Dam collapse due to heavy rains

Background

The new embankments were reinforced using soil nail walls. During an exceptionally long and heavy rainstorm, the walls were partially destroyed. The company carrying out the works proposed repairs and stated the associated costs in its claim.  

Given the significance of the claim, the contractors’ all risks insurer of the project owner requested Stelliant Loss Adjusting to study the proposed repairs and assess exactly the financial damage.

How Stelliant proceeded

Stelliant’s geo-technical loss adjuster observed significant damage at the site and carried out a technical analysis of the situation. The installation of the soil nail wall (shotcrete wall anchored to the soil by rebars) required moving the soil from top to bottom as the concrete was applied. This method exposed the lower earthworks during construction.  

The rainwater had hollowed out the soil just behind the soil nail wall. With the soil saturated, it began to liquefy and run off from the lower part of the works. The soil above then began to collapse and the soil nail wall started to topple. The nails became deformed and lost their anchoring. Finally, the land that was to be reinforced slid downstream. 

At this stage, the Stelliant loss adjuster studied the repair works envisioned by the companies after the collapse. It involved replacing the soil nail wall with a reinforced concrete gravity structure embedded at the base. Given the type of rock bed and resistance of the subsoil, the stability of the structure would have required the installation of piles. This type of foundation would be costly and take several months (construction and drying time for the concrete). 

Stelliant Loss Adjusting performed a comparison with an alternative solution using void-filled riprap. A wall of rocks of varying thickness would be built and the gaps filled in with loose material. This solution was chosen due to a nearby quarry being in operation. It also meant a lower cost as checked by Qantex, a quantity surveying subsidiary of the Stelliant Group. This work also decreased construction times and reduced the fixed costs of the site (downtime) as well as financial losses, such as lost electricity production, for the operator.  

The insurance payout for the collapse of the wall was limited to the initial market costs of the works, demolition and clearance costs, and other expenses relating to analyses.