A Rational Approach to Designing Spray Applied Polymeric Manhole Rehabilitation Products

Polymeric coatings consisting of epoxies, polyurethanes, and polyureas have been utilized in the municipal industry for years to rehabilitate manhole structures, typically with the intent of arresting infiltration and maintaining the structural stability of the manhole/soil structure. While spray applied products are an effective means of controlling infiltration and arresting deterioration, their use as fully structural solution is sometimes limited by practical installation and product limitations. As a result, the use of spray applied polymeric coatings as a fully structural rehabilitation system and specifically their use in non-circular applications can result in liner thicknesses exceeding the practical limits for application resulting in both installation issues and increasing costs. Recent experiences in the North American manhole rehabilitation market has highlighted a trend of adopting the North American sewer rehabilitation terminology of full and partial deterioration for describing host manhole conditions and liner structural requirements. Since candidates for spray applied manhole rehabilitation systems are typically not in a state of incipient failure and receive considerable stabilization and repair efforts as part of the rehabilitation process, the use of fully deteriorated load models requiring the liner to support all applied overburden loads is often unnecessary and can render liners unbuildable. Due to their vertical orientation within the soil strata manhole structures and liners behave differently and are exposed to different applied load models than gravity pipelines making the use of North American pipeline rehabilitation design methods problematic. Further, when moving from circular to non-circular structures, specifically those with flat walls there is a need to address both applied bending stresses and liner deflection. The lack of formal guidance on both circular and non-circular manhole liner design has resulted in the authors of this paper to develop design procedures based on first principles, considering applied bending forces, end support conditions, and serviceability criteria. This paper strives to define a rational approach to developing design criteria for spray applied polymeric coatings as well defining appropriate applied load models for use in both circular and non-circular applications. Properly, matching existing structure condition with the appropriate load models and structural requirements is critical for ensuring both a successful and cost effective rehabilitation program.