岩土工程技术

2023, 37(2): 1-1.

[Abstract](99) [FullText HTML] (35) [PDF 4502KB](37)

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2023, 37(2): 1-3.

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Engineering Characteristics of Deep High Liquid Limit Clayin Hangzhou Bay Area

Chen Mingju, Chi Hengtian, Wu Weiyong, Cheng Chunhong

2023, 37(2): 127-134. doi: 10.3969/j.issn.1007-2993.2023.02.001

[Abstract](155) [FullText HTML] (24) [PDF 1790KB](49)

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Ningbo Hangzhou Bay Area is located on the south side of the Yangtze River estuary. The geological environment and hydrodynamic conditions are complex, and the sedimentary environment is variable. The high liquid limit clay layer is widely distributed within the range of 40~60 m below the surface of the area. This layer of soil is often within the range of deep foundation bearing layer of construction engineering. Studying the engineering geological characteristics of this layer of soil has important social and economic value for the development and construction of Hangzhou Bay New Area. The engineering characteristics of the deep high liquid limit clay were studied from the aspects of conventional geotechnical parameters, mathematical statistics, structural properties, damage model parameters, and triaxial CU test. The results show that: (1) The physical properties of Hangzhou Bay high liquid limit clay are characterized by high natural water content, large void ratio, high liquid limit, etc., but the mechanical properties are close to the second hard soil layer of the alluvial lake in Ningbo area. (2) The physical and mechanical parameters are basically normal distribution through numerical calculation software. The physical index parameters can be regarded as constants, and the mechanical index can be regarded as variables. Time and space variability and regional characteristics should be considered. (3) According to the test results, the Hangzhou Bay high liquid limit clay can be quantitatively calculated as under-consolidated soil with high sensitivity. The undisturbed soil shows the characteristics of stress softening, while the remolded soil shows the characteristics of stress hardening.

Mechanical Response Analysis on Construction of Diaphragm Wall in PBA Underground Excavation Subway Station

Du Changlong, Zhu Yaqian, Ma Lu, Zhang Zhihong, Liu Xisheng, Sun Yuqing

2023, 37(2): 135-141. doi: 10.3969/j.issn.1007-2993.2023.02.002

[Abstract](105) [FullText HTML] (70) [PDF 4252KB](27)

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Based on the first underground diaphragm wall water stop project constructed in the side pilot tunnel of PBA underground excavation station of urban subway in China, MIDAS software was used to analyze the mechanical performance of underground diaphragm wall in the construction process of PBA underground station, and the results were compared with the actual field monitoring data. The results show that: (1) during the whole construction process of the station, the surface settlement caused by diaphragm wall construction is small, accounting for about 9% of the total surface settlement. (2) The horizontal displacement of diaphragm wall changes greatly in the construction stage of buckle arch, the excavation and support stage of station hall and platform layer. In practical engineering, these three construction stages need to strengthen the control and monitoring. (3) In each construction stage of the station, the vertical displacement of diaphragm wall is mainly uplift deformation, and the settlement deformation is not obvious. Along the longitudinal distribution of diaphragm wall, the settlement of the top of the wall fluctuates slightly in each construction stage, and tends to be evenly distributed on the whole. (4) After the construction of the main structure of the station, the tensile and compressive stress of the diaphragm wall does not exceed the allowable value of the compressive and tensile strength of the concrete, which can effectively ensure the safety performance of the diaphragm wall itself.

Efficient Expression Method of Foundation Settlement

Zhang Yanlin, Sun Lichao, Feng Dachong, Huan Xin, Ma Qingxun, Lyu Lianxun

2023, 37(2): 142-146. doi: 10.3969/j.issn.1007-2993.2023.02.003

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Settlement impact assessment units generally point out the maximum settlement and differential settlement on the settlement cloud map or settlement contour, but do not specify the settlement of key parts of foundation. This method not only affects the richness and accuracy of achievement expression, but also is not conducive to the settlement of other parts of the foundation. An efficient expression method for the settlement and differential settlement of key parts of building foundations was provided, and this method was applied in practical engineering projects. The results show that this method can read the numerical calculation results of PLAXIS3D. It can not only quickly draw the maps such as settlement cloud map, settlement contour, settlement and differential settlement of key parts of foundation, but also greatly enrich the achievement and improve the accuracy by overlaying the above maps.

