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28 February 2021, Volume 35 Issue 1 Previous Issue    Next Issue

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Ground Deformation During the Deep Excavation of Suzhou Metro Stations WANG Zhansheng, ZHANG Jiali, DU Jiangtao 2021, 35 (1):  1-5.  Abstract ( 445 )   Save The construction excavation support monitoring data of 29 metro stations in Suzhou City that using the diaphragm wall plus internal support were collected and statistically analyzed in order characterize the deformation of the deep excavation support system. The statistical data indicate that: 1) the maximum lateral deflection of the supporting structure, δhm, falls into the range between 0.13% He and 0.67%He with an average deflection value of 0.32%He, where He is the excavation depth; 2) The measured maximum deflection falls into the range from He-5 (meters) to He+3 (meters); 3) the maximum ground subsidence behind the supporting structure, δvm, is within a range between 0.07%He and 0.7%He with an average of 0.26%He; the horizontal influence zone of the ground subsidence is approximately 4.5He; 4) The ratio of ground vertical deformation behind the supporting structure over lateral deflection at the supporting structure, δvm/δhm, is between 0.346 and 1.54.  Related Articles | Metrics

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Deep Excavation Supporting Method Selections of Silty Fine Sandy Layers in Yellow River Alluvial Plains in Binzhou#br# MENG Yan, HOU Fang, JIANG Wenfu 2021, 35 (1):  6-10.  Abstract ( 275 )   Save This paper presents a case history of deep excavation support in Binzhou City, which is located in the Yellow River Alluvial Plain. The subsurface soil consists of saturated silty fine sand soil strata and the site is surrounded by the building structures. In the selection of deep excavation supporting method, this paper compares the advantages and disadvantages of Soil Mixing Wall (SMW) construction method combined with ground anchors and soil nails and the grouted soil nails with some local SMW method. The objective of the selection is to ensure the safety first. This paper also discusses the applicability, complexity, cost and redundancy during the construction. Related Articles | Metrics

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Full Casing and Full Circulation Cast-In-Place Reinforced Concrete Pile Installation Method in Kast Terrain LIU Biyan, ZHANG Hui, LI Hongwei, YE Zhimin, CHEN Bo 2021, 35 (1):  11-12.  Abstract ( 249 )   Save Cast-in-place reinforced concrete pile installation in the karst terrain by using conventional construction means and methods is usually problematic. Construction related hazards include no slurry return, caving of borehole. In addition to the difficulties in the pile installations, these hazards might induce the sinkholes collapses, over-turning of the construction equipment and even casualties of the construction crews. A new construction method, which is called all casing and full circulation method, that is specially designed for the cast-in-place reinforced concrete pile installation in the karst terrain, can minimize the construction related hazards. This paper presents a case history of using the new construction technique in the karst terrain. Related Articles | Metrics

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Consolidation Settlement in a Fill Site in Guilin SU Yang, ZHONG Xuan, LIU Zhikui, DU Ciyang, BAI Xiansong, JIANG Wende 2021, 35 (1):  13-16.  Abstract ( 406 )   Save The fill soil is characterized as having complex sources of composition, heterogeneous engineering properties, potential collapsibility, high compressibility and low shear strength. The engineering properties of fill soils are rarely investigated and there are no code recommendations available regarding the projects on fill soils. As a result, the unimproved fill soil cannot be directly used as the bearing soils for the engineering structures and facilities. This paper presents the results of geotechnical testing results from a fill soil site in Guilin. The geotechnical properties of the fill soil were investigated throughout the laboratory and insitu tests and the settlement of the fill soil under the surcharge soil load was predicted. The following results are obtained: in general, soil at shallow deposition is less compacted than that of at deeper depth; the tested compression indices are less than 0.2, which means that the fill soil at the site has low compressibility. After 1.5 years of surcharge, the test results on samples taken from depths between 4.2 and 6.45 meters indicate that the samples are close to the normally consolidated state. The observed settlement value at the site consistent with the predicted degree of consolidation. There is no unified and simple engineering way of reusing the fill soils due to their sources of composition and different in methods of backfills. Related Articles | Metrics

