluating the stability and safety of engineering structures built on compacted loess.

[Objective] In typical plain tidal river networks at the Yangtze River Delta front， dense waterways and frequent navigation significantly impact levee safety through channel operations and bed scour. Focusing on two typical levee structural types along the Huangpu River and its main tributaries， this study investigates the scour response under the coupling of structural dimensions and scour depth. The findings aim to provide a scientific basis for accurately identifying high-risk bank sections， optimizing bank protection structures， and enhancing the targeted management of levee engineering in tidal navigable rivers. [Methods] To examine the scour resistance sensitivity and its variation of levee structures in tidal navigable rivers， the theoretical scour depth was calculated based on the actual operating conditions of a navigable tributary in the upper Huangpu River. Using these calculated values as a reference， finite element models were developed to analyze the displacement responses of gravity-type and pile-founded levees under coupled conditions of varying structural dimensions and scour depths. This approach allowed for the determination of the scour resistance sensitivity and evolutionary trends for different levee structural types. [Results] The scour resistance sensitivity of gravity-type levees is primarily influenced by the base slab width and embedment depth. When the base slab width is <4 m or the embedment depth is <2 m， a toe scour 0.5-1.0 m triggers a sharp increase in the displacement rate at the wall top. Conversely， when the base slab width exceeds 5 m or the embedment depth exceeds 2 m， further increasing the dimensions yields significantly diminishing returns in scour resistance. The scour resistance sensitivity of pile-founded levees is mainly governed by the pile length. When the pile length is <15 m， the displacement growth rate accelerates markedly once the scour depth 1.0-1.5 m. Beyond a pile length of 15 m， the effectiveness of increasing pile length to enhance scour resistance weakens. [Conclusion] （1）The sensitivity of different structural types to toe scour must be fully considered during the selection and sizing of levee structures in tidal navigable rivers. Under the given typical boundary conditions， the scour resistance sensitivity increases with the base slab width， embedment depth， and pile length. However， beyond certain thresholds， the marginal gain in sensitivity decreases， making it economically inefficient to further improve scour resistance solely by enlarging structural dimensions. Instead， altering the structural type or controlling the scour depth is recommended to enhance levee safety. （2）For the design of gravity-type levees， it is advisable to maintain a base slab width of ≥4 m and an embedment depth of ≥3 m. If the anticipated scour depth exceeds 1 m， gravity-type structures are not recommended. For existing gravity levees， the impact of scour should be mitigated through strengthened vessel traffic management and the installation of protective structures. （3）For the design of pile-founded levees， the pile length should be controlled at ≥15 m. When the anticipated scour depth reaches 1 m， measures such as enhanced vessel traffic management and protective structures should be implemented to reduce scour impacts. The proposed structural dimensions and structural adaptability under varying scour conditions provide a scientific basis for the design and management of levees in tidal navigable rivers.

With the increasing internationalization of geotechnical engineering projects in China and the growth of international engineering cooperation， the demand for referencing and applying foreign technical standards in engineering practice is growing. As a widely used in-situ testing method， the technical requirements and application of plate load test （PLT） results vary across different standard systems. To facilitate international engineering practice and standard alignment， this paper provides a comparative analysis of the similarities and differences between current domestic and foreign PLT standards from three aspects： standard systems， testing methods， and data interpretation. The analysis reveals the following：（1） In terms of standard systems， foreign standards typically focus on specific fields by proposing mandatory provisions and technical requirements， featuring a relatively concise structure. （2） Regarding testing methods， foreign standards are primarily principle-based and guidance-oriented， imposing higher requirements on engineers to conduct tests based on actual field conditions. （3） In data interpretation， domestic standards usually determine the allowable bearing capacity directly from the load-settlement curve. In contrast， foreign standards derive the allowable bearing capacity by back-calculating strength parameters under specific conditions and applying ultimate bearing capacity theories. This study provides a valuable reference for conducting PLTs and analyzing results under foreign standard frameworks.

[Objective] The Bishan-Tongliang Line is an east-west municipal express railway in the suburbs of Chongqing， aimed at promoting rapid development in the western Chongqing area. During the construction of the Yunwu Mountain Tunnel—a critical control project—a sudden water inrush occurred in the adit. This study aims to accurately identify the causes of the water inrush， providing a scientific basis and technical support for waterproofing measures during construction and the identification of water inrush sources in similar tunnel projects. [Method] Taking the water inrush in this tunnel as a case study， potential water-conducting channels were analyzed based on a comprehensive review of regional engineering geology， hydrogeological characteristics， and the features of the adit water inrush. Through laboratory and field tests， as well as physical and chemical analysis methods， the differences and correlations between water samples from regional aquifer channels and the inrush water were investigated to achieve accurate and efficient identification of the water inrush source. [Result] The regional groundwater primarily consists of red bed fissure water， detrital rock pore-fissure water， and carbonate karst water. Potential sources of the adit water inrush include surface water leakage， bedrock fissure water， water accumulated in mined-out coal areas， water inrush from water-conducting faults， and karst water. Through a comprehensive multi-factor analysis combining field investigations， physical methods， and chemical methods， it was identified that the water inrush originated from confined fissure water in sandstone strata interbedded within impermeable shale， supplemented by reservoir water recharged through water-conducting faults. [Conclusion] This study provides a universal methodology for identifying water inrush sources in tunnel engineering under complex geological conditions. This approach involves predicting potential water inrush factors by integrating regional engineering and hydrogeological characteristics， followed by systematic investigation and comparative analysis of each factor using field surveys， physical methods， and chemical methods to accurately and effectively identify the source of tunnel water inrush.

