Collection of data from the PhD Thesis "Thermo-mechanical loading of intact rock and discontinuities" by J Woodman. This collection of data includes raw logged .csv datafiles of uniaxial compression testing and triaxial compression testing on intact synthetic compositions, as well as intact and discontinuous specimens of Thornhill Rock and Midgley Grit at both ambient temperatures, and temperatures up to 100°C.

This dataset shows both the micro-scale mechanisms and acoustic response involved in shear failure of a deforming porous rock. To our knowledge, this is the first such dataset to combine simultaneous acoustic measurements and x-ray tomography imaging. It comprises a time-series of 3D in-situ synchrotron x-ray microtomography (µCT) volumes showing a Clashach sandstone sample (CL10) undergoing triaxial deformation to failure under a constant acoustic emissions (AE) event rate. Use of a constant AE event rate slowed down the failure process after peak stress, enabling shear failure to be captured in unprecedented spatio-temporal detail by the µCT volumes. These volumes are accompanied by the local incremental 3D strain fields and simultaneously acquired waveforms from acoustic emissions and ultrasonic velocity surveys, as well as mechanical bulk stress and strain. These data are fully explained in Cartwright-Taylor et al. Seismic events miss important grain-scale mechanisms governed by kinematics during shear failure of porous rock, in review at Nature Communications. We also include an equivalent time-series of the same data types showing a second Clashach sandstone sample (CL04) undergoing triaxial deformation to failure, this time under a constant strain rate where failure happened abruptly, shortly after peak stress. Both collections were acquired in-situ on the beamline I12-JEEP at the Diamond Light Source, Didcot, UK, in September 2019. Each 3D µCT volume of the sample is contained in a .zip file labelled with the sequential scan number. Each volume comprises reconstructed 16-bit grey-scale data in a sequence of 2D image files (.tif), each numbered according to the depth at which it lies within the sample volume. The file dimensions are pixels, with an edge length of 7.91 µm. Two further .zip files contain the incremental 3D volumetric and deviatoric strain fields, obtained from digital volume correlation between neighbouring µCT volumes. Each strain field consists of a 32-bit 3D image file (.tif) in pixels with an edge length of 316.4 µm, labelled with its scan increment. Also included are (i) .csv files, containing the mechanical stress and strain time-series, the time and mechanical data at which each µCT volume was scanned, and the acoustic emissions event rate data, and (ii) .zip files containing times and waveforms for the acoustic emissions and ultrasonic velocity surveys as .ascii files. The .zip and .xlsx files are labelled with the sample name, the data type (grey-scale, strain-volumetric, strain-deviatoric, seismic, mechanical, mechCT, eventrateAE) and the sequential scan number (grey-scale only) according to the following convention: sample_datatype_scan#. We acknowledge Diamond Light Source for time on beamline I12-JEEP under proposal MG22517. This work is supported by the UK's Natural Environment Research Council (NERC) through the CATFAIL project NE/R001693/1 Catastrophic failure: what controls precursory localisation in rocks?

P* data obtained through hydrostatic loading experiments, using triaxial experimental apparatus, as well as yield curve data obtained through differential loading tests, prior to the discovery of P* for different synthetic sandstones. The methodology used was taken from Bedford et al. (2018, 2019). Grain size analysis data obtained using a Beckman Coulter LS 13 320 laser diffraction particle size analyser. Particle analysis was conducted on five different synthetic sandstones with different grain size distributions. Secondary electron and backscatter electron SEM images for natural and synthetic sandstones. Secondary electron images were stitched together to form a whole core image. They were then binarised following the methodology of Rabbani and Ayatollahi. (2015). Hexagon grid size data used to obtain the correct grid size for performing porosity analysis across an mage using Fiji software (Brown, 2000). Bedford, J. D., Faulkner, D. R., Leclère, H., & Wheeler, J. (2018). High-Resolution Mapping of Yield Curve Shape and Evolution for Porous Rock: The Effect of Inelastic Compaction on 476 Porous Bassanite. Journal of Geophysical Research: Solid Earth, 123(2), 1217–1234. Bedford, J. D., Faulkner, D. R., Wheeler, J., & Leclère, H. (2019). High-resolution mapping of yield curve shape and evolution for high porosity sandstone. Journal of Geophysical Research: Solid Earth. Brown, G. O., Hsieh, H. T., & Lucero, D. A. (2000). Evaluation of laboratory dolomite core sample size using representative elementary volume concepts. Water Resources Research, 36(5), 484 1199–1207. Rabbani, A., & Ayatollahi, S. (2015). Comparing three image processing algorithms to estimate the grain-size distribution of porous rocks from binary 2D images and sensitivity analysis of the grain overlapping degree. Special Topics & Reviews in Porous Media: An International Journal, 6(1).

