Philadelphia, PA –
The main water (8 inches inside diameter), and sewer (12 inches inside diameter), lines inside the Wells Fargo sports complex were supported by driven steel-piles and pile caps from its original construction in 1995. During the construction of an addition to the Wells Fargo Center in 2005, the pipe-supported hanger system was cut, leaving a 20 feet in length, unsupported utility. This resulted in several inches of settlement. Previous attempts to rectify the settlement problem were unsuccessful. The continued settlement resulted in the pipes lifting upwards off of their pipe hangers in the basement portion of the building. The owner was concerned that a rupture of either of these primary utilities would result in a disruption of the center’s busy schedule. Therefore, a conventional open excavation and pipe repair was unacceptable to the owner.
The geotechnical engineer recommended the use of compaction grouting to densify the fill soils beneath the utilities and lift the utilities to relieve the observed stress. In addition to grouting, a plan to support the utilities with new pile caps and beams, then remove and replace the distressed sections of pipe, was put into place. While one of the project goals was to lift the two utilities, there were concerns on how to lift them without causing further damage. Soil vacuum extraction was performed at several locations. A “tell-tale” was installed on top of each utility to evaluate the movement in real time during grouting operations. At each of the 15 grout locations, the depth of debris laden fill was verified by drilling a minimum of three feet into competent material. Low mobility grout was pumped in a controlled, bottom-up process to displace and densify the surrounding soils.
Approximately 700 cubic feet of grout was pumped for the soil improvement program. We were able to respond quickly to the problem, provide a cost effective solution, and the work did not interfere with previously scheduled events. The grouting provided plenty of support for the utilities and lifted the utilities very close to the original elevations, thus eliminating the need to use piles. Removal and replacement of the distressed utilities was avoided due to the success of lifting them very close to the original grades.