[Objective] The particle size distribution of fine-grained loess is a key indicator for evaluating its engineering mechanical properties. The traditional hydrometer method is limited by theoretical assumptions, experimental procedures, and dispersion effects, leading to insufficient measurement accuracy and long testing periods, which makes it difficult to meet the requirements for precise determination of particle size distribution of fine-grained soil. To address these issues, this study takes fine-grained loess from Lanzhou, Gansu Province, as the research object, and proposes a wet sieving test method suitable for fine-grained soil by modifying standard test sieves and using nylon filter cloth as a fine sieve medium. The study systematically investigates the determination of key test parameters and micromorphology. [Methods] After modifying the standard test sieves, multiple comparative tests were conducted focusing on key indicators including soil mass, water volume, test duration, and soil mass loss rate. Scanning electron microscopy (SEM) was employed to observe the micromorphology of particles in different size groups after separation. On this basis, comparative tests between the wet sieving method and the hydrometer method were conducted under conditions of full gradation and single-particle-size groups. [Results] The test results of key indicators determined the optimal test parameters as 30 g of soil and 4 000 mL of water. The duration of a single test was approximately 12 h, with the soil mass loss rate stably controlled within 3%. In contrast, the hydrometer method required approximately 48 h, indicating a fourfold improvement in efficiency. SEM results showed that the wet sieving method could achieve physical separation of fine-grained loess particles. The short-axis dimension of particles was identified as the key parameter controlling the sieving process. A high proportion of particles in the corresponding size groups after separation verified the reliability of the method. Comparative test results showed that the contents of clay and colloidal particles measured by the wet sieving method were significantly higher than those obtained by the hydrometer method, indicating that the traditional hydrometer method markedly underestimated the content of particles smaller than 0.005 mm in fine-grained loess. Further tests on single-particle-size groups confirmed that the hydrometer method exhibited large deviations in particle size determination for fine fractions, whereas the proposed method could directly and accurately reflect the particle size distribution. [Conclusion] This study indicates that the modified wet sieving method based on nylon filter cloth can accurately determine the particle size distribution of fine-grained loess and effectively compensate for the limitations of the traditional hydrometer method in fine particle testing. This method provides reliable technical support and experimental basis for precise geotechnical testing, engineering disaster prevention, and structural safety assessment in loess regions.

[Objective] Among numerical simulation methods for blasting fragmentation, the continuous medium simulation method has high efficiency, but its mechanical mechanisms are not rigorous and errors are significant when dealing with discontinuous problems; the discontinuous deformation analysis (DDA) method performs well for discontinuous problems, but when the fragment size becomes too small, excessively long computation time and non-convergence are likely to occur. This study aims to propose a numerical simulation method for blasting fragmentation that considers both computational efficiency and mechanical rationality. [Methods] Field tests were conducted to reveal the formation characteristics of blasting fragmentation, and the necessity of selecting appropriate numerical simulation methods for different fragment size ranges of blasting fragmentation was clarified. A continuous-discontinuous numerical simulation method for blasting fragmentation based on LS-DYNA+DDA coupling was proposed. In the near-field region of the blast hole, a continuous medium numerical simulation based on LS-DYNA was used to improve the computational efficiency of the crushing zone. In the middle- and far-field regions, a discontinuous method based on DDA was used to achieve discontinuous characterization of blasting fragmentation. The accuracy of using stress and velocity components as coupling parameters was compared. Finally, the LS-DYNA+DDA coupling method was validated based on the mining and blasting practice of Zhoushan Green Petrochemical Mine. [Results] Through field experiments and numerical simulation, it was determined that small-sized fragments were mainly concentrated within a very small range near the blast hole. The continuous medium method could efficiently simulate the distribution of small-sized fragments while ensuring accuracy. It was more reasonable to use DDA method to simulate the fragmentation of medium- and large-sized fragments. Using peak velocity as the coupling parameter between different methods could reduce the pressure loss during computation transmission. [Conclusion] Based on the measured results, comparison and validation between existing numerical simulation methods and the proposed LS-DYNA+DDA coupling method show that the proposed method improves the accuracy of blasting fragmentation prediction and has advantages in balancing the mechanical rationality of fragmentation mechanisms and computational efficiency. However, this method is currently applied in limited engineering scenarios, and its prediction efficiency needs further summary and optimization for different lithologies and blasting parameters.

