Evaluation of the Adaptability of an EPB TBM to Tunnelling through Highly Variable Composite Strata

Table 5

Difficulties encountered during tunnel excavation of Section C-H and Section N-Q.

Adverse geological conditions	Difficulties during tunnelling
Silt and soft soil layer	Loss of stability at excavation surfaces; excessive strata deformation causing surface collapse
Artificial accumulation layer	Complex soil compositions and properties; uneven hardness; difficult shield tunnelling
Clay layer	Large stratigraphic disturbances; tendency for formation of mud cakes; augers tending to squirt easily
Mix ground	Difficulty in controlling TBM attitude; poor adaptability of cutterheads and cutter bits to ground conditions, necessitating frequent changing of construction method
Layer with mildly weathered granite	Severe wear and tear of cutterheads due to very strong rocks
Layer with spherical weathered granite boulders	Severe wear and tear of cutterheads and cutter bits due to very strong boulders, affecting the progress of shield tunnelling
Fractured zone of faults	High likelihood of squirting; unstable TBM attitude
Fully saturated sand layer	High likelihood of water inrush and sand boiling; risk of excavation surface collapse