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30 April 2022, Volume 36 Issue 2 Previous Issue    Next Issue

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Cut-off Walls for Building Surrounded Deep Excavation in Saturated Sandy Stratum LUAN Jinlong, LIU Juncheng, FAN Dongdong, TAN Yong 2022, 36 (2):  115-121.  Abstract ( 381 )   Save The saturated sandy stratum has the characteristics of high groundwater level, large permeability coefficient, no cohesion, and well connected between the phreatic water and artesian water supply. The surrounding sensitive buildings will be easily affected during the deep excavations in this stratum, inducing with the differential settlement and even building structural damage. As an effective groundwater separation measure, the cut-off wall is widely used in soft soil stratum, but it is rarely used in saturated sandy strata. To explore the control effect of cut-off wall in the building deformation induced by the deep excavation in the saturated sandy stratum, combined with an engineering case history, a refined three-dimensional finite element model was established to study the building deformation under the two working conditions with and without the construction of the cutoff wall. The results show that: the cut-off wall can effectively isolate the area affected by the deep excavation and has a water-proof effect, can maintain the stability of water level at the building, reduce the impact of the deep excavation and discharging of the deep artesian water on buildings, and control the deformation of surrounding buildings within a safe range. Related Articles | Metrics

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Influencing Factors of Preloading Method in the Soil Improvement in Zouma Lake Project ZHU Fanghai, HU Shenggang 2022, 36 (2):  122-126.  Abstract ( 444 )   Save In airport engineering projects, there are strict requirements for the post construction settlement and post construction differential settlement in runways. The prefabricated vertical drainage method with surcharge preloading is often applied for the treatment of large soft soil areas. The spacing of the vertical drains as well as the surcharge ratio are the direct factors that affecting the quality and effect of the soft soil improvement. In the current design code for the soil improvement, the recommended vertical spacing varies between 0.7m and 2.1m with no clear theoretical recommendations on the applied surcharge ratio. Therefore, the quality and effect of soft improvement could not be guaranteed without careful engineering evaluation. In this paper, the Zouma Lake soil improvement was studied throughout the theoretical analysis and the model tests to illustrate the influence of spacing of the vertical drains and the surcharge ratio on the consolidation settlement. Based on the field settlement monitoring data, the influence effect of both factors on the soft soil consolidation was compared and analyzed, with indices of the predicted final settlement and the degree of soft soil consolidations. Related Articles | Metrics

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Application of HighPressure Jet Grouting in the Soil Improvement of a Deep Excavation Project ZHU Xingwang, SHI Jingge, LI Chunxiu 2022, 36 (2):  127-130.  Abstract ( 774 )   Save The high-pressure jet grout formed column in soils can effectively improve the overall shear strength of soft soils. It is an important content to evaluate and analyze the reinforcement effect of the high-pressure jet grout formed columns in deep excavation projects. In this paper, throughout a deep excavation project in Nanjing, a three-dimensional finite element models were established before and after the soil improvement using high pressure jet grout method. The bending moment, lateral displacement and the shear force in the supporting structures before and after reinforcement were compared. Further, the maximum lateral displacement at the supporting structure, the maximum rebound at the excavated base and the maximum settlement of the ground surface behind the excavation with studied with different jet grout formed wall thicknesses. The results show that after the high-pressure jet grout reinforcement, the moment, lateral displacement and establishment in the support structure are effectively reduced, and the lateral displacement in the support structure decreases by about 50%; with the increase of the column wall thickness, the maximum lateral displacement of the support structure, the maximum rebound at the base of the excavation and the maximum surface settlement behind the excavation decrease exponentially, and tend to converge gradually. Related Articles | Metrics

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Application of Vacuum Preloading Method in Narrow Road on Soft Ground Treatment Project ZHANG Ji 2022, 36 (2):  131-134.  Abstract ( 321 )   Save This paper presents a case history of using vacuum preloading method improving load narrow access roads for a residential project in Bangkok, Thailand. The principals, construction technique, construction monitoring, and soil improvements aspects of the vacuum preloading method are reviewed and summarized in the paper. Conventionally, the area to be improved by this method is between 20,000 and 40,000 square meters with the length to width ratio not greater than 10. In this project, the improvement area was only 3,637 square meters with a length to width ratio of 11.22, which was much lower than the ideal area of applying vacuum preloading method. From the improvement indices such as moisture content and shear strength, these parameters show some improvement but, comparing with the conventional area and ratio of length to width, the improvement results reduced, to some extent. Related Articles | Metrics