[Objective] Research on predicting the hydraulic conductivity of cohesive soils is relatively lacking. The classical Kozeny-Carman equation provides an effective method for estimating the hydraulic conductivity of coarse-grained soils, but it performs poorly in predicting the hydraulic conductivity of cohesive soils. This study aims to improve the Kozeny-Carman equation and establish a method for calculating the hydraulic conductivity of cohesive soils. [Methods] We first constructed a relationship between bound water content and liquid limit (LL) in cohesive soils using statistical methods based on their correlation analysis. With this relationship as a bridge, we established a correlation between the total void ratio and the effective void ratio of the soil. Accordingly, the Kozeny-Carman equation was modified to develop a method for calculating the hydraulic conductivity of cohesive soils. Considering that parameter C in the modified equation was difficult to obtain in engineering practice, we developed a calculation model for specific surface area of cohesive soils, incorporating bound water, free water, and soil particles, in order to establish an engineering-friendly equation. A semi-empirical equation relating the specific surface area (S_s) of soil particles to liquid limit was derived, leading to a formula that calculated parameter C based on specific surface area. Data of 105 cohesive soils from published literature were employed to calculate hydraulic conductivity using both the original and modified equations, and the results were compared with measured values. After predicting the saturated hydraulic conductivity of cohesive soils using the improved model, we further evaluated the model’s predictive performance using two error metrics: Mean Absolute Error (MAE) and Root Mean Square Error (RMSE). Subsequently, the sensitivity of each input parameter was analyzed using the cosine amplitude method. Finally, the influence of the main clay mineral types and the order of magnitude of the measured hydraulic conductivity values on the model’s predictive performance was analyzed. [Results] (1) As the water content increased in cohesive soils, the hydration of clay minerals proceeded sequentially through tightly bound water, loosely bound water, and free water phases. A strong linear correlation existed between the ineffective void ratio and the logarithm of liquid limit (lgLL), with a coefficient of determination (R²) of 0.98. A discernible linear correlation was observed between the reciprocal of specific surface area (1/S_s) and the reciprocal of liquid limit (1/LL), with R²=0.83. Parameter C in the Kozeny-Carman equation exhibited a power-law relationship with soil specific surface area, with R²=0.85. The prediction reliability of the classical Kozeny-Carman equation was 56.2%, while that of the improved equation achieved 81.9%, representing a 25.7% improvement in accuracy. However, predictions exhibited divergence, primarily due to the heterogeneity of the experimental data sources, the error propagation from the indirect estimation of specific surface area data, and the fact that the improved formula relied solely on void ratio and liquid limit, potentially neglecting factors like particle size distribution and pore channel tortuosity. (2) Sensitivity analysis revealed that both void ratio and liquid limit were the primary parameters affecting the prediction accuracy of hydraulic conductivity. The model’s performance metrics for the database were MAE=0.29 and RMSE=0.36. For kaolinite-dominated clay, prediction reliability reached 72.4% (MAE=0.29, RMSE=0.38); that of montmorillonite-dominated clay achieved 94.4% (MAE=0.30, RMSE=0.32); and that of illite-dominated clay showed 77.8% (MAE=0.35, RMSE=0.38). Overall, the type of clay mineral had little influence on model performance. When the measured hydraulic conductivity value was within the 10^-9 m/s order of magnitude, the prediction reliability was 88.2% (MAE=0.24, RMSE=0.29);when it was within the 10^-10 m/s order of magnitude,the prediction reliability was 93.3% (MAE=0.20,RMSE=0.25);when it was within the 10^-11 m/s order of magnitude, the prediction reliability was 65.9% (MAE=0.42,RMSE=0.47). [Conclusion] These results show that the prediction reliability of hydraulic conductivity at the 10^-11 m/s order of magnitude is significantly lower than at the 10^-9 and 10^-10 m/s order of magnitude, with the errors and divergence much higher for the 10^-11 m/s order of magnitude. Therefore, the magnitude of hydraulic conductivity has a great impact on model performance, and the model has better applicability for predictions within the 10^-9 to 10^-10 m/s order of magnitude. The modified Kozeny-Carman equation proposed in this study provides a reliable theoretical reference for estimating the hydraulic conductivity of cohesive soils in geotechnical engineering practice.

[Objective] This study aims to investigate the mechanical softening behavior of cataclastic granite under different in-situ stress conditions through true triaxial compression tests, thereby providing an experimental basis and theoretical references for the safe construction and long-term stability assessment of deep soft rock engineering. [Methods] Using the self-developed TAXW-5000 multi-field coupled true triaxial simulation system, true triaxial compression tests on cataclastic granite under different minimum principal stresses (σ₃) were conducted for the first time. The effects of the minimum principal stress on the mechanical response, post-peak softening behavior, and shear-dilation characteristics were systematically analyzed.Furthermore, in combination with 3D-CT scanning technology, the internal crack structures of the failed specimens were extracted and reconstructed, revealing the spatial distribution characteristics of the cracks. The damage evolution patterns of cataclastic granite under different in-situ stress environments were discussed. [Results] As the minimum principal stress (σ₃) increased from 1 MPa to 10 MPa, the peak stress of the cataclastic granite rose from 48.98 MPa to 80.42 MPa, and the residual stress increased from 27.17 MPa to 75.67 MPa. Meanwhile, the softening modulus decreased from 25.67 GPa to 4.81 GPa. During the softening stage, the shear-dilation coefficient decreased from 1.37 to 0.21 with increasing σ₃. In the residual stage, the shear-dilation coefficient first increased and then decreased with higher σ₃, reaching a maximum value of 1.21 at σ₃=5 MPa. CT scanning results indicated that a lower σ₃ led to a greater number and larger apertures of internal cracks in the failed specimens. The damage factor, calculated based on crack statistics, decreased from 0.29 to 0.12 as σ₃ increased from 1 MPa to 10 MPa. [Conclusion] With an increase in the minimum principal stress (σ₃), the softening modulus of cataclastic granite shows a negative correlation with σ₃. The shear-dilation coefficient in the residual stage is relatively high overall and exhibits a trend of first increasing and then decreasing with rising σ₃. In contrast, the shear-dilation coefficient in the softening stage decreases significantly, indicating a transition in the rock deformation mechanism from brittle to ductile failure. A higher σ₃ environment leads to more pronounced softening behavior in cataclastic granite, resulting in a lower degree of crack development and lower damage levels after failure, thereby enhancing the overall engineering stability.

