Estimating Residual Strength of Deteriorated 96" Interceptor and Strength Enhancement Provided by Lining Methods Using Computer Modeling and Forensic Investigation Tools

In 1985, the Trinity River Authority of Texas (TRA) completed the construction of Elm Fork Relief Interceptor Segment 1-A, consisting of 17,200 linear ft of a 96-in. diameter reinforced concrete pipe. A 1999 investigation revealed significant wall losses triggering the installation of a parallel 104-in. pipeline of similar capacity in 2007. In 2008 Espey Consultants were retained by TRA to evaluate different avenues for restoring the structural integrity and functionality of the original pipeline. Their investigation revealed that up to 30% of the wall thickness had been lost to corrosion for the majority of the length of the pipeline, and in some limited sections even greater wall loss, mainly in the crown region. The severe degree of corrosion demonstrated partially deteriorated and limited fully deteriorated pipe condition; however, completely neglecting the contribution of the host pipe resulted in a wall thickness that was likely to compromise the required hydraulic capacity. In an attempt to estimate the remaining structural capacity of the pipe, an extensive forensic engineering investigation was undertaken consisting of mechanical and chemical testing of physical cores taken from the pipe in 1999. Information from laboratory tests, along with information from a laser profiler study of the pipe's inner geometry, geotechnical information, ground and surface water loads, and data regarding original design parameters were used to construct a detailed 3-D finite element (FE) model of the in-situ pipe. Structural enhancement provided by two common rehabilitation methods, CIPP and GIPP, was superimposed on the FE model. An extensive parametric study was undertaken to gain insight as to possible contribution of the host pipe in resisting the various external loads and the anticipated structural capacity of the rehabilitated structure.