A novel hybrid finite-discrete element modeling approach to assess the impact of drilling-induced core damage on laboratory properties of hard brittle rocks

完整岩石的无侧限抗压强度（UCS）和杨氏模量（E）是深基坑工程设计所需的两个基本参数。这些参数通常是由取芯试样的实验室无侧限压缩试验确定的。已知的是，从深和高应力环境进行岩心钻探的过程可能由于钻探期间岩心经历的复杂应力路径和高拉伸应力而引起对取芯样品的损坏（微裂纹）。岩心损伤可能会影响岩石样本的实验室性质（例如，UCS和E）。因此，研究需要更好地了解和预测的影响，核心损害的实验室性质的脆性岩石，更可靠的设计深地下开挖。拟议的研究旨在开发一种新的方法，在商业数值模拟程序的基础上的混合离散元法（FDEM），被称为ESTZU，研究取芯应力路径对脆性损伤的影响和相关的变化，硬，脆岩石的属性。本研究的目标是：a）确定最合适的边界条件，以应用三维取心应力路径模拟二维FDEM模型中的岩心损伤：B）开发一种系统的方法，以一组输入参数校准FDEM模型，使其符合未损伤和损伤岩石试样的实验室性质和行为;以及c）研究非均匀性（预先存在的微裂纹和不同杨氏模量的矿物颗粒）对卸载引起的微裂纹的密度和特性的影响。这项研究将通过对钻孔方向和钻孔深度对岩心损害程度的影响提出建议来完成。这项工作预计将开发新的方法和工具，在ESTZU软件，以预测钻井引起的核心损害和可靠的估计原位岩石强度和变形特性。

The Unconfined Compressive Strength (UCS) and Young's modulus (E) of intact rocks are two fundamental parameters required for the design of deep underground excavations. These parameters are usually determined from laboratory unconfined compression tests on cored samples. It is known that the process of core drilling from deep and high-stress environments may induce damage (micro-cracks) to the cored samples due to complex stress paths and high tensile stresses experienced by the core during drilling. Core damage may affect the laboratory properties of rock specimens (e.g., UCS and E). Therefore, research is needed to better understand and predict the impact of core damage on laboratory properties of brittle rocks for a more reliable design of deep underground excavations. The proposed research aims to develop a novel methodology in a commercial numerical modelling program based on the hybrid Finite-Discrete Element Method (FDEM), known as Irazu, to investigate the influence of coring stress path on brittle damage and associated changes to the properties of hard, brittle rocks. The objectives of this research are: a) to determine the most suitable boundary conditions to apply 3D coring stress paths to simulate core damage in 2D FDEM models; b) to develop a systematic methodology to calibrate the FDEM model to the laboratory properties and behaviour of undamaged and damaged rock specimens with one set of input parameters; and c) to investigate the influence of heterogeneities (pre-existing microcracks and mineral grains of various Young's moduli) on density and characteristics of unloading-induced microcracks. This research will be completed by making recommendations on the impact of borehole orientation and drilling depth on the level of core damage. This work is anticipated to develop new methodologies and tools in the Irazu software to predict drilling-induced core damage and reliable estimate the in situ rock strength and deformation properties.