Hydraulic ram pumps and Sling Pumps

43. Simple drilling methodsIn many developing countries, water is obtained from handpumps installed above shallow (less than60m deep) boreholes. It can be expensive to drill the borehole, however, if traditional machinedrillingrigs are used. This Technical Brief outlines simple, low-cost drilling methods which may beused in various situations. Each can be used and maintained easily.Drilling constraintsWhatever drilling method is used, there are severalconsiderations which must be taken into account:nnnnThe amount of energy required to drill is governed bythe rock type. Unconsolidated formations such assand, silt or clay are weak and much easier to drill thanconsolidated rocks such as granite, basalt or slatewhich are hard, strong and dense.For hard rocks, cutting tools will need cooling andlubrication.Rock cuttings and debris must be removed.Unconsolidated formations will require support toprevent the hole from collapse.Drilling methodsThe following low-cost, appropriate drilling methods aredescribed and illustrated on the following pages:nnnnnnPercussion drillingHand-auger drillingJettingSludgingRotary-percussion drillingRotary drilling with flushThe table below may be used as a guide in the selectionof the most appropriate drilling method.Hand-auger drilling for boreholes up to 10m deepTable 1. Drilling-method selectionPercussiondrillingHand-augerdrillingJettingSludgingRotarypercussiondrillingRotary drillingwith flushGravel3?6663?6SandSiltClayUnconsolidatedformations3?3?3 slow33333?3333?3?3 slow333Sand with pebbles or boulders3?6663?6ShaleSandstoneLimestoneIgneous (granite, basalt)Metamorphic (slate, gneiss)Low to mediumstrengthformationsMedium tohigh-strengthformations333 slow3 slow3 v slow6666666666666663 slow3333333 slow66Rock with fractures or voids366633!Above water-table33?633Below water-table3?3333✓= Suitable drilling method ✓? = Danger of hole collapsing ✓! = Flush must be maintained to continue drilling ? = Possible problems ✖ = Inappropriate method of drillling41