Numerical Investigation on Time-Dependent Deformation in Roadway

The roadway deformation normally relates to time especially for underground coal roadway. The strength of soft coal is low, and therefore the deformation increases gradually under constant stress with time, which is called rheology deformation. In this study, based on a field case, the rock mass properties and deformation data of the roadway were obtained according to the field test. A 3D numerical model was then established, and the rheological deformation including horizontal and vertical deformation of the coal roadway was systematically analyzed. The results showed that the rheological deformation of horizontal sidewall accounts for almost 30% of the whole deformation, and the stable time for such roadway is around 60 days after excavation. The tendency of the roof deformation is similar to the sidewalls, and however, the floor deformation is different. Then the related suggestions for maintaining the stability of such roadway were proposed, which is useful in-field application.

Characterising fracture patterns at growing lava domes

<p>Volcanic domes form when lava is too viscous to flow away from an active volcanic vent; instead, the lava accumulates into a mound consisting of a hotter, ductile core and a colder, brittle outer layer. An existing lava dome grows when new material is injected into the core of the dome, causing the  outer layer to stretch and develop tensile fractures. With continued dome growth, these weaknesses can propagate to form an extensive fracture network and the dome may fail. Collapse events often generate rock falls and debris avalanches, lahars, and high-speed pyroclastic flows, endangering populations residing at the base of a volcano. Since such fractures represent potential failure planes, in this project we aim to understand the role they have in destabilising lava domes.</p><p>This project will build on the work published by Harnett et al. (2018), which demonstrates the suitability of a discrete element modelling approach to simulate dome emplacement and evolution. Specifically, this project is designed to:</p><p>1. Use high-resolution photogrammetry to characterise the possible fracture states of a dome;</p><p>2. Establish up-scaled rock-mass properties by performing geomechanical experiments on both fractured and non-fractured samples of dome rock from prior collapses;</p><p>3. Develop a numerical model to investigate how the presence and properties of fracture networks influence dome stability.</p><p>The model, developed using PFC, will be used to identify critical fracture states that can signify a dome collapse is likely to occur. Under the current model, parallel bonds simulate the fluid magma core and flat joints simulate the solid talus material. This project will build on this original model by incorporating discrete fracture networks into the smooth-joint model to implement dome fracturing. The new model will look to investigate the effect  of a fracture network on a static dome that, when in its unfractured state, is stable under gravity. Additionally, the model will be designed such that inputs can include experimentally derived rock-mass properties. It is hoped that, by incorporating observational and experimental data into a more  complex model, the dynamic evolution of fractures in a growing lava dome can be investigated and the ongoing likelihood of a dome collapse event can be assessed.</p><p> </p><p>Harnett, C. E. et al., 2018. J. Volcanol. Geoth. Res., 359: 68-77.</p>

Dynamic Analysis of Blasting Effect on Nanjung Tunnel Stability

This study aims to dynamically analyze blasting conducted in the Nanjung tunnel. Nanjung Tunnel is a twin tunnel that has a horseshoe-shaped section with each tunnel having a dimension of 10.2 m x 9.2 m, and 230 meters in length. The layers rock of this tunnel include silty clay, sandstone and dacite. Blasting was carried out on one of the tunnels consisting of dacite rock, having a 75-90% RQD and UCS 49-61 MPa. During the blast, PPV measurements were taken at several points around the tunnel using a minimate.Dynamic analysis is done by building a Nanjung Tunnel model on the RS2 software with the finite element method. Input data in this modeling is endeavored to approach actual conditions in the field, such as tunnel geometry, rock mass properties, and blasting plans carried out at STA 30-32 tunnels 2. This modeling is expected to produce PPV that is close to actual PPV and the results of this model will be continued to the stability analysis tunnel 1.Modeling results indicate that the tunnel 1 condition is stable during blasting. The stability of tunnel 1 based on smallest strength factor on the roof is around 2.6. Stability also seen from the strain level in dacite and sandstone rocks which are 0.07% and 0.38%. These strain levels are still permissible according to the Sakurai strain level diagram, 1983.