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Deep Excavations in Soft Soils with Irregular Supporting Shape Close to an Active Metro Line GAO Fenfen, GENG Yekuan, JIN Xuelian 2021, 35 (1):  17-19.  Abstract ( 431 )   Save This paper presents a case history of deep excavation design in soft soils with irregular supporting shape and close to an active metro line. The site-specific engineering and hydrological conditions, irregularity of the site on the plan view, and the excavation and supporting sequences due to the adjacent active metro line are comprehensively considered for an optimized excavation supporting solution. The supporting structure type and structure design details, access trestle arrangement and the construction impacts on the active metro line are discussed in the paper. Measures that could control the deformation of the supporting structures were implemented in the construction, the rehabilitation of the ventilation shaft of the active metro and the connection underpass were constructed after the completion of the deep excavation so that the safety of the metro operation was maintained. The predicted deformation values were also compared with the construction monitored values. The comparative values indicated that the excavation design and construction are successful. Related Articles | Metrics

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Mitigation of a Slope Failure at a Connection Ramp of an Expressway QIU Liqiu 2021, 35 (1):  20-23.  Abstract ( 321 )   Save The highway connection ramps usually have a small curvature and often cut into the toe of slope in the mountain areas. The slope toe cutting usually induces to potential geotechnical hazards such as slope failures. This paper presents a case history of mitigating the slope failure at Dongxiao Ramp F of Longyan-Xiamen Expressway Widening Project. The slope failure characteristics and hazards are discussed in the paper. Mitigation methods such as, unloading, drilled caisson for sliding control, retaining structure and improving drainage are also proposed. The simulated values were also compared with the construction measured values and the comparative results are satisfactory. Related Articles | Metrics

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Geotechnical Investigation of Shallow Deposited Natural Gas in a Changjiang River Crossing Tunnel in Jiangying WANG Meng, LI Shouming, SHA Xiaobing, ZHANG Xinquan 2021, 35 (1):  24-29.  Abstract ( 347 )   Save The shallow deposited methine gas poses potential risk hazards to the underground structures. The controlled emission of the natural gas is one of the major measures to minimize the potential hazards during the underground structure construction. Further measures during the construction and the operation of the construction and operation of the underground structures include the improving ventilation and natural gas emission monitoring. This paper presents a case history of the Jingjiang Changjiang River crossing tunnel in Jiangying City. The theoretical analysis, insitu experiments and natural gas tests were applied in this project, along with the application of modified cone penetration testing (CPT) in order to characterization the vertical and horizontal distribution, components, pressure and quantities of the natural gas within the project limits. The impact of the natural gas deposition on the construction of the shielded river crossing tunnel is discussed and the risk management measures are proposed for the design and construction purposes. Related Articles | Metrics

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Numerical Analysis of Seismic Stability of Rock Slopes Using Finite Element Method LI Wei 2021, 35 (1):  30-33.  Abstract ( 269 )   Save This paper presents the threedimensional numerical analysis results using elastoplastic constitutive model on the stress-deformation in a rock slope under seismic conditions. In the analysis, the Mohr Coulomb failure criterion, the nonlinear time history analytical method as well as the strength reduction theory were used and the stability of the rock slope is evaluated by the sudden displacement as well as the development of a throughout plastic zone in the model. The viscoelastic artificial boundaries were established in the model to absorb the radiational damping effect from the foundations and the effect of the gravitational field of the rock slope and the fracture zone or rock vein on the seismic stability of the rock slope were also considered. The results show that: under the sudden displacement criterion, the dynamic stability factor of safety corresponding to a sudden change in the displacement of the characteristic points along the slope elevation is greater than 1.35; when plastic zone penetration criterion used, the factor of safety increases with the gradual increase of the plastic yield zone. When the factor of safety is low, the plastic yield zone is relatively small; When the safety factor reaches 1.35, a large number of yielded plastic zones appear locally at the toe of slope. With the further development of the locally isolated yielded plastic zones at the excavation slope position gradually grow connected; Slope failure will occur when the factor of safety exceeds 1.5. Combined consideration of sudden change in displacement and the development of a throughout plastic zone in the slope failure consideration, a satisfactory dynamic stability factor of safety should be 1.35. Related Articles | Metrics

