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31 December 2024, Volume 38 Issue 6 Previous Issue    Next Issue

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Application of Long Cased Boring Method in a Deep Excavation Supporting of Qingdao Metro Project CHEN Chenwen, DU Guangmin 2024, 38 (6):  889-891.  Abstract ( 220 )   Save The depth of the foundation excavation of Zhoucun Station of Qingdao Metro Line No. 7 is large, and there are adverse geological conditions such as saturated sand layers and complex strata at the project site. The cast-in-place concrete pile has restrictive requirements for the borehole quality. Throughout the engineering experience and the analysis of the installation method of the bored piles with slurry wall and the long-cased drilling method, this paper proposes an application method of the bored pile with the long casing in the deep excavation support of the Qingdao Metro. The bored pile installation with long casing drilling is introduced in detail, including pile equipment set up, positioning and casing setup, positioning of the drilling rig, checking the casing plumbness, drilling in the soil, lowering of long casing, advancing and borehole cleanup, lowering the reinforcement cage, installation conduit, tremie concrete pouring, and lifting of steel pile casing. Related Articles | Metrics

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Analysis and Mitigation of Baolongyu Landslide in Chang’an District, Xi’an LU Zhi, SHANG Qi 2024, 38 (6):  892-895.  Abstract ( 283 )   Save This paper presents the case history of Baolongyu landslide in Chang’an District, Xi’an City. The basic characteristics of the subsurface conditions at the landslide site, possible factors that might triggering the landslide are evaluated and the stability of the landslide is also performed through the geotechnical data provided by the investigation and the back analysis. The geotechnical parameters required for the landslide mitigation design are obtained and the mitigation plan is therefore proposed. The research results show that the Baolongyu landslide is a shallow accumulation landslide induced by the rainfall; The landslide is in an unstable state under the natural conditions. According to the stability of the landslide analysis, the concept of comprehensive mitigation: “slope backfill + sheet pile wall + passive protective wire mesh net + reinforced concrete retaining wall + intercepting and drainage” is finally adopted. The wedgeshaped chute is backfilled, the sheet pile wall and the reinforced concrete retaining wall are arranged at the toe of the landslide slope, the passive protective wire mesh net is arranged at the top of the pile and the wall, and the chute and drainage ditch are arranged on the slope to drain the rainwater on the slope and to ensure the stability of the landslide. Related Articles | Metrics

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Application of Foamed Concrete in Karst Rock Cavity at the Riverside Pile Foundation SHU Zhihua, WANG Dingjun 2024, 38 (6):  896-898.  Abstract ( 141 )   Save The karst geological conditions of a shallowly buried pile foundation at the riverside are complicated, and the karst rock cavities are well developed. Before the pile installation, a detailed geological and geotechnical investigations are performed, and the technical research of underwater lightweight foamed concrete is also carried out. The lightweight foamed concrete is produced by the fully mixing foam agent and the cement mortar. Finally, an engineering drill is used to set up the pilot hole to the bottom of the karst rock cavity. The foamed concrete pouring pipe is buried and the underwater lightweight foamed concrete is poured through the this buried pipe. Related Articles | Metrics

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Interaction of Deep Excavation Groups Constructed with Ultra-Deep Diaphragm Walls LI Wenjun, HU Gang 2024, 38 (6):  899-904.  Abstract ( 152 )   Save A comprehensive underground engineering projects normally have concerns of mutual deep excavation groups affecting each other. Due to the close distance between deep excavations and staggered construction periods, the deformations and the stresses in deep excavation groups are usually more complex than a single excavation project. Based on an actual engineering project, this paper conducts two-dimensional numerical analysis of the interaction between the construction of the ultra-deep underground diaphragm wall deep excavation groups, considering the different earthwork excavation sequences of the adjacent ground walls. The results show that: 1) The main impact area for the physical deformation and the different earthwork excavation sequences of the underground diaphragm wall is the adjacent range of the underground diaphragm wall, with no effect on the external underground diaphragm wall; 2) The earth excavation sequence will affect the surface settlement among underground diaphragm walls, and the maximum settlement point will deviate from the area of ground walls excavated earlier; 3) The earthwork excavation sequence has limited settlement effects on the outside the ground wall; 4) The deformation of the pipeline is mainly affected by the excavation of the adjacent underground diaphragm wall, while the pipeline far from the underground diaphragm wall construction has had little impact. Related Articles | Metrics

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Design and Construction of a Complex Partition Deep Excavation Adjacent to Metro Tunnels ZHOU Yan, 2024, 38 (6):  905-912.  Abstract ( 200 )   Save This article, based on a project in Zhangjiang, Shanghai, introduces the design concept and key technologies of excavations adjacent to metro tunnels in soft soil areas, and analyzes the impact of the excavation on metro tunnels. The project is in the core development zone of Zhangjiang area in Shanghai. There are excavations under the construction simultaneously with the project on the east, west and north sides. The north side of the pit is adjacent to the tunnel of Metro Line No. 13. The design of the excavation supporting structure not only needs to fully consider the protection of roads, municipal pipelines, and existing tunnels but also needs to avoid the impact of the overlapping effects of largearea excavation groups on the tunnel. Through the reasonable zoning design, the project not only meets the overall construction needs of the main building structure but also shortens the construction period by coordinating the excavation sequence of adjacent blocks and dividing narrow strip excavations adjacent to the tunnel to reduce the impact of the large-area unloading on the tunnel. Site measurements show that the excavation construction’s impact on the metro tunnel is effectively controlled by measures such as reasonable selection of enclosing structures, internal reinforcement, automatic axial force servo compensation system for steel supports, symmetric balanced excavation, steel support clamping and dismantling and steel exchange support. This study provides a reference for similar engineering projects. Related Articles | Metrics

