King of Prussia, PA –
Soil stabilization and sinkhole mitigation was required to construct a proposed 306,000 square feet distribution facility with an attached administrative office and line haul office in King of Prussia, PA. Prior to construction, a subsurface exploration program consisting of soil test borings and electrical resistivity measurements, revealed evidence of sinkhole activity. Sinkhole activity was indicated by low blow counts, pyramid-like rock surfaces, and weathered and fractured rock zones. Approximately 140,000 square feet of this area was established for a compaction grouting program. Underlying soils consisted of silty fine sands and subsurface limestone bedrock with top of rock depths varying from 14 to 40+ feet below the ground surface; indicating potential of a much deeper bedrock elevation. Based on the data, an average top of rock depth of approximately 49 feet below the ground surface was estimated.
CGS worked closely with the construction manager to develop a grouting program. The program consisted of grout injection points within the specified area below all perimeter wall foundations at 15 feet on-center spacing, a single point below each exterior and interior column foundation, and a single point at the center of column bays for floor slab support. This plan called for a total of 141 grout injection locations. Grouting was performed by drilling a minimum of 5 feet into rock or a maximum depth of 60 feet at each location, then installing grout injection casings. Grout was injected from the bottom of the hole up to the bottom of the proposed footing or as close to the existing ground surface as possible. The crew performed grouting in 1 foot stages and each stage was terminated once grout refusal criteria was reached.
CGS drilled a total of 6495 linear feet and injected a total of 367 cubic yards of grout into 173 injection points. The project was completed almost 2 weeks ahead of schedule and well below the program budget using 2 grout crews.
Following the building shell construction, CGS was called back on site to perform compaction grouting work to stabilize several sinkholes that became apparent. The compaction grouting process was used and the work was performed using the remaining budget from the original project quote.