岩土工程技术

2022, 36(5): 1-1.

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2022, 36(5): 1-3.

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Load Bearing Characteristics of Prefabricated Ecological Retaining Wall

Bai Lihui, Zhu Cong, Huang Tianyuan, Yang Xinyuan, Tu Jiewen

2022, 36(5): 345-352. doi: 10.3969/j.issn.1007-2993.2022.05.001

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Aiming at the disadvantages of traditional column slab wall, such as poor drainage performance, poor greening ability and low degree of prefabrication, the column of column slab wall is segmented and hollowed out, and the components are connected by bolts. By improving the retaining plate, a shutter shaped retaining plate is obtained. In order to determine its applicability and safety, the full scale destructive test is carried out firstly, and then the three-dimensional numerical simulation of this kind of retaining wall is carried out by using ABAQUS finite element software. The following conclusions are obtained: when the load reaches 202.5 kN, the moment at the bottom of the column, that is, when the bending moment reaches 337.50 kN·m, it reaches the limit state of normal use; when the load reaches 335 kN, take the moment at the bottom of the column, that is, when the bending moment reaches 558.33 kN·m, it reaches the limit state. This kind of retaining wall is different when it is used for the shoulder wall and the embankment wall, which shows that when it is used for the embankment wall, it is an open bulging "U" curve, while when it is used for the shoulder wall, it is a closed bulging "U" curve. With the increase of vehicle load distance, the force reduction rate of retaining wall structure first increases and then decreases.

Deformation Control Technology of Soft Surrounding Rock in Shallow Buried Section of Surrounding Expanded Tunnel

Huang Liming, Zhou Weizheng, Jia Yanling

2022, 36(5): 353-359. doi: 10.3969/j.issn.1007-2993.2022.05.002

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Based on the in-situ extension project of a tunnel, the dynamic construction process of the surrounding extended-excavation was simulated through finite element method. The displacement and deformation, the stress distribution of the tunnel’s weak surrounding rock, and the mechanics and of the supporting structure are obtained. The calculation results are compared with the field monitoring data, and the two results are basically consistent. The following conclusions are obtained: (1) The use of step-by-step excavation and timely temporary support has a significant effect on controlling the deformation of weak surrounding rock. (2) The demolition of the existing lining has a great disturbance to the surrounding rock of the tunnel. There will be a certain range of plastic deformation at the side arch foot, and the design parameters of the pipe shed at the arch spandrels and the lock foot anchor rod at the arch foot should be strengthened to ensure the construction quality and improve the stability of the surrounding rock. (3) The spandrels and arch foot on the left and right sides of the primary support, and the connection between the initial support and the vertical temporary support are relatively weak positions. During the construction of the arch spandrels and the arch foot, more attention should be paid to the deformation and displacement of the surrounding rock and the support structure. It is hoped that the research results can provide reference for the design and construction of similar projects.

Numerical Simulation Analysis of the Advantages of Single-story Tunnel Pile Method over Traditional PBA Method and Reasonable Excavation Sequence

Sun Yuhui, Li Xiaomeng, Chen Changyan, Bai Chaoxu, Wang Jinming

2022, 36(5): 360-364. doi: 10.3969/j.issn.1007-2993.2022.05.003

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In the urban center with complex surrounding environment, it is particularly important to select the construction method of underground excavation station in order to ensure the safety of its own structure and surrounding environment. By introducing the principle of the tunnel pile method and the construction steps of the conventional PBA method and the single-layer pilot tunnel pile method, and comparing the differences between the two methods in terms of whether or not to excavate the lower pilot tunnel, it can be concluded that the single-layer tunnel pile method has less impact on the surrounding environment and better treatment and protection of groundwater. Taking an underground excavation station constructed by a single-layer tunnel pile method in Beijing as an example, FLAC3D is used for numerical simulation to analyze and summarize the influence of different pilot tunnel excavation, different primary support and arch buckle sequence and different secondary lining arch buckle sequence on the vertical and horizontal deformation of the surrounding surface, and the optimal sequence of pilot tunnel excavation, primary support and arch buckle sequence and secondary lining arch buckle sequence are obtained. The study can provide reference for similar engineering design and construction.

