By: Terry Meier, Sales Representative - Architectural Products
During the summer of 2007, Questar Gas Company requested that the University of Utah evaluate a conceptual EPS Geofoam cover system for a steel, natural gas pipeline crossing the Wasatch fault in the Salt Lake City valley. The fault rupture is expected to produce up to a magnitude 7.5 earthquake.
The goal of a Geofoam cover system on top of a buried pipeline is to reduce the lateral, longitudinal and vertical forces induced on the pipe as the surrounding ground undergoes deformation. The properties of Geofoam have distinct advantages that lead to improved pipe performance during large ground deformation.
There are two main advantages that Geofoam has over traditional earth cover materials. The first advantage is the low mass density of Geofoam in reducing the vertical and horizontal stresses on buried utilities and compressive soils. This reduction in loading and deformation will likely improve the performance of a pipeline during and after a major seismic event along the fault area.
The second advantage of Geofoam is its use as a compressible inclusion for systems undergoing static, monotonic and dynamic loadings. Geofoam is somewhat compressible and controlled compression can be used to reduce earth pressure against buried structures as well as deformation induced by structural loadings. The loadings that cause compression may include static and dynamic lateral earth pressure swells, frost heave pressures, settlements of support soils, faulting, liquefaction, landslides and traffic loads.
In most cases the Geofoam blocks are covered with a geomembrane. This membrane helps to reduce the vertical uplift stress by reducing the friction force between the Geofoam and the trench sidewall. In addition, placing a geomembrane around the Geofoam block will provide added protection against a potential petroleum spill.
According to Bret Lingwall, a staff engineer at Kleinfelder, “EPS Geofoam cover system offers a substantial benefit in improving the expected seismic performance of a pipeline that cross a normal fault. Compared with a sand cover system, the pipeline covered by a Geofoam system can undergo approximately 4 times greater vertical displacement before pipe yielding is predicted.”
Geofoam is indeed very beneficial, as it helps save time and money. Since this material is extremely light weight, it helps reduce bearing loads. Its installation in almost any weather conditions is one of the best advantages I like about Geofoam. Geofoam is a cost-effective solution for everyone.