Parameter Inversion of High Fill Foundation and Prediction of Post Construction Settlement Distribution

Fan zhuyi, Wang Qigui, Bian Xia, Wu Zhongming, Yuan Junping

2023, 37(2): 147-153. doi: 10.3969/j.issn.1007-2993.2023.02.004

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The terrain of Qiaojia high fill project site in Yunnan Province is rugged and the height difference is wide. There will be problems such as large post construction settlement and differential settlement. The current calculation methods for high fill settlement, such as theoretical calculation method and numerical simulation method, need parameter input, and high fill will cause parameter spatial variability due to the source of filling materials and construction technology. The errors between the prediction results of viscoelastic model, exponential model and hyperbolic model and 30 groups of measured settlement data were compared. The results show that the prediction accuracy of viscoelastic model for high fill settlement is obviously better than the other two models. The viscoelastic model was used to predict the post construction settlement distribution law of Yunnan Qiaojia high fill project, and the distribution area of maximum settlement rate and final settlement was proved, which provided a reasonable scientific basis for subsequent engineering measures. The compression modulus and viscosity coefficient of backfill materials of Yunnan Qiaojia high fill project retrieved based on viscoelastic constitutive model show significant spatial variability. If the spatial variability of parameters is not considered, significant errors will be generated in predicting post construction settlement. By meshing the monitoring areas, it can effectively improve the accuracy of prediction results to meet the engineering requirements.

Application Research of Chinese Fir Pole in Soft Soil Foundation Excavation

Li Xiaolong

2023, 37(2): 154-160. doi: 10.3969/j.issn.1007-2993.2023.02.005

[Abstract](119) [FullText HTML] (41) [PDF 1389KB](34)

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Underground diaphragm wall, CSM mixing wall, SMW construction method, cast-in-place pile, steel sheet pile, soil nailing wall and other support methods are often used in soft soil foundation excavation, which is very expensive. Chinese fir poles are readily available with low price and envrionment friendly, and have the advantages of strong corrosion resistance and convenience in construction. the tensile strength and the ultimate uplift bearing capacity of raw materials of Chinese fir pole were tested. According to the test results, reasonable parameters were selected for design and stability calculation, and the field test and foundation pit monitoring were carried out in a soft soil site in Qingdao. The field test and foundation pit monitoring results show that the Chinese fir pole can be used as soil nail. The design and stability calculation could be carried out according to the relevant calculation model of soil nail wall. It could improve the stability of foundation pit, reduce the space occupied by slope, reduce the excavation and backfilling earthwork of foundation pit, and then reduce the construction cost. It has good application value.

Engineering Geological Characteristics of Houhai Weathered Deep Trough in Shenzhen Bay Area

Wang Xianneng, Li Zhibo

2023, 37(2): 161-167. doi: 10.3969/j.issn.1007-2993.2023.02.006

[Abstract](107) [FullText HTML] (23) [PDF 825KB](29)

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There are many weathered deep troughs in Shenzhen Bay area, among which Houhai weathered deep trough is the largest exposed at present, with a bottom depth of 175.9 m. The existence of weathered deep troughs causes trouble to pile foundation engineering. The development scale and geotechnical engineering characteristics of weathered deep trough were analyzed, and the characteristics of fracture development in weathered deep trough were emphatically discussed. The results show that the fracture zone is the controlling factor for the formation of weathering deep trough. The Shenzhen Bay area is intersected by the northeast Wuhua-Shenzhen fault zone and the northwest Shiziyang-Pearl River Mouth fault zone. The fracture bandwidth and fracture mechanical properties are both compressional and tensional, which are conducive to the propagation of weathering deep. The fully and strongly weathered rock in Houhai weathered deep trough are particularly deep and the strength of weathered rock is low.

Discussion of Parameters Setting for Pile Structural Element in Anti-slide Pile Simulation with FLAC3D

Xu Wengang, Xin Li, Yu Xurong, Cao Qi, Cao Aiwu

2023, 37(2): 168-173. doi: 10.3969/j.issn.1007-2993.2023.02.007

[Abstract](283) [FullText HTML] (43) [PDF 1421KB](65)

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As a professional geotechnical numerical software, FLAC3D contains various build-in structural elements, in which the pile element has a potential to simulate anti-slide pile in slope engineering. However, the pile element has too many parameters which have not clarified for anti-slide pile simulation yet. The main parameters used in pile simulation were comparatively analyzed. The comparative analysis shows that the elastic modulus of the pile structural element has little effect on the numerical simulation results, the tangential parameters of the coupling spring have little effect on the stability coefficient of the slope reinforced by anti-slide pile. The internal force distribution of the anti-slide pile is very small, while the cohesion and friction angle in the normal parameters have obvious effect on the simulation results of the anti-slide pile. The larger the parameter value, the greater the slope stability obtained, and the greater the maximum shear force and maximum bending moment of the anti-slide pile. Based on the comparison of the traditional elastic foundation beam method, the parameters of the pile structure element in the anti-slide pile simulation are proposed.

