The use of reinforcing bar (rebar) anchored with resin is a common method of rock support in both hard and soft rock mining. The average bond strength, or the load that the support can sustain for a linear length of bond to the rock, is typically determined through a series of pull tests. The average value of bond strength varies widely, since it is dependent on in-situ rock properties and environment. It is an important value because it allows mine engineers to select the appropriate length and pattern spacing of installation for the support. When a stiff support, like resin-anchored rebar, is placed in a weak, soft material, such as potash, the average bond strength tends to be lower in magnitude than for a typical hard rock installation. This research was primarily aimed at determining the failure mechanism, in soft rock applications, by which the support loses adhesion and begins to fail by sliding. Results of field pull testing determined that the resin-rock bond strength was the limiting factor controlling when adhesion loss occurred. This study investigated how the bond strength may vary given a number of variables typically found in a potash mine environment. Results reported from testing did not indicate variation in the bond strength of resin anchored rebar, significant for mining applications, given changes in resin cure time, vicinity to active mining areas, or the rock type to which the resin was adjacent. Using the results of laboratory and field testing, an equation was developed to estimate load on in-situ resin anchored rebar given deformation measurements taken from the field. This equation will help determine safe limits for fracture separations opening in the backs of potash drifts. Investigating the behaviour of resin anchored rebar in potash may lead to methods to improve bond strength and calculation of factors of safety for patterned ground support.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 178-181). Also available via the Internet.

This research on Reusable Launchers was motivated by the need to reduce substantially the cost of space transportation. The specific objective was to explore the perception that launcher reusability is the key to achieving these major cost reductions. The exploration was achieved by undertaking a comparative system study on potentially feasible reusable launcher concepts, using a consistent set of design tools, a standard analysis methodology and a standard reference mission. To set the background for the research, the results of an extensive literature review are presented on the vehicle studies and technology developments that are engaged across the world on reusable launchers. Comprehensive vehicle studies appear to be engaged without justification for the choice of selected concepts in the absence of results from comparative system studies of reusable launchers. Technology developments also appear to be engaged without clear links to needs derived from vehicle system studies. The challenge of reusability is then addressed. Firstly, to set the performance and cost targets of reusable launchers, the capabilities of current expendable launchers are derived. Secondly, to establish the operational requirements for reusable launchers, the probable space transportation needs for the early 21st century are derived. Thirdly, the concepts and characteristics of reusable launchers are derived, allowing the selection, on a rationale basis, of a short-list of 13 potentially feasible reusable launcher concepts for analysis in the research. The performance equations of reusable launchers are then derived, leading to the preparation of the comparative analysis tools. The major work of the research, which comprises the performance analysis, technical feasibility assessment and cost analysis of each candidate vehicle, are then presented and compared. A set of acceptance requirements for performance, technical feasibility and operational costs of reusable launchers is then derived. The results of the comparative analysis for each candidate launcher are then measured against these requirements. The results of the comparative analysis show that only 2 of the 13 candidate reusable launcher concepts are able to meet all the acceptance requirements. These two acceptable vehicles are both rocket-propelled. They are, in order of preference: a single-stage-to-orbit, rocket-propelled, vertical launch and vertical landing vehicle; a two-stage-to-orbit, rocket-propelled, vertical launch and horizontal landing vehicle. The operational costs per launch for these two vehicles, based on a utilisation plan of 3 vehicles operating for 20 years at a launch rate of 12 launches per year, was calculated to be about 20% of the current costs of the European Ariane 44L expendable launcher. This warrants their further evaluation in a thorough feasibility study. The more complex, air-breathing propelled, horizontal launch and landing vehicles were found to be unable to meet the performance, technical feasibility and cost requirements; Several vehicles were found to be unable to deliver a positive payload mass to orbit; Several vehicles were found to have technology requirements that were deemed to be infeasible to achieve; Several vehicles were found to have operational costs ranging from equal to double that of the European Ariane 44L expendable launcher, which was adopted as a comparative reference vehicle. The contributions of this research to the advancement of knowledge on reusable launchers are: a clear identification of the performance capability limits of 13 plausible reusable launcher concepts; an analysis methodology for determining the performance capability limits for any reusable launcher concept; a clear identification of the reasons for the poor practical performance of air-breathing propulsion systems for Earth-to-orbit launchers, which results from their installed operational characteristics.

This thesis presents ground control best practices in weak rock environments including an augmentation to the existing Span Design curve by adding 463 case histories of RMR76 values ranging from 25 to 60. A Neural Network analysis of this data has been added and compared to the existing Span Design data of 292 case histories. Ground support is almost always used in weak rock environments, though the type of support used can vary widely. The development of the weak rock augmented Span Design Curve has also been calibrated to four different support categories; Category A: Pattern Friction Sets, Category B: Pattern Friction Sets with Spot Bolting of Rebar, Category C: Pattern Friction Sets with Pattern Rebar Bolts and Category D: Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill. Category A is considered “Unsupported” with an average Factor of Safety less than 1.2. Categories B, C and D are considered “Supported” with average Factors of Safety greater than 1.2. All categories are compared the original Critical Span Design Curve presented by Lang (1994). However, only Category A can be accurately compared to the original Critical Span Design Curve as it is “Unsupported” as well. Category A yields good results, however, Categories B, C and D do not, but still demonstrate that spans can remain stable at lower RMR76 values. Design of underground man-entry type excavations in North America relies heavily upon empirical analysis. This design requires a higher Factor of Safety than other non-man entry type excavations. A comparison of the calculated ½ span failure Factor of Safety between all the categories is also presented. The contribution this research provides to the mining industry is the "Unsupported" Weak Rock Updated Span Design Curve and awareness pertaining to the potentially detrimental effects of using resin grounted rebar in weak rock masses and the false sense of security that the use of resin grouted rebar may instill. It is also shown that spans in the “Unstable” zone of the new “Unsupported” Weak Rock Updated Span Design Curve can possibly be stabilized if detailed engineering design is applied to obtain “Supported” status.

