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LKAB’s underground mine in Kiirunavaara has experienced an increasing seismic activity the last ten years. This seismic activity is caused by the stress redistribution resulting from the mining method of large-scale sublevel caving. The energy from the seismic events propagate in the rock mass as seismic waves. If one of these waves interacts with an excavation, it will be subjected to dynamic loads, and damage can potentially occur. Damage can be caused by different mechanisms depending on many factors such as pre-existing structures in the rock mass and the state of stress. To prevent these damages, LKAB has installed a rock support system for handling dynamic loads. This thesis has analysed available damage mapping reports, investigations, pictures, seismic data and history, in order to evaluate the function of the support system when subjected to dynamic loads. The conclusion of the analysis is that the support system is well designed, but there are areas of improvement. The main damage mechanisms are bulking without ejection and rockfall due to seismic shaking. Bulking with ejection and ejection due to seismic energy transfer were concluded to not yet be a problem in the Kiirunavaara mine. This result implies that an improved stiffness, static strength and yieldability are to be considered in order to decrease the amount of bulking. For rockfall due to seismic shaking, there are two main areas of improvement. The structural mapping has to be given higher priority, and it should provide direct support recommendations if needed. The second part is to increase the static strength of the system in order to survive rockfall due to seismic shaking. Since bulking with ejection and ejection due to seismic energy transfer are not yet considered significant problems, there is no need to improve the support system with respect to absorption of kinetic energy. The location of the damages in the drift profiles were also analysed, and it was concluded that a majority of the damages that occurred in the footwall drifts were located in the corner of the abutment facing the orebody. In the crosscuts, a majority of the damages occurred in the abutment and roof. Based on this, it is suggested that the support should be improved in the abutment and roof of the crosscuts, and in the abutment facing the ore of the footwall drifts.

When planning for a tunnel, the ground conditions in which the tunnel is going to be excavated through will be investigated to different extent. Lack of relevant pre-investigation data or misinterpretations of the available data can cause both economical and/or unexpected stability problems. Weakness zones that are expected to cross the tunnel could be investigated thoroughly with a variety of methods. Refraction seismicity survey and 2D resistivity survey are two geophysical methods that are common in Norway for obtaining information about the rock quality in weakness zones. In this work, a twin tunnel under construction in Bodø (northern Norway) called the Bodøtunnel is studied. The predictions based on the pre-investigation for crossing of some expected weakness zones are compared to the actual conditions encountered during tunneling. Tunneling observations (Geological mapping and photos), rock samples and measurement while drilling (MWD) were used to describe the weakness zones that were encountered during tunneling. Rock samples were collected from two weakness zones and the general rock mass. These samples were tested in a point bearing machine for determination of their uniaxial compressive strength (UCS). These results indicated that the rock samples gathered from the weakness zones had significantly lower UCS than the samples from the rock mass. This was exceedingly clear for the samples of fault rock gathered in connection with a shear zone. The results from this work demonstrate that refraction seismicity had a high success rate for locating weakness zones, with the exception for the crossed narrow zones that were interpreted lacking a shear component. Empirical formulas relating Q-value and UCS with the seismic wave speed were used for calculating these factors for some interesting locations. The empirically calculated UCS was similar to the obtained UCS from the point bearing tests, while the empirically calculated Q-value showed large deviations from the mapped Q-value. The resistivity measurements had a low success rate so far in this project; the reason for this could be disturbances in the ground and the location of the resistivity profiles, which had to adapted to the nearby railroad. It should be noted that only one full resistivity profile has been crossed and the rest of the profiles are expected to be more accurate. Based on the results from the crossed profile(s), the suitability of resistivity survey 2D in urban areas can be brought to question. This work also stumbled upon problems regarding the definition of weakness zones. Shear/fault zones are one of the more common type of weakness zones encountered in tunneling. These kind of zones often consists of different parts. Depending on which parts are regarded as a weakness zone by the responsible engineers, the Q-value might differ due to the SRF. Different scenarios were also evaluated with numerical modeling for the expected remaining major weakness zones. This analysis highlights the importance of differentiation between more fractured zones and zones containing fault rock, such as breccia. The width of the zone had a major impact on the stability while the dip for wide zones had a minor impact on the stability, as long the zones dip is not so small that both tunnels are intersected at the same time. The rock mechanical parameter of the weakness zones that had the most impact on the overall stability was the cohesion.