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Dissolution of Guilin Limestone Carvings by Acid Rain and its Simulation LI Yiran, DONG Binghong, NI Zhe, TAN Mingcan, XI Danni 2021, 35 (1):  34-37.  Abstract ( 470 )   Save With the development of industrialization and urbanization, the occurrence of acid rain is more frequent than before. Many stone carvings in Guilin suffer from different degrees of erosion and damage. In order to prepare for the protection of Guilin limestone carvings and provide baseline information, the mechanism of limestone dissolution by acid rain was studied. Pure limestone samples were processed and soaked in acid solutions with different pH values. The pH value, Ca2+concentration and limestone mass loss were evaluated, and the dissolution mechanism was analyzed by the chemical thermodynamical calculation. The results show that the scratch dents can promote the dissolution of acid rain to a certain extent. The lower the pH value of acid rain is, the deeper the dissolution degree of limestone is. The greater the mass loss is, which is 2.26～9.21 times of that of acid rain with large pH, and the greater the dissolution degree of sulfuric acid than that of carbonate. Related Articles | Metrics

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Numerical Analysis of Excavation Process of a Shallow Buried Metro Station LIU Feng, DONG Xiaowei 2021, 35 (1):  38-41.  Abstract ( 331 )   Save The influence of underground excavation on the safety and stability of surface road has always been a concern for the subway metro construction. In order to maintain the safe operation of expressway during the shallow buried subway tunnel underpass construction by using the shielded excavation method, the perforated pipe shielding and grouting method can be used. Combined the engineering geological conditions at Metro No. 1 Line Station and the design parameters of metro tunnel excavation, a three-dimensional numerical simulation of the tunnel excavation process was performed by using the finite element method. The stress field, the plastic zone distribution and the expansion of the surrounding rock mass were numerically evaluated. The analysis results show that the supporting structure adopted in the construction scheme could effectively control the deformation of the tunnel and could meet the design requirements. Related Articles | Metrics

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The Sensitivity Analysis of Parameters of Affecting the Displacement in an Unstable Slope SU Jing, WANG Jieguang 2021, 35 (1):  42-45.  Abstract ( 272 )   Save This paper presents the evaluation of the influence of underlying water bearing marl on the vertical and horizontal movement of the upper unstable soil slope. Six factors that might potentially affecting the slope displacement, including slope height, slope angle, cohesion and internal friction angle of soil, Poisson’s ratio as well as elastic modulus of soil, were evaluated. Applying the strength reduction method in the finite element analysis and a single factor sensitivity evaluation method, the instability was therefore determined. The influence parameters analysis of the slope soil displacement and comparing the analysis results show that the order of sensitivity of the displacement influence parameters of the unstable slope is ranked in descending order: slope angle, slope height, elastic modulus, Poisson’s ratio, internal friction angle and cohesion. For slopes that are in an unstable state, the changes that affect the displacement are the slope angle and slope height. Under the same conditions, the displacement in the horizontal direction is always greater than the displacement in the vertical direction. Related Articles | Metrics

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Analysis of Critical Aspects and Quality Control of Bore and Cast-in-Place Concrete Pile Installations WEI Huiqiu, ZHAN Zhenyang 2021, 35 (1):  46-49.  Abstract ( 510 )   Save The construction of bored reinforced concrete cast-in-place pile might be affected by soil strata changes and surrounding environment. Critical aspects in the bored concrete pile installation are presented in this paper. Based on authors’ field construction experience, this paper analyzes the key and difficult problems that may be encountered before and during the installation of bored piles, and the correspondent control measures are also proposed. This paper mainly evaluates the construction equipment staging layout, pile foundation positioning, slurry and sediment control, waste concrete control at the top of pile and other aspects, as a guide for the better pile installation practice. Related Articles | Metrics

