Point Load Tests Of Deep Ore-rock Samples At Huize Mine And Stability Analysis Of Surrounding Rock By Mechanical Excavation

As shallow resources depleted,deep resources exploitation has become an inevitable trend all over the world.Deep and complex geological environment,such as high ground stress makes deep resources exploitation faces a series of complex problems,such as fast acquisition of in-situ rock mechanical parameters,to promote the efficiency of mining,to control rock burst and large deformation problems,etc.Based on the actual project of deep mine affiliated to Yunnan Chihong Zinc-Germanium Huize Mining Company in China,the surface elevation of shaft No.3 is 2380m,and the mining depth has reached 1000～1500m.In view of the trend of thinning and scattering of ore-body in deep mining,the applicability of mining technology for mining deep small ore-body with upward or downward approach will become increasingly prominent.The existing mining technology of the mine still has some problems,such as too high cutting ratio and instability of paste false roof in downward approach,which also affect the production safety and economic benefit of the mine to a certain extent.In addition,the deep ore rock in Huize is relatively broken,which makes it difficult to take core on site,and it is difficult to obtain rock mechanical parameters through traditional laboratory tests.Therefore,based on the existing drilling and blasting stope working face and the planned mechanized mining stope working face,this paper carried out spot load test of ore and rock,so as to quickly obtain the point load intensity index of ore and rock.On this basis,the status of surrounding rock classification was obtained through joint and fissure investigation,and the strength parameters of deep rock mass were obtained through surrounding rock classification.Further,FLAC^3D is used to conduct numerical simulation analysis of mechanical mining in deep stope to reveal the changes of surrounding rock stress field and displacement field in deep stope.The main research results are as follows:（1）Carry out field load test of irregular ore rock in deep stope to obtain mechanical properties of deep rock indirectly.The point load test is mainly carried out on the ore and rock samples obtained by drilling and blasting mining site and the ore and rock samples selected by mechanical mining site.The distribution law of point load intensity index is obtained through data modification and processing of irregular samples.The point load intensity index of ore and rock before and after modification is normal distribution.Due to the small size and great impact of blasting damage,the point load strength of irregular rock sample and ore sample is small.The predicted uniaxial compressive strength of the block samples obtained after mechanical mining is basically consistent with the laboratory test results of the same elevation strata conducted simultaneously in Huize Mine,which further indicates that the disturbance damage to the rock caused by mechanical excavation is smaller than that caused by drilling and blasting.（2）Joint and fissure investigation of surrounding rock of deep stope and tunneling roadway was carried out by measuring line method and 3D digital scanning.Field investigation shows that the dominant trend and trend of joints in the same layer are basically the same.Compared with the number of joints in mechanical excavation approach,there are more joints and fissured in surrounding rock or ore body after blasting.With the increase of mining depth,the joints and fissures increase obviously.According to the investigation results of joints and fractures,the rock mass with elevation of 1452m,1404m,1310m and 1286m is classified asⅲ,and the stability of surrounding rock is general.The orebody grade isⅳand the stability is poor.（3）Rock mechanics parameters are determined based on the classification of surrounding rock,and the stability analysis of surrounding rock of deep stope is carried out.Taking section 1404m as an example,FLAC^3D was used for numerical simulation of mechanical mining scheme of thin veins with different thickness of 1m,1.5m and 2m orebodies,and the displacement and maximum principal stress changes of roof,floor and horizontal direction were analyzed.It was found that there was no obvious concentration area of tensile strain in the three sections.With the increase of the thickness of ore body,the displacement in the direction of top and bottom decreases gradually.Secondly,the numerical model of the mining area is established for excavation,and the roof of the approach is supported by（bolt+concrete）.The analysis of roof displacement under different mining lengths of 3m,5m,8m,15m and 20m shows that when the total mining length reaches a certain value（20m）,the stability of surrounding rock decreases sharply.Therefore,support should be strengthened to control the mechanical mining length.Based on the actual mine engineering,this paper studies the influence factors of surrounding rock stability in deep stope,the investigation of joints and fissures,the stope point load intensity test with different mining methods and the stability analysis of stope mechanical excavation.The research results can provide important theoretical basis and technical reference for huize deep mine mining from traditional drilling and blasting construction to mechanized mining construction.