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. September, 2017. / This study investigates the mineralogical, petrographic and geochemical characteristics of target rocks and impact-formed breccias (impactites) intersected by the 368 m long M4 drillcore located 18 km NNW from the estimated centre of the 145 ± 2 Ma, Morokweng impact structure (MIS), South Africa. M4 is the only core from the central parts of the Morokweng impact structure not to intersect fractionated granophyric impact melt directly beneath 35-100 m of Cenozoic Kalahari Group sediments. Instead it intersects highly fractured, cataclased and shocked, crystalline target rocks that are cut by mm- to m-scale melt-matrix breccia and suevite dykes. The target rocks comprise granitic, granodioritic, trondhjemitic and dioritic Archaean gneisses, metadolerite and dolerite. The gneisses and metadolerite show signs of quartz veining and metasomatism linked to localised mylonitic to brittle fault deformation that predated the impact. The suevite and meltmatrix breccia dykes make up ~10% of the core. All rocks show signs of low-T hydrothermal effects that occurred after the impact. The target rocks contain a complex network of shear fractures that contain cataclasite and which grade into monomict lithic breccia. The cataclasite contains shocked mineral fragments, which indicates that the shear fracturing postdated the initial shock stage of the impact. The melt-matrix breccia and suevite dykes show signs that they intruded along the fractures, although there is also evidence that shear fracturing continued after quenching of the melt. This suggests that the intrusion of the dykes overlapped the brittle deformation of the target rocks. Shock features in the M4 core lithologies include planar fractures, feather features, decorated planar deformation features (PDF), mosaic extinction and toasting in quartz; oblique lamellae, reduced birefringence and patchy (mosaic) extinction in plagioclase, and chevron-style spindleshaped lamellae in microcline, as well as kink bands in biotite and planar fractures in titanite and zircon. Universal Stage measurements of PDF sets in quartz from 8 target rocks and 6 impactite dykes revealed four dominant sets: 0°(0001), 22.95°{ 3 1 10 }, 17.62°{ 4 1 10 }, 32.42°{ 2 1 10 }; with no significant change in shock intensity with depth nor significant differences in PDF orientations or intensity between melt-matrix breccias, suevites and target rocks. Based on these observations the average peak shock pressures are estimated at 10 - 25 GPa. Apart from one suevite dyke that contains exotic clasts and an unusual bulk composition, all suevite and melt-matrix breccia dykes show major, trace and REE compositions and lithic and mineral clasts that indicate that they were formed from the target rocks found in the M4 core. The individual impactite dykes show good compositional correlation with their wallrocks, which supports limited transport of the melt and suevite. This is also supported by evidence of small-scale variation of the melt composition in the melt-matrix breccias, which indicates that not enough time was available for complete mixing to happen. The similarity in matrix composition and in lithic and mineral clast types in the melt-matrix breccias to their wallrocks, is consistent with a friction melt origin. These dykes are thus interpreted as pseudotachylite. Macroscopic and microscopic evidence suggests that the melts intruded cataclasite-filled fractures and that interfingering and infolding between the melts and incohesive cataclasite allowed the melt to assimilate cataclasite. The melt clasts in the suevite show the same composition and clast features as the melt-matrix breccias. Based on this evidence it is proposed that the melt clasts in the suevite in the M4 core are fragments of quenched pseudotachylite that became separated and mechanically mixed into the cataclasite matrix when movement continued along the cataclasite-bearing fractures after the melt quenched. This was possible because the cataclasite was still incohesive and because strong vertical and horizontal displacements of the entire M4 sequence happened during the crater modification stage of the impact, possibly for 1-2 minutes after the impact. The melt-matrix breccias are compositionally distinct from the Morokweng granophyric impact-melt rock intersected in the other central borehole cores. Melt particles are pervasively hydrothermally altered to a secondary mineral assemblage of zeolites and smectites, attributed to impact-induced hydrothermal fluid circulation in the MIS. The upper parts of the core are marked by abundant haematite but in the deeper levels of the