Casing in the context of trenchless construction is the pipe that is driven into the bore hole by hydraulic jacks or ramming. The casing is usually not the product pipe. Installation of casing pipe is of paramount importance in the pilot bore because it acts as a support to the borehole to prevent it from collapsing inwards. As the drilling advances, the casing pipe, usually made of steel, fills the bore hole. Trenchless construction methods like horizontal auger boring (HAB), microtunneling, impact moling and pipe ramming are some methods that use casing prior to the installation of product pipe.
Trenchlesspedia Explains Casing
In some methods like HAB, and microtunneling, the cutter heads excavate the pilot bore, and the casing is pushed in with the help of hydraulic jacks as the bore hole progresses. Excavation, dirt removal and casing insertion are all done in a continuous process. In some methods like pipe ramming, the steel casing pipe is hammered into the earth using an air compressor. Once the casing pipe is installed, the dirt is removed. The product pipe is assembled and joined in the jacking pit and then pushed into the casing, and the end of the casing pipe around the carrier pipe is closed with a casing end seal. The annular space between the carrier pipe and the casing pipe are filled with appropriate fillers like flowable mortar as a backfill.