Radial collector wells in alluvium project. Final Report (no 3) on trenchless moling trials at Carmer Wood, Laughton, Lincolnshire

摘要

This report documents the results of the field trials carried out by BGS onudbehalr or OOA~to deve16p-an° rntetmed'iate~ technolog-y mettrodof constructingudcollector wells in unconsolidated sandy alluvium. A system has been developedudwhich uses a thrust-boring mole of the type now in common use in theudconstruction industry to install sub-surface service mains without excavation.udThe system has been developed with the aim of ut il is i ng the groundwaterudresources which are present in thin shallow uncemented sandy aquifers butudwhose exploitation by borehole or shaft-only dugwell would be marginal due toudsmall available drawdowns and moderate to low permeabilities. Mesh-wrappedudplastic screen is emplaced inside jacked-out temporary steel casing which isudthen retracted under a small positive hydraulic head in order to avoid sandlockingudand formation ingress into the main shaft. 38 mm 10 pipe has beenudused, and rapid autodevelopment by the radials has provided coll~ctors withudyields of 1.5 lis/radial from fine running sands. Arrays have been emplacedudto over 20 m length with a 98 mm ~ head at jacking forces of less thanud7 tonnes f. The equipment required for the construction of the collectors isudlight to transport and install and significantly less expensive than auddownhole rotary drill ing rig to buy and operate. The method is howeverudrestricted _ to uoconsolidated_ fine-grained alluvium, as the method isudessentially one of formation displacement, not removal.