Performance of counterweight balance on stability of undercut slope evaluated by physical modeling

The frictional behavior of a block of moist silica sand No. 6 on a Teflon plate is studied thru a series of slip tests. A relation was found between the supports on the sides and toe and the stability of the sand block. The critical slope angles for the stability of the sand block on the Teflon plate were obtained for three cases of without supports, with only side supports and with both side and toe supports. Based on the results from slip tests, a series of undercut slope physical model tests were conducted where moist sand was uniformly layered inside a rigid acrylic frame fixed on a sloping Teflon plate. The model was instrumented by a set of miniature pressure cells buried inside the model and a row of potentiometers at the top of the slope model. A high speed camera with a capture speed of 500 frames per second was employed to record the crack initiation of the model. Moreover movement distributions of the slopes were recorded and analyzed using particle image velocimetry (PIV) and image processing software. The effect of counterweight balance on the stability of the slope model was studied thru model tests with different counterweight balances in size. It was confirmed that as the pillars of the model become stronger, the width of the span of the excavated area could be increased before the failure of the slope.