Standard Installations becoming
new concrete pipe standard

By Mike Smith, P.Eng., Inland Pipe Limited, and
Mike Schmidtler, P.Eng., Lafarge Canada Inc.

Contractors found that the additional cost of extra granular material was more than offset by the savings in time compacting backfill.

Most North American bedding and backfill standards for concrete pipe are based on a design concept developed almost ninety years ago. It had not been updated to account for today's high quality products, modern installation practices and pipe-soil interaction research.

Engineers, contractors, developers, and concrete pipe producers have responded to aging standards by setting a benchmark for a new design process for concrete pipe installations. Opportunity for change presented itself in today's technology used for precast concrete pipe beddings, a greater understanding of the interaction of the pipe with bedding and backfill material, and a methodology for applying backfill.

Standard Installations use today's technological advances in soil classification and density testing, finite element analysis, pipe design, manufacturing, and construction practices.

In 1993, Standard Installations were adopted by the American Society for Civil Engineers (ASCE) as Specification 15-93-Standard Practice for Direct Design of Buried Precast Concrete Pipe Using Standard Installations. It was adopted later in the 1996 (16th) Edition of the American Association of State Highway and Transportation Officials (AASHTO) Standard Specification for Highway Bridges, Section 17, Soil-Reinforced Concrete Structure Interaction Systems. In 1997, Standard Installations were incorporated into the new Canadian National Bridge Design Code, and in 1999, the City of Edmonton adopted the design model in their specifications as the preferred method for designing concrete pipe.

The Standard Installations model for design and installation of concrete pipe was developed through the American Concrete Pipe Association's long-range research program which started in the 1970s. Implementation of the model came in the form of four Standard Installations; Types 1, 2, 3, and 4. Type 1 is a top quality installation with the highest requirements on backfill material and compaction levels. Type 4 is the installation with minimal requirements on bedding material and compaction (equivalent to the Class D bedding).

Breakthrough in Alberta

The City of Calgary, Alberta, is a focal point where the value of Standard Installations is being recognized. Current City of Calgary specifications permit engineers to design storm and sanitary sewers with only Class C bedding (granular material cradling 60% of the pipe width) or Class A (concrete) bedding for deeper fills. Calgary contractors had been installing concrete pipe using granular material at least to springline, despite the City's Class C bedding specifications.

The bedding material specified is typically a readily available 40 mm gap graded rock, which the City has always accepted as compacted to 95% Standard Proctor density when installed in a dumped condition. Contractors found that the additional cost of extra granular material was more than offset by the savings in time compacting backfill (specified in Class C bedding specification) below the springline.

The Calgary concrete pipe producers recognized that the bedding and backfill material, installed in this manner, was by definition a Type 1 Standard Installation.

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