Thesis (M.Eng.Sc.)--University of Western Australia, 2004.

Thesis (M.Sc.)--Memorial University of Newfoundland. / Typescript. Bibliography: leaves 128-136. Also available online.

Thesis (M. Sc.)--University of Hong Kong, 2004. / Also available in print.

Thesis (Ph. D.)--University of Queensland, 2003. / Includes bibliographical references.

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

No description available.

Rock bolts have been extensively used as a support element in coal mines in the US for about 40 years. Longwall development and partial extraction room-and-pillar mining systems now rely heavily on fully-grouted roof bolts as the primary support with as needed inclined bolts, trusses, and cable bolts as secondary support. These two coal mining systems develop 3- and 4-way intersections during extraction processes. A study of Illinois (2004-2008) and US coal mines found that over 70% of roof falls occurred at intersections. It is therefore necessary to perform additional research in stress and displacement distributions around intersections and then design support systems to improve stability of intersections. This thesis research, in cooperation with a bolt supplier and NIOSH, analyses the stress and strain redistribution in and around intersections in typical lithologies in the Illinois Basin coal mines with the goal to develop a better understanding of failure initiation and propagation mechanisms with and without roof supports. Analyses were corroborated with field observations wherever possible. Non-linear continuum analyses using the Generalized Hoek-Brown failure criterion with rock mass properties is the foundation for these analyses. The first task (Task 1) toward these goals was to develop rock mass properties from available laboratory data using estimates of Geological Strength Index (GSI) for different lithologies. An important subtask was to perform an error analysis in estimates of rock mass properties assuming an amount of error in GSI estimates. Analyses and field observations were done for typical 4-way intersections at two mines in southern Illinois operating at depths of 150 m and 80 m, respectively in the No. 6 coal seam, which averages 1.8 m in thickness. Pre-mining horizontal stresses of 7.58 MPa and 4.13 MPa were applied in the E-W and N-S directions. These coal companies provided geologic logs and rock mechanics data for roof and floor strata. Rock mass engineering properties for different roof and floor lithologies were developed using estimated values of Geological Strength Index (GSI), and Hoek-Brown (H-B) rock mass failure parameters. A recent laboratory study provided normal and shear stiffness properties of the immediate roof interfaces within the bolting range of 1.8 m. MSHA-approved roof support plans were used for initial modeling. Short Encapsulation Pull Test (SEPT) data provided by bolt suppliers in the region were used to assign bolting system stiffness and strength parameters. Task 2 analyzed normal and shearing stresses and strains in and around mine intersections for typical pre-mining stress fields and then identified critical areas of failure initiation and progressive failure propagation. Failure initiation was hypothesized to occur for critical values of compressive (1 mm/m), tensile (0.5 mm/m), and shearing (0.5 mm/m) strains based on a review of laboratory stress-strain properties. This approach allows quantifying areas in and around an intersection where failures are likely to initiate with and without artificial supports. It computes three reinforcement factors with and without supports: reinforcement against tensile (RFT), compressive (RFC) and shearing (RFSS) strains. Task 3 assessed the performance of currently practiced roof support plans and identified where inadequacies exist and how they could be improved through spatial distribution of supports and their characteristics. Analyses were completed for two mines with one orientation of pre-mining horizontal stress field. The next logical step (Task 4) was to extend analyses in Task 3 to assess the effect of maximum compressive stress orientation in relation to entry direction (0o, 30o, 60o & 90o) and different cut sequences and their effect on changes in failure initiation and failure propagation mechanisms. Numerical analyses have shown that stress and strain distributions are significantly different when the cut sequence is included in models. For a horizontal stress ratio of two (2), the 60o orientation provided maximum stability. Separate models with all cuts excavated simultaneously corresponded well with the well-established NIOSH software AHSM and previous research. The effect of cut sequence combined with the directional effect of pre-mining stresses becomes evident from the dissimilar results. A separate statistical study was conducted on 211 SEPT test data provided by a roof support manufacturer and marketing company in the region. Goals were to analyze the database for grip factor (GF) and anchorage stiffness (AS) characteristics using histograms and frequency distributions and, perform regression analyses to relate GF and AS values on the basis of height above coal seam and bolt diameter. Results were used for one stochastic run with variable GF and AS values assigned to different bolts in a roof control plan. Results indicated Gamma distribution best fitted AS and GF data. It was thought that the reinforcement factor for such a bolting layout would be more realistic than assigning a single value of GF and AS to bolts in the model.

The thesis falls naturally into four parts. The first constitutes a world-wide survey of the methods used in practice to design prestressed, cement grouted rock anchors. The major topics of overall stability and system geometry, the rock-grout and grout-steel interfaces, and grout and tendon selection, are reviewed in turn. Comparisons between the standard methods of practice, and the findings from theoretical and field studies, reveal important areas of uncertainty and contradiction, particularly with regard to the mechanisms of load transfer from tendon to rock. Part 2 describes the author's full scale test anchor programme, conducted at Withnell, Lancashire, devised to investigate the major problems associated with load transfer which were highlighted in Part 1. Full details are provided of the site and its geology, and the methods of construction, testing, recording and analysis employed. Most emphasis placed on the results obtained from the fifty-seven anchors: these are fully discussed and wherever possible compared with data presented in the review. The third part deals with the long term performance of rock anchor systems. Analogous to Parts 1 and 2, one chapter is devoted to a review of relevant published information, whereas the other chapter details the author's case study of ten production anchors at H.M. Dockyard, Devonport. In Part 4, conclusions on the field test programmes are summarised and indications are given of topics meriting further research.

Current methods for assessing the integrity of ground anchorages during service are primarily restricted to monitoring by load cells or load lift-off testing. Both are expensive and lift-off testing is time consuming and can damage the anchorage construction below the anchor head. Hence, only typically 5-10% of anchorages are monitored in service. As a result, The Institution of Civil Engineers reported that non-destructive test methods for ground anchorages need to be developed as a high priority (ICE, 1992). The Universities o f Aberdeen and Bradford have been conducting research since 1986 to investigate the response o f rock anchorages to dynamic loading arising from blasting operations. Full scale field trials were conducted during the construction of two tunnels in North Wales. An important finding from the research revealed that certain characteristics of the dynamic response of a rock bolt resulting from blasting operations, were similar for different blast sequences. This indicates that the dynamic response o f an anchorage system is dependant on the construction of the anchorage and the characteristics of the co-vibrating rock mass. Consequently, the University of Aberdeen has developed a new non-destructive condition monitoring and integrity assessment system for ground anchorages (GRANIT ™). A range of patent applications have been successful world-wide and the system has been exclusively licensed to AMEC Civil Engineering Limited. The system operates by applying an axial tensile impact load to the free end of an intact anchorage immediately after installation. The resulting vibrational response is monitored by an accelerometer, located at the anchorage head, which produces a datum signature for that anchorage. The condition of the anchorage is then inferred by comparing subsequent response signatures with the datum. A change in the signature indicates that there may be a potential change in the integrity of the anchorage. Artificial Intelligence systems are employed to compare response signatures. As part of the research programme, the author conducted commissioning tests on small scale laboratory test rigs and was responsible for the development of a prototype non-destructive test system, which included a means of applying an impact load and recording the vibrational response. In addition, the author conducted full scale laboratory tests and field trials to investigate the effect of prestress on the dynamic response of ground anchorage systems. As a result, the prototype non-destructive test system has been employed to successfully predict the amount of load within an anchorage installation.