ABSTRACT: The point estimation method can be applied to the safety factor (SF) equation for any specified rock slope failure mode (such as plane shear, step path, or wedge) to obtain reliable estimates of the mean and standard deviation of the SF probability distribution. A gamma probability density function is recommended for modeling this probability distribution, because it allows only for positive values and is flexible enough to provide symmetrical shapes and right-skewed, exponential-type shapes for the SF distribution. The mean and standard deviation define this distribution, which then can be integrated numerically from 0 to 1 to obtain the probability of sliding, P S (portion of the SF distribution where SF<1.0). The overall probability of failure, P F , for the potential slope failure mass is the joint probability that the rock discontinuities are long enough to allow kinematic failure (P L ) and that sliding occurs along the rock discontinuities (P S ); that is, P F = P S P L . This method for estimating the probability of sliding is extremely efficient computationally, and thus, expedites slope stability simulation routines used by NIOSH software to stochastically describe rock slope behavior and assist the engineer in designing catch benches for large rock slopes. Enhanced bench design translates into increased operational efficiency and safer working conditions in open pit mines and quarries. 1. INTRODUCTION Stochastic simulations of fractured rock masses can provide valuable information for the engineering design of rock slopes, particularly when the natural geologic discontinuities may form potential slope failure modes. An essential component of such engineering simulations is being able to compute the probability of sliding for a given potential failure mass once the geometry of that failure mass has been identified through spatial rock-fracture simulations. In cases where several thousand (or ore) simulations of possible failure geometries are needed to provide a realistic representation of the rock slope, computational efficiency is essential for the repetitious protocol used to calculate the probability of sliding. An example of applying this type of geotechnical approach to rock slope design was presented by Miller and others [1] in a paper focused on the design of catch benches for open pit mines and quarries. This issue is important to NIOSH (National Institute for Occupational Safety and Health) as part of its research mission to improve safety and health in the mining industry. Between 1995 and 2003 there were 42 reported fatalities dueto slope failure accidents at surface mines in the United States, at least one and as many as eleven each year. Additional accident statistics collected by the Mine Safety and Health Administration (MSHA) have shown that loose material from slope and bench failures can pose significant safety hazards to miners. To address these concerns the NIOSH Spokane Research Laboratory has been developing and testing rock slope stability software ver the past few years to provide advanced technical tools for analyzing bench stability. A key element of this software is a module used to compute the probability of sliding for a given viable failure geometry that has been simulated for the bench under study.

ABSTRACT: Existing borehole stability analysis tools are based on an assumed, fixed, circular borehole geometry. In a strict sense, these tools are valid only as long as the borehole remains circular. They cease to be valid and their applicability becomes limited when borehole breakouts or fractures are present at the borehole wall. Reliance on these methods can limit the ability to evaluate borehole stability and determine the safe mud weight window to the geometry or geometries on which the model being used is based-a circular borehole. When breakouts or fractures have formed, a different model is required to analyze the conditions around the borehole, to determine required mud weights, and to evaluate methods that can be employed to restabilize the borehole. The authors demonstrate this effect by analyzing and evaluating two specific borehole geometries-the circular borehole and a borehole intersected by an induced or natural fracture. Using existing borehole stability theories and basic hydraulic fracturing analysis, the authors review and evaluate various means available to alter the size of the mud weight window. Of particular interest are the two limiting cases: a circular borehole with no defects and a drilling-induced or natural fracture intersecting the borehole. Mechanisms reviewed include chemically altering the rock's mechanical properties or altering the borehole's surface characteristics, creating impermeable bridges within existing fractures, plugging existing or induced fractures with high-viscosity deformable or undeformable materials, and permanently sealing fractures with "rigid" cement. Calculations presented demonstrate the "borehole strengthening" that can be achieved by strengthening the rock matrix or by plugging an existing natural or induced fracture using materials that are deformable and do not rigidly adhere to the fracture walls (such as extremely viscous gel-like materials), materials that are not deformable (such as cement) and require time to cure, and materials that glue the fracture walls together. 1. INTRODUCTION Lost circulation during drilling operations continues to be a significant problem in the oil and gas industry. Control and remediation of lost circulation can require large expenditures and, if impossible, can result in the loss of the well. Lost-circulation problems will continue to plague the industry as it drills for oil and gas in reservoirs or fields with partially depleted sands that have to be penetrated to reach deeper productive intervals. Effective means to assess lost-circulation technologies are required. Lost circulation can occur in a number of ways. It can occur gradually through leakoff; abruptly as we penetrate into subsurface voids, rubbelized zones, and high-permeability intervals; or through the sudden initiation and continued propagation of a fracture. The remainder of this discussion focuses on the last of these lost-circulation issues-lost circulation through fracturing. Using existing borehole stability theories and basic hydraulic fracturing analysis, we review and evaluate various means available to help eliminate or remediate fracturing-related lost circulation. Of particular interest are two limiting cases: Avoidance of fracture initiation in a circular borehole with no defects ?Arresting or mitigating drilling-induced or natural fractures intersecting the borehole Mechanisms reviewed include chemically altering the rock's mechanical properties, altering the borehole's surface characteristics, creation of impermeable bridges within existing fractures, plugging existing or induced fractures with highviscosity deformable or undeformable materials, and permanently sealing fractures

