Evaluation of Soil Disturbance due to Sonic Drilling using Instrumentation and Cone Penetration Test Measurements

Sonic drilling is an efficient and versatile drilling technique to continuously core soils and soft rock, and it is increasingly used for geotechnical site characterization. During sonic drilling, the sonic head and attached drill string are vibrated to advance the drill string into the subsurface. These vibrations are transmitted to and propagated through the surrounding soil, causing some amount of disturbance to the soil. In some cases, SPT or thin-walled tube samples are driven below the drill casing to obtain site characterization information. To date, there has been little research quantifying the magnitude and zone of disturbance around the drill string, and it is unclear to what extent typical sampling methods are affected. This paper presents results from a three-part field program that attempts to quantify the zone of influence, magnitude of disturbance, and consequences for in-situ tests and sampling below the drill bit for sonic drilling using a) an array of in-situ instruments that measure soil motions during sonic drilling and b) changes in measured CPT values before and after sonic drilling.