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The utilisation of rock bolting for the support of British coal mine roadways can improve roadway strata conditions and, by permitting a reduction in the density, cross-section or total elimination of steel standing support, can produce considerable savings in roadway support costs. This study reviews worldwide experiences in the use of rock bolt reinforcement techniques to enhance the stability of coal mine roadways. Details of methods of geotechnical design data acquisition and assessment are given as well as a critical study of various empirical, analytical and observational methods of tunnel support design. The use of scale model studies is shown to be particularly effective for the design of rock bolt support systems for coal mine roadways. With reference to numerous case studies, descriptions are given of rock bolt systems available and their suitability to specific mine roadway conditions is discussed. Installation procedures and equipment are also reviewed. It is the author's intention that this study should be used as the basis for further detailed investigation of specific aspects of rock bolt support systems. A number of recommendations are made as to the fields in which further research should be undertaken.

The work describes a study of stress corrosion cracking (SCC) failure of rock bolts in underground coal mines. It focuses on understanding the environment in which failures occur and the mechanism behind failure. SCC tests which could be used in-situ in underground mines were also evaluated and validated in the laboratory. Analysis of the ground water was conducted for two mines (Mines A and B) which were known to have undergone a substantial number of SCC failures. Both mine waters were found to be alkaline and corrosive. The alkalinity was almost exclusively due to the presence of bicarbonate ions. The bicarbonate levels in Mine A were substantially higher than in Mine B. Microbiological analysis of water from Mine B showed that it contained both iron- and sulphur-reducing microorganisms. An investigation into the failure mechanism in rock bolts retrieved from these two mines was also conducted. This indicated that SCC in underground coal mines can occur by two different mechanisms. In high alkalinity mine water, SCC occurs by an anodic mechanism involving carbonate/bicarbonate cracking, whereas in low alkalinity mine water, a cathodic mechanism occurs involving hydrogen induced cracking. The two different SCC mechanisms are similar to the high pH carbonate/bicarbonate SCC and the near-neutral pH hydrogen induced SCC observed in buried pipelines. The occurrence of carbonate/bicarbonate rock bolt SCC has not been reported previously. The use of a pin-loaded slotted coupon SCC test was examined which was suitable for use in rock bolt bore holes while also retaining the physical and metallurgical features present at the surface of rock bolts. The test methodology was validated in the laboratory using an acidified sodium chloride sodium sulphide solution. Laboratory testing was subsequently conducted for 3 months in ground water extracted from Mine B using the pin-loaded specimen. Alternating 8 hour wet/8 hour dry cycling was used for the tests. No SCC failures were observed over the duration of the test. This may indicate that microorganisms, which did not survive when the water was removed from the mine, may be involved in the in-situ SCC process.

Full scale field trials, carried out during the construction of the Penmaenbach Tunnel in North Wales, have shown that two-speed resin bonded rock bolts are resilient to close proximity blasting. Fully grouted 6m long rock bolts, installed within 0.7m of the tunnel face, have shown no significant signs of distress or failure. Instantaneous loads of up to 40% of the characteristic strength of the bolt were observed together with average residual load losses of 5% of the working load, which compares favourably with the acceptable tolerance of 10% working load stipulated by current practice. Analysis has also shown that rock bolts with low prestress sustain greater vibrations and proportionately higher dynamic load changes during blasting. However, bolts with relatively high prestress loads sustain greater induced loads. Empirical relations have been established to describe rock bolt behaviour in terms of induced vibration and scaled distance. In particular, a predictive equation relating dynamic load changes in the experimental rock bolts to scaled distance, is presented. Calculations based on approximate bolting costs have indicated that cost savings of up to 38% of the total bolting cost could have been effected if the results of this work had been implemented at the design stage. Physical modelling work has confirmed that the distribution of loads in the fixed anchor of a resin bonded bolt are non-linear when both static and impulsive loads are applied to the bolt head. Corroboration of the field results has also been established with respect to the significant influence of initial prestress load on dynamic load change. Complementary finite element modelling work has successfully predicted fixed anchor load distributions under static and dynamic loading conditions. Attempts to establish a detailed relation between distance from blast, magnitude of charge and change in residual load, for low to medium capacity rock anchorages on the West Portal of the tunnel, were thwarted by the poor performance of instrumentation with respect to temperature sensitivity. However, a simplistic approach to analysis has enabled the establishment of a tentative predictive relationship.

Since its development in the 1920s, bolting has become the most dominant support method in underground construction. However, because of the geological environment, the design process for roof bolt systems is an art rather than a science. To quantify the selection of bolting systems a MSBT (minimum solid beam thickness) approach was developed. The ultimate goal of this bolt design paradigm was achieved by optimizing bolt length, bolt density, and bolt pretension during installation. The impact of the number of strata layers within bolting range and pretension applied to bolts upon the stability of an opening was investigated using FLAC model. Four statistical models for predicting optimum bolt supports using a minimum solid beam thickness were established, and based on these results, a design criterion was proposed. To meet support needs in various geological and geotechnical settings, a variety of bolt types have been developed. The installation of such bolt-based support systems is often complex and specialized, and thus imposes a challenge for engineers to identify the specific cause and to take appropriate remedial measures once problems arise. To solve these problems, a knowledge-based expert system (KBES) has been developed. The knowledge base includes the data accumulated from years of laboratory and field investigations conducted by the Mine Safety and Health Administration of the US Department of Labor. A user-friendly Windows-based program was implemented using KAPPA environment. After identifying the problem, the KBES searches its knowledge base and reasons out the most likely, secondary, and other potential causes, then provides solutions according to users' input. The results of this research are validated and demonstrated using case studies.

