岩土工程技术

Mechanical Performance Analysis and Design Method of a New Type of Assembled Pile Anchor Connection Device

Wang Jianan, Xu Chuanzhao, Lei Fangchao, Qi Changjun, Fan Kai

2021, 35(4): 211-215. doi: 10.3969/j.issn.1007-2993.2021.04.001

[Abstract](101) [FullText HTML] (19) [PDF 1234KB](42)

Abstract:
The anchored retaining structure is widely used in the field of geotechnical engineering prevention and control, such as foundation pit support and slope prevention. In view of the problems existing in the traditional anchor retaining structure, such as the uneven stress on the waist beam and the construction gap between the waist beam and the supporting pile, a new device for the connection of pile and anchor is provided, and the structure, stress performance and construction method of the device are introduced. The device can effectively solve the problem of uneven prestressed force transmission of anchor cable, strengthen the integrity of the pile anchor support system, save the use of steel to a greater extent, and improve the safety of the support system, which has high application value in the pile-anchor support system.

Numerical Analysis of the Influence of Root Erosion on the Stability of Earthen Sites Under Static Load

Wang Yanwu, Tie Zheng, Pei Qiangqiang, Guo Qinglin

2021, 35(4): 216-221, 227. doi: 10.3969/j.issn.1007-2993.2021.04.002

[Abstract](107) [FullText HTML] (18) [PDF 1332KB](28)

Abstract:
The stability of the Great Wall in Gulang County is taken as the research object. By using the finite difference software FLAC3D, the stability of the models with different root erosion depth of the Great Wall is analyzed under static forces, and the distribution of displacement and stress field of the different models are discussed. The results show that the overall deflection of the wall affected by the erosion, and the maximum horizontal displacement is located at the top of the wall. With the increase of the erosion depth, the compressive stress concentrates at the root of the erosion, and the tensile stress concentrates at the back of the wall. Under the action of dead load, when the erosion depth is 1/2 of the bottom width of the model, the wall reaches the critical failure threshold value. It can be used to guide engineering practice to establish a better fitting curve between erosion depth and safety factor and to judge the connectivity of plastic zone.

Civil Design Scheme of Subsea Tunnel Under Complex Conditions

Zhu Jian, Li Xingsheng, Wang Jian

2021, 35(4): 222-227. doi: 10.3969/j.issn.1007-2993.2021.04.003

[Abstract](88) [FullText HTML] (29) [PDF 6531KB](27)

Abstract:
The engineering geological conditions of Dalian subsea tunnel are complex. It is close to gas station, large ship manufacturing base and other buildings. Meanwhile, it is difficult and risky to pass through the existing subway, freight railway, military port and a large number of buildings. According to the characteristics and difficulties of subsea tunnel, the route scheme, construction method comparison, cross-section scheme, horizontal and vertical section scheme and shield segment design are studied. The main research conclusions are as follows: (1) Under the specific environmental conditions of the project, the construction method of cross sea tunnel adopts the scheme of single tunnel double track large shield with less environmental impact and low construction risk; (2) the deepest soil cover of the tunnel is the control condition of segment stress, and the maximum internal force is located at the vault; (3) considering the mechanical equipment and site conditions, 2 m segment ring width makes the number of circumferential joints in the tunnel the least, which is beneficial to improve the longitudinal stiffness of the tunnel, speed up the construction progress and reduce the cost; (4) the universal segment ring scheme with high assembly automation degree is adopted, which saves the number of steel formwork and is easy to rectify deviation; (5) the cross sea tunnel passes through the stratum with uneven hardness and soft, and the structural stress is relatively high. Considering the seismic requirements, the segment ring and longitudinal connection joints are all connected by inclined bolts.

Analysis on the Depth of a Soft Soil Deep Foundation Pit Supporting Pile

Wu Lianxiang

2021, 35(4): 228-232, 237. doi: 10.3969/j.issn.1007-2993.2021.04.004

[Abstract](174) [FullText HTML] (40) [PDF 895KB](75)

Abstract:
Pile anchor or pile bracing structure is generally used in soft soil deep foundation pit supporting. The depth of supporting pile directly affects the stability of supporting structure and the cost of supporting engineering. Determining the depth of supporting pile is an important content of deep foundation pit support design in soft soil area. Combined with an example of foundation pit in a soft soil area, the relevant calculation and analysis of various depth of supporting piles are carried out according to the national foundation pit code and Shanghai foundation pit code, and considering the favorable influence of engineering pile on the depth of supporting pile to ensure a safe, reasonable and economical depth of supporting pile. According to the code of Shanghai foundation pit, the depth of supporting pile of soft soil deep foundation pit can be shortened obviously. Considering the favorable influence of the engineering pile in the pit, the depth of the supporting pile can be further optimized, which could provide reference for similar foundation pit supporting design.

