Question

While precast concrete jacking pipes, from time to time grout holes are calculated inside these precast pipes. Give specific and key reasons?

Answer

Grout holes are there in precast jacking pipes for following reasons-

(i) They serve as locations for inoculation of bentonite or other lubricant. Lubricant is used for together granular top soils and cohesive soils to trim down frictional resistance. For cohesive soils, soils cannot get onto pipes by presence of lubricant and the shearing plane lies within lubricant. On other hand, for granular soils, lubricant mixes with soils with a considerably reduced friction. With use of lubricant, longer pipe lengths are able to be jacked without use of intermediate jacking station.

(ii) They give inlet locations for subsequent grouting works after completion of pipe jacking to fill totally the void space b/w pipes and surrounding soils.

(iii)They are used as lifting holes while placing precast jacking pipes into rails within jacking pits.