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Safety Studies of the New Constructed Tunnel Overpass the Existing Tunnels LI Jingbin, ZHAO Meng, TAN Chao 2024, 38 (6):  913-920.  Abstract ( 164 )   Save In order to study the impact of over pass of a proposed tunnel on the existing transportation lines, the shield tunneling project in the interval from Fuxing Road Station to Beiyanhu Station on the southern extension line of Line No. 4 of Hefei Rail Transit is presented as the case history. The proposed project crosses the existing Line No. 4 from the Science and Technology University Research Institute Station to the Beiyanhu Station. The numerical simulation combined with field measurements are used to investigate the deformation response of the existing transportation lines during the construction of the new tunnel. The results show that the construction of the new shield tunnel will disrupt the existing soil balance, causing the unloading rebound of the soil, thus resulting in the vertical uplift deformation primarily in the existing transportation lines and connection channels. Through the simulation based on the actual operating conditions, it is found that the maximum vertical deformation of the interval tunnel is 2.074mm, and the maximum vertical deformation of the connection channel is 2.075mm. According to the safety control requirements of the existing tunnel structure and the analysis based on the field measurements, both the simulation results and the measured data are below the warning threshold of 3mm, indicating that the existing interval tunnel is in a safe and stable state according to the simulation calculations. Related Articles | Metrics

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Impact of Soft Soil Retaining Walls and Their Backfills on the Existing Railways TANG Zhou 2024, 38 (6):  921-925.  Abstract ( 157 )   Save When constructing new structures around existing railways, it is necessary to consider the impact of additional loads on the existing railways. Especially in soft soil areas, the loading on one side of the existing roadbed might cause deformation of the foundation, and appropriate engineering measures are needed to be taken to ensure the safe operation of the existing railway. To study the impact of retaining walls and their backfill soil on the outside of existing railway embankments in soft soil areas, this paper selects a retaining wall and backfill soil project on the side of an existing railway near a park in Shaoxing City as an engineering example. Firstly, the deformation control values of the track and roadbed are determined according to relevant specifications. Then, numerical simulations and theoretical analysis are used to obtain the horizontal and vertical displacements of the existing railway track surface corresponding to different engineering measures under the action of backfill soil loads, the engineering measures are ultimately determined which could ensure the safety of the railway operation. The research results of this article can provide a reference for the design and construction of similar railway related projects. Related Articles | Metrics

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Influence of Pipe Jacking on Stress and Deformation of Existing Subway Tunnels YI Yujie, WANG Jia, TIAN Jianlong 2024, 38 (6):  926-930.  Abstract ( 174 )   Save To study the influence of the pipe jacking on the stress and deformation of the existing adjacent subway tunnel structures, this paper presents the numerical analysis results. The construction site environment, construction process, construction method and existing protection requirements of the subway structure are considered and the displacement and internal force of the subway tunnel structure under the relevant construction staging are simulated by using Midas GTS/NX software. Combined with the actual monitoring data, the safety evaluation of the pipe jacking construction method performed. The results show that the influence of the pipe jacking can be classified as the first class. The displacement in the Y direction (jacking direction) and the Z direction (vertical direction) of the subway structure after the entire pipe jacking construction process is 0.138 mm and 0.549mm respectively. The change rate of the force is not more than 3%, and the structure is still working within the tolerable range. From the real-time monitoring data, the maximum displacement of the subway structure in the Y direction and the Z direction is 1.76 mm and 0.65mm, respectively. The monitoring data is in a good correspondence with the simulation results, showing that the change of the tunnel structure affected first is greater than that of the tunnel structure affected later. Both the monitoring and the simulated displacement of the tunnel structure do not exceed the recommended 7mm, that is, the entire project is safe to advance under the normal construction conditions. Related Articles | Metrics

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Numerical Simulation of a Deep Excavation Supporting System HU Jianwei 2024, 38 (6):  931-937.  Abstract ( 130 )   Save This paper presents a case history of a deep excavation support project in the peat soil in Kunming. The influence of the deep excavation on the stability and the deformation of the soldier pile with ground anchor supporting system after the completion of the excavation is analyzed. A new reinforcement structure support system is then proposed. The FLAC3d numerical software is used to model and to analyze the horizontal and vertical displacements as well as the factor of safety of the overall stability of the supporting structure under three different loading conditions. The results show that the proposed supporting structure can be cost effectively applied to deep excavation in peat soil area. The construction period is shortened, and it has good economic and social benefits. The monitoring data of 114 times in 9 months are consistent with the numerical simulation results, which verifies the effectiveness of the composite reinforced structure system. The research results can solve the problem of the deep excavation after the construction of traditional supporting structure in the soft soil area, and provide a theoretical and practical basis for similar deep excavation supporting structure design. Related Articles | Metrics

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Application of In-situ Solidification Technology in Treatment of a Fill Soil FENG Zhongwen 2024, 38 (6):  938-941.  Abstract ( 166 )   Save The newly formed land site has the characteristics of various degrees of compaction, uncompleted settlement under the self-weight and loose soil structure. This type of soils may cause some engineering hazards, such as a low bearing capacity, poor drivability of construction equipment on the land, out of alignment of newly installed pile head in this soil. In response to those issues, this paper presents a case history of the electronic information industrial park project near the Zhuhai west railway station. The design and construction method of the shallow improvement of the newly filled soil by in-situ solidification of forced mixing method is introduced. The construction process and the effect of the solidification soil are also analyzed. The results show that the bearing capacity of the in-situ solidification soil is significantly improved, the superficial hard crust by the in-situ improvement is formed quickly to accommodate construction equipment and solve the problem of the misaligned of pile head.  Related Articles | Metrics

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Construction Method of Deep Excavation Closely Surrounding Existing Subway Bridge Piles WANG Le, MA Zhenwang, ZHAO Jin 2024, 38 (6):  942-946.  Abstract ( 135 )   Save This paper presents a case history of the impact of the closely deep excavation on the surrounding the existing subway viaduct piles. In the underground transfer center project at the proposed Suzhou Metro Line No. 8 and the existing Line No. 2, a three-dimensional finite element simulation numerical model was used to study the impact of different excavation sequences and soil reinforcement lengths on the safety of the existing bridge piles of the surrounding deep excavations. The numerical results are compared with the field monitoring data. The evaluation results show that the symmetrical synchronous excavation of the proposed foundations on both sides of bridge piles has less surrounding surface settlement, the less deformation of the retaining structure and the less deformation of viaduct piles than that of the sequential excavation. The ability of the soil surrounding the pile to resist deformation increases with the increase of the reinforcement length of the protective casing. When the reinforcement length exceeds the excavation depth, the improvement effect of the ability of the soil around the pile to resist deformation is no longer obvious, and the optimal reinforcement length of the bridge pile is basically the same as the excavation depth. Related Articles | Metrics

