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29 February 2024, Volume 38 Issue 1 Previous Issue    Next Issue

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Wedge Failure Mechanism Analysis on a Road Cutting Slope ZHOU Xiaomin, XU Baotian, CAO Yue, WANG Qiuyang 2024, 38 (1):  1-5.  Abstract ( 325 )   Save This paper presents the case history of a rock slope which failed six years after the excavation. The failure mechanism was analyzed throughout the field investigation before and after the sliding, physical and mechanical test of the rock mass and the stability evaluation. It is found that the failure modes of the slope are mainly wedge sliding. The excavation and the rainfall also accelerated the weathering of the slope rock mass. The XRD test showed that, compared with the fresh rock, the clay mineral composition in the weathered rock increased, which resulted in the decrease of the rock mass strength. The shear strength parameters of the weathered joints were determined by the Barton-Bandis criterion, and the stability of the was analyzed by the limit equilibrium method. Considering the dynamic change process of the groundwater, the slope stability was evaluated based on two types of water pressure models. The results showed that the slope stability decreases gradually, with the increase of the water pressure, and eventually led to the failure. According to the failure mechanism, suggestions were proposed for the slope treatment. Related Articles | Metrics

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Optimal Design and Analysis of Stability of a Deep Excavation Supporting Structure DING Longxiang 2024, 38 (1):  6-10.  Abstract ( 245 )   Save With the continuous development of urbanization, deep excavation projects for the high-rise buildings and subway stations are emerging, and the stability analysis of the deep excavation is gradually gaining the public attention. This paper introduces the key points and difficulties of the design and construction of a deep excavation supporting structure in Guangzhou. The stability of the supporting structure is also evaluated. It is concluded that a large surplus in the stability of the structure and two optimization schemes in order to take into account safety and economy are proposed. Comparing the analytical results, it can be seen that the first scheme is more economical and safer, and it is recommended to take the top 1:1 grading of the deep excavation supporting structure and cancel the second concrete support measures. This investigation result can provide reference for similar projects in the region. Related Articles | Metrics

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A Protective Measure for Upper Portion of the Pile Borehole SHEN Shouchang, CHEN Jianzhong, LU Jinghua 2024, 38 (1):  11-13.  Abstract ( 172 )   Save Pile foundation is a common foundation construction method, which has the advantages of wide adaptability and high single pile axial capacity. In the process of the pile foundation construction, falling is a very common type of safety hazard, which accounts for a large proportion of casualties, and there are no specific provisions for the protection measures for the top of the open pile borehole. By referring to relevant standards and norms and combining actual work experience, this paper introduces in detail a composite pile borehole top protection measure from three aspects: setting up protective nets, erecting protective railings and hanging safety signs in the railings. The protection measure can achieve a good protection for the upper opening of the pile borehole, meet the needs of the subsequent pile borehole detection, and at the same time, the material is convenient and durable. Through the strict implementation, the risk of falling potential at the borehole opening is reduced and the level of safe construction is improved. Related Articles | Metrics

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Stress and Deformation Characteristics of Underreamed Anchor in a Deep Excavation in Coastal Soft Soils LIU Kai, LI Wenhui, GENG Lin, ZHANG Wenbin, SUN Weiqing, YUAN Jingqiang 2024, 38 (1):  14-19.  Abstract ( 232 )   Save To solve the technical difficulties in a deep excavation support in the coastal soft soils such as new backfill soils and silty soils, the underreamed anchor by the jet grouting or ordinary prestressed anchor and cast-in-place pile are used in a project. The problems such as borehole collapse and insufficient anchoring force of the anchor construction in coastal soft soils are effectively solved by adopting such technologies as drilling with pipe, simultaneous installation of the anchor cable and full-length grouting, thus ensuring the safety and stability of the deep excavation supporting structure. On this basis, the acceptance test of the uplift capacity of the underreamed anchor by the jet grouting and ordinary anchor is performed. The acceptance test of the uplift capacity of anchor cable shows that the underreamed anchor by the jet grouting can provide enough uplift load in the coastal soft soils. Meanwhile, the result of the cable elongation value in the acceptance test less than the theoretical elongation value of the free section was discussed and analyzed, and improvement solutions were proposed.  Related Articles | Metrics

