Effect of support condition on the mechanical behavior of ductile iron pipes buried at shallow depth within the backfill of controlled low strength material

Abstract

The effect of support condition on the performance of a ductile iron pipe (DIP) buried at shallow depth and backfilled using controlled low strength material (CLSM) is investigated in this study. CLSM as a backfill material has numerous benefits including self-leveling, no need of compaction, and fast return to traffic. However, the feasibility under critical burial condition should be further investigated. Two DIPs (diameters of 300 mm and 500 mm) installed at a shallow depth are the research objects of this study. Two support conditions are designated to evaluate DIP performance with CLSM as the backfill material. The first simulates the DIP sitting directly on a stiff underground structure such as a culvert. The second assumes that there is no support underneath the trench, simulating a situation that the soil is lost due to water leakage. These two detrimental support conditions lead to a higher than usual loading. The results show that the support condition has a significant influence on the DIP stress and the CLSM cracking behavior. The strength of the CLSM also has an effect on the cracking behavior. Overall, the two DIP specimens sustain linear reactions without plastic deformation under the design truck load. The cement-mortar lining of the DIPs only develops a few fine cracks, but neither peels nor falls off. The results of the two experiments in this study offer valuable information about the performance of DIPs buried at shallow depth and backfilled with CLSM. The observations are useful for the installation design and hazard mitigation of DIP and other pipe materials.