Study on the dynamic tensile behaviour of conglomerate based on Brazilian disc test

Abstract

The strong heterogeneity of conglomerate, a main component of gravel layer, leads to severe vibration of drilling string and complex impact loadings. The strength and failure characteristics of conglomerate are not clear currently, which seriously restricts the drilling process. Based on the Brazilian disc test, the dynamic tensile properties of conglomerate under different strain rates were studied with the true triaxial Split Hopkinson Pressure Bar (3D SHPB) device, and the effect of axial static stress on the dynamic tensile strength (DTS) and its deformation characteristics were analysed. The results show that the dynamic tensile properties have a significant strain rate correlation, and with the increase of strain rate, the strength in the impact direction and axial direction increases and the strain decreases linearly. While there is no axial load and the strain rate is 140.31~248.95 s-1, the DTS is 75.86 ~ 109.91 MPa. As the energy absorbed by the specimen increases exponentially, a great number of cracks are produced accompanied by the collapse of large debris, mainly manifested as the volume crush. With the increase of axial stress, the dynamic tensile modulus and stress growth rate decrease linearly, leading to the reduction of DTS, while the failure strain and axial strength increase linearly. This research can provide useful parameters for the drilling in deep gravel layer.