On The Methods For Surrounding Rock Classification In Construction Stage Of Highway Tunnels With High Geostress

With a large number of deep-lying mountain highway tunnels'construction, the surrounding rock classification method can't satisfy the needs of surrounding rock classification in complicated geological conditions such as high geostress. So it is very necessary to establish surrounding rock classification during highway tunnel construction stage with high geostress.Aiming at the needs of surrounding rock classification of highway tunnels in complicated geological conditions, based on the previous research results, this paper applied geological investigation on field and collected geological data, consulted relevant data at home and abroad, and then maded induction and analysis on,adopted qualitative classification and quantitative classification and used numerical simulation method and extension method to discuss some aspects of surrounding rock classification on highway tunnels construction stage with high geostress, main results and understanding required were as follows:(1)Analysis and classification of the selected indexes of various surrounding rock classification methods at home and abroad and built surrounding rock qualitative classification schemes of highway tunnels in china, Selected three indexes including rock hard degree,rock integrity degree and other revising factors(geostress,groundwater and angle of dominant structure plane and tunnel axis) to build surrounding rock qualitative classification scheme tables.(2)The results of common surrounding rock classification methods as Q method and BQ method in design specification of highway show that classification results inⅣgrade andⅤgrade surrounding rock with in low geostress, the coincidence rate is well of the two surrounding rock classification methods'classification results and the practical,but surrounding rock classification results had low coincidence rate with practical surrounding rock quality in high geostress section and their practicality was poor.(3)Due to the poor classification practicality of BQ method in high geostress and rock burst or large deformation surrounding rock section,Aiming at the deficiency of reduction factor K3 of BQ method with high ground stress,This article introduced the rock burst and large deformation into surrounding rock classification.Devided the rock burst into four grades and large deformation into three grades by ratio of strength stress,every grade has on raletive reducing value,thus formed the reduction factor K31 of rock burst and non-rock burst and large deformation and non-large deformation, BQ-hg method will be builded based BQ method in high geostress.(4)This paper applied the extension method to make surrounding rock classification in highway tunnels.At first, selecting indexes(this paper choice Rc-uniaxil strength,RQD,Kv is rock mass integrity,groundwater state andσ1-groundstess) and using their parameter values in dimensionless processing, then establishing relevant classical field matter elements and segment field matter elements and determining weight of every index,finally obtaining the relevant surrounding rock grade by using correlation function.(5)Analyses and discussion influence of span on the stability of surrounding rock and support.According to the numerical simulation of surrounding rock at all levels in different excavation spans,discussion the influence of span on the stability of surrounding rock by qualitatively,increase of span will form adverse effect on stability of surrounding rock, more obviouse on the rock mass with the bad surrounding rock quality.Used various calculation formula of the surrounding rock pressure (including occupational standard,theoretical calculation formula,the formula recommended by foreign surrounding rock classification system) to calculate theⅣgrade,Ⅴgrade surrounding rock pressure,calculated the results and analyses and discusion the influence of span on surrounding rock pressure.