In-Situ Shear Test for Rock Fills

Large-scale in-situ shear tests were devised to determine the shear strength of soft rock and broken rockfill. A steel hollow box is sunk into rockfill to obtain an in-situ specimen for testing shear planes 2 or 4 ft (0.6 or 1.2 m) square. The shear strength of rockfills was found higher than that of the -3/16-in. (4.8-mm) fraction when compacted to attain the same void ratio. The ratio of creep strength to shearing resistance of the compacted crushed clay shale (of low plasticity) was determined to be 0.4. The value of coefficient of friction between stratified crushed clay shale fill layers decreased with an increase of normal pressure in a straight-line relationship. When the minimum ratio of 5:1 between the size of specimen and rock particles is not kept and there are large rock particles present, laboratory tests demonstrate the alteration in paths of shear cracks in compressive strength tests.