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A Study on the Deformation Characteristics of the Double-row Pile Support Structure under Eccentric Load WANG Bo, XIE Zhiying, XIAO Wei, CAO Fang, XIAO Taoli 2021, 35 (1):  50-54.  Abstract ( 252 )   Save This paper presents the three-dimensional numerical analysis results of a deep excavation supporting system for a parking structure at Donghuan Road area using MIDAS GTS finite element analysis software. The deformation of the double-row pile cantilever supporting structure under the eccentric load was predicted and the stresses in the supporting structure were also discussed in the paper. The following results can be obtained: under the combination of adjacent environment and the complicated geological conditions, the supporting structure had larger deformations under the eccentric loads. At the beginning of excavation, the eccentric load at different surface elevations increased the displacements and internal forces in the supporting structure. With the increase of the excavation depth, greater deformation and displacement are identified. Under the eccentric load, the overall tendency of the double-row pile cantilever structure are deformed inside are more obvious, and the surface settlement also increases with the depth of the excavation with a concave-shaped curve. However, the influence of the eccentric load on the bottom heave is not obvious. The internal force of the eccentric load inside the pile is greater than that of piles with concentric load. The position of the maximum bending moment do not change significantly in both loading conditions. Related Articles | Metrics

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Water Inrush Hazards and Risk Assessment in Highway Tunnels in Fujian Province ZHU Zhongquan 2021, 35 (1):  55-60.  Abstract ( 268 )   Save First, the main achievements of Fujian Province in highway tunnel construction are introduced. Then, the typical tunnel inrush cases under different geological conditions are described, which are limestone, sandstone and granite with frequent inrush disasters. At the same time, according to the reasoning of inrush cases, the risk index system of highway tunnel inrush disaster is constructed. Aiming at the multi-parameter and uncertainty of the evaluation index, an unascertained measure model for tunnel inrush safety risk evaluation based on unascertained measure and information entropy is proposed. The unascertained measure function and the weight of the evaluation index are established respectively, and the tunnel inrush risk level is evaluated according to the confidence recognition criterion. Finally, a risk assessment of inrush disaster was carried out for the Xiafang tunnel of Beijing-Taiwan Expressway. It can not only realize the safety risk assessment of tunnel inrush disaster, but also establish an evaluation method that does not rely on expert experience and subjective weighting, which can provide reference for related research. Related Articles | Metrics

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Analysis of Relationship Between Standard Soil Retention Moisture Content Test and Time LIU Jun, WANG Jinghong, ZHUO Huiying, ZHAO Zheqiang 2021, 35 (1):  61-64.  Abstract ( 440 )   Save The standard soil moisture retention content is one of the important indices for determining properties of the expansive soil samples. The relationship between the standard soil moisture retention content and the time was laboratory investigated and the quadratic polynomial relationship with time was established. The completion time in the standard soil moisture absorption test is observed mainly related to the soil type, the initial moisture content, the mineral composition in soil particles and the particle size. Throughout the analysis of these factors, the tests discussed in this paper provide guidelines for the practical testing of the standard soil moisture absorption tests also provides a theoretical basis for a better understanding of the physical meaning of the standard moisture absorption. Related Articles | Metrics

