The stability analysis of trapdoor and underground opening

The objective of this thesis is to investigate the stability problem of two-dimensional planar and circular trapdoor opening under both drained and undrained conditions. For the drained conditions, the analyzes were carried out, separating in two cases including active and passive failure which the soil media are cohesive-frictional soil. The internal trapdoor pressure (t) is obtained utilizing the three stability factors (Fc, Fs and F) approaches. On the other hand, the undrained stability analysis was performed solely in active conditions with the assumption of heterogeneity and anisotropic clay media. As a result, the new stability number is derived as well as the failure mechanism. However, for a variety of geometrical and physical situations, finite element limit analysis (FELA) is employed to compute the stability solutions to these problems with the rigorous upper and lower bound solutions. The numerical models and the parametric analysis were performed in the finite element software OptumG2 with a practical range of parameter as follows: (1) For cohesive-frictional soil, the considered parameters including soil friction angle (= 0 – 40) and cover-depth ratio (H/D = 0.5 – 10); (2) For undrained clay, the considered parameters including depth ratios (H/D = 0.5 – 10), strength gradients (m = 0 – 4) and anisotropic strength ratios (re = 0.5 – 1.0). Furthermore, the influence between those considered parameters to the three stability factors and the new stability number are provided and described respectively. Therefore, a comprehensive set of design charts, tables, and equations has been presented, along with some practical examples to clarify and implement these concepts in practice.