Stiffened Mats on Expansive Clay

A rational analysis procedure for the design of stiffened mats on expansive clay has been proposed and compared with an existing empirical design method proposed by the U.S. Building Research Advisory Board. The analysis uses the mechanics of beams-on-elastic foundation and is based on a probable distortion mechanism of the mat because of the unpredictable nature of the changing soil support offered by the differentially expanding clay. Long-term mechanical soil properties are required for this procedure and experimental values for them are given. The assumed distortion mechanisms are based on a synthesis of field observations conducted for the last three decades by engineers and geologists throughout the world. Ranges of validity of the BRAB design procedure are determined, the procedure giving unconservative design moments for differential movements as small as 1/2 in. in 30 ft for center heave cases, depending on the flexural stiffness of the foundation. Advantages of post-tensioned, prestressed concrete construction are shown.