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Three City Center



Allentown, PA


GTA provided geotechnical consultation services to facilitate the design and construction of the 166,000-SF, seven-story Class A office/retail building at 515 Hamilton Street in downtown Allentown. The subsurface profile was typical of karst geology in an urban landscape and included demolition debris from the former Colonial Theater, a highly variable rock surface, and fine-grained residual soils with several very soft soil layers. Due to the high column loads, initial preliminary design concepts included deep foundations consisting of micropiles; however, GTA was able to provide significant cost-savings through the use of a limited foundation over-excavation/replacement scheme combined with deeper soil improvement/void stabilization through the use of compaction grouting techniques. The combined over-excavation and stabilization methods minimized total and differential settlements across the building footprint which was underlain by variable materials consisting of shallow rock pinnacles to deep weathered soft soil troughs.

GTA also provided technical guidance throughout site excavation with sinkhole remediation recommendations, underpinning of the adjacent historic county courthouse, soldier pile and lagging installation, and design of a temporary precast modular block wall for excavation support along Hamilton Street. GTA also provided construction testing services throughout building construction including soils, concrete, masonry, structural steel, and sprayed fire resistive materials in general accordance with Chapter 17 (Special Inspections) of the International Building Code.

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