岩土工程技术

Development of FLAC3D Software Computing Platform Based on Cloud Computing Technology

Feng Lei, Chen Pingzhi, Chu Weijiang

2019, 33(6): 311-313,352. doi: 10.3969/j.issn.1007-2993.2019.06.001

[Abstract](92) [PDF 1189KB](16)

Abstract:
In order to solve the problem that FLAC3D software is slow in calculation and occupies too much computing resources,the FLAC3D software computing platform is developed based on the Flask framework and D3.js framework. The platform is fully functional and includes auxiliary modules such as billing module,file sharing module and security module. Users only need to input the computing resources and storage resources to automatically create a virtual server,and use the pre-installed FLAC3D software in the server. The platform greatly reduces the computational time of the FLAC3D software,and the calculation rate is particularly significant under multiple operating conditions. In addition,the platform implements the generation of cloud servers and remote online running software through the Internet in a cloud service mode,so that the hardware configuration is freed from geographical restrictions.

Tooth Arrangement Design of φ800 mm DTH Hammer Bit and Theoretical Discussion

Peng Wei, He Longfei

2019, 33(6): 314-317,340. doi: 10.3969/j.issn.1007-2993.2019.06.002

[Abstract](56) [PDF 2572KB](10)

Abstract:
In the drilling of DTH hammer with large diameter, the plan arrangement of cylindrical tooth and the choice of tooth type are the decisive factors affecting the drilling efficiency, the service life of drill bit and the quality of hole drilling. At present, developed design ideas have not yet been presented in this field at home and abroad. Based on the Equal Working Condition Tooth Arrangement Theory, through the rock breaking mechanism of cylindrical teeth, the effect of adjacent cylindrical teeth on rock breaking is discussed. Thus, the optimal tooth spacing, the optimal tooth position and reasonable number of teeth are determined. Impact energy is used to determine the number of teeth, and the selection methods are summarized, including cylindrical tooth, alloy materials of cylindrical tooth, etc. Two different designs of φ800 mm DTH hammer bit are proposed for different strata of soft rock and hard rock.

Stability Analysis and Prevention Measures of Ancient Landslide Accumulation Body of a Highway

Wang Lijun, Zheng Zhilong, Zhong Junhui

2019, 33(6): 318-322. doi: 10.3969/j.issn.1007-2993.2019.06.003

[Abstract](42) [PDF 9403KB](15)

Abstract:
A highway route in Guizhou is located on an ancient landslide deposit. There is a village on the platform of the landslide deposit. The amount of the slide body reaches 996000 m³. Most of the route has been completed in the way of bridge mode, and the slope needs to be excavated locally. During the construction of the road, the original balance conditions of the landslide is changed, which may jeopardize the safety of construction and operation. Based on the identification of the geological environment conditions, geological structure and deformation sliding mechanism of the landslide, a geological structure model is established. Its stability is analyzed by using the simplified Bishop method, and the prevention and control plans are suggested.

Application of Geo-Slope/W in Stability Analysis of a Mountain Construction Site

Wang Xiaobo, Duan Chuangui, Li Liangjie

2019, 33(6): 323-327. doi: 10.3969/j.issn.1007-2993.2019.06.004

[Abstract](74) [PDF 2599KB](16)

Abstract:
In the construction of mountainous area,the stability of construction site is the premise of project construction. In a mountain architectural planning, limit equilibrium analysis of Geo-Slope/W is used to analyze and evaluate the field stability under the natural condition and the heavy rain condition. It provides guidance for the stability evaluation of similar construction sites,the slope protections,and the selections of building foundation form and foundation treatment scheme,and it also provides reference for similar projects.

Mechanism of Rigid Pile Composite Foundation Influenced by Marine Soft Soil

Lin Zhiqiang

2019, 33(6): 328-333,371. doi: 10.3969/j.issn.1007-2993.2019.06.005

[Abstract](36) [PDF 1546KB](7)

