The Royal Commission considers that there must be greater focus on geotechnical investigations to reduce the risk of unsatisfactory foundation performance.
This is my letter to MBIE as I am concerned about these issues.
I have been looking at the Recommendations by the Royal Commission.
One of them is the following.
“Ground-improvement techniques used as part of the foundation system for a multistory building should have a proven performance in earthquake case studies.”
I live on a highly liquefiable land and we have 38m down to gravel. Land measures at 10.7m, highest tide in the area is supposedly at 11.2m
ULS subsidence is measured to be 340-400mm down to at least 20m depth. Lateral spreading 70-200cm.
Are you aware of any ground improvements with a proven performance in earthquake studies that would solve this problem?
Have any tests been made? Are there any solutions?
Then in general for TC3 ground improvements in the eastern suburbs.
In general the depth down to gravel is 30-40m.
Liquefaction induced settlement is down to at least 20m.
Any gravel platform or ribraft solutions on this land is likely to increase the settlement based on houses that have sunk into the ground in these areas.
The geotech reports I have seen so far are not according to any acceptable standard.
Typically assume drained soil, Exclude Liquefaction probability, exclude lateral spreading, assume no building on site, stated preliminary, Exclude the Z factor (seismic risk)
Commonly only calculate settlement down to 10 meters when it is known that subsidence reaches far greater depth.
Designers and engineers are excluded from all liability in the current building act. The only thing that is monitoring them is their own code of conduct.
I think it would be fair to say that these practices are not acceptable by society.
What is MBIE opinion of these practices?
What can be done to stop this?
What ground improvement solutions are proposed for these situations and how have they been tested?
The seismic risk in this area is extreme. Two active fault lines are under these suburbs and we have had a downward tectonic movement here.
I look forward to your response.
Update to come.