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    31 August 2024, Volume 38 Issue 4 Previous Issue    Next Issue
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    Highway Tunnel Crossing Fractured Fault Zone by Drilling and Blasting Method in Mountain-Plateau Region
    REN Shifang, YU Tanqiu, Zhang Huanyu, GUO Zhiwei
    2024, 38 (4):  567-572. 
    Abstract ( 239 )   Save
    This paper presents a case history of the highway tunnel construction of Xinjiang Wuwei Highway Package PPP Project YRTJ-04 Bid Section Bashkorgan Tunnel 2. Based on the environmental and geological conditions at the tunnel site, several technologies, such as, the tunnel excavation advanced prediction technique, tunnel construction ventilation methods, the oxygen supply method during the tunnel excavation as well as the drilling and blasting methods for the crossing over the fractured fault zone, are comprehensively studied. The results show that, in view of the tunnel construction in Xinjiang’s cold and high-altitude areas, considering the environmental factors brought by the increase in altitude, the design of the tunnel ventilation system is optimized accordingly. The technical parameters of the tunnel construction ventilation are defined to meet the requirements of the on-site construction ventilation; According to the characteristics of Xinjiang’s high-altitude, low pressure and anoxic environment, the recommended value of the critical oxygen supply altitude is determined, and the corresponding labor intensity classification is carried out according to the tunnel construction procedures. The oxygen supply standard required to consider the factors of labor intensity in different procedures is determined, and the oxygen supply scheme for the construction of Bashkorgan Tunnel 2 is proposed; In view of the tunnel crossing fractured fault zone and the well-developed joint fissure area, the key technologies such as the comprehensive advanced geological prediction detection and the concentrated water pressure smooth blasting are adopted to ensure the safe construction and the construction efficiency of the tunnel.
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    Study on Light Well Point Dewatering Technology in Silty Soils under High Groundwater Level
    JIN Tao, LI Xuefei, LIU Dazhao, RONG Chuanbiao, XIE Yangfa, ZHU Qiu
    2024, 38 (4):  573-577. 
    Abstract ( 191 )   Save
    High groundwater level will bring a series of geotechnical engineering hazards, especially for areas with large dewatering requirements, large groundwater changes and poor geology, and it will bring greater challenges to the underground construction. Combined with the engineering examples of the high groundwater level and the silty soil, at first, the advantages and disadvantages of different dewatering methods were compared, scientific and effective dewatering treatment technologies were selected, and then the construction process and precautions were evaluated, the dewater effect was analyzed, and finally the later settlement monitoring was followed up, so as to accumulate more technical application experience for the same type of construction projects in the future. The results show that, according to the actual site conditions, the dewater of the light well point is very effective in this project, and it can meet the subsequent construction. The post settlement was monitored, and the construction monitoring satisfied the requirements of the specification.
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    Application of Three-Dimensional Geogrids in the Widening of South Segment of the Fourth Highway Circle Line of Huizhou Coty
    WANG Chiheng, XIE Yuheng
    2024, 38 (4):  578-581. 
    Abstract ( 179 )   Save
    The use of geogrid is one of the major ways in the application of the roadway reinforcement, differential settlement control and the subgrade stability. This paper presents a case history of using the three-dimensional geogrid in the widening of South Segment of the Fourth Highway Circle Line in Huizhou City, Guangdong Province. Throughout the laboratory model static loading tests on the geogrid reinforced soils, the stress-strain characteristics in soils under the loading and the associated settlement are evaluated. The results indicate that, the slope stability of the roadway embankment is greatly improved. After the geogrid placement, higher composite strength is formed along the center of the roadway embankment. And the lower composite strength body is formed along the edge of the embankment. After the geogrid placement, higher settlement is observed at the centerline of the embankment, whereas, the edge of the embankment has larger settlement without the geogrid reinforcement.
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    Stability of a Metro Deep Excavation in Coastal Karst Stratum
    YANG Fugang, SHAO Pichun, XU Huaizhong, LIU Jingxu, REN Kun, BAI Haifeng
    2024, 38 (4):  582-586. 
    Abstract ( 145 )   Save
    The high groundwater level and the poor stability in the coastal karst strata are frequently encountered. It is difficult to construct the foundation pit of the subway station. In order to improve the stability and safety of the deep foundation pit process of the subway, taking Ganjingzi Station foundation pit project of Dalian Metro Line 5 as an example, this paper analyzes the construction method and technology of pile-anchor support structure according to the complicated geological conditions of coastal karst and the characteristics of surrounding buildings and pipelines. Based on the field monitoring data, lateral displacement of retaining piles, the development of uneven settlement of ground and around building (structures) was analyzed. During the construction of deep foundation pit, the supporting structure is stable and safe, the uneven settlement of the surface and surrounding buildings (structures) is within the controllable range, and the pile anchor supporting structure has strong adaptability and reliability, which can provide a reference for the construction of subway stations in karst strata.
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    Evaluation and Mitigation of the Secondary Lining Cracking of an Expressway Tunnel
    MENG Qin, SUN Qihua
    2024, 38 (4):  587-591. 
