In this thesis, the results of a number of rock mass classification systems applied to Dim-higway tunnel study area are presented. The tunnel ground was classified according to Rock Mas Rating (RMR), Modified Rock mass Rating (M-RMR), Rock mass quality (Q), Geological Strength Index (GSI) and New Austrian Tunneling Method (NATM). Dim Tunnel has a horse-shoe shape, with a diameter of 10 meters and maximum overburden thickness of 70 meters. During studies, the geological and geotechnical characteristics of the rock mass along the Dim Tunnel route were investigated. The main objective of rock mass classifications carried out in this study was to obtain adequate data that could be used in future excavation and support-design studies. In order to accomplish this task, literature survey was carried out, followed by a comprehensive field study and laboratorytesting. Field studies involved detailed discontinuity surveys of the exposed rock mass at the surface and on the cores taken within 10-20 meters of the borehole above the tunnel. A geological map and a geological cross-section along the tunnel axis were also prepared. Finally, correlations between the results of the rock mass classification systems were made carrying out statistical analyses for the Dim Tunnel study area. The results obtained from the RMR and M-RMR classifications indicate that M-RMR system estimates better rock mass quality ratings at the upper bounds of the rock mass condition, but worst ratings at the lower bounds (RMR is less than 40) as also suggested by the previous studies.

Os sistemas de classificação maciços rochosos e as redes neurais artificiais possuem diversas similaridades. Existem características que estão presentes nos dois tipos de sistemas: bases de dados são usadas para o seu desenvolvimento; e pesos são parte da representação do conhecimento. Os principais sistemas de classificação geomecânicas (Sistema Q e RMR) podem ser escritos como representações neurais locais. Tais representações permitem uma melhor compreensão do processo de classificação e identificação de padrões realizado pelas classificações convencionais. Experimentos convencionais foram realizados com modelos de redes neurais não-supervisionados. Os modelos não supervisionados permitiriam uma melhor compreensão da distribuição dos dados no espaço de feições. Um modelo supervisionado para escavações subterrâneas em todo domínio do espaço de feições. Importantes relações entre características foram encontradas. / Rock mass classification systems and artificial neural networks have several similarities. There is some characteristics present in both systems: data bases are used in they development, and weights are part of the knowledge representation. The main rock mass classification systems (Q-system and RMR) can be written as local neural network representations. This representation helps a better understanding of the pattern classification and identification process made by the conventional classifications. Computational experiments were made with unsupervised and supervised neural networks models. Unsupervised models allow a better understanding of the data in the feature space. A supervised model allow to make a mapping of the support type used in underground excavation in all feature space domain. Important relations between domain regions characteristics and type of support used were found.

This thesis analyzes the potential systematic errorin the characterization of the rock mass quality in borehole and tunnel mapping. The difference when assessing the rock mass quality refers to the fact that the characterization performed on drilled rock cores are commonly done on-meter length, while the tunnel section can be up to 20-25 m wide. At the same time, previous studies indicate that the engineering geologist tends to characterize the rock mass quality during tunnel excavation with a conservative estimation of the parameters defining the rock mass quality to ensure a sufficient rock support. In order to estimate this possible systematic error produced by the size difference when assessing the rock mass quality, a simulation was performed within a geological domain, representative of Stockholm city. In the simulation, each meter of the tunnel section was given a separate value of the rock mass quality, randomly chosen from a normal distribution representative for the studied geological domain. The minimum value was set to represent the characterized rock mass quality for that tunnel section. The results from the simulation produced a systematic error due to the difference between the geological domain, reproducing the borehole mapping, and the simulated values, representing the tunnel mapping. The results showed a systematic error in the RMR basic index around 15 points in average, which compared to the difference of 5-7 points obtained in Norrström and the Norrmalm tunnels in the Stockholm Citylink project recently constructed, are found to be excessive. However, in the simulation, it was assumed that (1) the results obtained were the same in the bore hole mapping and in the tunnel mapping, (2) with the only difference of the engineer geologist assigning to the tunnel section the lowest RMR basic value, and (3) that there was no spatial correlation between the quality RMR basic index. After analyzing the three assumptions the simulation was based upon, the absence of spatial correlation was found to be the most significative, which indicate that spatial correlation in rock mass quality needs to be included if a more correct value should be obtained.

Infrastructure is developing at an extremely fast pace which includes construction of metros, underground storage places, railway bridges, caverns and tunnels. Very often these structures are found in or on the rock masses. Rock masses are seldom found in nature without joints or discontinuities. Jointed rocks are characterized by the presence of inherent discontinuities of varied sizes with different orientations and intensities, which can have significant effect on their mechanical response. Constructions involving jointed rocks often become challenging jobs for Civil Engineers as the instability of slopes or excavations in these jointed rocks poses serious concerns, sometimes leading to the failure of structures built on them. Experimental investigations on jointed rock masses are not always feasible and pose formidable problems to the engineers. Apart from the technical difficulties of extracting undisturbed rock samples, it is very expensive and time consuming to conduct the experiments on jointed rock masses of huge dimensions. The most popular methods of evaluating the rock mass behaviour are the Numerical methods. In this thesis, numerical modelling of jointed rock masses is carried out using computer program FLAC (Fast Lagrangian Analysis of Continua). The objective of the present study is to study the effect of various joint parameters on the response of jointed rock masses in static as well as seismic shaking conditions. This is achieved through systematic series of numerical simulations of jointed rocks in triaxial compression, in underground openings and in large rock slopes. This thesis is an attempt to study the individual effect of different joint parameters on the rock mass behaviour and to integrate these results to provide useful insight into the behaviour of jointed rock mass under various joint conditions. In practice, it is almost impossible to explore all of the joint systems or to investigate all their mechanical characteristics and implementing them explicitly in the model. In these cases, the use of the equivalent continuum model to simulate the behaviour of jointed rock masses could be valuable. Hence this approach is mainly used in this thesis. Some numerical simulations with explicitly modelled joints are also presented for comparison with the continuum modelling. The applicability of Artificial Neural Networks for the prediction of stress-strain response of jointed rocks is also explored. Static, pseudo-static and dynamic analyses of a large rock slope in Himalayas is carried out and parametric seismic analysis of rock slope is carried out with varying input shaking, material damping and shear strength parameters. Results from the numerical studies showed that joint inclination is the most influencing parameter for the jointed rock mass behaviour. Rock masses exhibit lowest strength at critical angle of joint inclination and the deformations around excavations will be highest when the joints are inclined at an angle close to the critical angle. However at very high confining pressures, the influence of joint inclination gets subdued. Under seismic base shaking conditions, the deformations of rock masses largely depend on the acceleration response with time, frequency content and duration rather than the peak amplitude or the magnitude of earthquake. All these aspects are discussed in the light of results from numerical studies presented in this thesis.