Numerical modelling to predict fracturing rock (Thanet chalk) due to naturally occurring faults and fluid pressure

This is an accepted manuscript of an article published by Elsevier in Journal of Structural Geology on 30/07/2018, available online: https://doi.org/10.1016/j.jsg.2018.07.021 The accepted version of the publication may differ from the final published version.© 2018 Elsevier Ltd Outcrop mapping of a chalk cliff and wavecut platform in Thanet, Southeast England show a complex fracture pattern that seems to be controlled by meso-scale strike-slip faults within the chalk. The response of these faults to changes to in situ stress and fluid pressure is thought to control the nucleation and propagation of fractures in the chalk. In this study the DEM (Discrete Element Method) technique has been employed as a follow up to previous field and numerical (boundary and finite element method) investigations to ascertain the role of the faults in the initiation and nucleation of fractures The role of fluid pressure, in-situ stress, and fault geometry are recognised as focal factors. The generation of localised areas of tensile stresses due to fluid pressure and stress perturbations have been shown to cause the initiation of fractures around the fault bends. For releasing bends, localised tensile stresses tend to occur along the central segment of the fault bend, whereas for restraining bends, tensile stresses are more likely to develop on the outer edges of the fault bend. The dissimilarity in the fracturing process due to differences in the geometry of pre-existing faults demonstrates the significance of both fault geometry and fluid behaviour in controlling fracturing.Published versio

Experimental investigation of the permeability and mechanical behaviours of chemically corroded limestone under different unloading conditions

© 2019 The Authors. Published by Springer. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1007/s00603-019-01961-yThis paper investigates the mechanical properties and permeability of chemically corroded rock during deep underground tunneling. Nuclear magnetic resonance tests are carried out to quantify the chemical damage of limestone samples at the microscopic scale. Coupled hydrostatic pressure-unloading tests at different unloading rates are also conducted on these chemically corroded limestone samples to investigate permeability changes and chemical effects on mechanical behaviours. Magnetic resonance imaging, T2 spectrum distribution and porosity of the samples are obtained, and the chemical micro damage is visualized and quantified. The relationship between permeability and mechanical behaviors of the rock under hydrochemical–mechanical coupled effects is investigated. The results show that the permeability development process of the chemical corroded samples can be divided into three stages: at the first stage, the permeability initially decreases, and the second stage starts at the inflection point of the permeability curve, from where the permeability begins to increase slightly. At the third stage, the permeability of the limestone increases dramatically until the sample is ruptured. Chemical corrosion and unloading rates have a combined and significant influence on the development of micro cracks in rocks, which is the root cause of the permeability changes. A stress-permeability model is proposed to describe the permeability and stresses in chemical-corroded limestone; this can be adopted for other sedimentary rocks.Published versio