Analyzing Field Performance of Steel-Reinforced HDPE (SRHDPE) Pipes during Installation and under Traffic Loading

Abstract

Steel-Reinforced High Density Polyethylene (SRHDPE) pipes have been developed and introduced to the market to overcome the disadvantages of HDPE pipes (i.e., low strength and stiffness and high creep deformation and potential buckling) and steel pipes (i.e., corrosion). SRHDPE pipe uses steel ribs to carry load and plastic covers of steel ribs to prevent any possible corrosion. However, no widely accepted method is available to design the SRHDPE pipe. The objective of this study is to evaluate the field performance of the SRHDPE pipes during installation and under traffic loading and to recommend the parameters for the design method. A field test was conducted in Kansas City, Kansas to investigate the performance of the SRHDPE pipe during installation and under static loading. Four 2.13 m-long SRHDPE pipes with a diameter of 0.6 m were connected and buried in a trench with a dimension of 1.52 m wide, 9.15 m long, and 1.40 m deep. Two types of material were backfilled in the trench, namely, AB3 aggregate and crushed stone. Two pipes were buried in the AB3 aggregate section while the other two pipes were installed in the crushed stone section. Deflections in the vertical, horizontal, and 45o directions from the pipe crown were monitored during the backfilling process. Earth pressures and strains of the SRHDPE pipes were measured during the construction. Hardening soil model was used to simulate the backfill material under compaction, while an Equivalent Modulus Method (EMM) was proposed to model the SRHDPE pipe. The test results from the field were used to verify the effectiveness of the proposed numerical model. A parametric study was conducted to evaluate the effects of the trench width, the soil cover thickness, the magnitude of the compaction load and the friction angle of the backfill material on the performance of the SRHDPE pipe during installation. Earth pressure, pipe deflection, strains and moments in the pipes were measured to analyze the pipe performance. Considering the relative higher stiffness of the SRHDPE pipe, the pipe deflections during installation and under traffic loading should be small. The existing soil arching theories widely used to analyze the load transfer mechanism assume the soil is at a yielding state. This assumption may not be realistic in the soil cover above the SRHDPE pipe since the shear stress in the soil is highly related to the displacement. Partially-mobilized soil arching equations were derived in this study to investigate the load transfer mechanism in the soil cover above the SRHDPE pipe during installation and under traffic loading considering the displacement of backfill material in the soil cover is less than the critical displacement (i.e., a displacement of the soil can induce a shear stress equal to the shear strength). Two calculation examples are provided to illustrate the calculation procedures. Long-term monitoring (i.e. two years) of the performance of the SRHDPE pipe was conducted at a field test site in Lawrence, Kansas. The trench was 2 m wide, 1.72 m deep and 24 m long. Three SRHDPE pipes with a diameter of 0.9 m and a length of 7.2 m were installed in the trench. Half length of the trench was backfilled with AB3 aggregate and the other half was backfilled with crushed stone. Earth pressures, pipe deflections in the horizontal and the vertical directions, strains on steel ribs, plastic covers and plastic valleys were monitored. Two empirical correlations were developed to predict the Vertical Arching Factor (VAF) on the pipe top and the pipe stiffness factor (EI) at a specific time.