岩土工程技术

Precision Analysis and Applications of Trigonometric Leveling with Total Station

Yan Boduo, Zhang Lichen, Sun Jiuchang, Wang Yuping, Sun Huichao

2021, 35(6): 351-355, 360. doi: 10.3969/j.issn.1007-2993.2021.06.001

[Abstract](299) [FullText HTML] (83) [PDF 703KB](65)

Abstract:
The basic principle and accuracy of total station trigonometric leveling method are discussed by introducing the measurement methods such as reciprocal leveling, intermediate station observation and one-way double targets (prism) trigonometric leveling. By analyzing the relevant problems in practical application, it is considered that the main factors affecting the height difference measurement accuracy of the above methods are the size of zenith distance and its observation error, the error of atmospheric vertical refraction coefficient measurement. The measurement error of instrument height and target height is also one of the influencing factors, and the influence of ranging error is slight. Total station trigonometric leveling method can be widely used in urban and engineering surveying.

The Characteristics of Geostress and Its Geological Engineering Significance of Underground Water-sealed Cavern

Li Yepeng, Li Qiang, Cai Wujun, Luo Chonghong, Hu Huang

2021, 35(6): 356-360. doi: 10.3969/j.issn.1007-2993.2021.06.002

[Abstract](156) [FullText HTML] (37) [PDF 1159KB](35)

Abstract:
The geostress characteristics of one underground water-sealed cavern was investigated based on geostress data collected by hydraulic fracturing, and the axis direction of the cavern was testified by numerical simulation results. The results shows that: (1) the direction of regional maximum principal stress is NWW, and the regional maximum principal stress shows a tendency deflecting to the east as the depth increases; (2) the current stress field is one of the typical tectonic stress field, which is dominated by reverse fault stress mechanism; (3) both maximum and minimum horizontal principal stress show a linear rise with depth; (4) the coefficient of horizontal pressure lies within the envelope line of Chinese Mainland, showing the trait of dispersion in the shallow and convergence in the deep; (5) with the maximum horizontal principal stress being the maximum principal stress and the vertical principal stress being the minimum principal stress, the minimum horizontal principal stress is the intermediate principal stress; (6) the axis direction of the cavern is recommended as N55°W considering the influence of the maximum horizontal principal stress and preferred structural plane.

MATLAB GUI Design Based on Rapid Judgment of Shear Failure State of Soil

Li Qian, Li Jiaojiao, Chen Erzhong

2021, 35(6): 361-364, 372. doi: 10.3969/j.issn.1007-2993.2021.06.003

[Abstract](154) [FullText HTML] (44) [PDF 1058KB](43)

Abstract:
The shear failure of soil is the main form of soil failure. It is of great engineering application value to judge the shear failure of soil quickly based on the mechanical characteristics of soil. Starting from the engineering background, based on the Mohr-Coulomb strength theory, MATLAB GUI graphical user interface design method was applied and the soil shear calculation and the damage judgment system were developed. If direct shear test data of specific soil are input in the system, cohesive force and internal friction angle could be obtained quickly by fitting. At the same time, based on comparative laws of the maximum and minimum principal stress and internal friction angle, whether the soil shear failure occurred or not could be determined quickly. The reliability of the calculation system is proved by direct shear experiment. The results show that the system is fast, accurate and effective, and can be used to calculate the shear strength of soil and judge the failure state quickly in engineering practice.

Ground Treatment Optimization Design of Thick Red Clay Fill in a Project

Xue Xiang, Hou Dongli, Ma Bingwu

2021, 35(6): 365-372. doi: 10.3969/j.issn.1007-2993.2021.06.004

[Abstract](250) [FullText HTML] (168) [PDF 1087KB](77)

Abstract:
In recent years, more and more projects are carried out on the platform after the formation of the site. Engineering problems often occur due to improper design and construction. Combined with the actual situation and construction conditions of the project, after comprehensive comparative study and optimization of common foundation treatment methods, construction technology, cost and construction period, the treatment methods such as replacement of sheep gangue and water stabilized materials were finally adopted to solve the problem of thick red clay plain fill treatment of a project. In the design of replacement treatment, e-p curve method and e-lgp curve method considering stress history were adopted. At the same time, combined with the actual working conditions of the project, the foundation deformation after replacement treatment was estimated based on triaxial K₀ consolidation deformation curve method, which solves the difficult problems of settlement and post construction settlement estimation under complex conditions such as consolidation degree estimation of under-consolidated soil, over-consolidated soil and unsaturated soil. It provides theoretical and empirical support for the design scheme. After the successful implementation of the design scheme, the direct cost of more than 3 million Yuan was saved and the construction period was shortened. The design idea and deformation estimation method of red clay plain fill treatment have strong practical reference value.

