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20 August 2020, Volume 34 Issue 4 Previous Issue    Next Issue

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Rehabilitation Design Methods on Existing Retaining Walls in Shenzhen ZHANG Shihua, ZENG Jiangbo, WANG Zhen 2020, 34 (4):  391-395.  Abstract ( 476 )   Save When there are signs of failure due to the excessive deformation on a retaining wall, it is necessary to determine its stability state and whether the retaining wall worth to have it rehabilitated or not. The retaining wall rehabilitation design should consider the residual effective resistance of the original retaining wall, the cost effectiveness and safety of the new rehabilitated retaining wall. A viable method is to qualitatively and quantitatively determine the stability of existing retaining walls throughout comprehensive investigations. By estimating the residual effective resistance of the retaining wall, the effective resistance required by the new supporting structure can be determined. Considering engineering geological environment, hydrogeological conditions and site spatial conditions, an optimal rehabilitation method can be selected. Related Articles | Metrics

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Deep Excavation Support Design for a Sports Park HUI Yanglei, PANG Banghui, XIE Yifan 2020, 34 (4):  396-399.  Abstract ( 304 )   Save This paper presents a case history of the design of a deep excavation supporting system of a sports park using Lizheng geotechnical design software. The design considered various site conditions and the supporting system design utilized the cast-in-place reinforced concrete pile with three layers of ground anchors. The lateral deflection and the axial loads in the piles were estimated with the software and the results compared with long term monitoring data. The studies concluded that the analytical simulation of the construction process and construction monitoring can provide guidelines for the rest of construction procedures. Related Articles | Metrics

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Theoretical Analysis and Monitoring of High Energy Dynamic Compaction Replacement WEI Huan 2020, 34 (4):  400-403.  Abstract ( 298 )   Save This paper presents a settlement estimation of the soil improvement ground of thick fills by high energy dynamic replacement using the summation of sublayered settlement analysis method. The actual settlements of the improved ground at the perimeters of the tanks were monitored during and after construction considering the complication of the improved soil layers and limitation of the existing theoretical settlement estimation methods. After comparing the monitored and estimated settlement values, the following conclusions can be obtained: The high energy dynamic compaction replacement method can be used in improving the thick recent random fill site. Both estimated and monitored settlement values indicated that the total, differential settlements and tilting of the structure can meet the code requirements. The rate of settlement after the construction reduces with time and the settlement approaches to stable within six months after the construction. Related Articles | Metrics

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Stability in the Construction of a Double-Arched Tunnel without Pilot Tunnel Excavated ZHAO Jianxiong, LIU Junqi, ZHANG Dongyan, YUAN Liufeng, LIN Kongbin 2020, 34 (4):  404-411.  Abstract ( 328 )   Save In order to compare and evaluate the most safe and stable cross section type in the excavation of the multi-arch tunnel without a pilot tunnel excavated first as well as to improve the safety and stability of the tunnel lining structure during the tunnel excavation, this paper presents a case history of the excavation and evaluation results of a multi-arched tunnel in Fujian Province. Three different tunnel excavation sequences with the amount of backfill at the top of mid-wall area were numerically evaluated for the factors of safety for the lining structure at final stage, temporary supporting structures and midwall stability. The stability of the tunnel structures and its variation during three different tunnel excavation sequences at various stage of excavation are compared in detail. The results indicate that that the maximum stress changes are found in the lining structure at upper step of the later excavated tunnel. In all three excavation sequences, the immediate filling the gap between the lining structure and the mid-wall is beneficial to the stability of the lining structure. It is also concluded that the method three can be used as the crosssection type of the tunnel excavation without a pilot tunnel excavated. The stability of the lining structure in the multiarched tunnel excavation can be improved by the immediate backfilling of the top of mid-wall. Related Articles | Metrics

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Analysis of Deformation Characteristic of an Excavation Supporting Structure Adjacent to Slopes with Various Geometric Conditions ZHANG Ding, ZHANG Keneng, ZHANG Yunyi, WANG Yanzhi, CHEN Jun, WANG Yongzhao 2020, 34 (4):  412-417.  Abstract ( 322 )   Save A deep excavation project in Chenzhou City is located in the mountainous area of southern Hunan Province. Due to the topographic limitations, the engineering environment of the excavation site adjacent to the high slope is induced. The eccentric effect of the high slope on the deep excavation would result in an additional lateral earth pressure and additional deformation to the supporting structures of the excavation, which has a great influence on the stability and deformation of the deep excavation system. It is necessary to analyze the deformation characteristics of the supporting structure and study the degree of stability affected by the high slope. The MIDAS finite element simulation software was used to establish the numerical model. The deformation data of the supporting pile under the different geometric conditions were analyzed and summarized to obtain the deformation characteristics of the support structure under different conditions. The effect of the stability on the sidewall of the excavated area was evaluated. The results show that during the excavation process, the maximum deformation of the soldier pile appears to be between the two rows of anchors of the supporting structure. Under the same slope height condition, the foundation pit has a critical slope ratio with deformation value changes significantly. The deformation of the supporting structure is more regular under the condition that the slope ratio of the slope is fixed. Related Articles | Metrics