Abstract:
Rigid pile composite foundation is greatly influenced by soft marine clay.But it is neglected by many engineers due to the unclear influence mechanism,which causes serious engineering accidents.Based on the comprehensive analysis and research results of typical construction examples in recent years,the characteristics of consolidation settlement,structure and low-permeability of marine soft soil and the mechanism of rigid pile composite foundation influenced by the soft marine clay were researched.In combined with computational analysis of several construction examples and its field test data,the rationality of research conclusions is verified.The results prove that rigid pile composite foundation should not be directly used in marine soft soil.It is necessary to fully consider the influence of consolidation settlement,high sensitivity,compacting disturbance,and clear treatment effect after the field test construction.There are two different failure mode of composite foundation caused by consolidation settlement due to the different bearing stratum of the pile tips.If pile tips are suspended on the soft soil layer,it causes significant penetrating deformation of pile tips and plastic deformation of the soft soils among piles;if pile tips are embed into the harder soil layer,pile bodies would firstly be destroyed by strength failure and then soft soils among piles would be destroyed.The settlement soils of composite foundation do not converge for a long time and even accelerate subsidence in macroscopically.Because of the disturbance of construction,the marine soft soil pushed by foundation piles could be regarded as fluid.According to the property that the fluid always flows to the path with the least resistance,there are three different soil discharge paths: soil discharge upward along the plastic zone at the pile side,soil discharge upward along the whole site,and soil discharge laterally along the weak area around the site.Since the bearing capacity of marine soft soil foundation between piles is very low,sufficient soil arch height should be ensured under the action of upper load.Finally,the countermeasures and suggestions in the engineering practice of rigid pile composite foundation in marine soft soil area are proposed.

Application of Static Pressure Underpinned Piles in Foundation Reinforcement of a Collapsible Loess Site

Zhang Xiaohui, Liu Haiting, He Miao, Wu Qi, Wei Guoliang

2019, 33(6): 334-340. doi: 10.3969/j.issn.1007-2993.2019.06.006

[Abstract](38) [PDF 4809KB](11)

Abstract:
Focusing on the problem of large settlement of a test building, the main reasons for the foundation settlement and differential settlement are obtained through investigation of crack distribution and analysis of the observed settlement variation. The surface water seepage, the obvious rising groundwater level and the foundation settlement of adjacent buildings are the main reasons. In order to solve the problem of differential settlement of foundation caused by uneven collapsible deformation, a pit-type static pressure underpinned pile scheme was proposed to carry out the foundation reinforcement treatment, and the reinforcement design scheme and construction technology were introduced in detail. By comparing the settlement observation results before and after reinforcement, it shows that the pit-type static pressure underpinned pile has better reinforcement effect, which can effectively restrain the uneven foundation settlement of the collapsible loess site, and accumulate regional experience for similar reinforcement projects.

Analytical Formula of Pile and Stress Influence Coefficient for File Foundation Standard

Liu Dahai

2019, 33(6): 341-346,360. doi: 10.3969/j.issn.1007-2993.2019.06.007

[Abstract](36) [PDF 1723KB](9)

Abstract:
In the Technical Code for Building Pile Foundations (JGJ 94—2008), the uniform distribution and the triangular distribution of pile side stress against depth were considered, and the uniform distribution of pile end stress affected by pile diameter was also taken into account. Meanwhile, the Geddes analytical formula was used in the pile side stress influence coefficient, and the formula (33) in the paper "Calculation Formula of Vertical Stress in Foundation Based on Mindlin Formula" published by Xu Zhiying in the fourth issue of Civil Engineering Journal in 1957 was used in the pile end stress influence coefficient. However, the square root property of √(z-L)²=|z-L|≠z-L was neglected in Xu’s formula (33), so this formula was only applicable to the case under the pile end (z>L). Therefore, the uniformly distributed stress at pile end affected by pile diameter was considered on the basis of the Mindlin stress solution of buried depth concentration force, and then the one-dimensional integral analytic general solution of pile end stress influence coefficient on pile axis was derived again. The solution function is discontinuous to variable z at the pile end (z=L), and the discontinuity point is a jump discontinuity point. Moreover, the calculation results of the general solution were compared and verified by the one-dimensional and two-dimensional numerical integral values, as well as the Standard’s tabulated values.

Division of Rock Mass Units in a Nuclear Power Project

Liao Huake

2019, 33(6): 347-352. doi: 10.3969/j.issn.1007-2993.2019.06.008

[Abstract](48) [PDF 3057KB](12)

Abstract:
With the increasing demand for green and clean energy in China and the rapid development of nuclear power industry, sedimentary rocks and softer rocks are used as the foundations for nuclear power plant sites. A nuclear power station with sedimentary rock foundation is analyzed as an example. Based on the data of the foundation rocks, including spatial distribution characteristics of lithology, the weathering degree, integrity of rock mass, physical and mechanical parameters of rock mass, etc., reasonable division of the engineering geological unit of the foundation rock mass is conducted through statistical induction. The problem in geological units division of sedimentary rock foundation for nuclear power plant is effectively solved. This study reveals the real engineering characteristics of foundation rock mass, and provides scientific basis for foundation design of nuclear power plant.

