Tip Post-Grouting Using Smart Cells of 126 Drilled Shafts at Two Bridges in Bolivia

Abstract

A smart cell is a closed-type grout distribution system that is attached to the bottom of a reinforcement cage for drilled shaft foundations and acts in a similar manner to a hydraulic jack in bi-directional static load testing. Control of the grout is maintained during grouting, and a uniform stress is imparted across entire base area simultaneously. The goals of tip post-grouting are to improve the stiffness of the in situ soil, improve the shaft’s nominal axial resistance, and better align the load transfer curves to the project requirements. This paper will present an overview, basic principles, and the design methodology of tip post-grouting using this technique. The construction, tip post-grouting, select results, and general observations from the grouting performed on more than 120 total drilled shafts for Las Marotas vehicular bridge crossing the Paraí River and the Yapacani railway bridge structure crossing the Yapacani River, Bolivia, will also be presented and discussed. The general subsurface conditions for the sedimentary deposits at the two bridge sites consist of highly variable soil deposits, bedding, composition, and engineering characteristics. The diameter of the temporarily cased drilled shafts was either 1,200 mm (4 ft) or 1,500 mm (5 ft), and the length ranged from nearly 15 m (49 ft) to nearly 25 m (82 ft). Most of the drilled shaft foundations for these bridge structures were installed with a post-grouting cell at the bottom of its reinforcement cage to enhance performance and to reduce uncertainty. Using the measurements of the grouting operation, the premobilization of axial resistance and induced load imparted into the drilled shaft and to the soil beneath the base will be discussed.