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Preparation of Slurries of Permeability Grouting in Karst Area LI Liejian, ZUO Wengui 2022, 36 (2):  135-138.  Abstract ( 304 )   Save With the increasing requirements of the construction standardization technology in China, the current permeability grouting treatment technique in the karst terrain cannot meet the construction requirements due to its construction procedure and large grouting material loss. The research scopes of this study are the following: to improve the grouting slurry-water ratio to be applied in the highway subgrade in the karst terrain, and to determine the improved permeability grouting results throughout the surface wave methods, pore water pressure measurement, and subgrade soil preloading evaluation. The results show that, after the improvement of permeability grouting operation, the performance indicators of all aspects of the subgrade soils have been improved to some extent, which shows that the slurry-water ratio improvement method proposed in this study is feasible and practical. It is hoped that this study can provide some reference for the improving the highway construction procedures in karst terrain. Related Articles | Metrics

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The Rockfall Failure Modes and Mitigations in Guilin TAN Mingcan, LIU Zhikui, LI Shanmei, HE Tianjie, XI Danni, NI Zhe, WANG Xiang 2022, 36 (2):  139-144.  Abstract ( 479 )   Save While a spectacular natural landform has formed in Guilin due to the special karstic topographies, many geo-hazards have also encountered consequently. This paper presents the rock fall hazards evaluation methods in Guilin area. The potentially dangerous rock cliff formation, lithology, tectonic formation and failure modes are evaluated and analyzed. Throughout the quantitative stability evaluation, the rock failure potentials in this area could be divided into three types: sliding, toppling and falling, the commercial Rocfall software was used to simulate the rock trajectory, direction of the rock fall and rebounded height. This paper provides the potential mitigation measures such as the static blasting and passive protective rockfall net. Related Articles | Metrics

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Risk Analysis and Control of Deep Excavation in Soft Soils on the Adjacent Shielded Tunnel MA Jiangfeng 2022, 36 (2):  145-148.  Abstract ( 337 )   Save In order to study the deformation with time of the tunnel structure and surrounding soil on the adjacent subway shielded section tunnel induced by the excavation and unloading of a deep foundation pit in soft soils, the excavation control measures are necessary. This paper presents the case history of a deep excavation construction adjacent to the Metro Line 4 in Nanchang City. A commercial threedimensional finite element software was used to establish the numerical analysis model. The entire excavation process was numerically simulated. The impact of the deformation of the excavation supporting structure and the surrounding soil on the safe operation of the subway was evaluated. The results show that, with the increase of the excavation depth at the foundation pit, the greater the deformations at the adjacent ground surface, bottom of the excavated area, at the surrounding supporting structures and at the shielded subway tunnel structure. The deformation monitoring should be focused on the horizontal deformation of the tunnel segments. During the excavation, the measures such as stepwise and block excavation should be adopted to reduce the impact on the adjacent tunnel in active operation. Related Articles | Metrics

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Stability Evaluation of the Waste Soil Dump Site for a Limestone Quarry in Jinan MENG Yan, WANG Qian 2022, 36 (2):  149-153.  Abstract ( 397 )   Save This paper presents a case study of the stability evaluation of a waste soil dump site of a limestone quarry. The influencing factors of the stability are evaluated. The hierarchical structure, particle-size distribution of soils, the physico-mechanical property of waste soils, and the subsurface conditions of the dump site were obtained by technical means of geological mapping, geotechnical test borings, the heavy dynamic penetration tests and the laboratory tests on the remolded waste soils. Ultimately, the stability analysis and evaluation for this dump site were performed, and stability mitigation measures were proposed. In waste soils, the size of the crushed stone is gradually increased from the top to the bottom. The subsurface condition at the bottom of the dump site consists of moderately weathered karstic limestone with gravelly clay filled rock fissures at shallow karstic rock mass. Therefore, the foundation of the dump site is stable. The slopes within the dump site could be divided into four (4) different categories with the failure mode of short-range sliding mode within the waste soil body. The factor of safety is between 0.8 and 1.0 for all slopes by using Bishop Simplified Method, which indicate that the slopes are instable. Related Articles | Metrics

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Comprehensive Fuzzy Comprehensive Evaluation of Structural Defects of the Shilibei Tunnel SONG Xiuling 2022, 36 (2):  154-157.  Abstract ( 235 )   Save The structural health diagnosis of the Shilibei Tunnel was carried out by using the comprehensive fuzzy evaluation method. On the basis of statistical analysis on the structural defect detection results of the Shilibei Tunnel, a comprehensive weighting method that combining the product scaling method and the entropy weight method is used to calculate the weight of the defect indices, the number of defects and the weight obtained by the product scaling method are multiplied. The related methods have achieved good results in the engineering applications and have the value and prospects of popularization and application. The final comprehensive fuzzy evaluation result shows that the evaluation grade of the tunnel is 2A, which basically reflects the current situation of the tunnel, indicating that the relevant evaluation method has good engineering adaptability. Related Articles | Metrics