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Research on Test Method for Negative Skin Friction Resistance Measurement of PHC Pipe Piles HAN Liang, WANG Xiangping, FU Yonggang, WANG Yiheng, YAN Zhiyu 2021, 35 (1):  65-68.  Abstract ( 327 )   Save The theoretical method for calculation of the negative skin friction resistance of PHC pipe pile is difficult to obtain reliable results due to many complex factors, such as soil properties and consolidation conditions. Therefore, the distribution of negative skin friction and the position of neutral plane can only reliably be obtained by the field loading test by monitoring the internal force distributions. Based on summarizing the limitation of point measurement method of stress and strain, this paper presents a case study of a modified line measurement technique to be used in the negative skin friction in the PHC pipe pile. According to the characteristics of PHC pipe pile, a new method of postimplantation survey line was proposed to effectively resolve the difficulties in the negative skin friction field measurement in the PHC pipe pile. Through the regression data process, the measured strain and the average elastic modulus in the pile shaft under different load levels were obtained, which ensures the reliability of calculation of the axial force and the skin friction. It was shown from the results in the field test that the new field test method and calculation method of negative skin friction are very effective for the PHC pipe pile negative skin friction measurement. Related Articles | Metrics

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Improvement of Cone Penetration Test on the Offshore Platform SUN Yunkun, ZHOU Qi, XU Jian, CHEN Mei 2021, 35 (1):  69-71.  Abstract ( 362 )   Save As one of the primary insitu test application in the geotechnical investigation, the cone penetration testing (CPT) has the advantages of continuous probing, high efficient and relatively reliable test data. In the marine investigation, an offshore platform is usually used to provide stable base for the CPT probing. During the investigation, breakage of the drilling rods is frequently encountered due to the excessive length to rod diameter and the alternating deposition of the soft and hard soil layer below the seabed. Based on the CPT practice on the platform, this paper proposes a new testing method of applying a follow up casing behind the CPT cone tip. This new method was applied in the 10 site investigation projects of wind turbine installation and no CPT rod breakage occurred. At the same time, the construction time of each hole is reduced to 1 day. It is estimated that every time the rod breaking accident is reduced, the cost can be saved about 220000 yuan. This case history indicate that the new testing method can minimize the rod breakage, improve the efficient of penetration and reduce the CPT investigation cost. Related Articles | Metrics

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Deformation Monitoring and Numerical Analysis of Metro Deep Excavation Using ABAQUS LIU Houcheng, GUO Qijun 2021, 35 (1):  72-75.  Abstract ( 590 )   Save It is critically important in metro deep excavation to continuously monitor the deformation and its progressive development. This paper presents the numerical evaluation results of a metro station deep excavation of Transit No. 29 Line in Wuhan. The numerical analysis model was established based on the site geological and hydrological properties and the analytical deformation results were compared with the monitored results during the construction. The following results can be obtained: 1) when the excavation is within 5 meters, small values of deformation are observed. When the excavation depth is between 5 m and 15 m, the observed lateral deflection is gradually increase with a maximum lateral deflection of 19.22 mm. The maximum lateral deflection is at a depth of 12.3 me below the ground (or 2H/3, H is the depth of excavation). After the maximum lateral deflection, the observed deformation decreases with depth to the ground surface 2) the maximum ground subsidence occurs at a distance of H/2 to the edge of excavation, the ground settlement is between 6.65 and 9.15 mm, which is correspondent to a range of 0.04% to 0.05% of the excavation depth. From the construction monitoring results, both the lateral deflections observed at the excavation supporting structure and the settlement at the ground surface are satisfactory and meet the code requirement. Related Articles | Metrics

