Suggested Bedding Factors of Controlled Low-Strength Material for Concrete Pipe

Abstract

It is important for concrete pipe to have an adequate bedding layer with quality soil material to provide the best support condition for the pipe. Having a good bedding condition reduces the required strength of the concrete pipe, ensures a proper performance level, and long service life. Traditionally, concrete pipe has been bedded with a variety of soil types, with granular soil being the most commonly used. The use of Controlled Low-Strength Material (CLSM) as a concrete pipe bedding material has become more common in recent years, particularly for pipe installations where there is inadequate space for proper trenching, excavating, and bedding, or for situations where speed of installation is a primary concern. To prevent the design engineer from having to make uncertain assumptions about what actual bedding factors are for CLSM bedding, the purpose of this paper is to suggest a range of bedding factors for use with concrete pipe. This was accomplished by the use of a Finite Element Analysis (FEA) software program developed by the American Concrete Pipe Association (ACPA) called Soil-Pipe Interaction and Design Analysis (SPIDA) (5). The SPIDA finite element mesh provides an accurate picture of installed soil-pipe interaction forces, without having to conduct expensive field-testing. Typical SPIDA output results provide a summary of pipe ultimate thrusts and moments at the pipe invert, springline, and crown for various loading conditions and trench configurations that can be used to calculate the bedding factor.