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Analysis of the Influence of Precipitation on the Stability of Fangshan Slope in Nanjing LIU Haibo, XU Baotian, WANG Bo 2020, 34 (4):  418-422.  Abstract ( 540 )   Save This paper presents a case history examining the effect of precipitation on the stability of slopes in Nanjing at Fangshan Caidiegu Landslide. By analyzing the engineering and geological characteristics of the landslide, it is concluded that this landslide is a typical rainfall-induced landslide. Based on the actual precipitation conditions in Nanjing, the influence of the different precipitation conditions on the slope stability is analyzed by using a twodimensional finite element software based on the historical precipitation data. The results show that the stability of the Caidiegu slope is closely related to the precipitation which is the main factor inducing sliding. The infiltration of the rainwater results in a gradual increase of the moisture content in the slope. Then, the previously unsaturated zone becomes transiently saturated, and progressively extends downward from the surface. Therefore, the pore water pressure is continuously increased, resulting in a decrease in effective stress and the shear strength of the soils; the slope stability is very sensitive to the rainfall intensity, and the greater the rainfall intensity, the faster the stability declines. Related Articles | Metrics

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Application of CBR Test in the Pavement Engineering CAO Xueyu, LIU Yang 2020, 34 (4):  423-425.  Abstract ( 901 )   Save The California bearing ratio CBR is an indicator for evaluating the strength of soil materials. The CBR test has a very important application in pavement engineering. The “dry density-CBR” curve obtained from the test is combined with the compaction index required for subgrade construction to determine if the soil is appropriate to be used as desired subgrade material with given strength; It can also be determined whether the CBR strength of the in-situ subgrade soil of the zero-fill and cut zones meets the code requirements. In the practical projects, although some test inspectors are familiar with the procedures of the CBR test, and can obtain the dry density of three groups of test pieces and the corresponding CBR value through the test data, they do not know how to use these test results in combination with the pavement construction technical specifications to analyze the mechanical properties of soil. Based on this, a case history was presented to elaborate this issue with the graphical method and the analytical method, respectively, and then the pavement performance of the material was determined to provide a reference for the test inspectors and construction technicians. Related Articles | Metrics

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Role of Pile Cap in the Cantilever Piles as the Deep Excavation Supporting Structure YI Lili, MA Yun, NIE Jun, LI Song, ZHU Jia 2020, 34 (4):  426-429.  Abstract ( 538 )   Save The role of pile cap in using the cantilever piles at the deep excavation supporting structure is evaluated by the finite element method. The following results are obtained: 1) the pile cap has a significant effect in controlling the excavation deformation at the longer side and presence of the pile cap makes the excavation induced deformation more compatible. 2) Since the pile cap increases the lateral stiffness at the top of piles so that the deformational characterization of the cantilever supporting structure has improved. 3) Better lateral deflections can be obtained by increasing the number of pile caps in the supporting system. 4) The smaller pacing between the pile caps, the larger bending moment in the pile; the greater number of pile caps, the larger the bending moment in the pile. Related Articles | Metrics

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Stability Analysis and Mitigation of a Landslide at Huaishu Village LIU Kairui 2020, 34 (4):  430-433.  Abstract ( 347 )   Save The location of the slip surface and its shear strength parameters can be determined by using limit equilibrium method and transfer function with implicit solution with a relatively high accuracy. Considering the slip locations relatively close to the railroad alignment, the mitigation measures used both temporary solutions such as sealing off cracks and back surcharge at the toe of slip and long-term solutions such as permanent anti-slip caissons and drainage ditches at the mouth of the stable valley. It is approved that the mitigation measures are safe and effective. Related Articles | Metrics