Technology Application of Borehole Magnetic Gradient Method on Deeply Buried Ferromagnetic Pipeline Detection

Liang Xiaolong, Gu Xiaoshuang, Jiang Tiejun, Wang Xiaowei

2021, 35(6): 373-376. doi: 10.3969/j.issn.1007-2993.2021.06.005

[Abstract](115) [FullText HTML] (55) [PDF 663KB](27)

Abstract:
It is difficult to accurately detect the plane position and buried depth of deeply buried ferromagnetic pipelines by conventional geophysical methods. The plane position and buried depth of the parallel pipelines across the river are detected by borehole magnetic gradient method and borehole penetration. The results showed that the magnetic curves at different positions from the pipeline presented different characteristics with the change in distance, which verified the effectiveness and accuracy of the borehole magnetic gradient method in detecting deeply buried ferromagnetic pipelines. However, other detection methods are needed to improve the detection efficiency. The magnetic anomaly response of pipelines with different diameters in the same detection position and the magnetic anomaly range of the instrument are analyzed, which provides reference for the rapid and accurate detection of ferromagnetic pipelines with different diameters.

Precision Analysis and Application of Multi-mode GNSS Rapid Mapping in Special Environments

Zhou Yukun, Duan Zhigang, Shi Guangyi, Hou Zhijun, Jin Ye

2021, 35(6): 377-381. doi: 10.3969/j.issn.1007-2993.2021.06.006

[Abstract](106) [FullText HTML] (49) [PDF 726KB](19)

Abstract:
Based on the engineering practice of a certain area, multi-mode global navigation satellite system (Global Navigation Satellite System, GNSS) rapid control and measurement of different constellation were conducted combined positioning analysis, and China's Beidou Navigation Satellite System could obtain position information quickly and accurate in a special environment. Based on the refined fusion technology of multi-mode GNSS-RTK and quasi-geoid, the efficiency of road surface corner measurement could be greatly improved. The accuracy and ergonomics of the vehicle-mounted GNSS-RTK topographic measurement are studied and evaluated in the flat area, and the key quality control points in implementation process is proposed. The costs of field surveying and mapping could be saved and the efficiency could be improved.

Study on Seismic Liquefaction Discrimination Method of Deep Silt in Dam Overburden

Yu Min, Chen Xiyang

2021, 35(6): 382-386. doi: 10.3969/j.issn.1007-2993.2021.06.007

[Abstract](761) [FullText HTML] (79) [PDF 818KB](37)

Abstract:
Liquefaction discrimination was conducted in deep silt of a dam overburden within the range of 19.50~31 m. According to the particle gradation of soil samples, the initial liquefaction discrimination was accomplished. For the soil samples that can be liquefied in the initial discrimination, the relative water content method was used for the second discrimination. Combined with the results of the dynamic triaxial liquefaction test, the seed method was used to verify the possibility of soil liquefaction. The result shows that the deep silt within the range of 19.50~31 m of dam overburden may be liquefied. The method and results can provide reference for the liquefaction discrimination in the similar engineering.

Optimization Analysis of Anti-Floating Anchor Design

Wang Hao, Liu Yingjun, Wang Shuang

2021, 35(6): 387-394, 399. doi: 10.3969/j.issn.1007-2993.2021.06.008

[Abstract](228) [FullText HTML] (180) [PDF 7102KB](102)

Abstract:
With the improvement of the utilization of underground space in urban construction, the anti-floating design of large-size and deep-buried foundations has become the focus of structural design. Anti-floating fortification level is an important parameter of anti-floating design. The influence factors and recent changes of anti-floating fortification level in Beijing area are analyzed according to the character of the current building and the current planning. The design and optimization methods of anti-floating anchor are summarized. The optimization design of anti-floating anchor by numerical analysis method is introduced in detail through engineering examples, which could provide reliable experience for similar projects.

Analysis of A New Grouting Method for Pipe Implanted Pile

Xu Jianhua, Zhu Bin, Yang Dongyuan, Lu Bingxuan, Xu Letian

2021, 35(6): 395-399. doi: 10.3969/j.issn.1007-2993.2021.06.009

[Abstract](166) [FullText HTML] (34) [PDF 870KB](54)

Abstract:
Advantages and disadvantages of various pile foundation construction are analyzed, and the advantages and feasibility of a new grouting method for pipe implanted pile are proposed based on the successful case of grouting into pile and column in a certain integrated pile and column project. Based on basic principles of fluid mechanics, the rationality and feasibility of the new grouting method are demonstrated, and the operation mechanism and construction technology of the new grouting method are expounded. By virtue of the characteristics of pipe pile and the advantages of drilling machinery such as rotary excavator, this method can solve the problems of pipe pile foundation construction in hard rock stratum (especially in karst area), such as the difficulty in drilling holes and the large filling coefficient of concrete mortar. This method simplifies the pressed or hammer process in the pipe implanted pile method, and also enlarges the application scope of big pipe pile (over 1.30 m in diameter) in implanted pile. The implanted pipe pile is simple, economic, practical and environmental, and could provide basis for the popularization and application of pipe pile in hard rock, especially in karst areas in the future.

