1st North American Rock Mechanics Symposium

ABSTRACT: Poor ground conditions in one area of the Golden Giant mine made the recovery of the stopes very difficult. In order to minimize ground rehabilitation and the dilution coming from the hanging wall a modified stope geometry was proposed. It was decided to extract these stopes as double width (28 m along strike rather than 15 m). The design was based on results from a detailed rock mechanics study which included the Modified Mathew's Stability Analysis, an instrumentation programme and a numerical model. This methodology has been effective in predicting potential ground conditions problems and has been proven as a valuable tool for the successful recovery of the first double width stope.

RESUMEN Se presentan y analizan las soluciones aplicadas a mejorar las condiciones de estabilidad de un talud excavado, ubicado en el km 107+520 al 107+800, de la autopista Plan de Barrancas, situada en los límites de los estados de Jalisco y Nayarit en México. Esta excavación que se realizó hasta una profundidad de 65.0 m, en una formación riolítica muy hetérogenea con presencia preponderante de agua subterránea, sufrió derrumbes desde el proceso constructivo por lo cual fue necesario revisar el proyecto para determinar las acciones necesarias para lograr su estabilización.
ABSTRACT Solutions are applied to improve the stability conditions of an excavated slope are shown and analyzed. This slope is situaded on km 107+250 to 107+800 on the Plan de Barrancas Highway in the limits of the states of Jalisco and Nayarit in Mexico. This excavation realized down to a maximum depth of 65.0 m in a formation basically composed of rhyolitic rock very heterogenous with the prevailing presence of groundwater, suffered landslides since the constructive process, for which was necessary to review the project to determine the necessary actions to obtain its stabilization.

RESUMEN
El propósito de este trabajo es mastrar la utilidad y las repercusiones económicas que tiene el haber ejecutado un estudio de estabilidad de taludes en un tajo a cielo abierto para la extracción de minerales.

ABSTRACT: In situ stope leach mining is pan of a clean mining research program designed to increase the domestic supply of metals for the United States. The U. S. Bureau of Mines (USBM) is developing this innovative mineral recovery technology to help preserve the ecosystem. The USBM is applying a systems approach to develop mineral recovery methods that minimize environmental impact by selectively extracting and recovering targeted minerals. The motivation for this approach derives from the conviction that we can no longer afford the environmental or economic cost of moving large volumes of rock to recover small amounts of metal. To accomplish a clean mining system, one must maximize the solutions contact with ore minerals and also maintain control of the leach solutions. This can be achieved by performing in situ fragmentation to obtain relatively uniform rock particle size to increase rock mass permeability, and also minimize blast damage to the perimeter of the excavation. The USBM is investigating the feasibility of in situ stope leach mining, where leaching solutions are passed through rubblized ore. Rubblizing blocks of ore by blasting for subsequent underground in-stope leaching requires special applications of blasting techniques.
This paper presents the results of in situ fragmentation of a simulated cylindrical stope which is 1.8 m in diameter and 6.1 m high. The blast design combined conventional and smoothwall blasting techniques. Three drop-raise and smoothwall blasts were used to fragment the simulated test stope.
The average powder factor for the stope fragmentation was 2.6 kg per metric ton, compared to 1.10 kg per metric ton for routine drift development work at the mine. All the material from the first blast, 14.2 metric tons, was sieved. The resulting distribution was compared to the distribution predicted by empirical equations. The best fit was found with a USBM developed equation based on over 50 sieved, reduced-scale (1-to 2-m) high wall blasts. Comparing the broken rock distribution data for round I with the photo image processing data for rounds 1, 2, and 3 shows that using photo image processing is cost effective and reasonable when compared to screening and weighing.

ABSTRACT: In this paper, the authors propose a method for improving the accuracy of GPS displacement measurements. Adaptive filtering is adopted to formulate this method. The proposed method is one of the back analysis methods used for assessing field measurement results. In order to demonstrate the applicability of the method to practical problems, a numerical simulation is demonstrated.

