岩土工程技术

2022, 36(2): 1-3.

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Abstract:

2022, 36(2): 1-1.

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Study on the Design and Deformation Monitoring of Double-piles Retaining Structure

Jiang Hongming, Liu Chunlin

2022, 36(2): 87-92. doi: 10.3969/j.issn.1007-2993.2022.02.001

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Abstract:
Taking a double-piles foundation pit in Shenzhen as an example, the monitoring deformation of pit retaining structures as well as adjacent buildings were analyzed. The former 1/3 period of excavation stage was the most fast increase period of lateral deformation of double-piles retaining structure, and the significant increase in settlement of adjacent buildings occured in the latter 2/3 period. The monitoring data shows that the lateral deformation form of double-piles structure is changeable with some factors. The cement soil curtain between piles effectively increases the lateral stiffness of double-piles retaining structure.

Comparison of Different Methods for Calculating Persistence Based on Monte Carlo Simulation

Lan Zhiguang, Xu Yuan, Nie Xijiang, Guo Meng, Wang Haiyu

2022, 36(2): 93-99. doi: 10.3969/j.issn.1007-2993.2022.02.002

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Discontinuity persistence has always been a hot topic in the field of rock mass engineering, which plays an active role in the evaluation of rock strength and stability. The calculation of persistence based on Monte Carlo simulation is a more widely used and more economical method. At present, the methods of calculating persistence based on Monte Carlo simulation include bandwidth projection method, dynamic programming method and shortest path method. By comparing the three methods through examples, the results show that the persistence values calculated by the three methods are anisotropic; when the projection baseline (or shear, or search) direction is fixed, the persistence values calculated by the bandwidth projection method will continue to increase with the increase of bandwidth, while the persistence values calculated by the dynamic programming method and the shortest path method tend to be stable with the increase of bandwidth. The persistence calculated by dynamic programming method and shortest path method are consistent in different bandwidth. Based on comprehensive analysis and consideration, it is suggested that the shortest path method should be used to determine the recommended value of persistence in engineering practice.

Review of Research on Foundation for Liquefied Natural Gas (LNG) Storage Tank

Wang Wei, Nie Qingke, Li Ning, Liu Jingjing, Zhang Peng, Zhai Ziqiang

2022, 36(2): 100-104. doi: 10.3969/j.issn.1007-2993.2022.02.003

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The importance and complexity of the foundation of liquefied natural gas (LNG) storage tank are briefly described. The storage tank foundation is classified into six types: natural foundation raft foundation, composite foundation raft foundation, low cap pile foundation, double cap overhead foundation, high cap pile foundation and double cap overhead pile foundation. The definition, structure and applicable scope of various foundation forms are listed. The safety, economy and applicability are compared. At the same time, it is pointed out that the seismic design and deformation compatibility control of the foundation are the difficulties in the design of the tank foundation, and the theoretical research is far behind the engineering experience.

Bearing Capacity Analysis and Discussion of a Single Long Pile in Deviation

Yang Hanqi, Cai Dechang

2022, 36(2): 105-110. doi: 10.3969/j.issn.1007-2993.2022.02.004

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Combined with an example of an industrial powerhouse which the pored piles were deviation, whether a pile foundation that deflect dramatically could meet the requirements of bearing capacity was discussed. According to the calculation of the horizontal bearing capacity of single pile in current codes and research on the internal force and displacement of pile under load, the piles are classified by its reinforcement ratio. The calculation formula of the ultimate bending moment value of single pile under eccentric axial load was derived considering two conditions including controlled by body strength or controlled by top displacement. The limit value of the pile which could satisfy the safety requirements was obtained, providing references for single long pile foundation that deflect dramatically.