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Stability of A Daylight Bedding High and Steep Slope Near a Major Bridge in the Three Gorges Reservoir Area XU Shaojun, YU Song, XIANG Houjun, ZHANG Guochao, ZHAO Wen 2024, 38 (6):  947-952.  Abstract ( 150 )   Save The slope along the north bank of a major bridge in the Southwest Three Gorges Reservoir Area is a high and steep rock slope consisting of interbedded sandstone and mudstone. The stability of this slope is critical to the construction of the bridge. Geological mapping, drilling and digital borehole panoramic image are used to identify the geological characteristics of the daylighting slope. Based on the engineering geology and the stereographic projection analysis, the stability of the slope was preliminary assessed. Subsequently, the potential for the sliding along the bedding plane of the slope was analyzed by using the limit equilibrium method. The finite difference method (FLAC) and the discrete element computation program (UDEC) were then employed to simulate the failure mode, mechanical behavior, and strength of the rock mass, considering only the structural plane conditions of the slope. The results indicate that the daylighting slope is stable under both natural conditions and bridge foundation load conditions. There is no risk of sliding failure along the daylighting bedding plane. However, under the long-term effect of the natural gravity, local rock masses on the slope surface may suffer damage, resulting in retrogression of the bank slope, which could potentially affect the safety of the bridge foundation. It is recommended to appropriately fill in the grooves on the rock slope surface of the north bank and take corresponding treatment measures such as clearing and supporting the overhanging rock blocks. Related Articles | Metrics

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Practice and Analysis of the Support of a Large Deep Excavation with Reserved Platform in the Complex Urban Environment LIU Chen, WEN Jianpeng, WANG Wenbin, SUN Huihui, CAO Xuan, HU Zhengkun, QIU Jianjin, LEI Youkun 2024, 38 (6):  953-958.  Abstract ( 184 )   Save With the increasingly stringent constraints faced by the large deep excavation support structures, especially in the complex and densely populated urban environments, the selection of support structures is greatly restricted. Combined with the first phase project of the urban renewal unit of Shahe Village No. 5 in the Shahe Street, Nanshan District, Shenzhen, this paper introduces how to select a more appropriate deep excavation support structure when the prestressed ground anchor cannot be used due to the proximity to the planned subway line and the adjacent deep excavation, and when the conventional internal support system cannot be used to avoid the main tower structure. This deep excavation support structure adopts a more innovative reserved platform type, with good excavation support effect. There is no overlap or intersection between the support system and the main structure, which greatly promotes the construction progress of the main structure and provides great convenience for the planned subway construction. It can be used as a reference for similar projects. Related Articles | Metrics

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Control of Water Intrusion and Pressure Reduction in Deep Excavation, as Well as Pressure Sealing Technology in Pressure Reduction Wells ZHONG Guirong 2024, 38 (6):  959-963.  Abstract ( 243 )   Save The sudden water intrusion in the deep excavation can induce catastrophic consequences to project. The research on deep excavation water intrusion prevention and control system and related technologies is of great significance. Based on engineering case histories, the triggering factors of the sudden water intrusion the deep excavation are analyzed, and the main factors that prevented the water curtain from completely blocking artesian groundwater are the seepage around the bottom and horizontal seepage at the bottom of the mixing column water stop curtain. The permeability coefficient of the confined water layer was obtained through in-situ depressurization well pumping tests. The reasons for the increase in permeability coefficient were analyzed. The design of the deep excavation groundwater intrusion prevention and control should consider the impact of the increase in permeability coefficient of the confined water layer. This article introduces the prevention and the control system for the sudden groundwater intrusion and the pressure reduction in deep excavations, which includes the graded layout of pressure reduction wells, weight sealing bottom, zoning excavation, rapid bottom sealing, and strengthened monitoring. Among them, the graded layout of pressure reduction wells is the key. Developed pressure reducing well sealing technology for the pressurized water and applied it in engineering. Related research can provide reference for similar engineering design and construction. Related Articles | Metrics

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Investigation of Long and Short Pile Combination System for Single Point Support Structure in Thick Soft Soils Yin Hua 2024, 38 (6):  964-970.  Abstract ( 168 )   Save During the stability analysis of a single point support structure in thick, soft soils, the length to the point of fixity of the supporting pile often reaches 2~3 times of the excavation depth. This leads to a high cost of the engineering supporting pile system. Based on the current analysis method of the stress and deformation of the supporting structure for the deep excavation, a new analytical method is proposed in this paper. By investigating the characteristic of the internal force and the deformation for the different spacing of the long and short pile structure, it is proposed that the length of the long pile should be determined according to the overall stability of the support system, while the length of the short pile should be determined according to the length of effective bending moment. Comparing the bending moment and the deformation diagram of the long and short piles, the length of long and short piles can be further optimized. To verify the proposed analytical method, a three-dimensional numerical model is established to analyze the overall displacement and the internal force of the long and short piles. The effectiveness of this model is further applied and verified in a deep excavation project in Guangzhou. The proposed model can be used for deep excavation projects in deep soft ground. Related Articles | Metrics

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Analysis of Soil Squeezing Effect of Prefabricated Pipe Piles LI Hongwei, YANG Guangyu, XIE Liang 2024, 38 (6):  971-974.  Abstract ( 342 )   Save The case history of the1600mm acid pickling (HAPL) project of a stainless-steel company is presented in this paper. The ABAQUS software is used to simulate the soil squeezing effect of PHC pipe piles. The influence of PHC pipe pile diameter and the friction coefficient of the pile soil interface on the soil squeezing effect are discussed, and suggestions that controlling the soil squeezing effect of PHC pipe piles are proposed. The results show that, with the development of the PHC pipe pile installation process, the radial displacement of the soil increases gradually and decays rapidly after reaching the peak value in the pile tip area; The radial displacement of the soil decreases logarithmically with the increase of the distance from the pile center, and the influence range of the soil squeezing effect is about 9 times of the pile diameter. The diameter of the PHC pipe pile and the friction coefficient of the pile-soil interface have a great influence on the soil squeezing effect. With the increase of the friction coefficient, the radial displacement of the soil increases, while the surface uplift gradually decreases. The radial displacement of the soil and the surface uplift increase with the increase of the pile diameter. Related Articles | Metrics