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Foundation Construction Method for a Long-Span Feiyan Tied Arch Bridge-Using Hejiang Changjiang Highway Bridge as an Example YAN Jing, WEN Haoqi, LIU Bonan 2020, 34 (4):  434-437.  Abstract ( 284 )   Save The case history of foundation construction methods for the long-span Feiyan tied arch bridge for Hejiang-Changjiang highway project is presented in this paper. The key aspects during the caisson installations are also evaluatedin the paper. The following results are found: 1) For the striking drilling method, the appropriate stroke should be determined based on the stiffness of various soils. The stroke setting for the soft or loose soils should be 1.0 to 2.0 meters; 2.0 to 3.0 meters for medium soils and 3.0 to 5.0 meters for the dense or hard soils. However, the maximum stroke should not be higher than 6.0 meters. 2) The low stroke and fast striking method should be used for alternating of soft and hard soil stratigraphy, hard stone pieces can be dumped into the borehole to form a firm platform in the hole. 3) for the quality acceptance, the circulated slurry pumped from the borehole should be uniform and without debris; No solid particles with dimension 2 to 3 mm by using the hand touch; the specific gravity of the slurry should be between 1.03 and 1.10; sand content in the slurry should be less than 2%; the viscosity should be between 17 and 20 s; the thickness accumulated at the bottom of borehole should be less than 80 mm. At the same time, borehole cleanness examination and cleaning should be performed immediately before the concreting work. 4) due to the special hydrological conditions at the bridge site, the disposal of the drilling fluid should be arranged with the variation of the hydrological conditions dynamically: When the groundwater level is deep and the groundwater recharge to the borehole is not high, single borehole pump disposal can be used, however, when the groundwater recharge to the borehole is large, and the groundwater water level is shallow, multiple borehole pump disposal method can be used. If the caisson length is not large, drainage ditches can be used around the caisson locations. Related Articles | Metrics

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Pile Type Selection for the Commercial Residential Buildings in East Henan XIE Rui 2020, 34 (4):  438-441.  Abstract ( 314 )   Save Pile foundation is one of the most widely used foundations in China and its engineering quality involves the safety of superstructure. Besides the complexity of the pile foundation engineering due to the geotechnical engineering condition, foundation and structure design, interaction of pile-soil system, construction, professional technology level and experience, etc., pile construction also has a high degree of concealment, so its design, construction, quality inspection, etc. are often more complex than the upper structure of buildings and more likely to have quality risks. Throughout the comparison and verification of the static load testing on two types of pile in the same project, this paper provides the scientific and reliable test data and theoretical support for the design organization in the foundation pile type selection. Related Articles | Metrics

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Risk Analysis and Management Measures of Constructing an Extra-Large Diameter Shielded Tunnel Adjacent to an Existing Pile Supported Viaduct YUAN Peng 2020, 34 (4):  442-446.  Abstract ( 350 )   Save Huge potential risks exist during the construction of the extralarge diameter shielded tunnels passing through the pile supported foundation of adjacent existing buildings or other structures. This paper presents a shielded tunnel construction of Changjiang Road river crossing tunnel in Shanghai. Tunnel excavation near the pile supported viaduct of Yixian Road and Rail Transit Line #3 induced risks are identified and analyzed. The Metro Jet System (MJS) was used to isolate and to strengthen the pile supported foundations adjacent to areas to be undercrossed. The design and construction parameters for the under passing the pile supported foundations were able to be adjusted by the trail excavation and construction monitoring. The deformation of the isolated foundation structures were monitored during the construction until the deformation is stabilized and meet the allowable post construction deformation criteria. Related Articles | Metrics

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Application of Jack-up Beam in Rehabilitation of Tiled Rail Structures ZHAN Yinglong 2020, 34 (4):  447-450.  Abstract ( 222 )   Save The viaduct piers between Stations K92+670 and K107+550 as well as between Stations K108+790 and K111+320 of an intercityrailway were observed to be tilted by various degrees due to a municipal engineering construction project. The geometric dimensions of the high-speed railway track in both sections were deformed, which was seriously affected the smoothness and safety of the track alignments. In order to ensure the safety of railway operation, it is urgent to select appropriate measures to correct the piers. This paper presents a case history of correction tilted piers by using the jack-up and shifting box beam method. The principles, key installation aspects and construction monitoring of the box beam jackup and translation method are introduced in the paper. Related Articles | Metrics

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Improvement of Loose and Soft Boulderly Soils in Valley Area of Zhengzhou-Wanzhou High-Speed Rail Project CHEN Yuanhong 2020, 34 (4):  451-454.  Abstract ( 349 )   Save The loose and soft soils in the mountain area frequently contain random boulder sized rock blocks with various grain sizes. It is usually difficult to accurately characterizing the vertical and horizontal limits of boulderly soil strata by using the conventional boring spacing defined in the code. In accordance with the author’s experience of characterization of clayey, gravelly, and sandy soils strata in the valley area, the potential random boulderly soil lenses should be verified by using smaller bring spacing of 20 m to 40 m in the longitudinal direction. Further, in the transverse direction, at least two test borings should be arranged with a test boring spacing of 50 m to 100 m. Based on the proposed fill height and the boulderly soil distribution, various soil improvement and structural measures, such as, sheet pile with strong penetration; soil replacement and surcharging with large surcharging ratio, can be used to meet the settlement control requirement of high-speed rail projects. Related Articles | Metrics