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Mitigation and Cause Analysis of Water Gushing Hazard in Deep Excavation in Thick and Strong Permeable Soils ZHAO Qiqi 2024, 38 (1):  20-23.  Abstract ( 263 )   Save This paper presents the treatment process and causes analysis of the water gushing hazard in the process of a deep excavation in a subway station construction in Fuzhou. The lessons learned are as follows: Thick and strong permeable stratum has the characteristics of the large water volume and the strong permeability. The bottom of the excavated area has been sealed and reinforced, so that the water layer below the reinforcement layer has pressure bearing. On the basis of meeting the stability requirements of the artisan water against the sudden surge, the deep excavation should fully consider whether there are weak parts in the reinforcement layer through pumping test before construction. During the excavation process, the normal operation of the dewatering well should be ensured, and the occurrence of the water gushing hazard can prevent the expansion of the hazard. If the monitoring data changes greatly, the earth covering and backfilling should be conducted in time to ensure the safety of the excavated area. After the backfilling, the water gushing part should be blocked and grouted to ensure that the safety situation is controlled before the excavation. Related Articles | Metrics

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Design of a Subway Tunnel Crossing the Existing Old Tunnel at a Close Distance JIANG Lei, CHEN Li, CHEN Song 2024, 38 (1):  24-28.  Abstract ( 165 )   Save With the rapid development of the urban rail transit construction, the number of new subway tunnels crossing through existing old railway tunnels at short distance is increasing. Based on the complex geological environment of the existing old Beijing Guangzhou railway tunnel and the current condition of the structural damage and the serious water leakage, the alignment selection options of crossing the old tunnel by the east station of the Railway College and Yuhuating station of the Changsha Metro Line 7 is analyzed, the design options of the shielded, underground excavation and open excavation on the west line by means of numerical simulation are compared. After comprehensively considering the conflict with other projects and the slope of the line, the upper crossing options of the west line is selected. Based on the consideration that the disturbance to the existing old tunnel in the lower part is minimal and is conducive to the long-term protection of the existing old tunnel, the open excavation construction is selected and finally the open excavation is selected. This experience provides a reference for the design and construction of similar projects. Related Articles | Metrics

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Application of Both Long and Short Piles in a Deep Excavation Support in Thick Soft Soils Xiong Haiming, ZHOU Junyao, CHEN Shuang, ZHANG Wei 2024, 38 (1):  29-34.  Abstract ( 284 )   Save The safe and economical deep excavation supporting structure types in thick and soft soils are drawing increasingly concern by the practical engineers. This paper presents the design, analytical methods, construction monitoring aspects using both long and short piles in a deep excavation supporting project in Guangzhou. The results show that: (1) It is difficult to control the horizontal deformation of cantilever soldier piles top in soft soils, and it is a very effective measure to control the horizontal deformation of the soldier pile top by means of passive zone reinforcement from the bottom of the support beam. (2) when the excavated bottom is in the soft soils, and the excavated area must be supported by rows of piles and internal bracing, the spacing arrangement of both long and short piles is an effective optimization measure when other aspects cannot be optimized. (3) when both the long and short piles are used in the deep excavation support, the simplified model of “Considering only the action of long piles to analysis the overall stability and considering the reinforcement of the short piles and long piles together to evaluate the overall stability” can be adopted, the analytical models can be applied to the practical engineering and have achieved satisfactory results. Related Articles | Metrics

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Settlement Analysis and Control Measures for a Shielded Tunnel Closely Crossing an Existing Metro Station JI Wei 2024, 38 (1):  35-40.  Abstract ( 179 )   Save This paper presents a case history of a shielded tunnel of Nanjing Metro Line 7 from Gaomiao Road Station to Yongchu Road Station crossing the existing transit station. The MIDAS GTS NX finite element software is used to perform the numerical simulation on the entire construction process. Based on the actual monitoring data during the construction, the influence of the shielded tunnel construction on the settlement and deformation of the existing station is analyzed. The results show that when the shielded machine is excavating in the water-rich silty sand stratum, due to the disturbance to the surrounding soils, the change of the soil stress state causes the settlement and deformation of the existing structure; The existing structure deformation and the ground surface settlement caused by the shielded construction can be effectively controlled by selecting the reasonable range of the ground reinforcement, defining the reasonable earth pressure value, reducing the downtime and other measures, and at the same time controlling the grouting effects such as shielded tail synchronous grouting, lining and ground gap grouting filling. Related Articles | Metrics