The Construction and Thinking of Engineering Survey Enterprise Informatization

Qian Kaizhu, Guo Miwen, Wang Wei, Jia Junhui

2022, 36(2): 111-115. doi: 10.3969/j.issn.1007-2993.2022.02.005

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With the application of information technology, the engineering investigation industry has been acrossed the digitization stage, and is gradually developing to information and intelligence. Based on the development foundation in the "13th Five-Year Plan", it will be combined with the the new requirements of the "14th Five-Year Plan", and the engineering investigation information will have significant improvement and enhancement. Now, due to the restrictions, the informationization construction of these enterprises will focus on the specific business, among which the investigation informationization construction will be based on formation of enterprise production tool, while the mapping informationization construction will be based on customer project demand. According to its own business, the enterprise has built an engineering investigation project management system, a multi-source data integrated management platform, a community geospatial system and a settlement cloud map deformation monitoring system, etc., which form the solid foundation for the construction and development of enterprise informatization. For the future engineering investigation information construction, the thinking of government guidance and enterprise main body can be adopted, and Internet, Internet of things, big data, cloud computing and BIM technology as the main development directions, so as to realize the integrated development trend of "whole system, whole process and all elements". For the national infrastructure, regional discipline development and industrial technology innovation to provide a solid and effective scientific support.

Test Analysis of Post-Grouting Improvement Coefficient for Cast-in-situ Pile in Thick Sand Layers

Lu Pingzhen, Sun Hongwei, Fang Yunfei

2022, 36(2): 116-121. doi: 10.3969/j.issn.1007-2993.2022.02.006

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The experience of the post-grouting effect for cast-in-situ pile in thick sand layer is limited presently. Based on the static pile load test in a project of Tongzhou New Town, Beijing, the bearing capacity of single pile after post-grouting and without post-grouting was analyzed and compared, and the efficiency of post-grouting technology in this thick sand layer site was studied. It shows that post-grouting can effectively reduce settlement. Compared with the test results of pile without post-grouting, the comprehensive improvement coefficient of post-grouting can reach 2.22. Compared with the calculated value based on geotechnical report for bearing capacity of non-post-grouting pile, the comprehensive improvement coefficient of post-grouting for cast-in-situ pile is about 2.53～3.57. This study can provide reference for the subsequent design of pile foundation with similar geological conditions.

Structural Implementation Method of Yielding Support for Deep Tunnel in Weak Rock

Zhao Wei

2022, 36(2): 122-128. doi: 10.3969/j.issn.1007-2993.2022.02.007

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In order to make the yielding support scientifically applied in deformation control of deep tunnel in weak rock, the conventional support mode which mainly based on bending deformation yielding is changed, and the structural implementation approaches of yielding support is studied based on the theory of structural stability and large deformation mechanics. The conclusions can be listed as follows: (1) the stability of surrounding rock is analyzed with the arch structure as basic mechanical model, the integral and systematic control measures should be taken; (2) the influence of geometric nonlinearity should be reduced in the initial support, so as to realize the yielding demand of deforming largely, and avoid the occurrence of large deformation mechanical effect; (3) in the leveling process of variable stiffness " rigid-soft-rigid" of the initial support, it must be based on the premise that the bearing capacity and stability are guaranteed; (4) the key to the formation of composite structure between surrounding rock and primary support is the matching degree of mechanical properties and the shear resistance of contact surface.

Application of Survey Technology in Pile Foundation Construction of Special Structural Confined Water Field

Dang Zhirong, Wang Zhizhong, Dang Jingmao, Yang Shaofei

2022, 36(2): 129-134. doi: 10.3969/j.issn.1007-2993.2022.02.008

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In view of the serious phenomenon of water and sand gushing during the implementation of the rotary drilling cast-in-place pile, the problem was discussed according to survey technology. The problem of water and sand gushing comes from the effect of the special structural confined water. In order to solve this problem, reverse circulation drilling technology was proposed to reduce the head pressure of underground confined water and reduce or eliminate the sand gushing at the bottom of the hole by increasing the mud specific gravity and viscosity. Then, the post-grouting process was used to deal with the mud skin effect on the side of the pile and the sediment at the end of the pile, and the measures such as increasing the diameter and length of the pile were adopted to effectively solve the technical problems. It effectively solves the technical problem that the bearing capacity and deformation may be greatly different caused by different processes in the pile foundation construction of the project, and ensures that the bearing capacity and deformation of the pile foundation meet the requirements of the design and specifications.

