20 years of excavation response studies at AECL's Underground Research Laboratory

Read, Rodney S.

doi:10.1016/j.ijrmms.2004.09.012

Cited by 323 publications

(97 citation statements)

References 15 publications

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“…The onset of brittle failure (spalling or slabbing) occurred, therefore, at a stress level of 120/212 = 0.56 UCS. This 120 MPa value was also confirmed by Read (2004), by excavating tunnels with various shapes and various orientations relative to the in situ stress state at the 420 Level in the experiment mine. It was reported that the in situ stress magnitudes were r 1 = 60 ± 3, r 2 = 45 ± 4 and r 1 = 11 ± 2 MPa at the 420 Level.…”

Section: Failure Mode and The Slabbing Strength Of Hard Rocksupporting

confidence: 62%

Influence of Sample Height-to-Width Ratios on Failure Mode for Rectangular Prism Samples of Hard Rock Loaded In Uniaxial Compression

2010

Rock Mech Rock Eng

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Surface-parallel slabbing is a failure mode often observed in highly stressed hard rocks in underground excavations. This paper presents the results of experimental studies on slabbing failure of hard rock with different sample height-to-width ratios. The main purpose of this study was to find out the condition to create slabbing failure under uniaxial compression and to determine the slabbing strength of hard rock in the laboratory. Uniaxial compression tests were carried out using five groups of granite specimens. The mechanical parameters of the sample rock, Iddefjord granite from Norway, were measured on the cylindrical and Brazilian disc specimens. The transition of the failure mode was studied using rectangular prism specimens. The initiation and the propagation of slabbing fractures in specimens were identified by examining the relationship among the applied stress, strain and the acoustic emission. The stress thresholds identified were compared to those reported by other authors for crack initiation and brittle failure. It is observed that the macro failure mode will be transformed from shear to slabbing when the height/width ratio is reduced to 0.5 in the prism specimens under uniaxial compression. Micro r 1 -parallel fractures initiate when the lateral strain departs from its linearity. Slabbing fractures are approximately parallel to the loading direction. Labotatory tests show that the slabbing strength (r sl ) of hard rock is about 60% of its uniaxial compression strength. It means that if the maximum tangential stress surrounding an underground excavation reaches about the slabbing threshold, slabbing fractures may take place on the boundary of the excavation. Therefore, the best way to stop or eliminate slabbing failure is to control the excavation boundary to avoid the big stress concentration, so that the maximum tangential stress could be under the slabbing threshold.

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Section: Failure Mode and The Slabbing Strength Of Hard Rocksupporting

confidence: 62%

Influence of Sample Height-to-Width Ratios on Failure Mode for Rectangular Prism Samples of Hard Rock Loaded In Uniaxial Compression

2010

Rock Mech Rock Eng

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“…The particles' movements obey the Newtonian second law and the contact force is calculated according to the inherent relationship between force and displacement, which is determined by the contact models in PFC. Among these, the linear springs and contact bond which are often used to simulate the mechanical behavior of brittle rock materials in other literature (Read 2004;Deluzarche and Cambou 2006;Wang and Tonon 2009;Diederichs et al 2004) are selected. In addition, because PFC uses an explicit approach to solve the equations of motion, it can be conveniently used in dynamic simulations (Hentz et al 2004;Hazzard and Young 2004).…”

Section: Pfc Model Of the Shpb System With A Special Shape Strikermentioning

confidence: 99%

Numerical Simulation of the Rock SHPB Test with a Special Shape Striker Based on the Discrete Element Method

2013

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A split Hopkinson pressure bar (SHPB) system with a special shape striker has been suggested as the test method by the International Society for Rock Mechanics (ISRM) to determine the dynamic characteristics of rock materials. In order to further verify this testing technique and microscopically reveal the dynamic responses of specimens in SHPB tests, a numerical SHPB test system was established based on particle flow code (PFC). Numerical dynamic tests under different impact velocities were conducted. Investigation of the stresses at the ends of a specimen showed that the specimen could reach stress equilibrium after several wave reverberations, and this balance could be maintained well for a certain time period after the peak stress. In addition, analyses of the reflected waves showed that there was a clear relationship between the variation of the reflected wave and the stress equilibrium state in the specimen, and the turning point of the reflected wave corresponded well with the peak stress in the specimen. Furthermore, the reflected waves can be classified into three types according to their patterns. Under certain impact velocities, the specimen deforms at a constant strain rate during the whole loading process. Finally, the influence of the micro-strength ratio (s c =r c ) and distribution pattern on the dynamic increase factor (DIF) of the strength DIF were studied, and the lateral inertia confinement and heterogeneity were found to be two important factors causing the strain rate effect for rock materials.Keywords SHPB Á Special shape striker Á Discrete element method Á Strain rate effect Micro-strength ratio (ratio of contact-bond shear to normal strength) n Time-step N Current time-step DTðnÞ Interval time under time-step n(s) l Frictional coefficient at the specimen/bar interface

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“…The stress is relatively high for the depth with a high maximum horizontal stress. Figure 4.2.2 shows one well known example from these studies associated with a mine-by experiment (Read 2004). So-called spalling failure has occurred at the top and bottom and permeability changes of up to six orders of magnitude have been measured in this excavation damaged zone (Rutqvist and Stephansson 2003;Bäckblom and Martin 1999).…”

Section: Spalling Borehole Break-out and Disturbed Zonementioning

confidence: 99%

Deep Borehole Field Test Research Activities at LBNL

Dobson¹,

Tsang²,

Kneafsey³

et al. 2016

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SUMMARYThe goal of the U.S. Department of Energy Used Fuel Disposition's (UFD) Deep Borehole Field Test is to drill two 5 km large-diameter boreholes: a characterization borehole with a bottom-hole diameter of 8.5 inches and a field test borehole with a bottom-hole diameter of 17 inches. These boreholes will be used to demonstrate the ability to drill such holes in crystalline rocks, effectively characterize the bedrock repository system using geophysical, geochemical, and hydrological techniques, and emplace and retrieve test waste packages. These studies will be used to test the deep borehole disposal concept, which requires a hydrologically isolated environment characterized by low permeability, stable fluid density, reducing fluid chemistry conditions, and an effective borehole seal.During FY16, Lawrence Berkeley National Laboratory scientists conducted a number of research studies to support the UFD Deep Borehole Field Test effort. This work included providing supporting data for the Los Alamos National Laboratory geologic framework model for the proposed deep borehole site, conducting an analog study using an extensive suite of geoscience data and samples from a deep (2.5 km) research borehole in Sweden, conducting laboratory experiments and coupled process modeling related to borehole seals, and developing a suite of potential techniques that could be applied to the characterization and monitoring of the deep borehole environment. The results of these studies are presented in this report.

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20 years of excavation response studies at AECL's Underground Research Laboratory

Cited by 323 publications

References 15 publications

Influence of Sample Height-to-Width Ratios on Failure Mode for Rectangular Prism Samples of Hard Rock Loaded In Uniaxial Compression

Influence of Sample Height-to-Width Ratios on Failure Mode for Rectangular Prism Samples of Hard Rock Loaded In Uniaxial Compression

Numerical Simulation of the Rock SHPB Test with a Special Shape Striker Based on the Discrete Element Method

Deep Borehole Field Test Research Activities at LBNL

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