Monitoring and Numerical Analysis of Pile-anchor Supporting Structure in Deep and Large Foundation Pit

Zhou Zhenhong, Sun Huabo, Lv Guo, Cao Shichao

2021, 35(4): 233-237. doi: 10.3969/j.issn.1007-2993.2021.04.005

[Abstract](142) [FullText HTML] (48) [PDF 1159KB](73)

Abstract:
Comparative analysis of monitoring data and numerical calculation results is carried out based on a 27.4 m deep foundation pit pile-anchor supporting structure in Chinese PLA General Hospital. The results show that the horizontal displacement, the vertical displacement and deep horizontal displacement deformation of foundation pit support structure are small, which are far less than the pre-warning value specified in the code. All anchors are coordinated with each other, but the anchor bolt is far less than the pre-warning value. The maximum settlement of the surrounding road is 4.8 mm, which is far less than the early warning value of the foundation pit. The analysis shows that the design of the supporting structure selected for the foundation pit is reasonable, and the monitoring value of the supporting structure during the excavation process is in good agreement with the numerical calculation data, which can provide reference for similar projects.

Calculation of Combined Retaining Structure and Analysis of Its Impact on Existing Box Culverts

Xu Chuanbao, Zhou Peidong, Li Zhuoxun, Zhang Wenyu, Li Zhiyun

2021, 35(4): 238-243. doi: 10.3969/j.issn.1007-2993.2021.04.006

[Abstract](91) [FullText HTML] (31) [PDF 1385KB](35)

Abstract:
Existing box culverts in important water supply projects are more sensitive to the surrounding construction deformation. For the newly built combined retaining structure of pile and retaining wall around the existing box culverts, it is proposed to analyze the forces and deformation of the retaining structure itself by using "integral rigid frame model" and "support excavation model". Combined with specific projects, the safety analysis of the existing water supply box culvert in the entire process of the construction and operation of the project is conducted through a numerical model. Results verified by numerical analysis and field measurement can provide a reference for similar projects.

Application of UAV Aerial Survey Tilt Photography in Industrial and Mining Sites

Zhu Chao

2021, 35(4): 244-248, 254. doi: 10.3969/j.issn.1007-2993.2021.04.007

[Abstract](97) [FullText HTML] (38) [PDF 8074KB](27)

Abstract:
Characteristics of UAV aerial survey tilt photography technology are briefly introduced. Based on the application of industrial and mining sites aerial survey project, UAV aerial survey tilt photography technology are applied to produce digital orthophoto image, real 3D model and digital topographic map of survey areas. Surveying and mapping products are achieved, and the real 3D model in other fields is also applied, which could provide reference for the promotion and application of the real 3D model in the future.

Analysis of Post-construction Settlement After Foundation Treatment in an Airport of Yunnan

Wei Haitao, Sun Lanning, Cai Zhi, Song Bin

2021, 35(4): 249-254. doi: 10.3969/j.issn.1007-2993.2021.04.008

[Abstract](184) [FullText HTML] (48) [PDF 1345KB](58)

Abstract:
Based on the examples of airport projects built in southwestern China, in view of its complex geological conditions, high filling, short construction period and other characteristics, the commonly used economic and reasonable foundation treatment schemes are summarized. Taking the high-fill foundation engineering of an airport in Yunnan as the research object, through analogy with the stratum lithology and hydrogeological characteristics in the area, a technical solution for peaty soft soil and high-fill airport ground foundation treatment was proposed. According to the monitoring data of the soft foundation area, hyperbolic fitting is used to analyze the remaining post-construction settlement law to guide the subsequent procedures and provide a reference for similar projects.

Numerical Simulation and Verification of Water Inflow Calculation of Hanging Water-stop Curtain

Zhang Qinxi, Song Yatong, Yan Jinbo

2021, 35(4): 255-259. doi: 10.3969/j.issn.1007-2993.2021.04.009

[Abstract](140) [FullText HTML] (30) [PDF 1397KB](56)

Abstract:
In the foundation pit project, in order to reasonably protect the groundwater resources and save the project cost, the hanging water-stop curtain is more and more widely used in projects. In order to study the amount of water influx and the influence range of the impact radius of the hanging water-stop curtain pit, the foundation pit project of the First People’s Hospital of Dongcheng District is analyzed. The numerical simulation of the water inflow amount of the hanging water-stop curtain pit is carried out, and monitoring data is acquired to verify the numerical calculation results. The results show that: (1) the amount of water inflow in the foundation pit analyzed by the finite element numerical simulation software is the same as the actual monitored numerical trend, and the daily amount of water inflow could reach 1970 m³; (2) the foundation pit with hanging water-stop curtain is set up, and the original influence radius of foundation pit dewatering is no longer applicable, and the influence radius of dewatering is reduced compared with the original; (3) as the distance from the water-stop curtain increases, the head value outside the foundation pit becomes larger and larger; as the distance from the water-stop curtain increases, the trend of the increasing head value outside the foundation pit is getting smaller and smaller.