ABSTRACT: Analyzing the stability of the three-dimensional wedges created around underground excavations in rock masses is a common problem in rock engineering. Most existing algorithms for wedge failure analysis assume wedges to be in low stress environments. Under such conditions the influence of stresses on the wedge factor of safety can be ignored. In blocky rock masses experiencing high in situ stresses, however, such analysis can lead to conservative results. This paper discusses the incorporation of stresses calculated from boundary element analysis into the analysis of wedge stability. The new formulation assumes complete plane strain, allowing the analysis of tunnels arbitrarily oriented with respect to principal stress directions. The approached described in the paper is implemented in the program Unwedge. 1. INTRODUCTION The stability of wedges formed around underground excavations in blocky rock masses is a common problem in rock engineering. The wedges are formed by intersecting discontinuities and the free face created through excavation of an underground opening. Under the influence of gravity and other forces, roof and wall wedges may fail either by falling, sliding or rotating out of their sockets. The factors that control wedge stability include geometry (the size, shape and spatial location of a wedge), the strength characteristics of the discontinuity planes that create the wedge, and stresses within the rock mass. Most existing algorithms for underground wedge stability analysis assume that stresses are sufficiently low and can therefore be ignored. This is fine for wedges in low in situ stress environments, such as those encountered in shallow excavations [1]. When in situ stresses are high, however, exclusion of the effect of stresses leads to error. The assumption of zero stress results in very conservative results for certain cases. The stability of a wedge in the roof of an excavation is an example. Such a wedge fails by falling under the influence of self-weight. Traditional stability analysis approaches (which do not take stress into account) predict that this wedge has a factor of safety of zero, and can remain in place only when supported. Many practical situations defy this prediction. Roof wedges located in deep underground excavations have been observed to be stable. Kaiser et al [2] suggest that conventional underground wedge stability analyses are commonly too conservative because they ignore stress. The stability of wedges at significant depths can be explained by the clamping effect of the surrounding stress field. The components of confining stress normal to the discontinuity planes, which form a wedge, mobilize shear resistance sufficient to keep the wedge in place. Unfortunately, including stresses in wedge stability analysis is not a trivial exercise. To simplify the problem, techniques that have been suggested use assumptions such as: Two-dimensional wedge and stress geometry, and/or In situ stresses acting on wedges.

ABSTRACT ABSTRACT: The scope of this research was to evaluate the geometry of the cutting tool in order to cut the coal/rock efficiently and produce less fine particles. This study consists of three parts namely: 1)Holographic Interferometry, 2)Three Dimensional Stress Analysis of the tested specimen, 3)Acoustic Emission and Fracture Surface Analysis. The major part of this paper will be devoted for part 1 of this study, however major findings in part 2 and 3 will be described briefly.

ABSTRACT Viability of the impact-kerf-cutting (IKC) concept Impact rate of a tool and its effect on rock penetration within a velocity range of 10 to 20 ft/sec. Use of Schmidt Hammer for estimating unconfined compressive strength (UCS). The reliability of using UCS for production rate predictions. Production rate estimating procedures. ABSTRACT: This paper defines the principal aspects of primary and secondary rock fracture by impact. It discusses mechanical rock fragmentation and cutting tool design. And it investigates those physical rock properties that can be used to predict excavation rate performance. Items that are referred to for specific discussion are: This paper covers laboratory and field testing pertaining to the development of an impact slot-cutting/ridge breaking tool for excavating rock. This tool was developed for use on a hydraulic breaker with the intent of reducing the use of explosives in short or irregular shaped excavations. Laboratory drop testing was conducted at the Mining Equipment Research Facility (METF) of the US Bureau of Mines (Now NIOSH). Full-scale field tests were then conducted at two rock quarries and one foundation excavation project. It was found that the IKC tool, when mounted on a properly sized hydraulic breaker and operated by experienced people, can be production rate competitive with explosives for trenching, tunneling, vein mining

ABSTRACT ABSTRACT: In contrast to typical excavations in civil engineering construction, mine openings often create locally reduced confinement and relaxation or tension in the backs or walls. Boundary-parallel stress reduction, or relaxation, can have devastating consequences in structurally dominant ground or in situations where the ground has been previously damaged by high stress. Such relaxation is often neglected in limit equilibrium calculations and in empirical design techniques. The stability of hanging walls in open stopes is of particular concern with respect to the detrimental impact of relaxation on both rockmass stability and the capacity of standard cablebolt reinforcement systems. The voussoir analogue for jointed beam stability is used to investigate the impact of stress reduction parallel to the back and walls of underground mine stopes and to provide an relaxation adjustment factor for the empirical "Stability Graph", a technique for design of open stope dimensions and support.

ABSTRACT ABSTRACT: A computer analysis of bench stability has been developed to account for multiple occurrences of potential slope-failure modes in discontinuous rock masses. Bench-scale plane shears and tetrahedral wedges are simulated and stochastically analyzed to estimate the probability of retaining specified catch-bench widths. This geotechnical information is useful in designing bench configurations to improve pit-slope stability and help alleviate rockfall hazards.

ABSTRACT 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 ABSTRACT: The Santa Rosa Dam left bank stability problems date back to the construction stage in 1963 and continued until new geological exploration, geotechnical analyses and stabilization works where carried out in 1982. The results obtained from the instrumentation shows that from 1984 to 1993 there was a satisfactory performance.