    Abstract ( 187 )   Save
    With the expressway construction going into the mountain areas, the number of tunnels as structures are increasing due to the restriction of the highway alignments, the landform, the environmental protection requirements, the water sources and other factors. From many years of tunnel construction and operation practice experience, lining cracks are one of the most common major hazards. Effectively prevent and mitigate the lining cracking are the key technical problem related to the safety of the tunnel construction and operation. Based on a case history of the secondary lining cracking at the top of an expressway tunnel, this paper evaluates the distribution characteristics of cracks in the lining system, the patterns of these cracks and the deformation in the secondary lining of the tunnel by means of tunnel monitoring and measurement. On this basis, factors that inducing cracks are analyzed, and mitigation measures such as reinforcing the bottom, adding drainage pipe, and installing steel plate in the secondary lining reinforcement are proposed, which have achieved satisfactory results and also provide a reference for the mitigations of similar projects.
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    Design and Stability Analysis of a Supporting Structure for a Very-Large Deep Excavation
    XIAO Jing, ZHU Juntao, LI Dejie, RAO Weisheng, ZENG Xutao
    2024, 38 (4):  592-594. 
    Abstract ( 150 )   Save
    This paper presents a case history of a deep excavation support design project for a a river crossing tunnel in Jiangsu Province. The deep excavation supporting method of the diaphragm wall + internal support+ bottom reinforcement by using N-JET grouting is proposed. A three-dimensional numerical model is established by using the numerical simulation method to study the impact of deep excavation on the supporting structure and surrounding structures. The results show that, after the excavation, the displacement and stress of the supporting structure are small, the maximum horizontal displacement of the deep layer of the north diaphragm wall and the east and west diaphragm walls are 13.4 mm and 7.2 mm respectively, The maximum axial force on the supporting structure is about 14 868 kN, the maximum stress on the diaphragm wall is about 1.31 MPa, and the surrounding surface settlement is small, which verifies the effectiveness of the excavation support method and can ensure the smooth construction of the deep and large deep excavation project. The results can provide a good reference for the design and construction of similar projects.
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    Advanced Construction Method for a Soldier Pile and Lagging Retaining Wall
    YANG Haipeng, GENG Zehong
    2024, 38 (4):  595-599. 
    Abstract ( 233 )   Save
    Soldier pile retaining wall is composed of reinforced concrete soldier pile and the lagging plates in between, which can transfer lateral force to the solder pile and stabilize the soil slope through the soldier pile and laggings. The soldier pile and lagging wall can also be applied in constructing retaining walls in fill condition. The cast-in-place reinforced concrete soldier pile can be constructed first before the fill operation; then the lagging can be installed along with the fill to the desired final height. This method can be used in projects that require fill and retaining wall where the retaining structure can be constructed in advance. Based on the project practice, this paper presents the advanced construction of the soldier pile and lagging retaining wall in details. Ans provides a refence for the future construction of the similar projects.
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    Integral Stability Analysis of a Slag Yard High Slope
    LI Haining
    2024, 38 (4):  600-603. 
    Abstract ( 131 )   Save
    A finite element analysis with the shear strength reduction method and the limit equilibrium methods are used to study the integral stability of a high slope of a slag yard after the mitigation. A three-dimensional FEM model of the high slope is established based on the previous research results. The stability of the slope is analyzed by using the shear strength reduction finite element method to obtain the slope stability factor of safety and the potential sliding-plane. The stability of the slope is also analyzed by using the limit equilibrium method to obtain the factor of safety. The results show that the factor of safety for the slope stability by the shear strength reduction method is 1.25 and it is within the range of those by limit equilibrium method. The high slope of the slag yard after the mitigation is stable. The study in this paper can serve as a reference for the similar engineering projects. 
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    A Riverside Prefabricated Retaining Wall Tilting Mitigation and Reinforcement Design
    WANG Xu
    2024, 38 (4):  604-606. 
    Abstract ( 140 )   Save
    One of the hazards of the fabricated retaining wall is characterized by the tilting and the deformation of wall and the separation as well as the cracking at connections. For the hazard of this type of retaining wall, it can be mitigated by repairing the connection between the wall and the foundation. The potential causes of the tilting of a riverside prefabricated retaining wall are evaluated. The possible inner causes are the small stiffness of the retaining wall and the large areas of the backfill behind the wall. Whereas. the probable external causes are the rainwater infiltration into the backfill behind the wall. Based on the deformation characteristics of the prefabricated retaining wall, and the principle of maintaining the original appearance, economy and safety are considered to mitigate and reinforce the retaining wall. After the tilting correction and the reinforcement, the after construction monitoring data shows that the retaining wall has no deformation in the rainy season and winter.  
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    Pump Test and Dewatering Control Methods for the Deep Excavation of a High-Speed Railway Station in Huai’an
    HONG Disi, LIU Zhaocheng, LIU Xin
    2024, 38 (4):  607-612. 
    Abstract ( 217 )   Save
    The large-scale development and utilization of the urban underground space has made the excavation depth of foundation pits deeper and deeper. The pump test is particularly important for the deep excavation projects affected by the artesian water. A deep excavation project in the hub space of the Huai’an high-speed railway station is presented as a case history. A comprehensive overview of the design, point arrangements, test methods and results of the pump test wells is presented. After that, the different estimation methods are used to compare and analyze the hydrogeological parameters of the excavated area, and the permeability coefficient and the radius of the influence of the main aquifer are determined. Finally, based on the water influx within the set depth of the excavated area, recommendations for a point well precipitation program are proposed in combination with the characteristics of the excavated area. The impact of the precipitation on the surrounding structures and the environment is discussed and predicted in the paper.
