Organic “High-Build” Spray-in-Place Liners – An Emerging Class of Rehabilitation Methods

By Erez N. Allouche, PhD, P. Eng. and Eric J. Steward, Trenchless Technology Center, Louisiana Tech University | June 2009 Vol. 64 No. 6

Where Pf is the short-term burst pressure (psi), D is the diameter on the opening (inches) and the t is the thickness of the panel (inches). Equation [1] yields a relatively accurate, yet conservative value of the short-term burst pressure for a given combination of polyurethane liner thickness and opening (‘defect’) size. The equation is applicable only for liners with similar material properties to the material tested for this study. Equation 1 does not consider parameters that could control long-term strength of thermosetting materials, such as creep and fatigue.

In the case of the polyurea, Figure 12 provides a visual display of the failure pressure and thickness relationship for the five panels tested. The preliminary trend line generated from the results indicates a linear relationship between failure pressure and panel thickness (R2 = 0.842). To date only tests utilizing a 3” opening have been performed. Based on the preliminary results the following linear mathematical expression was derived:

Pf = 1069 (t) – 1.731 (Eq. 2)

Where Pf is the short-term burst pressure (psi) and the t is the thickness of the panel (inches). It is expected that testing of additional panels at varying thicknesses will provide an even higher level of confidence in this relationship. As additional formulations are tested, TTC researchers intend to incorporate the material properties as another variable in the regression model, allowing a further generalization of the prediction equation to cover a wide range of formulations.

Fig 12: Burst pressure vs. thickness for polyurea panels

Case Studies

Case Study 1: Rehabilitation of a water intake at Springerville Generating Station
Springerville, a town of 2,000 located in the eastern mountains of Arizona, is home to Tucson Electric Power’s (TEP) 1160 megawatt Springerville generating station, a modern, pollution-controlled coal-fired electric power plant that services private and public customers from southern Colorado to San Diego, California.