Block stability is common and has to be studied in detail for designing tunnels. Stability of block depends upon the shape and size of the blocks, stresses around the block and factors such as clamping forces and the ratio between joint stiffness. These factors are studied in detail and are the main objective of this thesis. In this thesis influence of loading and unloading of blocks on joint stiffness and thus on ultimate pullout force are analyzed. Normal stress on the joint plane is linked with shear stiffness of the joint and relaxation of forces. Changes of forces were considered to estimate joint stiffness and ultimate pullout force using new methods in the present thesis. First method takes into account changing clamping forces considering stiffness ratio constant (Crawford and Bray). The second method was developed in which the ratio between normal and shear stiffness was taken as a function of normal stress (Bagheri and Stille). In third method, gradually pullout force is increased which changes the normal stress and joint stiffness. The lower limit of joint stiffness gives a very conservative design. So a stiffness value based on the average of lower and upper limit of normal force has also been considered. A comparison between the new methods and the previous method proposed by Crawford and Bray which considers a constant ratio of normal and shear stiffness and constant clamping forces shows that Crawford and Bray’s solution overestimates the pullout forces hence the design is unsafe. It was observed that stiffness ratio is an important factor for estimating required rock support and safety.

Establishment of relationships for predicting the lateral drift demands of near-fault ground motions is one of the major challenges in earthquake engineering. Excessive lateral drifts caused by earthquake ground motions are the major causes of structural damage observed in structures. In this study, some of the fundamental characteristics of near-fault ground motions are examined. Response characteristics of elastic frame structures to near-fault ground motions are investigated. An approximate method for estimating the elastic ground story and interstory drifts for regular frame type structures is presented. Inelastic displacement demands imposed on elasto-plastic single degree of freedom (SDOF) systems subjected to near-fault ground are examined. Three equations for estimating the maximum lateral inelastic displacement demand from the maximum elastic displacement demand are established. Two of these equations relate the inelastic and elastic displacement demands through natural period and strength reduction factor. The third equation relates the inelastic and elastic displacement demands through the ratio of natural period to pulse period and the strength reduction factor. Efficiency of the natural period to pulse period ratio for estimating the inelastic displacement ratio is shown. Error statistics of the proposed equations are presented and compared with similar studies in the literature. According to the results, these equations can be used for quick and rough estimates of displacement demands imposed on regular elastic moment resisting frames and elasto-plastic single degree of systems.