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Deformation Analysis of Adjacent Subway Tunnel Caused by a Nearby Deep Excavation HU Chuanjia, YIN Rongyu 2024, 38 (1):  41-45.  Abstract ( 157 )   Save With the urbanization development, the subway has become an important mode of transportation. The excavation and unloading of excavated area will inevitably induce adverse stress and deformation on the adjacent subway tunnels, and even affect the safe operation of these tunnels. Based on a deep excavation project near a existing tunnel in Beijing, the monitored data of the tunnel settlement deformation, convergence deformation and track gauge are presented. The results are also compared with the tunnel displacement under different excavation conditions simulated by the finite element software. The deformations of the adjacent high-speed subway tunnel under the deep excavation are presented. The conclusions show that the excavation will induce settlement and convergent deformation to the tunnel. The closer the tunnel is to the excavated area, the more significant the tunnel settlement deformation and track gauge displacement. Timely completion of excavation support structure can reduce the deformation of adjacent tunnels. Related Articles | Metrics

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Slope Stability Analysis and Reinforcement Management Using Real-Time Monitoring Data WEN Huibo, ZHANG Bangxin, LONG Chunyu, XU Zhiwei 2024, 38 (1):  46-50.  Abstract ( 173 )   Save A highway side deformed slope is monitored by different measures. These methods combine with intelligent safety monitoring road networking system for slopes, monitor the slope deformation using Beidou GNSS and slope surface displacement sensors. The dynamic assessment of the slope stability based on the real-time monitoring data are presented. Throughout the comparative analysis of the slope stability and results of the real-time monitoring data, the verified the accuracy of slope stability assessment are obtained. During the implementation of the reinforcement program, the construction sequence and schedule are adjusted according to the results of dynamic assessment of the slope stability to ensure construction safety. The reinforcement results show that the real-time monitoring data can provide an important basis for the slope stability analysis, reinforcement plan and its effect evaluation, and guarantee construction safety, which can be used as a reference for similar projects. Related Articles | Metrics

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Safety and Stability Analysis of a Large Caisson Foundations for Long Span Bridges YANG Zhi, GUO Mingwei, XU An, JIANG Fan 2024, 38 (1):  51-56.  Abstract ( 207 )   Save An efficient and stable sinking is the goal of the sinking large-span bridge caisson foundations during the construction. This paper presents a case history of a foundation project of the large caisson on the north anchorage of the Zhangjinggao Yangtze River Bridge. In order to ensure the safety and stability of the large caisson during the sinking process, a three-dimensional finite element analysis method was used to analyze the deformation and stress characteristics of the caisson structure under five typical working conditions. Combined with the caisson sinking coefficient, the corresponding caisson sinking coefficient values for different specific working conditions were determined, it can be used to guide the construction of caisson foundations. The analytical results indicate that the deformation and stress characteristics of the caisson foundation under five typical working conditions are within the design permission range. At the same time, compared with the previous estimation of the settlement coefficient using a one-stage process, the settlement coefficient estimated based on the specific working conditions can better reflect the safety and stability of the caisson foundation after being elevated and sunk under the current state, providing strong technical support for the design and construction of the caisson foundation. Related Articles | Metrics

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Deep Excavation Practice under Complicated Urban Environmental Conditions ZHENG Wei, WANG Haicheng 2024, 38 (1):  57-61.  Abstract ( 147 )   Save A deep excavation project in Wuhan is in the key prevention and control area of deep and thick and soft soil area. The depth of the proposed excavation is large. The artisan water with high head exists in the deep sand layer and the aquifer has been exposed. At the same time, the project is in the main urban area of Wuhan. The construction site is narrow, and the adjacent environment is complicated. The deformation of the deep excavation is sensitive, and the requirements of the environmental protection are restrictive. By adopting the safe and effective design of supporting, dewatering and strictive quality assurance measures, the seepage failure can be avoided, and the deformation of the supporting system can be well controlled. The adverse effects on the adjacent environment can be avoided. Based on the characteristics of the project, the circular type of the internal supporting system with a reasonable force performance is adopted to release more space and improve the construction efficiency. The entire process of the deep excavation monitoring provides information support for a safe deep excavation. Related Articles | Metrics

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Research on Layout Method of Reinforced Concrete Support for a Foundation Pit Project in Xuzhou SHEN Rongfeng, YANG Ning, 2024, 38 (1):  62-66.  Abstract ( 141 )   Save Reinforced concrete support is a common type of support in the deep excavation supporting engineering. However, improper support layout often leads to the unreasonable stress and the uneconomical cost. Therefore, it is of practical significance to analyze the layout of the reinforced concrete support. This paper presents deep excavation project in Xuzhou, Jiangsu Province. The finite element analysis method of the spatial overall coordination is used to compare and to analyze different forms of support layouts. The evaluation and analysis results show that the support force superposition is generated in the corner bracing overlap area, resulting in an increase in the stress of the waler beam, and the displacement of the pile points to the outside of the excavated area, while the displacement at the other end of the corner bracing overlap area points to the inside of the excavated area and is larger, and the deformation around the deep excavation is not coordinated. Therefore, the process of arrangement of the supporting system should avoid the cross overlap. For a general rectangular excavated area, it is suggested using the form of corner bracing plus diagonal bracing to ensure the collaborative deformation around the excavated area. The study of the concrete support arrangement can provide a reference for the similar excavation engineering problems. Related Articles | Metrics