core, chlorite-epidote-andradite garnet is found, which may indicate a vertically-zoned hydrothermal system after the impact. The hydrothermal effects also explain the abundance of decorated PDF in shocked quartz grains and the lack of glass in the PDF in quartz. The 10-25 GPa shock levels in the target rocks support them lying close to the transient crater floor and initially close (<10 km) to the point of impact. The high structural position of the rocks relative to the impact-melt sheet suggests that the M4 sequence represents part of the peak ring of the Morokweng impact structure. The rocks of the peak ring would have experienced strong vertical and centrifugal displacement during the crater excavation and modification stages, which can explain the intense shear fracturing and cataclasis, brecciation and friction melting as well as the strong block movements that could disrupt and disperse the pseudotachylite melt dykes to produce suevite. A peak ring radius of 18 km would suggest that the original Morokweng crater rim diameter would have been >70 km, but between 1 and 2 km of post-impact erosion before the deposition of the Kalahari Group means that this could be a minimum estimate. / LG2018

Wellbore stability is a critical issue when drilling through tectonically stressed and complex geological conditions. Understanding wellbore stability issues before a well is drilled enables better planning of the drilling operation and helps to avoid borehole failure. This is of particular importance in underbalanced drilling where we are limited with our choice of drilling mud densities. This thesis examines the impact of fluid pressure change on wellbore stability during underbalanced drilling by using a timedependent poroelastic model. The poroelastic behaviour is analysed using numerical and analytical models. The finite element method (FEM) is used for the numerical model. Some simple techniques are developed and implemented to increase the speed and stability of the FEM solution. The common assumptions of plane strain and plane stress are explored. It is shown that the plane strain assumption results in high error while the error for plane stress is low. It is also shown that use of plane strain predicts more instability than use of plane stress and the stability difference is significant. From this it is concluded that the plane stress assumption should be used instead of the commonly used plane strain assumption. A sensitivity analysis is conducted to demonstrate the effect of several variables on wellbore stability during underbalanced drilling. These variables include mean in-situ horizontal stress, deviatoric in-situ horizontal stress, bulk compressibility and permeability. I various ways changes in these variables were shown to change the chance of shear failure, early time tensile failure through exfoliation and late time tensile failure through hydraulic fracture initiation.

The first section of this thesis (Chapter 2) describes the creation and analysis of a database on concrete and masonry dam incidents known as CONGDATA. The aim was to carry out as complete a study of concrete and masonry dam incidents as was practicable, with a greater emphasis than in other studies on the geology, mode of failure, and the warning signs that were observed. This analysis was used to develop a method of very approximately assessing probabilities of failure. This can be used in initial risk assessments of large concrete and masonry dams along with analysis of stability for various annual exceedance probability floods. The second and main section of this thesis (Chapters 3-6) had its origins in the results of Chapter 2 and the general interests of the author. It was found that failure through the foundation was common in the list of dams analysed and that information on how to assess the strength of the foundations of dams on rock masses was limited. This section applies to all applications of rock mass strength such as the stability of rock slopes. Methods used for assessing the shear strength of jointed rock masses are based on empirical criteria. As a general rule such criteria are based on laboratory scale specimens with very little, and often no, field validation. The Hoek-Brown empirical rock mass failure criterion was developed in 1980 for hard rock masses. Since its development it has become virtually universally accepted and is now used for all types of rock masses and in all stress regimes. This thesis uses case studies and databases of intact rock and rockfill triaxial tests collated by the author to review the current Hoek-Brown criterion. The results highlight the inability of the criterion to fit all types of intact rock and poor quality rock masses. This arose predominately due to the exponent a being restrained to approximately 0.5 to 0.62 and using rock type as a predictor of mi. Modifications to the equations for determining the Hoek-Brown parameters are provided that overcome these problems. In the course of reviewing the Hoek-Brown criterion new equations were derived for estimating the shear strength of intact rock and rockfill. Empirical slope design curves have also been developed for use as a preliminary tool for slope design.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.