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    Design and Practice of Inner Support System for a Diaphragm Wall in Deep Excavation Support
    HU Ke, HAN Shuai, TAI Jun, ZHAO Chenxi
    2024, 38 (4):  613-618. 
    Abstract ( 137 )   Save
    Compared with other areas in Wuhan, the Yangtze River I terrace has a structure with the upper soft clay layer and the lower sandy dual layer. Many geohazards of the super-large deep excavation projects indicate that the potential safety of such projects will result in a huge loss to the projects if they are not paid enough attention to. This paper focuses on the design and the estimation of deep excavation and use a project case history to perform the analysis. Two methods are used to analyze the stress and the deformation principles of the supporting structure: (1) using the elastic resistance method for the estimation; and (2) using the three-dimensional finite element software Geotechnical & Tunnel Analysis System to simulate and analyze the excavation process of the deep excavation. Based on the analysis of the deformation of the supporting structure, several models are used to estimate the deformation, and the results are compared with the actual construction monitoring data. The feasibility of the supporting structure is verified by the analytical results and the monitoring data, which provides guidance for similar projects.
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    Application of the Hydraulic Compaction Method in Ground Improvements for Building Foundations
    HUANG Junchao
    2024, 38 (4):  619-622. 
    Abstract ( 143 )   Save
    The hydraulic compaction method has been widely promoted and used in roadway engineering due to its mobility, high-frequency impact, and minimal side effects, but it is less applied in the ground improvement for the shallow foundation of buildings. A case history of a real estate construction projects is presented in this paper with the mechanism and the construction process of the hydraulic compaction method. By comparing this method with the current dynamic compaction method, the advantages and disadvantages are analyzed. Experiments are conducted on the soft soil replacement based on the site conditions, and the data after compaction is studied and analyzed. The results show that the hydraulic compaction method has a strong adaptability to the site and is more reliable comparing with the quality of replacement and the compaction. Its satisfactory compaction effect can effectively solve the problem for the building foundations meeting the requirements of bearing capacity and deformations after the soil replacement and compaction. The economic effect is significant.
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    Application of Pressure Grouting Using Perforated Steel Pipe in Saturated and Fractured Zones
    YAO Yanfei, LIU Qinghua, HUANG Xuhua, ZHAO Liquan
    2024, 38 (4):  623-626. 
    Abstract ( 128 )   Save
    Within the geological condition of the saturated and fracture zone, the construction of hand-dug piles for a highway bridge passing through the existing high-speed railway may not only adversely affect the piled foundation of a high-speed railway viaduct due to the collapse and instability of the hand-dug shaft caused by the broken and low strength of the bedrock and soils. This saturated and fractured zone might also affect the operation of the high-speed railway due to the differential ground settlement caused by the rapid drawdown of the groundwater level. Based on the comprehensive selection of the feasible mitigation methods, the static pressure grouting process by using the perforated steel pipe is adopted. Two circles of the pressure grouting are arranged in triangular spacing at 300 mm and 600 mm, respectively, on the perimeter of the concrete pipe wall of the hand-dug hole piles. The grouting slurry with water-cement ratio of 0.7:1 is used, mixed with 8% water glass, 0.5% salt mixing, 0.1% triethanolamine, and the pressure of the grouting is controlled to be 0.5 MPa~0.8 MPa. The on-site experiments, i.e. monitoring data show that: the filling rate of porosity of in the soil material has been increased by 108.3~162.4%. The coefficient of permeability has been reduced by 80.1% and 76.6%, respectively. No deformation of high-speed rail and the surrounding ground was observed in the construction process, which ensures the safety of high-speed rail during the construction period.
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    Application of a Construction Method in an Ultra Long Distance Pipe Jacking
    QIN Yaqiong, LIU Gang
    2024, 38 (4):  627-630. 
    Abstract ( 141 )   Save
    This paper presents a case history of the pipe jacking for the wastewater discharge project of Tangxun Lake Sewage Treatment Plant. The force mechanism during the long-distance and large-diameter pipe jacking process is analyzed, and the influencing factors of the pipe joint floating and the sinking in the complex strata are studied. The reason for the floating of the machine head was analyzed through factors such as the mechanical properties of the strata where the pipe jacking is located and construction control. Based on the comprehensive on-site conditions, measures such as the supplementary exploration and the identification of geology, pre reinforcement treatment of soft soil areas, ballast treatment inside the pipe, activation of the relay rooms, the opening of holes at the bottom and top of the pipe joint, strengthening of pipe jacking connection, control of the jacking speed, and the timely correction of the deviation are taken to control the displacement of the pipe joint, so that the peak of the pipe joint on site falls back and the pipe joint is maintained in a stable state. To provide the theoretical basis and the technical support for the prevention of the head from floating or downloading during the subsequent pipe jacking construction in complex and uneven geological areas, as well as controlling the deformation of pipelines during pipe jacking construction.
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    Discussions on the Optimization of an Anti-Slide Caisson Structure Design for the Baiguoshu Landslide
    LI Jian, YAN LiangYu, CAI Shangshang, ZHOU Liang, LI Xuan
    2024, 38 (4):  631-634. 
