Urban tunnelling can be highly challenging, especially in areas where limited ground settlements and environmental disturbance is required. Mechanised tunnelling is usually preferred in such ground environments, specifically Slurry or EPBM (Earth Pressure Balance Machine), depending on the ground properties. Being able to predict the anticipated tunnel behaviour at the preliminary stages of the project can be very beneficial in optimising not only the design, but also control the construction activities and completion times. In practice, the short-term excavation response and support performance focus primarily on design, since most site characterisation inputs are focused on material properties gained from short-term testing. Although the analysis of tunnelling is a three-dimensional (3D) problem, conventional approaches and design methods employed during the design and construction of underground openings are often based on the ground’s static response in two dimensions (2D). In this paper, an initial 2D model is generated in PLAXIS2D and RS2 (Rocscience) to test advanced constitutive models and compare transverse settlement profiles; subsequently, a complete 3D FEM numerical model in RS3 (Rocscience) was used to simulate an Earth Pressure Balance (EPB) excavation sequence. The 3D numerical model simulates the relevant EPB components such as face pressure, TBM shield, backfilling of the tail void (time-dependent hardening of the grout) and gradual segmental lining erections in the longitudinal direction. The presented numerical approach can be used by tunnel designers and engineers to predict the soil response in EPBM tunnelling.
The vertical penetration of sedimentary materials is of importance for many scientific and engineering purposes, including soil sampling and pile driving. One approach to this problem is to achieve orbital motion of a probe in a horizontal plane, thereby displacing the soil radially, with excitation produced by a rotating unbalance. The probe thus reacts with the soil, resulting in radial and tangential forces. The former produce hole enlargement, and the latter are in the nature of frictional drag related to orbital motion. The analysis indicates that such a system is bistable, with radial probe amplitudes dependent upon whirl frequency, soil friction, soil compressive resistance, probe mass, and exciter unbalance. Such a device exhibits several desirable operational characteristics, tending to enlarge the hole at increased radial resistance, and to decrease amplitude at reduced resistance, thus being somewhat self-regulating. A prototype has been built and tested experimentally; however, this paper is primarily a study of the steady-state vibratory behavior of a whirl-excited probe, with basic design equations presented.
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