Underpinning Pile Foundations of Two Adjacent Continuous Multi-Level Curved Steel Box Girder Structures

摘要

Construction of a light rail transit (LRT) system in Pittsburgh, Pennsylvania requires foundation underpinning of two adjacent multi-span steel structures. The viaducts are a series of curved three-span continuous box girders rigidly framed into support bents with end-bearing pile foundations below which the LRT alignment crosses; requiring removal of steel H-piles and construction of two individual underpinning systems. Each underpinning system consists of concrete transfer slab(s) supported by a pair of post-tensioned inverted concrete T-beams founded on drilled shafts. This paper details underpinning topics related to alternatives investigation, unique underpinning design approach, complex construction sequencing and tolerances and current construction status.