Research on Design of Foundation Pit Support for Suspended Wall in Soil and Rock Dual Structure Stratum Area

Xiong Lu

2022, 36(5): 365-370. doi: 10.3969/j.issn.1007-2993.2022.05.004

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With the deepening of the excavation depth of foundation pits, the geological conditions tend to become more complicated, and the forms of supporting structures tend to be diversified. Taking Guangzhou Metro Line 21 Yuancun Station as an example, for the soil-rock dual structure strata area, the foundation pit can be divided into two upper and lower sections for calculation. The upper section adopts the wall of "suspended base underground continuous wall + inner support (anchor cable)" supporting (anchor) system, and the lower section adopts the rock slope anchoring shotcrete system. The calculation results are compared with the on-site monitoring results. The results show that: (1)The recommended algorithm is suitable for the calculation of the suspended wall of the soil and rock dual structure; (2)The foot lock anchor cable of suspended wall has an obvious control effect on the horizontal displacement of the wall foot, which is greatly affected by the prestress of the anchor cable; (3)The supporting system of the suspended wall can effectively save construction period and investment, and the deformation of the foundation pit is about 15% compared with that of the conventional foundation pit.

Analysis and Research on Instability and Sliding Mechanism of High Fill Subgrade Slope in A Mountainous Area

Xia Zhiyuan, Wang Shuai, Ren Yanbin

2022, 36(5): 371-376. doi: 10.3969/j.issn.1007-2993.2022.05.005

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The instability and sliding of high fill subgrade slope in mountainous areas is often caused by the lack of effective treatment of subgrade filling, the existence of weak surface in the slope and the failure to take drainage measures in the surrounding areas. Based on the comprehensive analysis of the landslide shape and deformation characteristics, crack distribution, surrounding groundwater exposure and other aspects of a mountain high fill subgrade slope, the sliding mechanism of high fill subgrade landslide was discussed. The slope stability was calculated and evaluated by using Swedish slice method and finite element numerical simulation method, so as to provide reference for landslide treatment scheme. The engineering geological characteristics and key issues of this kind of landslide are sorted out and summarized, which can provide reference for similar situations.

Stability Evaluation Based on Geotechnical Back-analysis Method for Abandoned Slag Field of a Highway Tunnel in Tibet

Man Jun, Ren Zhishan, Sun Guangji, Deng Xiaolong

2022, 36(5): 377-381. doi: 10.3969/j.issn.1007-2993.2022.05.006

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Based on back-analysis of geotechnical technique, Morgenstern-Price method was employed to estimate the stability of an abandoned slag field of a highway tunnel in Tibet. The demonstrability of dammed lake formation was also analyzed. The results showed that the unstable slope of the abandoned slag field was recognized and caused by three main reasons: excavation of the slope foot, immoderately slagging and absence of drainage facility. Under normal conditions, the minimum safety factor of slope stability is 1.062, which is in a basically stable state. Under abnormal conditions (rainstorm conditions), the minimum safety factor of slope stability is 0.94, which is in an unstable state, and there was little chance of dammed lake induced by the landslide. The research results can provide reference for similar projects.

Absolute Positioning Method of 3D Laser Scanner

Gao Haiyan, Chen Zhen

2022, 36(5): 382-384. doi: 10.3969/j.issn.1007-2993.2022.05.007

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To locate the point cloud results of 3D laser scanning from local coordinate system to geodetic coordinate system, the spherical centers of four pairs of spherical targets were used as virtual homonymous points. With the combination of manual and automation methods, CloudCompare software was used for secondary development and programming, which realized the fitting calculation of the spherical center coordinates and radius of the target ball, as well as point cloud registration and point cloud positioning. This method further improves the accuracy of point cloud registration and absolute positioning, and has certain application value.

Application of High-density Electrical Method in Geological Exploration of Goaf in Coal Mine

Sun Fei

2022, 36(5): 385-388. doi: 10.3969/j.issn.1007-2993.2022.05.008

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In order to evaluate the suitability and limitation of the application of high-density electrical method in geological exploration of coal mining areas, high-density resistivity meter was used in goaf geological exploration in a coal mine of Dongying, Shandong Province. Inverse analysis was conducted based on 6 stratigraphic sections, and verified by drilling work. The analysis results show that the resistivity of the non-goaf section increases gradually with the increase of depth, and has obvious stratification characteristics. The resistivity increases from 5 Ω·m at the surface to 200 Ω·m at 25 m depth. The resistivity distributions of the 3 goaf sections are extremely uneven, and there are cavity areas with abnormally low resistivity in the sections. The high-density electrical method can be used to delineate the general distribution and scope of goaf. Therefore, high-density electrical method is an efficient and convenient method with good suitability in the application of goaf exploration.

