The subsurface investigation, which included the performance of 28 test borings extending to depths of at least 150 feet, uncovered complex subsurface conditions. The major concern were two relatively deep soft clay strata. Considering this, several foundation types were evaluated to determine feasibility and cost effectiveness. The project was on a fast track schedule and supporting the new building on piles was selected. GEODesign provided construction support including overseeing the test pile program, installation of driven and drilled piles and addressing unforeseen conditions.
The Solutions Unearthed
- Analyses indicated that if the new building were supported on spread footings, settlement of the clay strata was acceptable; however, the new building load would exceed the allowable bearing capacity of the soil. Conversely, the new building could be supported on a mat foundation without exceeding the allowable bearing capacity of the soil but the settlement of the clay strata was unacceptable and estimated to be approximately 6” or higher.
- It was recommended that the new building be supported on piles or a mat foundation with piles. Supporting the new building on a mat foundation with piles would require additional analyses and significant coordination between the structural and geotechnical engineers. The project schedule did not allow for this; therefore, supporting the new building on piles was selected.
- Considering the close proximity of adjacent buildings, the foundation was designed for driven and drilled piles with allowable compression capacities of 130 and 100 tons, respectively. The piles were installed through the clay strata to the lowest sand layer to prevent load transfer to the clay that could result in unacceptable building settlements.
- Production pile installation was scheduled less than a month from the start of the test pile program. Considering the results of the PDA testing and that the factor of safety for the design of the drilled piles were greater than 2.0, it was expected that the driven and drilled piles would pass the static load tests. The two clay strata presented challenges during the initial pile load tests. However, with quick thinking and ingenuity, the piles were redesigned, tested and passed the Code requirements prior to production pile installation.
Client: L&M Development Partners
