3 SEISMIC NONDESTRUCTIVE METHODS USED TO MONITOR CONCRETE SLAB INJECTION TESTS

A long term research program to determine the effectiveness of cement grouts injected in concrete dams was initialed by the Institute of Res earch in Electricity of Hydro-Quebec (IREQ) in 1986. To investigate th e effectiveness of the grouts, three nondestructive methods based on s eismic wave propagation were recently applied to various concrete slab s. The Impact-Echo method was used to determine the crack profile befo re the injection process began in one of the slabs. This method was us ed successfully and the detected internal crack depths agreed well wit h crack depths measured on the sides of the concrete slab. Acoustic Em ission was used to monitor the penetration of the grout inside the cra ck. This method also allowed the researchers to determine at which mom ent, during the injection test, the cement grout mixture needed to be changed. Sonic Tomography was used to produce a tomographic image of t he internal seismic wave velocities which traveled through the slab be fore and after the injection tests. Two different transmitter and rece iver arrangements were used to determine the best measurement configur ation. This paper illustrates the usefulness of combining various seis mic wave based nondestructive methods to obtain a better knowledge of fracture detection and cement grout propagation, which can eventually lead to practical applications on concrete structures and hence on con crete dams.