Effect of Caliche on the Behavior of Drilled Shafts

Dr. Rouzbeh Afshar recently joined the Twining family as a Project Engineer. He has over 4 years of experience performing soils and geotechnical engineering design, load testing of drilled shafts and complex analysis of deep and shallow foundation. We are pleased to present the following abstract from Dr. Afshar’s  thesis on the Effect of Caliche on the Behavior of Drilled Shafts.

The current test design methodology for a drilled shaft foundation is primarily based on ultimate skin friction values of drilled shafts. In order to obtain these values for each soil type, load tests such as Osterberg test are designed and performed. The Osterberg test layout is designed to estimate the capacity of drilled shaft by applying an upward load during the test and then calculating the downward capacity assuming the upward and downward capacity are the same. Dr. Afshar’s research showed in soils containing caliche, the ultimate skin friction is not achieved and shaft/caliche interaction is mostly elastic. In these cases, the behavior of the shaft when it is loaded from the bottom is different from when it is loaded from the top. His study explains that, the location of O-cell with respect to the caliche layers will influence the interpretation of test results.

The results of his study shows a test layout with O-cell at a location far from the caliche layers shown to have a higher capacity during conventional loading compared to interpreted test results from Osterberg load test. On the other hand, when O-cell is installed close to caliche, the top-down loading shows a similar behavior to interpreted test results from Osterberg load test.  In fact, when O-cell and caliche layers are close to each other, the test layout is similar to the procedure performed to estimate rock socketed drilled shafts capacity. The results of this study will help engineers to have better understanding of the drilled shafts behavior in soils containing caliche by introducing an appropriate test design and interpretation of the test results.