In response to the frequent water and sand leakage disasters caused by water-rich sandy strata in foundation pit engineering, this study utilizes a discrete-element method (DEM)-computational fluid dynamics (CFD) coupling simulation method based on a leakage incident in a deep foundation pit of Hangzhou Metro. The study investigates the deformation behavior of the stratum caused by foundation pit leakage and sand loss and proposes an empirical formula for predicting surface settlement. The results show that, first, compared to the no-flow condition, the slip region of soil particles develops more rapidly under seepage conditions, and its final extent is larger. Second, following soil particle loss, deep-layer displacement isovalues form elliptical surfaces of varying sizes. The effect of different water and sand leakage conditions on the extent of soil deformation is relatively minor. The two short semiaxes of the loosening ellipsoid are b = 0.69-0.77H and c = 0.6-0.68H. Furthermore, both water and sand leakage conditions, as well as sand loss-only conditions, exhibit a settlement trough in the surface settlement curves. At the same time step, the maximum surface settlement value Smax under water and sand leakage conditions is approximately 2-4 times that under sand-only leakage conditions. In addition, the surface settlement curve is fitted based on the Peck formula, and a simplified two-dimensional theoretical model is proposed. This model is then extended into three-dimensional space, resulting in an empirical formula that can effectively predict surface settlement. The theoretical value of the soil loss volume calculated using the formula shows a relative error of 6.5% compared to the actual value. The findings provide crucial theoretical guidance for emergency responses to water and sand leakage in foundation pits and for subsequent soil backfilling and layer compensation grouting.

Landfills are commonly employed for the disposal of solid waste; however, they pose a significant risk of groundwater contamination due to leachate. To address this concern, traditional impermeable systems composed of bentonite-sand composites are employed as liners at the base of landfills. This study investigates an alternative impermeable system featuring a composite material made from quarry stone chips and bentonite aimed at enhancing leachate containment. The primary objective is to assess the effects of varying bentonite dosage and various dry densities on the permeability performance of the stone chips-bentonite mixture. GDS permeation tests are conducted to assess the permeability performance of the soil mixture comprising stone chips and bentonite. Various dosages of bentonite (ranging from 3

To address the issue of inaccurate tunnel segmentation caused by solely relying on point cloud coordinates, this paper proposes two algorithms, GuSAC and TMatch, along with a ring-based cross-section extraction method to achieve high-precision tunnel lining segmentation and cross-section extraction. GuSAC, based on the RANSAC algorithm, introduces a minimum spanning tree to reconstruct the topological structure of the tunnel design axis. By using a sliding window, it effectively distinguishes between curved and straight sections of long tunnels while removing non-tunnel structural point clouds with normal vectors, thereby enhancing the lining boundary features and significantly improving the automation level of tunnel processing. At the same time, the TMatch algorithm, which combines cluster analysis and Gaussian Mixture Models (GMMs), achieves accurate segmentation of tunnel rings and inner ring areas and further determines the tunnel cross-section position based on this segmentation result to complete the cross-section extraction. Experimental results show that the proposed method achieves a segmentation accuracy of up to 95% on a standard tunnel point cloud dataset. Compared with traditional centerline extraction methods, the proposed cross-section extraction method does not require complex parameter settings, provides more stable positioning, and demonstrates high practicality and robustness.

Sand-bentonite mixtures are commonly used as vertical barriers to prevent contamination. However, their impermeability can be affected by dry–wet cycles. To analyze the impact of dry–wet cycles on the impermeability of sand-bentonite mixtures, this study adopts a microscopic perspective. Five experimental groups were established to investigate the effects of moisture content variations and the influence of heavy metal ions (Zn2+) on the impermeability of sand-bentonite mixtures. Permeability tests, SEM tests, and CT tests were conducted after 2, 4, 6, and 8 dry–wet cycles for each specimen. SEM images reveals that dry–wet cycles cause bending and loosening of bentonite particles, which weakens their bonding with sand particles and alters the skeletal structure, ultimately resulting in reduced impermeability. Moreover, CT analysis indicates that volumetric porosity, total pore area, total pore volume, average pore radius, and average throat radius are the main factors affecting the impermeability of sand-bentonite mixtures.

