Investigation of the development of an excavation damaged zone and its influence on the mechanical behaviors of a blasted tunnel

Abstract

An excavation damaged zone (EDZ) caused mainly by blasting is an important parameter for making reliable evaluations of the overall tunnel stability. Around a blasted tunnel, various rock properties are changed in the EDZ, which is dependent on the original rock properties, blasting design, and tunnel geometry. In this paper, the development of an EDZ and its influence on the mechanical behavior around an underground excavation were investigated using an in situ test and computer simulations. The variation of the rock properties in the EDZ was predicted by considering the blast design and compared with actual measurements using the Goodman jack test. The extent of the EDZ could be calculated from the characteristics of ground vibrations measured from a test blast. The reduction of the rock properties in EDZ could be predicted accurately with an overlapping effect due to sequential blasting. Numerical analyses using FLAC were made of several cases to determine the possible influence of the EDZ generated from different blasting designs and rock conditions.