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Analysis and Mitigation of a Highway Landslide in Hainan Province QI Shengwang, GAN Yu 2020, 34 (4):  455-458.  Abstract ( 357 )   Save This paper studies the failure modes and formation mechanism of a highway landslide in Hainan Province by using the combination0engineering geological mapping, engineering geophysical exploration and engineering geological drilling methods. Throughout the investigation, it is concluded that the landslide can be divided into three portions; the deep potential landslide, the historical surficial landslide at the west side of the highway and the recent surficial landslide at the east side of the highway. factors that directly attribute to the landslide are, the F1 well developed fissured zone within the landslide area and the excavations for the highway alignment in the east direction. Based on the stability analysis of the landslide, practical landslide mitigation and prevention measures are proposed in the paper. Related Articles | Metrics

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Accurate Evaluation of Deep Pebble Layer and Correct Selection of Pile Tip Bearing Layer ZHANG Guoyin 2020, 34 (4):  459-463.  Abstract ( 360 )   Save This paper presents a case history of deep pebble soil site investigations for the proposed large shopping mall. The preliminary geotechnical investigation at the project site did not fully understanding the limestone bedrock conditions, the vertical and horizontal limits of sandy and pebbly soil layer were not completely revealed. In the final subsurface investigation overcame the equipment limitations in the preliminary site explorations by using the improved geotechnical drilling methods such as, single tube drilling, and double-tube-double action and doubletubesingle action for sampling. The improved drilling methods successfully increased the recovery of rock cores. Different drilling slurries were used in the advancement of welldeveloped karst rock cavities to minimize the loss of drilling fluid. These slurries are drilling mud, cement slurry, vegetative slurry, and polymer slurry. These measures successfully minimize the borehole caving and loss of drilling fluid so that the accuracy of the in-situ geotechnical testing was improved. A total of 665 heavy dynamic cone penetrometer testing were performed in pebble soil layers and the results indicated that the pebble layer can be used as the bearing layer for the proposed pile tip. Related Articles | Metrics

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Assessments and Mitigation of Strength Insufficiency Defections in the Slope Protection Piles YUAN Changsheng, FU Zhibin, TANG Deping, LI Hongsen, QIAN Huiliang 2020, 34 (4):  464-468.  Abstract ( 463 )   Save The assessment of the strength insufficiency defects in slope protection piles for the deep excavation projects is a topic that receives few attentions in the geotechnical society. This paper presents a case history of testing and evaluation of the concrete strength from the slope protection piles. The compressive strength values, the representative cored samples from the pile, principles of strength determination and calculation of the compressive strength are thoroughly discussed in the paper. The method of assessment of the low strength in the slope protection piles are established and the mitigation of these defected piles are proposed. This approach can be applied in the continuation of the deep excavation and reuse the existing support structures. Related Articles | Metrics

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Influence of a Deep Excavation on the Adjacent Tunnel XIA Ming 2020, 34 (4):  469-473.  Abstract ( 284 )   Save With the increasing commercial estate opportunity along the subway lines, large size deep excavations are frequently encountered adjacent to the metro tunnel alignments. The excavation induced unloading at these large sized deep excavation projects might result in the deformation of the adjacent tunnels. If the excessive deformation occurs in the tunnel structures, the safe operation of the metro cars might be compromised. This paper presents a deep excavation history in Nanchang City. The influence of the deep excavation on the adjacent metro tunnel structures are investigated with three different analytical methods. Related Articles | Metrics

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Analysis of Seismic Performance of Earth & Rock Filled Dams In High Altitude Area LIAO Guangchen, WANG Shiqing, WEI Jianfei, GUO Yonggang, WANG Peiqing 2020, 34 (4):  474-478.  Abstract ( 285 )   Save This paper presents the principles of the analysis on the seismic performance of the earth and rock filled dams in Poindo, Tibet. The seismic response spectrum, seismic capacity of the dam structures and the required energy in earth and rock filled dam at failure are also summarized in the paper. The concepts of energy criteria for the seismic stability and the risk potential for the seismic failure for the Piondo earth and rock filled dams are also proposed and these concepts are used in the seismic analyses of the two dimensional structures such as dams in order to evaluate factors such as, the acceleration in dam, maximum seismic shear strain, maximum principal stress and maximum seismic deflection, on the dam safety. The results are proved to be reasonable. Related Articles | Metrics

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Comparisons of Foundation Bearing capacity Design Between Eurocode 7 and Chinese Code LI Fengmin 2020, 34 (4):  479-481.  Abstract ( 998 )   Save This paper briefly introduces the partial coefficient method based on probability theory inEurocode 7: Geotechnical design-part 1:General rules,this method has three different design methods for different situations.In addition, this paper provides a comparative analysis on the formula of bearing capacity of foundation in Code for Design of Building Foundations (GB50007-2011), Hubei Technical Code for Building foundations (DB42/242-2014) and Eurocode 7.The formula for calculating the bearing capacity of national standard is based on the formula of P1/4 of “elasticplastic method”,  Hubei local standard and European standard is based on the formula of “rigidplastic method”.The essential difference between the bearing capacity formula of Hubei local standard and that of the European standard lies in the total coefficient method adopted by Hubei local standard, while the partial coefficient method is adopted in the European standard. A numerical example is given to calculate the bearing capacity and acting force of the foundation according to the three codes, and the differences are compared. In order to learn foreign norms in foreignrelated projects to play a role in attracting new ideas. Related Articles | Metrics

