Effect of drilling fluid on concrete-soil/rock interface shear strength in seawater drilling environment

Abstract

In this article, the results of an experimental study on the effect of drilling fluid on concrete-soil/rock interface shear strength in the seawater drilling environment are presented. The series of direct shear tests using a purpose-designed shear box with seawater were performed considering different types of drilling fluid and base material, various normal stress levels at the interface, and filtration times. The results indicated that bentonite drilling fluid significantly decreased the concrete-soil/rock interface shear strength while a negligibly small effect was observed for polymer drilling fluid, confirming the findings from the previous studies. It was also observed that the degree of interface shear strength reduction when using bentonite drilling fluid varied with the type of base material as well as the level of normal stress at the interface. The results also confirmed that the groundwater chemistry does not alter governing mechanism of the drilling fluids and the concrete-soil/rock interface interaction and that significant benefit can also be expected when using polymer-based drilling fluid over bentonite in terms of the side resistance of a drilled shaft in seawater drilling environment as well.