岩土工程技术

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2022, 36(6): 1-1.

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2022, 36(6): 1-3.

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Discussion on Special Cases in Investigations of Xi’an Ground Fissures

Wang Fuhui, Xu Zhangjian, Yan Jianlong, Wang Yonggang, Zhao Zhihai

2022, 36(6): 431-436. doi: 10.3969/j.issn.1007-2993.2022.06.001

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The investigation method of ground fissure in general site in Xi’an is relatively comprehensive, but there is no improved criterion for ground fissure investigation in complex site. According to the geological structure, sedimentary environment, formation causes and special engineering geological properties of Xi’an ground fissure site, combined with the distribution law and development characteristics of Xi'an ground fissure, on the basis of general site ground fissure investigation methods and the ground fissure investigation experience of complex site, several special situations of Xi’an ground fissure investigation are summarized and discussed. The investigation methods and criteria are obtained for class 2 sites where the fault of class 2 marker layer is not obvious, the intersection of class 2 and class 3 sites, class 3 sites with exposure signs near surface, and sites with abnormal groundwater level on both sides of ground fissures. The analysis results can provide reference for the investigation of Xi’an ground fissures in complex sites.

Research on Deformation of Surrounding Rock by Linear Monitoring Technology in Large Underground Cavity with High Geostress

Zhang Shilei, Tian Zhenhua

2022, 36(6): 437-442. doi: 10.3969/j.issn.1007-2993.2022.06.002

[Abstract](69) [FullText HTML] (26) [PDF 2284KB](13)

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Based on the monitoring data of INCREX Mobile Extensometer implemented on the dome and engineering geological investigation in large underground cavity, the deformation characteristics of surrounding rock of dome in the cylindrical cavern and the middle wall of the long corridor-shaped underground cavern are discussed, as well as the development of relaxation circle. The spatial differentiation and evolution law of deformation in the cylindrical cavern dome are analyzed. The range and evolution characteristics of relaxation zone of mid-partition in large underground caverns are clarified. The results show that: (1) The structural plane has little influence on the deformation magnitude of the surrounding rock of the cylindrical cavern dome (within 5 mm), and the deformation law of the joint rock in the dome is similar to that of the grade III surrounding rock. The deformation of the surrounding rock mainly occurs in the construction period near the excavation face, and the influence range is limited to the normal dome. (2) The air in the measuring micrometer borehole is connected with the air in the cavern, and the measured value has a periodic variation. (3) The range of relaxation zone is proportional to the degree of stress concentration, and the maximal depth of relaxation zone is about 1/3 of the excavation height. The development of relaxation zone is mainly concentrated in the excavation stage, and there is basically no expansion after the cavity is formed. The research results can provide reference for the optimization and stability evaluation of the supporting structure of deep buried caverns under high geostress.

Deformation Monitoring of Deep Surrounding Rock of Large-section Water Conveyance Tunnel Based on Weak Grating Technology

Zhang Honggang, Lu Binqiang, Jia Lixiang, Zhang Wenxuan

2022, 36(6): 443-447. doi: 10.3969/j.issn.1007-2993.2022.06.003

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Accurate monitoring of the deformation of the deep surrounding rock of the tunnel can improve the efficiency and safety during tunnel construction. Weak grating technology was used to monitor the deformation of the deep surrounding rock of a water conveyance tunnel in Pingyang. The monitoring results show that the strain change of tunnel surrounding rock is small, and the stability of surrounding rock is generally good. The monitoring results of the weak fiber grating sensing cable is basically consistent with the traditional monitoring results, which are in line with the facts. The monitoring plan and monitoring results can provide reference for similar projects.

Soil Layer Structure and Wave Properties of Coral Reef in Maldives

Li Shuo, Xu Qingqing, Qiao Jianwei

2022, 36(6): 448-451. doi: 10.3969/j.issn.1007-2993.2022.06.004

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Maldives is located in the tropical marine environment, with coral reef rock and soil widely developed. Through engineering geological drilling, laboratory test and wave velocity test, the stratigraphic structure and wave velocity characteristics of coral reef were studied. The results show that the coral reef soil in Maldives is composed of coral sand and coral reef limestone. According to the grain composition, the coral sand can be divided into fine medium sand and coarse gravel sand. According to the degree of cementation, the coral reef limestone can be divided into massive reef limestone and columnar reef limestone. The shear wave velocity of coral sand increases with depth, ranging from 156 m/s to 370 m/s, and the equivalent shear wave velocity is 262.3 m/s. According to the integrity coefficient, reef limestones can be divided into five types: extremely broken, broken, relatively broken, relatively complete and complete. Reef limestones show regular sedimentary cycles.