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Discussions on the Reliability of Recommended Geotechnical Parameters for Pile Foundations PENG Gongxun 2020, 34 (4):  482-486.  Abstract ( 343 )   Save In this paper, a point that the recommended values of geotechnical parameters should be considered in the entire process of the engineering characteristics is proposed. As inthe pile supported foundations, the influencing factors of geotechnical parameters test value arebrieflyevaluated. Further, the difference reliability requirements on the geotechnical parameters for the pile supported foundation are discussed in the paper. Based on the above evaluations, the method of providing reliable and reasonable recommendation values of geotechnical parameters for the pile foundation in accordance with the statistical data of physical and mechanical test indexes is also proposed. Related Articles | Metrics

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Validity Verification of the Segregation Potential in Evaluating the Sensitivity of Soil Frost Heave ZHOU Jiawei, LIN Chunmei, ZHANG Qu 2020, 34 (4):  487-489.  Abstract ( 545 )   Save Frost heave rate, as a conventional frost heave index, can only estimate the frost heave deformation of soils. In order to better evaluate the frost heave property of the soil and verify whether the segregation potential model can effectively evaluate the frost heave sensitivity of the soil, the temperature distribution and deformation development of the soil during the freezing process are measured under the laboratory conditions. The segregation potential is then calculated according to the model proposed by Konrad. The relationship between the segregation potential and the freezing time, the segregation potential and the frost heave deformation and the frost heave rate are analyzed. The studies show that the segregation potential of the saturated silty clay has a good positive correlation with the frost heave deformation and frost heave rate under the onedimension freezing condition. The segregation potential can effectively evaluate the frost heave sensitivity of the soil and can characterize the degree and trend of frost heave. Related Articles | Metrics

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Parameters for the Digital Detonator for Excavation of a Rock Slope Adjacent to Buildings ZENG Chuntao, LI Zhe, 2020, 34 (4):  490-492.  Abstract ( 571 )   Save Although the digital detonator has many advantages over the conventional electrondelay detonator, the application of the digital detonator on the blasting excavation of the rock slope is rarely reported. In this study, a high rock slope was planned to be excavated at the HeBai Expressway between stations K41+016 and K41+273 and the digital detonator was used in the excavation of the slope. Due to the presence of building structures adjacent to proposed slope to be excavated, a trail study was carried out for providing the design blasting parameters. According to the field measurement of vibration velocity, the maximum tested vibration velocity of the adjacent building was 0.87 cm/s, which was much lower than the controlling threshold of 2 cm/s, indicated that the safety of the adjacent buildings during blasting excavation could be warranted. Related Articles | Metrics

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Application of BP Neural Network in Prediction Collapsibility Coefficient of Loess ZHAN Hongzhi, LIN Jianfeng 2020, 34 (4):  493-496.  Abstract ( 319 )   Save In order to apply the back propagation (BP) neural network to the evaluation of collapsibility of loess,on the basis of eliminating the correlation between physical and mechanical indices by using the principle of factor analysis,this paper proposes and establishesa BP neural network prediction model of loess collapsibility coefficient based on four physical and mechanical indices including water content, porosity ratio, plasticity index and compression coefficient. The geotechnical test results on loess soil samples from project site of Dingxi to Lintao Expressway were taken as the training and test samples. The predicted value and measured value are compared and analyzed. The results show that the determination coefficient of the training results is 0.95, and the relative error between the predicted value and the measured value is generally less than 11.1% in the prediction analysis.It shows that the proposed BP neural network model can be used to predict the collapsibility of loess. Related Articles | Metrics

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Shear Creep Characteristic of Mica-Schist Using Modified Bugers Model LIU Ting 2020, 34 (4):  497-501.  Abstract ( 424 )   Save Based on the shear creep tests of mica-schist samples, the time and horizontal creep displacement curves under different stress conditions are obtained in this paper. The constitutive model based on the original and modified Burgers models is proposed to simulate the entire process of the shearing creep. The model parameters under various horizontal shear strain are obtained and the test data are compared with the previous fitted data. The results indicate the proposed is appropriate and reasonable. The conclusions can be used for the evaluation of the long-term stability and safety of rock mass after excavation. Related Articles | Metrics