[Objective] The non-filter membrane straw drainage body (NSD) offers significant advantages in vacuum preloading treatment of dredged sludge, such as eliminating the need for filter membranes and preventing clogging, making it a promising solution for practical applications. However, the permeability characteristics and pore structure of the straw filter layer are not yet well understood, which limits its widespread adoption. [Methods] Laboratory permeability tests were conducted to investigate the variation in the permeability coefficient of the non-filter membrane straw drainage body with vacuum preloading time, filter layer thickness, and the initial water content of the dredged sludge. CT scanning was also used to further explore the influence of pore structure evolution under different treatment conditions on the permeability characteristics. [Results] (1) Initially, the NSD contained vertically and horizontally interconnected fissure drainage channels, and these channels formed a continuous seepage network through the connection of pores, which endowed the NSD with superior permeability. The voids occupied 31.42% of the total volume of the NSD, and the volume of fissure structures was 14 times greater than that of the pore structures. (2) The permeability performance of the straw filter layer was superior to that of conventional geotextile filter membranes. The permeability coefficient of the NSD-Reverse (NSD-R) filtration system decreased rapidly and then stabilized with increasing vacuum preloading time, ultimately reaching a stable value on the order of 10^-5 cm/s after 30 minutes, which was one order of magnitude higher than that of the reverse filtration system using geotextile filter membranes for clay (around 10^-6 cm/s). An increase in the filter layer thickness led to a decrease in the permeability coefficient of the filtration system, while a higher initial water content of the dredged sludge corresponded to a larger permeability coefficient of the NSD-R filtration system. (3) As vacuum preloading time increased, the pore structure of the straw filter layer in the NSD-R filtration system evolved. With the increase in preloading time, the porosity of the NSD filter layer decreased rapidly, with the proportion of centimeter-scale fissure structures significantly reduced, effectively blocking the continuous migration of fine particles. Subsequently, the proportion of millimeter-scale pore structures increased, enhancing soil retention while ensuring water permeability, thereby achieving a balance between soil retention and water permeability. [Conclusion] These findings provide theoretical support for the engineering application of NSD in environmentally sustainable stabilization of dredged sludge.

[Objective] The soil water characteristic curve (SWCC) can effectively reflect the relationship between soil water suction (matric potential) and water content, yet conventional testing methods pose challenges for the calibration of in situ soil hydraulic parameters. A more convenient, economical and reliable in situ testing approach is required for the rapid evaluation of in situ soil water status and hydraulic characteristics. [Methods] This study integrated soil dielectric theory with a soil water characteristic curve model and, by considering clay mineral composition, bound water, and free water, derived and established an evaluation model for the soil equivalent dielectric constant-matric suction characteristic curve (SEDCC). For model verification, remolded red clay samples with an average dry density of 1.2 g/cm³ were prepared from six regions of Yunnan Province. The prediction accuracy of the SEDCC curves for red clay across different regions was then systematically analyzed, and the feasibility of indirectly evaluating the SWCC of red clay using dielectric theory parameters of electromagnetic waves was further discussed. [Results] The results showed that the water retention characteristics of red clay were influenced by formation conditions, mineral composition, pore structure, and climatic environment, resulting in regional differences in the fitting accuracy of the Fredlund model. Volumetric water content was the key factor driving changes in matric suction and the equivalent dielectric constant. Using volumetric water content as a bridge, the equivalent dielectric constant gradually decreased as matric suction increased. By fitting the correlation between the equivalent dielectric constant and matric suction using the SEDCC model, the fitting accuracy of the SEDCC model in all regions was greater than 95%. An approximately symmetric relationship was observed between the matric suction inversion curve of red clay and the dielectric theory prediction curve. However, this relationship was still influenced by regional differences. By comparing the predicted values from the dielectric theory inversion curve with the measured values obtained by the filter paper method, it was found that the change trends of the soil water characteristic curves derived from the two were basically consistent, with an average relative error of 6.42%. [Conclusion] Therefore, the SEDCC curve proposed based on dielectric theory can fully reflect the coupling relationship between the soil equivalent dielectric constant and matric suction, indicating that the equivalent dielectric constant is a feasible indirect indicator for evaluating matric suction in red clay. Compared with traditional methods, this model is efficient, convenient, and nondestructive, and it shows potential for indirectly inverting the soil water characteristic curve using dielectric theory, thereby providing a convenient approach as well as theoretical model support and reference for the rapid and accurate detection of soil hydraulic parameters using electromagnetic wave techniques.

