Performance of Cast-Iron-Pipe Bell-Spigot Joints Subjected to Overburden Pressure and Ground Movement

摘要

Bell split, in which a shard is separated from the bell end of a bell-spigot joint, is a predominant failure mode (in addition to longitudinal facture) that is observed in lead-caulked bell-spigot joints of large-diameter cast-iron pipes installed between 1850 and the early 1960s. This paper addresses three specific issues related to this type of failure of lead-caulked bell-spigot joints: (1) the extent to which cast-iron pipe joints can rotate without inducing stress in the bell; (2) the behavior of the bell-spigot lead-caulked joints; and (3) an estimate of the degree of settlement that two or more contiguous segments of jointed cast-iron pipe can tolerate before failure. The procedures described in this paper were motivated by the need to understand and explain the circumstances that lead to this failure mode in large-diameter cast-iron pipes. A mechanistic model accounts for lead material nonlinearity, wet and dry joint conditions encountered in water and gas pipelines, respectively, and existence or absence of asphalt coating on the outer pipe surface. The model is validated against experimental tests conducted in the mid-1930s on lead-caulked bell-spigot joints and is subsequently used to develop another model to predict the cumulative joint response of two or more contiguous pipe segments resting on an elastic medium and subject to overburden pressure followed by ground movement. Illustrative analyses of 400 and 1,200 mm diameter pipes clearly show that the extent to which a pipe joint can rotate without failure when subjected to ground movement gets smaller as the pipes become larger. The models developed in this paper to characterize joint behavior can be used to monitor pipe joint condition if actual joint rotations are measured when conducting pipe inspection.