The failure mechanisms of reinforced soil segmental walls with extensible reinforcements were studied by performing a numerical analysis using the finite element method. The numerical approach was first verified against the results of three instrumented full-scale structures reported in the literature. Finite element models with different combinations of reinforcement spacing, reinforcement length and backfill soil were analysed. The ϕ–c reduction method, which is a special shear strength parameter reduction technique, was applied to simulate the failure conditions. The results of ϕ–c reduction analysis were used to evaluate assumptions used in current design procedures for geosynthetic-reinforced soil walls. In particular, shear strains were used to identify failure surfaces. Interpretation of the results indicated that, for both granular and cohesive backfills, the potential failure surface gradually shifts to a direct sliding mode as the system approaches failure. As a result, under working loads the potential failure surface used in current design analysis is correct, but the failure plane of a geosynthetic-reinforced soil-retaining wall at failure approaches a direct sliding type or a bilinear plane, which starts from the toe of the wall with a very shallow slope. The failure mechanisms of reinforced soil segmental walls with extensible reinforcements were studied by performing a numerical analysis using the finite element method. The numerical approach was first verified against the results of three instrumented full-scale structures reported in the literature. Finite element models with different combinations of reinforcement spacing, reinforcement length and backfill soil were analysed. The ϕ–c reduction method, which is a special shear strength parameter reduction technique, was applied to simulate the failure conditions. The results of ϕ–c reduction analysis were used to evaluate assumptions used in current design procedures for geosynthetic-reinforced soil walls. In particular, shear strains were used to identify failure surfaces. Interpretation of the results indicated that, for both granular and cohesive backfills, the potential failure surface gradually shifts to a direct sliding mode as the system approaches failure. As a result, under working loads the potential failure surface used in current design analysis is correct, but the failure plane of a geosynthetic-reinforced soil-retaining wall at failure approaches a direct sliding type or a bilinear plane, which starts from the toe of the wall with a very shallow slope.

Pipe jacking is a technique used to construct tunnels by pushing prefabricated pipes through the ground from an entrance shaft to an exit shaft. This technique is referred as microtunneling in U.S. terminology, therefore, in the rest of the text, pipejacking and microtunneling will be used as having the same meaning. Pipe jacking is a more economical alternative to segmental lined tunnels. However, the main limitation of pipe jacking is the jacking distance, which is directly dependent on the friction between the pipe and the soil. Therefore, reducing the friction between the pipe and soil is a critical issue in terms of economy and construction speed. In pipe jacking, in order to reduce the friction between pipe and soil, a bentonite injection is applied. In this paper, a new laboratory test setup was prepared to simulate pipe jacking. The main aim of this test setup was to find the effects of bentonite pressure on the lubrication efficiency, which has not been clarified in the literature yet. In...