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31 December 2023, Volume 37 Issue 6 Previous Issue    Next Issue

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Analysis and Treatment of a Deep Excavation Seepage Induced Hazards in Chengdu PENG Ying 2023, 37 (6):  841-844.  Abstract ( 188 )   Save When the unexpected seepage in the deep excavation site results in the excessive deformation of the excavation supporting structure, which might seriously threaten the excavation safety. When this unexpected seepage occurs, the excessive deformation adjacent to the supporting structures is often obvious. This paper presents a case history of the mitigation of a seepage induced accident in Chengdu. The factors that might cause the unexpected seepage, seepage mitigation measures and results are also discussed in the paper. When the seepage induced hazard occurred, the seepage locations should be immediately sealed by using the pressure grouting with water glass into soils in-between the solder piles. Due to the large amount of seepage, the results of the pressure grouting might not have the expected results since the cohesive soils at the excavated walls were soaked and softened, so that the water glass could be washed away. When the large deformations at the excavation side walls, the backfilling measure should be used followed by the pressure grouting after the soil movements are stabilized. The mitigation results indicated that the pressure grouting with water glass plus the backfilling are an effective way of mitigating the unexpected seepage induced hazards.  Related Articles | Metrics

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Application of Soil Mixed Wall Inserted with Hot Rolled Steel Beam in to Preformed Hole for a Deep Excavation Support Project CHU Wei, PENG Peng, DAI Ye, GAO Li 2023, 37 (6):  845-851.  Abstract ( 139 )   Save This paper presents a deep excavation support case history of Jingchu Mansion in Jiangxia District, Wuhan City. The application of soil mixed tangent pile wall inserted with hot rolled steel beams into the preformed hole plus the reusable hot formed ground anchor in the deep excavation in the Wuhan old clay strata is the focus of this paper. The deep excavation used soil-cement mixed column tangent pile wall with hot rolled steel beam inserting into preformed holes plus one layer of reinforced concrete waler plus some local hot formed reusable ground anchors as the supporting structure. The excavation monitoring data indicate that, both the deformation of the supporting structures and the settlement of the adjacent buildings and utilities are controlled within the acceptable range. The innovative supporting structure could effectively reduce the construction cost and shorten the construction schedule and further provides references for the excavation supporting in similar conditions. The typical construction problems such as excessive excavation are also discussed in the paper. Related Articles | Metrics

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Influence of Deep Excavation on the Adjacent Roadways SHU Shuo 2023, 37 (6):  852-855.  Abstract ( 166 )   Save With the rapid development of the economy, the contradiction between the speed of urbanization and the limited land resources becomes more and more prominent, so the urban development turns towards the underground space development. The construction of the underground space has led to the emergence of many deep excavation projects with the complex surrounding environment. This paper presents a case history of deep excavation support using tangent pile with inner bracing project in Zhongyi Road in Zhengzhou City. The excavation construction process was numerically simulated by FLAC3D commercial finite element software. The monitored and predicted deformation of supporting structure are compared to calibrate the analytical model. The validated model was then used to examine the influence of deep excavation on the adjacent roadways. The results indicate that, the roadways near the excavated would be influenced and the deformations are within the code acceptable range. Related Articles | Metrics

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Numerical Simulation of Both Long and Short Piles in the Deep Excavation in Soft Soils KUANG Wenzhuang, SHAO Jin, ZHANG Yufeng, WU Yuliang, JIANG Shanchao 2023, 37 (6):  856-860.  Abstract ( 185 )   Save The frequently used deep excavation supporting methods in Wuhan are slope down with open cut, equal length soldier piles and passive zone improvement. However, the utilization of a uniform length of soldier piles in soft soils leads to an excessive construction cost. To reduce the excavation support cost, a case history of different soldier pile length is presented in this paper. The stress-strain relationship in the soldier piles with various lengths are evaluated by using ABAQUS finite element analysis and Tianhan commercial deep excavation software and compared with the excavation supported by the uniform length soldier piles. Both the monitored data and the analytical results are compared to validate the numerical simulation approach. Then, based on the validated uniform length soldier pile excavation supporting model, the threedimensional model with different length soldier pile excavation support was established by using ABAQUS software. The stress and deformation of four different types of soldier pile lengths are evaluated and the optimized soldier pile length arrangement is obtained through the analysis. Compared with the other model, the one long and one short soldier pile arrangement can effectively provide the excavation support. Related Articles | Metrics

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Application of BIM Technology in the Earth Excavation XU Bin, WU Zhongyi 2023, 37 (6):  861-864.  Abstract ( 132 )   Save This paper presents the state of the practice in the application of Building Information Modeling (BIM) technology in the residential building development project. The current BIM application is the visualization of the excavation requirements based on the design drawing and cannot provide a refined guidance for the construction management. The current visualized earth excavation model is further developed and deepened for the accurately determining the locations of building alignments, water collection pits and elevator locations. After the visualization model been reviewed and approved by the experts, shop drawings are then produced and then served as the construction guidance. This visualized BIM model has the characteristics of multi bottom of water collection pits elevations and excavation pits within the pits. These locations are positioned by using the CADD insertion function in the BIM software and are efficiently projected on the site by using the GPS total stations.   Related Articles | Metrics

