Valley Forge Laboratories, Inc.

Location:   The Pennsylvania State University, State College, PA

Client:   The Pennsylvania State University

Description:
In spite of the sinkhole history of the area and a maximum column design load of 1500 kips., the six-level garage is supported by a standard shallow foundation system - the first heavy structure on campus not built using caissons. This has been accomplished with confidence, at a savings of about $400,000 to the university, by implementing an extensive geotechnical investigation and compaction grouting program at the site.

VFL’s geotechnical investigation consisted of soil boring and rock coring at all 56 major column locations of the structure. The drilling revealed that sinkhole activity was concentrated in one corner of the site, affecting only 7 column locations. The zones of weak and compressible clays were carefully delineated. VFL’s laboratory testing included 18 engineering classifications to establish the site’s geotechnical cross section. Four critical samples were then tested under triaxial compression to determine the shear strength properties for design. Consolidation testing was also carried out to define the deformation properties of the clays for calculation of foundation settlements.

A thorough geotechnical analysis, accounting for column load eccentricity, revealed that the majority of the soils at the site were compatible with strip and spread footings with an allowable bearing pressure of 6 ksf. Having established this, VFL addressed the 7 problem column locations and determined compaction grouting would be the most effective soil improvement technique. Thus, compaction grouting was carried out under the direction of VFL. A low slump (2-3 in.) and high pressure (200 psi) were used to densify the foundation soils prior to excavation for the footings.

Following completion of the parking structure, a post-construction settlement monitoring program was initiated by VFL in cooperation with Penn State to obtain foundation performance data. Ten columns were selected to represent the diverse subsurface conditions and structural loading at the site. Three were grouted locations, while the remainder represented column footings on clay, bedrock and decomposed dolomite. For 14 months after construction, monthly monitoring was performed using surveying equipment with an accuracy of 3mm, resulting in negligible settlements.