Axial stresses in pressure pipe liners spanning joints with initial gap, opening as a result of differential ground movements

Abstract

The mechanical behavior of a pressure pipe liner is studied where it stretches across a ring fracture or joint. Peak axial stresses are calculated for the case where there is an initial gap between the ends of the host pipe, and/or when the gap extends as a result of ground movements. A finite element model is established and evaluated against results from available solutions. The minimum difference between the finite element and the existing closed form solution is 0.15%, and the maximum difference is 6.79%. A parametric investigation is presented considering various values of initial gap width, liner diameter, internal fluid pressure, friction coefficient between the liner and host pipe, and the liner thickness. Finally, a simplified equation for the maximum axial stress in the liner is fitted from 524 data sets. The results show that when there is an initial gap, longitudinal bending leads to development of a tensile stress on the outer face of the liner, which peaks at the midpoint of the gap, and compressive stress occurs on the outside of the liner at the edges of the gap. The initial gap can significantly reduce the ability of the liner to tolerate ground movements that subsequently lead to gap extension. The new equation for maximum axial stress can be used to predict the liner stress when a host pipe with an initial gap (which previous existing solutions do not address) experiences gap extension.