Key Points of Foundation Investigation and Causes of Main Diseases of Ancient Pagodas in Collapsible Loess Area

Cai Huaien, Zhang Jiwen, Liu Shuai, Zhang Peng, Li An

2022, 36(2): 135-139. doi: 10.3969/j.issn.1007-2993.2022.02.009

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Chinese ancient pagodas are of great value in cultural relics, tourism and scientific research. Based on the engineering practice, the main points of the ancient pagoda foundation investigation and the causes of the main diseases were analyzed, and suggestions on the protection measures were proposed in order to protect the ancient pagoda in loess area. In addition to the physical and mechanical properties of the foundation soil, the disease characteristics, foundation types, original foundation treatment methods and effects of the pagoda should be found out. The causes of the disease were analyzed and suggestions for maintenance and reinforcement were proposed. In the process of investigation, excessive damage to the pagoda foundation should be avoided. The original foundation treatment effect of the pagoda cannot meet the requirements of modern specifications, the collapsibility of the natural soil layer and the bearing capacity cannot bear the upper load requirements are the common reasons for the tilt of the ancient pagoda and the deformation of the pagoda foundation in the loess area. Also, the foundation deformation is intensified when soaking in water. Strengthening waterproof and drainage, strengthening surrounding underground caverns and treating slopes that affect the stability of tower foundation are important measures for the protection of ancient pagodas in loess area.

Pipe Point Data Making for 3D Modeling of Underground Pipe Network Based on Skyline

Yang Zhenjie, Yuan Ruihong, Zhu Zeyu, Han Song, Li Yuanyuan

2022, 36(2): 140-144. doi: 10.3969/j.issn.1007-2993.2022.02.010

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The management and design of underground pipe network lead to increasing requirements for 3D visualization. Skyline is a 3D visualization software supporting multiple data formats and convenient for secondary development. Based on Skyline, a method of sorting out the pipe point data for a large number of 3D pipeline automatic modeling is summarized. This method can greatly improve the work efficiency in practical projects that do not require high visualization precision, and can achieve the effect of shortening the construction period and saving costs.

Application of a New Multi-functional Frame Shed Tunnel

Xing Qian

2022, 36(2): 145-150. doi: 10.3969/j.issn.1007-2993.2022.02.011

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In order to optimize the structural design of mountain side road in mountainous towns and solve the problem of support design of excavated subgrade slope affected by mountain terrain, an anti-slide shed tunnel scheme with double row anti-slide piles and building frame structure is proposed. According to the application of specific engineering projects, the stress characteristics of the shed tunnel was analyzed, and the techniques of the shed tunnel structure and the traditional subgrade retaining structure were compared. The structural calculation and construction process simulation were discussed. The research shows that the shed tunnel structure has strong lateral stiffness, and each beam and column structure could bear force as a whole. The construction safety could be achieved because of top-down method, and new scheme for the development and utilization of urban public space are provided.

Comparative Study on Application of Chinese and Foreign Codes in Port Engineering Survey

Chen Zhixin, Peng Manhua, Zhang Haishun, Huang Chengzhi

2022, 36(2): 151-155. doi: 10.3969/j.issn.1007-2993.2022.02.012

[Abstract](140) [FullText HTML] (55) [PDF 464KB](26)

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From the perspective of port engineering project survey, a comparative study of Chinese, European and American codes was conducted, including survey workload, drilling and sampling, geotechnical classification, SPT, CPT, VST, strength parameter selection and calculation of vertical compressive bearing capacity of single pile. In these codes, drilling and sampling, CPT, VST are similar, but there are differences in workload, geotechnical classification, application of SPT results, selection of strength parameters and calculation of vertical compressive bearing capacity of single pile. The research results could be used as reference.

