Tunnel Seismic Prediction (TSP) is a geophysical investigation method used to predict the rock conditions ahead of the tunnel face. The method has been used in different types of rock and rock conditions. The Swedish Transport Administration, Trafikverket, has used the investigation method in multiple locations in the large infrastructure project E4 The Stockholm Bypass. The method is however rather new to Swedish rock conditions, and there is therefore a need to evaluate the method to assess its strengths and weaknesses. In this thesis, the TSP method is compared to other investigation methods used in the Stockholm Bypass project at the location Sätra-Kungshatt where the tunnels cross underneath Lake Mälaren. The investigation methods include geological mapping and Measurement While Drilling (MWD). The TSP results are also compared to the engineering geological prognosis. An evaluation of how the seismic primary and secondary waves, Vp and Vs, correlates to rock quality was carried out, and a linear regression analysis was performed to determine if the wave velocities found using the TSP method correlate with the Q value retrieved through the geological mapping. It was found that the TSP method is capable of detecting weaker zones of rock mass, however no correlation between the wave velocities and the Q value used to describe the quality of the rock mass was found. When comparing the TSP results to the MWD results, it was found that the methods could be used as complements to each other as the different methods sometimes detected weakness zones where the other method did not. As the geology in this location of Stockholm Bypass overall was found to be complex with rather poor rock mass quality, it could be concluded that the TSP method might be better suited for less complex geology where the contrast in rock quality is greater. / Tunnel Seismic Prediction (TSP) är en geofysisk undersökningsmetod för att tillhandhålla en prognos av berget framför tunnelstuffen. Metoden har använts i olika typer av berg och bergförhållanden. I Sverige har metoden använts av Trafikverket vid flertalet tillfällen i infrastrukturprojektet E4 Förbifart Stockholm. Metoden är dock relativt ny för de svenska bergförhållandena, vilket gör att det finns ett behov av att utvärdera metodens styrkor och svagheter i dessa förhållanden. I detta masterprojekt har resultaten som tillhandahållits från TSP-metoden jämförts med resultat från andra undersökningsmetoder som använts vid vattenpassagen vid Sätra-Kungshatt där tunneln korsar under Mälaren. Dessa undersökningsmetoder inkluderar geologisk kartering och Measurement While Drilling (MWD). TSP-resultaten har även jämförts med den ingenjörsgeologiska prognosen för området. Vikt har lagts på hur den seismiska primärvågen, Vp, och sekundärvågen, Vs, förhåller sig till den karterade bergkvaliteten. En regressionsanalys har även utförts för att avgöra om resultaten från TSP-metoden korrelerar med resultaten från den geologiska karteringen. Jämförelsen mellan de olika undersökningsmetoderna visade på att TSP kan påvisa svaghetszoner i bergmassan. Dock kunde ingen korrelation mellan våghastigheterna och Q värdet påvisas. Jämförelsen mellan TSP och MWD visade att de båda metoderna generellt visade liknande resultat. Dock kunde vissa avvikelser mellan resultaten från metoderna hittas, vilket göra att metoderna skulle kunna användas som komplement till varandra. Detta då de olika metoderna ibland kunde identifiera svaghetszoner som den andra metoden inte kunde identifiera. De svåra geologiska förhållandena på platsen kan ha bidragit till att TSP-resultaten över lag är relativt svårtolkade, vilket gör att TSP-metoden möjligtvis är bättre lämpad för mindre komplexa bergförhållanden där kontrasten mellan bra och dålig bergkvalitet är tydligare.

This research is carried out to better understand the nature of the rock mass and to have a better anticipation of rock fragmentation before blasting the rock mass. Current practices of assessing rock mass usually involve techniques that focus on the surface or outcrop of the rock mass such as scanline surveys, window surveys, photogrammetry and laser scanning etc. These techniques generally lack the ability of providing sufficient information about the rock mass as well as bear various inherent constraints such as safety issues, time requirements, user biasness, equipment requirements and reproducibility of results. Similarly, the rock fragmentation is predicted using different mathematical equations known as fragmentation models. However, these models ignore some key factors that significantly affect the nature of fragmentation such as chargeability of blastholes, drilling information e.g. borehole deviation and require numerous rock parameters which are not well known in most cases. These models are often site-specific and are mostly developed for surface mines. Therefore, their application in underground mining is not so common. The aim of this research is to investigate the possibility of eliminating the constraints and supporting the current practices of rock mass assessment and rock fragmentation prediction. In this regard, drill monitoring technique has been selected as a potential tool for analysing the rock mass and forecast the rock fragmentation. To test the selected technique, measurement while drilling (MWD) data was collected from three different mines. The variations in MWD data were analysed to identify different zones and structures present inside the rock mass. The results were compared to 3D images obtained by close-range terrestrial digital photogrammetry for validation, which showed a close agreement with each other. Similarly, MWD data was used to classify the rock mass into five different classes i.e. solid, slightly fractured, highly fractured, having cavities, and major cavities in a sublevel caving operation. The loading operation of the blasted rock was filmed and digital images of LHD buckets containing blasted rock were extracted from the video recordings. The blasted rock inside the buckets were categorized as fine, medium, coarse and oversize fragmentation based on their median fragment size (X50). A statistical analysis was carried out to see the correlation between MWD based rock mass classes and fragmentation classes. The results showed that fine and medium size fragmentation has better correlation and can be predicted with higher accuracy using MWD data as compared to coarse and oversize fragmentation. The results suggest that the drill monitoring technique has the potential to assess rock mass as well as predict rock fragmentation to some extent. It can be used to differentiate between a weak or strong rock mass or between a fractured or competent rock mass. It can be used to differentiate between joints, cavities or foliations etc. It can also be used to predict finer and medium size fractions of the blasted rock with reasonable accuracy. However, the coarser and oversize fragmentation didn’t have a reliable correlation with MWD data. The potential of using drill monitoring technique for rock mass assessment and rock fragment prediction can be further explored and validated using other established rock mass and fragmentation assessment techniques. It can largely overcome the time, cost and safety constraints associated with the methods already in practice.