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Evolution Analysis of Pore Structure of Coral Reef Limestone Under Cyclic Loading JIA Xibei, MENG Qingshan, WU Kai, SONG Xiaolong 2024, 38 (6):  975-981.  Abstract ( 163 )   Save The complexity of the mechanical behavior of the coral reef limestone induces challenges to the construction of the projects for the Belt and Road Initiative and the Maritime Silk Road. In this paper, the damage evolution characteristics of the coral reef limestone under the variable amplitude cyclic loading are quantitatively evaluated based on the in-situ CT scanning triaxial test equipment. The structural changes of the coral reef limestone under different stress conditions are studied by the CT scanning and the digital image analysis technique. The results show that the secant modulus of the coral gravel limestone increases first and then decreases with the pressurization and evolution of the damage, while the elastic modulus decreases in the pressurization stage. The stress concentration occurs at the tip of inner pores of the coral reef limestone under the external load, and cracks expand first in the area with the largest porosity and the most complex pore structure. According to the distribution characteristics of cracks in the three-dimensional space and the slice analysis, the specimen under the cyclic load of 6 MPa occurs the tension-shear failure mainly with the shear. The research results provide a reference for the security and stability evaluation of surrounding rock in island and reef engineering construction. Related Articles | Metrics

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Pullout Mechanism of Soil Anchor Considering Embedded Depth and Relative Displacement Relationship at Interface CHEN Xiaowei, ZHU Haofeng, LIU Ting 2024, 38 (6):  982-989.  Abstract ( 132 )   Save Based on the laboratory interface shear test results, a method of estimating the pullout load-displacement is proposed considering the embedded depth and the relative displacement relationship of the grout-soil interface. Firstly, the normal stress for the interface shear test can been obtained according to the embedded depth of the soil anchor. Then the fitting formulas were obtained by the laboratory interface shear tests and the curve fitting method. Secondly, based on the elastic deformation assumption of the anchoring segment and the Mindlin solution of the soil deformation, the relative displacement formula is proposed for the anchoring segment and the soil of interface. Finally, according to fitting curves of the shear test and the interface relative deformation, a formula for the pullout load with the displacement is established. The results indicate that curves of the anchor pullout load-displacement are more consistent with curves by the laboratory shear test than the other theoretical methods. The axial force and the relative displacement of the anchoring segment interface raised from the top to the end with the improvement of the pullout load of the soil anchor. The relative displacement curves show an obvious concave-characteristics, while the axial force curves of the anchoring segment show the strong convex-characteristics. In addition, with the increase of the pullout load, the friction resistance increases gradually, and range of friction resistance is gradually expanded. The greater the embedded depth, the smaller the resistance. The friction resistance of the anchoring segment has an obvious hysteresis phenomenon for the embedded depth of the soil anchor. Related Articles | Metrics

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Discussion on Geotechnical Engineering problems of antenna area at QTT site LI Mingshuai, LI Haitao, WANG Na, CHEN Maozheng 2024, 38 (6):  990-995.  Abstract ( 357 )   Save Qtai Radio Telescope (QTT), as a powerful tool for the deep space exploration by astronomers in the future, is in a syncline fold zone of the North Tianshan Mountains, which is belonging to the Cenozoic depression, with faults, folds and other structures throughout the field. Due to the special engineering significance and the large construction volume of the QTT project, there are few geotechnical engineering reference cases with such weight, high pointing accuracy and high sensitivity requirements for the single-port telescopes domestically and abroad. Based on the particularity and complexity of geotechnical engineering conditions, in this paper, the potential causes, hazards and risk prevention of geotechnical engineering problems in the QTT antenna area are systematically analyzed and evaluated, and corresponding protective measures and construction points are formulated to meet the requirements of the nonuniform settlement of the largediameter antenna foundation, and to provide theoretical basis and experience for the geotechnical engineering investigation, construction and protection of similar major scientific engineering facilities in the future. Related Articles | Metrics

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Re-development of a Constitutive Model in ABAQUS for Soft Soil Considering Strain Rate effects and Strain Softening#br# GUO Jianxiang, WEI Xiaobin, 2024, 38 (6):  996-999.  Abstract ( 211 )   Save The study of cone penetration process has been a hot topic in the geotechnical engineering, and its results are mainly used to predict the strength of granular soils. In cone penetration process, the strain softening, and strain rate effect of the granular soil have a significant impact on its strength. It is difficult to describe the influence on the penetration results through theoretical methods, instead, numerical methods can well simulate the cone in the process of penetration. To evaluate the influence of the strain softening and strain rate effects on the penetration results, the subprogram of the soft soil constitutive model was compiled by using the re-development platform provided by ABAQUS. The soil constitutive model is applied to the numerical model calculation throughout the subprogram interface VUSDFLD, and the subprogram interface form and subprogram activation method are demonstrated. The Coupled Eulerian-Lagrangian method was used to simulate the cone penetration process. Firstly, the mesh sensitivity analysis of the model is carried out, and it is concluded that when the mesh density is less than 0.2mm, the influence on results is negligible; secondly, the numerical simulation results are compared with previous experiments and numerical cases, and the results show that the penetration depth and the penetration velocity of the cone are in good agreement with previous studies, which indicating that the analysis can better simulate the motion characteristics of the cone during the cone penetration process. The results show that the re-development procedure can well simulation the application of the strain rate effect and the strain softening soil constitutive model in ABAQUS. Related Articles | Metrics

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Strength Prediction of the Modified Soil Using on D-P Criterion WANG Xiaojiao, ZHOU Li’an, QI Chengzhi, CHEN Haoxiang, JIAO Weiling, LIN Kun 2024, 38 (6):  1000-1005.  Abstract ( 237 )   Save The reinforcement of geotechnical materials plays an important role in the durability and safety of buildings. The construction waste is a huge, wasted resource and is currently largely produced in China. To improve the strength, the recycled powder construction waste is added to the soft soil. Based on the unconfined compressive strength test and the direct shear test of modified soil, re-developed constitutive model that combined with Drucker-Prager criterion is established by using platform ABAQUS platform. The geotechnical user material subroutine UMAT was used to predict the strength of the modified soil. The new constitutive model considers the influence of intermediate principal stress, the tensile stress and the hydrostatic pressure on the mechanical properties of the soil. The prediction results by the re-development platform are compared with the unconfined compression test results the soil specimens. Combined with the test and verification results, the appropriate amount of recycled powder was obtained to improve the soil strength. The results show that, it is beneficial to increase the strength of soil when the content of reclaimed fine powder is about 15 %. This subroutine command of ABAQUS can be used to describe and to predicte the mechanical properties of the modified soil well. Related Articles | Metrics