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Deformation Evolution Characteristics Analysis of The Existing Tunnel During the Deep Excavation Above ZHANG Lei, ZHANG Shuzhan, QU Chengkun, LI Ying, LI Changjun, LU Yuquan, 2024, 38 (1):  67-70.  Abstract ( 134 )   Save With the increasing utilization of the underground space in urban areas, studying the deformation characteristics of the deep excavation above the existing tunnels is of significant importance for the construction safety and the support design. Based on the Tianmu Mountain Road transformation project, the surface settlement of both the excavated area and adjacent excavations were analyzed during the excavation process, and the general rules of settlement deformation of the underlying existing tunnel were monitored and obtained. The results showed that a reasonable supporting structure can effectively control the settlement deformation around the foundation pit, and during the reinforcement stage above the foundation pit, the existing tunnel below was significantly affected, resulting in significant settlement deformation. However, the deformation during the construction stage after reinforced was relatively small. The finding of this study has reference value for construction design and risk control. Related Articles | Metrics

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Spatial Effect of Deep Excavation Under Unbalanced Earth Pressures CAO Ming 2024, 38 (1):  71-75.  Abstract ( 181 )   Save The traditional analysis theory of the deep excavation and the conventional excavation engineering design software cannot fully consider the spatial effect in the deep excavation construction process. This paper presents an excavation engineering in Wuhan. The finite difference numerical software was used to establish the three-dimensional numerical model of the area to be excavated. Through the estimation of the displacement field and the stress field of the supporting system and the surrounding environment, analysis of variation of the uneven terrains, the construction deformation induced by the unbalanced earth pressures in the process of deep foundation are investigated. The results show that the unbalanced earth pressure has obvious influence on the bearing deformation characteristics of the excavated area. The supporting structure may be globally tilted due to the unbalanced earth pressures. There are significant spatial effects in the process of the deep excavation construction. The long side and the short side of the excavated area are mutual supports, but the supporting effect of the long side to the short side is more significant than that of the short side to the long side. Related Articles | Metrics

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Damage of High-Rise Building Substructure Caused by Groundwater Fluctuations BAI Junfeng, LIU Xinlong, FU Xu, LI Qian, YIN Baoyin 2024, 38 (1):  76-80.  Abstract ( 182 )   Save To study the influence of the variation of the groundwater level on the damage of high-rise building substructures, this paper investigates potential factors. Throughout the literature review and comparative analysis, this paper presents the erosion of the pile foundation caused by the groundwater, damage of underground structure caused by the groundwater fluctuation, the settlement of the underground structure and coordinated deformation of underground structure system. The results show that: (1) the finite element analysis of the variation of the groundwater level on the underground structure, such as water level withdrew process after the groundwater level rise, needs further experimental and simulation studies; (2) reasonable design of basement, timely reduce the impact of rising groundwater level; (3) The variation of the groundwater level will cause the settlement of the foundation and irregular deformation of the underground structure; (4) considering the interaction between the components in the design will have a satisfactory effect on the practical engineering analysis. Related Articles | Metrics

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Post Grouting Methods for Bored and Cast-In-Cast Concrete Piles LIU Fang 2024, 38 (1):  81-85.  Abstract ( 124 )   Save With the fast development of the infrastructure construction, foundation construction difficulties are encountered at different geological areas with the most difficulties in the soft soils. Among these, the ground improvement in the soft soil areas is the most important and is critical to the entire construction quality. The post grouting technique for the bored and cast-in-place concrete piles is more and more applied in the construction. This paper presents the state-of-the-art review of the post grouting mehtods. Related Articles | Metrics

