Damage initiation through extension fracturing in a moderately jointed brittle rock mass

Castro, Luiz; Grabinsky, Murray; McCreath, D.R.

doi:10.1016/s1365-1609(97)00053-1

Cited by 15 publications

(14 citation statements)

References 12 publications

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“…At low confining stresses, spalling strength in the field occurs at 0.33 to 0.5 times the UCS of that determined in the laboratory. The field spalling strength has been found to be comparable to the crack initiation (CI) threshold in the laboratory with a slope considering the HB criterion of mi = 0 (Martin 1993;Castro et al 1997;Diederichs 1999). At higher confining pressures, the field peak strength is typically found to be around a factor of 0.8 lower (i.e.…”

Section: Strength Envelopes and Confinement Dependent Failure Processmentioning

confidence: 97%

Importance of understanding laboratory strength and modulus testing data for deep mining in hard brittle rocks

Bewick¹,

Ouellet²,

Otto³

et al. 2017

Proceedings of the International Conference on Deep and High Stress Mining

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One common aspect of deep mining is the massive rock mass conditions leading to a failure process where new fractures are created through the rock. Therefore, the three dominate rock mass characteristics required for deep mining deposits are the strength, elastic properties, and pre-mining stress state. This paper focuses on characterising the strength parameters and elastic properties of rocks for deep mining purposes. Too often, strength testing data does not receive proper attention. Details are provided on the specification of confining pressures for both low (excavation skin) and high (squat pillars) confinement design specific challenges, the filtering of data to assess Hoek-Brown intact rock strength envelopes, and the interpretation of testing results. Laboratory testing data from a deep mining deposit is presented to show appropriate filtering for the determination of strength by failure type. Next the importance of understanding the elastic properties is discussed and it is shown how different relative magnitudes in elastic moduli and lithologic unit geometry impact stress and strain changes between rock units. This understanding assists engineers in determining the modulus differences leading to potential stress but, more importantly, strain gradients in the rock mass that have the potential for the generation of seismicity and rockbursts.

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Section: Strength Envelopes and Confinement Dependent Failure Processmentioning

confidence: 97%

Importance of understanding laboratory strength and modulus testing data for deep mining in hard brittle rocks

Bewick¹,

Ouellet²,

Otto³

et al. 2017

Proceedings of the International Conference on Deep and High Stress Mining

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“…The difference between the major and minor principal stresses gives the highest shearing effect possible, and it is an important parameter that is used frequently in the assessment of mining-induced stress within a rock mass (Castro 1996;Castro et al 1997;Diederichs 1999;Martin et al 1999). The maximum shear stress is half this differential stress as given in Equation (2) and the brittle shear ratio (BSR) is derived when the latter is divided by the unconfined compressive strength of an intact rock sample as presented in Equation (3) (Castro et al 2012;Martin et al 1999).…”

