岩土工程技术

Defects and Proposals of Soil Microstructure Tests

Zhao Heng, Li Mingjun

2020, 34(1): 1-6,17. doi: 10.3969/j.issn.1007-2993.2020.01.001

[Abstract](80) [PDF 3023KB](12)

Abstract:
The history and present application of soil microstructure tests are reviewed. Focusing on currently main soil microstructure test methods, the key techniques and theories are introduced, and the scope of application, as well as the pros and cons are pointed out separately. The deficiencies in parameter extraction, dynamic observation and structure parameters are proposed, and some proposals are submitted.

Semi-automatic Detection of Rock Mass Discontinuity Trace Based on Image Processing

Zhan Wei, Zhang Yangsong

2020, 34(1): 7-12,42. doi: 10.3969/j.issn.1007-2993.2020.01.002

[Abstract](57) [PDF 29323KB](9)

Abstract:
A semi-automatic detection method of rock mass discontinuity trace based on image processing was presented.The basic ideas are as following:A small number of main crack control points which are difficult to identify are manually designated in the image,and then the image is divided into two parts,and edge detection is carried out respectively.Two segmented line pictures including discontinuity trace and fake edge are obtained.According to the principle of distance and angle,the segmented lines in the two images are connected iteratively.Finally,the results are superposed to get the complete fissure trace detection results.This method could reduce the interference between the primary and secondary fissures by detecting them separately,and ensure the integrity and correctness of the identification of the primary and secondary fissures with higher accuracy.

Application Conditions of Total Station Free Station Method in Building Foundation Pit Monitoring

Liu Hongchen, Sun Yuanping, Chen Lei

2020, 34(1): 13-17. doi: 10.3969/j.issn.1007-2993.2020.01.003

[Abstract](89) [PDF 10518KB](14)

Abstract:
There are two characteristics of free station method.Firstly it can overcome the restriction of visual condition in complex construction situation;secondly it is easy to obtain high observation accuracy.It is widely used in the deformation monitoring of horizontal displacement of deep foundation pits in cities.According to the principle of survey adjustment,the affecting factors of the measurement accuracy of free station method are deduced,and the influencing law of various factors on measurement accuracy is proposed.The application conditions of satisfying different accuracy requirements in the horizontal displacement monitoring of foundation pits are also summarized.The conclusions are of practical significance for the deformation monitoring of foundation pits and other similar projects.

Water Inflow Calculation of Foundation Pit under the Condition of Bottom-type Waterproof Curtain

Lv Binquan, Feng Xiaola, Cai Jiaojiao, Xiong Zonghai

2020, 34(1): 18-23. doi: 10.3969/j.issn.1007-2993.2020.01.004

[Abstract](104) [PDF 1977KB](25)

Abstract:
The water inflow calculation of foundation pit under the condition of bottom-type waterproof curtain is a technical problem to be solved because of the existence of leakage point.Aiming at the uncertainty of groundwater seepage in bottom-falling foundation pit,the hydrogeological model for dewatering of partially penetrating wells of bottom-type foundation pit in artesian aquifer is established.Based on the Theis theory of unsteady flow of partially penetrating wells and the mirror method,the calculation formula of equivalent permeability coefficient is deduced,and the leakage coefficient method is proposed to evaluate the effect of waterproof curtain and to calculate the water inflow of foundation pit.Finally,taking a deep foundation pit dewatering project in Wuhan as an example,the water inflow of the foundation pit is calculated by using the leakage coefficient method,and compared with the measured results and the calculation results of the traditional method.The comparison results show that the calculation error of the leakage coefficient method is slight,and the calculation process is simple.The research results can be used to guide engineering design,and have certain practical application value.

Uniformity Evaluation of Compacted Fill Foundation with Large Thickness in Yan'an New District

Zhang Ruisong, Tang Hui, Gao Jianzhong

2020, 34(1): 24-26,52. doi: 10.3969/j.issn.1007-2993.2020.01.005

[Abstract](128) [PDF 862KB](19)

Abstract:
Due to the particularity of the formation process of large-thickness compacted fill in Yan'an New Area,there is no specific evaluation basis and criterion for the uniformity evaluation of its foundation in current codes.On the basis of the engineering properties of compacted fill and the influencing factors of differential settlement, a concept of differential settlement sensitivity of compacted fill foundation is proposed innovatively,and a concrete method to determine the uniformity of compacted fill foundation is introduced,which is convenient to evaluate the uniformity.It provides a basis for general layout of buildings,foundation treatment and foundation design.The non-uniform foundation with large thickness compacted fill should be treated pertinently,and necessary structural measures should also be carried out.Settlement observation of buildings should be strengthened for thorough long-term study.

Design and Construction of Dynamic Compaction Foundation Treatment in a Pakistan Project

Zhou Junhong

2020, 34(1): 27-32,59. doi: 10.3969/j.issn.1007-2993.2020.01.006

[Abstract](76) [PDF 3369KB](14)

Abstract:
Combining with a large-span factory building project in Pakistan,the design and construction technology of dynamic compaction foundation treatment in this project are introduced.After dynamic compaction,the foundation is tested by static load test and standard penetration test,which proves that dynamic compaction technology can meet the requirements of structural design very well,and create good economic and social benefits.Valuable experience obtained in this project could be further applied in engineering with similar geological conditions in this area.

