Application of TBM operational parameters to estimate the drop modulus, case study: Karaj–Tehran water conveyance tunnel of Iran

Abstract

The drop modulus is an important parameter to estimate the post peak behavior of rock mass. It is the slope for the softening stage of rock mass that related to quality of rock mass and confinement stress as increasing in the quality of rock mass and decreasing in the confinement stress can increase the drop modulus and it is true inversely. One of the most important applications of this parameter is to predict the rock burst, squeezing and etc because the mentioned phenomena are directly related to post peak behavior of rock mass. In this study, a new empirical method is proposed to estimate the drop modulus using the double shield TBM specifications of Karaj–Tehran water conveyance tunnel in Iran. It is estimated based on the penetration rate of TBM, the equivalent thrust per cutter and the torque of TBM. The result shows that there are inverse relations between the drop modulus of rock mass with the penetration rate and the torque of TBM and a direct relation between the drop modulus and the equivalent thrust per cutter. In this study, new power equations are proposed to estimate the drop modulus using the penetration rate and the equivalent thrust per cutter respectively. Also a new linear equation is suggested to estimate the drop modulus using the torque of TBM. Finally, the most useful equation to estimate the drop modulus is achieved using the ratio of the equivalent thrust per cutter to product of TBM penetration rate on torque of TBM because it is a function of three parameters.