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Influence of Outfall Ditch on the Stability of a Daylighted Slope in Shenzhen TANG Kaizhong, LIANG Zhi, LI Wenfa, WAN Yi, LENG Xianlun, 2024, 38 (6):  1006-1010.  Abstract ( 194 )   Save This paper presents a case history of a local deformation and failure of a daylighted slope in Shenzhen during the construction period. The major potential factors triggering the local instability of the slope are analyzed through on-site geological survey, combined with investigation and design data, on-site construction procedures and monitoring data. On this basis, the Phase2 numerical model that can reflect the characteristics of the slope, such as rock stratum, the outfall ditch and the supporting structure, is established. The slope construction process under four different conditions is analyzed, and the potential triggering mechanism of the local instability of the slope is studied. The results show that the outfall ditch is the main inducing factor of the local deformation and instability of the slope. The potential triggering mechanism is that the excavation of the outfall ditch leads to the weak sliding surface at the rock stratum, and the water in the catchment leads to the softening of the rock mass at the foot of the slope, resulting in the failure of the daylighted bedding plane in the fourth-grade slope. When there is no water the catchment after the excavation of the outfall ditch, the safety factor of the slope without support structure is 1.03, which is in an unstable state. After the support is applied, the safety factor increases to 1.09, which basically meets the stability requirements. When the water in the catchment is presented, the safety factor is 0.85 when there is no support, which is in an unstable state. After the support is applied, the safety factor is 0.99, which is in a critical slip state. The ground anchor with supporting beam can effectively prevent the local slope instability induced by the drop ditch when there is no water in the catchment, but the supporting effect is not good when the water in the catchment slope softens. Related Articles | Metrics

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Stability Analysis of Reticulated Soil Landslide Using on Deformation Zoning GE Yanming, SONG Huijuan, LIN Dajiang, 2024, 38 (6):  1011-1014.  Abstract ( 124 )   Save The reticulated red soil is a widely distributed soil in the hilly area of central Hunan. The existence of the vertical micro-cracks in the soil makes the surface water easy to infiltrate, and the dry-wet alternate environment accelerates the expansion and the shrinkage deformation of hydrophilic minerals, which has a significant impact on the stability of the slope. In the process of surveying a reticulated soil landslide, the slide body was divided into plane zones based on deformation signs. The slope stability was evaluated by the region so that the landslide survey can be more refined and the amount of engineering support can be reduced. On the basis of the stability analysis of the existing sliding surface of the uniform soil landslide, the stability check of the deeply seated potential sliding surface of the slope can effectively avoid the failure of landslide control. Based on the simplified Bishop method, the stability analysis of a reticulated red clay landslide is performed. The slope is at the marginally stable state, and heavy rainfall will induce the slope to produce a larger and deeply seated overall sliding. Related Articles | Metrics

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Kinematic Analysis Method for Stability of High and Steep Granite Slopes YANG Yunlin 2024, 38 (6):  1015-1021.  Abstract ( 118 )   Save Granite is one of the most widely distributed rock types on Earth. Its characteristic of penetrating diabase veins and locally developed fracture zones affect the stability of the rock mass and pose a safety hazard to construction sites. A kinematic analysis method based on threedimensional projection and the vector algebra theory was established to analyze the overall and local failure modes of a granite steep slope. The DISP software was applied to analysis the stability of the local slope. The probability of overall planar sliding, wedge shaped deformation, and toppling failure of the southern, western, and northern slopes is very low when only considering the condition of penetrating structural planes. When considering other structural planes simultaneously, there is a higher possibility of the local wedge failure in the southern slope. Further combining the mechanical parameters of the structural plane, the calculated wedge stability coefficient meets the requirements of the specifications. The results of the failure mode and the stability analysis have also been verified by the actual on-site condition and slope deformation monitoring data. The exploration in this article will provide a reference for the failure mode and the stability analysis method of granite steep building slopes. Related Articles | Metrics

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Impact of Deep Foundation Excavation on Adjacent Subway Tunnels JIANG Haiqing, LI Zhuangzhuang 2024, 38 (6):  1022-1026.  Abstract ( 153 )   Save The excavation and unloading of foundation pits inevitably cause disturbance to the surrounding rock and soil, which in turn has adverse effects on adjacent existing subway tunnels. A finite element modeling analysis method was used to comprehensively analyze and evaluate the total displacement, horizontal, and vertical displacements of the adjacent underground tunnel caused by the entire process of the supporting structure construction, deep excavation, basement construction, demolishing and backfilling, and the upper structure construction for a deep foundation pit project near a subway tunnel in Shenzhen. Research has shown that by comparing the overall displacement, horizontal and vertical displacements estimation results of tunnel structures under various working conditions, the deformation of tunnel structures caused by the excavation of foundation pits is mainly manifested as the horizontal and vertical displacements can be basically neglected. Comparing the displacement of the left and right tunnel lines under various working conditions, the closer the distance to the foundation pit, the greater the overall displacement, horizontal and vertical displacements of the tunnel structure caused by excavation. The overall displacement, horizontal and vertical displacements caused by the excavation of the foundation pit gradually increase with the excavation process, reaching an extreme value when the foundation pit is excavated to the bottom, and then gradually decreasing. The overall displacement and deformation of the subway tunnel caused by the excavation of the project foundation pit under various working conditions meet the control requirement of 5mm deformation control for Shenzhen subway tunnels.  Related Articles | Metrics

