Study of Ground Settlement and Volume loss Associated with TBM Tunnelling by Analytical and Numerical methods-Paper

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The study evaluates ground settlement and volume loss associated with twin TBM tunnels in an Indian metro project. The 862.6 m alignment passes through variable ground, including soil, weathered rock, hard rock, and mixed conditions. Tunnel overburden ranges from 7 to 13.8 m, and the tunnels are spaced 15.49 m apart.<br /><br />Settlement predictions were made using empirical analytical methods and a two-dimensional PLAXIS finite-element model. Both methods assumed 1% volume loss; the analytical calculation also used a trough-width coefficient of 0.4. In PLAXIS, volume loss was simulated by applying 1% line contraction to each tunnel lining. The predicted settlements were compared with ground-monitoring data collected along the alignment.<br /><br />At chainages 10 m and 140 m, measured maximum settlements were 10 mm and 5 mm, respectively. Analytical predictions were 23.0 mm and 24.9 mm, while numerical predictions were 17.4 mm and 18.0 mm. The numerical estimates were approximately 72–75% of the analytical estimates, although both methods produced similar settlement-trough shapes. Back-calculation from the field measurements gave volume-loss estimates of 0.25% and 0.45% at the two locations.<br /><br />Overall, observed settlements were substantially lower than predictions based on 1% volume loss, indicating that actual field volume loss was lower than the assumed value. The findings highlight the importance of controlling volume loss during tunnelling and using instrumentation to verify ground response and refine predictions.

Keywords

TBM tunneling

ground settlement

volume loss

Indian metro project

PLAXIS finite element model

analytical prediction

twin tunnels

tunnel alignment

soil-rock conditions

settlement monitoring