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Analysis of the Slope Instability of an Operative Expressway in Northeast Yunnan TIAN Ran, ZHANG Jun, YE Xian 2022, 36 (2):  158-162.  Abstract ( 243 )   Save Due to its soft lithology, the red bed rock is generally characterized as the soft rock in the engineering geology industry. Under the action of the cold, hot temperature dry, wet moisture cycles, the rock mass is easy to be weathered and disintegrated in the water. The engineering geological characteristics of this rock mass are extremely poor, and the highway geo-hazards induced by the red bed rock slope is not easily to be detected. Due to the lack of corresponding highway slope maintenance technical specifications, it is difficult for maintenance personnel to accurately grasp the highway slope safety in the operation, which is to propose targeted maintenance measures at right time. This paper presents a stability evaluation case history of the expressway in Northeast Yunnan Province. Throughout the engineering geological survey, the characteristics of slope instability are evaluated. The failure of the highway slope was mainly induced by the failure of the slope protection measures and the presence of the excessive groundwater.  The stability development of the slope and the potential mitigation measures are also proposed. Related Articles | Metrics

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Pile Type Selection for a Foundation Project in Shanghai Soft Soils HUANG Hui 2022, 36 (2):  163-167.  Abstract ( 261 )   Save The prestressed high-strength concrete pipe pile (PHC) has the advantages of high strength, good bending performance and high single pile axial capacity, which is suitable for subsurface conditions. It also has short construction duration and less impact on the adjacent environment. This paper presents a case of pile type selection for a high-rise building complex in Shanghai soft soils. The subsurface conditions under the project area were evaluated and pile bearing stratum was selected based on field geotechnical investigations and laboratory tests. Both advantages and disadvantages of installing PHC pile and cast-in-situ concrete pile to be applied in this project are presented in the paper. Based on the analysis, the axial analysis of both types of piles were satisfactory but the selection of the PHC pile was more appropriate. Related Articles | Metrics

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Practice and Analysis of Deep Excavation Support in Soft Soils WANG Haicheng, WANG Wei, ZHANG Long 2022, 36 (2):  168-172.  Abstract ( 301 )   Save In the area of geotechnical engineering practice, the deep excavation engineering requires complicated and comprehensive approach for a better solution. A deep excavation project, from the initial selectin of the method of support of excavation to the final implementation and construction of supporting structures, many factors could potentially affect its success. These factors include, but not limit to, feasibility of the supporting structures, construction safety of cost considerations, adjacent environmental conditions, subsurface conditions and construction equipment loadings. This paper presents an urban deep excavation supporting design in the soft soil area case history. Factors and challenges in the deep excavation supporting structure design is also introduced. The project was surrounded by the municipal streets, existing building structures and a gas station and the excavation support design utilized double-row soldier pile plus strengthening in the passive soil zone method as well as soldier pile lagging plus internal support method. The localized area reinforcement design and minor design adjustment due to the change of subsurface soil conditions are also introduced in the paper. Related Articles | Metrics

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Evaluation of Coastal Rapid Land Reclamation Pretreatment Results MA Zhongwu, HU Bo, LI Bo 2022, 36 (2):  173-177.  Abstract ( 214 )   Save This paper presents a case history of a comparative evaluation of soil properties before and after the pretreatment of a fast land reclamation site for a petroleum project site in the coastal area. The pre-fabricated vertical drain with surcharging preloading method was used as the pretreatment method in this soft soil site with thick and un-even thickness peaty soils. The soil improvement results were evaluated by the in-situ tests and laboratory tests on samples collected from the site before and after the pretreatment. The laboratory test items included, void ratio, coefficient of compression and compression modulus and the in-situ testing methods are, Standard Penetration Tests (SPT), Cone Penetration Tests (CPT) value shear test and dilatometer test. The results indicate that the site predominantly consists of peaty clayey soils and the void ratio in the cohesive soils reduced significantly after the pretreatment with an average reduction of 24.6%. The coefficient of compression has an average reduction of 23.7%. The modulus of compression has an average increase of 5.5 times. The in-situ test results also indicate that the shear strength of the subsurface soil has a significant increase, at various locations, these increase are, 4.1, 3.9 and 1.29 time, respectively. Related Articles | Metrics

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Cofferdam Stability and Seepage Control Technique in Cobble-Peaty Mixture Soils CHEN Yanqing, ZHANG Xinjun 2022, 36 (2):  178-181.  Abstract ( 319 )   Save The cofferdam cut-and-cover method is a common underwater tunnel construction method. The seepage control and the stability of the cofferdam are critical to the safety of the entire tunnel construction. The deep embedded and thick cobble and peaty soils which are widely deposited underneath the project site impose a significant challenge for the stability and seepage control of the cofferdam. To overcome these difficulties, the riprap plus Trench cutting Re-mixing Deep Wall (TRD) method was used in the excavation of the tunnel underneath the Qingshan Lake project. The result shows that the 30 day cumulative surface settlement of the earth-rock cofferdam structure combined with riprap and TRD was less than 4.5 mm, the maximum horizontal displacement change was less than 7 mm, and the average permeability coefficient of cement and soil was 4.30×10-7 cm·s-1. The stability and the seepage resistance of the cofferdam could meet the design needs. Related Articles | Metrics