Analysis and Treatment of Shallow Pit Accident in Deep Soft Soil Areas in Reclamation Area

Zhou Changbiao, Qiao Liping

2022, 36(6): 452-455. doi: 10.3969/j.issn.1007-2993.2022.06.005

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Taking a shallow foundation pit in deep and soft soil in Shenzhen as an example, the support type, uplift accident, accident cause analysis and treatments of the foundation pit were introduced. Compared with the third-party monitoring results, the conclusions are as follows: (1) When the deep soft soil shallow foundation pit is supported by slope, the soil stability within the range of at least twice the depth of the foundation pit below the base should be calculated, and the load on the slope top should be limited strictly, otherwise the pit bottom is prone to uplift failure. (2) When the cantilever pile is used to support the shallow foundation pit in deep and soft soil, the supporting pile shall penetrate the silt layer to ensure sufficient effective embedded depth. (3) Strengthening the passive area of shallow foundation pit in deep soft soil with mixing pile can improve the mechanical properties of soil, effectively control the deformation of supporting structure and avoid the uplift deformation of pit bottom. The engineering experience and analysis conclusion have reference significance for similar projects.

Application of BIM Technology in Highway Geological Survey

Wang Pengwei

2022, 36(6): 456-459. doi: 10.3969/j.issn.1007-2993.2022.06.006

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Taking Nanchuan Tunnel as an example, BIM technology is used to integrate multi-source geological information data such as geological mapping, exploration, and geological profile to build a three-dimensional geological model. BIM Technology could quickly generate a three-dimensional model of structures, integrate the highway BIM model into three-dimensional geological survey information, and comprehensively display highway geological information, making up for the shortcomings of BIM application in highway engineering construction. The results show that the collaborative work between 3D geological visualization results and highway specialty could be realized based on BIM technology, and the geological environment of the structure site could be displayed comprehensively and stereoscopically. Geological risks could be identified more accurately, and technical support could be provided for the progress of highway construction.

Application of Semi-closed Curtain of Diaphragm Wall in Deep Foundation Pit Adjacent to Subway

Liu Xiuzhen, Xia Chao

2022, 36(6): 460-464. doi: 10.3969/j.issn.1007-2993.2022.06.007

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In the area of first terrace of the Yangtze River, the design of deep foundation pit is faced with problems such as poor soil quality and abundant groundwater. The design of foundation pit adjacent to the subway is often provided with a vertical water-stopping curtain. A foundation pit is close to the Fanhu Station of Wuhan Metro Line 2. The semi-closed curtain and semi-suspended diaphragm wall was used as a vertical retaining structure and also as a water-stopping curtain. Two layers of concrete ring supports were set up, supplemented by dewatering in the foundation pit. During the operation of the foundation pit, there was no adverse impact on the surrounding roads, subways and other structures. Compared with the closed curtain (or diaphragm wall), the economic benefits are significant, which can be used as a reference for similar projects.

Investigation of Overhead Transmission Lines after the Implementation of "General Code for Engineering Investigation"

Hao Bing, Li Congyun, Liu Shiyan, Liu Yingguang

2022, 36(6): 465-468. doi: 10.3969/j.issn.1007-2993.2022.06.008

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General Code for Engineering Investigation is the basic code for engineering construction and the mandatory provisions of the full text. The number and depth of exploratory hole, as well as the requirements for sampling, testing and laboratory testing are specified. Due to industry and historical reasons, electric power engineering investigation has distinct industry characteristics. Through comparative analysis, there are certain differences between the overhead transmission line and the provisions of the general code in investigation method, holes layout, sampling, testing, laboratory test and the content of results. The implementation of geotechnical engineering investigation need to make some appropriate adjustments to meet the requirements of General Code for Engineering Investigation. The revision of industry and group codes should also provide clearer requirements accordingly.

