The measurement and interpretation of in-situ stress using an overcoring technique from surface

Gray, Ian; See, L.

doi:10.1201/noe0415444019-c89

Cited by 6 publications

(3 citation statements)

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“…Two relief methods commonly used in hard rock mining are acoustic emissions testing and overcoring; they are indirect stress measurements that are inferred from the elastic response of stress relief by the overcoring process (Gray & See 2007;Hakala et al 2003;Kanagawa et al 1986;Worotnicki 1993). The strain gauge data is used to determine the complete 3D stress tensor (Figure 1).…”

Section: Relief Methodsmentioning

confidence: 99%

In situ stress data management and analysis: implications for numerical modelling

Musolino¹,

Chester²,

Ford³

2022

Caving 2022: Fifth International Conference on Block and Sublevel Caving

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The measurement of in situ stresses is a costly and time intensive procedure, requiring significant experience, diligence and planning to obtain reliable results. Therefore, it is important to have good data management and analysis to maintain investment costs and reduce estimate uncertainty. Geotechnical design considerations rely on accurate estimates of the stress regime to predict subsurface rock behaviour. Some uses include cave deconfinement, cave preconditioning, planning drive orientation and ground support design. Two simple numerical models are presented. The first demonstrates stress redistribution around a cave zone and how it may influence optimal crusher chamber placement. The second model is of an undercut level and the stress experienced by the drawbell drives below. The models demonstrate the impact of in situ stress uncertainty, with potential consequences for design decisions by altering the stress trend and plunge. Currently, pragmatic workflows are not publicly available that holistically detail the key steps in in situ stress data analysis. In addition, rarely are end-users of the data demonstrated the uncertainty in the values provided. Instead, they are presented with a single stress average gradient and trend. This manuscript offers a workflow for those embarking on in situ stress testing campaigns and serves as a tool to communicate the complexities to potential end-users. The workflow utilises the Euclidian mean rather than scalar averaging of the stress tensor and relates 'loading methods' (hydrofracking) and 'other' (borehole breakout observations) methods of stress estimation with the full tensor resolved from relief methods (overcore and acoustic emissions). A software application within the mXrap suite is presented as a potential aid to stress data management and analysis. Implications of stress uncertainty are demonstrated and discussed concerning design, expected induced fracture orientations, and future workflow enhancements. The numerical models indicate optimal placement for a crusher chamber around a simulated cave zone was observed to be in the orientation of SHmax. Increasing the stress field plunge by 20° impacted optimal crusher placement. The second numerical model demonstrates that a rotation of the horizontal stress trend by 20° has noticeable impact on the differential stress in the backs of a tunnel where drawbells will be created, this has implications for planning the undercut veranda length.

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Section: Relief Methodsmentioning

confidence: 99%

In situ stress data management and analysis: implications for numerical modelling

Musolino¹,

Chester²,

Ford³

2022

Caving 2022: Fifth International Conference on Block and Sublevel Caving

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“…Rib pillar stability control is possible with the methods connected with the stress-strain analysis, indirect geophysical estimates and instrumental measurement of deformations. The first group methods are based on measurement of unloading deformations and their conversion to stresses, or on recording of force interaction between a sensor and enclosing rocks [12,13]. The same group methods include compensation techniques such as borehole slotter or overcoring, with subsequent stress recovery using hydraulic jacks and hydraulic cushions [14,15], and also stress measurement using various memory effects in rocks [16,17].…”

Section: Introductionmentioning

confidence: 99%

Operational control of rib pillar stability

Baryah¹,

Evseev²,

Lomakin³

et al. 2020

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In room-and-pillar mineral mining, rib pillars should support overlying rock mass for the specified time limit of production. Therefore, one of the mining safety components is monitoring of the behavior of rib pillars in the course of time. For the conditions of the room-andpillar method of mining, the authors propose a monitoring procedure for rib pillar deformation based on operational measurements of horizontal convergence in stopes. The theoretical and experimental research proves that transverse deformation of rib pillars is an informative parameter suitable for generalized assessment of pillar failure. The obtained ranges of critical transverse deformation rates (50–100 mm/m/yr) in rib pillars can tentatively be used as an indicator of the critical stability of load-bearing structures in room-and-pillar mining. In-situ determination of the integral transverse deformation rates in rib pillars is based on the ratio of the measured horizontal convergence in stopes to the width of pillars. Implementation of the proposed approach in the Upper Kama potash salt mines has proved its applicability to identification of rock mass areas where intense deformation is expected. The comparison of the monitoring data of the transverse deformation rates and their critical values determined makes it possible to predict service life of rib pillars, which is very important in terms of safety of mining operations. This study was supported by the Russian Science Foundation, Grant No. 19-77-30008.

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“…Hence a knowledge of the azimuths of cleat and joints in coal, as well as in-situ stress azimuths, is fundamental to CSG production. For a review of the influence of stress azimuth and magnitude on coal permeability the reader is referred to Bell, 2006 (and paper reviews therein), Gray and See, 2007, Titheridge, 2014and Mukherjee et al, 2017 that are represented by lineations on an image log (Figures 1 and 2). These are definitions of simplicity and convenience for this paper (cf Laubach et al, 1998;Dawson and Esterle, 2010).…”

Section: Introductionmentioning

confidence: 99%

The Use of Coring-Induced Petal Fractures in Coal to Supplement and Ground Truth the Interpretation of Image Logs

Titheridge¹,

Mukherjee

2018

ASEG Extended Abstracts

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In this paper the term "joint" refers to planar Mode 1 extension joints that intersect the entirety of the bore wall. A joint is represented by a sinusoidal trace on an image log. The term "cleat" refers to smaller scale features, that intersect one or both sides of the bore wall SUMMARYResistivity and acoustic scanner image logs, in both the CSG and coal-mining industries, are the preferred means of determining azimuths of joints and cleat in coal. This paper indicates the need for care when interpreting cleat azimuths from image logs.Image logs of the bore wall often exhibit large fractures (joints) that intersect the entirety of the bore wall. They are visible as sinusoidal traces. Those fractures that have low height (cleat), and intersect the bore wall in one or two places, are represented by vertical to sub-vertical linear traces on an image log. These lineations can be represented on a stereo-or polar net as a point with a plunge and trend. Both joints and cleat generally have high dips (greater than 75°).Resistivity image logs detect both joints and cleat. Acoustic image logs often only record joints. The value of obtaining cleat, joint and horizontal stress azimuths, is in planning the optimal orientation of deviated in-seam (lateral) production wells.An image log of a cleat lineation records the bore wall intersection azimuth (BIAZ), that is an apparent azimuth, as well as the apparent dip (or plunge) of the lineation. The best way to determine true azimuth of cleat from lineations, on an image log, is from a statistical weighted mean of numerous BIAZ measurements. In some instances, cleat azimuth has been calculated as 90° to BIAZ. Some interpreters view the dispersion of azimuths as a natural feature, when the dispersion is an artefact arising from the intersection of cleat of the same azimuth, at varying distances from the centre of a bore wall.Petal fractures (PF) in coal, when combined with breakout information, can also be used to determine or ground truth joint/cleat azimuths of both large and small scale fractures. Bedding-plane observations of core also provides cleat/fracture information not obtainable from an image log.

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The measurement and interpretation of in-situ stress using an overcoring technique from surface

Cited by 6 publications

References 0 publications

In situ stress data management and analysis: implications for numerical modelling

In situ stress data management and analysis: implications for numerical modelling

Operational control of rib pillar stability

The Use of Coring-Induced Petal Fractures in Coal to Supplement and Ground Truth the Interpretation of Image Logs

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