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Numerical Simulation Study on Fluid-Solid Coupling of Submerged Soil Arch Collapse ZHANG Lei, XIANG Xiqiong, LIU Hong, LI Linwei, WANG Wenjun 2024, 38 (6):  1027-1032.  Abstract ( 290 )   Save The red clay has poor permeability from top to bottom, making it difficult for suffusion-induced soil arch phenomena to occur naturally. The repeated rise and fall of groundwater enhance the erosion at the rock-soil interface, causing the clay minerals within the red clay to disintegrate upon contact with water. This easily leads to the formation of localized blocks, promoting the development of soil arches, disrupting the soil structure, and providing conditions for suffusion due to the instability of the internal structure, ultimately leading to the collapse of the suffusion-induced soil arches.To elucidate the development process of this collapse type, this study combines typical collapse incidents in recent years at Dongdiu, Libo, Qiannan. By utilizing the Geo-Studio numerical simulation software, the study simplifies the groundwater erosion process as excavation to investigate the process of red clay suffusion-induced collapse in the shallow buried cover layers in karst regions. The results indicate that groundwater erosion directly impacts the seepage field and stress field of the cover layer, leading to localized stress concentration and changes in the seepage field. During seepage, the reduction in effective stress results in an increase in localized displacement of the cover layer under its own gravity, accelerating the instability of the soil structure, and promoting the development of suffusion, ultimately leading to collapse. Related Articles | Metrics

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Analysis of Influence of Deep Excavation on Adjacent Subway Tunnels ZHAO Yuanyuan, ZUO Reyu, ZHANG Xinran, XIE Yidong 2024, 38 (6):  1033-1038.  Abstract ( 165 )   Save In recent years, with the development of high-rise buildings and the underground space utilization, the number of deep excavation projects in China is increasing, especially in the large cities, where the subway network is dense, the construction of foundation excavation has a great impact on the surrounding environment. Reasonable measures shall be taken to protect adjacent structures and utilities from damage. This paper presents a case history of a deep excavation project of Tianyin Mansion, which is close to the Subway Line No. 2 tunnel. A three-dimensional nonlinear numerical analysis model of the interaction between the tunnel soil mass and the deep excavation support structure is established by using the finite element software MIDAS GTS NX. The deformation of the deep excavation support structure and subway tunnel in the entire process of deep excavation are analyzed. The analysis results show that the deep excavation changes the deformation field of the adjacent subway tunnels. With the increase of the excavation depth, the lateral displacement of the tunnel changes little, and the vertical displacement changes slightly. The deformation of the deep excavation support structure and the subway tunnel meet the deformation control requirements in the specifications, which proves that the interlocking pile + internal support adopted in the project can effectively control the deformation of the surrounding environment. At the same time, it also proves that the modified Mohr Coulomb model can be used to simulate the deformation of the subway tunnel caused by the excavation in complex environment. Related Articles | Metrics

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Factors Affecting the Construction of Shallow Buried Tunnels Passing Through Existing Steel High-Voltage Towers ZENG Xiangjin 2024, 38 (6):  1039-1043.  Abstract ( 302 )   Save To analyze the impact of the shallow buried tunnel construction on the existing steel high-voltage iron towers, a two-dimensional numerical analysis model was established for the Damoshan Tunnel project. The safety of the tunnel excavation plan is verified, and the sensitivity factor analysis on the settlement of the tunnel arch top during the construction of the tunnel under the existing steel high-voltage tower is carried out by using the orthogonal experimental method. The effects of the tunnel embedment depth, the horizontal distance between the tunnel and the steel tower, excavation method, and changes in tunnel width on the vertical displacement of the tunnel arch top are evaluated. The following conclusions are drawn: 1) Surface grouting can effectively control the settlement of steel tower foundations and has a significant effect on preventing the tower instability. 2) The conclusion of the orthogonal experiment indicates that the embedment depth has a controlling effect on the settlement of the tunnel arch crown. As the depth of the tunnel increases, the settlement of the tunnel arch shows a downward trend. The increase in the horizontal distance between the tunnel and the center of the steel tower, as well as the width of the tunnel, will increase the settlement of the tunnel arch. The research results have some guiding and reference significance for the tunnel construction under similar conditions and the protection of adjacent existing buildings and structures. Related Articles | Metrics

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Study on the Time Series Linkage Law of the Construction Monitoring of Pipe Jacking Foundation Pit LUO Weijin, DENG Changzhong, XU Binfeng, ZHENG Bin, SHAO Yuqi 2024, 38 (6):  1044-1049.  Abstract ( 142 )   Save Deep foundation pit engineering widely exists in the process of urban construction. It is an important part of disaster prevention and mitigation to analyze the monitoring data and study the environmental effects in the process of deep foundation pit construction. It is of great significance to analyze and predict the changes of the surrounding environment during the construction of deep foundation pit by using the monitoring data with high quality and combining the artificial intelligence technology. Relying on the pipe jacking project, this paper analyzes the impact of the excavation of the foundation pit of the starting shaft on the surrounding environment. The important monitoring parameters are processed into a time series, and advanced cyclic neural network (LSTM) is employed to achieve the advance prediction of monitoring parameters. The results show that there is a linkage law among the monitoring variables, but the linkage of the monitoring variables is relatively weak due to the lack of monitoring data or the impact of construction accidents, and the prediction of the cyclic neural network is not ideal. These works are of forward-looking significance for improving the early warning theory of foundation pit. Related Articles | Metrics

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Experimental Study on the Cumulative Settlement of Single Pile in Double-Layer Foundation Soils Under Large Numbers of Cyclic Loads ZONG Hang, LIU Kaifu, XU Yuedong 2024, 38 (6):  1050-1054.  Abstract ( 120 )   Save Traffic loads will affect the performance of the pile foundation underneath the expressway and high-speed railway. To analyze the influence of cyclic loads on the settlement of the pile foundation, laboratory model tests are used to study the effects of the cyclic number of loads, the cyclic load ratio (CLR), the static deflection load ratio (SLR) on the pile head cumulative settlement of the single pile in the double-layer foundations. The results show that the pile head cumulative settlement of the single pile under cyclic loads is obviously affected by the number of cycles, SLR and CLR. The pile head cumulative settlement increases with the number of cycles, CLR and SLR. The pile head cumulative settlement development under cyclic loads has the trend of increasing rapidly first and then slowly. If the values of the SLR and the CLR are small, the pile head accumulated settlement in the later stage increases very slowly or not. If the values of SLR and CLR are large, the pile head accumulated settlement increases faster in the later stage. When the value of SLR + CLR is constant, the more the proportion of the CLR is, the larger the pile head cumulative settlement is. The effects of the CLR and the SLR should be considered in the engineering design.  Related Articles | Metrics