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Influence River Dredging Excavation above a Shielded Tunnel in Mucky Soils XIONG Shudan, YANG Lanqiang, XU Da, XIONG Chuyan 2022, 36 (2):  182-186.  Abstract ( 323 )   Save River dredging excavation is an unloading process, which is easily to cause deformation of the shielded tunnel below. Therefore, the influence of river dredging excavation on the deformation of the shielded tunnel section of the rail transit Line No. 2 and the adjacent subway stations is studied by using the three-dimensional finite element method (FEM). The results show that the lateral displacement and the settlement of the tunnel structure are easily to be caused when the river dredging excavation is located on the side of the shielded tunnel. When the river dredging excavation is directly above the shielded section of the rail transit, the tunnel buoyancy caused by the soil excavation in this area is the largest. The overall stiffness of the station structure is much larger than that of the shielded structure, so the deformation of the main structure of the station is much smaller than that of the shielded structure during the river dredging excavation. The influence of the river dredging excavation on the deformation of shielded tunnel and the subway station can be effectively reduced by adopting measures such as portal soil reinforcement, “Tofu Cutting” excavation and the river bottom counterweight. Related Articles | Metrics

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Optimization of a Zoned Excavation of a Foundation Pit Adjacent to the Subway QIU Jingwei 2022, 36 (2):  187-190.  Abstract ( 268 )   Save For the deep and large foundation pit adjacent to the subway, the pit construction method needs to be adopted in order to ensure the safety of the pit and the surrounding structures and utilities. To solve the problem of slow construction progress induced by the divisional excavation, combined with an engineering example, the support replacement condition of a deep foundation pit adjacent to the subway is optimized. Throughout review, evaluation and analysis, the results show that the safety envelope still meets the requirements, and the impact on the surrounding environment is manageable. Subsequently, the coupling design of different working conditions can be carried out in advance according to the actual needs of the site, so as to achieve the multi-dimensional optimization of the excavation sequence of adjacent zones. While ensuring the self-safety and environmental safety of the foundation pit, the construction speed of the foundation pit can be accelerated to the greatest extent and better economic benefits can be achieved.  Related Articles | Metrics

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Influence of Slope Cracking on a Tunnel Portal XU Ke, SHU Xiaojuan, WANG Zhichao, ZHAO Yang 2022, 36 (2):  191-196.  Abstract ( 724 )   Save Slope cracking is an important stage in the entire process of a landslide formation failure. The soil strength reduction at the slope due to the precipitation and/or the disturbance of the construction was numerically simulated with the commercial software ABAQUS by using strength reduction method. In the analysis, a plastic yielding zone in the slope was obtained and the factors that might induing the slope cracking at the tunnel portal were investigated. The results show that: the distribution characteristics of the plastic strain zone in the soil mass after the finite element strength reduction are in good agreement with the soil cracking characteristics in the slope, and the plastic strain zone of the slope soil can be used to analyze the cracking problem of the slope; with the tunnel portal advancing forward, the plastic strain zone of the slope soil will change, especially when the tunnel face passes through the plastic strain zone; the plastic strain zone of the slope soil will change. The plastic zone of slope soil has not developed to the vault area of the tunnel, which indicates that the influence of tunnel construction on the soil cracking area of the slope far away from the tunnel face is limited; the left side slope will be in an unstable state with high landslide risk, so it is necessary to monitor its deformation, but the sliding surface will not affect the tunnel vault area. Related Articles | Metrics

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Application of Information Based and Visualized Construction Management System in a Large Deep Excavation YANG Youjiang, CHENG Lehua, XI Mingjun, ZHANG Jiaxin, HUA Zhijin, FAN Bo, XU Dingping, JIANG Quan 2022, 36 (2):  197-201.  Abstract ( 296 )   Save The establishment of informatization management system is helpful for the fast response and real time managing the safety related risks during the excavation of a large foundation pit. This paper presents a typical deep excavation project in Wuhan, which was closed to a subway tunnel and surrounded by densely distributed high-rise buildings. An information based and visualized construction management system for the deep excavation was established to assist the real-time early safety warning and emergency response. Through this system, the dynamic feedback analysis and the construction optimization of the large deep excavation stability can be realized by integrating the geological survey, design, construction, safety monitoring, and project management. Thereafter, it forms a complete set of technologies for information-based and visualized construction management of large deep excavation project. The results can provide a reference for the design and construction of similar deep excavations. Related Articles | Metrics

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Deformation of Reinforced Retaining Wall in Western Henan Loess Soils under Seismic Loads LI Hongjuan 2022, 36 (2):  202-207.  Abstract ( 282 )   Save In order to study of the deformation of the reinforced retaining walls in Western Henan loess soils under the seismic loads, this paper uses FLAC3D nonlinear finite difference method for the failure mechanism of a retaining wall reinforced by the geocell and the geogrid. The seismic deformation of the retaining wall improved by the geocell and the geogrid compared with that of the retaining wall without. The influence of length as well as the spacing of the geocell and the geogrid on the deformation are also evaluated. The results show that the lateral displacement at the wall side of geocell retaining wall is slightly smaller than that of the middle wall and the back wall under earthquake action, and the control effect of geocell on lateral displacement is obvious. The lateral displacement of retaining wall can be reduced effectively by increasing the length of reinforcement and decreasing the spacing of reinforcement, and the displacement control at the top of the wall is better than that at other positions. Related Articles | Metrics

