Effect of Nonuniform Foundation Support on Concrete Slab Responses

Paper by Alexander S. Brand and Jeffery R. Roesler from 10th ICCP Quebec 2012

The ability to spatially map the stiffness of the foundation layers under concrete pavements with intelligent compaction has created a need to define limits on the allowable stiffness variations in a given construction area as well as the maximum size of a non-complaint area which does not require remedial action. In order to work towards this goal, a two-dimensional finite element analysis was completed to determine the effects of four nonuniform subgrade support conditions (relative to uniform support) on the tensile stresses in a concrete slab under tandem axle loading and temperature curling. The slab responses showed that certain nonuniform subgrade support conditions have a greater impact on the slab tensile stresses relative to the uniform support irrespective if the slab is experiencing curling. A soft support along the longitudinal slab edge and a subgrade with randomly assigned 9 ft2 (0.84 m2) soft and stiff areas were found to decrease the slab performance relative to a uniform subgrade assumption. In the most extreme case, the nonuniform support with soft longitudinal edges had a maximum stress that was 63 percent greater than the uniform soft support. In this analysis, subgrade nonuniformities produced the potential for bottom-up or top-down fatigue cracking depending on the interaction of the axle location, temperature differential, and local support condition. Key words: nonuniform support, concrete slab, finite element analysis, intelligent compaction, foundation layer. Demonstration for ISCP Board only.

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