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Residential Building Foundation Type Selection and Design LIN Yixiang, JIAO Yang, WANG Shicui 2023, 37 (6):  865-870.  Abstract ( 160 )   Save This paper presents a case history of foundation type selection for a residential building development project in the backfilled area of a former sand quarry site. The subsurface geotechnical conditions of the project site, including, soil stratigraphy, geological conditions as well as physical and mechanical properties, are introduced in detail. Different foundation types and their associated ground improvement methods are evaluated and compared.The advantages, disadvantages, and applicability of each scheme are analyzed, and the safety, economy, rationality, and construction feasibility are also considered. The shallow foundation with soil-cement mixing piles is selected as the optimized method for this project. The ground improvement design method for the project is briefly presented. The static load tests were performed on both single soil-cement mixed piles and composite ground. The test results indicates that the bearing capacity of the improved ground meet the design requirements and the selected ground improvement method is feasible for the project. It’s can provide reference for foundation design and foundation treatment schemes of similar sites. Related Articles | Metrics

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Analysis of the Influence of a Deep Excavation on the Adjacent Subway Tunnels and Stations LI Wei 2023, 37 (6):  871-876.  Abstract ( 133 )   Save A deep excavation project in Xuzhou is adjacent to a live subway and a station and has therefore restrictive requirements on the excavation support. This paper presents the key aspects of the excavation support design and selection. Both two and three-dimensional finite element simulations of the influence of the deep excavation process on the live subway operation and the station by using MIDA GTS commercial software. The results indicate that, the effect of the deep excavation on adjacent structures and utilities are within the allowable range. The feedback information from the numerical analysis results is used to provide excavation construction guidance. The construction monitoring results indicate that the monitored structure and utility deformation values are within the allowable range and the excavation support design effectively protected the safe operation of the adjacent subway and the station. Related Articles | Metrics

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Deformation Safety Analysis of an Excessively Deep Excavation Supporting Structure LI Jingbin, ZHAO Meng, WEI Bingchao, MENG Yiping, ZHU Jinlong 2023, 37 (6):  877-881.  Abstract ( 131 )   Save This paper presents a case history of the deep excavation safety of the excavation supporting structure for the underground fourth floor of Beiyihuan station of Hefei Metro No. 5 Line. The deformation structure responses for this excessively deep excavation are evaluated throughout the numerical analysis and the construction monitoring. The results indicate that the numerical simulated data are close to the construction monitoring data. The deformation values of the adjacent ground surface are far less than the alarming threshold value. With the increased excavation depth, the seepage area near the bottom of the diaphragm wall increases and the increased pore pressure differences between the excavated area and outside are observed. The horizontal deformation of the diaphragm wall increases with the excavation depth and the maximum lateral deformation value is observed at the middle lower portion. The maximum axial load is observed in the first level of concrete bracing and increases with the excavation depth.  Related Articles | Metrics

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Application of Combination of Soil Nailing Wall and Inclined Jet Grouting Cut-Off Wall as Deep Excavation Supporting Structure ZHANG Junjian, LI Yingjie, TAN Sheng 2023, 37 (6):  882-886.  Abstract ( 139 )   Save The inclined high-pressure jet grout cut-off wall with the soil nails as the excavation support structure was applied to the deep excavation in saturated sandy soils. The deformation at the top of the supporting structure and the selected prestressed soil nails are instrumented and monitored. The deep excavation monitoring data pit show that the maximum horizontal displacement and vertical settlement of the top of the inclined high-pressure jet grout cut-off wall with soil nails are only 0.84H‰ (H is the excavation depth), which is much smaller than the current code and specifications allowable values, and basically equivalent to the 0.57H‰ and 0.51H‰ of the soldier pile wall with the ground anchor supported structure. In the deep foundation in the saturated sand layers, the inclined cut-off wall with soil nail supporting structure can replace the soldier pile wall with ground anchored supported structure. The cost of the inclined cut-off wall with soil nail supporting structure is only 90% and 73% of the vertical cut-off wall with soil nail wall supporting structure and the soldier pile wall with ground anchored supporting structure, which demonstrates a very good cost-effective way for the excavation supporting structure. The specially designed inclined jet grouting drilling machine solves the bottleneck problem of the limitations of the previous construction equipment, and therefore provides a large growth space for the wider applications. Related Articles | Metrics

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Geotechnical Investigation Practice in a Cement Plant in Zambia JIANG Leju, LIU Nanchang 2023, 37 (6):  887-891.  Abstract ( 213 )   Save The Zambia Cement Plant Project is an aggressive attempt for the export of the Sinoma entire equipment and procedures of the cement industry. The geotechnical survey and investigation project is also a fruitful result from the work in the foreign environments. During the exploration, there were relatively very limited available geological reference data, and the project organization and implementation were difficult. This article discusses the practical aspects of the exploration results of the Zambia Cement Plant. Based on the collection and analysis of early regional geological data, methods such as drilling, in-situ testing, and laboratory testing were utilized to focus on the identifying complex lithology properties and mechanical characteristics within the site area; The required design parameters of the power equipment foundation are measured through the wave velocity testing; the seismic design requirements of the project are determined by consulting the geological and mineral departments of the local government and referencing the examples from the similar projects completed in the area. The project practice provides some basis and suggestions for the project implementation and provide a reference for the similar foreign projects. Related Articles | Metrics

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Safety Analysis of a Deep Excavation for a Viaduct Project LI Ming 2023, 37 (6):  892-896.  Abstract ( 155 )   Save As a result of urban development, a deep excavation for the viaduct construction utilized the open cut with a slope of 1H:1V. In order to ensure the safety of the viaduct substructure during the excavation, the investigation and analysis of the surrounding environment of the viaduct are used before the analysis. The finite element analysis software MIDAS GTS was used to simulate the construction process of soil layer, structure and excavation. The results show that the displacement, internal force and stress in the piles of for the viaduct structure before and after the deep excavation are not significantly changed. The axial capacity of the pile is almost unchanged compared with that of before the excavation. The axial pile capacity of the single pile meets the code requirement. Therefore, the numerical analysis provides a viable support for the safe excavation. At the same time, during excavation, it is necessary to monitor the vertical and horizontal deflections at the bridge piers and working shafts. Related Articles | Metrics

