A NEW METHOD FOR PREDICTING 3D FRACTURES AT NEXT TUNNEL EXCAVATION SPACE FOR PERPENDICULAR SETS TO TUNNEL AXIS

Phí Trường Thành

Hanoi University of Natural Resources and Environment

Abstract: The fractures in rock would strongly affect rock mass stability, if the rock mass is excavated. Therefore, understanding of fracture distribution to predict the presence of them in rock mass before excavating is necessary. However, predicting fracture locations ahead is not easy, especially parallel fractures to tunnel excavation face and it will not be predicted, if the rock mass has not excavated yet. This paper proposes a new methodology for analyzing fracture spacings and predicting fracture locations at next tunnel excavation space for perpendicular sets to tunnel axis based on fracture spacings from previous excavated faces. The fracture spacings are determined as distances between central projection points of fracture traces at each excavation face on the line that is normal to average plane of set orientation. The analyzing fracture spacings is carried out by simply plotting fracture spacings in sequential manner (cumulative plot). The predicting fracture locations at next excavation space is to solve inversed problem; It is carried out by inserting fracture cluster based on distribution of previous fracture spacings on cumulative plot. At the same time, the 3D fractures will be automatically plotted at the next tunnel excavation space adding fracture cluster. The result of applying this methodology at BongHwang tunnel, Chungbuk province, Korea using Tunnel Mapper tools have shown the utility of this method.

Keywords: Fracture spacings, Fracture distribution, Predicting fracture, Fracture set, Tunnel excavation.