    Abstract ( 157 )   Save
    To study the optimized design of the anti-slide caissons, this paper presents the case history of the Baiguoshu landslide. Based on the soil arch effect and combined with the shear strength index of the soil behind the caisson, the optimized caisson spacing of the anti-slide caisson is selected. Based on determining the caisson spacing, the mechanical analysis of the anti-slide caisson structure is carried out by using the the design bending moment of the positive section of the anti-slide caisson and the design shear force of the oblique section. The design optimization of the retaining structure is carried out, which shows that increasing of the cross-section of the anti-slide caisson can effectively reduce the amount of the longitudinal steel bars within a certain range, and on the premise of satisfying the estimation of the bending bearing capacity of the positive section of the anti-slide caisson, the height of the concrete compression zone is close to the height of the compression zone of the structural boundary as far as possible so that the compressive strength of the concrete can be fully utilized.
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    Slope Stabilization Methods for an Unstable Slope in an Expressway
    CAI Yuewei, HE Haidong
    2024, 38 (4):  635-639. 
    Abstract ( 138 )   Save
    The high and steep slopes along highways are prone to have a sudden hazard such as landslides under the influence of multiple factors as heavy rainfalls and earthquakes. It is crucial to quickly provide the mitigation plans to reduce economic and property losses. This article selects the landslide hazard of a highway slope in Yunnan Province as the case history. The potential sliding surface of the slope and the mechanical parameters of the rock and soil through geological surveys and laboratory tests are determined. Based on the highway slope safety control standard, three working conditions for the engineering practice are established and the stability standard is determined. Two methods are proposed: “prestressed ground anchor reinforcement” and “prestressed ground anchor plus the sheet pile wall combine mitigation”. Based on the required slope safety factor in the specifications, the corresponding design is carried out by using the limit equilibrium method and verified that the slope will remain stable under the above two methods. The results provide a reference for the design and mitigation methods for similar projects.
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    Application of the Prefabricated Steel Support on the Reaction Frame for the Shielded Tunnel Excavations
    JIANG Wei
    2024, 38 (4):  640-645. 
    Abstract ( 289 )   Save
    As a critical load-bearing structure at the shield launching stage, the reaction frame system must meet the requirements for strength, rigidity, and stability to withstand the substantial thrust generated during the launching stage. Currently, in shield construction, the reaction frame support needs to be fabricated and installed on-site, often facing challenges such as high construction difficulty, low work efficiency, poor reliability, and high costs. These issues severely limit the construction progress and safety of the shield tunneling method. To circumvent these problems, this study innovatively proposes an approach that uses prefabricated reaction frame steel supports to replace traditional steel supports. This approach not only reduces the difficulty of on-site construction work, effectively controls construction risks and schedules but also significantly saves construction costs and reduces unnecessary resource waste. By increasing the usage frequency of the prefabricated reaction frame steel supports, it will highlight the great advantages of the present research method over the on-site fabrication and installation method. The application of prefabricated support systems offers a broad scope for the high-quality development of construction levels during the shield launching stage, aiming to provide guidance for the safe execution of similar projects.
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    Pile Foundation Design and Foundation Settlement Analysis of a Super High-rise Building in Singapore
    YU Dawei, HE Li
    2024, 38 (4):  646-650. 
    Abstract ( 224 )   Save
    Super high-rise buildings have high requirements on foundation bearing capacity and settlement control. This paper takes a super high-rise building project in Singapore as an example to study the pile foundation design of the building and the settlement of its piled raft foundation. This paper takes a high-rise building project in Singapore as an example. First, the geological conditions of the area were analyzed based on the soil investigate report and the corresponding geological parameters were obtained. Then a numerical model was established, and the settlement of the piled raft foundation of the super high-rise building was analyzed based on the numerical calculation results, and the pile foundation design parameters were reviewed. The calculation results show that the maximum settlement of the raft foundation is about 21 mm, which is less than the design requirement of 40 mm; the maximum differential settlement is 1∶1 400, which is less than the design requirement of 1:500; the existing six large-diameter piles bear a load less than the working load. Therefore, the design of the piled raft foundation of this super high-rise building meets the requirements of the specifications.
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    Analysis of Shear strength of High Slope Clay with different Water saturation
    ZHANG Ruifu, LIANG Songlin, LU Di
    2024, 38 (4):  651-654. 
    Abstract ( 200 )   Save
    In this paper, the consolidated undrained tests of the remolded clay samples of a high slope under different water content were performed under different consolidation pressures (50, 100, 200 and 400 kPa). The results show that the water content has a significant influence on the shear strength of the remolded clay. The lower vertical pressure will make the pore water pressure in the sample dissipate incompletely in the short-term consolidation process, resulting in a lower effective stress, resulting in obvious hardening or softening. When the degree of saturation is more than 80.23%, the cohesion of the sample decreases obviously. In addition, combined with nuclear magnetic resonance analyzer, the pore water distribution in soil samples with different degrees of saturation is analyzed. It is proved that the water in the small pores will flow into macropores under external load, which provides evidence for the sudden decrease of cohesion in the direct shear test.
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    Early Warning of Risks in the Deep Excavation Using Fuzzy Algorithm
    WANG Peng, LIANG Zhengzhao, ZHANG Zhenghu, HAN Ju, ZHAN Bixiong, LIU Tiexin
    2024, 38 (4):  655-659. 