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Study on the Effect of Fault on Rock Burst Potential in Coal Mining ZENG Linsheng, SONG Guihong, YAO Tianbo 2020, 34 (4):  502-506.  Abstract ( 396 )   Save By considering differentdip angles and different mechanical properties of fault, the effect of fault onrockburst potential in coal mining is studied numerically. The results show that the advancement length of the working face, the inclination of the fault and the mechanical properties of the fault have great influence on the occurrence of rock burst.It is concluded that, (1) the abutment pressure increases with the increase of the advancement length of the working face. The existence of fault makes the peak abutment pressure increase more pronounced. (2) The increase of the dip angle of the fault will increase the fluctuation of the normal stress and the shear stress of the fault plane. The relative slip of fault planes increases with the increase of the 〖JP2〗advancement length of the working face. (3) The increase of the fault mechanical properties can reduce the peak value of the peak abutment pressure to a certain extent. The decrease of the fault mechanical properties will hinder the transfer of the stress and increase the rock burst risk. The study can provide a reference for the evaluation of the rock burst risk induced by fault in coal mining. Related Articles | Metrics

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Discussions of Bearing Capacity Evaluation Methods for Foundation Soils QIU Shoucui 2020, 34 (4):  507-510.  Abstract ( 422 )   Save In geotechnical engineering investigation, it is necessary to use a variety of investigation means and methods to obtain the foundation bearing capacity. Because of the heterogeneity of soil, sampling disturbance, indoor test and field insitu test operations, the bearing capacity values obtained by the standard table or theoretical calculation might usually be significantly different. The bearing capacity values for the foundation soils should be determined by comprehensive analyses. This paper analyzes the influence of the indices obtained by the indoor geotechnical test and the insitu test methods on the bearing capacity of the foundation soils, and evaluates the reliability, in order to provide an economic and reasonable warrantee for the design and construction of the foundation and a reference for the bearing capacity in the geotechnical investigation. Related Articles | Metrics

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Geotechnical Investigations for a Deeply Embedded Tunnel in the Karst Area in Wuhan City LONG Zhiguo, PENG Huazhong, HU Shuai 2020, 34 (4):  511-514.  Abstract ( 316 )   Save The sewer transferring systems engineering in the core area of Greater East Lake is the first deep embedded tunnel for sewer transferring project in Wuhan, which is predominantly constructed by the shielded tunneling method. This paper presents a case history of the sewer transmission system project in the core area of Greater East Lake. The geotechnical investigation methods of the deeply embedded tunnel excavation in the karst terrain of Wuhan city is discussed. Through the data collection and engineering geological mapping and survey, the regional geological and hydrogeological conditions can be quantified. The geotechnical investigation methods combined the geotechnical drilling and samples, as well as insitu testing methods for the soil stratigraphy, the condition of karstic bedrock and hydrogeological conditions of the project site. The specialty investigation methods, such as electromagnetic wave computer tomography (CT) scan, borehole color television, hydrogeological testing, hydrological survey and laboratory testing on soil, rock and water, are also used to provide parameters for the design and construction. Related Articles | Metrics

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Movements of Sediment Particles Near the Inlet of a Brine Discharge Pipe of a Salt Cavern for Gas Storage WANG Bin 2020, 34 (4):  515-519.  Abstract ( 359 )   Save Debrining by gas injection is one of the most important processes for the construction of a salt cavern for the natural gas storage. Accurately describe the movement state of the insoluble particles around the inlet brine discharge pipe is the basis and prerequisite for determination of the depth brine discharge pipe. A numerical model is established to predict the brine flow distribution around the inlet of the brine discharge pipe. The brine flow fields distribution under different conditions are numerically investigated. The resultant brine flow field distribution is serviced as the boundary condition. The distance between the inlet of the brine discharge pipe and the insoluble sediment particles is optimized. The results show the flow field distribution of the zone only around the inlet of the brine discharge pipe varies significantly. The insoluble sediment particles locating directly underneath the inlet of the brine discharge pipe is more likely to be affected by the brine flow fields, and that of the other location is less affected. The insoluble sediment particles concentrate around the inlet of brine discharge pipe. The distance between the inlet of brine discharge pipe and the insoluble sediments for the debrining of Jintan salt cavern gas storage is then proposed as 2.0 m, which has been used for an actual debrining and is approved an appropriate application. Related Articles | Metrics

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Discussions of CPT Derived Undrained Shear Strength of Cohesive Soil in Chengdao Oilfield HAN Meng, LI Guo, YE Jichao, HOU Fang 2020, 34 (4):  520-524.  Abstract ( 385 )   Save A large amount of clay is deposited at the seabed of the Chengdao Offshore Oilfield, and its undrained shear strength is an important mechanical parameter for the foundation design of marine structures. In this paper, by comparing three methods for estimating the undrained shear strength of cohesive soil. Both the advantages and disadvantages of each test method are evaluated and summarized. Combined with engineering examples, a linear regression analysis of the undrained shear strength obtained by the triaxial test and the resistance of the cone penetration tip was conducted to obtain the correlations between the cone tip resistance and the calculated undrained shear strength. Then throughout the error analysis and verification, it is considered that the method is feasible and accurate for the undrained shear strength of the seabed clay in Chengdao Offshore Oilfield. Finally, a further detailed analysis was conducted to obtain the key parameter selection methods for the undrained shear strength of clay soil with buried depths of 0~5 m, 5~10 m, and 10~20 m. Related Articles | Metrics