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Study of the Thixotropy of the Zhanjiang Formation Structural Clay Using Grey Association Analysis ZHAO Shengnan, LENG Yukun, LIU Xueguang 2024, 38 (1):  86-89.  Abstract ( 189 )   Save The thixotropy of structural soils is a description of the strength recovery after soil disturbance. To accurately distinguish the degrees of the strength recovery of soil, a comprehensive thixotropy evaluation method is proposed. In this paper, the thixotropy of a structural clay in Zhanjiang Formation is studied. Considering the factors affecting the thixotropy of the structural clay in Zhanjiang Formation, the unconfined compressive strength test was performed, and the thixotropy evaluation index system of the structural clay in Zhanjiang Formation was established based on the water content, the void ratio and the sensitivity. The grey correlation analysis method was used to analyze the correlation degree between the thixotropy of the structural clay in Zhanjiang Formation and each evaluation index, and to judge the influence of each factor level on the thixotropy. The results show that the high moisture content and the void ratio inhibit the correlation with the thixotropy, while the high sensitivity promotes the correlation with the thixotropy. Related Articles | Metrics

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Variation of Axial and Shear Forces of the Ground Anchor During Shearing LIU Shunchang, LI Li, XU Dexin, ZHU Linfeng, TIAN Jianlin 2024, 38 (1):  90-95.  Abstract ( 144 )   Save This paper presents the evolution and contribution of axial and shear forces of the ground anchor during the shearing process of anchored joint interface. A numerical simulation of the direct shear test on the anchored joint interface was performed by using the FLAC3D software. The “pile” element is used instead of the conventionally used “cable” element to simulate the ground anchor. The distribution and evolution characteristics of both the axial and the shear forces of the anchor are studied during the shearing process. The effects of the ground anchor diameter, anchor inclination, and surrounding rock strength on the axial and shear forces of the bolt are analyzed. The results show that: (1) The shear force and the axial force of the ground anchor at the joint reach the maximum value, which are small at both ends, the shear force reaches a large value with a small displacement, and the exertion of the axial force is relatively lagging, two “plastic hinge” points appeared on the bolt within a range of about 5D on both sides of the joint, and there is a “pullshear zone” in which the bolt deforms sharply between the plastic hinge points. (2) The peak shear strength of the joint is increased by about 70% after the anchoring, and the reinforcing effect of the ground anchor on the joint can be equivalent to increasing the cohesion of the joint. (3) With the diameter increases, the shear force of the anchor increases significantly, but the axial force decreases. When the inclination of the bolt is 60°, the maximum equivalent shear strength of the joint converted from the axial force and the shear force is obtained; Compared with the soft rock, hard rock is more conducive to the exertion of the bolt's axial and shear forces. Related Articles | Metrics

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Advance and Review on Shear-Flow Coupling of Fractured Rock MA Chishuai 2024, 38 (1):  96-102.  Abstract ( 159 )   Save A modified energy criterion of the rock burst is proposed, by accounting for the brittleness index and the rock burst energy criteria comprehensively. The energy accumulation in the rock burst incubation process was tracked and analyzed quantitatively, and the intensity and the position of the rock burst in the excavation process of the underground engineering under the high stress were predicted reasonably based on the numerical simulations. The evolution of the rock burst incubation was explored. The rationality and effectiveness of the modified energy criterion were verified by comparing the original prediction index applied to the typical rock burst case. Related Articles | Metrics

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Influence of Water Content on Mechanical Properties of Interface Between Steel and Plateau Frozen Soil QIONG Ji 2024, 38 (1):  103-106.  Abstract ( 101 )   Save The research on the behavior of the interface between the structure and the plateau frozen soil can play a reference significance for the construction of the pile foundation in high altitude and cold regions. To analyze the influence of the soil water content on the interface shear properties, the shear tests of the interface between the plateau soil and the steel under different water content were performed. The results show that when the water content of the soil is less than the optimal water content, the shear stress increases first and then stabilizes with the shear displacement. The shear stressshear displacement relationship can be expressed by the exponential function. When the water content is greater than the optimal water content, the shear stress shows the relationship of the strengtheningattenuationresidual stability, and the shear stress-shear displacement relationship can be expressed by the piecewise function. The interface shear strength and the residual strength increase with the normal stress, and first increase and then decrease with the water content. With the increase of water content, the interface friction angle decreases gradually, and the interface cohesion reaches the maximum near the optimal water content. Related Articles | Metrics

