Case study of subsidence in interstratified sedimentary bedrock: Parking garage distress investigation and remediation

This case study illustrates the investigation and remediation of distress and subsidence on a multilevel, posttension, cast-in-place concrete parking garage that was constructed at the crest and over the side of a gentle sloping hillside. A comprehensive exploration program was conducted to determine the cause of the subsidence. The investigation included core borings through the distressed caissons and the underlying bedrock and the use of a downhole camera to determine the rock conditions. Based on the investigation, it was concluded that the caisson subsidence was caused by the collapse of a large cavity underlying the sandstone. A grouting program was performed to reduce the potential of further settlement. This paper summarizes the findings and conclusions derived from this investigation and the remedial measures undertaken to reduce the potential of further distress to the structure.