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Shear Strength Tests of Collapsible Loess Improved by Recycled Aggregate from Construction Waste ZHANG Xiao, HUANG Xiufen 2020, 34 (4):  525-527.  Abstract ( 256 )   Save In order to evaluate the influence of the recycled aggregate content on the shear strength of the collapsible loess soils, the optimum moisture content and maximum dry density of collapsible loess with different recycled aggregate content were determined by preparing test samples with a heavy compactor reaching the degree of compaction of 98% and the direct shear tests were performed. The results show that with the increase of the recycled aggregate content, the maximum dry density of the collapsible loess improved by the recycled aggregate first increases and then decreases, while the optimal moisture content gradually decreases. The cohesion and the internal friction angle of the collapsible loess improved by the recycled aggregate first increases and then decreases. The cohesion of collapsible loess improved by the recycled aggregate from the construction waste first decreases, then increases and then decreases, while the internal friction angle first increases and then decreases. When the content of the recycled aggregate from the construction waste is 40%, the cohesion and the internal friction angle reach the maximum values. Related Articles | Metrics

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Applications of SDMT and CPT in Geotechnical Investigation ZENG Xiaohong 2020, 34 (4):  528-531.  Abstract ( 470 )   Save The seismic dilatometer test (SDMT) has additional shear wave velocity testing module in the conventional flat dilatometer probe. The SDMT device can acquire the dynamic shear modulus and shear wave velocity of soil, and greatly improve the capability of in-situ testing methods for the characterization of subsurface soils. As another popular in-situ test method, the cone penetration test (CPT) has been widely used in the geotechnical engineering investigation of various soils. It is particularly important to compare and to evaluate the test parameters obtained from both methods. Parameters such as, compression modulus, undrained shear strength, internal friction angle and shear wave velocity of soil, are obtained from the SDMT. The tip resistance (qt), sleeve frictional resistance (fs) and piezocone resistance (qc) are collected from the CPT. Pore pressure distribution (uc) was also determined piezocone module of a CPT device. On this basis, combined with the conventional soil boring, the site soil stratigraphy can be accurately characterized as predominantly silty sand to sandy soils. This paper presents a comprehensive evaluation of the results from SDMT and CPT. Both advantages and disadvantages of these methods are discussed extensively. Related Articles | Metrics

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Characterization of Stress History of Sandy Soils by Flat Dilatometer and Cone Penetrometer Testing#br# XIAO Wei 2020, 34 (4):  532-536.  Abstract ( 381 )   Save The stress history of soil reflects the evolution of effective stress in natural soils in the geological history. The evaluation of the stress history of the soil is an important aspect in the geotechnical engineering investigation. This paper presents the insitu evaluation of overconsolidation ratio (OCR) in sandy soils. In particular the correlation between the OCR values and the compression modulus from the flat dilatometer testing (DMT) as well as the tip resistance ratio from cone penetrometer testing (CPT) are2 established. The case history shows that the empirical relationship using the singlet parameter KD is not applicable to all sandy soils, but the overconsolidation ratio established from the ratio multi parameters are more applicable in different soil types. Related Articles | Metrics

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A New Method for Predicting Soil Shear Wave Velocity Based on In-situ Testing SONG Changhang 2020, 34 (4):  537-541.  Abstract ( 324 )   Save The direct measurement of shear wave velocity of stratum is obviously preferable, but the establishment of correlation among various in-situ parameters is beneficial to understanding the law of soil stress and deformation, to comprehensively reflect the internal relationship among soil mechanical parameters and other in-situ methods can obtain more accurate estimates in the absence of in-situ shear wave velocity measurement. In this paper, by selecting and analyzing the in-situ test at six different sites in Wuhan. The paper examines the correlations to obtain rough estimates of the shear wave velocity Vs from conventional dilatometer tests (DMT) and cone penetration tests (CPT). The experimental results suggest that the DMT predictions of Vs  from the parameters ID (material index), KD (horizontal stress index), MDMT (constrained modulus) are more reliable and consistent than the CPT predictions from qc (cone resistance), presumably because of the availability, by DMT, of the stress history index KD . Related Articles | Metrics

