We are often asked how we can stop a building cracking, by preventing movement in the ground, especially when the foundations need to be constructed as close as possible to an adjoining property owners house, or another fragile/delicate building. The truth? You can’t stop movement in the ground, and you can’t stop a building moving as the ground underneath that building moves. Be careful of anyone saying that using their method the ground will definitely not move. This is simply not possible.
All digging and drilling in the ground will cause some movement in the adjacent ground. It has to.
What you can do is take precautions to ensure that the ground moves as little as possible, and the building that you want to protect is protected from any movement.
Access Piering recommends the following five tips to help you on your next sensitive excavation:
1. Get Good Geotechnical Engineering Advice
Sounds obvious I know, but don’t try and scrimp and save on your Geotech. Ask your Geotechnical Engineer what their advice is. Push them to give you an answer regarding the potential for ground movement and what they recommend for options for the foundations. Unfortunately the Geotechnical Engineers are limited by the information they can determine from drilling. On some sites we see the Geotechnical Engineer only had one borehole to determine what was in the ground. If you are limited on your site in access, consider using our specialist geotech drilling rigs – call us for more information.
2. Understand the zone of influence
The Zone of Influence is the area of the ground under and beside the foundations that is under pressure from the weight or load of the foundations. Generally if you are digging anywhere below a 45 degree line below the horizontal point where the foundations meet the ground, you are in the Zone of Influence. This means that any excavation in this Zone could affect the foundations.
We strongly recommend you only use CFA drilling or shoring wall prior to any excavation if you need to excavate in the Zone of Influence.
3. Understand all options before you start
If you have a sensitive project you should understand all your options for foundations. We suggest that you don’t rush into one option that appears to be the cheapest and the best, as this could be the one option with the highest risk to you, and the lowest risk to the Contractor. Other options might have a higher cost, but will provide you with better certainty. If time and cost needs to be contained, then talk with us about what your options are.
4. Ask us about Low Vibration Drilling
For highly sensitive ground drilling Access Piering has developed a unique technique that imparts a high torque but low vibration into the ground. This was developed from years of drilling in Sydney in rock and soft soils right alongside multi-million dollar mansions.
We recently had our Low Vibration Drilling technique checked by Geotechnical Engineer for vibration and noise and for both we were well below the criteria set.
5. Consider ground movement dampening techniques
Like eggshell insulation in a recording studio, there are techniques that Access Piering can adopt on your project to absorb the ground movement. Each project tends to be different, so each project requires it own design.
As always we are happy to talk to you about your next project.