Influence of Internal Force in the Rectangular Shaft for the Pipe Jacking with a Reserved Hole

Hai Han, He Wei, Zhan Yuan, Chen Xiaoxiang, Gong Jianwu

2023, 37(2): 174-180. doi: 10.3969/j.issn.1007-2993.2023.02.008

[Abstract](82) [FullText HTML] (19) [PDF 1886KB](19)

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The launching shaft or the receiving shaft are the most critical structures in the pipe jacking project, and circular holes of different sizes are needed on the shaft wall for the pipes to enter and exit. The setting of the holes affects the stress of the shaft structure. Relying on a DN3500 inner diameter electrical power pipe jacking project in Xi'an, the influence law of the shaft wall opening constructed by the open excavation method on the shaft structure was studied using the finite element method. The results were compared with the open caisson under the same conditions. The internal force calculation results of the design are compared, and the internal force variation law before and after the open excavation of the shaft with different methods was obtained. The corresponding structure optimization design suggestions are put forward and provide reference for the design and analysis of related projects.

Mechanical Characteristic and Rapid Construction of the Steel Arch Frame in Tunnel Shaft Initial Support

Ran Hua, Duan Xingming, Xu Chuhao, Zou Yulai

2023, 37(2): 181-185. doi: 10.3969/j.issn.1007-2993.2023.02.009

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The erection mode and stress characteristics of steel arch frame in highway tunnel are the key points of initial support construction of highway tunnel shaft. Taking the Taihe tunnel of the Expressway from Mojiang to Lincang in Yunnan Province as the research object, the rapid construction method of installing steel arch frame with open-box hook was proposed, and the effect of wedge blocks on controlling surrounding rock deformation was studied. The analysis results show that: the using of opening box hook improves the working efficiency of shaft construction and reduces the time cost of construction in installing the steel arch. The deformation of surrounding rock could be controlled better by using wedge block. The research results provide a reference for the rapid construction of steel arch support in the initial stage of shaft.

Mechanism and Discrimination of the Large Deformation of Schist Highway Tunnel in Proximal Parallel Tectonic Environment

Li Qiang, Huang Feng, Gan Lisong

2023, 37(2): 186-193. doi: 10.3969/j.issn.1007-2993.2023.02.010

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The large deformation occurred several times since Derong No. 1 tunnel was excavated to its deep buried section, which seriously affected the construction safety and the construction period. In order to take targeted and effective prevention measures to control the large deformation of tunnel surrounding rock, the controlled factors and failure mechanism of the large deformation of surrounding rock are comprehensively analyzed. The results show that the large deformation of tunnel surrounding rock was induced by the coupling mechanism of the plastic flow deformation, plastic shear slip deformation, dipping layered bending deformation and progressive looseness extension deformation, which was promoted by engineering disturbed factors under the mutual coupling effect of weak surrounding rock, crushed rock structure, high crustal stress, groundwater and serious deviatoric pressure. On this basis, according to the current traffic industry norms and combined with the deformation characteristics, it is summarized that the comprehensive index scheme for the large deformation grading of surrounding rock in the construction site of two-lane highway tunnel. It provides a more reasonable and reliable basis for guiding the tunnel construction design.

Physical and Mechanical Properties and BPNN Prediction Model of Silty Soil in Coastal Area of Jiangsu Province

Xie Hongping, Han Chao, Du Changqing, Wang Bo, Yuan Shuai

2023, 37(2): 194-200. doi: 10.3969/j.issn.1007-2993.2023.02.011

[Abstract](96) [FullText HTML] (18) [PDF 1235KB](20)

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Shallow soil deposits in coastal area of Jiangsu Province are mainly composed of silty soil and muddy silty soil that formed by Quaternary marine sediment or marine and terrestrial sediment. High groundwater level and poor geotechnical properties of the soil will directly affect the infrastructure construction and later operation safety. Based on the in-situ and lab test data of several new substation projects in coastal area of Jiangsu, the change ranges, variability and correlations of physical and mechanical characteristics of the typical silt soil were summarized. It shows that coefficient of variation of mechanical indexes (such as soil cohesion etc.) is about 0.5, which is significantly greater than that of physical indexes (such as soil density and liquid plastic limit etc.). A BPNN model of silty soil was constructed by using neural network method and the predicted result is good for reflecting the complex non-linear relationship between silty soil parameters. The prediction accuracy of soil compression indexes are better than that of shear strength indexes by using RMSE and MAE.

