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.

The international definition of microtunneling includes pipe with diameter up to 1,000mm only. However, in the United States, it allows for larger pipe size when defining microtunneling in which pipe with diameters up to 144 inches are also counted within the ambit of microtunneling.

The basic concept of microtunneling has changed gradually owing to recent technological developments and past experience. For instance, the use of alignment control system with advanced surveying techniques allows for longer drives with good control and curved microtunneling. The use of automatic lubrication system enhances lower jacking forces. The employment of gripper in microtunneling machines helps develop adequate loads on cutter discs for cutting rock.

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.

Pipe jacking is a general technique of the installation of pipes with a tunneling shield in front and the pipes are jacked from a jacking pit to a receiving pit. The tunneling shield for pipe jacking can be electrical and mechanical equipment for conducting the excavation work or it can be a manual shield for workers going inside the shield to carry out manual excavation. For microtunneling, it is a kind of pipe jacking of small sized non-man-entry pipes which are remotely controlled. In general, there are two common types of micro-tunneling machines:

(i) Pressurised slurry
Similar to the Pressurised slurry TBM, excavated material is transported from the excavation face to the surface suspended in a slurry.

(ii) Auger machine
Excavated material is transported from the excavation face to the drive pit through a cased screw auger.

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.

Butt end type with mild steel band is commonly used for storm water application. The mild steel band serves to prevent lateral displacement if pipe joint during pipe jacking.

Socketed in-wall rubber ring type is normally used for sewer and pressure pipe situation and for pipe size exceeding 1200mm in diameter. The rubber ring is designed to provide a seal to pipe joint to ensure water tightness, which is essential in sewage pipelines.

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.

The shield connected to lead pipe is normally sharp-edged in design because:

(i) It helps to reduce the resistance when the shield enters into soils;

(ii) It reduces the amount of soil dropping into the shield.

Sometimes the shield is equipped with jacks so that it allows tilting of the shield and adjustment could be made to the direction of pipe jacking.

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.