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Engineering Geological Characteristics and Stability Analysis of Taozhou Ancient Landslide XI Renshuang 2024, 38 (1):  107-111.  Abstract ( 146 )   Save The ancient landslide is of ancient origin, complex in cause, and difficult to locate. However, when engineering activities pass through, due to the impact of the human disturbance, ancient landslides are very prone to reactivation, posing a serious threat potential to the engineering projects. The Taozhou ancient landslide is presented in this paper as an example. The combination of the drilling and the geophysical exploration methods was used to conduct engineering geological investigations of the ancient landslide site, obtaining the engineering geological conditions of the area. The landslide site is a medium-thick layer large landslide body formed by accumulation and traction. Based on the nature and the characteristics of the landslide deformation, combined with survey data, key factors affecting the stability of the ancient landslide were identified: the material composition and the structural characteristics; topographic conditions; the continuous rainfall and the groundwater; and the human engineering activities. The limit equilibrium method was used to evaluate the stability of the ancient landslide. The analytical results indicate that the ancient landslide site is overall in a marginally stable state; however, since the landslide body is mainly loose accumulation, the results of local stability analysis show that the small-scale accumulation landslides will occur at the front of the ancient landslide. This analysis result is consistent with the on-site investigation, where two small collapses were observed at the front of the landslide. Finally, a comprehensive analysis of the above results provides some suggestions for the highway alignment and the treatment of the collapsed body at the front of the landslide. Related Articles | Metrics

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Evaluation of a Large Landslide with Large and Long Cracks and Failure Modes ZHANG Ya, LIU Shihong, LEI Qing, FANG Zhengfeng, JIANG Bo 2024, 38 (1):  112-116.  Abstract ( 170 )   Save The slope failure modes under the control of long and large cracks in Ganlong landslide hazards are analyzed based on the measured geological tectonic structure and threedimensional numerical simulation. The results show that:(1) the landslide is a V-shaped tensile shear landslide controlled by the long and large cracks; (2) after the landslide starts, the central sliding body in the I zone slides along the free face of the long and large cracks cut rock mass, and the mountain at the back edge is damaged by the traction and tension. The sliding body turns to the right edge of the landslide when it meets the barrier of the steep wall at the left edge, and then pushes and shears the front slope body in the I zone, and finally deposits to the channel in a “7” shape；(3) with the increase of the penetrating length and the depth of the fracture, the length and depth of the cut rock mass, the free surface of the rock mass, and the wedge form formed by the combination with the plane, the peak displacement and the deformation area near the boundary of the landslide increase in different degrees, once the cracks developed through the sliding surface, a wedge shaped landslide will be formed. Related Articles | Metrics

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State-of-the-Practice and Perspective of Geotechnical Investigations for the Expressway Widening Engineering LIN Jianan, YAN Junfeng, YANG Xin 2024, 38 (1):  117-119.  Abstract ( 136 )   Save With the rapid development of the nation’s economy, China is actively improving the highway system and widening engineering to meet the increasing traffic demand. At present, there is no relevant standards and guidelines and few reference literatures for the highway widening geotechnical investigations. By collecting the reference data, this paper state-of-the-practice of the geotechnical investigations for the highway widening projects. Issues that need to be paid attention in the highway widening project geotechnical investigations, such as the utilization of the existing investigation data, reasonable distribution of the investigation workload, combination of the current and existing investigation data for the current widening plan, utilization of the “digital investigation” and “green investigation”. Some of the existing hard copies can be digitized into electronic files so that the information can be rejuvenated and integrated.  Related Articles | Metrics

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Study on Permeability Characteristics of Clay Samples Using Seepage Tests XU Lingmin, CHENG Yun, LI Yuhong, WANG Jingjing, SU Hao 2024, 38 (1):  120-124.  Abstract ( 230 )   Save Both the soil property and the void ratio are important factors affecting the permeability coefficient of the fine-grained soils. The influence of the soil property is mainly reflected in the reduction of effective seepage diameter of the soil voids by the thickness of the bonded water film in the soil particles. To analyze the influence of the void ratio change on the permeability coefficient, this time, an improved seepage test device was used to perform the permeability test on the old clay, the alluvial-diluvial silty clay and the Dianchi Peat soil samples. The relationship between the permeability coefficient K and the void ratio change of these three typical soil samples was systematically analyzed. The test shows that, with the decrease of the void ratio, the permeability coefficient gradually decreases, showing a positive correlation, and a power function relationship, the relationship is, different soil types, the value of B is different. For old clays, the void ratio has little effect, but for silty clays, the special structure and material composition of peaty clays play a decisive role. Related Articles | Metrics

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Experimental Study on Treatment of Cleaning and Grouting of Sediments at Bottom of Bored Piles FAN Rongxia, ZHAN Shaoquan, CHEN Chong 2024, 38 (1):  125-128.  Abstract ( 119 )   Save Through the cleaning the sediment at the bottom of the bored piles and grouting treatment, the bearing behavior can be improved so that it can take the design load. Due to geological conditions, construction methods and other factors, the bored and cast-in-place concrete piles are prone to accumulate thick sediment at the bottom of the borehole. The load settlement (Q～S) curve of the static load test shows a steep drop type, the total settlement is too large, and the bearing capacity generally cannot meet the design requirements. Through the pile top drilling, high-pressure water flushing and waste removal, combined with pile end grouting to produce compaction, condensation, and consolidation effects, improve the axial bearing characteristics at the pile end, improve its strength and stiffness, reduce the settlement at the pile end and improve the axial bearing capacity of a single pile. Therefore, the comparison of the axial bearing characteristics of the pile end before and after the test can significantly improve the axial bearing characteristics of the pile end. Related Articles | Metrics