Compacted clay is often used as liner material in landfills due to its excellent impermeability. However, its poor crack resistance can lead to cracking under deformation conditions, which further impacts the impermeability of the liner. To investigate the variation in permeability performance of a liner system under deformation conditions, a model test apparatus was designed to simulate the deformation and permeability of a sand–bentonite liner system. Particle image velocimetry was used to analyse the deformation characteristics of the liner system. The experimental results showed that changes in the deformation and thickness of the liner significantly affected the permeability performance of the liner system. For the same liner thickness, an increase in the liner deformation increased the number and width of cracks in the system, leading to more seepage channels and reduced impermeability under deformation conditions. Conversely, for the same deformation, an increase in liner thickness enhanced the effective thickness of the liner, thereby improving its impermeability under deformation conditions.

Foundation pit excavation causes the deformation of adjacent tunnels,which in turn affects the safe operation of subway in tunnels.Therefore,how to accurately predict the deformation of adjacent tunnels is a problem worth studying.According to the non-limit earth pressure computational method,the earth pressure on the unloading pit wall during foundation pit excavation is calculated.With the aid of the Mindlin solution,the additional load acting on the side tunnel during the excavation stage of the foundation pit is obtained.The tunnel structure is considered as a Euler beam on the Winkler foundation beam and the differential equation of the elastic foundation beam is established.An analytical method for the horizontal displacement and deformation of the tunnel is given.Based on this method,the horizontal displacement of adjacent tunnels caused by foundation pit excavation is analyzed.The results show that the horizontal displacement of the tunnel increases with the increase of excavation depth of the foundation pit.The horizontal displacement of the tunnel calculated by considering non-limit earth pressure is relatively close to the value measured,and the overall relative error is smaller than 20％.Compared with the traditional method proposed,the author method is more practical.

The coherence of axial force between steel struts in excavation (axial force coherence) is an important factor affecting the axial force control of servo struts. To understand the law of axial force loss of adjacent struts caused by servo struts loading, this paper proposes a calculation method based on the theory of nonlimiting earth pressure. First, the diaphragm wall is simplified to a simply supported beam with both endpoints free horizontally, the soil on both sides of the diaphragm wall is divided into n small sections ( n as big as possible) along the depth direction, and the average nonlimiting earth pressure combined force within each section is calculated. Second, a system of nonlinear force-displacement equations is constructed by applying the "graph multiplication" method to calculate the combined nonlimiting soil pressure and deflection of the wall from the axial force of the servo steel strut at each level. The Newton-Raphson method is applied to obtain a recursive equation for the wall displacements. The accuracy of the method is verified by comparison with field measurements. Then, based on the method in this paper, the effect of prestressing and adjustment on the axial variation of each strut course is investigated. The method can provide a reference for the loading scheme of servo steel struts in deep excavation in soft-soil areas.

Calcareous sand, a special geotechnical material employed as foundation fill in numerous reef constructions, exhibits susceptibility to seepage deformation in complex marine dynamic environments. Its permeability characteristics are notably distinct from conventional terrestrial soil, making the understanding of these properties critical for further applications. This study conducted vertical seepage tests on coarse-grained calcareous sand samples with varying coefficients of uniformity (Cu), coefficients of curvature (Cc), relative compactions (Dr), and soil skeletal structures. These tests utilized a custom-designed apparatus, supplemented with image binarization and particle image velocimetry techniques. Based on the results, the findings revealed a three-stage vertical seepage process: steady seepage, hydraulic adjustment, and seepage failure. The permeability coefficient k20 of the calcareous sand samples was observed to transition from a decreasing to an increasing trend with rising Cu and Cc values. Moreover, the k20 of tightly compacted and medium-tightly compacted samples exceeded that during the steady seepage stage upon entering the second stage, while the opposite holds true for relatively loose samples. The spatial organization of the sample skeleton had a considerable impact on its permeability, with coarse-grained calcareous sand imposing a greater constraint on fine particle migration compared to river sand.

