In-site core disking phenomenon and break mechanism of hard marble: Investigation in 2400 m deep-buried underground laboratory

Abstract

The core-disk phenomenon has been observed generally in the drilling process under high-stress conditions. This paper presents the in-situ experimental study of the coring-disking failure mechanism of marble in an underground cavens with 2400 m depth. Based on the disk samples in several boreholes with different diameters, both macro- and micro-morphological characteristics of core-disks’ break surface were analysis, using 3D optical scanning and electron microscope scanning. Moreover, the numerical back analysis was also used to simulate the drilling process for demonstrating the development of core disking. The in-situ experiment results showed that the failure types of core disking consisted of tensile break and shear break, i.e., the shear break usually appears in the edge part of break surface, and tensile break appears in the central part. What’s more, the ration of core-disks thickness to borehole diameter is in a relatively stable range. Numerical back analysis indicated this micro asynchronous break of hard marble is induced by high geostress and unloading drill.

Keywords

rock mechanics / deep engineering / shear break / tensile break / high geostress

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