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Design of In-situ 3D Ground Stress Measuring Apparatus for Deep Boreholes Using Wall Stress Relief Method WU Zhenjun, TANG Hua, QIN Yuqiao, YUAN Hui 2020, 34 (4):  542-548.  Abstract ( 326 )   Save The measurement of deep ground stress is widely applied in shale gas extraction, conventional oil and natural gas exploration, large hydroelectricity and irrigation projects, deep mining and fundamental earth science research areas. The borehole wall local stress relief method is suitable for the rock stress measurement at a great depth. This paper presents an improved three-dimensional deep rock stress measurement apparatus based on the existing ground stress measurement device, BWSRM-H01 in a horizontal borehole. The improved device can perform the locating, installation of the strain gauges at the borehole surface, relieving of the borehole surface and strain measurement. The design approach of key components of the device is introduced in this paper. The in-situ rock stress measuring procedure of the improved apparatus is also briefly presented. The design and development of the apparatus has the in-house owned intellectual property. Currently, the pressure and temperature resistance of the instrument is suitable for the measurement of 1 200 m deep borehole.  Related Articles | Metrics

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Quality Control Indices for the Degree of Compaction of Sandy Gravel Soils ZHU Hengyuan, HAN Jinbao 2020, 34 (4):  549-551.  Abstract ( 474 )   Save This paper presents a case history of an airport construction project for quality control methods and compaction indices of sandy gravel soils. Typical sandy gravel samples were collected and classified as the well graded rounded sandy gravel from the grain size distribution tests. It is determined that this material can be used as the fill material for the runway and its associated areas. Based on the grain size distribution analysis results and analytical approaches, the density of the sandy gravel is commonly determined by the in-situ solid ratio method (water preplacement method). This is paper discusses the influence of the test pit diameter on the accuracy of the density of the soil test by the water replacement method. Under the sample compaction parameters (loose thickness of soil 35~40 cm and vibratory compaction of 14 passes) and a test pit diameter of 60 cm, the QA-QC acceptance criteria for the compaction of runway area using sandy gravel soil are: dry density greater than 2.20 g·cm-3and the solid ratio greater than 85%. Related Articles | Metrics

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Geotechnical Properties of Xigeda Formation in Zhaizi Village Near Jinsha River DAN Luzhao, WANG Jianhong, TANG Hongbo, CHEN He, FU Xiaodong 2020, 34 (4):  552-556.  Abstract ( 318 )   Save A series of laboratory tests and plate load tests under different conditions of water immersion were conducted aim at solving a lack of researches on Xigeda formation siltcaused by lake deposit located in Zhaizi Village, Yunnan Province, China. The experimental data were then compared with the researches on widely distributed Xigeda strata situated at Panzhihua and Xichang regions. The results demonstrate that the Xigeda strata located in Zhaizi Village, Yunnan Province are mainly composed of silt granules and sand granules, and present horizontal bedding formation, which are semiforming rocks with poorer mechanical properties. Local shear failure plays a major role after plate loading for this kind of rocks. The strength indictors, elastic moduli and deformation moduliobtained from the tests on Xigeda formation silt are larger than those situated at Panzhihua and Xichang regions. The strength of these rocks decreases rapidly under the condition of fully immersion in water. Related Articles | Metrics

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Application of Solidification Method in the Improvement of Hydraulically Dredged Soils MENG Ruijun 2020, 34 (4):  557-562.  Abstract ( 298 )   Save An artificial hard crust can be formed at the surface of soft soils by using soil solidification method. However, the type, component, the mixture procedure and the depth of the improvement of using these solidification agents can significantly affect the results and project construction cost. The dust induced by the quick lime also adversely affect the vegetation of adjacent soils. This paper presents a case history of solidification of a hydraulically dredged soft soils. Both the laboratory and situ testing were conducted by using various ratio of solidification agents. The results indicated that, the moisture contents reduce within the depth range of improvement with improved physical and mechanical properties. The hard layer crust with improved bearing capacity and strength could be formed quickly. Related Articles | Metrics

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Permeability Fine-Grained Soils with Natural Gas Hydrate MA Huilong, YIN Liangkui, WANG Huajun, YAN Rongtao 2020, 34 (4):  563-566.  Abstract ( 424 )   Save The permeability of porous material is an important physical parameter that affects the exploitation of natural gas hydrate. In order to study the effect of natural gas hydrate on the permeability of the hydrate deposition, this paper presents the laboratory tests of fine-grained soil samples containing natural gas hydrate. The gradation of the fine-grained soils contained tetrahydrofuran hydrate was similar to the grain size distribution of soils in in Shenhu area of the South China Sea. Then, the permeability of fine-grained soil samples with different hydrate saturations was tested based on the steady state method. The test results show that the permeability of fine-grained soil containing hydrate in this test is between 11.41 mD and 61.63 mD. As the hydrate saturation increases, the relative permeability of the hydrate containing fine-grained soil decreases significantly, mainly due to the hydrate formation that fills the pores of the sediment and reduces the porosity. In addition, hydrates may also block the porous fluid seepage, thereby reducing the permeability. The test results were compared using the existing permeability model, and it was found that the result was close to the Masuda Model (N=3). Related Articles | Metrics