Experimental investigation on mode I fracture behavior of sandstone after grouting filling under three-point bending

Abstract

The widespread presence of fissures in natural rock masses poses numerous challenges to the design and construction of rock engineering. As an effective reinforcement method, grouting filling is crucial for maintaining the safety and stability of underground engineering. In this study, a testing and monitoring system was established to perform three-point bending tests on sandstone specimens with a pre-notch after grouting filling utilizing high-definition cameras and the rock mechanics testing machine. Combined with the digital image correlation (DIC) method and 3D scanning technique, the influence of grouting filling type on the mechanical behavior and fracture characteristics of sandstones was investigated. Simultaneously, a novel approach for quantitatively determining crack initiation and propagation was proposed based on the maximum principal strain theory. The results indicated that the peak load of specimens all tends to rise with the increase of filling rate and filling material strength. The fracture toughness and nominal tensile strength initially ascend and then slightly decline when the filling rate goes up, whereas both grow continuously as the filling material strength improves. Increasing the filling rate and filling material strength can decrease the opening degree of the pre-notch and postpone the development of the fracture process zone (FPZ). The crack propagates steadily to a certain length before remarkably increasing as the load rises, while the FPZ length exhibits a growth trend from slow to rapid and subsequently to sluggish. Moreover, the grouting filling effect will also have a pronounced impact on the crack propagation path and fracture surface morphology.