[Objective] The integrated support structure of precast piles with dentiform curtains can effectively reduce the earth pressure acting on the support structure and enhance its overall performance. This study aims to quantitatively analyze the load-reduction characteristics of the dentiform walls in this structure, reveal the key mechanisms of load reduction, and provide a theoretical reference for the design and calculation of this novel composite support technology. [Methods] Based on the load-reduction mechanisms of the dentiform walls in an integrated support system of precast piles with curtains, a cycloidal slip surface conforming to the actual sliding failure mode of the soil behind the walls was introduced. A calculation method for the load-reduction effect of the dentiform walls under soil sliding conditions was developed using the horizontal thin-layer differential theory. Based on the validation through calculation examples, the impact of key parameters—including dentiform wall structural parameters (spacing, width, thickness), soil strength parameters (cohesion, internal friction angle), and soil-wall interface strength parameters (soil-wall cohesion, soil-wall external friction angle)—on the load-reduction effect of earth pressure was further analyzed. [Results] When the dentiform wall spacing decreased from 3 m to 1.2 m, the load-reduction ratio increased from 23.77% to 44.02%. When the dentiform wall width increased from 0.5 m to 3 m, the load-reduction ratio increased from 17.16% to 46.34%. When the dentiform wall thickness increased from 0.4 m to 1.0 m, the load-reduction ratio only increased from 32.66% to 36.66%. When soil cohesion (c) increased from 1 kPa to 16 kPa, the load-reduction ratio increased from 28.14% to 59.86%. When the soil internal friction angle increased from 16° to 31°, the load-reduction ratio increased from 20.43% to 42.68%. When the soil-wall interface cohesion (c₁) increased from 0.6 kPa to 9.6 kPa, the load-reduction ratio increased from 27.41% to 50.41%. When the soil-wall interface external friction angle increased from 9.6° to 18.6°, the load-reduction ratio increased from 30.33% to 36.21%, with the rate of increase gradually slowing down. [Conclusion] The developed calculation method effectively solves the problem that earth pressure is difficult to quantitatively analyze when the integrated support system of precast piles with curtains has dentiform walls. The dentiform walls exhibit a significant load-reduction effect, with the load-reduction ratio of earth pressure from the sliding soil behind the walls reaching over 50%. Decreasing the dentiform wall spacing and increasing its width can both significantly enhance the load-reduction effect. Since the walls have a certain width, the contact area between the back of the dentiform walls and the sliding soil mass is limited, and increasing the wall thickness does not lead to a notable improvement in the load-reduction effect. Increases in both the cohesion and internal friction angle of the soil behind the walls can significantly raise the load-reduction ratio of the dentiform walls. Therefore, on sites with better soil conditions, adding dentiform walls is more beneficial for improving the performance of integrated support of precast piles with curtains. The increase in the strength of the soil-wall interface also contributes to a higher load-reduction ratio of the dentiform walls, but the increase in soil-wall cohesion has a relatively more significant impact.

[Objective] To investigate the drag reduction effect of residual layers in periodic debris flows, we quantitatively revealed the amplification effect of the impact of subsequent waves due to the presence of residual layers. We propose evaluation indicators centered on the impact force ratio F^* (amplification of subsequent wave impact relative to the first wave) and the momentum ratio R (amplification of total momentum flux relative to the head momentum flux), aiming to elucidate the dynamic mechanisms responsible for the increased destructiveness of subsequent waves. [Methods] Using a mesoscale flume, we examined debris flows with three different solid contents (40%, 50%, and 60%). Sensors measured flow height, normal stress, shear stress, and pore water pressure. Considering that the movement of subsequent waves over residual layers can be approximated as quasi-steady hydraulic jumps, we calculated unit width impact forces from post-jump velocities and water depths based on momentum conservation. Dimensionless indicators F^* and R were constructed to quantify the amplification effects of multi-wave impacts and intra-wave momentum due to residual layers. [Results] (1) Higher solid content resulted in thicker residual layers, which tended toward a quasi-equilibrium state of erosion and deposition under multiple wave actions. (2) The presence of residual layers altered the flow regime of subsequent waves, with the initial wave typically exhibiting the highest Froude number (Fr). Subsequent waves showed an overall decrease in Fr, indicating a shift from inertia-dominated to gravity-dominated flow control. Increased solid content significantly reduced liquefaction and mobility, as indicated by decreased liquefaction degree λ with increasing solid content, suggesting enhanced effective stress and reduced fluidity. This change influenced the interaction intensity between subsequent waves and residual layers. (3) Residual layers significantly amplified the impact forces of subsequent waves, showing an “increase then stabilize” trend. Under all solid contents tested, impact forces generally exhibited a “rapid increase followed by stabilization”, consistent with the thickening and stabilization process of residual layers. Impact force ratios F^* were greater than 1 for subsequent waves, indicating amplified peak impact forces under identical release conditions. (4) Momentum analysis revealed that R stabilized in later waves, aligning with the trend of F^*. As R>1 indicated total momentum flux exceeding head momentum flux, the share of momentum carried by thicker residual layers drove stronger impacts of subsequent waves, especially pronounced under higher solid contents and thicker residual layers. [Conclusion] (1) In periodic debris flows, the formation and stabilization of residual layers constitute the primary processes leading to enhanced destructiveness of subsequent waves. Even if release conditions are identical for each wave, significant increases in impact loads can occur due to residual layer influences. (2) The indicator system F^* (for comparing external manifestations across waves) and R (characterizing internal momentum distribution within a single debris flow wave) provides a concise assessment framework with clear physical meanings: residual layers amplify impacts by contributing “hidden momentum”, thereby influencing destructiveness amplification. (3) Engineering practices focusing solely on the first wave’s impact for protective structure verification may underestimate the destructiveness amplification effects of multi-wave events. It is recommended to consider the influence of residual layers in designing check dam scales, dam heights, and safety factors.

