Experiment And Numerical Simulation Study On Rock Breaking By TBM Cutter In Mixed Rock Strata

Nowadays,with the vigorous development of economy and comprehensive national strength,the demand for tunnel construction is increasing.Due to its obvious advantages in engineering cost,construction period,tunnel(lane)road excavation,stratum disturbance,environmental impact,construction safety,etc,full-section rock tunneling machine(TBM)has been widely used in tunnel and subway construction projects.China's vast territory will inevitably encounter a variety of unfavorable geological conditions,such as soft and hard mixed rock strata.The arrangement of the TBM in the mixed rock strata cannot be simply adopted in the case of homogeneous formation.Therefore,this paper conducts indoor rock breaking test on a composite rock formation with a sandstone and granite volume ratio of 4:6,and uses PFC3D for other volume ratios.The numerical simulation of mixed rock strata is carried out to study the influence of cutter spacing and penetration on rock breaking efficiency and the optimal s/p(s:cutter spacing,p:penetration).The research contents and main conclusions are as follows:First of all,the uniaxial compression and the Brazilian splitting test were carried out indoors to determine the physical and mechanical parameters of granite and sandstone,and the microscopic parameters of PFC3D were calibrated according to this parameter by“trial-and-error method”.Secondly,for the mixed rock strata with the volume ratio of sandstone and granite 4:6,the rotary cutting test of 3 cutters with 3 penetration degrees(5mm/r,6mm/r,7mm/r)with 5 sets of cutter spacing(60mm,70mm,80mm,90mm,100mm)was conducted.Monitoring in the process of rock damage total normal force,the total torque,and the two kinds of rock slag were collected for screening and weighed,on the basis of experimental results it is concluded that:the average normal force and the average torque were separated by the knife spacing.The penetration degree increases and the increase trend of the two is different,that is,the average normal force increases almost linearly with the increase of the penetration degree,and the average torque decreases with the increase of the penetration degree.Different optimal cutter spacing exist under different penetration degrees;the rock breaking efficiency is the highest when the ratio of knife spacing to penetration is about 14.Finally,with the test under the same conditions set up by adopting the PFC3D rotary rock,through the data and the rock fragmentation process of rock crack compared to verify the rationality,and then simulate the sandstone cutting length of total cutting length(L_r/L),followed by 0%,20%,40%,60%,80%and 100%in 5 kinds of mixed rock strata of cutter spacing,6 kinds of 3 cutters rotating under the penetration process of rock fragmentation.Through the analysis of normal force,torque and specific energy,it is concluded that the normal force,torque and specific energy gradually decrease with the increase of L_r/L.The optimal penetration degree corresponding to the same knife spacing is not completely the same,and decreases with the increase of L_r/L;The specific energy of all L_r/L decreases first and then increases with the increase of s/p;In different L_r/L,the optimal s/p is not the same.With the increase of L_r/L,the optimal s/p gradually increases.The L_r/L applicable for different s/p is obtained according to the percentage difference between the specific energy under different s/p and the optimal s/p under different L_r/L.