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Acoustic Velocity Characteristics of Frozen Soils During Freezing SHI Jie, XIONG Yali, WEI Xinyu, YU Hongfei 2024, 38 (6):  1055-1058.  Abstract ( 136 )   Save To study the effects of the initial dry density and the initial water content on the strength and stiffness of the frozen soil during freezing. Under the condition of 10 ℃, the frozen soil samples with different initial dry densities and initial water contents were tested for the acoustic wave, and the changes of P-wave velocity during freezing were observed. The test results show that the freezing process of the clayey silt can be divided into three stages, namely, the slow rising stage, the fast-climbing stage and the stable stage. The acoustic test data show that the freezing can significantly improve the P-wave velocity of samples. With the increase of the initial water content, the peak wave velocity of frozen soil increases gradually, and the rising speed of wave velocity accelerates gradually during freezing. The initial dry density has a significant influence on the change of the wave velocity of the frozen soil. The higher the initial dry density, the higher the density of the sample is; the larger the peak wave velocity during freezing, but the rising speed of the wave velocity is almost the same. Related Articles | Metrics

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Study of the Improvement Effect and Field Test of CFG Composite Columns in Soft Soils LIU Peng, GU Liqiang, ZHANG Zhaobin, WANG Liang, ZHANG Lifeng, GU Zhichao 2024, 38 (6):  1059-1063.  Abstract ( 132 )   Save This paper presents a case study of the improvement effect of the CFG columns in soft soils. The numerical simulation of the CFG column composite soil is established by using FLAC3D finite difference software. At the same time, the in-situ tests are also performed. The engineering characteristics of the cushion and the influence of the loading level, the area replacement ratio, the column strength and other conditions on the composite soil settlement and deformation are also evaluated. The in-situ static quick load and sustained static load tests are performed to compare and to analyze the deformation characteristics of the composite soils under the two static load test methods. The final settlement value of the composite is quickly predicted and validated by the sustained static load test. The conclusions are as follows: (1) according to the numerical analysis results, the settlement and deformation of the composite soil can be effectively controlled by changing the cushion thickness and materials. The optimal cushion thickness therefore be determined in order to achieve the best settlement control effect. (2) by comparing the in-situ loading tests using the elastic cushion method and the code method, it is concluded that the elastic cushion method is closer to the actual loading condition of the foundation. (3) the settlement of the composite soil can be effectively predicted by the sustained static load test, and the results meet the code requirements. Related Articles | Metrics

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Experimental Study on the Rock Anchor Foundation in Water Softened Broken Soft Rock Mass ZHAO Yunchuan, RAO Chuanyou, LIU Jie 2024, 38 (6):  1064-1067.  Abstract ( 126 )   Save Under the action of wind, ice and other loads, the transmission line tower foundations will inevitably resist large horizontal force, which will lead to an uplift force in foundations. In this paper, the typical geological conditions of the interbedded highly weathered argillaceous sandstone and mudstone encountered underneath the transmission line foundations are presented in the paper and the typical rock samples are collected. After being exposed in natural rainfall for one month, the rock strength of the samples was tested and compared with the rock core samples without the rainfall exposure. Several insitu load tests were also performed on the single rock anchors and the failure mechanisms of the anchor were analyzed. According to the engineering analogy, the effective anchor length of this type of rock mass is analyzed, and the bond strength between the grout and rock of this type of rock mass is obtained. Combined with other similar engineering data, the relationship between the anchor length and the ultimate uplift deformation value of the soft rock mass and the similar stratum structure is analyzed. Related Articles | Metrics

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Experimental Study of the Permeability Characteristics of Quartz Sand under High Confining Pressure LI Wei, YANG Chuan, CAO Ziming, ZHANG Xiaoming 2024, 38 (6):  1068-1073.  Abstract ( 149 )   Save In the study of the sand permeability characteristics, most of them are based on normal pressure conditions, while the penetration characteristics of the sand under the high pressure is less. In the water conservancy engineering, the sand in deep mines is often under high pressure conditions, in order to study the permeability of the deep quartz sand, this paper uses the high pressure triaxial shear test equipment to perform permeability tests under the high confining pressures and high osmotic pressures. The permeability characteristics with different confining pressures under the same osmotic pressure and with different osmotic pressures under the same confining pressures are tested. The results show that under the same osmotic pressure, the coefficient permeability decreases with the increase of the confining pressure and the reduction rate is smaller and smaller. Under the same confining pressure, the coefficient of permeability is reduced, and the magnitude reduction is less and less. Further, this paper also analyzes the grain size variation before and after the tests. It is observed that the particle breakage is occurred during the test, and the fine particles of the particle size of <0.1 mm in the sample are increased, so that the coefficient permeability of the quartz sand is reduced.  Related Articles | Metrics

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Experimental Study on Direct Shear Behaviors of Interface Between Steel and Low Liquid Limit Clay XU Junjie, GUO Jukun, WANG Rui, XU Youguang, LIU Xianliang, LIU Zhiqiang 2024, 38 (6):  1074-1078.  Abstract ( 109 )   Save It is of great significance to study the shear behavior of the structure-soil interface for foundation engineering design and construction. With the improved direct shear apparatus, considering the interface type and the soil water content, the direct shear tests of interface between steel and low liquid limit clay were performed, and the rate of shear, stress strain relationship and the volume change were analyzed. The results show that the shear stress presents three stages; namely, fast increase, slow increase and maintain stability, with the shear displacement. The relationship between the shear stress and the shear displacement can be expressed by the Gompertz model. When the soil mass is at the optimum water content, the interface shear strength and the index are the largest. The shear strength and the index of the rough interface are larger than those of the smooth interface. The shear shrinkage of the soil under the rough interface is more obvious than that under the smooth interface. The shear shrinkage characteristics of the soil become more significant with the water content. Related Articles | Metrics

