What are the situations which warrant the use of microtunneling instead of other trenchless methods?
There are two main advantages of microtunneling:
(i) Difficult ground conditions
Microtunnels could operate under a water head of 30m or more. It is capable of handling a wide range of soils such as cobble, boulders and rock without the need of dewatering.
(ii) Surface settlement
Surface settlement could be minimized by using microtunneling. For example, the use of earth pressure balance method in microtunneling helps balance the external soil loads and groundwater. Moreover, the rate of advancement of machine and the rate of excavation of tunnel face can be readily controlled so that it reduces the occurrence of over-excavation at tunnel face and hence the ground settlement.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.