Stress Analysis of Three-row Pile Rigid Frame Retaining Structure in High Slope with Deep and Thick Backfill Soil

Shi Yanghai, Zhao Xiaoyun, Wang Xianneng, Zhou Luncai, Wang Yue

2023, 37(2): 201-206. doi: 10.3969/j.issn.1007-2993.2023.02.012

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The supporting structures of single row cantilever pile, pile-anchor support, double row pile, H-type pile and other supporting structures have deficiencies in high slope with deep and thick backfill soil. In view of the deficiencies, three-row pile rigid frame retaining structure was analyzed. In supporting deep fill high slope, the three-row pile rigid frame retaining structure can simultaneously play the role of "retracting slope" and "reinforce the foot of the slope". The application of this structure could save land and realize retaining effectively. Through engineering examples, displacement method and MIDAS GTX NX finite element software were used for calculation and analysis. The comparison results show that the simplified displacement method can be used to approximate the bending moment of three-row pile rigid frame retaining structure. The section rigidity of front pile and connecting beam should be strengthened in the design, and ensure that the nodes are rigidly connected. The grading height of rigid frame structure should be roughly uniform and the cantilever height of rear pile should be reduced as much as possible.

Research on Low Strain Detection Technology of Foundation Pile in Residential Building Engineering

Yang Lipeng

2023, 37(2): 207-212. doi: 10.3969/j.issn.1007-2993.2023.02.013

[Abstract](99) [FullText HTML] (26) [PDF 825KB](33)

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A low strain detection technology for residential building engineering foundation piles was studied. Reflected wave signals reflected from the pile body were collected through sensors. In order to improve signal quality, the EEMD method was used to denoise the signals. Time domain and frequency domain characteristics of reflected wave signals from foundation piles of different defect categories were extracted and used as input. BP neural network was used to classify and identify models to detect the extent of foundation pile defects, and locate the defect location based on relevant parameters to complete low strain detection of foundation piles. The test results show that the error between the detection results of foundation pile defects and the actual defect location is smaller, and the detection results are more accurate, which has good application value.

New Prestressed Retaining Pile Structure System and Reinforcement Method

Zhang Qinxi, Guo Donglai, Shao Weixin, Chen Hao

2023, 37(2): 213-219. doi: 10.3969/j.issn.1007-2993.2023.02.014

[Abstract](88) [FullText HTML] (37) [PDF 4071KB](26)

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A large number of reinforcing bars in the conventional pile anchor support structure system cannot be recycled and become construction waste. Under the background of the carbon peaking and carbon neutrality goals, a new type of prestressed support pile with recyclable main bars was proposed. This new type of support pile was introduced from the aspects of structural structure, material selection, construction process, technical points of recycling main bars, etc. The bearing mode and working mechanism of this new type of pile were deeply studied, and a new reinforcement calculation method was proposed based on the traditional calculation method. The rationality of the formula was analyzed. In order to determine the reasonable value range of the tension control stress, ABAQUS finite element software was used to carry out numerical simulation and analysis, and the bending bearing capacity of this new type of support pile under different working conditions was obtained. Compared with the bending bearing capacity calculated by the new reinforcement method proposed, the research shows that the new reinforcement method is applicable to the situation where the tension control stress does not exceed 300 MPa.

Treatment of Saline Soil with Soil Water Isolating Coagulant

Chen Chao, Zheng Weihua, Yang Xiong, Zhang Lin, Li Quanyu

2023, 37(2): 220-225. doi: 10.3969/j.issn.1007-2993.2023.02.015

[Abstract](61) [FullText HTML] (55) [PDF 1138KB](20)

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Expansion problems occurred in many electricity substation yard site in Lanzhou, which caused severe cracking of adjacent concrete road and affectted the operation safety of the substation. A new soil water isolating coagulant (SWIC) was used to solve such problems. The water absorption, expansion in water, unconfined compressive strength, and softening coefficient of the specimen added different dosage of SWIC were tested after curing for 7 days. The results show that the addition of SWIC can significantly improve the unconfined compressive strength, whether air dried or immersed in water for 24 h. The softening coefficient which indicate the water resistance was improved, and the water absorption, water expansion were reduced. The infiltration of water and expansion problems can be effectively reduced as it was used in engineering.