During the construction of tunnel mining, the surrounding rock of different fracture zones needs to be supported by steel arch frame. If the construction and design are improper, the steel arch frame may suffer deformation and compression damage, which will affect the overall quality and safety of tunnel construction. This paper analyzes the role of steel arch support in tunnel, discusses the principle of various kinds of tunnel retractable steel arch, summarizes the development and application of retractable steel arch, and puts forward the direction of further research.

根据已完成的四边不出筋密拼连接叠合双向板原位加载试验研究成果,分析了钢筋桁架叠合双向板与现浇板抗弯刚度、挠度存在差异的机理.考虑弯矩调整、裂缝分布、支座附加筋及钢筋桁架等因素引入相关挠度折减系数对既有挠度计算方法进行修正.基于ACI318有效惯性矩方法、修正ASCE方法对叠合双向板挠度进行理论计算得出,ACI318有效惯性矩方法计算结果高估了叠合双向板弹性阶段刚度,修正ASCE方法适用于弹性阶段.解析刚度法结合修正挠度计算方法可用于计算叠合双向板挠度,适用于叠合双向板弹性和塑性阶段,计算值与实测值吻合较好.通过数值模拟开展参数分析得出,叠合双向板的抗弯刚度随现浇层与预制底板厚度比值的增大而提升明显,但钢筋桁架与支座附加筋等因素的刚度增强效应会减小.

Floating piles have been widely employed as foundations in coastal regions abounding with marine clay. A growing concern for these floating piles is their long-term performance of bearing capacity. To better understand the time-dependent mechanisms behind the bearing capacity, in this paper a series of shear creep tests was conducted to study the effects of load paths/steps and roughness on shear strain of the marine clay-concrete interface. Four main empirical features were observed from the experimental results. First, the creep process of the marine clay-concrete interface can be largely decomposed into the instantaneous creep stage, the attenuation creep stage and the uniform creep stage. Second, the creep stability time and the shear creep displacement generally increase as the shear stress level increases. Third, the shear displacement rises as the number of loading steps drops under the same shear stress. The fourth feature is that under the shear stress condition, the rougher the interface is, the smaller the shear displacement is. Besides, the load-unloading shear creep tests suggest that: (a) shear creep displacement typically contains both viscoelastic and viscoplastic deformation; and (b) the proportion of unrecoverable plastic deformation increases with increasing shear stress. These tests confirm that the Nishihara model can provide a well-defined description of the shear creep behavior of marine clay-concrete interfaces.

Bentonite liners are used as a barrier system in a landfill. Their performance will degrade when exposed to heavy metals and other harmful substances. Unit cell tests are conducted to analyze the effect of Zn 2+ on the permeability characteristics of bentonite and the improvement effect of zeolite on the swelling properties of bentonite. The research results show that the addition of zeolite can improve the free swelling index of bentonite and the best effect will be achieved for a content at 12.5%. With the increase of zeolite content, the permeability of mixed soil is improved and the permeability coefficient decreases from 10 -7 cm/s to 10 -8 cm/s. For a given zeolite content, the Zn 2+ concentration increases but the permeability decreases. When zeolite is added, bentonite expands and adhere to the surface of stone filings, absorbing ions in leachate. Therefore, mixed soil has a stronger adsorption capacity and the Zn 2+ content in leachate decreases. The research results can provide reference for the design and application of landfill liner systems.