Design and Practice of High Mountain Slope Engineering in Rail Transit Parking Lot

Song Keying, Zhang Qi, Xue Runkun

2021, 35(4): 260-264. doi: 10.3969/j.issn.1007-2993.2021.04.010

[Abstract](79) [FullText HTML] (19) [PDF 1219KB](37)

Abstract:
Taking an urban rail transit parking lot construction project as an example, the key points of the engineering design of the fragmented strongly weathered sandstone super-mountain slope are introduced. The project is an underground parking lot with a buried depth of about 13 m. The parking lot is separated from the slope support structure and the maximum height of the slope is 55.0 m. Considering the requirements of the ground and surrounding environment, the support scheme of pile anchor + anchor bar lattice beam is adopted for slope support. During the implementation of the project, the whole process of slope monitoring is carried out. The monitoring results show that the support scheme is reasonable and safe, which can be used as reference for similar projects.

Detection Methods of Deep Buried Pipelines in Shanghai

Zhuo Lulu, Sun Leijiang

2021, 35(4): 265-268. doi: 10.3969/j.issn.1007-2993.2021.04.011

[Abstract](140) [FullText HTML] (34) [PDF 1103KB](61)

Abstract:
The characteristics of the existing trenchless deep buried pipelines in Shanghai is summarized, and the detection methods of deep buried pipelines commonly used in current engineerings are comprehensively discussed. The applicability and limitations of each method in this area are analyzed in combination with the engineering geological conditions and pipeline types in Shanghai. Based on engineering practice, the pipeline instrument is used for preliminary tracking and positioning, and the gradient method is used to detect the depth accurately. The direct method is also used in this project to verify the effectiveness of the detection results, which provides a reference for the preparation of detection schemes for similar engineering.

Recent Advances in Geotechnical In-situ Testing Techniques in the Last 30 Years

Wang Yunnan, Zhang Long, Zheng Jianguo, Liu Zhenghong, Yu Yongtang, Meng Qingbo

2021, 35(4): 269-274. doi: 10.3969/j.issn.1007-2993.2021.04.012

[Abstract](571) [FullText HTML] (90) [PDF 611KB](155)

Abstract:
At present, most geotechnical engineering survey enterprises use the traditional in-situ testing method. In order to summarize the latest development of geotechnical in-situ testing technology, the latest research progress of geotechnical in-situ testing technology and equipment since 1990s are analyzed from four aspects, including deformation characteristics test, shear strength test, permeability test and penetration test. The results show that the current in-situ testing technology has four characteristics: automation, informationization, multi-function and technology upgrading, but there are still some problems, such as high cost, weak theoretical basis, limitations of the test itself and slow progress. According to the practical problems, prospects are put forward from the aspects of strengthening the theoretical basis, accelerating information technology and multi-functional equipment research, expanding the research area and so on.

Analysis of Single Well and Group Wells Pumping Tests for Deep Excavation in Water-rich Sand

Liu Xiangyong, Long Yingying, Jing Xucheng, Hong Xiaoxing, Fan Dongdong, Tan Yong

2021, 35(4): 275-281. doi: 10.3969/j.issn.1007-2993.2021.04.013

[Abstract](131) [FullText HTML] (31) [PDF 2093KB](49)

Abstract:
Water-rich sandy strata has the characteristics of low cohesion, poor stability, and strong permeability. Excavation construction in this strata can be risky. Hydraulic characteristics of this strata were studied to ensure the safety of construction. Based on the field pumping test and three-dimensional inversion analysis, the following conclusions are drawn: (1) The hydraulic connection between aquifers ③, ⑤₁, ⑤₂, and ⑤₃ are not strong, and layers ④₂, ⑤_t and ⑤₂ are poorly permeable. The influence radius of aquifers ⑤₁ and ③ are 135 m and 52 m, respectively. (2) The hydraulic parameters of the main aquifers, including permeability coefficient, hydraulic conductivity and specific storage, were determined by numerical inversion. (3) The settlement caused by the group-well pumping in aquifer ⑤₁can rebound by about 25%; while the pumping-induced settlement of group-well pumping in aquifers ⑤₂ and ⑤₃ rebounds by more than 40%. At each stage of water level recovery, there is an obvious time lag of settlement rebound.

2021 Vol. 35, No. 4