Hi,
We are nearly at contract signing stage and an issue has come up with foundations.
Our builder/Engineer has designed foundations to use blade piles. We are on reclaimed swamp in Carrum Vic. The soil report has been classified as CLASS P.
Soil Details below. The soil acidity has also been tested and found to be highly acidic. PH in order of 3.1. Dues to this high acidity, the blade piles are required to be thickened (5mm) and double dipped in Gal. This has blown out the cost for blade pile foundations to around $45K. They are also saying they will only guarantee the piles for 50 years before they potentially rust out.
I have asked for concrete piers to be priced and their engineering has come back saying it can't be done because of the abnormal moisture conditions and soil requires a load limit of 200KPa, but will only support 100KPa. When asked why 200KPa limit was needed, their engineering responded with:
"Bore logs for this job indicate silty sand which is non-cohesive; so we need to rely on end bearing only and bored piers will not have any side friction resistance. The double storey structure require min. of 50kN which is achievable by a 600 dia. Bored pier on 200 kPa allowable bearing capacity. (unfactored point load for B12 beam DL+FLL – 53 kN – obtained from Framing computations). Blade pile offers min. 75kN working load to satisfy above requirement."
I have issues with this as there is a nearly identical build currently being built 2 doors down with concrete piers. There are also 2 developments directly across the road of 4 double story units (8 in total) that are using concrete piers. Also the double story properties either side of ours both used concrete piers when built.
All the designs are all very similar. Rectangular house with alfresco area. Hebel on ground/rendered foam on second floor and concrete tiles.
I have pushed back on the builder and he has said they have used this engineer for a number of years, and the engineer won't budge.
Is there anything I can do in this situation? Get a second opinion? Have it re-engineered by someone else? What other options are there? The extra cost has pushed the build outside of our budget.
Thanks
SOIL REPORT:
"The site has been classified P due to existing filling on this site and abnormal moisture conditions caused by existing trees on this site and adjoining sites and proposed removal of existing structure and footings."
"The underlying natural soil has been classified as MODIFIED CLASS S."
800:
Loose to medium density brown, grey and orange SAND moist/ wet
silty sand
- containing marine deposits
- becoming wet below 2000mm