Host Rock Mass Research Articles

Experimental study of the hydro-mechanical behavior of rock joints using a parallel-plate model containing contact areas and artificial fractures

In recent years, geological disposal of radioactive wastes is considered to be the most promising option, which requires the understanding of the coupled mechanical, hydraulic and thermal properties of the host rock masses and rock fractures. The hydro-mechanical behavior and properties of rock fractures are usually determined by laboratory experiments on fracture specimens that serve as the basic building block of the constitutive models of fractured rock masses. Laboratory testing of rock fractures involve a number of technical issues that may have significant impacts on the reliability and applicability of the testing results, chief among them are the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions, and the sealing techniques when fluid flow during shear is involved. In this study, a new shear-flow testing apparatus with specially designed fluid sealing techniques for rock fractures were developed, under constant normal load (CNL) or constant normal stiffness (CNS) constraint. The topographical data of all fracture specimens were measured before testing to constitute the geometrical models for simulating the change of mechanical aperture distributions during shearing. A number of shear-flow coupling tests were carried out on three kinds of rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro-mechanical behaviour. Some empirical relations were proposed to evaluate the effects of contact area and surface roughness on the behavior of fluid flow through rock fractures.

Using Electronic Detonators to Improve All-Round Blasting Performances

Over the past 18 months the De Beers Consolidated Mines Ltd operations have made a concerted effort to move away from using the traditional shock tube initiating systems. These systems are being systematically replaced by the use of electronic delay detonators (EDD). Various trials were conducted in both host rock and kimberlite rock masses to improve tunnel advance as well as to optimise delay timing during trough openings [1-3]. The high cost of EDD’s, when compared with traditional initiation systems, led to a number of detailed studies being conducted on the mines where EDD’s were being used. These studies aimed to quantify the additional benefits when blasting with electronic detonators. The studies showed that the change was justified on the basis of increased quality control and reliability gained through the use of EDD’s. However, these benefits attract other related benefits, like fragmentation control, and backbreak reductions. When compared to the shock tube initiating systems the increased dev...

Evaluation and application of controlling parameters for seismic events in hard-rock mines

A method is proposed for quantitative assessment and interpretation of the seismic hazard of planned excavation in a hard-rock mine. The quantitative assessment is derived from three-dimensional, elastic, boundary element modelling of the host rock mass. Parameters obtained from the modelling are associated with historical observations of seismicity in the mine to generate probabilistic relations between seismic event occurrence and event strength. The parameters used in the event spatial occurrence relations and the event strength estimates are the Factor of Safety against seismic failure for different types of seismic events, which are inferred from back analysis of field observations, and the Modelled Ground Work. The estimates of these parameters are related to the controlling quantities for a seismic event, which are a local state of stress sufficient to cause rock mass failure, and an unstable local concentration of strain energy, i.e. energy in excess of that which can be dissipated non-violently in rock mass failure. Application of the method is illustrated by reference to several case studies of mine seismicity.

Dynamic compaction properties of bentonite

Bentonite has been proposed as a primary material for sealing shafts of nuclear waste repositories. It possesses low permeability, chemical and physical stability, and compatibility with most host rock masses and groundwater chemistries. This paper investigates the construction properties of bentonite and evaluates the use of dynamic compaction in constructing an effective bentonite shaft seal. Extensive laboratory tests of dynamic compaction have been conducted to study the densification of granular bentonite mixed with distilled deionized water or with brine from the Waste Isolation Pilot Plant (WIPP). Results of the dynamic compaction investigations delineate the influence of moisture content, compactive energy, mixed brine content, lift thickness, and rammer weight on the achievable dry density. Dynamic compaction can densify bentonite to a dry density of 1.86 Mg/m 3 when mixed with WIPP brine and 1.74 Mg/m 3 when mixed with distilled deionized water. At these densities bentonite exhibits permeabilities on the order of 1.0×10 −19 m 2 .

Rock mechanics design for high pressure gas storage in shallow lined caverns : Barton, N; Monsen, K; Chyrssanthakis, P; Norheim, O Proc International Conference on Storage of Gases in Rock Caverns, Trondheim, 26–28 June 1989P159–176. Publ Rotterdam: A A Balkema, 1989

Gas storage in lined caverns with moderate rock cover has been studied from a rock mechanics viewpoint. Some of the required characteristics of the host rock mass have been identified. Studies have included numerical continuum and discontinuum modelling, the latter with various degrees of jointing. Rock cover has ranged from 50 to 150 meters. Important factors for successful storage include the need for joints of less continuity than the depth of rock cover, a need for reasonable degrees of joint roughness, and a need for a general absence of significant clay filling to ensure adequate shear strength

Heat-induced moisture movement within a clay-based sealing material

The bentonite-sand buffer material, which isolates the nuclear-fuel waste containers from the host rock mass, is a vital component of the multiple engineered barrier scheme advocated by the Canadian Nuclear Fuel Waste Management Program. This paper presents results of laboratory investigations which examine the influence of the container surface temperatures on the moisture migration within a compacted buffer in a borehole environment.