Classification Method Of Surrounding Rock Of Sandy Dolomite Tunnel And Its Engineering Applicatio

The water conveyance tunnel of Yuxi section of central Yunnan water diversion project crosses 14.406km long sandy dolomite stratum.During the tunnel construction,surrounding rock collapse,mud and water inrush and other disasters occur frequently,delaying the construction period and seriously threatening the safety of tunnel construction.There are few studies on the classification of dolomite sandy grade and the classification of tunnel surrounding rock,which is far from meeting the needs of engineering construction.Therefore,clarifying the sandy classification of dolomite and establishing the surrounding rock classification system suitable for sandy dolomite tunnel can provide direct basis and guidance for the construction of sandy dolomite tunnel,and then provide guarantee for the safety of tunnel construction,which has important engineering scientific value.In this paper,the relationship between the physical and mechanical properties of dolomite and the degree of sanding is analyzed through in-situ and indoor experiments.Combined with the regional geological environment,the classification standard of dolomite sanding grade is established;The applicability and correlation of common surrounding rock classification methods such as Q system,RMR method and BQ method in the surrounding rock classification of sandy dolomite tunnel are studied;Based on the above research,a comprehensive surrounding rock classification system SHF for sandy dolomite tunnel is proposed and applied in engineering.The research work and main conclusions of this paper are as follows:(1)Through point load test,needle penetration test and rebound test,the relationship between physical and mechanical properties of sandy dolomite and sandy grade is studied,and the influence range of structural fault zone on sandy degree is counted.Combined with the structural characteristics of sandy dolomite rock mass,the classification standard of dolomite sandy grade is established,and the qualitative and quantitative method of Fuzzy AHP is introduced to divide the sandy grade of dolomite into:Micro new rock mass,weak sandy upper section There are six grades of weak sandy lower section,strong sandy upper section,strong sandy lower section and severe Sandy.(2)Q system,BQ method and RMR method are used to classify the surrounding rock of Xiaopu 2#construction adit and the upstream and downstream tunnel sections of the main tunnel,and compared with the actual exposed surrounding rock categories.The results show that the coincidence rate of Q system is 44%,which is one grade higher than the actual surrounding rock category,accounting for 43%,and the applicability is medium and lower;The coincidence rate of BQ method is 72%,which is one grade lower than the actual surrounding rock,accounting for 23%;The coincidence rate of RMR method is 36%,which is one grade higher than the actual surrounding rock category,accounting for 57%,and the applicability is low.(3)The numerical correlation analysis of the results of common methods shows that the classification results of Q system and BQ method in sandy dolomite tunnel are well correlated,and the classification grade of Q system in a few sandy tunnel sections is one category higher than that of BQ method.The R~2 of the fitting function between Q value and[BQ]value in the sandy dolomite tunnel is 0.2438,and the correlation is poor;The classification results of RMR method have poor correlation with Q system and BQ method.The classification grade of RMR method in most sandy tunnel sections is one or two categories higher than that of Q system and BQ method.The R~2 of the fitting function of RMR value,Q value and[BQ]value in the sandy dolomite tunnel is 0.5031 and 0.689 respectively,with general correlation.(4)Combined with the engineering geological characteristics of sandy dolomite,taking the sandy grade and structural plane development characteristics as the main factors and the relationship between groundwater,in-situ stress,main structural plane occurrence and tunnel axis as the correction factors,a surrounding rock classification method SHF suitable for sandy dolomite tunnel is established.The subcategories are divided into class III,class IV and class V surrounding rock,and the corresponding initial support measures are put forward for the surrounding rock category of sandy dolomite tunnel.(5)The coincidence degree of SHF in Xiaopu 2#construction adit and the excavated tunnel sections upstream and downstream of the main tunnel reaches 84%,which is more in line with the actual surrounding rock category on site.Rapid discrimination and accurate classification are realized,which provides a reference basis for tunnel construction support.