Instability and Deformation Mechanism Analysis and Treatment Design of Cutting Slope under Complex Conditions

Wang Ruichun, Wang Xuetong

2022, 36(6): 469-476. doi: 10.3969/j.issn.1007-2993.2022.06.009

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Taking landslide treatment of an expressway in Huadu, Guangzhou as an example, the instability and deformation mechanism of bedding cutting slope with soft interlayer and multistage sliding surface was analyzed, and the stable state of slope was determined. On the basis of the emergency treatment of gravel back pressure, combined with the back pressure body, limit equilibrium method and finite element method were used to analyze and calculate. Considering all kinds of restraining factors, the comprehensive treatment measures of prestressed anchor cable and circular anti-slip pile were adopted. According to the monitoring situation during construction and operation, the landslide treatment is effective.

Deformation Law Analysis of Bedding Slope at Entrance of Highway Tunnel

Hu Shiming, Yang Weihong, Li Tao, Li Xinkun

2022, 36(6): 477-482. doi: 10.3969/j.issn.1007-2993.2022.06.010

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The geological conditions of the bedding slope at the entrance of the tunnel are complicated, and it is easy to cause the landslide deformation of the side slope and the inverted slope during excavation. The construction process of right line outlet section of Moziping tunnel was monitored, and the deformation characteristics of the lining and the failure mode of the slope were analyzed. The effectiveness of the reinforcement measures was also evaluated. The results show that the deformation of upper soil and surrounding rock in the tunnel increases gradually with the construction, and the deformation of monitoring points increases sharply during the excavation of the section. The displacement at the junction of upper soil and soil rock is obviously greater than that of bedrock, which has the risk of bedding landslide. The deformation of tunnel arch shoulder and arch crown is the largest, and the support needs to be strengthened. After the bedding slope enters the bedrock and the inverted arch is closed, the deformation of the slope and tunnel surrounding rock gradually tends to be stable. The study can provide practical experience for the slope excavation construction of tunnel portal section.

Study of Remedial Measures for Existing Unauthorised Basement Over-excavation Renovation Works

Yu Qiang

2022, 36(6): 483-488. doi: 10.3969/j.issn.1007-2993.2022.06.011

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Comprehensive over-excavation renovation works of an unauthorized basement have been studied. Based on the identification of safety hazards and taking into full consideration the uncertainty of structural instability induced by the over-excavated basement, the small construction site and the short construction period, the overall treatment plan combining temporary risk reduction and permanent reinforcement was proposed. The combination of geotechnical and structural measures, such as drainage, backpressure, light weight foam concrete backfills, high pressure rotary pile foundation reinforcement, and the addition of a new pile bearing platform were used. Finally, the effectiveness of the combined geotechnical and structural reinforcement measures in the remediation of the unauthorized basement was verified by combining on-site monitoring. The research results can provide some reference significance for the design and construction of similar renovation works.

Engineering Practice of Large Area Shallow Foundation Pit Support in Distribution Area of Shallow Buried Thick Silty Soil

Zhu Junjie

2022, 36(6): 489-493. doi: 10.3969/j.issn.1007-2993.2022.06.012

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Due to the fact that enclosure system of shallow foundation pit engineering can not isolate the water-bearing layer effectively in distribution area of shallow buried thick silty soil, the dewatering inside foundation pit shows the characteristic of three-dimensional seepage, and the design and construction of foundation pit face severe challenges especially when the soil quality is poor or the surrounding environment is complex. Taking a large-area shallow foundation pit engineering in Chongming District of Shanghai as an example, the relationship between foundation pit dewatering and enclosure structure system on the safety of foundation pit were discussed. The integrated design idea which considers enclosure structure system of foundation pit, water-stopping curtain and foundation pit dewatering as a whole was put forward. The calculation method and basis on the depth of enclosure structure, tube well and suspended impervious curtain were introduced, and the importance of technical tests on foundation pit supporting plan was emphasized. Foundation pit excavation and monitoring data showed that it is feasible and effective to adopt the scheme of suspended impervious curtain, tube well dewatering inside foundation pit and slope or gravity retaining wall for supporting foundation pit and controlling groundwater.