New Type of Composite Supporting System in Backfill Foundation Pit Engineering

Zhang Bo, Zhang Jiao, Chen Jinxiang

2019, 33(6): 353-357,366. doi: 10.3969/j.issn.1007-2993.2019.06.009

[Abstract](57) [PDF 2155KB](19)

Abstract:
Combined with the application a new type of composite supporting system in a deep excavation engineering in Beijing, the supporting form and structure features of the system are analyzed and introduced. Theoretical calculation, numerical simulation and field monitoring analysis of the support system are carried out. The result shows that the support system successfully solves the technical difficulties of deep foundation pit, such as deep artificial fill, small space and complicated surrounding environment. It can effectively control the deformation of the foundation pit, shorten the construction period, save the cost of the project, ensure the safe use of the foundation pit engineering, and provide an effective reference experience for similar projects.

Graded Waterproof Curtain Technology in Modification of a Dock

Li Yucan, Zhai Jianwei

2019, 33(6): 358-360. doi: 10.3969/j.issn.1007-2993.2019.06.010

[Abstract](50) [PDF 2174KB](12)

Abstract:
Application of graded waterproof curtain technology in riprap dams and coarse-grained strata under dynamic water pressure is introduced, and the principle, technology, construction method and waterproof effect are also presented. Through engineering examples, the filling technology of graded dry powder and the splitting grouting technology of third-sequence holes are introduced in detail. Graded waterproof curtain technology has been proved to be effective by engineering, which is suitable to be applied in practice under similar working conditions.

Influence of Mix Ratio on Shear Strength of Tabia

Wang Liwei, Fang Qi, Liu Penghui

2019, 33(6): 361-366. doi: 10.3969/j.issn.1007-2993.2019.06.011

[Abstract](60) [PDF 1305KB](15)

Abstract:
Nine groups of mix proportions of tabia are proposed by complete test design method with 2 factors and 3 levels, and compaction test of each group is carried out. Shear strength test blocks are made according to the maximum dry density and the corresponding optimum moisture content of each group, and maintained on standard conditions for 7 days and 28 days respectively for shear strength test. The shear strength index of cohesion and internal friction angle of each test group are obtained. The following conclusions are obtained through range analysis and trend analysis. The influence of sand in tabia with 7 days and 28 days on the internal friction angle is greater than the influence of clay; the influence of sand with 7 days on cohesion is greater than that of clay, while influence of sand with 28 days on cohesion is less than that of clay. The mix ratio of tabia that reached maximum internal friction angle is lime: clay: sand=1:4:5, and the mix ratio of tabia that reached maximum cohesion is lime: clay: sand =1:6:3. For 7 days, taking the vertical pressure of 196 kPa as critical value in magnitude, two kinds of mix proportions with maximum shear strength of tabia can be obtained respectively. The research results may provide reference for rational selection of mix proportion of tabia in engineering application.

UU Triaxial Test and FLAC3D Numerical Simulation of Thick Soft Soil in Wenzhou Area

Zhao Xin, Zhang Wenshuai

2019, 33(6): 367-371. doi: 10.3969/j.issn.1007-2993.2019.06.012

[Abstract](104) [PDF 2559KB](21)

Abstract:
The shear strength parameters obtained by the triaxial test are indispensable parameters for the geological survey of major projects. According to the geotechnical test method standard, the UU triaxial test was carried out on the saturated thick soft soil in Wenzhou, and the principal stress diffenrence-axial strain relationship curves, the shear strength envelope curves, as well as the shear strength parameters of the soil were obtained. There are a series of problems during the test, such as difficulty in preparation of the sample, low shearing efficiency and high requirements on the test conditions. Therefore, based on the results of UU triaxial test, FLAC3D numerical analysis software was used to carry out the numerical simulation test for UU triaxial test of thick soft soil. The results show that the variation tendency of the principal stress difference-axial strain curve and the shear strength envelope curve is basically consistent between the numerical simulation test and the laboratory test. Although the phenomenons of slightly higher cohesive force and slightly lower internal friction angle appears, they are all within the range of test error. The numerical simulation test can simulate the UU triaxial test of thick soft soil well, and obtain shear strength parameters, providing references for similar soils to obtain shear strength parameters through numerical simulation test.

2019 Vol. 33, No. 6