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 mining industry is a major consumer of rock bolts in the United States. Due to the high humidity in the underground mining environment, the rock bolts corrode and loose their load bearing capacity which in turn reduces the life expectancy of the ground support and, thus, creates operational difficulties and number of safety concerns [1]. Research on rock anchor corrosion has not been adequately extensive in the past and the effects of several factors in the mine atmosphere and waters are not clearly understood. One of the probable reasons for this lack of research may be attributed to the time required for gathering meaningful data that makes the study of corrosion quite challenging. In this particular work underground water samples from different mines in the Illinois coal basin were collected and the major chemical content was analyzed and used for the laboratory testing. The corrosion performance of the different commercial rock anchors was investigated by techniques such as laboratory immersion tests in five different corrosion chambers, and potentiodynamic polarization tests in simulated ground waters based on the Illinois coal basin. The experiments were conducted with simulate underground mining conditions (corrosive). The tensile strengths were measured for the selected rock anchors taken every 3 months from the salt spray corrosion chambers maintained at different pH values and temperatures. The corrosion potential (Ecorr), corrosion current (Icorr) and the corresponding corrosion rates (CR) of the selected commercial rock bolts: #5, #6, #6 epoxy coated and #7 forged head rebar steels, #6 and #7 threaded head rebar steels were measured at the solution pH values of 5 and 8 at room temperature. The open circuit potential (OCP) values of the different rock anchors were recorded in 3 selected underground coal mines (A, B & C) in the Illinois coal basin and the data compared with the laboratory electrochemical tests for analyzing the life of the rock anchors installed in the mines with respect to corrosion potential and corrosion current measured. The results of this research were statistically validated. This research will have direct consequence to the rock related safety. The results of this research indicate that certain corrosive conditions are commonly found in mines but uniform corrosion (around 0.01-0.03mm loss per year across the diameter) is generally not considered a serious issue. From this study, longer term research for long-term excavation support is recommended that could quantify the problem depending on the rock anchor used and specific strata conditions.

The Fully Encapsulated Resin Bolt (FERB) is widely utilised for strata control and ground support in civil and mining applications worldwide, with approximately 6 million installed per annum by the Australian coal mining industry. Independent studies have concluded that 30-35% of these rockbolts, which represents an annual expenditure of $40 million, are ineffective. The anchorage and failure mechanisms of FERB are yet to be quantified, and support systems are designed primarily from empirical rather than scientific methods. There are no standardised methods of assessing FERB components, installation techniques and support behaviour. The majority of research into FERB support systems remains commercial intellectual property, with little information released into the public domain. This thesis investigated several variables of FERB support systems, and also examined differences between field and laboratory pull-out test load distributions. This research was conducted in two phases, with Phase 1 seeking standardised methodology and repeatability in results, while Phase 2 further refined Phase 1 methods and extended the range of tests. The results in both phases were encouraging, with reasonable repeatability attained in all testing series. The findings included: ??? Annulus Thickness: There was little change in load capacity with small annulus thickness, however the maximum peak load (MPL) significantly reduced once annulus thickness exceeded 4mm ??? Resin Installation Spin Time: Underspinning of cartridge resin was found to have an insignificant effect on rockbolt load/deformation characteristics. Overspinning, however, led to a dramatic reduction in anchorage performance with a lessening in both MPL and stiffness ??? Rockbolt Load Transfer: The magnitude of an applied load reduced to zero along the length of the rockbolt, being greatest nearest the rock free surface (the point of load application). An exponential reduction was found when tested in the manner of laboratory tests, with the loading jack reacting against the free surface. This reduction was linear when the load was applied as in the field, with no load placed on the free surface This basic investigation into FERB support systems has validated many empirical understandings of rockbolts, while highlighting the need for further testing into several key areas.

The Fully Encapsulated Resin Bolt (FERB) is widely utilised for strata control and ground support in civil and mining applications worldwide, with approximately 6 million installed per annum by the Australian coal mining industry. Independent studies have concluded that 30-35% of these rockbolts, which represents an annual expenditure of $40 million, are ineffective. The anchorage and failure mechanisms of FERB are yet to be quantified, and support systems are designed primarily from empirical rather than scientific methods. There are no standardised methods of assessing FERB components, installation techniques and support behaviour. The majority of research into FERB support systems remains commercial intellectual property, with little information released into the public domain. This thesis investigated several variables of FERB support systems, and also examined differences between field and laboratory pull-out test load distributions. This research was conducted in two phases, with Phase 1 seeking standardised methodology and repeatability in results, while Phase 2 further refined Phase 1 methods and extended the range of tests. The results in both phases were encouraging, with reasonable repeatability attained in all testing series. The findings included: ??? Annulus Thickness: There was little change in load capacity with small annulus thickness, however the maximum peak load (MPL) significantly reduced once annulus thickness exceeded 4mm ??? Resin Installation Spin Time: Underspinning of cartridge resin was found to have an insignificant effect on rockbolt load/deformation characteristics. Overspinning, however, led to a dramatic reduction in anchorage performance with a lessening in both MPL and stiffness ??? Rockbolt Load Transfer: The magnitude of an applied load reduced to zero along the length of the rockbolt, being greatest nearest the rock free surface (the point of load application). An exponential reduction was found when tested in the manner of laboratory tests, with the loading jack reacting against the free surface. This reduction was linear when the load was applied as in the field, with no load placed on the free surface This basic investigation into FERB support systems has validated many empirical understandings of rockbolts, while highlighting the need for further testing into several key areas.

