Research On BQ Classification Of Improved Layered Rock Mass Based On The Stress State And The Mechanism Surface Shape Correction Factor

The Standard of Engineering Classification of Rock Masses(BQ system)is a multi-factor,multi-variable,qualitative and quantitative combination of classification method.In this method,the rock saturation uniaxial compressive strength and rock integrity index are selected to calculate the value of the rock mass basic quality [BQ],and then the modification of rock mass is made considering the field conditions of engineering rock mass.Making BQ classification method both to ensure the objectivity of classification,but also reduces the difficulty of the scene classification.However,in some complex geological conditions,such as layered rock mass,BQ classification has the limitation of qualitative evaluation of correction coefficient.The actual use of the subjective judgment due to different field engineer,in the junction of two types of rock classification often occur classification phenomenon.In this paper,from the strength characteristics of rock,the quantitative calculation of BQ classification coefficient and initial geostress state correction coefficient in layered rock is studied.The main work and conclusions are:The results show that the uniaxial compressive strength curve of layered rock mass presents a U-shape change through the uniaxial compression test of shale and relevant data collected by predecessors.Introduce Jaeger-Donath single structure rules describe the layered rock structure plane Angle on the uniaxial compressive strength and the influence of Jaeger-Donath criterion is verified the reliability of the prediction of layered rock mass strength,it is concluded that layered rock uniaxial compressive strength mainly by the lithology and rock bedding Angle of the rock mass itself from two aspects,on the layered rock mass structural plane occurrence of BQ classification correction coefficient was improved:The excavation of rock mass is often a unloading process.Compared with the traditional triaxial loading test,the triaxial unloading test is more in line with theactual engineering practice.Study of layered rock mass in the unloading process,with the decrease of the horizontal stress,rock mass volume increases first and then,by comparing the stress and strain of the specimens under different working condition,the stress and strain,and the change of energy during the unloading process,it is concluded that high geostress lower compressive strength of rock mass are not controlled by bedding angle,anisotropy of rock mass.By introducing the Mogi-coulomb criterion and comparing the energy changes in the process of the test,it is pointed out that the application of the weakly planar rock mass under the circumferential stress will produce a certain deviation under the high circumferential stress due to the fast energy absorption of the weakly planar rock mass under the circumferential stress,and the correction coefficient of the initial in-situ stress state in the stratified rock mass BQ classification is improved according to the above results:By comparing the classification method of national standard BQ and the improved BQ classification method for different grades of rock mass in Muzhailing tunnel of Lanyu railway,it is concluded that the improved BQ correction method reduces the fluctuation range of rock mass engineering quality index while keeping the basic quality index of rock mass unchanged,and makes accurate judgment on the site of the project.