A Modified Borehole Jack

Various method of determining the modulus of rockmass as well as Goodman Jack and its main dis-adventages are briefly introduced in this paper. The mismatch between platen and borehole wall as well as the bending of the platen in Goodman Jack have been improved in the new jack. Furthermore the new jack has higher resolution and more accuracy. Calibration tests have shown that the measured modulus Ecalc no longer needs correcting. For the rock block the error of Ecalc compared with Etrue is less than 10% when platen contact angle 2β =45° is chosen. For the blockes of cast steel and iron with higher moduli they are about 5% when the jack is equipped with 2 β =30°platen. Field tests have shown that Ecalc is about the same value as measured by laboratory tests.