Prior to an underground excavation a site investigation is carried out. This includes reviewing and analysing existing data, field data collected through outcrop mapping, drill core logging and geophysical investigations. These data sources are combined and used to characterise, quantify and classify the rock mass for the tunnel design process and excavation method selection. Despite the best approaches used in a site investigation, it cannot reveal the required level of detail. Such gaps in information might become significant during the actual construction stage. This can lead to; for example, over-break due to unfavourable geological conditions. Even more so, an underestimation of the rock mass properties can lead to unplanned stoppages and tunnel rehabilitation. On-the-other-hand, the excavation method itself, in this case, drill and blast, can also cause severe damage to the rock mass. This can result in over-break and reduction of the strength and quality of the remaining rock mass. Both of these attributes pose risks for the tunnel during excavation and after project delivery. Blast damage encompasses over-break and the Excavation Damage Zone (EDZ). In the latter irreversible changes occur within the remaining rock mass inside this zone, which are physically manifested as blast fractures. In this thesis, a number of methods to determine blast damage have been investigated in two ramp tunnels of the Stockholm bypass. Herein, a comparison between the most common methods for blast damage investigation employed nowadays is performed. This comparison can be used to select the most suitable methods for blast damage investigation in tunnelling, based on the environment and the available resources. In this thesis Ground Penetrating Radar, core logging (for fractures) and P-wave velocity measurements were applied to determine the extent of the blast damage. Furthermore, the study of the two tunnels in the Stockholm bypass shows a significant overestimation of the actual rock mass quality during the site investigation. In order to gain a more accurate picture of the rock mass quality, Measurement While Drilling (MWD) technology was applied. The technology was investigated for rock mass quality prediction, quantifying the extent of blast damage, as well as to investigate the potential to forecast the required rock support. MWD data was collected from both grout and blast holes. These data sets were used to determine rock quality indices e.g. Fracture Indication and Hardness Indicator calculated by the MWD parameters. The Fracture Index was then compared with the installed rock support at the measurement location. Lastly, the extent of the damage is investigated by evaluating if the MWD parameters could forecast the extent of the EDZ. The study clearly shows the capability of MWD data to predict the rock mass characteristics, e.g. fractures and other zones of weakness. This study demonstrated that there is a correlation between the Fracture Index (MWD) and the Q-value, a parameter widely used to determine the required rock support. The study also shows a correlation between the extent of the blast damage zone, MWD data, design and excavation parameters (for example tunnel cross section and charge concentration).

[pt] Alguns dos problemas mais comuns relatados durante a perfuração de poços petrolíferos, como a instabilidade, a perda de circulação e o colapso das paredes, podem ser evitados com o acesso em tempo real, dentre outros, à resistência à com-pressão não confinada das rochas. Os métodos mais usuais de estimativa da resis-tência não confinada apresentam três principais restrições quanto à aplicação em tempo real: i) a perfilagem em tempo real pode não ocorrer ao longo de toda a tra-jetória do poço e é mais costumeira em profundidades próximas ao reservatório; ii) a obtenção de amostras provenientes do poço para ensaios de laboratório é prática custosa e pouco usual e; iii) as informações relativas à geometria da broca são res-tritas aos fabricantes. Nesse contexto, esta dissertação tem como foco a adaptação de um método de estimativa da resistência não confinada para tornar possível a aplicação em tempo real, partindo da hipótese de que a perfuração é fundamental-mente controlada pela interação entre a broca e a formação rochosa e que a resis-tência à compressão confinada está relacionada a uma parcela da energia mecânica específica. A metodologia desenvolvida foi aplicada em um poço, testada em outros nove poços e será implementada no programa de estabilidade SEST TR 2.0. Sa-bendo que a resistência não confinada é função da coesão e do ângulo de atrito, a coesão da formação rochosa também foi calculada. Este estudo conclui que é pos-sível estimar ambas as propriedades mecânicas em tempo real dispondo apenas dos parâmetros operacionais de perfuração. / [en] Some of the most common problems reported during well drilling, such as instability, loss of circulation and wellbore collapse can be avoided with real-time access, among others, to the unconfined compressive strength of rocks. The most usual methods for estimating unconfined compressive strength have three main re-strictions regarding their real time application: i) real-time logging may not occur along the entire trajectory of the well and is more common at depths close to the reservoir; ii) obtaining samples from the well for laboratory tests is costly and un-usual practice and; iii) information regarding drill bit geometry is restricted to man-ufacturers. In this context, this research focuses on the adaptation of an unconfined compressive strength estimation method to make real-time application possible, based on the hypothesis that drilling is fundamentally controlled by the interaction between the drill bit and rock formation and that the confined compressive strength is related to a portion of the mechanical specific energy. The developed methodol-ogy was applied in one well, tested in nine other wells and will be implemented in the SEST TR 2.0 stability program. Knowing that unconfined compressive strength is a function of cohesion and friction angle, the cohesion of the rock for-mation was also calculated. This study concludes that it is possible to estimate both mechanical properties in real time using only drilling data.

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