In Part 1 of this series, I showed a foundation lower project, not unlike many that we performed many times in the past…..but it has taken us over 4 months to complete… why?
In the past we have use air excavation tools to remove the gravel layer underneath the slab of a post tensioned slab in order to lower it while the piles on the perimeter hold it up. ABC or sand and gravel are fairly easily removed with highly compresses air and high suction vacuums.
The 3 wrinkles on this project
- There was very little or almost no ABC under this slab. Instead there was very compact very hard naturally cemented clays. Try moving those with compressed air. Almost impossible.
- This particular house had drop down monolithic grade beams located in the center portions of the house with right angles in them and some overlapping. This exponentially affects the problem with no ABC as blowing the soil across the slab to the opposite side makes it nearly impossible.
- This project differed with other excavation lowering projects in that the entire south portion of the house had heaved as opposed to just the corners requiring middle to be lowered….. where there were plenty of grade beams.
So now you fully understand the primary challenges. This was information that was not fully known or appreciated in the early stages of the work.
Stay tuned for the sequence of events in Part 3!