Site Characterization during Bridge Foundation Construction Using Electrical Resistivity Tomography

A shallow underground water-filled cavity was encountered in limestone bedrock during the construction of a new column footing for the Gasconade River Bridge over Interstate 44. Five electrical resistivity tomography (ERT) profiles and borehole control were acquired in immediate proximity to the existing and the new column footings in order to assess the integrity of the rock beneath the foundation columns and characterize the encountered cavity. Two parallel southwest-northeast trending fracture zones were identified on the acquired ERT profiles and competent rock was differentiated from more extensively fractured rock. The volumetric extent of the void was mapped based on the interpretation of the ERT, borehole and injected grout data. A conceptual model for the development of the water-filled cavity was proposed.