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Direct Shear Test on Dilatancy And Softening Properties of Granular Media JIANG Yu, LU Yong, DENG Yanbo, HU Xiaozhu 2021, 35 (1):  76-80.  Abstract ( 517 )   Save Particle is one of a large number of media forms and is widely existed in the nature. Particles are widely used as engineering materials, such as dam rockfills, railway ballasts, and foundation backfills. The macro-mechanical behavior of granular media is closely related to its micro-structural evolution. It involves the overlapping effects of factors such as porosity ratio, particle morphology, particle fragmentation, and anisotropy. Analyzing the independent influence of each factor reveals that the macro-mechanical behavior of granular media is an important way of mechanism. In the investigation, the DRS-I type ultra-high-pressure direct shear test system was used to perform direct shear tests on steel balls with three different particle sizes under normal pressures ranging from 0.4 to 12 MPa to avoid the overlapping effects of particle morphology, particle fragmentation and anisotropy. The correlation of peak strength, residual strength and porosity evolution was analyzed separately, in order to provide a reference for revealing the meso-mechanical mechanism of granular media. The results show that: 1) the spherical granular media prepared by the falling rain method generally exhibits shear softening characteristics, and there are obvious peak stresses and residual stresses during the shearing process; 2) the peak intensity shows a certain degree of decrease as the confining pressure increases the small trend corresponds to the extreme value of the change slope of the porosity ratio; 3) the residual strength is basically not affected by the particle size and the confining pressure, corresponding to the stable value of the porosity ratio, that is, the critical state; A good description of the correlation between the strength characteristics of the granular media and the volume change characteristics. Related Articles | Metrics

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Experimental Study on Lime-Treated Expansive Soil Subjected to Wetting and Dissecting Cycles Under Axial Stress ZHAO Kelie 2021, 35 (1):  81-85.  Abstract ( 346 )   Save The influence of moisture variation induced by the environmental change on subgrade soils, especially on the lime-treated expansive soils, has increasingly received attentions in the engineering practices. However, the contact pressures applied on the subgrade soils induced by the super structures are generally ignored in the evaluation of the wetting and dissecting cycles on the expansive soil performances. An innovative device that can provide constant axial pressure and lateral restraint, as well as precisely control the variation of moisture content of soil samples, was used in testing of the wetting and dissecting process of lime-treated expansive soil samples. In addition, the conventional method that dries sample in the air and wets sample by springing water were also utilized for comparative study. The GDS dynamic triaxial test equipment was used to test the accumulative axial strain of the samples that experienced different times of wetting and dissecting cycles. It is observed that, under the axial pressure and lateral restraint provided by this innovative device can effectively reduce the damage on samples induced by wetting and dissecting cycles. The results show that the stress state of subgrade soil cannot be ignored when studying the impact of wetting and dissecting cycles. Related Articles | Metrics

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Field Test of Grouted Umbrella-Shaped Ground Anchors FENG Dang, HUANG Peng 2021, 35 (1):  86-90.  Abstract ( 817 )   Save In order to evaluate the anchoring effect and the control failure mode of the umbrellashaped ground anchor in the rapid reinforcement of expansive soil slope failures, and to further increase the anchoring results with permanent corrosion protection, a series of field tests were performed on the umbrella-shaped ground anchors with/without grouts and with various anchoring length. The following results can be obtained: 1. In an anchor grouted length range, the ultimate pullout resistance of the conventional grouted ground anchor demonstrates a linear with the bonding length, while for the grouted umbrella-shaped ground anchor, the pull-out resistance first increases nonlinearly with the increase of displacement rapidly, and then the pull-out resistance increases linearly gradually with the displacement value; 2. Since the adhesion between anchor and the surrounding soils induced by the grouts will reach its ultimate value when the displacement of anchor reaches a critical value, a pre-tension load should be applied on the umbrella-shaped anchors so that the ground anchor can reach a much higher pull-out resistance by mobilizing both the umbrella effect and the grouting effect at the same time. After the grouting of the umbrella-shaped ground anchor, the bonding zone can be integrated so that the bonding zone can have a more uniform stress distribution. When the umbrella-shaped ground anchor reaches the ultimate resistance, it still can maintain the ultimate load; 3. Compared with the conventional ground anchor, which need to have an effective length beyond the sliding zone of 21 meters, only 15 meters are necessary for the grouted umbrella-shaped ground anchor with the same pull-out resistance. It is concluded that the new ground anchor has advantages over the conventional ground anchors and can be used in the rapid response of failures in expansive slopes. Related Articles | Metrics