Grouting of Deep Foundations at the Thames River Bridge

This paper describes an unusually deep grouting program that was undertaken to arrest the unexpected settlement that occurred during construction of an Amtrak bridge over the Thames River in Connecticut. During construction, a caisson started to settle and tilt when new, adjacent piles were installed. A remedial grouting program was performed to arrest the settlement. The target grout zone was the permeable and erratically-dense sand and gravel stratum beneath the caisson, at a depth of about 40 to 52 m (130 to 170 ft) below the river surface. Grout holes were placed around the perimeter of the caissons as well as through each caisson. A computerized data acquisition system was used to provide real time monitoring of grout injection parameters and rapid evaluation of the effectiveness of grouting as work progressed. Over one million gallons of microfine cement grout were pumped during the course of 11 months work. Cores of the grouted soils were obtained to confirm grout coverage and properties of the grouted soil. Eventually, the grout stabilized the pier and halted the creep movement. This paper describes the grouting program, grout mixtures, effects of various admixtures, and quality control measures.