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Monitoring of Geosynthetic Reinforced Soil-Integrated Bridge System LI Haoyu, ZUO Binli, YU Xiaoxiao 2024, 38 (6):  1079-1084.  Abstract ( 108 )   Save Compared with the traditional abutments, the GRS-IBS has the advantages of reducing the span length of the bridge superstructure, avoiding the bridge jump, no joints on the bridge, rapid construction and low carbon emission. The structure has received wider applications and promoting values under the current background of promoting green road, accelerated construction and improving the quality of engineering. Based on the construction monitoring results of the Wuwei to Yuexi high-speed GRS-IBS abutments, this paper introduces the details of the monitoring purpose, content and selection of monitoring components of the project, and summarizes the implementation and matters for the field monitoring. The field monitoring is of great significance to the study of the working mechanism and the service performance of GRS-IBS, This paper also provides a reference for the monitoring plan design of similar projects. Related Articles | Metrics

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Experimental Plate Loading Test Study of Geogrid Reinforced Soils LI Qihui, ZHENG Zhigang 2024, 38 (6):  1085-1087.  Abstract ( 144 )   Save To explore the bearing capacity and deformation characteristics of geogrid reinforced foundations, this paper designs and performs model tests with 5. 7 and 17 layers of geogrid reinforced foundations. The settlement, lateral earth pressures and horizontal displacement of the reinforced earth soils are compared with the performance of natural soil with reinforcement. The results indicate that, for soil without the reinforcement, the surface soil settlement increases significantly after the foundation pressure greater than 400 kPa, the the soil demonstrates an obvious brittle failure mode. Using the same settlement magnitude at an ultimate bearing capacity of 400 kPa as the reference value, the bearing capacity for 5 layers of geogrid reinforcement is 505 kPa, 565 kPa for 7 layers and 660 for 16 layers of reinforcement, respectively. Under the same settlement value, various reinforcement layers of geogrid increase 26%, 39.5% and 63.5%, respectively. The foundation soil receives a significant improvement. After the geogrid improvement, the lateral earth pressures, horizontal displacement are reduced comparing with the natural soil without the soil reinforcement.  Related Articles | Metrics

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Discussion of Hydraulic Pile Hammer Driving Criteria based on Pilot Hole in Hard Rock Strata LIN Huiting, GONG Dengzhuan, TANG Jianbin, TANG Jun, HE Yujun 2024, 38 (6):  1088-1092.  Abstract ( 253 )   Save Due to the high damage rate of driven piles under geological conditions containing hard rock strata, the conventional practice is to first create mechanical pilot holes, and then grouting in the holes to form piles. This project innovatively uses a submerged hammer to fill soil into the pilot holes, and then uses a hydraulic pile hammer to drive piles. It is necessary to explore the hammer driving criteria under on this condition. The result of the DANISH formula was s=70mm at the last three blows, which is too large, and the reference value provided by the Guangdong standard is difficult to accurately select. The result of the Hilley formula is s=17.5mm, which is relatively close. It is assumed that the PHC500 pipe pile has a wall thickness of 125mm, and the penetration rate of each of the last three blows is no more than 20mm. Combined with the test results of the axial compressive resistance, it is shown that the hammer driving criteria can not only reduce the loss rate but also exert the normal potential of axial compressive resistance. Related Articles | Metrics

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Mechanical Properties of Black Soil Under Dry-Wet, Freeze-Thaw Cycles LU Zheng, GAO Shijun, ZHAO Mingyang, SU Anshuang, WANG Miao, LUO Xingwen 2024, 38 (6):  1093-1098.  Abstract ( 141 )   Save To analyze the mechanical property changes of the black soil under dry-wet and freeze-thaw cycles, the fissure observation, volumetric strain measurements, direct shear tests and unconfined compression tests are performed on black soil samples under the two cycling modes. The results show that: (1) Black soils are characterized by the wet swelling and the dry shrinkage, the frost swelling and the melt shrinkage. After the first dry-wet cycle, the net volumetric strain is 12.5% and obvious cracks occur; After the first freeze-thaw cycle, the net volumetric strain is 0.45% without obvious cracks. (2) The internal friction angle of black soil samples decreases the most after the first dry-wet cycle, from 25.2° to 23.7°, and is basically stable after the third cycle. The internal friction angle decreases from 25.2° to 23.4° after the first freeze-thaw cycle and then fluctuates around 23.4°. In both cycling modes, the cohesion decreases with the increase of the number of cycles, and the decay of the cohesion is greater after the dry-wet cycles. (3) After the first dry-wet cycle, the unconfined compressive strength of the black soil samples decreases by 32.3%. After the first freeze-thaw cycle, the unconfined compressive strength deceases by 38.2%. The unconfined compressive strength of black soil samples is stabilized in the third cycle. Related Articles | Metrics

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A Comparative Analysis of Monitoring Results for Cast-in-Place Pile, Steel Sheet Pile, and SMW Columns in the Supporting Structures in Basement Excavation Projects in Taicang City WEI Cheng 2024, 38 (6):  1099-1112.  Abstract ( 199 )   Save Different types of supporting structures in the deep excavation projects often exhibit different behaviors even under the same engineering conditions. This paper presents a comprehensive pipe gallery deep excavation project in Taicang. This article compares three types of supporting structures: cast-in-place concrete piles, steel sheet piles, and Soil Mixing Wall columns. Through analysis of the vertical displacement of the top of the deep excavation supporting structures, the deep horizontal level of the support piles, and the settlement results of the surrounding ground surface, it is found that the deformation analysis of the SMW retaining structures and the cast-in-place concrete piles are basically the same. The SMW retaining structures have lower stiffness than the drilled cast-in-place concrete piles, and the deformation of the pile shaft is relatively larger. The Larson steel sheet piles perform the worst under the current excavation depth conditions. In terms of the impact on the surrounding environment, the SMW retaining structures have a smaller impact than that of the cast-in-place concrete piles. At the same time, due to the limitations such as the on-site construction conditions, time span factors have a certain impact on this observation. The Larson steel sheet piles have reached the limit of the retaining soil under the current weak soil conditions, and the settlement change of the surrounding soil has undergone a sudden change during the observation period, which has the greatest impact on the surrounding environment. In terms of the vertical displacement at the top of the pile, the three types of supporting structures perform similarly. Related Articles | Metrics