Understanding Failure Mechanism of Non-Persistent Discontinuities Using 3D-Printed Synthetic Rock Mass

完整岩石和岩石节理的力学水力特性和破坏机理通常是通过室内小尺度试样试验来确定的。实验室试验结果是估计强度参数和评估岩体破坏行为的基础，该岩体由两部分组成：完整的岩石和空间分布的不同方向和持久性节理。虽然这些基本组成部分的个别地质力学性质可以在实验室中适当地确定，但在岩体尺度上的地质力学性质及其破坏行为的估计仍然高度不确定。这些主要的不确定性主要与节理通常有限的持久性和完整岩石桥在平面上或单个节理之间的空间分布有关。因此，非持久节理和含有非持久节理的岩体的行为受复杂相互作用的支配。对含有非持久节理的岩石样品进行实验室测试的解释面临两个主要困难：1)很难充分表征天然节理的持久性或岩石桥的空间分布；2)完整岩石的地质力学性质的自然变异性非常高。因此，要充分量化空间分布的非持续性结构面对岩体强度和破坏行为的影响是极其困难的。本项目重点研究非持久节理及含非持久节理岩体的强度、变形特征及破坏机制。为了克服上述两个限制，我们使用3d打印的“合成”砂岩样品，其行为类似于脆性岩石。岩石强度和节理空间分布均可通过3D打印机进行精确设计和3D打印。该方法需要证明：1)打印合成完整岩石的行为与天然脆性岩石相似；2)完全持久节理与天然节理的强度相似；3)需要系统地测试各种预先定义的岩桥分布配置。该方法的主要优点是允许在相同物理条件下对样品进行“可重复”的实验室测试，从而降低了不确定度。提出的方法的主要结果是提高了目前对非持久节理岩体强度和破坏机制的认识。

The mechanical and hydraulic characteristics and failure mechanism of intact rocks and rock joints are commonly determined by carrying out laboratory testing on small scale samples. The results from laboratory tests are fundamental for estimating the strength parameters and evaluating the failure behavior of a rock mass, that consists of a complex interplay of two components: intact rock and spatially distributed joints of various orientation and persistence. Although the individual geomechanical properties of these fundamental components can be properly determined in the laboratory, estimates of geomechanical properties at the rock mass scale and its failure behavior remain highly uncertain.These major uncertainties are mainly related to the often limited persistence of joints and the spatial distribution of intact rock bridges in the plane or between individual joints. Thus, the behaviour of non-persistent joints and rock mass containing non-persistent joints are dominated by complex interactions. The interpretation of laboratory tests on rock samples that contain non-persistent joints suffer from two major difficulties: 1) it is very difficult to adequately characterize the persistence of natural joints or spatial distribution of rock bridges, and 2) the natural variability in geomechanical properties of intact rock is very high. As a consequence, it is extremely difficult to adequately quantify the effect of spatially distributed non-persistent discontinuities on the rock mass strength and failure behaviour.In this project we focus on understanding the strength, deformational characteristics and failure mechanism of non-persistent joints and rock mass containing non-persistent joints. In order to overcome the two above mentioned limitations, we use 3D-printed “synthetic” sandstone samples which behave similar to brittle rocks. Both, the rock strength and the spatial distribution of joints can be precisely designed and printed in 3D using 3D printer. The approach requires to demonstrate that 1) the printed synthetic intact rock behaves similar a natural brittle rock, 2) fully persistent joints can show similar strength compared to natural joints and 3) various configuration of pre-defined rock bridge distributions need to be systematically tested. The key advantage of the proposed method is to allow for carrying out “repeatable” laboratory testing on samples with the same physical conditions, reducing the level of uncertainties. The primary outcome of proposed approach is to improve the current understanding of the strength and failure mechanism of the rock mass with non-persistent joints.