A Piling "Revolution" Gathers Pace

A recent Perth project highlighted the state of play in Western Australia's civil's construction industry and the importance of competent geotechnical, environmental, engineering management and civil works practises. There appears to be a few unqualified unexperienced individuals presenting themselves as capable of producing safe quality outcomes only to create sizeable headaches for builders. Lack of understanding in engineering seems to be a recurring problem. How do we know? For one thing our insurance premiums keep going up even though we've never made a claim. Secondly, we keep getting phone calls for urgent help.

This redevelopment site is surrounded by multi-story apartments including a suspended concrete slab carpark and bitumen access laneways and road to all boundaries. Site location is approximately 250m from the Swan River. New multiple luxury apartments are being built by a respected and experienced local builder.

A civil's contractor was initially engaged to come up with a piling and dewatering solution.

Geotechnically, the site consists of a thin layer of sand overlying saturated peat sands over medium/dense-dense saturated sand. The site is located within a "Class 1" (high to moderate risk of ASS (acid sulphate soils up to 3.0m BGL)), so it was critical not to introduce oxygen into the soil.

WA's State Department of Water & Environment website references:"Acid sulfate soils (ASS) occur naturally in Western Australia and are harmless when left in a waterlogged, undisturbed environment. However, when exposed to air, through drainage or excavation, the iron sulfides in the soils react with oxygen and water to produce iron compounds and sulfuric acid. This acid can release other substances, including heavy metals, from the soil and into the surrounding environment and waterways. Activities with the potential to disturb ASS must be managed carefully to avoid serious environmental harm."

So with this in mind, we question the original civil contractor decision making process in so far as: a) dewatering the site ran the risk of introducing oxygen into the ground, b) was a PASS/ASS groundwater study conducted/management plan submitted/approved for extracting/disposing/recycling the groundwater? Just pumping it down a drain or sewer is illegal, c) why construct bored concrete piles when the process again introduces oxygen into the soil? d) why cantilever concrete piles were only installed to 2.5m deep when the peat soil extends beyond that depth?

Contiguous concrete bored piles were installed by the original civil contractor on the boundary to a depth of 2.5m. Dewatering started and site-works excavation commenced. Soon the original boundary walls and foundations started to rotate in towards the excavation as the contiguous bored piles started to fail. Numerous sinkholes started to appear under neighbouring property laneways and road and was immediately closed to vehicle access due to significant safety concerns.

The builder responded quickly, removing the civil contractor and their equipment from site and proceeded to urgently repair all the damage. Fortunately no damage occurred to the adjoining buildings. That's when we received the call for help. Our brief was to urgently come up with a solution that enabled the builder to bring the construction timetable back to the scheduled forecast as quickly as possible. The solution? Conduct our own site testing and design a best possible outcome. Our proposal called for minimal earthworks & in consultation with the builder we proposed the installation of 230 x 200kN x 4m screwpiles to be installed in 3 stages. Stage 1 was piling to the new (replacement) brick boundary retaining and screen wall foundations so that laneways could be quickly stabilised and re-bitumened to allow neighbours usable access to their vehicles as they were having to revert to public transport, Uber & taxi's. Stage 2 was piles to the rear ? of the new buildings footings. Stage 3 was to pile to the front ? of buildings foundation footprint.

Despite the fact we were slightly more expensive than a competitor the builder acknowledged the efforts we went to, our attention to detail and peace of mind our Quality Assurance & Engineering Management Systems provided him.

So what's the take-a-way here? We love these types of challenges. It give us the opportunity to showcase our technology and our capabilities.

We believe it's more than knowing which contractor to use, in fact it's a whole lot more. In a previous Article titled: Understanding & Acknowledging Gauge Theory (link), we highlighted critical component, performance predictability and competency in industry disciplines. More-so, it weighs industry players for value for money, quality of engineered and actual outcomes a builder could expect to receive. Its just another example of screwpiles trumping concrete.