This practice provides a rational method for structural design of thermoplastic stormwater chambers. The loads, capacities, and limit states are based on accepted load and resistance factor design for thermoplastic pipes; however, existing design specifications for thermoplastic pipes do not adequately address the design of chambers due to (1) open-bottom geometry, (2) support on integral foot, (3) varying circumferential corrugation geometry, and (4) manufacture with alternative thermoplastic resin. This practice standardizes recommendations for designers to adequately address these aspects of chamber design.

This practice is written to allow chamber manufacturers to evaluate chambers meeting existing classifications and to design chambers for new classifications as they are developed.

1.1 This practice standardizes structural design of thermoplastic corrugated wall arch-shaped chambers used for collection, detention, and retention of stormwater runoff. The practice is for chambers installed in a trench or bed and subjected to earth and live loads. Structural design includes the composite system made up of the chamber arch, the chamber foot, and the soil envelope. Relevant recognized practices include design of thermoplastic culvert pipes and design of foundations.

1.2 This practice standardizes methods for manufacturers of buried thermoplastic structures to design for the time dependent behavior of plastics using soil support as an integral part of the structural system. This practice is not applicable to thermoplastic structures that do not include soil support as a component of the structural system.

1.3 This practice is limited to structural design and does not provide guidance on hydraulic, hydrologic, or environmental design considerations that may need to be addressed for functional use of stormwater collection chambers.

1.4 Stormwater chambers are most commonly embedded in open graded, angular aggregate which provide both structural support and open porosity for water storage. Should soils other than open graded, angular aggregate be specified for embedment, other installation and functional concerns may need to be addressed that are outside the scope of this practice.

1.5 Chambers are produced in arch shapes to meet classifications that specify chamber rise, chamber span, minimum foot width, minimum wall thickness, and minimum arch stiffness constant. Chambers are manufactured with integral footings.