Application of Piezocone Penetration Test and Flat Dilatometer Test in Shanghai Soft Clay

Lu Shun

2022, 36(6): 494-501. doi: 10.3969/j.issn.1007-2993.2022.06.013

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Based on the geotechnical engineering survey project of Shanghai Rail Transit Airport connecting line, the piezocone penetration test and flat dilatometer test were carried out, and the high-quality sampling compression test results were obtained. The effects of different tests and different chart classification methods on the classification effect were studied, and the relationship between flat dilatometer test and over consolidation ratio, cone tip resistance and compression modulus were analyzed. The results show that the chart method of pore pressure static cone penetration test has a good classification effect on Shanghai soft clay, but it is not ideal for transition soil (silt) and "mixed soil", and the classification method of flat dilatometer test can achieve a good classification effect. The soft clay is overconsolidation soil while the burial depth is less than 18.0 m in Shanghai area. Its overconsolidation ratio decreases with the depth increase, and the soft clay is normally consolidated soil while the burial depth is greater than 18.0 m. For different types of soft clay, there is an obvious linear correlation between cone tip resistance and compression modulus, which can be expressed by a unified formula.

Study on Blasting Relaxation Test and Stability Influence of Underground Powerhouse Rock Wall Beam

Zhou Chunguo, Wang Rongfu, Liu Xingtang, Feng Lei, Liu Gang

2022, 36(6): 502-506. doi: 10.3969/j.issn.1007-2993.2022.06.014

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In view of the difficulty in forming the surrounding rock in the rock wall beam area under special geological structures, and the difficulty of assessing the stability of the rock wall beam, a blasting test and sonic test were carried out in the rock wall beam area of an engineering to study the reinforcement measures and stress in the rock beam area. The depth of the relaxation zone was used to modify the results of the stability evaluation of rock wall beams through experimental data modification. The results show that the average depth of the relaxation zone at each measuring point before blasting is 1.73 m, and the average depth of each measuring point after blasting is about 2.51 m. Comparing the results of each test section, the rock wall beam resin anchor pre-reinforcement scheme has a better surrounding rock forming effect. Use the test data to recheck the surrounding rock and structural surface parameters, and modify the numerical simulation calculation results. The safety factor of anti-sliding stability of the rock wall crane beam and the joint surface of the rock wall is 6.89 when the depth of the stress relaxation zone is not considered. When considering the depth of stress relaxation zone, the safety factor is reduced to 3.13, and the rock wall beam is in a stable state. The blasting relaxation test method and stability calculation method of rock wall beam can provide reference for similar projects.

Experimental Study on Shear Strength of High Fill Loess under Different Moisture Content

Wang Hongqi, Sun Jielong, Li Dawei, Yang Hongxia, Song Tao

2022, 36(6): 507-510. doi: 10.3969/j.issn.1007-2993.2022.06.015

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Shear strength of high fill loess is an important parameter to analyze the stability of high fill loess slope. To study the influence of moisture content on the shear strength of high fill loess, the shear strength tests of high fill loess with different moisture content (2%, 4%, 6%, 10%, 12%, 15%, 20%, 25%) were carried out, respectively. The experimental results show that when the moisture content is in the range of 2%～25%, the shear strength of high-filled loess increases first and then decreases with the change of moisture content, and reaches the peak when the moisture content is 15%; with the increase of moisture content, the internal friction angle and cohesion of the high-filled loess firstly increase and then decrease, and the moisture content has a great effect on the cohesion; the slope of shear displacement and shear stress curve increases gradually, when moisture content is 12% and 15%, and the relationship between shear displacement and shear stress is basically linear. The experimental results have certain reference value for the stability evaluation of high fill loess slope.

Construction Technology and Pull-out Test of Underreamed Anchor in Expansive Soil

Tang Yangui, Yue Dachang, Zhu Weixin

2022, 36(6): 511-515. doi: 10.3969/j.issn.1007-2993.2022.06.016

[Abstract](74) [FullText HTML] (14) [PDF 3190KB](21)

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To enlarge anchorage diameter and to make a change in shape of anchorage body are critical methods to improve bearing capacity of anchor directly. In the expansive soil, the mechanical extruding reaming process was used to construct the multi section underreamed anchors, and the multi-stage cyclic loading test was carried out. According to the load-displacement curve, the failure mode of the anchor is determined as the failure of the bonding interface between the rod and the anchorage body. The test result shows that the construction technology of underreamed anchor in expansive soil layer is feasible. The uplift bearing capacity is one time higher than general anchorage. The bearing capacity value of underreamed anchors increases with decreasing anchor spacing, but the increase range is rarely. The test results could provide reference for the study of the influencing factor of anchorage bearing capacity and failure mechanism of anchorage.

2022 Vol. 36, No. 6