A laboratory test apparatus for simulating core drilling under high in-situ stress

What is it about?

The drilling-sampling test apparatus is capable of applying loads in two perpendicular horizontal directions to the rock block, simulating the in-situ stress environment that is perpendicular to the borehole direction in deep rock masses. Rock cores are obtained by drilling under different stress conditions. The apparatus is specifically designed for systematic investigation of disturbance damage in rock cores resulting from stress release during sampling in deep rock mass engineering. The self-development drilling-sampling test apparatus mainly consists of three components: Sampling frame system, Lateral pressure servo loading system, Core sampling drill system. Future studies plan to harness the utility of this apparatus to evaluate the macro-mechanical properties of rock cores, gathered under diverse stress conditions. These properties will be juxtaposed with those of intact rocks and scrutinous comparison will help understand the repercussions of sampling damage on rock strength and deformation patterns. A thorough investigation will be undertaken into the properties of microcrack expansion and the formation processes of microstructural damage. The execution of drilling cores will take several influential factors into account, ranging from rock lithology, cubic rock block size, and drilling speed to stress magnitude and drill bit size. The incubation process of sampling damage will also be given additional attention, providing clearer understanding of this phenomenon. Adopting numerical simulation methods, an optimization process will be initiated to conceive a stress-relief-based method to mitigate sampling damage. The findings from these studies are anticipated to enrich the understanding of rock mechanics parameters, proving invaluable for their assessment in engineering applications.

Featured Image

Photo by Ashim D’Silva on Unsplash

Photo by Ashim D’Silva on Unsplash

Why is it important?

As the exploitation of resources gradually extends to the deeper layers of the Earth, the evaluation of rock mechanics properties, in the context of deep rock engineering design, construction, and safety assessment, poses numerous new challenges. Core drilling, a commonly used geological exploration method, serves as the basis for obtaining physical and mechanical parameters of engineering rock masses through laboratory experiments. However, during core drilling under high in-situ stress conditions, stress release can induce permanent damage to rock cores. In severe cases, it can lead to core disking, resulting in significant deviations in physical and mechanical properties from those of in-situ rock. Neglecting such sampling disturbances can lead to unreasonable estimates of in-situ rock properties, which are detrimental to the design, construction, and operation of engineering structures, thereby posing long-term stability concerns in deep rock engineering. To address this challenge, a laboratory test apparatus has been developed that can apply specific pressure to shallow rock materials to simulate high in-situ stress environments and drilling-coring to simulate the sampling process of deep rock masses.

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