This collection comprises two time-series of 3D in-situ synchrotron x-ray microtomography (μCT) volumes showing two Ailsa Craig micro-granite samples (ACfresh02 and ACHT01) undergoing triaxial deformation. These data were collected in-situ at the PSICHE beamline at the SOLEIL synchrotron, Gif-sur-Yvette, France in December 2016 (standard proposal 20160434) and are fully explained in Cartwright-Taylor A., Main, I.G., Butler, I.B., Fusseis, F., Flynn M. and King, A. (in press), Catastrophic failure: how and when? Insights from 4D in-situ x-ray micro-tomography, J. Geophys. Res. Solid Earth. Together, these two time-series show the influence of heterogeneity on the micro-crack network evolution. Ailsa Craig micro-granite is known for being virtually crack-free. One sample (ACfresh02) remained as-received from the quarry until it was deformed, while the second (ACHT01) was slowly heated to 600 degC and then slowly cooled prior to deformation in order to introduce material disorder in the form of a network of nano-scale thermal cracks. Thus these two samples represent two extreme end-members: (i) ACfresh02 with the lowest possible (to our knowledge) natural pre-existing crack density, and so is a relatively homogeneous sample and (ii) ACHT01 with a thermally-induced nano-crack network imprinted over the nominally crack-free microstructure, and therefore has increased heterogeneity relative to ACfresh02. Each 3D μCT volume shows the sub-region of each sample in which the majority of damage was located and has three parts. Part one is reconstructed 16-bit greyscale data. Part two is 8-bit binary data showing individual voids (pores and micro-cracks) in the dataset after segmentation. Part three is 32-bit data showing the local thickness of each void, as in Cartwright-Taylor et al. (in press) Figures 4 and 5. Each part is a zip file containing a sequence of 2D image files (.tif), sequentially numbered according to the depth (in pixels, parallel to the loading axis) at which it lies within the sample volume. File dimensions are in pixels (2D), with an edge length of 2.7 microns. Each zip file is labelled with the sample name, the relevant letter for each 3D volume as given in Cartwright-Taylor et al. (in press) Tables 3 and 4, part 1, 2 or 3 (depending whether the data are greyscale, binary or local thickness respectively), the differential stress (MPa) on the sample, and the associated ram pressure (bar) to link with individual file names. The following convention is used: sample_letter_part_differentialstress_rampressure_datatype. Also included are (i) two spreadsheets (.xlsx), one for each sample, containing processing parameters and the mechanical stress and strain at which each volume was scanned, and (ii) zip files containing .csv files containing measurement data for the labelled voids in each volume. N.B. void label numbers are not consistent between volumes so they can only be used to obtain global statistics, not to track individual voids.

The mechanics of olivine deformation play a key role in long-term planetary processes, including the response of the lithosphere to tectonic loading or the response of the solid Earth to tidal forces, and in short-term processes, such as post-seismic creep within the upper mantle. Previous studies have emphasized the importance of grain-size effects in the deformation of olivine. Most of our understanding of the role of grain boundaries in the deformation of olivine is inferred from comparison of experiments on single crystals to experiments on polycrystalline samples, as there are no direct studies of the mechanical properties of individual grain boundaries in olivine. In this study, we use high-precision mechanical testing of synthetic forsterite bicrystals with well characterized interfaces to directly observe and quantify the mechanical properties of olivine grain boundaries. We conduct in-situ micropillar compression tests at high-temperature (700°C) on bicrystals containing low-angle (4• tilt about [100] on (014)) and high-angle (60• tilt about [100] on (011)) boundaries. During the in-situ tests, we observe differences in deformation style between the pillars containing the grain boundary and the pillars in the crystal interior. In the pillars containing the grain boundary, the interface is oriented at ∼ 45° to the loading direction to promote shear. In-situ observations and analysis of the mechanical data indicate that pillars containing the grain boundary consistently support elastic loading to higher stresses than the pillars without a grain boundary. Moreover, the pillars without the grain boundary sustain larger plastic strain. Post-deformation microstructural characterization confirms that under the conditions of these deformation experiments, sliding did not occur along the grain boundary. These observations support the hypothesis that grain boundaries are stronger relative to the crystal interior at these conditions. This data set is associated with the pre-print manuscript with the DOI: 10.22541/essoar.167979601.17867144/v1

These data contain time series of stress, strain, confining pressure, pore pressure, pore volume, permeability and elastic wave velocities of samples of Purbeck Limestone deformed under hydrostatic and triaxial conditions at room temperature. All samples were saturated with decane as pore fluid.This dataset is used and fully described/interpreted in the paper: Brantut, N., M. Baker, L. N. Hansen and P. Baud, Microstructural control of physical properties during deformation of porous limestone, submitted to J. Geophys. Res.

