Flaw is a key factor influencing failure behavior of a fractured specimen. In the present study, rectangular‐flawed specimens were prepared using sandstone to investigate the effect of flaw on failure behavior of rock. Open flaw and cylindrical hole were simultaneously precut within rock specimens using high‐pressure water jet cutting technology. Five series of specimens including intact, single‐hole‐alone, two‐hole‐alone, single‐hole and two‐flaw, and two‐hole and single‐flaw blocks were prepared. Uniaxial compressive tests using a rigid servo control instrument were carried out to investigate the fracture processes of these flawed specimens. It is observed that during loading, internal stress always intensively distributed at both sidewalls of open hole, especially at midpoint of sidewalls, so rock crumb flaking was firstly observed among all sandstone specimens containing single hole or two holes. Cracking around open hole is associated with the flaw inclination angle which was observed in Series III and V. Crack easily initiated at the tips of flaw with inclination angles of 0°, 30°, and 60° but hard for 90° in Series III and V. Rock burst was the major failure mode among most tested specimens, which generally induced new cracks and finally created crater shape. Additionally, due to extrusion between blocks, new shear or tensile cracks were generated and the rock specimen surface spalled. Eventually, four typical failure processes including rock crumb flaking, crack initiation and propagation, rock burst, and second rupture, were summarized.

Embedding single-row piles is often adopted to stabilize slopes in engineering practice. However, for large-scale and complex slopes, single-row piles might not be able to stabilize the slope; rather, double-row piles, even multirow piles, should be adopted. Currently, the optimal locations of double-row stabilizing piles considering local instability of the slope have rarely been studied. In this paper, a simplified analytical model used to analyze double-row pile stabilized slopes is proposed, where the local failure of the slope above the first row of piles is considered. Through the kinematic approach of limit analysis combined with the strength reduction technique, the required resistance forces provided by double-row piles respectively are derived for different pile locations denoted by the rotational angle. Moreover, a framework is developed for analyzing the optimal locations of multirow piles considering multistage potential slip surfaces. The results of an illustrative example are presented, and the reasonableness of the proposed method is verified. It is concluded that the optimal locations of double-row piles lie within middle-lower part of the corresponding stabilized part of the slope. Finally, discussion illustrates the influences of the seismic effects and soil shear strength parameters on the derived optimal pile locations. This study provides novel scientific insight into the optimized design of stabilizing pile locations in engineering practice.

Two series of intermittent rock joints containing three joints arranged along the central shear axis were considered in this study. The failure behavior under direct shear loads was investigated by means of both physical tests and numerical simulations. The cracking behavior was found to be distinctly associated with the joint arrangement. Several types of main and secondary cracks were identified. The variation trends of the crack initiation stress ratio with inclination angle were analyzed and found to be partly different for the two series of intermittent joints. The whole fracturing process was characterized by three phases. Not all samples have to experience all three phases. The second phase is alternative and can be reflected by the shearing curve. Hence, two types of shearing curves, including single and double peaks, were identified. The double peak is due to the extrusion or sawteeth cutting in the second phase. Moreover, the numerical micromechanical analysis was performed to explain the shear behavior using the contact force and microcrack within the specimen. Based on the numerically measured local stresses, maximum and minimum principal stresses around the middle joint at crack initiation stress and peak shear stress were analyzed.