Peter Brett (PBA) | Windsor Drive Sinkhole, Hertford Following leaking drains, a ground collapse occurred below the rear corner of the house breaking service connections, causing major crack damage and subsidence of the house wall, the foundations, patio and nearby garden shed. PBA was engaged to determine the cause of ground movement and damage. The subsidence occurred in an area where glacial sands & gravels overlay chalk and many local sinkholes were recorded in the PBA Natural Cavities database. A series of dynamic probes and boreholes revealed a deep solution pipe underlying the surface sinkhole that extended to around 30m depth below ground level. The disturbed ground within the solution pipe was loose with further possible upward migrating voids. Ground stabilisation was recommended

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