Laboratory Test on Mixed Cement-soil Material for Filling Narrow Underground Space

Jiang Baojing, Liu Mingwei, Liu Jiangang

2023, 37(2): 226-231. doi: 10.3969/j.issn.1007-2993.2023.02.016

[Abstract](76) [FullText HTML] (24) [PDF 1212KB](14)

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A cement-soil filling material is proposed for the quality problem of backfilling in narrow spaces that commonly exists in the development and utilization of underground spaces. The unconfined compressive strength test and direct shear test were conducted for the mixed fluid cement-soil. The effect of cement content, cement-soil ratio, curing method and curing time on the strength of cement-soil were studied, and the deformation modulus, cohesion and internal friction angle of cement-soil material were obtained. The experimental study shows that the mixed cement-soil has good physical and mechanical indexes. The deformation modulus is 98.4~112.7 MPa, the cohesion is 185.54~213.45 kPa, and the internal friction angle is 32°~39°, which can effectively reduce the surface settlement caused by the quality of backfill construction.

Application of Multiple Support Types for Super-large Deep Foundation Pits in Soft Soil Area

An Ran, Cheng Yichong, Gong Dikuai, Xu Guan

2023, 37(2): 232-237. doi: 10.3969/j.issn.1007-2993.2023.02.017

[Abstract](109) [FullText HTML] (55) [PDF 2880KB](54)

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The engineering geological conditions of a large area deep foundation pit in Ningbo are complex, and the deformation control is difficult. According to the excavation process and section characteristics of the foundation pit, pile-anchor and pile-braced composite supporting structures were adopted in the foundation pit, and the supporting structure of gravity retaining wall plus slope were used at the junction of different basement development sites. Combined with the monitoring data of the foundation pit, the excavation process of the foundation pit was analyzed, and the internal force and deformation control effect of different anchor cable types were mainly discussed. The practice of this project can provide reference for similar projects.

Deformation Characteristics of the Pile-anchor Supporting Structure of Deep Foundation Pit with Cracks

Wang Di, Tian Dalang

2023, 37(2): 238-246. doi: 10.3969/j.issn.1007-2993.2023.02.018

[Abstract](78) [FullText HTML] (34) [PDF 3379KB](25)

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Due to the characteristics of a large amount of excavation, long construction period and complex construction environment, deep foundation pit engineering is easy to induce construction safety accidents. The full excavation process of the foundation pit supported by multi-layer prestressed anchor cable pile plate retaining wall was simulated utilizing a three-dimensional numerical model established by FLAC3D, based on the deep foundation pit project with cracks in Chongqing. Soil and supporting structure's deformation characteristics in the excavation process were analyzed based on the numerical results. Numerical result and actual measurement indicate that: (1) the deformation of supporting structure system and the settlement distribution outside the pit have obvious spatial effect under the influence of cracks and adjacent foundation pit buildings; (2) the relationship between the bending moment of the crown beam at the corner of the foundation pit and the excavation depth is obviously different from that in the middle of the foundation pit; (3) the deformation of the supporting pile in the middle of north and south side of the foundation pit is compound type, while deformation of the supporting pile in the central part of the east and west side is cantilever type; (4) the results obtained by HS soil constitutive model are in good agreement with the measured results. The numerical results of surface subsidence at the monitoring point are close to the measured data, which confirms the reliability of the numerical model. The research results can provide practical reference for similar projects in the future.

Reinforcement Mechanism and Optimization Design of Soil Reinforcement in Passive Area of Foundation Pit Supporting

Yang Peitao, Shan Tingdong

2023, 37(2): 247-252. doi: 10.3969/j.issn.1007-2993.2023.02.019

[Abstract](193) [FullText HTML] (96) [PDF 1334KB](49)

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Due to the insufficient of lateral resistance in the passive area, the deformation and displacement of the supporting pile and wall increase with the deepening of the foundation pit excavation, so it is necessary to strengthen the control of the deformation and displacement of the supporting pile and wall by strengthening the soil in the passive area to improve the embedding condition of the soft soil at the bottom of the pit. Combined with practical engineering of supporting pile, a fitting method of the optimal reinforcement depth and width of cantilever support foundation pit bottom was provided. Numerical simulation of the strengthening effect of different depth and width were analyzed, and the passive area soil consolidation mechanism and optimization were further studied, which provides practical reference in similar project.

2023 Vol. 37, No. 2