On Uniaxial Compression Tests of Rock-like Materials Using a New Type of High Stiff Testing Machine

In planning of underground structures stability analysis of rock masses requires precise properties of fractured rocks. In this paper, an experimental study of rock-like materials by uniaxial compression tests is presented using a new type of high stiff loading machine. Four kinds of rocks were selected, namely, Oya-stone (green tuff), Kobe-tuff, cement mortar and marble stone. Three differrent loading procedures were employed, i.e., static loading, incrementally cyclic loading and cyclic loading in post-failure region (see Fig. 4). The machine used in these experiments has high stiffness about 312 ton/mm, and is capable of controlling either deformation or load of the specimen by mechanical action of the wedges under steel blocks installed in parallel with a specimen. This loading machine is very practical and efficient to obtain complete stress-strain curve of geologic materials. Main results are summarized as follows: (1) Obtained stress-strain curves are resolved into four characteristic regions due to the progress of fracturing, namely, intact, crack, fracture, and flow regions. The strains corresponding to each region are related to the strength, or the fablic of materials. (2) Tests of incrementally cyclic loading show that the envelop of unloading and reloading curve is coincident with the statical loading curve. (3) Relationship between plastic strain and total strain on incrementally cyclic loading are distributed by Weibull's probability. (4) Fatigue life under cyclic loading in post-failure region are influenced significantly by crypto-damage due to initial loading and applied stress level