WPXI Channel 11

Project Details:

Owner: WPXI
General Contractor: Mascaro Construction Company, LP
Duration of Work: 3 weeks
Subsurface Conditions: drilled shaft foundations. Re­moval and replacement of the fill was not practical due to the depth that the fill
Approximate Key Quantities: 40,000 square feet of Dynamic Compaction

 

Project Overview:

This project was developed on a construction spoil fill site located along I-279 in the northern part of Pittsburgh, Pennsylvania. Ground improvement was needed to support a two story building and satellite dish farm totaling an area of about 40,000 square feet. Maximum column loads ranged from 40 to 200 kips. The building was constructed using a slab-on-grade and spread footings approach. The fill at the site originated from the construction of I-279, where excavated rock and soil were dumped in a valley located at the now current WPXI building location.

The initial design called the for the building to be placed on drilled shaft foundations. Removal and replacement of the fill was not practical due to the depth that the fill extended. A ground improvement approach of dynamic compaction (DC) was ultimately suggested by the owner’s engineer and was determined to be most economical.

Ground Conditions:

The proposed building site was underlain by up to 35 feet of loose soil and rock fill. The fill material was heterogeneous both in composition and in-situ density. It varied in composition from fine-grained silty clay with some rock fragments and construction debris to predominantly coarse-grained rock fragments in a matrix of silty sand and clay. Based on the standard penetration test resistance values (SPT-N values), the fill was medium dense to dense. However, it was recognized that some of the higher blow counts may have been attributed to the presence of larger boulders and may erroneously have suggested higher densities. Accordingly, the fill had the potential for experiencing large differential settlements with time. The fill layer was deemed not suitable to support a slab-on-grade and spread footings structure.

Solution:

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