1 INTRODUCTION

Although the chaotic fabric of melange (from the French, mélange, or mixture) is characteristic of rocks formed within the accretion prisms of subduction zones, geologists disagree about the details of melange formation (Raymond and Terranova, 1984), as reflected in the many aliases of melange (e.g., chaotic formations, wildflysch, mega-breccia, argille scagliose and friction carpets). For engineering purposes, Medley (1994) considers melange to be a bimrock (block-in-matrix rock) which he defines as "a mixture of relatively large, competent blocks within a bonded matrix of finer and weaker texture", a definition that ignores rock genesis. Bimrocks similar to melange that are formed from cataclasis and fragmentation include breccias, coarse pyroclastics, lahars and tillites. Other bimrocks form from weathering (decomposed granite) or sedimentation (boulder conglomerates). Analagous soils, such as colluvium and till are termed bimsoils.
Melange bodies have been identified in the mountains of over 60 countries (Medley, 1994) and are exemplified by the Franciscan Assemblage (the Franciscan) a regional-scale jumble in northern California. Typically, the Franciscan contains chaotic zones of relatively strong blocks of greywacke sandstone, chert, basalts, limestone and exotic metamorphic rocks embedded within a matrix of pervasively sheared shale and argillite. The blocks range between sand particles and mountain masses, are irregularly shaped, and generally trend NNW-SSE (Figure 1). Shears are confined to the weak shale matrix, which flows around the closely jointed blocks. The sheared shale, and the sheared serpentinite bodies common in the Franciscan, are both responsible for the myriad earth-flow landslides of the Fransciscan. Also, encounters with unpredictably distributed blocks in melanges cause expensive surprises during earthwork excavations and foundation preparations.

ABSTRACT: Rock Mechanics techniques are becoming increasingly important in oil and gas reservoir exploration and development. The discrete fracture approach is one of the most promising of these, since it provides a more realistic geological description of in situ conditions. This paper provides an overview of recent developments in continuum and discontinuum rock mechanics approaches for oil and gas applications, and presents a number of brief case studies of applications of discrete fracture approaches.

ABSTRACT: Scaly clay is an argillaceous sediment, with a pervasive fabric of lenticular, highly polished, curved, slickensided surfaces and is commonly associated with mélange formations. In regions subject to tropical weathering regimes outcrops of this material erode rapidly giving rise to extensive badlands topography. Islands such as Barbados and Taiwan lose considerable areas of agricultural land to badlands generation each year and associated landslides disrupt settlements and communications.
A programme of laboratory studies has been completed to characterise the physical, mineralogical and mechanical properties of undisturbed samples of these materials. The samples, collected from different depths within weathering profiles, between ground surface and fresh materials with no sign of weathering at depth were each subject to similar experiments. These data illustrate important changes during weathering, including destruction of the original sedimentary structure, a large increase in pore volume and variations in strength.

ABSTRACT: The geometric evolution of a fracture set in a controlled laboratory experiment is accurately predicted using a physically-based network simulator (PBNS). The experimental fracture sets were produced by straining a brittle coating applied to an acrylic substrate. The physically-based fracture sets are generated using iterative solutions to the boundary value problem for multiple cracks in an otherwise homogeneous, isotropic, and linear elastic solid subject to uniform remote stress boundary conditions. A preliminary methodology for conditioning the PBNS networks to data from seismic surveys and well bore flow tests is also presented. The advantage of this methodology is that information concerning the elastic and fracture characteristics of the rocks and the mechanics of the rock fracture process can be combined with other well bore data to better estimate the geometry of a particular fractured formation.

ABSTRACT: As a part of the Canadian Rockburst Research. Programme (aimed at investigating the performance of rock support under rockbursting conditions) in-situ dynamic monitoring of various types of rockbolts loaded by blasts was performed. The aim of the monitoring was to investigate and explain the interaction of the dynamic load with the rock-rockbolt system. The measured strain waves on the bolt and the dynamic movement of the rock surface were successfully simulated numerically using a one dimensional finite difference representation of the mechanical system involving the wave source, the rockmass, the mechanical rockbolt, and the anchor and head connections. The model was calibrated using field data from the blasts, and parametric studies of the influence of various system parameters on the dynamic behaviour of the rockbolt were carried out. It was found that the wave source, rockmass modulus, tensile strength, connections at the rockbolt ends, and rockbolt pre-tension all play important roles in determining the dynamic stress levels in rockbolts.