Detecting Sinkholes

A sinkhole is a hole in the ground created when land collapses. A sinkhole occurs when the roof of a cave collapses and the surface caves into the void created. A sinkhole can also occur when water dissolves bedrock, creating an underground cavern. Without supporting rock, the surface collapses into the gap, forming a sinkhole.

Ground Penetrating Radar (GPR) can be used to detect and map out the presence and extent of sinkholes, as well as underground voids and subsidence. A GPR void detection survey is a low-risk method to scan an area of ground and determine the location of sinkholes.

Ground Penetrating Radar (GPR) is the best way to detect sinkholes. A GPR survey is a low-risk method to determine the location of sinkholes. This can form part of a risk assessment to check the integrity of the ground or to determine the extent of voids when remediation planning.

During the construction of a new tower block in Manchester (UK), the road collapsed underneath a lorry delivering construction materials for a new block, virtually swallowing the lorry into a sinkhole 4m deep and several meters across; fortunately, no one was injured during the incident. The cause was determined to be the prior collapse of a sewer dating from the Victorian era creating a sinkhole 4m beneath the road surface. Over time material had been progressively washed into the sewer until the sinkhole grew to reach the surface and then spread underneath the stable reinforced concrete layer.

Due to nature of the reinforced concrete road, there was no surface evidence that the sinkhole existed and therefor no warning before the lorry fell through the road. The reinforced concrete beneath the road also dated to the Victorian era and the rebars were significantly corroded, reducing its load bearing capacity.