A performance approach to the design and specification of foundations for industrial ground bearing slabs and pavements

The foundations for industrial flooring and pavements are normally designed based on measurements, or prediction, of the California Bearing Ratio (CBR) of the subgrade, and from this the design thickness of the foundation is chosen utilising long established empirical relationships. The modulus of subgrade reaction (k) measured by static plate bearing tests may also be used, and is correlated to CBR. The thickness design charts are the same as those used for the design of highway foundations and are based primarily on observed performance. The foundations are then constructed to a recipe specification whereby specific (tightly graded) materials are placed and compacted upon the subgrade with specified plant. The soil CBR can only be regarded as an index property and does not directly or explicitly assess the primary functional performance parameters, of stiffness or strength. If CBR were replaced with direct measurement of these parameters, then the current empirical approach could be replaced with more powerful analytical design. Performance of the as-built foundation could then be better assured by compliance testing (end product) on site during construction. By moving to a performance-based specification approach, requiring some analytical foundation design, it is anticipated that more appropriate and efficient use of plant and materials can be made. This should enable better quality construction to be achieved, more efficient use of recycled materials or stabilisation of weak subgrades, hence leading to more sustainable construction. Recent research at Loughborough University has developed such a performance-based specification approach for the design of (major) highway foundations, and has assessed those devices suitable to measure the performance parameters for both design and compliance testing. In this paper the transfer of this technology to industrial flooring and paving is suggested. The benefits of a performance-based approach to foundation design and specification are explained. The loading and function of a foundation is described and the performance parameters required to perform these functions are detailed. Suitable methods currently available to measure these performance parameters are described in brief. Finally, the implications and benefits of a move to a performance-based specification approach are discussed.