Vitrified Clay Pipe Joint Behaviour Under Differential Ground Movement

Abstract

Field-scale experiments were used to investigate the behaviour of pipe joints connecting four segments of vitrified clay pipe subjected to differential ground movement. Firstly, linear potentiometers, inclinometers and strain gauges were installed to monitor joint rotations, joint axial compression or extension, and pipe strain. An articulation test using a servo-controlled hydraulic actuator was then employed to assess the instrumentation functionality and accuracy. The second stage of the project involved design and construction of a field-scale test chamber to simulate a normal ground fault. This facility employs manually operated screw jacks to displace a moveable floor. A test using olivine sand was conducted with floor displaced downwards by 122 mm, and this demonstrated that the new test chamber simulates normal ground faulting safely and within the design requirements. Thirdly, two tests were conducted where the pipe assembly was buried at different depths in the olivine sand and subjected to differential ground motion resulting from 30 mm of vertical floor displacement. Analysis of the experimental results included examinations of how joint rotations, joint axial compression or extension, and pipe strains increased with floor (i.e. fault) displacement, how burial depth influenced the observed behaviour, and how measured joint responses compared to two simple geometrical models. The relationship between joint rotation and vertical floor (i.e. fault) displacement was almost linear, and close to a simple trigonometric relationship developed in an earlier project. Joint axial compressions/extensions were non-linear functions of vertical floor (fault) displacement. This included a transitional event, where after the joint experienced a small amount of axial compression or extension that axial response reversed direction and much larger (i.e. dominant) extension or compression developed. Pipe burial depth had little effect on joint rotations, but a substantial effect on joint compressions or extensions. While total net axial extension was similar to that predicted using a simple geometric relationship, the values at individual joints were substantially higher. Maximum bending strains of 114 and 300 microstrain were measured along the pipe segments at 0.6m and 1.2m burial depth, respectively. The larger value is about 1/3 of the tensile strain capacity of vitrified clay.