[Objective] This study aims to propose a new grouting technology to effectively solve the anti-seepage problem of fully-strongly weathered granite strata by optimizing grouting technology and material mix proportion, and to investigate the anti-seepage effects of frequency-pressure grouting technology in such strata. [Methods] An anti-seepage project of fully-strongly weathered granite strata in the upper reservoir of a pumped-storage power station under construction was taken as the research object. An equilateral triangle hole layout was adopted, and five groups of grouting tests (A, B, C, D, E) were conducted sequentially in Ⅰ, Ⅱ, and Ⅲ holes. The influences of grouting technologies (constant-pressure grouting and frequency-pressure grouting), grouting hole spacing (60, 120, 180 cm), and grouting materials (pure cement slurry and cement-bentonite mixed slurry with five water-to-cement ratios of 5∶1, 3∶1, 2∶1, 1∶1, and 0.5∶1) on the anti-seepage effects of grouting in such strata were compared and analyzed. The grouting effects were further evaluated using permeability tests, single-hole ultrasonic tests, single-hole shear wave velocity tests, and borehole color television tests. [Results] Field grouting trials demonstrated that frequency-pressure grouting technology significantly optimized the grouting effect of fully-strongly weathered granite strata through dynamic pressure adaptation and precise flow control, and it was superior to traditional constant-pressure grouting in terms of permeability coefficient control, material cost efficiency, and fracture filling integrity. Cement-bentonite mixed slurry had better controllability than pure cement slurry, especially in addressing leakage during grouting, and it also greatly reduced the large grout consumption caused by grout leakage and the extended construction period caused by multiple waiting times for grout to set. For fully-strongly weathered granite strata with low strength and loose soil, water pressure tests could not be completed, and only water injection tests were conducted to assess permeability before and after grouting. Single-hole shear wave velocity tests could reflect the density of strata before and after grouting to some extent. Grouting spacing in the range of 60-180 cm had no significant effect on the grouting outcomes, whereas the use of frequency-pressure grouting technology effectively improved the compactness of strata and notably increased shear wave velocity. After frequency-pressure grouting treatment, the permeability coefficient of fully-strongly weathered granite strata decreased from the order of magnitude of 10^-3 to 10^-5, indicating a great improvement in anti-seepage capacity. This demonstrated the feasibility of applying frequency-pressure grouting technology for anti-seepage treatment of fully-strongly weathered granite strata, and it could partially or completely replace the traditional cut-off wall scheme, thereby simplifying anti-seepage treatment, reducing construction cost, and minimizing strata excavation. [Conclusion] Compared with traditional grouting methods, frequency-pressure grouting can smoothly adjust grouting pressure and inflow rate according to the characteristics of the grouted strata and real-time grouting feedback, which can avoid excessive fracturing of low-strength strata, uncontrolled grout diffusion, and excessive grout consumption. This technology can be applied to anti-seepage treatment of fully-strongly weathered granite strata. Combined with cement-bentonite mixed slurry, this technology can effectively solve problems such as grout leakage and excessive grout consumption encountered with traditional grouting methods.

[Objective] This study focuses on water content as the key controlling factor to clarify the time-dependent patterns of thixotropic strength recovery of Zhanjiang Formation structural clay under different initial water contents. The microscopic mechanism is interpreted through three pathways: pore structure evolution, particle reorganization, and water action. The findings are expected to provide experimental evidence and theoretical support for predicting strength recovery and evaluating the stability of thixotropic clay foundations. [Methods] Remolded Zhanjiang Formation structural clay specimens were prepared and subjected to a 150-day thixotropy test. Specimens at different thixotropic durations were investigated using macroscopic and microscopic tests. For macromechanical testing, unconfined compressive strength (UCS) tests were conducted on cylindrical specimens. Direct shear tests were conducted on ring-knife specimens to obtain UCS, cohesion (c), and internal friction angle (φ), which were used to evaluate thixotropic evolution. A thixotropic strength ratio was defined as A_t = m_t/m₀, and two indicators—A_t(q) (based on UCS) and A_t(τ) (based on cohesion)—were used to compare recovery characteristics among different strength parameters. For microstructure, fabric evolution was observed using an SEM. Pore parameters, including porosity (M) and abundance (C), were extracted to quantitatively analyze pore structure evolution. Particle parameters, namely probability entropy (H) and distribution fractal dimension (D), were used to quantitatively characterize particle orientation/orderliness and aggregation degree, respectively. [Results] (1) Stage-dependent recovery: Both UCS and cohesion (c) increased with thixotropic duration and showed two stages: a rapid and significant recovery phase during 0-30 d, followed by a slower, stable phase during 30-150 d. The increment during 100-150 d was small, indicating near-stabilization, after which the test was terminated. (2) Dual effect of water content: At the same thixotropic duration, UCS generally decreased with increasing water content, reflecting weakened particle contacts and bonding and thus reduced instantaneous strength. However, higher water content resulted in a faster strength recovery rate, especially at early stage, indicating that water promoted the kinetics of self-adaptive structural adjustment during thixotropic process. (3) Indicator-dependent differences: Cohesion exhibited a higher thixotropic strength ratio and faster recovery within 1 d, suggesting that shearing promoted directional particle alignment and optimized the friction-bonding interface, making c more sensitive to structural rebuilding than UCS. (4) Coordinated micro-parameter evolution: As thixotropic duration increased, M and c decreased continuously. Pores shifted from “large and numerous inter-aggregate pores” to “small and fewer intra-aggregate pores”, while the overall pore shapes remained mainly quasi-equant but became denser. Additionally, H and D decreased synchronously, indicating enhanced particle orientation/orderliness and increased aggregation. These changes were most significant within the first 30 d, consistent with the rapid macroscopic recovery stage. SEM observations revealed a transition from an “open flocculated-dispersed” fabric to a “closed flocculated-aggregated” fabric. Pores between and within aggregates decreased, while particle contacts and continuity of force-transfer paths improved, thereby supporting strength recovery. [Conclusion] The thixotropic strength recovery of Zhanjiang Formation structural clay exhibits distinct time-stage characteristics and strong sensitivity to water content. Recovery generally progresses through a rapid phase (0-30 d) and a stable phase (30-150 d). Higher water content reduces the strength level but significantly accelerates the strength recovery rate. Cohesion exhibits a higher thixotropic strength ratio than UCS because shear-induced particle orientation facilitates more effective structural reconstruction. Microscopically, synchronous decreases in M/C and H/D indicate pore reduction, particle ordering, and aggregation densification. Water enhances particle activity by altering relative particle positions and expanding migration pathways, thereby accelerating self-adaptive adjustment and strength recovery during thixotropic process. Innovations included: (1) parallel comparison of UCS and rapid direct shear parameters within a single thixotropic framework, revealing the cohesion recovery advantage caused by shear-induced particle orientation; (2) linking the macroscopic two-stage recovery pattern with the coordinated evolution of M, c, H, and D, forming an evidence chain of “structural rearrangement—aggregation densification—strength recovery”; and (3) demonstrating that higher water content, while reducing instantaneous strength, accelerates recovery by enhancing particle mobility/activity.