Experimental Study on Uniaxial Compressive Fatigue Property of Cracked Rock-like Materials

Tao Wei, Ye Tangjin, Zhang Wenhai, Wang Xiaoyu, Liu Congcong

2022, 36(5): 389-394. doi: 10.3969/j.issn.1007-2993.2022.05.009

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To study the fatigue failure behavior of rocks with penetration cracks and reveal the fatigue damage and failure mechanism of rocks with defects, the cracked white cement specimens were prepared by pre-embedded strip method. The effects of various crack inclination angles and stress distribution on crack propagation was revealed by uniaxial compression fatigue test. The result showed that the fracture trajectory of the low cycle fatigue test was basically the same as that of the static test. The crack initiated from the crack tip and the crack angle was about 45°~75°, which could be considered as typical tensile Mode I fracture. The relationship between crack propagation length and the number of cycles revealed that the crack growth rate increased rapidly with the number of cycles and then underwent a stable phase and finally increased rapidly, which has been verified that the fatigue failure process went through three stages: initial plastic deformation stage, slow growth stage and rapid infiltration stage. According to the analysis of fatigue strain energy, energy required by the crack in the initiation stage was relatively large, and after the crack started to expand, the strain energy density remained basically unchanged, indicating that the energy required in the process of crack expansion tended to be stable. Comparing the strain energy density curves of different stress levels and stress ratios, the strain energy density gradually increased at larger stress levels and stress ratios, indicating that the sample could absorb more energy under larger stress levels and stress ratios, and the energy of crack initiation and propagation was faster.

Mechanical Properties and Engineering Properties of Weathered Slate in Damen Area of Yunnan Province

Cun Chunfa, Zhao Yongshun, Huan Jiuyang, Qiu Zijuan, He Mingming

2022, 36(5): 395-403. doi: 10.3969/j.issn.1007-2993.2022.05.010

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A clear understanding of the geotechnical mechanical properties and engineering characteristics of foundation rock mass is very important to evaluate the safety and stability of engineering projects. Based on a large infrastructure project during the 13th Five-Year Plan period in Yuxi, Yunnan Province, the physical and mechanical properties of moderately weathered and strongly weathered carbonaceous slate in the main foundation soil layers in this area were deeply discussed. Firstly, uniaxial compression tests of moderately weathered slate under natural and saturated conditions were carried out based on indoor physical tests. The influence of water content on the uniaxial compressive strength of slate was revealed, and the typical failure mode of slate under uniaxial stress was discussed. Secondly, the gradation characteristics of strongly weathered slate were described based on the indoor particle analysis test. What is more, the variation of shear strength index of strongly weathered slate under different water content was discussed based on the in-situ shear test. Finally, the chemical composition of moderately weathered slate and the permeability and bearing capacity of strongly weathered slate were studied in detail based on three kinds of geotechnical tests. The results can provide guidance for the construction with similar geological conditions in this area.

Experimental Study on Shear Strength Evolution of Xiashu Loess under Rainfall Infiltration

Cai Yuchen, Liu Shunqing, Zheng Liming, Zhou Ping, Mei Pengfei, He Sijie

2022, 36(5): 404-408. doi: 10.3969/j.issn.1007-2993.2022.05.011

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Under the actual rainfall infiltration condition, the research on the shear strength evolution law of Xiashu loess is insufficient. According to the change of water contents under the condition of rainfall infiltration obtained by automatic monitoring, the experimental research on the shear strength evolution law of Xiashu loess under the condition of rainfall infiltration was carried out in two typical slopes in Zhenjiang. The results show that the shear strength of Xiashu loess is greatly affected by the water content, and the strength characteristics of Xiashu loess are different near limit water content. With the increase of water contents, the cohesion of Xiashu loess decreases slightly at first, then decreases sharply, finally decreases slightly and remains stable. With the increase of water contents, the internal friction angle of Xiashu loess decreases sharply at first, then decreases slightly and finally remains stable. The research results can provide a theoretical basis for the protection and treatment of Xiashu loess slope, and have practical engineering significance.

