| To reduce the impact force by rock falling，a sand cushion with 90cm thickness is commonly seton the roof of rock-sheds．The impact forces have usually been evaluated by a conventional design formula based on the Hertzs contact theory，However，according to analytical results abtained by using one-dimensional and/or axi-symmetrical wave theory，the transmitted impact force onto a rigid base is double of the input impact force．In this paper，to rationally evaluate the real impact force caused by rock falling ，large scale field tests on weight falling onto a sand cushion were performed，Heavy weights of 2tf and 3tf estimated by meas uring the weight acceleration at the impact and the transmitted impact stress onto the rigid base through a sand cushion According to the results obtained from these experi-ments，it was made clear that：1）the maximum transmitted impact force is about twice the maximum weight impact force，and 2）the maximum transmitted impact force can be estimated using the conven-tional formula assuming Lame’s constant λ＝1000tf/㎡ |