[Objective] The accurate prediction of pipe roof deformation is critical for ensuring construction safety in ultra-shallow buried tunnels. Existing analytical methods frequently oversimplify the complex interaction mechanisms between the pipe roof and surrounding soil, particularly neglecting the load transfer mechanism, stress release effects during excavation, disturbance-induced soil weakening, and the time-dependent behavior of initial support systems. This study aims to develop a comprehensive theoretical framework that integrates these multiple effects into a unified model. The primary objectives include: establishing a vertical load equation that incorporates both the soil arching effect at the tunnel crown and the circumferential micro-arching effect between pipes; utilizing the Pasternak elastic foundation beam theory to simulate soil-structure interaction more accurately; introducing variable subgrade coefficients and a load release coefficient to represent stress redistribution and excavation disturbances; and ultimately formulating a reliable method for predicting pipe roof deformation under realistic construction conditions. The proposed model seeks to provide a practical and theoretically sound tool for design optimization and risk mitigation in pipe-roofed tunnel projects. [Methods] The research methodology combined theoretical derivation, numerical discretization, and empirical validation. First, the vertical load acting on the pipe roof was calculated by considering dual arching effects: the soil arching above the tunnel crown, modeled based on Terzaghi’s trap-door theory with inclined slip surfaces, and the micro-arching between adjacent pipes, with the load distribution derived assuming a parabolic arch axis between pipe contact points. The pipe roof was then modeled as an Euler-Bernoulli beam resting on a Pasternak elastic foundation, accounting for shear interaction between adjacent soil springs, offering a significant improvement over traditional Winkler-based models. To capture the construction-phase effects, the longitudinal span of the pipe roof was divided into five distinct zones: a fully enclosed support zone, an unenclosed support zone, an unsupported zone, a plastically disturbed zone, and an elastically disturbed zone, each with specific definitions of subgrade modulus and stress release rate. The governing differential equation was discretized using the finite difference method, with virtual nodes introduced to handle boundary conditions, and solved programmatically using MATLAB. The model was calibrated and validated against field monitoring data from a real-world ultra-shallow tunnel project, with additional comparative analysis against existing analytical models to demonstrate its superior performance. A detailed parametric study was conducted to evaluate the influence of the subgrade coefficient in front of the face, the excavation advance length, and the length of the unenclosed support segment. [Results] Validation against field data showed excellent agreement, with the predicted maximum deflection of 22.1 mm differing by only 5% from the measured value of 23.2 mm, confirming the model’s accuracy. The deformation curve generated by the proposed method was wider and smoother than those from existing theories, more accurately reflecting the continuous beam behavior of the pipe roof and aligning closely with monitoring results. Parametric analysis revealed that increasing the subgrade coefficient (k₀) of the soil in front of the excavation face from 10 MPa/m to 90 MPa/m significantly reduced the maximum deformation from 33 mm to 17 mm, although the marginal benefit diminished beyond 90 MPa/m. In contrast, the excavation advance length (s) had an exponential impact on deformation. Increasing s from 1.0 m to 3.0 m caused the maximum deflection to approach 160 mm, far exceeding the typical control limit of 20 mm and severely threatening face stability. The length of the unenclosed support segment (b) was found to have a negligible effect on deformation. Furthermore, the load transfer capacity of the pipe roof was observed to be highly sensitive to all three parameters under high overburden ratios (H/B). Excessive increases in k₀, s, or b under these conditions led to a significant transfer of load onto the soil in front of the face, increasing the risk of face instability. [Conclusion] This study successfully develops a multi-effect coupled analytical method for predicting pipe roof deformation in ultra-shallow buried tunnels. The integration of the soil arching effect, micro-arching effect, stress release, excavation disturbance, and support delay into a single model provides a more realistic and accurate representation of mechanical behavior than previously available methods. It emphasizes the effectiveness of improving the soil modulus in front of the tunnel face and strictly controlling the excavation advance length to manage deformation, while indicating that minimizing the unenclosed support length has limited benefits. However, the current study does not consider shear forces between differential elements, soil stiffness hardening, or small-strain behavior. Future research should incorporate these aspects to further enhance the model’s comprehensiveness and accuracy for a wider range of geotechnical conditions.