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Deformation Monitoring and Numerical Analysis of a Deep Excavation Supporting Structure LU Silian, YUAN Jinxin, ZHANG Ye, LU Jinghui, WANG Yuexiang 2024, 38 (1):  129-134.  Abstract ( 109 )   Save Combined with a deep excavation project in Suzhou, the monitoring results of the horizontal and vertical displacement at the top of pile (slope), groundwater level and surface outside the excavated area with different supporting structures in the process of the deep excavation construction are collected and the monitoring data are systematically analyzed. The results show that with the excavation progress, the horizontal displacement of pile (slope) top of different retaining structures gradually shifts to the inside of excavated area. The cumulative absolute value of the vertical displacement of pile (slope) top increases gradually, and the change trend of time history curve of the vertical displacement of pile (slope) top at each measuring point is essentially the same. The soil around the excavated area has settlement, but the cumulative value of the surface settlement outside the pit is not large and is within the allowable value. Therefore, the support form of the SMW method pile, bored pile combined with triaxial mixing pile and twostage slope combined with mixing pile is effective. Finally, the numerical analysis of the deep excavation supporting structure is performed by using the ABAQUS finite element software. The results show that the variation relationship of the numerical simulation and monitoring results is consistent, indicating that the design of the deep excavation supporting structure is reasonable. Related Articles | Metrics

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Water Content Variation on the Mechanical Characteristics of Granite Residual Soil in Guangzhou YAO Tenghao, QI Guishang YANG Xueqiang, HUANG Xianlun, ZHU Chengyuan, MAO Jimin 2024, 38 (1):  135-138.  Abstract ( 228 )   Save The unconsolidated-undrained direct shear tests were carried out on the undisturbed and remolded granite residual soil samples, and the test curves between the moisture content and shear strength of the granite residual remolded soil in Guangdong University of Technology area were obtained. The experimental results show that, under the same water content and dry density, when the vertical pressure is less than the initial consolidation pressure, the cohesion of the remolded soil is less than that of the undisturbed soil, and the internal friction angle of the remolded soil is also less than that of the undisturbed soil. When the vertical pressure is greater than the initial consolidation pressure, the shear strength of the remolded soil is gradually close to that of the undisturbed soil; as the vertical pressure is greater than 135kPa, the shear strength of the undisturbed soil begins to be smaller than that of the remolded soil, and the internal friction angle of the remolded soil is larger than that of the undisturbed soil. In the comparison of the unconsolidated-undrained shear tests of granite residual remolded soil with different water content, the shear strength of soil increases with the increase of vertical pressure, the cohesion of remolded soil decreases significantly with the increase of water content, while the internal friction angle decreases slightly with the increase of water content. Related Articles | Metrics

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Application of Low Strain Method Combined with Coring in Pile Length Estimation MENG Xinqiu 2024, 38 (1):  139-142.  Abstract ( 207 )   Save The low strain method can be used to estimate the integrity along the pile shaft and the length of pile. When the test results of pile length are in question, the coring method can be used to verify. When the pile lengths of the entire project are tested, a representative value of the wave velocity can be determined by combining the low strain method and the core drilling method. When the wave velocity of the pile is greater than the representative value of the wave velocity, the length of the pile can be determined. Combined with engineering examples, this paper introduces the combination of the low strain method and coring method to verify the pile length detection of all CFG piles on a composite foundation. The low strain method and coring method can demonstrate their own advantages in the process of the pile length estimation and complement each other; The actual strength grade and the elastic modulus of the pile concrete can be determined by the compressive strength test of the cored sample. The representative value of the wave velocity can be calculated according to the theoretical formula of the relationship between the wave velocity of concrete and the elastic modulus as well as mass density. The theoretical calculation results and the field test results can verify each other and achieve the good results. Related Articles | Metrics

