Automating the Process for Estimating Tunneling Induced Ground Stability and Settlement

An automatic process for estimating ground stability and settlement of circular tunnels is
developed for practitioners in this paper using finite difference method FLAC code. The numerical
model aims to simulate the movement and relaxation of the soil around the shield and lining annulus
that occurs due to the overcutting and grouting of the tunnel void by a tunnel boring machine. To
achieve this, the model uses a pressure relaxation technique that progressively reduces the tunnel
support pressure from the initial at rest condition until a point of failure is detected. At this stage, the
stability number is calculated, and settlement data are exported for analysis. This is conducted for a
range of geometry and soil ratios which cover most practical cases for cohesive soils. These stability
numbers are then compared to rigorous upper and lower bound solutions. Using the settlement data,
a trough width parameter ix is also determined for each case using regression of the commonly used
Gaussian equation. The results of this study are quite positive, with the stability results from this
study remaining within 5% of the upper and lower bound solutions; settlement results also compare
well with previous experimental and observational results. The proposed automatic process can be
used effectively and efficiently in most practical design projects.