Modelling of the effect of discontinuities on the extent of the fracture zone surrounding deep tunnels

Sellers, Ewan; Klerck, P.A.

doi:10.1016/s0886-7798(01)00015-3

Cited by 81 publications

(38 citation statements)

References 14 publications

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“…The strength (cohesion) was reduced to between 48 and 58% of laboratory values, in accordance with York (1998), to represent in situ rock mass properties. For the contact planes, Sellers and Klerck (2000) used a friction angle of 30° (and zero cohesion) between rock layers to simulate laboratory experiments.…”

Section: Calibration Of a Numerical Model For Bore-and-fill Miningmentioning

confidence: 99%

“…In an idealized triaxial stress field, where the intermediate principal stress is oriented parallel to the hole axis, high tangential shear stresses are developed along the borehole sidewalls oriented parallel to the minor principal stress axis. Failure will either take the form of conjugate fracture zones which intersect at some distance from the borehole wall (Haimson and Song, 1993), or extensile fracturing sub-parallel to the borehole wall and parallel to the major compressive stress direction (Ewy and Cook, 1990;Lee and Haimson, 1993;Sellers and Klerck, 2000). The former results in wedge-shaped fallout bounded by shear fractures, and generally occurs in weak sedimentary rocks.…”

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confidence: 99%

“…This model has subsequently been implemented in the main FLAC and FLAC3D codes. Sellers and Klerck (2000) performed tests on cubes of quartzite and norite containing a cylindrical hole drilled halfway through the samples. Solid and layered samples were tested.…”

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confidence: 99%

“…Sellers and Klerck (2000) showed that the presence of contact planes influences the fracturing, tending to constrain the damage between these planes. This was also observed between CLR contacts at the pilot site.…”

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Calibration of a numerical model for bore-and-fill mining

Roberts¹

2017

J. South. Afr. Inst. Min. Metall.

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Tau Tona mine has historically experienced damaging seismicity during attempts to extract its high-grade, highly stressed shaft pillar (Murphy, 2012). In an attempt to reduce the potential for seismic events a new mining method that involves the boring of largediameter holes on-reef has been trialled. The rationale behind reef boring is that it reduces the effective stoping height, thus limiting the influence of the excavation on the surrounding rock mass. This is particularly important in the shaft pillar, as high deformation and closure are associated with increased seismic hazard.Optimization of the boring sequence and in-hole support enable the extraction of as much of the reef as possible, while minimizing waste rock mining. Support must be installed in such a way that workers are never required to enter the holes. Filling the holes with a stiff, strong material will achieve these goals. Concrete, for example, has low porosity, can be engineered to have high strength and stiffness, and is easily poured or pumped into the holes from service excavations.This paper describes how observations and measurements at a reef-boring pilot site were used to calibrate nonlinear numerical models. Initial models were calibrated based on observations of breakout and additional fracturing that was exposed when a raise was mined along the axis of an existing hole. A novel criterion for simulating breakout was developed, based on displacement into the hole and parallel to the minor stress axis. This criterion was used with the calibrated model to simulate the drilling and filling of a sequence of five holes. Some of these holes were instrumented with stress-change gauges and some were scanned and surveyed. The in situ data was compared with modelled outcomes.The feasibility of reef boring was considered by Jager, Westcott, and Cook (1975). They analysed various reefs in terms of deviation from planarity, presenting charts and tables to indicate optimal hole diameters in different mining areas. Adams (1978) describes stoping using a raiseboring machine on the Carbon Leader Reef (CLR) at West Driefontein mine. Holes were drilled adjacent to each other to create a continuous slot between reef drives. Pilot holes were bored and then used to guide a raisebore reamer from the upper reef drive. The completed slot is shown in Figure 1. Calibration of a numerical model for bore-and-fill mining by D. RobertsBore-and-fill mining was implemented at a pilot site in Tau Tona mine's shaft pillar on 97 level. Observations, scan data, and measurements from this site were used to calibrate an inelastic numerical model of bore-andfill mining within the Carbon Leader Reef (CLR).Borehole breakout was found to occur around holes at the site as they were bored. A strike-parallel exposure showed that fracturing within the Carbon Leader stratum extended far beyond the breakout (up to 1.2 m from the hole sidewall). This was confirmed by borehole camera observations in a hole drilled on-reef through a bored-and-filled hole.A Mohr-Coulomb strain-softeni...

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Section: Calibration Of a Numerical Model For Bore-and-fill Miningmentioning

confidence: 99%

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Calibration of a numerical model for bore-and-fill mining

Roberts¹

2017

J. South. Afr. Inst. Min. Metall.

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“…Many specialists have implemented several types of methods to explain the phenomenon. Sellers and Klerck (2000) believed discontinuous surfaces could be one of the origins of zonal disintegration. Malan and Spottiswoode (1997) analysed the relationship between shock bumps and zonal disintegration.…”

Section: Introductionmentioning

confidence: 99%

Analogical model test and theoretical analysis on zonal disintegration based on filed monitoring in deep tunnel

Chen¹,

Wang²,

Zhang³

et al. 2013

European Journal of Environmental and Civil Engineering

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Fracture propagation in Indiana Limestone interpreted via linear softening cohesive fracture model

2015

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We examine the use of a linear softening cohesive fracture model (LCFM) to predict single-trace fracture growth in short-rod (SR) and notched 3-point-bend (N3PB) test configurations in Indiana Limestone. The broad goal of this work is to (a) understand the underlying assumptions of LCFM and (b) use experimental similarities and deviations from the LCFM to understand the role of loading paths of tensile fracture propagation. Cohesive fracture models are being applied in prediction of structural and subsurface fracture propagation in geomaterials. They lump the inelastic processes occurring during fracture propagation into a thin zone between elastic subdomains. LCFM assumes that the cohesive zone initially deforms elastically to a maximum tensile stress (σ max ) and then softens linearly from the crack opening width at σ max to zero stress at a critical crack opening width w 1 . Using commercial finite element software, we developed LCFMs for the SR and N3PB configurations. After fixing σ max with results from cylinder splitting tests and finding an initial Young's modulus (E) with unconfined compressive strength tests, we manually calibrate E and w 1 in the SR model against an envelope of experimental data. We apply the calibrated LCFM parameters in the N3PB geometry and compare the model against an envelope of N3PB experiments. For accurate simulation of fracture propagation, simulated off-crack stresses are high enough to require inclusion of damage. Different elastic moduli are needed in tension and compression. We hypothesize that the timing and location of shear versus extensional micromechanical failures control the qualitative macroscopic force-versus-displacement response in different tests. For accurate prediction, the LCFM requires a constant style of failure, which the SR configuration maintains until very late in deformation. The N3PB configuration does not maintain this constancy. To be broadly applicable between geometries and failure styles, the LCFM would require additional physics, possibly including elastoplastic damage in the bulk material and more complicated cohesive softening models.

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Modelling of the effect of discontinuities on the extent of the fracture zone surrounding deep tunnels

Cited by 81 publications

References 14 publications

Calibration of a numerical model for bore-and-fill mining

Calibration of a numerical model for bore-and-fill mining

Analogical model test and theoretical analysis on zonal disintegration based on filed monitoring in deep tunnel

Fracture propagation in Indiana Limestone interpreted via linear softening cohesive fracture model

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