Abstract：Testing study is made on the mini-crack development around a prefabricated fracture in a limestone plate specimen subject to uniaxial compression. The rock used for test is limestone，and direct SEM observation is used for testing. The elastic modulus of rock specimen is about 93.7 GPa，Poisson′s ratio 0.25 and uniaxial compressive strength 201 MPa. The specimen is a plate of 25 mm×13 mm×1.1 mm in size with a prefabricated central circular or a slot about 0.6 mm wide and 6.0 mm long. The major axis of the prefabricated slot is inclined to the loading direction at 30°，45°，60°，respectively. The tests are carried out in the vacuum chamber of a SEM using a vise-type loading frame. Its loading capacity is 2 000 N and the load on the specimen is measured by the piezoelectric transducer with an accuracy of ±0.5 N. The development of mini-cracks in limestone specimen under uniaxial loading is photographed and analyzed. The test results are compared with those in marble and sandstone specimens from the previous study. It is shown from the comparison that the initiation points of cracks are similar in all three rock specimens，but there are less multiple mini-cracks development in limestone specimen. Finite element computation of the mini-crack process is performed using NOLM program with a strain-softening constitutive model of low tensile resistance. The computation result represents the experimental observation fairly well. The calculated results are compared with testing data，and they are agreed well with each other.
