In the present-day context, man-made sources of ground-borne vibration are rising at a very rapid rate due to increasing construction work, blasting activities, and rapidly expanding rail and road traffic systems. As a consequence, amplified levels of ground-borne vibration occur, causing annoyance to residents living in nearby areas, posing a threat to the stability of old structures, and interfering with instrumentation works in industries. This paper discusses an investigation into the use of trenches as a means of mitigating ground vibration caused by propagation of surface (Rayleigh) waves. Two- and three-dimensional (2D and 3D) finite-element models were developed using PLAXIS for identifying key factors affecting the vibration isolation efficiency of open and infill trenches. Parametric studies were carried out, and the results were analyzed to arrive at optimum values of geometrical and material properties of trenches. Numerical analysis showed that, for open trenches, normalized depth is the decisive factor and width is of importance in trenches that are very shallow. For infill trenches, it was observed that low-density materials perform exceedingly well as infill materials but their performance is highly sensitive to the relative shear-wave velocity between the infill material and the in situ soil. Finally, an in-depth analysis was carried out to investigate the performance of polyurethane foam trenches in mitigating vibrations caused by harmonic loads. The analysis was extended to study the effectiveness of these geofoam barriers in damping out the vibrations generated by a moving train. In this case, barrier efficiency was shown to increase with increasing train speed. The key findings suggest that trenches are a simple and effective solution for reducing ground-borne vibrations.

This research work presents an experimental and numerical study of the coupled thermo-hydro-mechanical (THM) processes that occur during soil freezing. With focusing on the artificial ground freezing (AGF) technology, a new testing device is built, which considers a variety of AGF-related boundary conditions and different freezing directions. In the conducted experiments, a distinction is made between two thermal states: (1) The thermal transient state, which is associated with ice penetration, small deformations, and insignificant water suction. (2) The thermal (quasi-) steady state, which has a much longer duration and is associated with significant ice lens formation due to water suction. In the numerical modeling, a special focus is laid on the processes that occur during the thermal transient state. Besides, a demonstration of the micro-cryo-suction mechanism and its realization in the continuum model through a phenomenological retention-curve-like formulation is presented. This allows modeling the ice lens formation and the stiffness degradation observed in the experiments. Assuming a fully saturated soil as a biphasic porous material, a phase-change THM approach is applied in the numerical modeling. The governing equations are based on the continuum mechanical theory of porous media (TPM) extended by the phase-field modeling (PFM) approach. The model proceeds from a small-strain assumption, whereas the pore fluid can be found in liquid water or solid ice state with a unified kinematics treatment of both states. Comparisons with the experimental data demonstrate the ability and usefulness of the considered model in describing the freezing of saturated soils.

For shallow tunnel constructions, settlement of the ground surface is a main issue. Recent technical developments in shield tunneling technique have enabled a decrease in such settlements due to tunneling under ground deformation controls. However, surface settlements are still considerable. The objective of this paper is to investigate ground behavior due to grouting of the tail void in shield tunneling. Tail void grouting is a common practice in shield tunneling that reduces ground movements and changes in the stress state of the ground due to tunnel excavation. In order to investigate the influence of tail void grouting, three dimensional FEsimulations were performed for the simple case of a tunnel heading in homogeneous sandy soil below the ground water table. In a sensitivity analysis, the initial relative density of the ground, which determines the stress-strain relationship, was changed. Focusing on the stress and volume change of the tail void grout with time, the simulation results were evaluated with respect to the deformation and stress state of the ground. Surface settlement depends both on the volume loss due to tunnel construction and on the volume change of the ground around the tunnel. Additionally, such volume change is influenced by pore water pressure.