What is underpinning? Why do we need underpinning?
The word underpinning is used to describe a problem situation, that affects a number of buildings, who's owners find that their building is sinking - cracking of walls - cracking of floors - windows and doors will not open or close properly.
Causes of needing underpinning
This is due to three main reasons, the most common cause is due to footings set in reactive soils. It does not matter how good the footings are, in coastal Queensland, we are subject to prevailing east/southeast winds, that bring quite a lot of rain at times. The buildings east facing flank, gets wetter than the west facing flank, swelling the ground unevenly, resulting in fracturing of slabs and walls.
The second most likely cause is in buildings constructed on made up graound, or backfilled ground, buried tree stumps, or near deep drains, put in at an earlier stage and ground not compacted properly prior to any start on the building. The third is footings not big enough, or reinforced enough, or deep enough to withstand ground pressures, between wet and dry times. We have over the years found footing failures, particularly at corners.
When and how do we underpin
We go down 1.8m to 2.0m deep where the ground does not dry out. Even in the driest times we still have moisture there and if it stays moist, it's consistency does not change, therefore it does not move. This is where we start operating. We use a special concrete mix, vibrated in. We use a number of 20,000kg jacks, these are left permanently in place. We also use our locking grid system, to keep the building together while lifting takes place. The lifting is a very precise process, over lifting can cause reverse stress and fracturing.
When do we need to underpin
As a guide line, a 10mm drop is cause for concern. A 25mm drop needs immediate attention. A 50mm drop means real trouble, resulting in walls exploding sideways, this is because the downward movement can no longer be contained.
When can this system be used
This procedure can be applied to just about any building, Brick - Block - Single or Double storey - Residential or Commercial. They can be lifted right back to their original position.
Our work is fully guaranteed.
We are fully covered by insurance for our works.