How a house at Yamba, NSW, was re-supported by Uretek PowerPiles, a new way to strengthen very weak ground and lift structures.
This is a Typical PowerPile Case Study:
A house at Yamba, NSW, stood on extremely weak foundation ground, so it required substantially increased support. Working in conjunction with civil engineers, GHD, Uretek applied PowerPiles in combination with Deep-Injection of structural expanding resins.
The House Construction
This house was a single storey, rendered masonry veneer duplex with a tiled roof. It was supported by a slab-on-ground footing system, 400mm deep x 300mm wide edge beams founded approximately 300mm below the surface.
Problem: Weak, non-cohesive foundation soil
In very weak, non-cohesive soils, very sandy or very muddy, injection of expanding resins can be problematic. Pressure from the expansion can be wasted on the lateral movement of the soil.
To remedy that potential problem, Uretek has developed a unique containment mechanism. This keeps the zone of pressure directly beneath the chosen part of the structure to be supported.
Patented and initially offered as UPP Compaction, PowerPiles are prefabricated elements which are inserted through 36 mm Ø holes made into the ground under the building footings. Through a central pipe they are injected with Uretek expanding structural resin. This injection expands the strong but flexible sheath around the pipe to as much as 330mm in diameter.
This creates a concentration of soil densification in a very defined volume. Uretek PowerPiles thus provide pile-type support with skin friction and end-bearing characteristics.
Solution: Contain ground strengthening directly under the building
Of course it was essential to locate and avoid underground services including 1. a stormwater pipe along the eastern boundary of the site just 500mm away from the building, at a depth of 1000mm; and 2. a 225mm diameter sewer pipe.
The ground strengthening required soil investigations. Five dynamic cone penetrometer tests and one hand auger excavation to depth of approximately 1200 mm revealed that the site should be classified "P" (Problem Site) due to the "very loose to loose" soil encountered to a depth of 2000mm. The hand auger results showed Silty Sand, dark grey, and the water table at 700mm below ground level.
Six PowerPiles were required
Six 2000mm long Uretek PowerPiles "Type 300" were installed beneath the existing footings to provide support through the weak soils and to increase the bearing capacity of the surrounding soils. The elements were installed at approximately 2000mm centres beneath the eastern wall and footing.
Uretek Deep-Injection was then applied by injecting at 500mm and then 1000mm below surface along the eastern footing, to ensure uniform support and further improve the supporting soils.
Result: The re-support and lift succeeded as intended
An average lift of four to five millimetres was achieved to confirm support by way of positive up-lift on the structure. Thus the house was completely re-supported. The home-owners were very satisfied and the GHD Engineers were impressed with the performance of the new PowerPile technology.
The results were completely satisfactory. The structure was fully re-supported.