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Geotechnical Investigation Case History of a TEL 1×330 MW Coal-Burning Power Station Project in Thar Pakistan MEN Qingbo, QIAO Jianwei, XIA Yuyun, YUAN Jia 2023, 37 (6):  897-901.  Abstract ( 115 )   Save The Thar Coalfield area in Pakistan is a widely developed with collapsible sandy soil, which is a typical special soil for the engineering construction in this area. From the perspective of geotechnical engineering investigation case history, the causes and types of the collapsible sandy soil and the geophysical characteristics of geotechnical and electrical layers of TEL 1×330 MW Power Plant Project in Thar Coalfield Block II, Pakistan was analyzed, the engineering characteristic of the collapsed-sand foundation is evaluated by using the results of laboratory collapsed-sand and the in-situ immersion load tests. This paper proposes the engineering treatment measures and predicts the possibility of selfweight collapsibility, and the correction coefficient β of the sand collapsibility and the principles and measures of the foundation treatment in this area are proposed, the scheme of foundation and the problems in the geotechnical construction are also proposed according to the characteristics of the site. Related Articles | Metrics

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Deformation Control of Deep Excavation Support in Soft Soils with Complex Environment GAO Yongwei 2023, 37 (6):  902-907.  Abstract ( 122 )   Save The deformation control in the deep excavation in the soft soils is critical, especially, near the shielded tunnel and other complex environment. Based on the deep excavation project of an open cut tunnel in soft soils in Hangzhou City, this paper presents a case history of Wenyi West Road area. The deformation control measures and results are evaluated by the combination of both numerical analysis and construction monitoring results. The results show that: (1) the maximum horizontal displacement of the support structure can be significantly reduced by preloading the supporting axial force on the support structure. At the same time, with the increase of the preloading axial force, it also has an obvious control effect on the surface settlement. (2) In the process of excavation, the support servo system has a significant effect on the deformation control, which can effectively control the horizontal deformation of the support structure, reduce the surface settlement, and help reduce the impact on the surrounding environment. Related Articles | Metrics

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Deformation Analysis of a Metro Deep Excavation Supporting in Soft Peaty Cohesive Soils in Shaoxing FANG Jianhua, CHEN Wei, HUANG Baosen, ZOU Xiong, XU Peng 2023, 37 (6):  908-914.  Abstract ( 110 )   Save A deep excavation supporting in the soft peaty cohesive soils for the metro project in Shaoxing has the characteristics of poor geotechnical subsurface conditions and complex surrounding environments. The informative monitoring system was established during the process of the excavation. The lateral deflection of the supporting structure, axial loads in the strut structure and ground subsidence data are collected and evaluated. The results show that: 1) a relatively large lateral deformation within the supporting structure was observed. Especially, an obvious lateral deflection in the supporting structure occurred when the last excavation at the bottom was observed; the spatial effect at the corners of the excavation controlled the lateral deflection. 2) The deformation characteristics of the supporting structure in different parts of the deep excavation in the soft peaty cohesive soils are obviously different under the joint action of eccentric pressure from adjacent soils. At the same time, the pressure of the first reinforced concrete beam supports decreases instead of increasing with the increasing depth of excavation, and the axial force in each layer of support on horizontal and vertical planes shows obvious joint movement. 3) The distribution of the surrounding ground subsidence approximates the Perk ground subsidence shape. The value of xmax of the distance between the maximum subsidence point and the edge of excavation retaining structure is 8~13 m (0.5h~0.9h), and the inflection point σ of the curve in Perk formula is 4 m~7 m. Related Articles | Metrics

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Analysis of an Embankment Slope Stability by Using Transfer Function Method GENG Xuefeng 2023, 37 (6):  915-919.  Abstract ( 175 )   Save The slope stability analysis is a complicated process, and the stability of the different slopes are affected by different factors. The stability of fill embankment is influence by the height of the slope, slope angle, type of embankment material, age of the embankment and the groundwater conditions. This paper presents the stability analysis results of the backfill embankment for a former gravel quarry by using the transfer function method. The stability before and after improvement of the south side fill embankment of the Shuixi section of Guangzhou Metro No. 21 Line was evaluated and the mitigation methods was recommended. The effectiveness of the proposed supporting structure was validated throughout using the commercial analytical software. The results indicate that, the transfer function method can be used for the global stability of the backfill embankment. The location of supporting and magnitude of the forces in the supporting structure can be identified through the transfer function method. Related Articles | Metrics

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Design and Analysis of Deep Excavation Under a Historical Building in Soft Soil Area HUANG Kaiyong, LIANG Zhirong, WAN Yanyang 2023, 37 (6):  920-925.  Abstract ( 124 )   Save This paper presents a case history of the foundation construction under a preserved historical building. Aspects of partitioned bottom-up construction and partial covered excavation of the underground space under a historical building in soft soil area are discussed. Before the historical building was transferred to the permanent position for the required underpinning, the vertical supporting systems and the basement ceiling at the final location were constructed first. The excavation was partitioned in consideration of its complicated surroundings, the zone with the historical building was constructed in bottom-up method after the other one was completed. The region under the historical building was partial covered excavated. Diaphragm walls with four-layer reinforced concrete struts were utilized as the supporting structures. The monitoring data indicated the preserved historical building structure was safe and stable during the entire excavation and the lateral displacements of the supporting structures well met the protection requirements of the surroundings. The deformations in the short side or at the corner of long side were significantly smaller than those in the middle of the long side, and the wall deflections of the small zone were evidently smaller than those of the larger excavated area. Related Articles | Metrics

