Design Study Report Objectives 2020: Finite Element Analysis for Tunnelling Problems

Objectives of the Design Study Report

1. To use finite element methods in a rational and controlled manner and to avoid common pitfalls.

2. To demonstrate understanding of the theory of finite elements and their application.

3. To demonstrate understanding of numerical modelling methodology as applied to tunnelling problems, such as: 2d plane strain soil elements and structural elements boundary conditions mesh density and mesh dependency of the analysis constitutive models validation and error checking interpretation and presentation of results.

4. To learn how to present the methodology and results of numerical analyses in report form. Software.

5. All fea models should be developed with plaxis 2d. Assignment the description of the assignment is on the following page. Perform the analyses and write a report. The report needs to demonstrate to the reader that all appropriate steps have been taken to ensure the numerical model is working properly and the results of the analyses are sensible. Sufficient information is required for the reader to be able to replicate what you have done and what steps you have taken in your analysis (e.g. Include model dimensions, soil profile, structural elements’ specs, calculation phases etc.). Also ensure that you have done the following: • determination of the required boundary distances.

5. Making sure that the element types and boundary conditions are explained in the report, giving reasons for why they were selected.

6. It is recommended that you try to plot graphs at critical points (using curve manager) when presenting results rather than many contour plots. As contours only give the reader a qualitative view of the pattern of behaviour, which can be worthwhile but think about what the purpose of each table/graph/plot is and ensure they are all discussed in the text and are important to the point you are making. Do not put lots of contour plots in the appendix. Msc tunnelling and underground space es96v fem for tunnelling design study report 2 description of the coursework:

Parallel tunnels use a 2d plane strain model to simulate the construction of a metro tunnel extension in london that is 4 km long, followed by construction of a second, identical, tunnel parallel to it. The tunnels are to be constructed with a moderate angle that changes the depth of the tunnels from 20 m below the ground surface at the start to 30 m bellow the ground surface at the end. Also, at mid-way, the tunnels are passing through a historical area where at parts deep piles (over 30 m deep) are in the vicinity. The tunnels are to be constructed with natm approach. Ground water table shows seasonal variations between depths of 5 m to 15 m. O use appropriate soil parameters for london clay, and use the modified cam-clay (mcc) constitutive model.

Carry out the analyses at 3 different critical cross sections.

Thoroughly explain the initial and boundary conditions considered for the analyses, together with the specifications of the design (i.e. Placement of lining with respect to the tunnel face during the excavation) vary the size of the tunnels and the spacing between them and analyse the stresses and the effects on surface settlements, lining deformations and group of piles as a guideline for a distinction level mark (i.e. ≥70%), the above needs to have been done very well and reported impeccably, as well as going beyond the brief in one or more of the following ways:

Using a different constitutive model (e.g. Mohr-coulomb or hardening soil) and show/discuss their effect on the numerical predictions comparison of surface settlement predictions with the empirical gaussian settlement trough for surface settlements, does superposition hold true (i.e. Could the surface settlements due to construction of the first tunnel be superposed for the second tunnel, or do the subsequent tunnel causes more/less settlement than the first?) comparison to numerical modelling or field measurements of similar scenarios in the literature use of different k0 values (still appropriate to london clay) and discussion of their effect on results. Considerations made for the effect of ground water level variations and their implications.