A Discussion of E' versus Depth

摘要

The Reclamation table of presumptive E' (Modulus of Soil Reaction) values appears in many standards, guides, and manuals. The E' value represents the stiffness of the soil placed on the sides of the pipe and is used for estimating the deflection of buried flexible pipe. In the Reclamation table, E' varies with the type of embedment soil and the degree of compaction, but not with the depth of cover over the pipe. However, soil moduli generally change with confining pressure. Accordingly, some standards and guides have recently expanded design tables showing E' varying with depth. This study is a new analysis of forty-five field tests where deflection was measured as the depth of cover over the pipe increased. The data show a strong linear relationship between the vertical deflection and the depth of cover, indicating that E' does not vary with depth. Consequently, tables including E' variation with depth may not be warranted for design use for pipe with cover of 25 feet or less, and in many cases, 50 feet.