Study On Influence Mechanism Of Microstructure And Mineral Composition On The Strength Of Phosphorite

The mining of phosphate ore resources has gradually shifted from surface mining and shallow underground mining to deep underground mining.Due to the complexity of underground engineering the safety of personnel and equipment in mining process is becoming more and more serious.Taking the Wawu mining area in Xingshan County,Hubei Province as the engineering background,this paper makes an in-depth analysis and discussion on the phosphorous block rock and the surrounding rock.The mechanism of the influence of the microstructure of phosphate rock on rock strength is analyzed based on the mechanical and microscopic experiments,and the correlation between the rock strength and mineral composition of roadway surrounding rock is studied.This provides theoretical basis and guidance for the safe mining of phosphate rock in the future.In order to study the influence mechanism of microstructure and mineral composition on the strength of phosphate rock,the following work was carried out: 1.Basing on the engineering background of Wawu mining,field investigation and sampling were performed to grind the rock blocks into standard test pieces.2.The stress-strain curves and the basic physical and mechanical parameters were obtained by indoor macroscopic failure strength experiments.3.Meanwhile,acoustic emission was used to carry out crack propagation observation tests on the interior of the phosphate rock,and three-dimensional fracture images of the rock samples were obtained.4.Using the microscopic scanning electron microscope and its accessories to obtain the mineral composition and content of the rock sample debris and the microstructure observation map.Then the relationship between the rock composition and the rock strength was analyzed.It is found that the difference in microstructure has an impact on the macro mechanical properties of the rock,and it is also reflected in its macroscopic damage.The main results are as follows: 1.Through triaxial strength tests,it was found that the top and bottom dolomites and dense phosphorous blocks follow the law of higher triaxial compressive strength as the confining pressure increases.However,the compressive strength of phosphorous blocks with horizontal stripes decreases when the confining pressure increases.2.The acoustic emission test was used to observe the three-dimensional image of the crack propagation process,and it was found that the cracks,pores and horizontal stripes of the phosphorous block damaged the integrity of the rock and reduced its compressive strength.And the failure point mainly appears at the intersection of horizontal stripes,which indicates that this is the structural weak surface of the phosphorous block.3.By testing the mineral composition of the rock sample fracture surface and rock burst sheets and combining with the on-site failure of the rock mass,it was found that the presence of a large amount of siliceous matter in the rock mass improves the overall strength of the rock mass,and In terms of improving the rock's ability to store elastic strain energy,the surrounding rock mass becomes a rock burst high energy storage body,which reflects a higher rock burst tendency.4.Through microstructural observation experiments,it was found that the grain boundary weakness of the phosphate rock is the junction of the horizontal stripes,which is easy to cause cracks and damage,and it reflected as the weak structural surface of the rock macroscopically.And the destruction of microstructure is consistent with its macroscopic destruction.5.By analyzing the relationship between the weak surface morphology of the rock sample and its compressive strength,the strength change law of the rock with weak surface under pressure is obtained:(1)The compressive strength of the rock is related to whether there are cracks or grain boundary weakness in the rock.The existence of grain boundary weakness in strip phosphorite makes its compressive strength lower than that of intact phosphorite.(2)The direction of cracks and grain boundary weakness in rocks will affect the compressive strength of rocks.When the weak surface in the rock sample is along the vertical direction(axial pressure direction),the larger the confining pressure,the more difficult it is for the cracks to expand,and therefore the greater the compressive strength of the rock.When it is along the horizontal direction(confining pressure direction),the larger the confining pressure,the easier the weak surface is to generate cracks and continue to expand,and the compressive strength of the rock is lower.