Study on Field Immersion Test of Large Thickness Self-weight Collapsible Loess Sites

Wang Qingman, Fan Hanguang, Liu Yi, Fang Shengnan, Zhang Xin

2022, 36(5): 409-416. doi: 10.3969/j.issn.1007-2993.2022.05.012

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To solve the problems of collapsibility evaluation and foundation treatment in construction of large thickness self-weight collapsible loess sites, field immersion test was conducted. The rule of water injection rate, the movement of moisture field, the collapse characteristics of surface and underground, the development characteristics of cracks around the test pit, the influence range of both immersion and saturation, the permeability coefficient of foundation soil, the lower limit depth of self-weight collapsible loess and criteria were studied. On this basis, a method is proposed to calculate the correction coefficient β₀ which varies with the soil quality in different areas by considering the sedimentary age of the strata. A preliminary discussion on criteria of self-weight collapse of loess has been conducted. The result is: 0.015 is appropriate for Q₃ loess but not for Q₂. It is suggested that field immersion test should be conducted to evaluate self-weight collapse of Q₂ loess. The research results can provide reference for regional engineering construction.

Triaxial Compression Deformation of Unsaturated Sericite Schist Residual Soil

Zhi Taiqiang, Liu Huan, Wang Yun, Bai Mingyuan

2022, 36(5): 417-420. doi: 10.3969/j.issn.1007-2993.2022.05.013

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To study the triaxial compression characteristics of unsaturated sericite schist residual soil, the compression tests of controlling matric suction and net mean stress were carried out by using unsaturated triaxial creep apparatus. The results show that: when the matric suction is the same, the compression deformation increases with the increase of net mean stress. In a certain range, with the increase of matrix suction, the yield stress of sericite schist residual soil also increases, and when the dry density is high, the yield stress is high. When the net mean stress is the same, the deformation decreases with the increase of matrix suction. Comparing the compression tests under the two kinds of stress change, it can be found that the main reason for deformation is the application of load after reaching the yield suction.

Analysis of Relationship Between Standard Moisture Absorption and Soil Particle Composition

Liu Jun, Zhao Wenyue

2022, 36(5): 421-424. doi: 10.3969/j.issn.1007-2993.2022.05.014

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The standard moisture absorption of soil is one of the important basis to judge the expansibility of soil. The relationship between the standard moisture absorption of soil and the composition of different particle sizes of soil were analyzed, and a certain linear function relationship between the standard moisture absorption of soil and the clay content (clay mineral content) was concluded. The foundation is established for the auxiliary judgment of the standard moisture content, and it is concluded that the standard moisture content is about 1/10 of the clay content numerically. At the same time, the mineral composition corresponding to different particle sizes of soil is analyzed, which provides the theoretical basis for determining the standard moisture content by clay content. By comparing with free expansion rate and plasticity index, the advantages of standard moisture content to judge soil expansion and particle composition to judge standard moisture content are analyzed.

Influence of Particle Size Distribution on Characteristics of Clay Sand Mixed Soil

Zhang Qichang, Wang Lu

2022, 36(5): 425-430. doi: 10.3969/j.issn.1007-2993.2022.05.015

[Abstract](75) [FullText HTML] (14) [PDF 6642KB](19)

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Based on a practical engineering case, indoor test and large-scale consolidation direct shear test on clay sand mixed soil samples were conducted, including physical and mechanical property indexes such as strength parameters and deformation parameters. Mixed soil was prepared according to the mass ratio, and the indoor consolidation test and quick shear test were also conducted. The influence of particle size on the strength and deformation characteristics of the mixed soil was discussed. Based on the quantitative description of particle gradation by fractal dimension, the functional relationship between strength parameters, deformation parameters and fractal dimension of mixed soil is established. The phenomenon of sudden change of mechanical properties of mixed soil caused by particle gradation is reflected by fractal dimension.

2022 Vol. 36, No. 5