Melkoumian, NouneHashemi, Sam S.Heo, Jun Hyuk2022-12-202022-12-202022https://hdl.handle.net/2440/137091Drilling a borehole below the surface of the Earth is a mechanical process widely implemented by resource industries for various purposes, including geotechnical investigation and mineral exploration. Significant numbers of exploration boreholes are often drilled through poorly cemented formations worldwide, particularly in Australia, and often they result in technical difficulties such as stuck pipes. As such, the ability to predict the failure behaviour of poorly cemented formations due to borehole drilling is important for minimising borehole instability problems and designing effective borehole supports. This thesis presents a series of journal and conference papers studying the effect of cement content on the failure behaviour of poorly cemented sandstones in the vicinity of borehole excavation by experimental and numerical methods. Three different cement contents have been considered. There has been limited experimental research conducted to investigate the failure behaviour of poorly cemented sandstone using a convergence measuring device. In this research, a series of comprehensive laboratory studies were conducted to investigate the borehole deformation in poorly cemented sandstone rocks under different stress path regimes by using convergence measuring device (CMD) designed for laboratory scale studies. Synthetic thick-walled hollow cylinder (TWHC) specimens comprising of sand grains, Portland cement and water were prepared for this study. Mechanical properties of the synthetic sandstone specimens were investigated by conducting UCS and triaxial compression (Hoek cell) tests. The CMD was deployed inside the TWHC specimen to measure the borehole deformation. Five different stress paths were applied to the specimens to investigate the effect of stress paths and three different cement agent contents (10%, 12% and 14%) were considered to study the effect of cement content on the borehole failure. These laboratory studies showed that the stress path has a significant influence on the failure behaviour of the borehole. Due to poor cementation and granular behaviour of poorly cemented formations, Discrete Element Method (DEM) was identified as the most appropriate numerical method for generating realistic numerical models. Numerical simulations were conducted to study the influence of micro-parameters of DEM model on the results obtained from laboratory studies poorly cemented sandstone specimens.enborehole deformationconvergence measuring devicethick-walled hollow cylinderborehole monitoringThesis