Back Analysis of Plane Sliding Failure of Rock Slope Aiming at Failure Probability

Sun Lichuan, Zhao Zaili, Chen Lipu

2020, 34(1): 33-38. doi: 10.3969/j.issn.1007-2993.2020.01.007

[Abstract](49) [PDF 6542KB](8)

Abstract:
By combining reliability theory with back analysis method,the plane sliding failure of rock slope was analyzed.The back calculation method aiming at stability coefficient and failure probability was discussed,and the calculation process of the plane sliding failure was expounded.According to the limit state function of plane sliding of rock slope with no posterior edge tension crack,Monte Carlo method was used to analyze the plane sliding failure of foundation pit slope in a nuclear power project.The shortcomings in the analysis of the normal values based on the stability coefficient was pointed out,and the influence of the variable coefficient,the truncation position,and the correlation coefficient on the calculation results was discussed.It is believed that the variation coefficient and correlation coefficient of the shear strength index have little effect on the back calculation results,and the truncation position could meet the requirements in accordance with the “3σ” principle and the setting method of the empirical range of the variation coefficient.

Influence of Temperature Change on Temperature Effect of Steel Shotcrete for Deep Excaration

Lu Shanjia

2020, 34(1): 39-42. doi: 10.3969/j.issn.1007-2993.2020.01.008

[Abstract](52) [PDF 3424KB](13)

Abstract:
In the foundation pit enclosure engineering,a large number of internal support structure systems are used,and the steel shotcrete is the most widely used in the support system.Steel shotcrete is a metal material,and the influence of temperature change on the support structure cannot be ignored.Based on the basic principles of elastic thermodynamics,the thermal stress formula of the hollow cylinder is deduced,and the lateral horizontal displacement of the surrounding structure is considered.The influence of temperature change on the axial force of the steel shotcrete is analyzed quantitatively,and the calculation formula is verified through the measured axial force value and numerical solution.The results show that the analytical solution is larger than the numerical solution,and larger than the measured value,which is conservative.This calculation formula with minor error could be used as a safety reserve for engineering design,which is a reference in the future design.

Current Research and Prospect on Physical and Mechanical Properties of Red Clay in China

Deng Shaoyun

2020, 34(1): 43-47. doi: 10.3969/j.issn.1007-2993.2020.01.009

[Abstract](57) [PDF 1035KB](15)

Abstract:
Current research of red clay is summarized and commented by literature review.The physical and mechanical properties,as well as the performance improvement of red clay are summarized.The difference in the physical and mechanical properties of red clay is due to the individual differences in microstructure.The difficulty in improving the performance of red clay lies in the water sensitivity and heat sensitivity,and the key to improving the performance is to control its moisture content.The research deficiency is that the general adoptability theory and the knowledge system are not established,and the improvement methods and technical exploration should be strengthened.Research on the mechanism of physical-chemical-biological coupling of red clay performance improvement,and the development as well as the application of composite technology are prospected.

Single Pile Bearing Capacity of High Pressure Rotating Jet Grouting Pile

Wang Bo, Xing Xiaoying

2020, 34(1): 48-52. doi: 10.3969/j.issn.1007-2993.2020.01.010

[Abstract](158) [PDF 7799KB](23)

Abstract:
Jet grouting started at Japan in 1968,and was introduced to China to be studied in 1970s.At present,high pressure rotating jet grouting is the most widely used method with the most mature technology.The quality of rotating jet grouting and the bearing capacity of single pile are studied and analyzed,which provides design reference for the application of ground and foundation engineering,hydro engineering,water sealing and reinforcement engineering.Three test sites were selected in a built-up community in Yan'an city,Shaanxi Province,and the piles were made according to different construction techniques of rotating jet grouting.Through detection of pile body integrality and test of single pile bearing capacity,the quality of rotating jet grouting and the bearing capacity of single pile were analyzed.

Experimental Study on Development of Dynamic Pore Water Pressure in Saturated Gravelly Soil

Yang Zhe, Zhang Ting, Wang Zhanbin, He Xiaomin, Xiao Zhiwei

2020, 34(1): 53-59. doi: 10.3969/j.issn.1007-2993.2020.01.011

[Abstract](41) [PDF 1405KB](4)

Abstract:
The dynamic triaxial tests have been conducted to study the effect of gravel content and cyclic frequency on the development of dynamic pore water pressure in gravelly soil by using the GDS apparatus.It could be concluded that the pore pressure increases with the increasing gravel content or cyclic frequency.Several stress-based pore pressure models are applied to describing the pore water pressure development,and the adopted parameters are given to get a good performance.There is a strain-based pore pressure model revised with the parameters of gravel contents and cyclic frequencies to express it and the parameters have been given.

Experimental Reasearch on Anti-floating Anchor of Mudstone Stratum

Luo Yunhai, Liu Jun

2020, 34(1): 60-63. doi: 10.3969/j.issn.1007-2993.2020.01.012

[Abstract](95) [PDF 1007KB](20)

Abstract:
In order to study the load transfer mechanism and the bearing capacity of the fully bonded anti floating anchor in the mudstone stratum,the field test and the axial force of the anchor rod were carried out for the anti-floating anchor in the mudstone stratum of Ankang area,Shaanxi Province.The test results show that the axial force distribution of the anchor body is not uniform, and it gradually decreases from the top of the bolt to the bottom,and it will not be stressed after it exceeds a certain length.At the same time,the bond stress distribution along the whole length of the anchorage end is also uneven when the bolt is stressed,and there is a limit to the distribution length of the effective bond stress.The effective anchorage length,the standard value of ultimate bond strength for the anti-floating anchor rod with a diameter of 150 mm,and the influence coefficient of 8 m long anchorage segment on the bond strength were determined in the mudstone stratum in this area,which provided the basis for the design of anti-floating anchor in similar mudstone stratum.

2020 Vol. 34, No. 1