[Objective] Existing grouting theories and engineering experience are mostly based on hydrostatic or weakly flowing water conditions, making it difficult to accurately describe the diffusion and evolution characteristics of grout under dynamic water-flow environments. It is necessary to systematically reveal the diffusion mechanisms of grout in water-flowing fractures so as to provide theoretical support for grouting design under complex water inrush conditions in water-sealed caverns. In response to engineering conditions involving stable flowing water in a single fracture, this study aims to: (1) reveal the influence mechanisms of fracture geometric characteristics and construction parameters on grout diffusion behavior; (2) quantitatively analyze the controlling effects of key factors on grout diffusion distance, diffusion time, and sealing efficiency; and (3) clarify the relative importance of different influencing factors in the grouting of water-flowing fractures, thereby providing a basis for optimization of grouting parameters and construction decision-making for water-sealed caverns. [Methods] Based on the grout-water two-phase flow theory, a numerical model of grouting in a single fracture with flowing water was established using the finite element method. Variations in water flow velocity within the fracture and the driving effect of grouting pressure were comprehensively considered, and the diffusion, advection, and deposition processes of grout within the fracture were simulated. Through parametric comparative analysis, the effects of fracture aperture, fracture inclination, grouting pressure, flowing water velocity, and fracture boundary extent on the evolution of grout diffusion were systematically investigated. On this basis, a sealing efficiency index was introduced to comprehensively evaluate the grouting performance under different working conditions. [Results] Under flowing water conditions, the grout diffusion pattern, stabilization time, and final sealing performance within fractures were jointly controlled by multiple coupled factors. (1) Fracture inclination had a significant inhibiting effect on grout diffusion. As the fracture inclination increased, the coupling between the gravitational component and the flowing water direction was enhanced, causing the grout to more easily deviate along the down-dip direction. As a result, the ability of grout to migrate against the water flow was weakened, and the diffusion range was markedly restricted. (2) The time required for grout diffusion to reach a stable state increased significantly with an increase in the extent of the fracture domain, because a larger boundary extent provided a greater seepage space for grout diffusion. In contrast, increasing grouting pressure effectively accelerated the advance of the grout diffusion front and shortened the stabilization time, exhibiting a pronounced accelerating effect. (3) In terms of diffusion distance, the effective diffusion distance of grout was inversely proportional to fracture boundary extent and flowing water velocity. Higher flowing water velocity resulted in stronger scouring and transport effects on the grout, thereby reducing its retention capacity within the fracture. Conversely, increases in fracture aperture and grouting pressure facilitated the grout in overcoming water flow resistance, enabling longer diffusion distances and more sufficient fracture filling. (4) Comparative analysis of the influence degrees of various factors indicated that fracture aperture had the most significant effect on grout sealing efficiency, followed in descending order by flowing water velocity, grouting pressure, and fracture boundary extent. This demonstrated that fracture geometric characteristics and hydrodynamic conditions were the key factors controlling the success or failure of grouting under flowing water conditions. [Conclusion] Overall, in strong flowing water environments, relying solely on increasing grouting pressure does not significantly improve grouting performance, and comprehensive design must be carried out by jointly considering fracture aperture characteristics and groundwater hydrodynamic conditions. For areas with larger fracture apertures and higher flowing water velocities, measures such as staged grouting or advance water reduction should be preferentially adopted to enhance grout retention and sealing capacity within fractures.

[Objective] This study aims to investigate the influence of super-large-diameter double-circular pipe jacking construction on the settlement deformation of underground pipelines. Taking the water quality assurance project of Tiegang-Shiyan Reservoir in Shenzhen as the background, and based on the modified Peck formula, this study uses a combination of numerical simulation and field monitoring to systematically analyze the effects of multiple factors such as pipeline burial depth, material, pipe diameter, pipe jacking spacing, and spatial position. [Methods] The variable normalization method was used to analyze the influence degree of each factor on the pipeline, and the safety performance of the pipeline was evaluated. [Results] When the jacking pipes vertically crossed under the pipeline, the induced settlement range was the smallest, indicating a relatively reasonable construction method. When the pipeline burial depth, material, or pipe diameter was changed, the stratum displacement field ultimately showed a “V”-shaped distribution. However, when the spacing between the two jacking pipes increased to 1.5 times the jacking pipe diameter (i.e., 6 m), the displacement field shape transformed into a “W”-shaped pattern, and the influence range of pipeline deformation significantly expanded. Sensitivity analysis showed that the spacing between the two jacking pipes was the most significant factor affecting pipeline settlement (sensitivity=0.54), while pipeline diameter had the least influence (sensitivity=0.06), and pipeline burial depth had a moderate influence (sensitivity=0.40). Furthermore, the safety state of the sewage pipeline was evaluated using the allowable joint rotation angle. The calculated joint rotation angle under field monitoring conditions was 0.54°, which was lower than the standard control value of 1.15°, indicating that the pipeline joints remained in a safe state during construction and did not suffer damage due to uneven settlement. [Conclusion] Currently, there is considerable research on settlement deformation of underground pipelines caused by single-line pipe jacking construction, but research on the influence of super-large-diameter double-line pipe jacking with shallow burial depth is limited. This study clarifies the influencing mechanisms of key construction parameters, providing theoretical basis and data support for engineering practices involving large-diameter pipe jacking undercrossing existing pipelines.