Thesis (M. E.)--University of New South Wales, 2003. / "The precursor to this thesis was an industry-sponsored project, completed in 2000 by C. Offner at the School of Mining Engineering, UNSW ; this project is referred to as the Stage 1 project"--summary. Also available online.

Thesis (PhD.(Mining Engineering)--University of Pretoria, 2008. / Summary in English. On title page: Submitted in partial fulfilment of the requirements for the degree Philosophiae Doctor in the Faculty of Engineering, Built Environment and Information Technology, University of Pretoria. Includes bibliographical references.

According to the National Institute of Occupational Safety and Health (NIOSH), about 100 million rock anchors were installed in the USA mining industry during 1999 (Dolinar, 2000). The rock bolt usage in US coal mining industry fell from 85 million in the year 1988 to 68 million by 2005 (Tadolini, 2006), and is assumed to be close to that number of rock anchors consumed currently since, the tonnage from underground is almost the same. Most underground coal mines have conditions such as moisture in the atmosphere, ground water with different chemical contents that are conducive for corrosion of rock anchors and ancillaries (such as plates), and the effects of this on the performance of the anchors had been researched in the US to an extent from the past research at Southern Illinois University Carbondale (SIUC). In addition to the general corrosion like pitting and crevice, stress corrosion adds to the process a potentially serious threat and results in material failure underground due to stress corrosion cracking (SCC) yet the effects are not fully understood in the USA. The results of this research therefore will have a positive and direct effect on rock related safety. During this research project in situ specific tests were conducted with bolts to try and determine the corrosion potential in a specific coal-mining region. The coal mining areas were divided into three regions and were named as East, Mid-West and West respectively. To enhance the value/importance of the field data collected from the mines, a metal mine and a salt mine (two non-coal mines) were included in the plan and the data analysis proved that the methodology developed for determining the corrosion potential underground is applicable to any underground mines. The Insitu studies include water samples collection and analysis and open circuit potential (OCP/Eoc) testing and analysis. Open Circuit Potential (OCP) data were recorded to estimate probability of active corrosion. Hypothetically, probability of active corrosion is lower if the actual OCP of roof bolts in the mine is less than the characteristic OCP of the steel grade, and vice versa. The effects of certain factors such as the roof condition, reference distance (distance between bolt and reference electrode) on the open circuit potential data during the measurements were studied to ensure its impact on the corrosion potential determination technique developed. The findings from this research helps standardize the corrosion potential determination methodology. The preliminary study of stress corrosion cracking of the subject test sample (Grade 60 rebar roof bolt) was conducted in this research work. The experimental study invloves testing a complete roof bolt in the mine simulated environment. The mine simulated environment in the test cell consists of the roof strata material collected from the mine site with continuous flow of water at slower and varaible flow rate (0 to 3 ml/minute) with pH in the range of 7.5 to 9.0. The results showed that stress corrosion could be very serious problem when it comes to long term mining applications. The stress corrosion test cell developed and tested was proved to be significant in conducting the long term stress corrosion tests. The strength results of the Grade 60 rebar roof bolt tested had a significant strength loss after 3 months of testing in the stress corrosion cell. Hence, more SCC studies are deemed necessary to evaluate the seriousness of the problem and if possible eliminate it.

Safety is the most important aspect to the mining industry. Research having a direct and positive impact on mine safety is always needed and should be supported. There are several different types of primary roof supports that are used to try to maintain stable mine workings in order to extract the coal safely. The majority of roof bolts installed annually in underground coal mines in the USA use resin cartridges (Tadolini, 2006). The standard roof bolt used is a fully grouted resin rebar bolt. This is considered a passive (un-tensioned) support. Technological advances in roof support anchored with resin grout systems have resulted in the development of supports that are active (tensioned during installation). Generally it is thought that active anchors are superior in performance as roof support except in highly laminated weak roof. The assumption is that since an active system applies some pre-tension to the roof, it will provide a more stable roof beam. There is, however, a lack of real data to back up this perception. A systematic attempt is through this project that addresses this knowledge gap. Without a clear idea on how different roof bolt systems work in-situ, the consequences could have a significant impact on the safety of the miners working underground as well as production costs. Supports are now often only chosen based on perceived ideas instead of real data. Such assumed superior performance of the support system could lead to false economy. Essentially, it needs to be demonstrated to what degree or under what conditions, if any, these technological advances in roof support improve ground conditions and opening stability and ultimately improve the safety of the miners. There is an argument regarding whether passive bolts could truly be better than active bolts. The focus is centralized towards a cost and performance issue. The overall goal of the proposed project was to develop an understanding of the interaction between different roof bolt types and the immediate strata in a longwall headgate as the longwall face progresses. In order to monitor the interactions between the strata and roof bolts, specially instrumented bolts were installed with six strain gauges that were electronically accessed. A look into the initial bolt loads was used to compare three different bolt types (both tensioned and untensioned) upon installation. These loads continued to be monitored and analyzed as the longwall face approached and passed the location of the instrumented bolts. Along with analyzing instrumented bolt data compared to a passing longwall face, a limited finite element model was set up within Flac3D to represent real conditions, and compare the in situ data collected to the computer outputs in order to establish beginning phases of validating the results.