Time-dependent characterisation of rocks for the entire strain range (i.e. up to and beyond the yield point, where rocks are expected to be fractured) have received considerable attention for improving the long-term stability of deep underground openings. Although extensive experimental studies have been carried out on creep of different types of rocks, very limited studies exist, which investigate intact as well as fractured rock samples taken from the same type of rock. In this paper, the time-dependent behaviour of muddy siltstone was investigated to determine and compare creep properties of intact and fractured rock samples. A series of multistage uniaxial and triaxial creep tests were conducted on the rock samples at room temperature. In addition, multistage triaxial testing was conducted on the rock (intact and fractured) to determine the instantaneous (short-term) stiffness and explore its correlation with creep properties. All stain curves showed an initial instantaneous strain followed by two phases of timedependent strain including transient creep phase (particularly for the first loading stage) and a steady state creep phase. The results indicate that both the instantaneous and creep strain are proportional to the deviatoric stress and confining pressure. This is clearly evident in the fractured rock samples, where larger deviatoric stress resulted in an increased creep strain and strain rate. The relationship between axial strain and time was successfully fitted to Burgers creep model. In comparison with the intact rock, creep parameters (of the Burgers model) for the fractured rock were found to be significantly smaller, corresponding to the larger creep deformation and steady-state creep rate experienced by the fractured rock samples. Despite this difference between the intact and fractured rock samples, the study showed a considerable correlation between the creep parameters of both types of rock samples and their instantaneous elastic modulus (obtained at typical confining pressures). Regression analysis revealed that creep parameters could be reasonably estimated from instantaneous elastic modulus using an exponential function. Furthermore, based on the experimental findings, an improved characterisation of timedependent properties was proposed. We believe this approach provides a good basis for future research to enhance geotechnical modelling of long-term stability of abandoned mines as well as for the application of underground disposal of radioactive waste and oil and gas storage.

© ICE Publishing, all rights reserved. This is an author produced version of a paper published in International Journal of Physical Modelling in Geotechnics. Uploaded in accordance with the publisher's self-archiving policy.eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.Effect of high temperatures on sandstone -a computed tomography scan study The impact of high temperatures on rocks is a topic of growing importance in geotechnical engineering because of its relevance to applications such as underground nuclear fuel storage, geothermal energy resource exploration, and underground coal gasification (UCG). This paper presents results from tests performed on samples of sandstone treated to a range of temperatures between 20 and 1000°C. Sandstone samples obtained from underground coal gasification (UCG) trial sites in Poland were selected for the tests. Multistage triaxial tests were used to determine the mechanical properties of the samples.X-ray diffraction (XRD) and thermal analyses (TA) were performed to investigate the changes in the physical and chemical properties of the samples under increasing temperature. Micro-computed gomography analyses were carried out on selected samples in order to reveal the microstructural changes that take place as a result of the heating process. 3D characterization of the sample porosity and pore size distribution were performed to obtain a quantitative comparison between samples subjected to different temperature treatments. The relationship between micro-structure and macro-mechanical characteristics of sandstone at high temperature is discussed. The results illustrate that the mechanical properties of sandstone are closely related to alterations of microstructure that result from increased temperatures. IntroductionThe effect of high temperature on the thermo-mechanical response of rocks is important for several engineering applications, including underground nuclear waste storage, geothermal energy resource exploration, and underground coal gasification (UCG). Generally, the scope of high temperature ranges from normal temperatures (10-50 ¡C) to extreme temperatures (1000-1500 ¡C). Under the influence of high temperatures, the mechanical properties o...

During the last thirty years, the Boulby Potash Mine has replaced the concrete shaft linings in sections of both shafts on two occasions following progressive deterioration. A third replacement lining is now under construction in the man shaft. This paper reports the results of two-dimensional (2D) and three-dimensional (3D) numerical modelling of the shaft linings and their surrounding strata. The numerical modelling, using FLAC 2D and FLAC 3D has considered the detrimental effect to lining stability of a weak rock zone surrounding the shafts at depth. The 3D modelling work has also taken into account the formation of an inset and roadway leading from the shaft. This research aimed to identify the failure mechanisms of the shaft linings in the affected zone and their causes. The research also supplied reference data to allow the prediction of stress and deformation conditions in the newly designed third shaft relining system.

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk Abstract:Probabilistic analysis and numerical modelling techniques have been combined to analyse a deep coal mine roadway. Using the Monte Carlo method, a correlation control algorithm and a FLAC 2D finite difference model, a probability distribution of roof displacements has been calculated and compared to a set of measurements from an actual mine roadway. The importance of correlation between input parameters is also considered. The results show that the analysis performs relatively well, but does tend to over predict the magnitude of displacements. Correlation between parameters is shown to be very important, particularly between the three model stresses.

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