    Abstract ( 260 )   Save
    The construction risk early warning of the deep excavation is an important task to ensure the safe construction of the excavation. However, the existing deep excavation’s early warning idea is based on the failure of one or more monitoring points as the instability of the deep excavation. Using the principles of ensuring the safety of the deep excavation, the safety early warning of the excavation is carried out from the safety of the excavation monitoring points and the safety of the entire excavation system. The early warning for the safety of the deep excavation monitoring points is realized by using the established safety early warning classification. The early warning of the safety and stability of the excavation system is to achieve a qualitative and quantitative evaluation of the safety and stability of the entire system by establishing an Analytic Hierarchy Framework (AHP) between monitoring data and the stability of the entire system throughout the monitoring project safety early warning grading table. The early warning method effectively combines the monitoring and the early warning and transforms the fuzzy relationship between the two into a clear and quantitative mathematical relationship, which provides a new idea to effectively solve the deep excavation safety early warning problem.
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    Reliability Analysis of the Toudaohe No. II Landslide Considering Parameter Ambiguity
    SUN Hao, DONG Qingzhi, LIU Yajun, XIA Ziqing
    2024, 38 (4):  660-663. 
    Abstract ( 151 )   Save
    A reliability analysis method for the Toudaohe No. II landslide is presented in this paper, which considers the fuzzy randomness of rock and soil parameters and the transition interval between the fuzzy randomness of rock and soil parameters and the fuzzy slope, in response to the failure to consider the Ambiguity of the shear strength parameters in the stability analysis of the Toudaohe No. II landslide. The method converts the random values of the soil sample tested mechanical parameters into the fuzzy random variables. Based on the fuzzy random variables and fuzzy transition intervals, a fuzzy random limit state equation is established. Different geotechnical parameters λ as well as the upper and lower limits and their corresponding limits state equations are also determined. A formula for calculating the reliability of the Toudaohe No. II landslide that is only related to geotechnical parameter variables is derived. By using the Geostudio software, the fuzzy random reliability of the Toudaohe No. II landslide is simulated and estimated. Finally, the reliability estimated by the traditional Monte Carlo simulation method is presented in the paper. It is found that, when the failure probability obtained by using the traditional reliability estimating methods is 8.04%, and considering the ambiguity of shear strength parameters, the landslide failure probability is 11.99%. This indicates that the failure probability of the Toudaohe No. II landslide considering the fuzziness and randomness of geotechnical parameters has increased.
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    Monitoring and Analysis of a Building Slope
    CHEN Xu, LU Ping
    2024, 38 (4):  664-668. 
    Abstract ( 140 )   Save
    To study the post construction stability and the deformation of a reinforced building slope, this paper presents a history of the surface deformation monitoring of a building slope in Guizhou. By using the site investigation data, the surface movement of the building slope was monitored, and the stability of the slope was analyzed from May of 1028 to February 2019. The results indicate that, ①within the monitoring period, the slope movement has a trend of stabilized, rapid and then stabilized movement. The most rapid movement was observed in the period between May and September 2018 with a largest movement of 971.8 mm. ②Localized movement and tension crack throughout the entire slope at the top. The global stability of the slope is relatively questionable. ③the slope monitoring data indicate that a slope stability hazard is existed in this building slope and the in-depth stability evaluation of this building slope is suggested so that a comprehensive mitigation plan can be implemented. Continued movement monitoring of the slope is also suggested.
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    Variation in Degree of Saturation and Wetting of Collapse Strain of a Loess Soil in Xining and its Numerical Simulation
    YE Runze, LIU Hong, YAN Tianzhu
    2024, 38 (4):  669-673. 
    Abstract ( 184 )   Save
    To explore the deformation characteristics of the collapsibility of a loess soil in Xining City and its numerical simulation method are presented in this paper. The current simulation methods on the collapsibility of loess soils do not fully consider the variation of the degree of saturation and the collapsible strain in the process of the water saturation. To better reflect the characteristics of the collapsibility of loess soils, a numerical simulation of the collapsibility of the loess considering the variation is proposed. The onsite geological investigations on the land subsidence and ground subsidence hazard caused by the collapse of the loess soils in Xining City were performed. The laboratory test results on the collapsibility were also performed to obtain the collapsible strain characteristics of soil samples with a range of degree of saturation from of 40% to 100%. The collapsing strain characteristic curve was studied by using the moisture swelling module of the numerical simulation software ABAQUS material library. The results show that the method can effectively establish the numerical analysis model of the collapsible loess soils in Xining City. The simulation results are generally consistent with the actual observed conditions. It is verified that the established model and the method are effective and feasible.
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    Numerical Analysis on Optimization of Skip Construction of SMW Pile Adjacent to Buildings
    WEI Chenliang, LIN Chao, JIANG Rong, XIAO Shucong, ZHAO Baofeng
    2024, 38 (4):  674-680. 
