Failure characteristics of sandstone specimens with randomly distributed pre-cracks under uniaxial compression

Setting the number (or density) of pre-cracks as a variable, the effects of randomly-distributed pre-cracks on the mechanical properties and the corresponding failure process of sandstone are studied using Particle Flow Code software (PFC). The result shows that, as the number and total length of the pre-cracks increase, Unconfined Compressive Strength (UCS) of the sandstone specimen approximately shows a negative exponential variation, while the elastic modulus decreased near-linearly. With the increase of pre-crack number, both the UCS and the new crack number corresponding to the failure of the sandstone are gradually reduced; in addition, the angle of new cracks, as the data approximately obeyed the normal distribution, are mainly concentrated at about 90 degrees. Partition damage phenomenon is more obvious for the specimen with less pre-cracks. And there are stress shielding region distributed above and below the near-horizontal pre-cracks, and the concentrated stress is more likely to exist at whose tips. The strength theory of rock damage is established based on the Mori-Tanaka method in this paper, by introducing a density coefficient eta for the non-uniform arrangement of pre-cracks, the evolution strength of cracked sandstone can be well-described.