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Influence of Deep Excavation for a Water Gate in Soft Soils on the Adjacent Environment LAN Shigang 2023, 37 (6):  926-932.  Abstract ( 150 )   Save This paper introduces the supporting structure for the deep excavation for a water gate and its deformation monitoring points for the adjacent complex environment. The importance of the deep horizontal displacement monitoring points to the stability and safety of the adjacent flood walls, municipal utility pipelines and surroundings are evaluated. The monitoring results indicate that the deformations surrounding the excavated area were monitored throughout the entire excavation and the deep lateral deflection of the soil is the major factor that affecting the adjacent environment. The construction of the jet grout cutoff wall has a significant impact, and the rheological characteristics of soft soils are also affecting the deformation of the adjacent environment. This article analyzes the factors affecting the environmental deformation surrounding the excavated area through specific monitoring points during the construction and proposes some viable measures to control the deformation. These measures have positive significance in further reducing environmental deformation of the surroundings. Related Articles | Metrics

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State of the Practice of Soil Replacement by Blasting Method XIANG Aihua, WANG Aizhong, PAN Chaohao, QIN Wei, YAN Juefu, ZHANG Liujun, ZHANG Zhizhou, GENG Peng 2023, 37 (6):  933-939.  Abstract ( 267 )   Save The soil replacement by blasting method is often used for the improvement of thick, soft soils, such as, roadway subgrade over tidal zone and nearshore embankments, that conventional soil improvement methods are difficult to apply. This method has the advantage of high efficiency and low construction cost. Based on the literature review, the mechanism, construction sequence and result monitoring aspects of the soft soil replacement with stone by blasting are discussed in the paper. From the mechanism point of view the “cavity theory” and the “sudden drop of undrained shear strength theory” are the widely accepted by the practitioners, but both theories could not completely explain the on-site performance of the blasting replacement, specially, the blasting replacement in the excessively thick soft soil layers (more than 60 meters thick). In the past 40 years, the construction technology of this method has been improved significantly, and the thickness of the treated soft soils has increased from the initial 12 meters to the current more than 40 meters. The testing of the soil replacement by blasting is mainly a combination of several testing methods. This paper briefly introduces the principle and advantages and disadvantages of each method. The application of soil replacement by blasting exists areas to be improved, such as, uncertain improvement mechanism, uneven treatment depths and the unclear effect on the adjacent. Related Articles | Metrics

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State of the Practice of Prefabricated Supporting Structures LIU Fang 2023, 37 (6):  940-944.  Abstract ( 195 )   Save With the increasing economic development, increasing urban populations require more and comprehensive municipal facilities. In turn, the investment into the infrastructure construction facilitates the innovative construction methods in the slope and deep excavation supporting area. As the important aspect of the urban developments, the traditional methods used in the slope and excavation supporting have the disadvantage of low efficient and have a very high potential of improvement potential. The new prefabricated supporting structure has advantages of fast construction, easy installation, the less manpower, reliable structure and short construction duration but its application is still limited due to the less popularity and lack of design theory. This paper presents the state of the practice of using the prefabricated supporting structure. Related Articles | Metrics

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Time-Dependent Effect in a Deep Excavation in the Coastal Soft Soils QIN Shanliang, XIONG Hao, SUN Mengyao, CHEN Baoguo 2023, 37 (6):  945-949.  Abstract ( 208 )   Save During the deep excavation in soft soils, the exposed soil in the excavated area will experience creep effect under the earth pressures. The deflection of the supporting structure will also increase with the increase of exposed time. At the same time, the strength of the reinforced concrete strut will also increase with the increase of curation time, therefore, the capacity of deformation control of the strut will also increase. Therefore, balancing the creep time and the curation age of the reinforced inner strut has a special meaning for the deformation control of the excavation supporting structure. This paper presents a case history of a deep excavation supporting project Qianhai Station of Shenzhen near shore marine soft soils. The influence of creep in the soft soils and the curation time of the reinforced concrete on the deformation of the supporting structure and the internal force in the strut are discussed. The results indicate that, under the curation time of 28 days, if the creep effect is considered in the supporting structure, the deformation increased 13.9%, 9.3% and 5.3%. If both the curation and the creep effect are considered, each excavation has an optimized period of 12-16 days. When the excavation depth is shallow, the effects of both creep in the soft soils and the curation time in the reinforced concrete curation time should be considered. When the excavation depth is large, enough curation time in the reinforced concrete strut should be considered since the stiffness of the strut is important in this stage. Related Articles | Metrics

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Effects of Chloride Ions on the Performance and Structure of Concrete for Marine Infrastructure under Continuous Loading SHEN Shiyi, MEI Kaiyuan, WANG Bin, ZHANG Liwei, LI Mei 2023, 37 (6):  950-953.  Abstract ( 131 )   Save Concrete used in marine structures is corroded most seriously in tidal splash area caused by frequent dry-wet alternating environment. The influence of Cl- invasion in seawater and continuous loading on the mechanical properties of the concrete was investigated by applying continuous stress to the dry-wet cycles test samples. By using the micro-CT technology, the influence of Cl- invasion on concrete structure and uniaxial compressive strength under continuous loading was investigated from the micro-porous level. The results of mechanical property tests show that the continuous loading condition has a positive effect on maintaining the mechanical strength of the concrete, while the uniaxial compressive strength of concrete declines slowly with the increase of dry-wet cycles. Combined with pore size distribution analysis, it can be seen that Cl- constantly invaded into concrete pores and deposited but has little influence on the mechanical property deterioration of concrete. Related Articles | Metrics

