Stability around underground openings in rock with dilative, non-persistent and multi-scale wavy joints using a discrete element method.

摘要

The localized stability around underground openings in jointed rock masses depends on geology, geometry, and properties of discontinuities between rock masses. Excavation and construction procedures in tunneling have a significant influence on the change in stress distribution around underground openings and its support requirement.; Two versions of New Joint Model are developed in this study to account for the frequently observed essential joint behaviors, which play a critical role in the stability evaluation of an underground opening in jointed rock masses. Such essential joint behaviors that are modeled in New Joint Model include dilation of a joint, degradation of joint asperities, a joint with combination of multiple scales of asperity, and the behavior of persistent and non-persistent joint.; New joint model in this work has an advantage to utilize both data from lab-scale experiments and field-scale observation. Two versions of New Joint model were developed for two distinct purposes of application. New Joint Model A can be used for the cases where a certain value of peak friction angle should be used. New Joint Model B can be used in cases where degradation of small asperity angle and dilation angle are expected under various surrounding stress level.; The stability of rock wedges with smooth, rough and non-persistent joints under various conditions such as depth, K_o, rock strength, rock stiffness, and apical angle were analyzed with the new joint model.; Analysis of two stations, Dupont Circle in sheared ground and Medical Center in blocky ground on Washington Metro are performed in accordance with its construction stages and changes in construction scheme. The distinct element numerical results using the New Joint Model compared closely with the extensive field measurements in the Washington Metro station chambers and shows the capability of the model in simulating rock displacements and lining strains and loads over a wide range of rock joint properties.; The new joint model and the growing knowledge through wedge analyses and Washington Metro System case study will facilitate the understanding of the mechanism of tunneling and its required support in rock mechanic practice.