Formation of crushed zone around tunnel in mechanized excavation of hard rock mass under high stress and its effect on the selection of mechanized drilling machine type

Dorodian Movahed, Behrooz; Ahangari, Kaveh; Nourzad, Ali

Formation of crushed zone around tunnel in mechanized excavation of hard rock mass under high stress and its effect on the selection of mechanized drilling machine type

Document Type : Original Article

Authors

Behrooz Dorodian Movahed ¹

Kaveh Ahangari ²

Ali Nourzad ³

¹ Department of Mining Engineering, Faculty of Engineering and Technology, Islamic Azad University, Tehran Science and Research Branch, Tehran, Iran.

² Department of Mining Engineering, Faculty of Engineering and Technology, Science and Research Branch, Islamic Azad University, Tehran, Iran.

³ Faculty of Civil Engineering, Shahid Beheshti University, Tehran, Iran.

Abstract

Unlike the drilling and blasting methods, mechanized drilling causes minimal disturbance to the rock mass around the tunnel. However, drilling in hard rock under high stress, along with changes in the stress level, can cause crack development and destruction of the rock mass around the tunnel. The formation of the destruction zone in such conditions appears as rock peeling, and considering that the gripper machine must jack up the tunnel wall to drill, the formation of the crushed zone will disrupt the performance of the mechanized tunnel drilling machine, especially the gripper machine. In this study, the thickness of the damage zone around the drilling space in hard rock was determined based on the damage initiation and peeling limit (DISL) method and using 3D numerical modeling in Midas GTS NX software. Based on the results of the analyses, it was determined that hard rock mass under high overburden (more than 1000 meters) or with low overburden but under specific tectonic conditions, including reverse faulting with a horizontal to vertical stress ratio of 4 times, is susceptible to the formation of a crushing zone around the drilling space.

Keywords

Rock flaking

DISL method

Midas GTS NX software

Mechanized drilling

hard rock under high stress