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Numerical Simulation of a Deep Excavation Support in Class I Terrace of the Yangtze River in Wuhan SHUAI Hongyan, SHAO Yong, LI Guangcheng, WANG Jianxiao 2023, 37 (6):  954-958.  Abstract ( 144 )   Save The combined action of the deep excavation supporting structure, internal struts and the adjacent soils is numerically simulated by using MIDAS GTS software. A deep excavation in the first terrace of Yangtze River used cast-in-pace bored tangent piles plus internal strut as the supporting structure and its three-dimensional finite element analysis model with modified Mohr-Coulomb constitutive soil model is established. The entire excavation process was numerically simulated under the assumptions of artisan and non-artisan groundwater conditions. The deformation and internal force variations in the supporting structure during the excavation, strut installation, and dewatering process are simulated. The impact of the dewatering on the excavated area and the settlement of adjacent soils are evaluated. The deformation and stress of the supporting structure including the horizontal struts under various working conditions are discussed. The analytical results provide technical supports for the excavation optimization design. Related Articles | Metrics

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Numerical Simulation of SoilCaisson Interaction in the Caisson Installation in Pipe Jacking MAO Jimin, YANG Xueqiang, LIAN Jiye, WU Yingyi, ZHANG Min, DU Kehan 2023, 37 (6):  959-965.  Abstract ( 200 )   Save The jet grouting improved soil surrounding the caisson for a pipe jacking for a power transmission project in Shunde District, Foshan City, Guangdong Province, is numerically simulated by using the ABAQUS software. The internal force variation and displacement of the jet grouting improved caisson and surrounding soil before and after pipe jacking construction of small diameter pipe jacking shaft are evaluated by the finite element method. The wall deformation and soil three-dimensional failure modes of the small diameter electric caisson after passing through layered soil and applying jacking force are evaluated. The following conclusions are made during the excavation, the surrounding soil is easy to cave into the excavated area due to the soil unloading effect, and the pile tends to be extruded by soil. Under different jacking forces, the locations where the maximum displacement in the active zone are consistent; the performance of both soil and pile are similar and no separation is observed. In the passive area, larger differences between soil and pile are observed. With the push force reaches the limit state, the displacements of the soil and pile are large, and the pile is likely to be damaged. When the pile passes through two different soil layers, the stress at the interface changes, and the stress in the loading region forms an open gourd shape. The shape of this gourd becomes obvious with the increase of the jacking force. The internal force distribution is uniform at the low jacking force, but the main bearing part becomes passive pile with increasing jacking force. When the thrust force reaches a certain limit, the passive settlement area develops stably, while the upward displacement area expands rapidly, resulting in serious uplift of surface soil. Due to the pile support in the active zone, the tensile cracking degree of soil under the jacking force is small, indicating that the installation of jet grouting pile can greatly improve the performance of soil and effectively prevent the cracking development in the active zone soil. Related Articles | Metrics

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Influence of Cushion Thickness on the Settlement Characteristics of Foundation over Thick Soft Soils PU Siqi, CHEN Junhua, SU Chunhui 2023, 37 (6):  966-970.  Abstract ( 158 )   Save The performance of a cushion layer with a thickness of 0.6m to 1.2 m over the rigid column improved soft soil layer is numerically simulated by using ABAQUS software. The cushion thickness on the stress ratio in the soil-column system and the settlement characteristics are evaluated. The results indicate that with the increase of cushion thickness, the foundation settlement increases, and the column-soil stress ratio decreases first and then increases slowly. When the cushion thickness is one meter, the column-soil stress ratio is the smallest, and this thickness is the optimal cushion thickness. Therefore, the use of large thickness cushion in the rigid column composite foundation for the soil improvement of thick, soft soil area can effectively reduce the stress ratio of foundation column to soil and the soil contribution to the bearing resistance could be fully utilized. Related Articles | Metrics

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Numerical Analysis of Deformation Effect of the Supporting Structure of a Deep Excavation XIE Baojin 2023, 37 (6):  971-974.  Abstract ( 99 )   Save This paper presents a case history of the deep excavation support for a 13 stories high building. The deformation and stress in the supporting structure using plane strain numerical analysis method is utilized to simulate soil nail wall with prestressed ground anchor for deep excavation. The numerical analysis results are compared with the construction monitoring data and the feasibility of the supporting structure is validated. The results indicate that, the deformation of excavated area can be effectively constrained by the support structure combining the soil nails and prestressed ground anchors. The horizontal deformation of the surface near the edge of the excavation is 45 % of that when the excavated area having no support. This effectively ensures the safety of excavated area. The pre-stressed ground anchor is the major loading carrying structure when the foundation is excavated, and the maximum internal stress is about 97 kN. Under the effect of the prestressed ground anchor, the excavated surface can be divided by two areas, in the upper area, the deformation is relatively small, and the deformation is fast converged, whereas in the lower area, the deformation is relatively large, and the deformation is slowly converged. Under the effect of the pre-stressed ground anchor, the horizontal deformation of the excavated surface in the upper area is merely 25~50% of that of the lower area. Related Articles | Metrics