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An Application of EVS Hybrid Modeling Method HUANG Shirui, LIU Junli, 2022, 36 (2):  208-213.  Abstract ( 353 )   Save In this paper, a hybrid modeling method using Earth Volumetric Studio (EVS) is proposed in order to resolve the problem of the EVS program could not divide the sequence of karst rock cavities when using the stratigraphic modeling method alone in a karst terrain. The lithology modeling method alone, it could not clearly reflect the defects at the interface relationship among the layers. Throughout analyzing the principles of the Kriging Method in the geostatistics, the proposed hybrid modeling method can not only present the interlayer interface relationship of geology, but also model the karst rock cavities. Based on data measured in 58 boreholes in a college bridge site area of Yangshuo County, Guilin, a hybrid modeling method was used to conduct a three-dimensional geological modeling study on the geologic conditions of the project site. The original lithology modeling method was compared and analyzed. Both the hybrid model and the lithology model were cross validated, which showed that the theoretical accuracy of the proposed hybrid model was better. The three-dimensional geological model established by this method can be used to predict the problems encountered in the pile installation. Related Articles | Metrics

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Numerical Back Analysis of Soil Strength near Failure Plane using Particle Swarm Optimization and Differential Evolution Coupled Method ZHANG Shutao, PENG Jun 2022, 36 (2):  214-218.  Abstract ( 265 )   Save The failure plane is a critical part of the entire landslide components and plays a key role in the form, development and evolution of a landslide. Therefore, the determination of the shear strength parameters at the failure plane is very important in the landslide stability evaluation. However, it is difficult to accurately obtain the design parameters due to the discrete nature of the failure plane distribution, the sampling disturbance and the potential testing errors. For landslide with complicated sliding bodies, the strength parameters obtained from the back analysis with the three-dimensional numerical analysis is still a good method, although the many disadvantages exist in the trial-and-error method in the numerical analysis. This paper presents a case history of three-dimensional numerical back analysis results on a landslide at the Yunnan Tengchong Airport using Particle Swarm Optimization and Differential Evolution approach. The detailed numerical model was established based on the actual topographical conditions and the strength parameters at the failure plane were obtained. This method significantly improves the efficiency of the back analysis process.  Related Articles | Metrics

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Influence of Deep Excavation on the Adjacent Buildings Considering Coupling Effect of Both Seepage and Stress MA Jiabing, BI Qingtao, FENG Qiaoyun, YANG Jintao 2022, 36 (2):  219-223.  Abstract ( 357 )   Save This paper presents a case history of a deep excavation for a residential building on the adjacent structures in Zhoukou area by considering the effect of the seepage and stress coupling. A numerical analysis model of the deep excavation was established by considering the precipitation data of the area as the boundary conditions. The measured values of the ground subsidence behind the supporting structure and the horizontal deflection of the cut-off wall were compared with the numerical results so that the reliability of the numerical model was validated. Based on the numerical analysis results, it was concluded that the deformation of the cut-off wall and the adjacent buildings are acceptable. The laboratory tested soil strength parameters under various precipitations were used in the numerical models so that the influence of the rainfall on the performance of the deep excavation supporting structures could be numerically investigated. Related Articles | Metrics

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Factors that Affecting the Restitution Coefficient in Rockfall Analysis Using Discrete Element Method ZHANG Zhican, YAN Jinzhou, JIANG Wei, 2022, 36 (2):  224-229.  Abstract ( 492 )   Save In the rockfall analysis, the restitution coefficient is an essential parameter for the prediction of the rock trajectory. The success of a rock fall mitigation project is strongly influenced by an accurate determination of the restitution coefficient. In this paper, the MatDEM, a discrete element software, is utilized to simulate the process that a falling rock impacts a slope. The influence of the rock and soil properties of the slope, the impact velocity and the incident angle on the restitution coefficient are also investigated. Range analysis on the results of the overall orthogonal experiments shows that the rock and soil properties of the slope have the most significant impact on the restitution coefficient. The normal restitution coefficient increases when the slope hardness improves and decreases when improving the incident angle and the impact velocity. The tangential restitution coefficient increases when the slope hardness improves and decreases when improving the impact velocity. Related Articles | Metrics