Influence of Adjacent Asymmetric Foundation Pit Excavation on the Existing Building and the Optimized Analysis

Zhu Chun, Ren Yakun, Tan Xin, Xu Peijun, Zhou Kang

2021, 35(6): 400-405, 410. doi: 10.3969/j.issn.1007-2993.2021.06.010

[Abstract](165) [FullText HTML] (57) [PDF 1643KB](65)

Abstract:
Based on the asymmetric excavation project adjacent to an existing shallow foundation building in Changsha, the proposed study used the finite difference numerical program to establish numerical models that considers the interaction between the structural foundation and the ground. Through the numerical simulation method, the influence of different excavation schemes on the ground deformation, the deformation and force of existing buildings has been analyzed. Numerical analysis results show that the existence of shallow foundation building affects the settlement curve of the ground surface caused by excavations. The asymmetric excavation sequence has an important influence on ground deformation and structural forces of adjacent existing buildings. Taking into account the construction conditions and the impact of excavations on the deformation of the ground and buildings, priority should be given to the excavation of the foundation pit on the far side of the existing building, and then the foundation pit excavation on the near side.

Study on the Influence of Burning Temperature on Organic Matter Content Test

Cheng Yun, Yang Weiqing, Zhang Wei, Li Yuhong, Shen Jiaren

2021, 35(6): 406-410. doi: 10.3969/j.issn.1007-2993.2021.06.011

[Abstract](201) [FullText HTML] (30) [PDF 813KB](42)

Abstract:
Aiming at the Dian Lake sedimentary peat soil, the ignition loss method was used to test the organic matter content. The variation characteristics and internal mechanism of the ignition loss, specific gravity and color of the peat soil at different burning temperatures (75℃, 85℃, 105℃, 200℃, 250℃, 300℃, 350℃, 400℃, 550℃, 650℃, 950℃) were studied. The results show that the ignition loss gradually increases with the rise of temperature and finally stabilizes. According to the variation of ignition loss, it can be divided into four development stages: basically unchanged, rapid growth, slow growth and basically stable stage. The specific gravity of soil increases with the rise of temperature. The color of soil changed from black to dark gray, brown to brick red, reflecting the decomposition loss of organic matter and mineral transformation process at different burning temperatures. On the basis of experimental research, it is suggested that the reasonable burning temperature should be 400℃ to 550℃ to test organic matter content for the Dian Lake peat soil or the same type of soil. The results have certain guiding significance for test of organic matter content and determination of peat soil.

Engineering Geological Characteristics and Cause Analysis of Grayish-white Clay in Beihai

Rong Yanli, Tao Xuguang

2021, 35(6): 411-415. doi: 10.3969/j.issn.1007-2993.2021.06.012

[Abstract](80) [FullText HTML] (23) [PDF 726KB](32)

Abstract:
A very stiff grayish-white clay layer containing quartz particles is widely distributed within the depth of 40 m below seabed in Beihai, Guangxi. The soil has low water content, high density, small specific gravity, small void ratio, low compressibility, high shear strength in natural state, and very weak permeability. It has characteristics of swelling due to water absorption and softening, and cracks due to water loss and shrinkage, which will quickly disintegrate to the peptized state after immersion in water again. Mathematical statistical analysis was conducted on the indoor physical and mechanical test results of 200 grayish-white clay samples from 49 boreholes in the sea area. The engineering geological characteristics of the grayish-white clay layer in Beihai was comprehensively analyzed. XRD mineral composition analysis, carbonate content, soil corrosion, 950°C loss on ignition were carried out selectively. The internal factors are evaluated combined with Guangxi geological data and previous research results on Beihai clay, from the formation of soil and material composition, which provide a scientific basis for the rational evaluation of the engineering geological properties of this type of soil, and also provide reference for its development, utilization and engineering management.

Correlation Between Pressuremeter Test and Standard Penetration Test on Sand Deformation Modulus

Shen Zhen, Qu Pengfei, Meng Kejing, Zhao Zhanyu

2021, 35(6): 416-419. doi: 10.3969/j.issn.1007-2993.2021.06.013

[Abstract](162) [FullText HTML] (66) [PDF 658KB](61)

Abstract:
To determine the deformation modulus of sand conveniently and accurately, based on the special geological survey of DN2200 Water Pipeline Reinforcement in Shuiyuanjiuchang, the blow count of standard penetration test and deformation modulus of pressuremeter test were statistically compared and analyzed, and the function relation between standard penetration blow count and deformation modulus was established. Considering the influence of different particle sizes of sand, fine sand and medium coarse sand were statistically analyzed respectively, and the function relationships were established. The results show that there is a high positive correlation between the blow count and deformation modulus of fine sand. Through the relationship, the deformation modulus index parameters of sandy soil can be conveniently calculated by using the standard penetration test, so as to meet the practical needs of engineering.

2021 Vol. 35, No. 6