Study On Judgment Method Of Surrounding Rock Grade During The Tunnel Construction

Tunnel engineering in the survey phase or construction phase will be affected by the complex terrain and geological conditions.Therefore,the advanced prediction of engineering geology and the classification of surrounding rock during the tunnel construction period are the basis for the design and construction of the tunnel structure.During the construction of the tunnel,the geological condition in tunnel face is not known.The construction has great uncertainty may causes the tunnel to collapse,water inflow,and other accidents.Such problem Seriously affect the construction schedule and project safety.Because of this,geological surveys should be conducted on the tunnel construction site in a timely manner.Using the method of determining the grade of surrounding rock in the tunnel construction project will provide better guidance for the structural design and increase the construction safety factor.1)The rapid grading method of surrounding rock in the tunnel construction stage is based on the determination of the BQ value to determine R_c(rock strength)and K_v(rock integrity coefficient)rapidly,then establish the classification method of surrounding rock in the construction of the tunnel.2)The rebound value,longitudinal wave velocity,and uniaxial compressive strength of rock specimens were measured by laboratory tests.A prediction model of rock strength based on rebound and strength and a regression model of rock strength prediction by acoustic wave-rebound synthesis method were established.Based on the neural network model and SVM support vector machine model,it is concluded that the new acoustic rebound-rebound synthesis method is more accurate in predicting rock strength.The SVM algorithm can be applied to this project better in various algorithm comparisons.3)Using acoustic emission instrument to measure the fracture surface wave velocity V_p of the rock mass at the tunnel site and the velocity V_r of the deep intact rock mass,and quickly calculate the K_v value of the rock mass integrity of the face rock face during construction.4)The engineering application is based on the Shimen tunnel under construction in Baohan high-speed.Based on the basic quality index BQ of the surrounding rock,the R_c value is predicted by the SVM model,the K_v value is calculated in the field test,and the BQ value is calculated to judging the surrounding rock level(preliminary),combined with the on-site geological conditions(initial ground stress,groundwater state,weaken structural planes)of the tunnel face,the[BQ]value was modified to achieve a detailed classification of the surrounding rock mass.The detailed classification of the surrounding rock of the ten sections during the construction phase is somewhat different from that determined during the design.This is due to the limited engineering geological data in the initial stage of design,and therefore it is an effective supplement and correction to the determination of surrounding rock grades during the design phase.Can better ensure the safety of construction.