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Application of Random Field Theory in the Reliability Assessment of Soft Soils Improved by Vacuum Preloading JIANG Xiong, XIAO Yi, ZHOU Xudong, ZHAO Xiaodong 2022, 36 (2):  230-234.  Abstract ( 286 )   Save The vacuum preloading method is widely used in the improvement of large area with deep soft cohesive soils in the coastal plains, which can accelerate the drainage consolidation of the soft clay and improve the shear strength. Based on the in-situ and laboratory tests before and after the vacuum preloading improvement, the physical and mechanical indices (moisture content and void ratio) as well as strength indies (shear strength and penetration resistance) of the soft clay before and after the reinforcement were compared and analyzed by mathematical statistics approach. Based on the difficulties that frequently encountered in the engineering practice of using the conventional analytical approach, such as, small reliability indices, and large deviation from the measure conditions, this paper presents the use of random field approach to obtain the correlation distance and variance reduction function values of soil indices after soft clay improvement in this region. The results are applied to the foundation soil reliability evaluation. The results show that the soil indies of the soft clay after the vacuum preloading improvement are consistent with the values in the random field theory model, and the reliability indices of the soil bearing capacity considering the correlation of soil indies is significantly improved, which is more in line with the engineering practice. Related Articles | Metrics

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Determination of Soft Rock Expansion Characteristics in Hemaquan Area of Urumqi LIU Xuejun, LI Yanjun, XIE Liangfu 2022, 36 (2):  235-240.  Abstract ( 267 )   Save This paper presents the qualitative and quantitative testing results of expansion characteristics of rock samples by testing the relative content of montmorillonite and other clay minerals in the rock samples from Hemaquan Area by X-ray diffraction test and the existence of lamellar crystals and the development of rock fractures in the microscopic characteristics of rock samples. The results of X-ray diffraction test and the content of mineral composition combined with the results of electron microscope scanning test reasonably explain the phenomenon of disintegration, expansion and even argillization of the soft rock in Hemaquan area. In order to further quantify the expansion performance of rocks in Hemaquan area, through the free expansion rate test without load, the test shows that the free expansion rate of rock samples is basically 30% ～40%, and some are even as high as 103%. The results show that there is no correlation between the free expansion rate and the self-weight stress. Related Articles | Metrics

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Methods for Emergent Groundwater Contamination Investigation  MENG Junsheng, YIN Nan, LIANG Minbo, PAN Junxin 2022, 36 (2):  241-245.  Abstract ( 358 )   Save Emergent investigation of groundwater pollution is an important technical support for the emergent disposal of sudden environmental events. This paper analyzes the groundwater contamination pattern and the characteristics of the emergent investigation aspects which include the purpose of contamination tracing, the emergent disposal, data collection, rapid analyses, hydrogeological conditions, emergency monitoring, groundwater contamination tracing and safety matters, etc. The paper presents the use of geophysical testing equipment, portable fast testing equipment, appliable hydrogeological investigation and other field investigation methods. The emergent investigation of a groundwater contamination incident was introduced as an example and the emergent investigation principles and methods for the groundwater contamination applications are presented in the paper.  Related Articles | Metrics

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Seepage Characteristics of A Non-Homogeneous Porous Media Considering Compaction Effect WANG Xiaoxu, YAN Junfeng, HU Le 2022, 36 (2):  246-249.  Abstract ( 284 )   Save A typical soil material has an extremely complex internal pore structure and is a typical porous medium. The coefficient of permeability, as one of the important physical properties of geotechnical materials, was evaluated with various potential influencing factors, but the effect of inhomogeneity on the coefficient of permeability is relatively rare evaluated. In order to explore the effect of this non-homogeneity on the permeability characteristics of the porous media, this paper establishes different two-dimensional porous media seepage models that considering the compaction effect through a numerical simulation software. The numerical study results are combined with the actual test results, and therefore, investigates the influence of different distribution patterns of soil particles on the permeability values. The results show that the non-uniform distribution of the soil particles has an obvious influence on the seepage characteristics. When the concentrated distribution of soil particles impedes fluid flow, the permeability decreases significantly. Further, when the non-homogeneity does not actually change the seepage channel size, the effect is smaller. Related Articles | Metrics

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Research on Internal Force Distribution Characteristics and Seam Optimization of High-fill Channel Faceplate WANG Bin 2022, 36 (2):  250-253.  Abstract ( 295 )   Save Relying on a high fill channel engineering project, with the help of finite element analysis software, the distribution characteristics and control factors of the internal force of the lining faceplate under the influence of post-construction settlement of the channel were studied. In addition, the influence law of the seam on the distribution characteristics of the faceplate internal force was explored. The results show that the internal force distribution of the faceplate during post-construction settlement is controlled alternately by the uneven deflection of the faceplate and the friction between the slope and the faceplate. The faceplate near the bottom of the slope is the main compression area, and its internal force is mainly controlled by the friction force of the slope on the faceplate. However, the faceplate near the top of the slope is the main tension area, and its internal force is mainly controlled by the uneven deflection of the faceplate; the seam treatment in the tensile area of the faceplate will increase the tensile stress level of the faceplate, which is unfavorable to the stress state of the faceplate. If the seam treatment is performed in the faceplate compression area, the internal force distribution of the faceplate caused by post-construction settlement will be changed, and the range of the faceplate compression area will be increased. On the one hand, it gives full play to the advantages of strong compressive performance of concrete faceplates, and on the other hand effectively reduces the risk of faceplate cracking under tension. Related Articles | Metrics