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Optimization of Pile Axial Capacity Parameters in a Coastal Area ZHOU Peifeng 2023, 37 (6):  975-978.  Abstract ( 137 )   Save The ultimate side friction, ultimate tip resistance and the unconfined compressive strength of the rock cores are usually provided in a typical geotechnical investigation report for the estimating of the theoretical axial pile capacity. The high strain dynamic loading test is used to determine the axial compressive capacity and the pile integrity of a single pile through wave theory. The static loading test is a compressive test conducted on piles in accordance with the design requirements. Based on the tests, the axial capacity of a single pile is obtained, and the ultimate side resistance of each soil layer around the pile is measured and calculated through strain measuring elements embedded at various locations along the shaft of the pile. The article compares and analyzes the recommended value of the ultimate axial capacity of a single pile estimated based on the theoretical data provided in the geotechnical investigation report and the actual value obtained from the test pile, based on the bored pile test in a coastal engineering project, and puts forward reasonable suggestions for pile foundation design. Related Articles | Metrics

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Statistical Analysis of the Variability of Engineering Characteristics of Soft Soil in the Lixiahe Area LIU Jiazheng 2023, 37 (6):  979-981.  Abstract ( 130 )   Save Soil is a product of nature, and influenced by factors such as sedimentation process, sedimentation conditions, and sedimentation environment. The engineering characteristic parameters of soils have variability, resulting in various indicator parameters obtained from the exploration sampling points being unable to describe the engineering characteristics of the soil layer within the scope. Based on the expressway construction project in Lixiahe area, this paper uses the random field theory to conduct the probability statistical analysis on the variability of engineering characteristic parameters of the lagoon soft soils in this area and summarizes the statistical results of variability of mechanical indexes and deformation indexes of soft soil in other regions in China. The analysis shows that the variability of physical properties indicators of soft soil in the Lixia River lagoon phase is low, while the variability of the mechanical and deformation properties indicators is relatively high. There is an obvious trend component along the depth direction, which has a significant impact on variability. After removing the trend component, the coefficient of variation can be reduced by about half. Related Articles | Metrics

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Influence of Deep Excavation on the Adjacent Existing Shielded Tunnel in Hangzhou Area JIAN Ruohan, HUANG Rui, XU Chengxiao 2023, 37 (6):  982-986.  Abstract ( 133 )   Save The influence of the deep excavation on adjacent structures has always been a hot button issue. The shielded tunnel structure is sensitive to the deformation. The influence of excavation on the deformation of the existing tunnel deserves special attention. Seventeen existing subway shielded tunnels in Hangzhou area are selected as examples to study the influence of excavation on the deformation of the tunnel structure, and to analyze the influence of spatial parameters such as the horizontal net distance, the relative height difference and the excavation depth between the excavated area and the tunnel. The results show that the unloading of the deep excavation will cause the additional deformation of the adjacent tunnel structure, and the horizontal displacement is usually larger than the vertical settlement. The influence of the tunnel deformation decreases non-linearly with the increase of the horizontal net distance from the excavated area. The settlement of tunnel increases linearly with the increase of excavation depth, and the sensitivity of different excavation depth is different. Related Articles | Metrics

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Soil Parameters Object Modeling and Development Using Delphi HU Bangyi, XU Xueyong, HU Lizhen, 2023, 37 (6):  987-991.  Abstract ( 97 )   Save The axial capacity of a single pile is an important factor in the pile foundation design. But in the complex geological conditions, the soil data often have many categories with a wide variation. There are many inconveniences in the fast determining the axial capacity of a single pile. Due to the complexity and diversity of soil data, it is difficult to save and access. The idea of parametric modeling is therefore adopted. An object model of soil layer is proposed by using Delphi platform. Based on this object model, the software for predicting the single pile axial capacity is developed. The results show that the parameterized object model is simple and convenient. It is also convenient to modify, save and access data. The single pile axial capacity prediction software, developed by using the object model, is simple to operate and computationally efficient. Related Articles | Metrics

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Numerical Analysis of the Effect of Double Spudcan Penetration on Adjacent Steel Cylinders JIANG Ying, ZHANG Xun, CAO Yong, WANG Fengyun, QI Zhen, WANG Yin 2023, 37 (6):  992-997.  Abstract ( 153 )   Save The underwater oil production system is usually arranged on the seabed, and its protection measures are crucial for the working stability and safety of the production system. According to the actual marine environmental conditions and the requirements of water channels, there are currently projects that innovatively use large-diameter steel cylinders embedded below the seabed as protection structures for underwater production systems. For this type of protective structure and engineering application, the stability of the steel cylinder will be affected when the spudcan penetration and extraction operation is performed near the jack-up drilling ship, which will bring potential safety hazards. In this paper, the coupled Euler and Lagrangian finite element numerical method is used to simulate and analyze the disturbance of the steel cylinder caused by double spudcans penetration. The deformation and stress changes of the soil and the steel cylinder foundation during the spudcan penetration process are studied, so as to analyze the stability and safety of the steel cylinder protection structure. The results show that the additional stress and displacement of the wall of the steel cylinder increase with the penetration depth of the spudcan at the initial stage and tend to be stable after reaching the peak; when the spudcan penetrates to a certain depth, the soil on the upper part of the spudcan reflows. As a result, the influence on the steel cylinder is reduced; the influence of the double spudcans on the steel cylinder is weakened with the increase of the distance between the spudcans and steel cylinder, but its influence range is significantly expanded compared with the single spudcan. The numerical analysis results in this paper will provide an effective reference for the design and field application of protection measures for underwater oil production systems. Related Articles | Metrics

