2. Will water trigger a landslide? Are mitigation works planned? [SH]
The slope stability and preliminary sensitivity analysis showed that the Quarry Spoil Tip is likely to be marginally stable, but likely to be unstable as a result of a significant weather event increasing porewater pressures in the tip (or increasing the groundwater table). If the Quarry Spoil Tip were to be scrutinised to modern safety criteria, it would need significant alteration or betterment to increase its stability or remedial options would be needed to reduce the risk it poses to elements at risk to low.
An option from our previous assessment (ESP.7234e.02.3302 Rev 2 (February 2020)) was a combined approach of incorporating drainage to create betterment, installing monitoring points and producing a warning system. NPTCBC discounted due to:
- Uncertainties at this stage in achieving a ‘stable’ condition that meets modern design standards.
- Confidence in the efficacy of a warning system, and safeguarding of school users, without significant investment in supplementary investigation, long-term ground monitoring and assessment. It is likely the school would remain displaced until defined.
- The unknown scale of remedial work following any future ground movement with a remaining risk of future displacement of the school.
It is likely that current landowners will be responsible for ongoing maintenance and stability matters, including risks presented to downslope people, property, and infrastructure.