    Abstract ( 99 )   Save
    The SMW columns are widely applied in strengthening the urban soft soils because of its advantages of fast installation and good groundwater seepage blocking performance. This paper presents a deep excavation project case history in the saturated soft soils with adjacent old building in Liuyanjing station of Nanchang Metro Line 3. The sequential installation of the conventional SMW columns is easily to induce the disturbance of adjacent building stratum in the early stage of cementsoil hardening. Therefore, the safety of the surrounding buildings cannot be warranted. Two analytical conditions of SMW column sequential and skip installations are established based on the numerical method, and the mechanical responses of the surrounding strata caused by the SMW column installation under different working conditions are compared and analyzed. By setting up the numerical model of different installation length and skip distance, combining the requirement of the installation condition and the efficiency, this paper presents the feasibility and advantage of column skip installation by SMW method in adjacent buildings. According to the analysis combined with the actual installation requirements of the construction method, the construction method of skip one distance is determined. On the conditions of ensuring safety, the disturbance to the surrounding strata is minimized and the installation efficiency is improved.
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    Basal Stability Evaluation for Excavations by Using Optimization Width
    DING Qifeng, YANG Jibao
    2024, 38 (4):  681-684. 
    Abstract ( 150 )   Save
    At present, the current code for checking the basal heave stability of excavation uses the Prandtl bearing capacity formula, which assumes that the foundation undergoes bilateral sliding failure and does not consider the limiting effect of the soil inside the enclosure on the heave failure of the excavation. This assumption is inconsistent with the actual conditions. Considering the contribution of the shear strength of soils inside the excavation to the basal stability at the bottom of excavation, the minimum width of the foundation for the one-way sliding uplift failure of the excavation enclosure wall is obtained based on the formula of the ultimate bearing capacity of the Terzaghi soils by utilizing optimization method. The formula of the ultimate bearing capacity for the basal stability at the bottom of the excavation is also derived. The results of this formula indicate that the factor of safety of the unilateral uplift sliding is smaller than the estimated value of the Prandtl bearing capacity formula in the current code.
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    Analysis of Surrounding Rock Mass and Structural Response Induced by the Multi-Arch Tunnel without Central Guide Tunnel
    SU Wenxuan, CHEN Huanmei, BI Taijun
    2024, 38 (4):  685-690. 
    Abstract ( 182 )   Save
    Due to its unique structure, the non-central guide tunnel has a wide applicability in the highway tunnel construction. Based on the construction of the double arch tunnels in Yunnan, this paper uses the three-dimensional numerical simulation to study the impact response of the rear tunnel construction on the surrounding rock mass and the lining of the first tunnel. The stress, displacement, and the plastic zone distribution of several monitoring points are selected as the research objects, including the displacement of the top, double arch position, and arch bottom of the first tunnel, the horizontal convergence of the cross-section, stress of the support structure of the first tunnel, and stress and plastic zone distribution of the surrounding rock mass of the tunnel. The focus is on analyzing the settlement of the arch crown, horizontal convergence of the arch waist, and stress state of the surrounding rock mass and lining during the excavation process of the rear tunnel under the different excavation depths. By comparing the mechanical state of the surrounding rock mass and lining before and after the excavation of the front tunnel, the impact of the rear tunnel excavation on the existing front tunnel is explained and analyzed. The results shown that: (1) the overall vertical displacement distribution of the tunnel is asymmetric, and the excavation of the rear tunnel increases the settlement of the arch top of the front tunnel. The settlement of the arch top of the front tunnel caused by the excavation of the rear tunnel accounts for about 15% of the overall settlement of the front tunnel; (2) The excavation of the rear tunnel has a significant impact on the stress distribution of the support structure of the front tunnel: (3) After the construction of the rear tunnel is completed, the maximum principal stress of the monitoring section support structure of the front tunnel is increased by about 1.4 times compared to the construction of the front tunnel. After the tunnel excavation is completed, the tensile stress zone is mainly concentrated at the arch corner of the leading tunnel near the following tunnel.
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    Generalized Reliability Analysis of Weathered Slate Slope Considering Fuzzy Randomness of Parameters
    LIU Wenjie, CHAO Wanli, GUO Yipeng
    2024, 38 (4):  691-696. 
    Abstract ( 149 )   Save
    To study the influence of the randomness and fuzziness of geotechnical parameters on the slope stability, this paper presents a case history of a slate slope of an expressway in Hunan Province. The generalized reliability analysis is performed by using the membership function and the Rosenblueth method. The method is compared with the traditional method with a fixed safety factor. The membership function and cut-set numbers influence on reliability are studied. Suggestions for the reasonable analysis are proposed. The results show that the mean value of safety factors at different cut-set levels cannot reflect the fuzziness of geotechnical parameters, while the reliability index has a good correlation with the fuzziness of parameters. With the increase of the fuzzy cut-set level, the reliability index increases. For this slope, the failure probability obtained by the fuzzy reliability method is 0.889% < 5%, which means a stable state and is more consistent with the actual situation compared with the fixed safety factor method. The parameter membership function form and the cut-set number have a great influence on the generalized reliability index of slope. When using fuzzy point estimation method, the trapezoidal or triangular membership distribution should be selected first. The number of cut-set is suggested to be nine. The generalized reliability analysis of the slope considers the fuzzy randomness of the shear strength parameters, avoiding the problem of the parameter accuracy of the fixed safety factor method. Therefore, the thinking of slope stability judgment is more scientific. The study results provide a reasonable reference for the analysis of similar slope projects.
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    Formation and Model of Geological Landslide Hazards in Weixi County, Yunnan Province
    CHEN Rongyan, ZHANG Dan, ZHANG Ziming, ZHAO Peng
    2024, 38 (4):  697-701. 
