MONITORING OF INJECTION BY ACOUSTICAL EMI SSION

The injection of grout in the microfissures of concrete darns in opera tion is very tricky because of the high pressures required to penetrat e the slightly opened fissures. These conditions of grouting may resul t in the propagation of the fissures and contribute to the loss of sta bility of the mass. The technique using acoustical emission to follow the injection in real time has been evaluated. Water injection tests h ave been carried out on large dimensions (2.64 m X 1.42 m X 0.40 m) fi ssured concrete slabs instrumented with pressure, load, and displaceme nt transducers. According to a study comparing two types of acoustical emission transducers, the low-frequency transducers would be more app ropriate for this type of application. Moreover, the detected acoustic al signals are not due to a constant pressure flow, but to the acceler ations and decelerations of the grout, and to the mechanisms resulting from the variations of pressure and flow of the fluid (opening and cl osure of the fissure). Thus these observations confirm that the acoust ical emission may be an interesting means to control the injections an d, in particular, to determine the process of grout flow.