Section: Mining-induced Stressesmentioning

confidence: 99%

Assessment of stope sequence alternatives in a diminishing ore pillar

Shnorhokian¹,

Mitri²,

Moreau–Verlaan³

2014

Proceedings of the International Conference on Deep and High Stress Mining

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One of the primary mine planning abilities of numerical models is their assessment of stope sequence alternatives in terms of the redistribution of mining-induced stresses and the amount of rock face displacements in each of them. The models used for these studies are large and complex in nature as they need to replicate the entire orebody within which the stope sequence is being planned, in addition to the surrounding rock mass. In this paper, a case study is conducted at Vale's Garson Mine for the stope sequence options of mining in Orebody #1 Shear West, which will result in a central diminishing ore pillar before final extraction. A mine-wide numerical model is first constructed in FLAC3D and calibrated based on an in situ stress measurement point on 4900L (1,495 m) such that the values read in the field are correlated to those generated by the model. The historical stope sequence followed at the mine is then replicated between the years 2001 and 2011, which is when mining is planned to commence between the levels of interest in #1 Shear West. Extraction is planned from both the eastern and western sides of the orebody, and the default sequence is considered to alternate between the two in each successive step as they move towards the diminishing ore pillar. Using the brittle shear ratio-the relationship between the differential stress (sigma 1 to sigma 3) and unconfined compressive strength of intact rock-and volumetric analysis, the planned stope sequence is assessed within the diminishing ore pillar. A threshold of 0.7 is considered as indicative of ore at risk based on the literature and Vale guidelines. A second sequence alternative, in which extraction in the east is accelerated thrice, is also considered and compared with the planned one. A new stope sequence planning tool is introduced to visually and quantitatively compare amongst the two sequences. It is shown that by using the planning tool, the volume of unmined ore (of operational and economical interest) and the volume of ore at risk (of ground control interest) can be quantitatively estimated at any given mining step. Finally, variations in rock mass properties based on laboratory results and borehole logs are considered to assess their effect on the volume of ore at risk in the alternative sequence. https://papers.acg.uwa.edu.au/p/1410_32_Shnorhokian/ Assessment of stope sequence alternatives in a diminishing ore pillar S Shnorhokian et al. 472 Deep Mining 2014, Sudbury, Canada McKinnon 2006; Mercer & Bawden 2005a, b) such as seismic data analysis, statistical analysis, triggered seismicity, and clustering.

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“…A second criterion discussed in the literature relates the differential stress (1 -3) to the unconfined compressive strength of intact rock samples (UCSintact), and is known as the brittle shear ratio (BSR). The BSR is used mainly in the vicinity of underground openings as an indicator of fracture development within intact rock mass and strainbursts (Brace et al 1966;Castro 1996;Castro et al 2012;Castro et al 1997;Diederichs 1999;Martin 1997;Martin and Chandler 1994), and is calculated by:…”

Section: Differential Stress Indicatorsmentioning

confidence: 99%

Analysis of microseismic cluster locations based on the evolution of mining-induced stresses

Shnorhokian¹,

Mitri²,

Moreau–Verlaan³

2014

Proceedings of the International Conference on Deep and High Stress Mining

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Numerical modelling is increasingly being used in the mining industry as part of the planning process. Its areas of application range from the estimation of in situ stresses at planned locations of underground facilities, to the effects of stope sequence alternatives on drift instability. In terms of the size of their study area, numerical models can range from a section of a given level to mine-wide dimensions, with an increase in complexity and input information requirements. Microseismic activities induced by mining operations can be studied using mine-wide numerical models that have been properly calibrated. In this paper, mining-induced seismicity at the Vale Garson Mine is examined between 2006 and 2008 with a numerical model constructed in FLAC3D. Two sets of microseismic activities are used as a basis of the study; events from the microseismic database with energy outputs greater than 100 kJ, and events that have resulted in rockbursts within developments, regardless of their energy outputs, for a total of 24 events. In the first phase of the study, the coordinates and location error of each event, as obtained from the microseismic database, are used to construct a location cube defining the maximum boundaries within which the actual coordinates must lie. Based on the 24 location cubes plotted, four microseismic clusters are identified. In the second phase, the mine-wide model is calibrated based on laboratory results of rock samples, borehole data of rock mass properties, and an in situ stress measurement point on 4900L (1,495 m). The historical stope sequence followed at the mine is replicated in the model from 2001 to 2008. Mining-induced stresses within the location cubes of two clusters are examined using the maximum shear stress, brittle shear ratio, and the continuous change in differential stress (CC-DS) when compared to pre-mining conditions. It is shown that all event location cubes studied register an abrupt increase in CC-DS some time before or during the occurrence of that event. In the final phase, the most microseismically active zone in one of the geological units is compared to relatively quiet zones in terms of CC-DS conditions. It is shown that the CC-DS values are mostly constant in the latter zone, while they typically undergo abrupt and sudden changes in the active one prior to microseismic events. Hence, a new method of analysis with the potential of predicting the location of microseismic clusters is introduced.

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Damage initiation through extension fracturing in a moderately jointed brittle rock mass

Cited by 15 publications

References 12 publications

Importance of understanding laboratory strength and modulus testing data for deep mining in hard brittle rocks

Importance of understanding laboratory strength and modulus testing data for deep mining in hard brittle rocks

Assessment of stope sequence alternatives in a diminishing ore pillar

Analysis of microseismic cluster locations based on the evolution of mining-induced stresses

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