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Static Load Test Results on Static Pressed-in Square Piles LI Ming 2024, 38 (1):  143-147.  Abstract ( 183 )   Save In a project, 12 static pressedin square piles were selected for the sacrificial static pile loading testing, which provides a basis for the design of production piles. By calculating the characteristic values of the theoretical ultimate axial capacity of each single pile, and then converting them into the standard values (hereinafter referred to as theoretical values) and comparing them with the ultimate axial capacity of the single pile under the vertical compression (hereinafter referred to as test values), the relationship between the theoretical value and the experimental value and the ending pressure are analyzed by monitoring the peak value and the ending pressure. It is found that the end pressure of the pile with clay soil as bearing stratum is smaller than the test value, and the end pressure of the pile with sandy soil as bearing stratum is larger than the test value The experimental and theoretical values of the long pile foundation with clayey soil as bearing stratum accord with the linear regression equation of single variable and the fitting degree is high. Suggestions to guide the construction of the production piles are obtained by observing the stratum where the pile tip is located when the peak of pile pressure presented. Related Articles | Metrics

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Testing of Effect of Dynamic Compaction in a Mountain Area ZHOU Peifeng 2024, 38 (1):  148-151.  Abstract ( 126 )   Save During the dynamic compaction, multiple testing methods are used to verify the effectiveness of the ground improvement. However, the duration of some of the testing methods is long. How to quickly and effectively determine the effectiveness of dynamic compaction, to provide preliminary testing results in a timely manner, and to shorten the testing cycle have become a problem that needs to be resolved in on-site testing work. Based on the analysis of the reference test project for the dynamic compaction in a mountainous area, different detection methods such as standard penetration test, shallow plate load test on the treated soil, and multi-channel transient surface wave test were used on site to evaluate the bearing capacity and effectiveness of the dynamic compaction. And by comparing and analyzing the surface wave test results before and after dynamic compaction in each experimental area, combined with the standard penetration test results, the relationship between the shear wave velocity and soil compaction degrees in the plain fill experimental area is obtained, providing a good basis for the large-scale dynamic compaction construction in the later stage. Related Articles | Metrics

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Study on CT Scan Technology for Detecting Karst Rock Cavities and Distribution LI Jing 2024, 38 (1):  152-156.  Abstract ( 126 )   Save The electronic-magnetic computed tomography (CT) is an important means and method for the engineering exploration of karst cavities. The development type and degree of the underground karst cavities and their distribution characteristics have important reference value for the engineering design. This paper presents a case history of a subway station in Wuhan. The chemical and mineral composition analysis of the soluble carbonate at the site were analyzed to investigate the karst type and development degrees. The CT scan method was used to study the spatial distribution characteristics of the karst from the vertical height of karst anomalies, elevation distribution, and spatial relationship with bedrock. Meanwhile, borehole technology is used to verify the detection results. The results show that, the structures of the soluble rock are mainly marl, bioclastic limestone and micrite, and the mineral composition is mainly composed of calcite and dolomite, and karst is moderately developed in the field. The locations of the karst anomalies inferred by the geophysical CT are consistent with those revealed by borehole methods. The vertical height of karst anomalies is mainly distributed in 0~4m, and there are few anomalies with the vertical height greater than 4m. The elevation of the karst anomaly points mainly distributed in 27m ~ 13m, accounting for 70% of the total, while the proportion of karst cavities exposed by the drilling is 60% affected by factors such as the drilling density. Karst anomalies and karst cavities are concentrated within 6m below the bedrock surface, accounting for about 63% of the total, and the number of the karst anomalies and karst anomalies decreases with the increase of the depth. The above research indicates that CT detection of karst cavity development and distribution is completely feasible. Related Articles | Metrics

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Experimental and Numerical Simulations of the Mechanical Properties of Shale Under High Temperature MENG Xiangrui, WU Zhonghu 2024, 38 (1):  157-162.  Abstract ( 119 )   Save The black shale samples of Niutitang Formation of the Lower Cambrian in the northern Guizhou region were tested under a 1011BS electric blast drying oven simulated high-temperature environment by the RMT-301 loading system. The uniaxial compression tests were performed on shale samples at different heating temperatures. A numerical model using the real rock fracture analysis system RFPA2D Thermal was established to simulate the fracture process of the shale at the same temperature. The results indicate that the temperature significantly affects the compressive strength of the shale sample. Starting from the room temperature, as the temperature increases, the maximum acoustic energy, the brittleness, and the peak intensity of the shale samples continue to increase, reaching their highest value at 120 ℃. Afterwards, as the temperature increases, these parameters decrease. The occurrence of the macroscopic cracks in shale samples at 200 ℃ after the temperature treatment, which propagate and penetrate during the uniaxial compression, is an important reason for their severe strength degradation.  Related Articles | Metrics