Defender Concrete Solutions Case Studies: Unstable Portico
A portico had sank on the front edge portion. The slab supporting the portico had a 6" slab connected to the front steps, but had pulled away from the steps as well. Under the front of the slab that originally held the support beams in place an additional 2' footer x 8" deep was poured for additional support. The weight in the front of the structure compared to the weight in the back near the steps, in my opinion was part of the reason it began to sink. This poses a challenge when lifting with PolyLevel because there is no counter balance on the back, so when lift the entire slab naturally wants to "lean" forward. This can result in the foam wanting to go to the back of the structure since there is less pressure from above and the foam wants to follow the path of least resistance. The challenge then becomes getting the slab to lift more evenly back into original place while supporting it from below. On top of this the support beam has to be put into proper position before too much pressure is placed upon it.
Defender Concrete Solutions had the proper plan in place to face the challenge. Defender first dug out around the edge of the concrete to assess how deep and how far the footer extended. Slab Jacks were then placed in strategic areas under the slab. Hydraulic pressure was then applied at an even pace until the slab was lifted on the front edge. While this was happening the support beam was moved into original position concurrently with the lift. By lifting the slab on the front edge, pressure was relieved against the soil below. This created a void under the footer and front edge of the Portico.
The next step was to stabilize the Portico. Since we had the slab lifted with the slab jacks, we could now begin pumping PolyLevel foam under the lifted portion. PolyLevel foam has a controlled reaction time, so with the help of digital levels we can monitor precisely where the foam is going and when it is beginning to support the structure without the aide of the jacks. Once we knew we were stabilized on the front edge and the support beams were solid and stable, we moved to the port holes near the back of the slab to "void" fill those areas and lift to insure we still had proper drainage grade away from the house.
This photo was taken after the portico was lifted and stabilized back into original position.