Effects of Temporary Casing on the Side Shear of Small Scale Rock Sockets in Limestone

The presence of temporary casing between freshly placed concrete and surrounding limestone formations may inadvertently leave crumbled debris upon casing extraction that may lead to side shear reduction. The primary objective of this work was to quantify how different methods of installation and extraction of temporary casings affect the side shear resistance on small scale limestone sockets. About 29 miniature shaft specimens were cast in six different simulated limestone beds ranging in strengths from 65 to 885 psi. Three casing installation/extraction methods were used: rotated with coarse cutting teeth, rotated with fine cutting teeth, and driven. At least one of the sockets in each bed was selected to be an uncased control, in which the casing was extracted and all debris were cleaned out prior to concreting. Results showed that the presence of casing caused loss in capacity. Weaker, more voided limestone was less affected than stronger, more contiguous material.