The development of sewer screw piles in 1996 by Screwpile Australia created a quite revolution in the way buildings & structures foundations were piled within WaterCorp easements. Prior to then concrete piles were the norm. Sewer screwpiles eliminate inherant construction problems associated with concrete piles such as, high water-tables, hole collapse and caverning, and hard ground penetration, all resulting in difficulties to achieving the minimum specified pile depth to below the sewers invert level.
In a strange way our success at introducing screwpiles in this industry segment has created a rod for our backs. Read on and see if you agree?
Over the years the relaxing of mandatory augured hole depth inspections by WaterCorp, to one of sporadic spot checks, meant sites that were experiencing augering problems often failed to deliver the specified pile depth minimums. To some this may not sound like a big deal but in reality this means some of the records held by the WaterCorp’s assets management department will be incorrect and should excavation ever occur? I’ll leave that to your imagination.
The primary intent of piling structures above a easements zone of influence is two fold:
1) To ensure there is no surcharge load imposed on the ministers sewer as a result of the new construction
2) To ensure any surcharge load is transferred down lower than the zone of influence should future excavation & shoring of the sewer be required.
As part of Building License approvals any new construction must include the WaterCorp sewerage and waterworks approval. Part of that process requires builder's to provide an “Engineers Piling Detail & Certification” for piling requirements should a buildings foundation be within the easement. Historically these “piling” details vary from one engineering firm to another. Regardless of the piling detail itself, so long as the minimum pile depth for the location is specified (300mm or 600mm below the sewer's zone of influence invert level) and it had a signed engineers wet stamp, WaterCorp approval would be granted and this is where the issue gets rather clouded.
When Screwpile Australia introduced sewer screw piles into Western Australia every site was visited by a WaterCorp inspector who dilligently measured augured pile hole depths prior to any concrete footing pour. Where concrete pile holes were short due to collapse etc. screwpiles were urgently substituted. After a few years sewer screw piles became the preferred option for builders and the WaterCorp as it simplified the construction process and delivered pile depth reliability. At about the same time certifying structural engineering’s started to offer a builder the choice between a concrete or a screwpile option on their drawing details. The screw pile detail typically left the actual screw pile design up to the piling contractor based on the design loads that were specified. So, unless the screw piling contractor provided an additional engineers design certificate for the design of the screwpile where’s the piling structural certification? See any clouds yet?
Historically it wasn’t an issue as for years Screwpile Australia was the only contractor installing screwpiles and their own engineers structurally designed everything. More recently however there's a plethora of unqualified contractors installing all kinds of uncertified screw piles. Industry awareness is critical in identifying design and certification shortcomings. As part of that awareness Screwpile Australia’s consulting design engineers Foundation Engineering Pty Ltd are contacting WA’s structural engineering firms recommending the following piling certification design notes are included on any piling drawing detail produced by them. It will go along way in eliminating careless or unscrupulous practises by those in question.