Friction coefficient and frictional stability (rate & state parameter) data for triaxially compressed direct shear experiments on kaolinite-rich china clay and Mg-montmorillonite fault gouges (<2micron grain size). A total of 19 raw experimental datasets are presented as detailed in the index files: 13 on kaolinite-rich china clay, and 6 on cation-exchanged Mg-Montmorillonite. The raw data files, logged at either 1 or 2Hz, comprise confining pressures, upstream and downstream fluid pressures, force experienced by the direct shear assembly during triaxial compression, and absolute volumes of the confining pressure and fluid pressure reservoirs. Data is provided as measured by gauges in the pressure vessel in Volts, and also as calculated in MPa, kN and mm3. Also presented are the outputs of MATLAB models run to simulate the rate and state parameters k, a, b, dc and f0 for each experiment, with error data presented as 2sigma and standard error values. Parameters were determined using a non-linear least-squares fitting routine with the machine stiffness treated as a fitting parameter (c.f. Noda and Shimamoto, 2009). Data were fit by a single set of state variables (a, b, dc) with a linear detrend. Also presented are the outputs of Specific Thermogravimetric Analyses on kaolinite-rich china clay and Mg-montmorillonite.

Geomechanical strength data of mudstone samples collected from the Gunthorpe Member, of the Sidmouth Mudstone Formation of the Mercia Mudstone Group. Testing includes Uniaxial Compressive Strength (UCS), Indirect Tensile Strength (ITS) and Triaxial strength testing completed at the University of Leeds (UoL) and Point Load testing and thermal loading testing completed at the British Geological Survey (BGS). All sample preparation, preservation and testing were completed to the specification outlined by the ISRM (2007) unless otherwise stated. For all Triaxial testing, each sample was deformed under standard triaxial stress conditions, where the primary principal stress corresponds to the axial stress and the intermediate and minimum principal stresses are equal to that of the confining pressure. The data are separated into individual Excel files (.xlsx), with each file representing a single test. Each file contains time, force, stress, displacement, and strain data.

Geomechanical strength data of mudstone samples collected from the Gunthorpe Member, of the Sidmouth Mudstone Formation of the Mercia Mudstone Group. The testing was completed at the British Geological Survey (BGS). All sample preparation, preservation and testing were completed to the specification outlined by the ISRM (ISRM, 1978b; ISRM, 1978a; Bieniawski and Bernede, 1979; ISRM, 1985 for determining the indirect tensile strength, triaxial strength, UCS and point load strength respectively) unless otherwise stated. Each test was comprised of three main stages: 1) A heating stage where the sample is heated to a set temperature loading scheme under pressure conditions of 1-1.4 MPa axial stress and 0.5 MPa confining pressure throughout the heating stage 2) A preloading stage, where the confining pressure is increased to 5 MPa which was held throughout the triaxial compression test. 3) Triaxial compression test, during the active deformation phase, the samples were axially loaded using a constant displacement rate of 0.0012 mm s-1. The data are separated into individual Microsoft Excel files, with each file representing a single test. Each file contains time, force, stress, displacement, and strain data. The data are separated into individual Excel files (.xlsx), with each file representing a single test. Each file contains time, force, stress, displacement, and strain data.

Geomechanical strength data of mudstone samples collected from the Grey Shale Member, of the Whitby Mudstone Formation of the Lias Group. Testing includes Uniaxial Compressive Strength (UCS), Indirect Tensile Strength (ITS) and Triaxial strength testing completed at the University of Leeds (UoL) and Point Load testing completed at the British Geological Survey (BGS). All sample preparation, preservation and testing were completed to the specification outlined by the ISRM (2007) unless otherwise stated. For all Triaxial testing, each sample was deformed under standard triaxial stress conditions, where the primary principal stress corresponds to the axial stress and the intermediate and minimum principal stresses are equal to that of the confining pressure. The data are separated into individual Excel files (.xlsx), with each file representing a single test. Each file contains time, force, stress, displacement, and strain data.