Rain infiltration is a critical factor in frequent landslides, and the existence of weak interlayers in slope rock mass controls the stability of rock mass. To reveal the effect of rainfall infiltration on the seepage characteristics and the stability of double-layer weak interlayer slopes, a numerical method is used to simulate the variations in matrix suction and moisture content of slope under different rainfall intensities and to explore the effect of number of weak interlayers and rainfall intensity on the stability of slopes. The results show that for landslide with weak interlayers under rainfall conditions, a sliding zone forms owing to poor permeability and strong water retention and great reduction in strength. Rainfall has a great influence on the matrix suction of double-layer weak interlayer slopes. The greater the rainfall intensity is, the faster the dissipation rate of matrix suction is. When the total rainfall is constant and the weak interlayer is located in the middle of the landslide, a stronger rainfall intensity, more weak intercalations, deeper weak intercalations, and a more intense slope deformation results in an easier transition from “stable” to “unstable” state of a slope.

Sleeve valve pipe grouting will cause a deformation of the surrounding soil, thus affecting the safety of adjacent structures. Based on a project in Hangzhou, the deformation variations of soil during sleeve valve grouting are studied by a field test and the relationship between the grouting parameters and the stone volume is further analyzed. The experimental results show that the horizontal deformation of the adjacent soil caused by grouting has a certain regularity. The horizontal displacement increases with the increase of grouting amount but decreases with the dissipation of pore water pressure. With the increase of distance from the grouting hole, the horizontal displacement decreases gradually. The effect of grouting depth on the horizontal displacement is small and the maximum horizontal displacement is reached near the grouting depth. The pore water pressure first increases and then decreases before and after grouting. The larger the distance from the grouting hole is, the smaller the change of pore water pressure is. After excavation, the volume of the stone body is about 30% grouting amount. The research results provide certain reference for the design and construction of sleeve valve grouting and similar projects.

Bentonite is frequently utilized as a landfill lining material due to its high impermeability. Due to the fact that heavy metal ions in leachate can alter the permeability of bentonite liner, the impermeability and metal adsorption effect of bentonite liner is typically enhanced by the use of external admixtures. In this investigation, zeolite was combined with stone chips and bentonite. Using a flexible wall permeation test, zeta potential test, and X-ray diffraction test, the effect of zeolite on the permeability and adsorption properties of the mixture was investigated. The results indicate that the addition of zeolite can enhance the impermeability of the mixed soil. The permeability coefficient of the mixed soil in DIW is 3.74 × 10−7 cm/s when bentonite is incorporated at 11% and decreases to 6.55 × 10−8, 4.65 × 10−8, and 5.10 × 10−8 cm/s when 12.50%, 25%, and 50% of zeolite are incorporated; the permeability coefficient of the mixed soil in DIW was 3.74 × 10−7 cm/s when the permeate concentration was 0.01 mol/L of ZnCl2 solution, the permeation coefficients were 5.73 × 10−7, 5.98 × 10−8, 5.8 × 10−8, and 5.7 × 10−8 cm/s when the zeolite doping was 0, 12.50, 25, or 50%, respectively, and the Zn2+ concentration of the leachate decreased compared to the no-zeolite case by 92.48, 97.29, and 98.65%, respectively; the competitive adsorption of metal ions by zeolites in ionic solutions of different concentrations reduced the ionic concentration in the solution and decreased the inhibition of bentonite swelling, while the adsorption characteristics of stone chip-bentonite-zeolite mixture on Zn2+ were measured by the Langmuir and Freundlich et al. model.

Municipal solid waste (MSW) landfills in China generally have high leachate mounds, which potentially induce severe geotechnical and environmental issues. In this study, laboratory model tests were carried out to preliminarily investigate the performance of vertical drainage wells accompanied with vacuum pumping (VDW-VP) on leachate drawdown in MSW landfills with high leachate levels. Leachate drawdown tests through VDW-VP under conditions with and without gas injection were performed. Different vacuum pressures (0~−9.5 kPa) were imposed during the tests. Results indicated that the leachate pumping processes for both the two conditions were characterized by a stage of continuous effluent followed by a stage of discontinuous effluent, corresponding to the periods before and after the leachate level in the vertical well dropped to the bottom, respectively. During the stage of continuous effluent, as the vacuum pressure increased, the effluent rate decreased and the leachate level in the vertical well needed a longer time to reach the bottom. During the stage of discontinuous effluent, the leachate level in the MSW gradually approached that in the vertical well. A higher vacuum pressure rendered a larger cumulative leachate pumping volume for the condition with a gas injection, but this was not the case for the condition without a gas injection. In addition, some local pore water pressures were observed to suddenly increase and drop under the condition with the gas injection, attributed to the migration of entrapped gas zones. The increase in vacuum pressure might promote the migration of entrapped gas zones and hence increase the cumulative leachate pumping volume.

