Development of t-z Curves for Cemented Fine-Grained Soil Deposits

Abstract

Drilled shaft load-settlement analysis is frequently performed using load-transfer curves known as t-z curves. Many t-z curves are discussed in the literature, and are often used for approximate analyses. The peak skin friction is generally considered to be developed with deflections on the order of 6–12 mm (0.25–0.5 in.) or 0.5–1% of the shaft diameter. The results of several load tests in calcareous cemented fine-grained soils in the arid southwestern United States are reviewed. It is demonstrated that significantly higher deflections are required to develop the peak skin friction in these soils than in the soils for which most of the available curves were developed. Deflections at peak skin friction are typically 25 mm (1 in.) or more. This results in an increase in the deflection required to attain a given fraction of ultimate load. Although cemented soil deposits have high shear-strength parameters, deflections may exceed expectations for working loads.