    Abstract ( 239 )   Save
    Yunnan Province is one of the areas where landslide hazards occur frequently in our country. This paper presents a case history of landslide investigation in Weixi County in the northwest of Yunnan Province. It summarizes the formation mechanism and hazard model of landslides, which has a practical and guiding significance for promoting the landslide control in the southwest of our country. Weixi County is one of the counties in Yunnan Province for the refined investigation and the risk assessment of the geological hazards in key areas in 2020. A total of 384 landslides have been identified, and there are mainly weathering debris flow type, subsurface erosion and subsidence type, and shear erosion loading type for the formation mechanisms of landslides. The formation of a landslide may be the result of several formation mechanisms. Taking into the hazard bearing body and the landslide movement account, the main hazard models of the landslides in Weixi county include the creep rupture, the follow-up, the high-speed debris flow and the landslide debris flow chain hazard models. Analyzing the formation mechanism and the hazard models of landslides can provide guidance for the prevention and reduction of the geological landslide hazards in the county and similar areas.
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    Geotechnical Engineering and Numerical Analysis of a Building Over the Subway Structure
    GAO Tao
    2024, 38 (4):  702-705. 
    Abstract ( 118 )   Save
    The Shenzhen Caiwuwei Excavation Support Project serves as a prototypical case that profoundly underscores the intricacies and challenges associated with the excavation support and the earthwork excavation in the proximity to subway tunnels. Given its strategic location overlying a subway tunnel, the project posed numerous technical challenges and safety concerns that required meticulous planning and execution. To overcome these obstacles, a comprehensive approach, leveraging advanced numerical analysis techniques to precisely forecast the stress and deformation states of the subway tunnel structure during the excavation process are implemented. These measures ensured that any potential impacts on the tunnel’s integrity and the operational safety were minimized, thereby guaranteeing the safety and controllability of the entire project. During the construction phase, a strictly adherence to the predefined plan was used, while continuously monitoring and adjusting the approach to ensure the optimal performance. The rigorous monitoring measures, including real-time data acquisition and analysis, to detect any potential deviations or issues promptly are implemented so that the corrective actions can be used swiftly and minimizing any adverse impacts on the project’s progress and safety. The successful implementation of the Caiwuwei Excavation Support Project not only validates the feasibility of our technical solutions and construction techniques but also establishes a new benchmark for similar engineering projects worldwide. It demonstrates the author’s capability in overcoming the unique challenges posed by the excavation over the subway tunnels and achieving harmonious coexistence between engineering safety and urban development. Moreover, the project offers invaluable insights into the design and execution of the future excavation support systems. It serves as a precious resource for the engineers and planners, providing practical guidance and lessons learned that can be applied to analogous.
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    Prediction Model of Surface Subsidence after the Construction of Guiyang Metro Tunnel
    LI Yingxiao, LIU Yuanming, ZHENG Tao, ZHOU Yuhang, TENG Zhaolei
    2024, 38 (4):  706-709. 
    Abstract ( 126 )   Save
    The postconstruction surface subsidence of subway tunnels is an important safety hazard, which will seriously affect the safety of subway tunnels and neighboring buildings if it is not properly controlled. Therefore, an in-depth study of the law of post-work surface subsidence in subway tunnels is a necessary prerequisite for taking effective control measures. In this study, the regularity of the post-work surface subsidence of subway tunnels is explored by analyzing the on-site monitoring data in the Guiyang subway Line No. 3 interval tunnel as an example. A mathematical model was used to predict the post-work surface subsidence of the Guiyang subway tunnel, and a comparative analysis of the prediction effect was carried out. The results show that the exponential function model and the logarithmic function model perform well in fitting the measured data, but for the post-work surface subsidence of the tunnel in this zone, the exponential function model has a higher prediction accuracy in the middle and late stages, showing better applicability.
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    Effect of Acidity Control on Electrochemical Improvement in Loess Area
    ZHANG Shu, WANG Ningwei, LI Wei, LUO Yuechun, XIA Bintong
    2024, 38 (4):  710-714. 
    Abstract ( 122 )   Save
    The authors designed three groups of unsaturated loess electrochemical improvement specimens, and injected different concentrations of the acidic adjustment solution into the cathodes of three groups of specimens (the concentration of the regulating solution of soil A was 1%~5%, soil B sample was 6%~10%, and soil sample C was 11%~15%). The effect of the concentration of the regulating liquid on the modified consolidation of the electrochemical improvement of the loess samples was discussed through comparative experiments, and the following main conclusions were made by analyzing the current, displacement, energy consumption and the improvement strength of different curing ages after the test: (1) Compared with the traditional electrochemical improvement, the injection of the acidic adjustment liquid into the cathode can expand the drainage channel of the loess samples, thereby extending the drainage time and thus improving the reinforcement effect; (2) The higher the concentration of the acidic adjustment liquid, the more the unit energy consumption and drainage; (3) The higher the concentration of the acidic adjustment solution, the higher the soil strength after the improvement.
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    Tensile Properties of Polypropylene Fiber Reinforced Red Clay
    YU Mingbo, GONG Huan, WU Yuancheng, CHEN Yun
    2024, 38 (4):  715-719. 
