Concrete Pipe Classification
Concrete pipe class selection is a relatively easy process. Using the LRFD Fill Height Tables for Concrete Pipe makes proper pipe selection an easy, worry-free process.
The LRFD Fill Height Tables for Concrete Pipe are very conservative. Pipe is assumed to be installed in a positive projecting embankment with a soil unit weight of 120 pounds per cubic foot. Live load is based on AASHTO HL-93. Fill heights are measured to the top of the pipe.
Standard reinforced concrete pipe is categorized in Class 2 through Class 5. Special designs are also available. There are four types of backfill, ranging from Type 1 through Type 4. Type 4 allows clays and silts for backfill material with little or no compaction, which provides the least support. Type 1 consists of highly compacted granular material and provides the most support. Concrete pipe class and installation type can be blended to optimize the use of on-site soils, giving the owner the best installation at the lowest cost.
Cemcast’s standard stock reinforced concrete pipe is produced in these classes:
- Class V 12” RCP
- Class IV 15” RCP
- Class III 18” through 72” RCP
Referring to the LRFD Fill Height Table makes it easy to determine the proper class of RCP necessary, combining bury depth and bedding type. Type 3 compaction levels, for example, are included in the tables and are readily attainable by the contractor.
For standard installations of 12” through 72” RCP with 1’ to 13’ of cover above the pipe, Cemcast standard stock class and a Type 3 bedding will handle all but 2 of 143 possible scenarios. Class 4 RCP is required in sizes 18” and 30” when only 1’ of cover is available with a Type 3 bedding. From 1’ to 13’ of cover, these are the only two exceptions in which a standard Cemcast stock class will not suffice.
The design tables make specification of proper pipe class extremely easy. In short, our standard stock RCP and a Type 3 bedding will handle nearly every possible scenario up to 13’ of cover that you will encounter in designing projects.
By comparison, when planning a plastic pipe installation, the engineer needs to work through 21 equations for each pipe diameter, bury depth, and soil type. The structural integrity of RCP simplifies every part of the process – from soil analysis and bedding through installation. When designing a pipe installation, you can’t control who becomes the low bidder, but you can control the pipe material.