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Empirical Formula for Estimating Strength of Lime Mixed Soils Considering Degree of Compaction, Lime Ratio and Curing Age DU Wenbo, LIU Lei, SHI Ting, SONG Bo, 2023, 37 (6):  998-1002.  Abstract ( 253 )   Save In order to explore the effects of the degree of compaction, lime content, curing age and water content on the strength characteristics of lime mixed Suqian clay samples, the lime mixed soil samples are prepared and tested. Usually, the lime mixed soil sampled was prepared under the laboratory standard curing conditions for 7 days and tested for the unconfined compressive strength. The factors such as, void ratio in the mixed sample, lime content and sample moisture content, on the unconfined compressive strength are studied. The experimental results show that the unconfined compressive strength of lime mixed soil sample increases linearly with the increase of degree of compaction, increases approximately linearly with the increase of lime content, and increases differently with the curing age. While the change of water content does not have a significant effect on the unconfined compressive strength of the lime mixed soil. In this paper, a comprehensive characterization parameter that can comprehensively reflect the influence of the degree of compaction, lime content and curing age on the strength of the lime mixed soil is proposed, which a certain engineering significance. Related Articles | Metrics

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Study on Sample Size Effect Based on Direct Undrained Shear Test SU Hao, CHENG Yun, LI Yuhong, WANG Jingjing, XU Lingmin 2023, 37 (6):  1003-1008.  Abstract ( 224 )   Save As a special granular material, the soil sample demonstrates obvious anisotropy and inhomogeneity. The characteristics of the shear failure surface in the direct shear test and other factors lead to its different failure modes from other materials. Direct shear tests of four types of soil samples were conducted by using samples with diameters of 61.8mm and 150mm, respectively. Based on the test results, the size effect of the soil shear strength is analyzed. The results show that the change of sample size does not affect the stress-strain deformation characteristics of the sample. However, with the increase of sample size, the peak shear strength appears later and the resistance to deformation is stronger. With the increase of sample size, the proportion of effective shear area increases, resulting in the increase of theoretical shear strength. For cohesive soil, the increase of cohesion is mainly manifested while the angle of internal friction doesn't change much. On the contrary, the increase of internal friction Angle is the main performance for sandy soil. Related Articles | Metrics

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Experimental Study on the Strength and Deformation Characteristics of Artificially Cemented Silty Clay HU Xiaozhu, LU Yong, ZHOU Ya, FENG Haihua 2023, 37 (6):  1009-1015.  Abstract ( 175 )   Save The artificially cemented soil is widely used to improve the physical and mechanical properties of the natural ground. However, this type of the cemented soil often exhibits a strong nonlinear mechanical behavior while having the high strength and stiffness. This paper takes cementbonded silty clay as an example to systematically analyze the strength and deformation characteristics of samples with different degrees of the cemented structure. The results show that the artificially cemented soil often exhibits significant strain softening characteristics (brittle failure), and its peak strength presents as a statedependent parameter that is significantly affected by the confining pressure and the structure degree, while the residual strength presents as a stateindependent parameter that is less affected by the confining pressure and the structure degree. The compressive stiffness of the cemented soil is significantly higher than that of the remodeled one, and the degradation of cemented structure under the high pressure will cause the isotropic compression line (ICL) to yield and gradually converge to the normal consolidation line (NCL) of the remodeled cemented soil, which provides a way to determine the NCL of the cemented soil. Different from the “shear dilatancy softening” of the over-consolidated clay or the dense sand, the “shear shrinkage softening” phenomenon of the cemented soil often occur due to the degradation of the cemented structure. In addition, the strain localization phenomenon in the cemented soil will affect the overall volumetric change of the sample, resulting in some difference in the critical state lines of artificially cemented soil and corresponding remodeled one. Related Articles | Metrics

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Development of a Seepage Test System for the Leakage in Construction Joints of the Tunnel Lining SU Jingbin, HAN Weiwei, WANG Xiaoguo 2023, 37 (6):  1016-1022.  Abstract ( 161 )   Save With the rapid development of the national economy, the transportation infrastructures have entered a period of large-scale construction, and more and more tunnels have entered the frequent hazard occurrence period. The problem of water leakage from construction joints is one of the main hazards in the process of tunnel construction and operation. First, it seriously affects the safety and durability of the tunnel structure. In order to study the leakage pattern from tunnel construction joints, a seepage model test system was developed, which consists of a hydraulic loading device, an air pressure loading device, a seepage test block model and a data acquisition device. Through the analysis of the information such as the amount of water leakage and the time of starting leakage, the anti-leakage performance of the tunnel lining construction joint itself is analyzed, and the influence of different factors on the leakage of the construction joint is studied. Simulating the unfavorable construction conditions that may occur during the on-site construction, quantitatively evaluates the influence of unfavorable construction on the leakage of the tunnel lining construction joint. Related Articles | Metrics

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Effect of Clay Content on the Physical and Mechanical Properties of Guilin Red Clay WANG Liangyu, LI Shujiang, YANG Bai, LIU Baochen 2023, 37 (6):  1023-1026.  Abstract ( 114 )   Save The clay content in red clay is very high. In order to explore the influence of clay content on the physical and mechanical properties of the red clay, the Guilin Red Clay samples are used as the research object. The tested clay content in the soil samples is 42.3%. The clay sample is prepared by using the principle of clean water sedimentation. Different clay contents are added to different Guiling Red Clay samples, and the specific gravity test, water content test and triaxial shear test are performed on these samples. The results show that, the specific gravity of soil particles first decreases and then increases with the increase of clay contents. The water content ratio gradually increases with the increase of clay contents and the cohesion increases step by step with the increase of clay contents. The internal friction angle decreases step by step with the increase of clay contents. The specific gravity curve and water content ratio curve are fitted, and the results are close to the form of power function. Related Articles | Metrics

