Performance of Post-Tensioned Foundation Slab on Shrink-Swell Soils: A Case Study of the Briaud’s Tennis Court Slab, College Station, Texas

Post-tensioned foundation slabs is considered as a functional and cost effective solution for playing surfaces on shrink-swell soils such as tennis courts. The post tensioning increases the yield bending moment of the slab and to a lesser extent its stiffness hence, cracking during bending is minimized. Compared with conventional reinforced concrete foundation slabs, cost benefits of the post-tensioned slabs are achieved by reductions in quantities of concrete, steel, and excavation, which in turn reduce labor costs. A tennis court, located in the backyard of Prof. Briaud’s residence in College Station, TX, was founded on a clay formation of high shrink-swell potential. The Briaud’s tennis court (BTC) is a nearly rectangular post-tensioned slab-on-grade with approximate dimensions of 18.3 by 36.6 m and a slab thickness of about 0.1 m. The BTC was constructed in 1990 and has exhibited good foundation slab performance, so far. Subsurface soil conditions at the site were explored, soil index properties were determined and unsaturated soil moisture diffusion and volume change characteristics were assessed. Movements of the post-tensioned court slab were monitored every month for 2 years using 194 surveying points. The period covered was March 2005 to February 2007. The tennis court slab movements are analyzed and discussed in light of subsurface soil moisture diffusion and volume change characteristics. The BTC slab performance showed fluctuations in slab edge movements both heave and drop influenced by seasonal weather variations. Moreover, an adjacent tree significantly affected the BTC slab edge movements’ patterns within its root zone.