Study On Mechanical Properties Of Plateau Special Gravel Soil In Bangpu Mine In Tibet With Large Scale Shear Test

In recent years, along with our country to all sorts of infrastructure investment is increasing continuously, roads, bridges, mine, water conservancy and other civil engineering construction entered the great development period.All kinds of engineering slope, especially large-scale mine slope instability due to shear failure.Accurate grasp of the strength characteristics is the key to the rock mass stability analysis and the engineering design., it plays an extremely important role in the security rationality and economy of the construction. In the various methods of geotechnical strength tests, Direct shear test is most widely used.Tibet Bangpu mine is located in Maizhokunggar County the west of Lhasa. Mining area terrain ups and downs. Quaternary loose natural deposits development.the gravel soil cover layer thicker bun not uniform. It prone to shear failure and causes the occurrence of landslides and other geological disasters. The elevation of Bangpu mine is between4640m to5264m.It perennial withstand the seasonal cycle of freezing and thawing. Freezing and thawing will change the structure of links and arrangement between soil particles,thus changing the mechanical properties of the gravel soil, and soil particles rearranges, that forms large particles, small coupling force plateau special gravel soil. A variety of physical and mechanical properties of gravelly soil in the high altitude, high stress and seasonal freezing and thawing with ordinary gravel soil showed a greater difference. Only grasping the physical and mechanical properties of plateau gravel soil accurately that the accurate parameters can be provided to slope stability calculation and the mine engineering design. In the slope control projects in the plateau seasonal frozen soil areas it is necessary to make research on the physical and mechanical properties of these special gravel soil.Based on the limitations of the test apparatus, the conventional direct shear tests must remove large particles of gravel, it can only test the mechanics parameters of small particles of gravel and soil. not a true reflection of the mechanical characteristics of gravel soil. The conventional direct shear test has defects that the normal stress load unsteadily,it has friction between the shear box wall and the soil sample, shear rate unstably fluctuate, effective shear area is decreasing and so on. In this paper We use plateau gravel soil in Tibet Bangpu mine as the research object,the main research on indoor large-scale shear test and comparatively study the results of the small shear test, described in detail the principles, characteristics and test methods of large-scale shear test, explore the various factors on the shear strength of soil samples during the shear process. Through the research of the large-scale shear test the analysis of the special plateau gravel soil strength theory the numerical simulation research of the distribution and trends of the the shear stress shear strain and normal on the stress shear plane based on the finite difference method FLAC3D software and such ways can detailly studied the plateau special gravel soil mechanical properties. Research in this topic has certain reference value in construction and prevention of geological disasters in the region distribution of Plateau gravel soil.The main contents and results obtained are as follows:1.This article describes the development process of the direct shear apparatus development status and structure and working principle. Summarizes the advantages disadvantages and applicable conditionsof all kinds of direct shear apparatus. Traditional direct shear apparatus mainly exist in the following problems:stress and strain unevenly distributed, horizontal shear rate unstably fluctuate, vertical pressure system unstably load, the actual shear area is decreasing, it has friction between the shear box wall and the soil sample.2.Described in detail the working principles, structure and applicable conditions of new large-scale multi-purpose shear apparatus.When we designed the ahear box of the large-scale direct shear apparatus a shear seam between the top sheae and the next shear box was made inorder to reduce the role of the constraints of rigid shear box wall on coarse particles of the gravelly soil. By the vertical loading system of hydraulic jacks and vertical load sensors to ensure the stability of the vertical loading process. Be able to run repeatedly push and pull shear test. We use mobile vertical loading of the power transmission system to ensure that the vertical load will not eccentric during the test process. We use the shear load sensors, precision screw, automatic frequency deceleration system and such horizontal loading force transmission system inorder to ensure that We can strictly and precisely control the shear displacement. To ensure the stability of the shear rate of soil in the test process. In addition, this large-scale direct shear apparatus also has structural integrity, security, broader scope of application, overall removable feature uniform shear deformation accurate measurement data, and such advantages.3.For the first time indoor large-scale direct shear test is applied to the research on mechanics properties of special plateau gravel soil.Through the instrument testing and large shear performance test results are shown, the performance of new large-scale multi-purpose shear apparatus is stable in in the plateau gravel soil test. The test data are reliable and can be further applied to all kinds of plateau gravel soil-related scientific research, production projects.4.Through the analysis of the large-scale shear test of shear properties by finite difference software FLAC3D.We can analyse the influence on the result of the test from the shear box sidewall friction. Simulate soil sample shearing process. Get the distribution of shear stress, shear strain and normal stress in the shear plane and their trend in shearing process.5. The paper studies the shear strength properties of plateau gravel soils, contrast research on test results of original state gravel soils and the test results of remolded soil. Contrast reveals structural strength properties of plateau gravel soils through the test results; Verify the applicability, reliability and accuracy of plateau gravel soils in large-scale shear test through the test results. Acquire the basic law of moisture content, lime content, shear rate, wide aspect ratio of shear box and such factors affect the mechanical properties of gravel soils.