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Determination of Mechanical Strength Indies of a Dynamic Compaction Improved Crushed Stone Site WANG Hui, XIE Zhaoyu 2022, 36 (2):  254-257.  Abstract ( 239 )   Save An existing dynamic compaction improved crushed stone site has served as a raw material storage yard for many years. The storage yard needs to be intelligently upgraded and the accurate determination of the site shear strength indices are required from the geotechnical investigations. This paper analyzes a large amount of in-situ plate loading test and large scale direct shear test results and the results are used to calibrate the Beker Cone Penetration Test results. The results indicate that the shear strength parameters obtained from the in-situ plate loading tests and in-situ large scale direct shear tests are more reliable for the crushed stone soils. Related Articles | Metrics

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Experimental Study on Seepage Characteristics of 3D Printing Rock Fractures LI Peixin, ZHANG Yan 2022, 36 (2):  258-260.  Abstract ( 358 )   Save Seepage performance in rock fractures is of the great significance to the safety assessment in the underground engineering. Seepage test through the laboratory prepare on six (6) 3D printed rock fractures samples in accordance with the standard profile curve of the joint roughness coefficient (JRC) with a single opening fracture width of 2.5 mm. The test results show that: (1) when the flow velocity gradually increases, the seepage flow quantity, q, per unit width and the hydraulic gradient, I, presents a strong non-linear relationship. If only the cubic relation is used in the quantity estimation, the hydraulic gradient in the model changes could be significantly underestimated, and therefore, presents an obvious deviation from the estimated value. (2) the JRC has a great influence on the rock fracture seepage. When the inlet flow rate remains unchanged, with the increase of the joint roughness, the pressure on both sides of the rock fracture gradually increases. The non-linearity relationship between the seepage flow quantity, q, per unit width and the hydraulic gradient, I, becomes stronger and stronger. Related Articles | Metrics

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Experimental Study on the Modification of Lime Stabilized Recycled Subgrade with Polypropylene Fiber QIAN Biao, LI Ben, FANG Rui, YU Wenjie, WU Yanting 2022, 36 (2):  261-264.  Abstract ( 283 )   Save In order to study the effect of polypropylene fiber on the unconfined compression performance of the lime stabilized recycled subgrade, the unconfined compression strength tests of 6 mm, 9 mm and 12 mm length polypropylene fiber modified lime stabilized recycled subgrade materials at sample curing ages of 7 days and 28 days, respectively, were conducted. The test results show that: (1) at the curing age of 7 days, the polypropylene fiber has no effect on improving the unconfined compressive strength of the lime stabilized recycled subgrade; at the curing age of 28 days, the polypropylene fiber has obvious improvement effect on the unconfined compressive strength of the lime stabilized recycled subgrade. Among them, the fiber with a length of 6 mm has the most obvious improving effect, and the unconfined compressive strength of the lime stabilized recycled subgrade with non fiber modified was increased by 42.2%. (2) The addition of the polypropylene fiber greatly improves the durability of the lime stabilized recycled subgrade, and the residual strength of the sample increases with the increase of fiber length. (3) The ductility of the lime stabilized recycled subgrade increases with the increase of the fiber length.  Related Articles | Metrics

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Correlation Analysis Between N-Value and Shear Strength Indices of a Sandy Soil ZHANG Xiangying, ZHOU Yufeng, YANG Haojun, TENG Hongjun, DU Liang, ZHENG Xingxie, 2022, 36 (2):  265-268.  Abstract ( 394 )   Save Based on the increasingly understanding of the engineering properties of typical sandy soils, the empirical relationship between the Standard Penetration Test (SPT) N values and the shear strength indices is proposed. The proposed relationship was compared with the results of current design code recommended formula as well as the previous proposed relationship. The comparative results indicate that, compared with the proposed relationship, conservative design is usually obtained from both code recommended and previous recommended relationships when it is applied into the typical sandy soils. The design values could be slightly improved by applying the proposed empirical recommendations. The empirical formula for the cohesion shows that the cohesion of sandy soils and the SPT N values are reversely correlated. The empirical formula for the internal friction angle has a slight improvement in the accuracy of the results compared with the Peck and other three models. The proposed relationship provides a new approach for the evaluation of shear strength indies of the sandy soils in the studied site, and potentially saves the construction cost. Related Articles | Metrics

