Building Collapse Due to Shallow Trench Excavation

A building collapse is investigated in which a shallow trench, excavated along the length of the building, resulted in the building\u27s collapse. An investigation indicated that the trench had been excavated within 1 ft (0.3 m) of the foundation and that the foundation had been constructed on approximately 7 ft (2.1 m) of soft silty clay with the bottom portion of this soil highly saturated. The bearing capacity of the foundation, prior to excavation, was estimated to have a safety factor as low as 1.5. As a result of the proximity of the trench to the foundation and the soft soils, the trench collapsed soon after excavation. It is believed that the lower portion of the soil flowed into the trench causing a loss of bearing capacity. An understanding of the geologic setting of the foundation soils, coupled with soils information from the USDA\u27s Soil Conservation Service indicated the hazards of excavating in this soil