    Abstract ( 149 )   Save
    In order to further study the interaction mechanism between the fiber and the soil in the fiber reinforced red clay samples and to improve the tensile strength of the soil, this paper presents an investigation result of Guilin red clay using the soil tensile strength testing device and microscope, the tensile tests of different polypropylene fiber content under the maximum dry density and optimal moisture contents. The microscopic mechanism was observed. The experimental results show that the content of the polypropylene fiber can greatly improve the tensile strength and the strain of the red clay, and make red clay sustain a greater tensile deformation. With the increase of the polypropylene fiber content, the tensile strength increases obviously, and the failure type of the red clay changes from the brittle failure mode to the plastic failure mode. Compared with the plain soil samples, the polypropylene fiber content makes the soil appear obvious inflection point when it is failed under the loading. The ultimate tensile strain of the red clay samples increases by 329.9% with the increase of the fiber content. After analysis, the tensile behavior of the fiber improved red clay samples is mainly attributed to the mechanical adhesion force between the soil particles and fibers, which friction each other to resist the fracture. As well as the fiber and fiber interweave to form a fiber network, which is acted by the threedimensional multidirectional tendons to improve the tensile strength of soil samples.
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    Comprehensive Geophysical Response Characteristics of the Underground Engineering
    XU Caiqi, ZHANG Jianzhi
    2024, 38 (4):  720-724. 
    Abstract ( 179 )   Save
    The mitigation and monitoring of the hidden underground civil defense tunnels are difficult to avoid in many of the old city reconstruction projects. To conduct a comprehensive exploration of these underground civil defense facilities by using ERT method, Microtremor survey are performed. The ERT for the underground tunnel of water filling levels and locating have higher reliability. The microtremor survey locating of the underground tunnel results in a better accuracy. Throughout the practice, it is confirmed that, using ERT combined with the micro integrated geophysical methods can achieve a better result in detecting the characterization of the abandoned underground civil defense tunnels and provides a reference for the similar projects.
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    Evaluation of Dynamic Compaction in Silty Fine Sand Soils
    CHEN Guofu, ZHANG Zhen, ZHAO Baolin, WANG Zhongyang,
    2024, 38 (4):  725-728. 
    Abstract ( 98 )   Save
    This trial compaction area for a typical silty fine sand layer site of a project in Guangdong is presented as a case history in this paper. After three times of the dynamic compaction using the 5 000 kN·m energy level in A1 trial compaction area, the site soil was tested, analyzed, and evaluated by using the static plate load test, the standard penetration test and the cone penetration test. The results show that: (1) Compared with before the dynamic compaction, the effect of the soil improvement after the compaction is obvious; (2) The effective improvement depth of the silty fine sand layer is about 7 to 9 meters; (3) Both the standard penetration test and the cone penetration test can evaluate the compaction effect of the foundations soils after the dynamic compaction improvement. The results of the two types of tests are close to each other; (4) It is determined that the site liquefaction potential is eliminated after the dynamic compaction through the blow counts of the standard penetration test in A1 trial compaction area.
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    Study on crack development law and strength relationship of red clay under dry-wet cycle
    ZHANG Zhongzhong, ZHAO Daiyao, CHEN Jun, YANG Yongyu, CHEN Taixu
    2024, 38 (4):  729-734. 
    Abstract ( 419 )   Save
    The relationship between the development of cracks and the strength of the original and the remolded red clay in Guizhou under the action of dry-wet cycles are studied in this paper. The mechanical indicators are obtained through dry-wet cycle tests and direct shear tests. The particles (pores) and fracture images are used to identify. The analysis system (PCAS) processes the image and analyzes the fracture index. The results show that: (1) the degree of fissure development of the undisturbed soil is higher than that of the remolded soil; (2) as the number of cycles increases, there is a positive correlation between the surface crack rate, the number of cracks, and the total length of fissures in undisturbed soil samples. The development of soil cracks does not change much with the number of cycles; (3) The number of cycles has an impact on the integrity of the damaged soil samples, and there is an inflection point value for the number of cycles (3-4 times), indicating that the dry-wet cycles only affect the soil under a certain number of times. The development of the sample fissures will have an impact, and the fissures in the soil sample will not increase due to the increase in the number of cycles. In addition, the mechanical properties of the reshaped red clay samples are lower than that of the original red clay. The cohesion of the original red clay decreases with the development of cracks, and the change of the cohesive force of the remolded red clay is less affected by the development of cracks. The angle of the internal friction all increased slightly.
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    Mechanical Parameters of Completely Weathered Granite by Using Pressuremeter Test
    ZHANG Yuxue
    2024, 38 (4):  735-738. 
    Abstract ( 363 )   Save
    The prebored pressuremeter test has the characteristics of small soil disturbance, strong adaptability, and intuitive results. It is suitable for the exploration of the completely weathered granite. This article is based on the survey of the first section of the North Extension Channel Project of Qiaocheng East Road and provides a detailed introduction to the principles and testing process of the prebored pressuremeter test. The P-V curves of the completely weathered granite at the different exploration points in the study area were obtained through the on-site investigation, and the mechanical properties such as the shear modulus, pressuremeter modulus, and characteristic values of the soil bearing capacity were presented. The results show that the mechanical parameters related to the fully weathered granite gradually increase with the increasing of the testing depth. The characteristic values of the soil bearing capacity measured by the pressuremeter test are similar to but slightly larger than the results of the standard penetration test, which indicates the reasonableness of the pressuremeter test.

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