foundation system of burj al arab

Restoration of Chocked-Up Tube Wells

About 2% of the handpump tubewells get chocked up annually in Bangladesh. In absolute term, this put a huge number of tubewell out of operation each year. Of these chocked up tubewells, a considerable portion gets chocked within a very short period after installation. The main reasons for such premature chocking is inadequate development leading to deposition of sand exceeding the holding capacity of the blind pipe within the tube well. The deposited sand blocks the screen and prevents the inflow of water. Study shows thta desanding process can successfully rehabilitate 20 % of all new and old chocked up tubewells.

Tubewells are also chocked up due to other reasons such as improper selection of aquifer or screen, incrustation of screen by physical and chemical reasons, entry of clay or sand through defective joints holes caused by corrosion. In such cases, desanding cannot rehabilitate the tubewells. Re-sinking of these tubewells is needed after successfull withdrawl.

Desanding:

Desanding of chocked up tubewells is done by sludger method. The pumphead of the tubewells are usually 38 mm in diameter threaded PVC pipes with 30 cm long toothed cutter GI pipe at thge tip used. A 1/3 cut pil barrel is properly mounted on the top of the tubewell to hold and provide continuous flow of water as sludging proceeds. With the removal of sand, additional sludging pipes are added till the entire tubewell is cleaned of sand. Scaffolding is usually require d to perform the operation as the total weight is within the capacity of a person. The tubewell must be developed by continuous pumping after desanding for several hours until sand free water is discharged by by tubewell.

Re-sinking

Re-sinking of tubewell is needed when restoration of chocked up tubewell by desanding fails. Shallow tubewells installed with properly connected GI pipes can be easily withdrawn for re-sinking by direct vertical pull but weaker PVC pipes usually tear off under high pull. Boring by the side the side of the pipe is usually employed to the extent required to withdraw a tubewell without tearing. A metallic ring attached to the boring pipe slides around the existing pipe of the tubewell to make it free from surrounding soil. The technique is known as side digging. The process reduces the friction between pipes and soil during withdrawal of the pipes by vertical pull. Sometimes side digging is required along the total length of the pipes to make the weak pipes free but it may not be cost effective. The re-sinking procedure of a tubewell is similar to sinking of a tubewell.

No comments:

Post a Comment

Followers