Condition Assessment of Building Foundation in Karst Terrain Using both Electrical Resistivity Tomography and Multi-channel Analysis Surface Wave Techniques

In foundation survey projects for hotel buildings in Kentucky, assisted by drilling data, an integrated geophysical survey was undertaken. The main goal of the project was to investigate the depth of the top rock and the void locations, if any present. The project used shallow non-invasive geophysical survey methods, including electrical resistivity tomography (ERT) and multi-channel analysis of surface wave (MASW). A shallow subsurface survey was performed using the MASW equipped with a 24-geophone array, equipped with 4.5 Hz geophones to estimate the clay/soil thickness. The 22 2-d ERT profiles for imaging resistivity changes in subterranean formations were used to survey the top rock and delineate possible karst areas in the area. These methods successfully reflect the top of the rock at an average depth of about 60 ft. Additionally, several relatively large karst feature zones in the study area were mapped with the use of the ERT data. Finally, the 2-d ERT profiles were used to study the geological properties of the foundation structure. Using the established geophysical model, the internal structure of the foundation was revealed. The results are in good agreement with the actual situation in the study area as evinced by available borehole data, and can guide engineers when solving foundation problems and reveal the weakness of the karst lava development area that may appear under a foundation during its construction.