Recently, many studies have been conducted on the stratum deformation induced by earth pressure balance (EPB) shield tunneling in soft soil and sand. Movement laws vary largely among different strata. However, at present, relevant research mainly focuses on soft soil and sand, whereas little attention has been paid to the movement law of round gravel stratum with higher instability. In this study, a field monitoring test was carried out on the EPB shield machine when it passes through the round gravel stratum. Based on the analysis of monitoring results under different chamber earth pressures, thrust force, the torque of the cutter, grouting pressure, and grouting volume, the relationships between shield tunneling parameters and their influence on the disturbance of the surrounding soil mass were investigated. It was found that the surface deformation shape of the monitoring section of the south and north lines conforms to the Gaussian curve. The vertical deformation of the stratum at the tunnel axis is the largest. The maximum value is observed when the cutter head reaches the monitoring section. The horizontal deformation reaches a maximum value at the stage of the shield tail pass section. The strata deformation is not only related to the strata properties but also has a strong positive correlation with the shield tunneling parameters. The chamber earth pressure is the main factor affecting the stratum deformation before the arrival of the cutter head, and the grouting volume is the main factor affecting the strata deformation during the stage of the shield tail pass section.

Frictional energy piles have been emerging as a proenvironmental means in the industry to exploit shallow geothermal energy. A growing concern for energy piles is their bearing capacity typically subjected to temperature variations. To better understand the temperature-dependent behavior involving bearing capacity, herein a series of direct shear tests were carried out to examine the effects of temperature and thermal cycles on the frictional behavior of the pile-soil interface for energy piles. The pile-soil interface consisting of fine-aggregate concrete and kaolin clay was tested under four normal stress levels, i.e., 50, 100, 200, and 300 kPa. The results suggest that: (1) a positive correlation may exist between temperature and the shear strength of the pile-soil interface; (2) the adhesion of the interface may vary with temperature in terms of a nonmonotonic function; and (3) the shear strength of the interface appears to decrease with an increasing thermal cycle and/or an increasing fluctuation amplitude of temperature within a temperature cycle. The experimental data obtained here may help enrich the understanding of the complex behavior of the shear strength of the pile-soil interface for energy piles and related soil-structure interaction.

顶管机在顶进过程中受到管节与土之间的摩擦力,泥浆性质直接影响管节表面的摩擦力.本文通过调整泥浆液中膨润土及增稠剂的掺量,采用流变仪分析计算了宾汉方程与幂律方程的4个参数及漏斗粘度.结果 表明:当膨润土的掺量在8％～12％时,泥浆的流变性能较为适合;膨润土和CMC含量增加,泥浆变浓稠内摩擦增大,易形成网状结构,因此动切力增大,尤其当膨润土和CMC掺量在较高水平时,这一现象更为显著;流性指数随膨润土含量增高而降低;稠度系数会随膨润土含量提升而增大;膨润土及CMC掺量增加会使漏斗粘度上升.

袖阀管注浆过程会引起周围土体变形,从而影响邻近建(构)筑物的安全.本文依托杭州某工程现场实测数据,结合PLAXIS有限元软件分析注浆对周围土体位移的影响,并将实测结果和数值分析结果进行对比,验证数值模拟分析的有效性.结果 表明,数值模拟分析结果和实测结果拟合良好,土体水平位移的变化趋势基本一致,最大位移均发生在注浆所在深度附近.本研究成果对于注浆及类似工程的设计和施工具有一定的参考价值和指导意义.