“Cut-and-cover” method involves the construction of open cut at the first place, followed by the construction of tunnels under open excavation. Upon completion of the structure, backfilling and reinstatement would be subsequently carried out.

“Cover-and-cut” method involves firstly the construction of cover followed by the second stage in which construction activities are carried out under the cover. As such, the disturbance to the public owing to constructional activities could be reduced to a minimum.

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 concept of ground freezing involves the lowering of temperature of ground near the excavation area. Drillholes with designed spacing are installed so that a chilled brine or liquid nitrogen is introduced into the holes. Brine requires continuous circulation while liquid nitrogen is for rapid freezing and it is unrecoverable. With the addition of a chilled brine or liquid nitrogen, the groundwater is frozen into ice. Upon frozen, soils exhibit higher shear strength and the frozen zone acts as an impermeable barrier so that water could not enter the excavation zone.

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.

For pipes used for pipe jacking, they should possess the following characteristics:

(i) Pipes should have high concrete strength to withstand the stress induced during the jacking process.

(ii) There is tight tolerance in pipe dimension and the pipe joints are specially designed to provide trouble-free joint details. Two commonly available joints are rebated joint and butt end joint.

(iii) Pipes preferably should have smooth external concrete finishes to reduce the friction between the pipes and surrounding soil.

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.

Since in pipe jacking, the jacked pipes could hardly be jacked in the designed level and alignment and some deviation from the original one is commonly acceptable provided that the deviation are within the tolerance of the Contract. However, in order to avoid damage made to the pipe joints due to overstressing, it is necessary to estimate the stress concentrations resulting from these angular deflections.

Note: Pipe jacking is a trenchless method in which pipes are jacked underground from jacking pits and receiving pits.

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 lubricating fluid serves to reduce the jacking force in the following ways:

(i) It saturates the overcut leading to partial and complete buoyancy of the jacking pipe in the cavity. As such, the contact surface area between the jacking pipe and soils is decreased.

(ii) It stabilizes the cavity by limiting the radial effective stress acting on the jacking pipe.

(iii) The interface friction angle between the soils and the jacking pipe are reduced by the lubricants.

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.