1st North American Rock Mechanics Symposium

ABSTRACT: We measured guided wave trapped in a subsurface artificial fracture in Higashi-Hachimantai Hot Dry Rock model field, Japan. The subsurface fracture was produced at about 370 m depth in an intact welled tuff layer by hydraulic fracturing. We used a downhole air gun as a wave source. Because energy of the guided waves concentrates in a fluid layer, a hydrophone was used to detect the guided waves. We determine the arrival of guided wave by an analysis of tube wave, to which the guided wave converts at an intersection of a borehole and the subsurface fracture.
We found that travel time of the guided wave increased corresponding to pressurization of fracture. This phenomenon cannot be explained by the simple parallel wall fracture model. Observed velocity decrease is thought to be caused by effects of actual properties of the subsurface fracture; contact of asperities of the fracture surfaces and elastic variation of the rock due to pressurization.

ABSTRACT: Rock indentation experiments in granite and marble are carried out using a hemispherical indenter. A thorough investigation of the indenting process is made and quantitative data of rock fragmentation and fracture obtained. A two dimensional micro-mechanics constitutive model is applied to simulate the actual median fracture system. The model simulation reveals quantitatively the effects of loading force, rock mechanical properties and micro fractures on the median crack system.

ABSTRACT: Durability is the one factor that has proven to be of utmost concern in the cost of rock for erosion control. Three areas of knowledge having the greatest effect on selecting a durable product if properly utilized are (1) intrinsic rock properties, (2) quarrying techniques, and (3) weathering processes. A correlation between rock properties and durability may improve the results of the exploration efforts. Employment of proper quarrying techniques may result in production of a more durable stone. Knowledge of the relationship between weathering processes and both rock properties and quarrying techniques will lead to a more durable stone product.

ABSTRACT: The interaction of impact generated elastic stress waves with discontinuities in solids is considered. In this contribution, the evolution in time of damage at a bimaterial interface is described by an exponential growth law of Kachanov-type and a finite difference method has been adapted for the investigation of progressive deterioration of an interface. The particular case of a shear wave impacted stick-slip-interface is presented.

ABSTRACT: Both laboratory and field tests show that the seismic amplitude tomography (SAT) owns higher capability in sensing joint properties and distribution than the available velocity tomography Experimental comparisons between amplitude and velocity are illustrated concerning joint parameters such as aperture, joint roughness, joint frequency, and dilation under various normal and shear stresses. Then, two kinds of mapping by SVT and SAT which were obtained from the investigation of the dam site are discussed in terms of joint orientation and distribution.

ABSTRACT: Through analysis of geomechanical mechanisms controlling deformation and fracture development around excavations in bedded salt, analysis of ten years of geomechanical instrument data, and direct monitoring of a large roof fall, a basis for roof fall monitoring and prediction has been developed for excavations at the Waste Isolation Pilot Plant.

ABSTRACT: Canadian hardrock mines recognize the need to radically improve competitiveness in increasingly deeper reserves. The interaction between mining rock mechanics and the new information and automation technologies is examined as a means to re-engineer the mining process at depth. This will be dependent upon advances in mining methods, geosensing, machine intelligence, and intelligent planning and control systems.

ABSTRACT: Reinforced shotcrete maintains its functionality and sustains only minor damage when exposed to peak particle velocities of 1.5 to 2 m/s (60 to 80 in/s) due to nearby blasting. Mesh reinforced shotcrete performs better than steel fibre reinforced shotcrete under very severe dynamic loading conditions. Mesh reinforced shotcrete can continue to retain broken rock even when extensively cracked, whereas fibre reinforced shotcrete loses this ability and may itself become a safety hazard.