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Experimental Study on Dynamic Characteristics of Improved Expansive Soil with the Optimum Phosphorus Tailings Content LIN Wanfeng, ZHUANG Xinshan 2022, 36 (2):  269-272.  Abstract ( 307 )   Save The dynamic properties of Hefei expansive soil improved by an optimized content of 7% of phosphorus tailing by product additives were laboratory studied by the GDS dynamic triaxial testing devices under cyclic loading conditions. The improved Hefei expansive soil samples were tested under different loading frequencies and confining pressures so that the dynamic modulus and damping ratios relationship with these potential influence factors could be investigated. The results indicate that, the stress-strain relationship is strongly influenced by the confining pressures. Under different sample confining pressures, the dynamic modulus values varied significantly. Under the same amount of deformation, the higher confining pressure induces a higher dynamic modulus; so does the loading frequency on the dynamic modulus. With the increase of confining pressures and lading frequencies, plastic deformation in the soil samples reduces and elastic deformation increases with the same value of dynamic modulus in the soil sample, Ed. Related Articles | Metrics

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Experimental Study on the Optimization of Pile Installation in a River Valley Floodplain QU Pengchong, ZHANG Renhao, DAI Yanxiong, FAN Hanguang, ZHANG Fang, 2022, 36 (2):  273-277.  Abstract ( 242 )   Save In order to reasonably improve the projet schedule and to reduce the construction cost, the based on a survey project in Tianshui, the pile foundation was optimized by static pile loading tests so that the pile bearing layer and construction technique were able to be selected. The results show that the gravel soil stratum is relatively dense in the construction site so that the pebble layer ④ as the bearing layer for piles is appropriate; As the bearing layer, the pebble soil layer is obviously better than that of the interbedded layer ⑤ of the strongly weathered to moderately weathered mudstone and conglomerate, which can be also used as the pile end bearing layer. In addition, the settlement stability of the test pile under the external load is better than that of the test pile without post grouting. Related Articles | Metrics

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Application of Single Hole Wave Velocity Test in the Geotechnical Investigation in Hangzhou SONG Jian, KANG Jiashuai, XIE Yanling 2022, 36 (2):  278-282.  Abstract ( 408 )   Save The geophysical method was used to provide the seismic design information of a project in Hangzhou. According to the site geological conditions, a total of four (4) test borings with the in-situ single-hole wave velocity test were planned and the original waveform figures within different soil layers were obtained. The average shear wave velocity in different soil layers and the thickness of each soil layer were determined. The seismic site class and the seismic design intensity could be established based on the obtained seismic shear wave velocity. The results indicate that, the project site class belongs to I1 to II and the seismic design intensity is six degrees. The design seismic group belongs to the first group, and the characteristic period of the site category I1 is 0.25s, the site category Ⅱ is 0.35s. The investigation results also show that the single-hole wave velocity test could be directly used in the site geophysical testing, and the result is relatively accurate and convenient. Related Articles | Metrics

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Experimental Study of Axial Behavior of Cement-Soil Mixed Columns with Tapered Rigid Inclusions HE Jie, LIU Mengxin, ZOU Changchun, GUO Duanwei 2022, 36 (2):  283-288.  Abstract ( 365 )   Save  The cement-soil mixed column with tapered rigid inclusion is a new type of composite column applied in the soil improvement projects. To study the axial behaviors of this type of composite column, axial pile loading tests on four composite columns with different tapering angles, inclusion length ratios and average area core ratios were performed. The load-displacement curve, axial force distribution along the rigid inclusions, end resistance and shaft resistance of the piles were studied and evaluated. The test results show that the ultimate axial capacity of the cement-soil mixed column with a tapered rigid inclusion is about 1.2 to 1.4 times of that of the cement-soil mixed column with a uniform section rigid inclusion; The axial force within the cement-soil mixed column changes abruptly at the bottom section of the rigid inclusion, so the strength at the bottom of the rigid inclusion should be checked in the design; In the process of load transfer, only 5.3% to 21.4% of the interface resistance between rigid inclusion and the cement-soil mixed column is mobilized; The rigid inclusion shares more than 90% of the applied axial load, and increasing the taper angle will increase the load sharing ratio of the rigid inclusion, but the average area core ratio and rigid inclusion length ratio have limited effect on the load sharing. Related Articles | Metrics

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Experimental Study on Consolidation and Permeability Characteristics of Gassy Soft Soil ZHANG Junjie, YU Song, SUN Jizhu, WANG Yong 2022, 36 (2):  289-294.  Abstract ( 337 )   Save In order to investigate the consolidation and permeability characteristics of gassy submarine soft soil, a new device that could perform the consolidation and the permeability tests was developed. In the new device, the automatic separation and measurement of water and gas drained from the gassy soil sample and the desired water and gas tight during the test were achieved and the friction in the sample ring and piston was effectively reduced. The test results show that the compression index of gassy soft soil has a linear relationship with the gas content in the soil sample; the permeability coefficient is controlled by both the void ratio and gas content; gas content only affects the value of permeability coefficient but has no significant effect on the evolution law of the permeability coefficient; with the increase of the initial gas content, the growth of gassy soft soil consolidation speed slows down, or even decreases. Related Articles | Metrics