Determination of the deformability modulus of weak rock masses by means of large flat jacks (LFJ)

This paper deals with the interpretation of the results of large flat jack ( LFJ ) tests performed in weak rock masses. The influence of the in-situ state of stress on the results, as well as the determination of the deformability modulus and some special aspects in the testing technique are discussed. Results already obtained in several test localities (with values of the deformability modulus lying between 118 and 2170 MPa) and tables which allow the calculation of the deformability modulus for different cases of LFJ association are presented.