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Effect of Lime Content and Curing Age on CBR Value of Improved Soils XU Fan, YANG Yongjing 2023, 37 (6):  1027-1030.  Abstract ( 214 )   Save The load-bearing ratio test was first proposed by the California Highway Administration in 1928 to compare the strength of the material when California conducted the asphalt pavement damage survey, also known as the California Bearing Ratio, which referred to as the CBR (California Bearing Ratio) test, which is used to test the extreme bearing capacity of the highway subgrade in an unfavorable state, which is one of the main parameters of pavement design. Now more and more road projects in China require the tested CBR values for the preliminary design. Under normal circumstances, the CBR value for clay is difficult to meet the construction requirements, and the subgrade soil needs the lime improvement treatment. In order to study the influence of lime content and different curing ages on CBR value, the representative subgrade soil material of a section of Wuhan-Dawu Expressway was selected for testing, and the influence of different lime mixing conditions of improved soil on CBR value was analyzed. The optimal lime mixing contents for the three groups of soil samples were determined, and the influence of different curing ages on the CBR value when the soil reached the standard value under the condition of certain lime mixing ratio. Related Articles | Metrics

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Reasons and Mitigation of Floating Pipe Piles in Coastal Soft Soils QIU Zhihua, 2023, 37 (6):  1031-1034.  Abstract ( 158 )   Save A large number of floating piles in a project in the coastal soft soils were detected through the large strain dynamic pile loading tests on the prestressed concrete piles. The floating pile phenomena were comparatively studied by the various static axial loading tests and low strain tests. The potential factors that triggering the floating pile are discussed in the paper and the mitigation methods for the floating pile are proposed. The results indicate that when pipe piles are used in soft soil area, the high strain method can be used to preliminarily verify if a floating pile exists; In the case of deep silt soil layer, the pile type should be carefully selected in accordance with the local subsurface soil conditions; The restriking method can effectively mitigate the floating problem of pipe piles, and it is suggested to give priority to the free falling hammer re driving combined with high strain method monitoring in soft soil areas, which has important reference and reference significance for similar projects. Related Articles | Metrics

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Monitoring of a Deep Excavation Near the Comprehensive Subway Viaducts DAI Zhonghai, WU Wenjie 2023, 37 (6):  1035-1039.  Abstract ( 144 )   Save Based on a complex deep excavation project near the comprehensive subway viaducts, the displacement at the top of excavation support structure, settlement and deep horizontal displacement of the soil, and axial force of the bracing during the process of the deep excavation were monitored. The relationship between the displacement at the top of supporting structure and time, as well as the changes in deep horizontal displacement and the axial force in the bracing were evaluated. The results showed that the horizontal displacement at top of the supporting structure shifted towards the inner side of the excavation as the excavation progressed; The settlement of the supporting structure has a similar trend in different parts, but the numerical values vary, it is mainly affected by the construction load; The deep horizontal displacement of the diaphragm wall shows a trend of “small at both ends and large in the middle” with the excavation depth, and the maximum horizontal displacement of the deep layer increases with the construction progress; The bracing of the deep excavation can effectively share the active soil pressure.  Related Articles | Metrics

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Comprehensive Experimental Study on the Shear Strength Characteristics of Completely Weathered Tuff HU Pucha, XIONG Shihu, XIA Hai 2023, 37 (6):  1040-1043.  Abstract ( 366 )   Save The completely weathered tuff is encountered in the dam site area of Beikeng Reservoir, and its feasibility as a dam foundation is an important factor that affecting the project investment and the engineering safety. In-situ large-scale direct shear tests, laboratory direct shear tests and triaxial compression test are performed on the completely weathered tuff to study the shear strength characteristics and provide the basis of shear strength parameters for the dam foundation stability analysis. By comparing and analyzing the test results of different test methods and different water contents, the following shear deformation and strength characteristics of the completely weathered tuff are observed: 1) With the increase of the shear stress, the shear stiffness decreases and the shear strain increases rapidly. The normal deformation increases with the increase of shear stress, indicating the shear shrinkage characteristics. 2) The internal friction angle decreases with the increase of the water content. 3) The in-situ direct shear is essentially unconsolidated undrained shear, and the test results of the internal friction angle is lower than that of the laboratory consolidated quick shear. 4) Affected by the original rock structure, the cohesion of the in-situ direct shear is significantly greater than that of the laboratory direct shear and the triaxial shear tests. Related Articles | Metrics

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Numerical Simulation of Single-Hole Shale Under Different Hydraulic Pressure Increments XIA Xi, WANG Wentao 2023, 37 (6):  1044-1048.  Abstract ( 135 )   Save To explore the fracture growth in the single-hole shale by the hydraulic fracturing under the fluid-structure interaction, the RFPA2D-Flow shale fracture analysis software was used to establish seven numerical models under different hydraulic pressure increments, and hydraulic fracturing tests were also performed. The results show that the initial crack starts from the borehole circumference of the single-hole shale during the loading process along the weakest part of the shale matrix and quartz junction, and the crack expands along the edge of the quartz grain. Its final failure modes can be divided into oblique Y type and oblique X type; Due to the coupled of confining pressure and water pressure, the damage degradation occurs twice in the failure process, and when the water pressure increment is 0.45MPa/step, the shale damage failure stress is the largest, and the damage failure value is 60.97MPa; When the internal stress balance is broken, the microfractures generated by shale will be compacted, and when the hydraulic fracturing increment is 0.45MPa/step, the fracture rate reaches the maximum. Related Articles | Metrics