Field testing of weak rock deformation in water tunnels: A practical review of the flatjack test

Abstract

The flatjack test is normally used to measure the average normal stress at a rock surface and to evaluate the rock mass deformation modulus. The aim of this manuscript is to present a modified variant of the flatjack test for the long-term monitoring of pressure and deformation development in the headrace tunnel of Moglicë hydropower project. The aim is to determine the behavior of the rock mass after water filling of the tunnel and during the first year of operation. The monitoring rig installed will continuously record pressure and deformation development in the rock mass behind the shotcrete liner and data will be stored in the dataloggers submerged in the headrace tunnel. This application is, to the authors’ knowledge, one of the first of its kind in hydropower construction. Since data acquisition will not be possible before 2020, this manuscript presents modified test procedure of the flatjacks and rig as a whole. The practical challenges experienced during the instrumentation process of the rig is highlighted.