Experimental study on cracking damage characteristics of a soil and rock mixture by UPV testing

Abstract

This paper investigates the ultrasonic pulse velocity (UPV), mechanical properties and cracking characteristics of a soil and rock mixture (SRM) with varying rock percentages under uniaxial compression. Cylindrical SRM specimens (50 mm diameter and 100 mm height) with rock percentages of 20, 30, 40 and 50 % were produced to perform a series of uniaxial compressive strength (UCS) tests. A P-wave transducer (500 kHz) and associated equipment were employed for all the testing to record the ultrasonic parameters during the whole deformation process. Test results indicates the UCS and UPV decreased with increasing rock percentages for all specimens. The failure mechanism of all specimens showed a splitting-sliding mixed pattern; macro-cracks have a direction of 0°–10° parallel or sub-parallel to the normal stress. In addition, an equation was proposed for the relationship between UPV and crack width. Crack initiation stress was lower for specimens with a high rock percentage. The crack initiation stress level was about 0.2–0.5 times of peak-strength, and the total width of cracks was about 2–5 mm at peak-strength. Based on the width of cracks and UPV, the total stress–strain curve was divided into three stages: the linear-elastic stage; the damage initiation and stable development stage; and the damage acceleration stage. Moreover, a three-stage damage evolution equation and constitutive model were established and compared with the testing data. These results confirm that the UPV and mechanical properties of SRMs are closely related to the rock percentage. In this regard, the UPV test can be suitably exploited for determing the cracking evolution characteristics for SRM.