Stress Corrosion Cracking (SCC) is a failure mechanism which has been observed to affect rockbolts installed in a number of Australian and overseas underground mines. SCC requires the application of a tensile stress on a material placed in an appropriately corrosive environment. SCC is characterised by the growth of fine fractures, originating from the surface of a material, which will continue to grow until they reach a critical length at which the material fails by mechanical overload. An extensive literature survey into rockbolt corrosion and SCC identified the need for a dedicated testing system for investigating SCC in full-scale rockbolt specimens. This thesis has focused on the design and development such a testing system. This system included a novel testing methodology, the Bending and Tension Loading Apparatus (BaTLA), which was housed within a Controlled Mine Environment (CME) laboratory, capable of recreating the atmospheric conditions present in an underground mine, as well as conduncting ‘accelerated’ tests using synthetic testing solutions. The development of this laboratory was based on the findings of a detailed field study conducted to characterise the geological, geotechnical, hydrological and atmospheric environment of two underground coal mines which have presented cases of rockbolt SCC. This newly developed laboratory was used to carry out an extensive testing program consisting of over 40, 000 hours worth of experimentation. This extensive testing program assessed the performance of both bending and tension loading in the BaTLA for investigating SCC in rockbolts. Both static and Slow Strain Rate (SSR) loading conditions were examined and each were found to be useful for investigating specific aspects of SCC. It was found that static testing provided the most appropriate means for examining mechanistic aspects of rockbolt SCC such as critical stress threshold, while SSR testing was found to be better suited to comparing material and environmental factors. A comparison of a number of steel grades and finishing treatments showed that lower strength 300 grade steel was far more resilient to SCC than both 1355 and HSAC 840 steel, and that surface treatments such as galvanising and grit blasting both provided notable improvements to a rockbolt’s SCC resilience. The testing program has also utilised small, representative coupon specimens. The coupon specimens used included the standard ASTM International G39 bent beam specimen and a slotted split pin specimen. A comparison of rockbolt steel grades finishing treatments using slotted specimens revealed that 1355 grade steel is much more susceptible to SCC than HSAC 840 grade steel, and that galvanising provided a significant improvement in SCC resilience. The ASTM G39 coupon specimens were used to examine critical stress thresholds for SCC and it was found that rockbolt steel may be susceptible to SCC at stresses as low as 580MPa. Secondary testing carried out by calculating the plastic strain experienced by rockbolts at failure by examining their rib profile supported this observation of a low critical stress threshold, showing that a large proportion of in-situ rockbolts experienced SCC failure at, or slightly above their yield strength.

The distinct element method (DEM) is a useful tool in rock engineering to model jointed rock masses. To simulate a jointed rock mass realistically, the main challenge is to be able to capture its complex geometry which consists of blocks with various shapes and sizes, and to model the interactions between these blocks. The main contribution of this thesis is the development of novel algorithms in the DEM to model jointed rock masses, namely rock slicing procedures for block generation, and algorithms for contact detection between polygonal blocks in 2-D or polyhedral blocks in 3-D. These algorithms make use of convex optimisation techniques, for which there exist efficient solution procedures. They do not rely on conventional vertex-edge-face hierarchical data structures and tedious housekeeping algorithms. The algorithms have been verified against analytical and numerical solutions, as well as validated against experimental results published in the literature. Among those, the results of DEM simulations were compared against the experimental model tests and numerical simulations of jointed beams carried out by Talesnick et al. (2007) and Tsesarsky & Talesnick (2007) respectively. Emphasis was placed on modelling the stiffness of the block interfaces accurately, and this was accomplished by reinterpreting the laboratory data published by the investigators. The capabilities of the numerical tools are also examined and demonstrated in areas for which the DEM has found practical application. A substantial fraction of this thesis is devoted to illustrating how these tools can assist the engineer in designing support systems; for example, designing the length and spacing of rock bolts and the lining thickness for a tunnel. Algorithms to model rock bolt and lining support were implemented for this purpose. Interesting comparisons with elastic solutions for supported openings were obtained. Further, it is shown that the relative benefit of introducing more rock bolts or thicker lining can be evaluated using the numerical tools with the aid of an interaction diagram. In the final part of this thesis, the case history of the 1963 Vaiont rock slide in Italy is studied. The 2-D analyses led to useful insights concerning the influence of the reservoir water level, the rock mass strength and deformability, and the slide surface shear stiffness. 3-D analyses were undertaken to investigate the influence of the eastern boundary of the slope, and interesting insights were obtained concerning the slope kinematics. Overall, the case study shows that the tools are capable of modelling problems with specific physical and geometrical detail in both 2-D and 3-D.

