Effects of Soft Tip and Soft Sidewall Anomalies on Geotechnical Resistances of Drilled Shafts

Document Info

Title: Effects of Soft Tip and Soft Sidewall Anomalies on Geotechnical Resistances of Drilled Shafts

Document Type: Article

Authored By: Naresh C. Samtani, PhD, PE, BC.GE, F.ASCE

Sponsoring Agency: NCS GeoResources, LLC

Abstract

Non-destructive tests (NDTs) conducted on drilled shafts after construction often reveal anomalies such as soft tip (base or bottom) and soft sidewall. The designer of record has to evaluate whether these anomalies will have an adverse effect on the performance of the drilled shafts and the facility supported by them. Nowadays the design of drilled shafts is commonly done using the concept of limit states such as the Load and Resistance Factor Design (LRFD) approach of the American Association of State Highway and Transportation Officials (AASHTO) and the Federal Highway Administration (FHWA). Unlike the Allowable Stress Design (ASD) design approach where a single factor of safety is used to consider the combined uncertainty in loads as well as resistances, the LRFD approach explicitly considers the uncertainties for various types of loads and resistances in terms specific limit states. With respect to geotechnical resistances there are different limit states for sidewall resistance, tip resistance, and lateral resistance. Thus, the effects of soft tip and soft sidewall need to be considered in context of these three geotechnical resistances and limit states. This article provides information on the effects of soft tip and soft sidewall anomalies on geotechnical resistances of drilled shafts and how to evaluate these effects.