This thesis presents ground control best practices in weak rock environments including an augmentation to the existing Span Design curve by adding 463 case histories of RMR76 values ranging from 25 to 60. A Neural Network analysis of this data has been added and compared to the existing Span Design data of 292 case histories. Ground support is almost always used in weak rock environments, though the type of support used can vary widely. The development of the weak rock augmented Span Design Curve has also been calibrated to four different support categories; Category A: Pattern Friction Sets, Category B: Pattern Friction Sets with Spot Bolting of Rebar, Category C: Pattern Friction Sets with Pattern Rebar Bolts and Category D: Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill. Category A is considered “Unsupported” with an average Factor of Safety less than 1.2. Categories B, C and D are considered “Supported” with average Factors of Safety greater than 1.2. All categories are compared the original Critical Span Design Curve presented by Lang (1994). However, only Category A can be accurately compared to the original Critical Span Design Curve as it is “Unsupported” as well. Category A yields good results, however, Categories B, C and D do not, but still demonstrate that spans can remain stable at lower RMR76 values. Design of underground man-entry type excavations in North America relies heavily upon empirical analysis. This design requires a higher Factor of Safety than other non-man entry type excavations. A comparison of the calculated ½ span failure Factor of Safety between all the categories is also presented. The contribution this research provides to the mining industry is the "Unsupported" Weak Rock Updated Span Design Curve and awareness pertaining to the potentially detrimental effects of using resin grounted rebar in weak rock masses and the false sense of security that the use of resin grouted rebar may instill. It is also shown that spans in the “Unstable” zone of the new “Unsupported” Weak Rock Updated Span Design Curve can possibly be stabilized if detailed engineering design is applied to obtain “Supported” status.

Thesis (M.S. in Systems Management) Naval Postgraduate School, March 1997. / Thesis advisors, Donald R. Eaton, James G. Taylor, Gordon R. Nakagawa. Includes bibliographical references (p. 81-82). Also available online.

This thesis presents ground control best practices in weak rock environments including an augmentation to the existing Span Design curve by adding 463 case histories of RMR76 values ranging from 25 to 60. A Neural Network analysis of this data has been added and compared to the existing Span Design data of 292 case histories. Ground support is almost always used in weak rock environments, though the type of support used can vary widely. The development of the weak rock augmented Span Design Curve has also been calibrated to four different support categories; Category A: Pattern Friction Sets, Category B: Pattern Friction Sets with Spot Bolting of Rebar, Category C: Pattern Friction Sets with Pattern Rebar Bolts and Category D: Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill. Category A is considered “Unsupported” with an average Factor of Safety less than 1.2. Categories B, C and D are considered “Supported” with average Factors of Safety greater than 1.2. All categories are compared the original Critical Span Design Curve presented by Lang (1994). However, only Category A can be accurately compared to the original Critical Span Design Curve as it is “Unsupported” as well. Category A yields good results, however, Categories B, C and D do not, but still demonstrate that spans can remain stable at lower RMR76 values. Design of underground man-entry type excavations in North America relies heavily upon empirical analysis. This design requires a higher Factor of Safety than other non-man entry type excavations. A comparison of the calculated ½ span failure Factor of Safety between all the categories is also presented. The contribution this research provides to the mining industry is the "Unsupported" Weak Rock Updated Span Design Curve and awareness pertaining to the potentially detrimental effects of using resin grounted rebar in weak rock masses and the false sense of security that the use of resin grouted rebar may instill. It is also shown that spans in the “Unstable” zone of the new “Unsupported” Weak Rock Updated Span Design Curve can possibly be stabilized if detailed engineering design is applied to obtain “Supported” status. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

No description available.

Thesis (M.M.A.S.)--School of Advanced Airpower Studies, 1995. / Subject: Command and control and responsiveness of close air support. Cover page date: June 1995. Vita. Includes bibliographical references.

Engineering problems involving the development of cheap, easy-to-use, and effective packet communications terminals for connectivity to low-earth-orbit satellites (PACSATs) are addressed. Two prototype terminals were developed: a base station for maximum duration connectivity to the satellite, and a smaller station for portability and low cost. Commercially available systems for related amateur radio uses were integrated for these prototypes. The prototypes illustrated areas for further development before widespread use of PACSATs can be realized. To better understand some of the issues for PACSATs, two analyses were developed. The first analysis approach characterizes PACSAT orbits so that tradeoffs are readily identified and quantified. Results from an analysis of one PACSAT orbit indicate conflicting needs for the two terminal types. The second analysis approach addresses issues involving the use of an increasingly popular method for transmitting 9600 baud FSK which combines the spectral efficiency of premodulation pulse shaping with the simplicity of using FM discriminators for demodulation. The spectrum of the transmitted signal is studied and the performance of the demodulator is compared to that of an appropriate coherent receiver. Doppler shifts on the channel is particularly important for PACSAT communications. An analysis approach that addresses the mistuning problem is presented. Results of this analysis identify changes that would better suit the needs of PACSAT terminals. / Master of Science