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Sludger Technique


The "Sludger Technique" for constructing 49 Tubewells in the Pipra Pokhariya Scheme, Nepal

$15,121.20 recently donated by New Zealand Water and Wastes Association members supplemented with the NZ Government Voluntary Agency Support Scheme subsidy was sent to Nepal via UK on Monday 9 October where a 6,325 pound UNICEF grant was added. Gratitude and appreciation of the NZ Water and Wastes Association members support was made in a fax just received from Greg Whiteside, the WaterAid Country Representative for Nepal based in Kathmandu. Greg is a water engineer who has given generously over a number of years to Water for Survival as his money returns to Nepal usually quadrupled in value!

The Pipra Pokhariya Tubewells scheme will benefit 486 school students and 3,325 village people who are subsistence level farmers in the Rautahat district of Terai region in Central Nepal. Objectives of the project are to provide sustainable improvements to the quality and quantity of water available, to reduce journey times for water collection, to encourage improvements in the sanitation and hygiene behavior of the community and improve the management capabilities of the local implementing agency, Jana Sewa Yuba Club. The project includes the training of caretakers for each well, three health motivators and one sanitation worker who will encourage better health and hygiene including the construction of latrines and drying racks.

The 49 tubewells will be constructed using the "sludger technique", a traditional low-cost well sinking method appropriate to the area. The cost of drilling by sludger and well pointing techniques rarely exceeds NZ$3.00 per person benefiting, while the methods are simple allowing villagers to participate fully in the planning and installation of their facility. Sludging is used extensively in many parts of Asia to bore holes of 25mm to 150mm in diameter to depths of up to 60 meters. The water table must lie within 6.5m of the surface and the strata must be soft alluvial deposits such as those found in the river flood plains of Bangladesh, Nepal and northern India.

Sludging most often uses a 40mm galvanized iron pipe which is moved up and down by the action of a bamboo lever pivoted about a simple frame. Drilling starts initially from a small excavated pit filled with a mixture of water and cow dung used as a drilling mud which helps to stabilize the bore during the sludging operation. The pipe is raised and lowered by two assistants, usually villagers, using the bamboo lever. On each upstroke the Mistri (technician) uses his hand to seal the top end of the open pipe. This creates a vacuum causing the column of water inside the pipe to be lifted as the pipe is raised. On the down stroke the Mistri removes his hand as the pipe drops faster than the column of water inside it. The cycle is repeated with the column of water moving upwards relative to the pipe until it begins to be pumped out at the top. The weight of the pipe acting on a case- hardened cutting socket on the bottom of the pipe helps to fluidize the soil in the bore on each down-stroke. The soil is then sucked up with the pipe and spills out of the top a few cycles later. Sinking rates of up to 20m per hour may be achieved.

At 1.5m intervals the discharge is sampled and the strata layer identified and usually logged. An experienced mistri is able to gauge this not only visually but also by the feel and note of the boring pipe impacting in the hole. Additional pipe lengths are added as the sinking continues to a depth of about 2m below the preferred screen depth. The galvanized iron pipe is then withdrawn and replaced by a PVC rising main fitted with a sand trap at 1m and well screen at 2m above the bottom. The PVC pipe is joined to a galvanized pipe within 3m of the ground surface where it is fitted with a mild steel cross and firmly concreted into the pump platform. A suction handpump is then fitted and a drained concrete apron slab constructed to keep well area clean and hygienic.

A constraint to the sludging technique is the difficulty of penetrating through hard materials. A single small stone in the path of the boring pipe may cause problems, but a simple technique to avoid the abandonment of a borehole uses a modification of the well pointing technique known locally as "hammering". This involves a simple fabricated driver acting on the boring pipe. The boring pipe is fitted with an oversized cone at its lower end and a driving socket at its upper end. The outside diameter of the cone should be the same as the sludging socket.

If further stones are anticipated, then hammering is used to the desired depth. In these circumstances it is usually not possible to withdraw the pipes and they have to be left in place to form the rising main incorporating a well screen. A 32mm PVC spiral-cut screen is inserted into a pre-drilled 40mm galvanized pipe located by flanges top and bottom. The upper flange butting the lowest joint in the rising main is secured using a standard socket, while the lower flange of slightly smaller diameter seals the bottom of the screen allowing a natural gravel pack to develop over time in the space between the PVC and galvanized iron pipes. This arrangement ensures the screen is protected during driving and allows considerable cost savings over commercially fabricated metal screens.

A drawback of the procedure is that there is little knowledge of the aquifer and the relative position of the screen during driving. Test pumping at regular intervals during hammering will help determine the presence of water and the quantity available.

Information and diagrams on sludging and well pointing techniques were obtained from a paper by Greg Whiteside and Simon Trace published in Waterlines Magazine January 1993. If you would like more information on this technique or any of the other interesting Water for Survival projects, please contact John La Roche at P O Box 6208, Wellesley Street, Auckland, or phone 09-528-9759. Water for Survival is a voluntary charity which raises money for water supply and sanitation projects in developing countries.

Contact John La Roche Phone/Fax 09 528 9759 or Email wfs@kiwi.gen.nz

 


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