Rock bolts and cable bolts are widely used as roof support systems in underground mines. Over the last two decades there have been increasing reports of failure of rock bolts and, more recently, cable bolts. While rock bolt failure has been studied extensively, no study has been made previously of cable bolt failures. The present study was undertaken to examine the failure of cable bolts in detail. Service failed bolts retrieved from two different mines were examined fractographically. The role that anaerobic sulphate reducing bacteria (SRB) such as Desulfovibrio vulgaris might play in causing failure was examined, and also the possible contribution from aerobic bacteria such as Acidithiobacillus ferrooxidans. A test coupon for in-situ testing for SCC in underground mines was developed. The efficacy of various coatings in mitigating against SCC was also examined. The results showed that failure of the cable bolts was due to hydrogen-induced stress corrosion cracking (HISCC). It was found that the bacteria Desulfovibrio vulgaris could also produce HISCC of cable bolt wires when added to extracted mine water. However, HISCC did not occur when D. vulgaris was added to sterilised mine water indicating that other microorganisms, likely the sulphur-reducing bacteria Sulfurospirillum sp, were also involved. Acidithiobacillus ferrooxidans was found to promote pitting corrosion of the wires in extracted mine water and this could be significant for initiating HISCC. A test specimen which can replicate HISCC in-situ in underground mines was developed. The Jennmar proprietary coating PyFlexU was found to have excellent potential for protecting both rock bolts and cable bolts from HISCC.

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.

Six service-failed rock bolts, all broken through the threaded region at the end of the bolt, were examined. All bolts were made from 840 Grade steel, a medium carbon manganese silicon vanadium hot rolled microalloyed steel, and had a diameter of 22 mm. All six bolts had been installed in a single mine which had a high-pH, sulphate-rich groundwater. Prior to investigating the failed bolts, some preliminary studies were undertaken to provide background information for the work. The first of these involved tensile testing of notched and un-notched rock bolts made from the same steel as the failed rock bolts. The notched rock bolt contained a 2 mm deep flat-bottomed V notch with a bottom width of 0.5 mm, while the full rock bolt profile was retained for the un-notched test. The un-notched rock bolt underwent substantial necking and failed by microvoid coalescence. The notched rock bolt showed no appreciable macroscopic plasticity and failed by cleavage. Additionally, a sample from the same rock bolt steel was loaded through the threads in bending until failure occurred. Fracture initiated at the base of one of the threads and propagated in a ductile manner by microvoid coalescence for the first 1.5 mm of the fracture, but thereafter by brittle cleavage. Stable cracks were also produced at the base of the adjoining threads. The effect of corrosion by mine water on the appearance of ductile (microvoid coalescence) and brittle (cleavage) fracture surfaces in the same steel was also examined. Corrosion substantially changed the appearance of both types of fracture surface, but the two different types of fracture were still quite different in appearance. Five of the six rock bolts were found to have failed by stress corrosion, with cracking initiating at the base of one of the threads. In two of these cases, the stress corrosion crack initiated from a 1-2 mm deep pre-existing crack, considered to have been induced by bending. One of the six bolts failed by overload. Laps were seen frequently at the root of the cold rolled threads but these did not appear to have played a significant role in the failures.

The provision of a safe and economic rock support system is of primary importance for any excavation programme. If the excavation is to be developed by explosives, then the effect of blast forces on the performance of the rock support system must be considered. A review of current literature has highlighted a general lack of information regarding rock anchorage performance under blast loading. With this in mind, a full scale field test programme was undertaken to study the effect of close proximity blasting on resin bonded rock bolts, during the construction of the Pen y Clip Tunnel in North Wales together with a re-analysis of data from a previous study at the nearby Penmaenbach Tunnel. In both cases, accelerometers were used to monitor vibration and hydraulic load cells recorded the changes in rock bolt load during production face blasting. For the Pen y Clip trials, an additional monitoring system was developed which incorporated load cells positioned along the length of specially made experimental rock bolts. Further trials were conducted at an Edinburgh City Centre site to assess the likelihood of damage to temporary, cement grouted rock anchorages whose fixed anchors were positioned as close as 5m from nearby tunnel blasting. These trials involved the measurement of vibrations, both on the anchor head and down specially constructed boreholes, together with lift off load testing. Analysis consisted of the time and frequency domain examination of the signals, recorded on FM magnetic tape, from the three sets of field trials. Resin bonded rock bolts installed in microdiorite and rhyolite were found to be highly resilient to blasting, even those positioned down to lm from full face tunnel blasting. Temporary anchorages in mudstone were more susceptible to blasting but damage could be limited by monitoring of vibrations and careful control of blast parameters. The frequency response of the anchor head was found to be dependent on the characteristics of the anchorage and the nature of the environment in which it was installed. This raises the possibility that the analysis of spectral responses could form the basis of a technique for the non destructive testing of rock anchorages.