Ben C. Gerwick

Post-Grouting of Drilled Shaft Tips on the Sutong Bridge: A Case History

The Sutong Bridge across the lower Yangtze River in China will have, when completed, the longest span (1,088 m) and the highest towers (306 m) of any cable stayed bridge in the world. The foundations for this record-setting span are drilled shafts under each of the main pylons. The North Pylon is supported on 131 drilled shafts, 2.5 m diameter and 114 m long. The South Pylon is supported on 131 drilled shafts 2.5 m in diameter and 117 m long. The tips of all drilled shafts were post-grouted after an extensive test program confirmed significant increase in capacity with post-grouting. This paper presents a description of the post-grouting test program, the results obtained, and the construction methods used for post grouting of the production drilled shafts.

Properties of Concretes for Thin Underwater Placements and Repairs

This paper describes how many marine and hydraulic structures must be constructed and repaired while submerged under water. Frequently, this requires the placement of relatively thin (0.5 m or less) layers of concrete to fill voids in exposed surfaces or submerged formwork. Concretes placed underwater should flow readily and with little segregation and resist erosion from underwater currents. The hardened concrete should achieve excellent adhesion to underlying surfaces and develop high strengths. To achieve the desired performance, the concrete should contain a moderate amount of anti-washout admixture, a cement content of approximately 350 kg/m³, 25 kg/m³ of silica fume to enhance durability, and 18 kg/m³ fly ash to improve workability of the fresh concrete. A hard, natural gravel, representing approximately 54 percent of the aggregate content, should be used for wear resistance, and with the lowest possible water cement ration (w/c) (0.41 +/- 0.03, typically) consistent with placement requirements, to maintain strengths. Prior to the actual field placement, several rheological and mechanical properties should be determined to insure proper placability, homogeneity, and therefore increase the success probability and cost effectiveness of site trials and subsequent actual field placements.