Laboratory and Field Performance of Buried Steel-Reinforced High Density Polyethylene (SRHDPE) Pipes in a Ditch Condition under a Shallow Cover

Abstract

Metal and plastic pipes have been used extensively as storm sewers and buried drainage structures in transportation projects. Metal pipes have high strength and stiffness but are susceptible to corrosion from wastewaters containing acid, and from aggressive soils. Plastic pipes are resistant to corrosion, erosion, and biological attack but have certain disadvantages including lower long-term strength and stiffness (dimensional reliability), buckling, and tearing of pipe wall. To address the disadvantages of metal and plastic pipes, a new product, steel-reinforced high-density polyethylene (SRHDPE) pipe, has been developed and introduced to the market, which has high-strength steel reinforcing ribs wound helically and covered by corrosion-resistant high density polyethylene (HDPE) resin inside and outside. The steel reinforcement adds ring stiffness to the pipe to maintain the cross-section shape during installation and to support overburden stresses and traffic loading. The HDPE resin protects the steel against corrosion and provides a smooth inner wall. The combination of steel and plastic materials results in a strong and durable material with a smooth inner wall. Different methods are available for the design of metal and plastic pipes. The American Water Works Association (AWWA) Manual M11 (2004) provided the design procedure for metal pipes and the 2007 ASSHTO LRFD Bridge Design Specifications had separate design procedures for metal and plastic pipes. However, it is not clear whether any of these procedures for metal and plastic pipes can be used to design an SRHDPE pipe. Moreover, no approved installation or design specification is available SPECIFICALLY for the SRHDPE pipes. Some research has been conducted on SRHDPE pipes to understand the performance of SRHDPE pipes in the laboratory including the laboratory tests conducted by Khatri (2012). To investigate the performance of the pipe with various backfills, in addition to the laboratory tests conducted by Khatri (2012) with the sand backfill, a laboratory test with the crushed stone backfill was conducted in a ditch condition under 2 feet of shallow cover. This was performed in a large geotechnical testing box 10 feet long x 6.6 feet wide x 6.6 feet high. Based on the laboratory testing and analysis on the SRHDPE pipes, it can be concluded that (1) the pipe wall-soil interface should be designed as a fully bonded interface to be conservative, (2) the Giroud and Han (2004) method and the simplified distribution method in the 2007 AASHTO LRFD Bridge Design Specifications reasonably predicted the pressures on the top of the SRHDPE pipes induced by static and cyclic loadings, (3) the modified Iowa formula (1958) under predicted the deflections of the SRHDPE pipes during the installation and over-predicted the deflections during static and cyclic loadings, (4) the formula provided by Masada (2000) can be comfortably used to determine the ratio of the vertical to horizontal deflection of the SRHDPE pipe, (5) the pipe wall area was enough to resist the wall thrust during installation and loadings, and (6) the highest measured strains recorded in steel and plastic during the installation and loadings in all the tests were within the permissible values. The laboratory tests however have some limitations. For example, the installation procedure of the pipe in the test box may be different from the field installation due to the limited space and construction equipment in the laboratory. The laboratory box tests may have a boundary effect. Therefore, a field test was conducted to verify the lab test results The results obtained in the field test were found in agreement with the results obtained for the laboratory test during the installation and the traffic loading.