Measurement Method of Building Facade Based on Three-Dimensional Laser Scanner and Total Station Technology

Yao Peijun, Yin Yanyun

2022, 36(2): 156-159. doi: 10.3969/j.issn.1007-2993.2022.02.013

[Abstract](163) [FullText HTML] (53) [PDF 563KB](24)

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The traditional building facade measurement with total station has the disadvantage of low efficiency. With the development of technology, 3D laser scanning technology is widely used in building facade measurement. Aiming at the problem of scanner dead angle, a method of fixed-point supplementary survey by using total station free prism measurement technology is proposed, and ground three-dimensional laser scanner combined with total station is provided to quickly and efficiently complete the building facade drawing. Combined with the engineering practice, the problems that should be paid attention to in the process of field work and interior drawing are summarized.

Practiceand Analysis of Deep Foundation Pit in Soft Soil Area and Complex Environment

Wang Haicheng, Liu Xiuzhen, Zhang Long

2022, 36(2): 160-164. doi: 10.3969/j.issn.1007-2993.2022.02.014

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Taking a soft soil foundation pit project in a complex environment in Wuhan as an example, the key points, difficulties and countermeasures of the deep soft soil foundation pit design is introduced. The project is close to residential areas, municipal roads and viaducts. There is about 8～10 m deep soft soil on the side wall and base of the foundation pit. Through the scheme comparison, the support mode of cast-in-place pile + two-layer reinforced concrete internal support + triaxial mixing pile water stop is finally adopted. For one side of the viaduct with strict deformation requirements, targeted protection measures of adding passive area reinforcement are adopted to reduce the impact of foundation pit excavation. The monitoring data of the whole excavation process of the foundation pit show that the deformation of the reinforcement side of the passive area is about 27.2% less than that of other parts, which verifies the rationality of the support scheme and protection measures, and has reference significance for similar projects.

Study on the Flexural Resistance of Artificial Frozen Soil in Ningbo Area

Liu Huaji

2022, 36(2): 165-168. doi: 10.3969/j.issn.1007-2993.2022.02.015

[Abstract](109) [FullText HTML] (44) [PDF 747KB](22)

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Based on the Jintang undersea tunnel project in Ningbo area, to study the laws and characteristics of the flexural strength of artificial frozen soil, the flexural strength tests of silty soil and silty clay in the tunnel were carried out under different temperatures and water content. The results show that the flexure strength of silty soil and silty clay increases with the decrease of freezing temperature, and the flexure strength of frozen soil is obviously affected by freezing temperature. Different water content has a certain effect on the flexural strength of silt and silty clay. The flexural strength of silty soil samples reaches maximum when the water content is 30%. When the water content is 34%, the flexural strength of silty clay is the highest. When the soil moisture content exceeds the optimal saturated moisture content, the flexural strength of frozen soil decreases. The experimental results can provide scientific guidance for the design and construction of freezing method of Jintang submarine tunnel.

Comparative Test Research on Temperature Shrinkage Performance of Modified Soil in Yellow River Flood Field

Wang Zhe, Zhang Lei, Wang Wei, Sun Zhaoyun, Xiang Guowei, Hu Guiling

2022, 36(2): 169-172. doi: 10.3969/j.issn.1007-2993.2022.02.016

[Abstract](139) [FullText HTML] (53) [PDF 528KB](29)

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Yellow River flood field of Shandong Province is a seasonally frozen soil area, and it is easy to crack when the temperature difference between day and night is large, which affects the integrity and continuity of the road surface. The soil in the yellow river flood field has poor particle gradation and low strength, which needs to be modified. In this study, the temperature shrinkage properties of three types of soil were compared, and results showed that cement and asphalt powder had an inhibitory effect on the temperature shrinkage and cracking of soil. Moreover, the temperature shrinkage coefficients were arranged in the following order: asphalt powder modified soil <cement modified soil < plain soil.

2022 Vol. 36, No. 2