A three-dimensional analysis of the effects of erosion voids on rigid pipes

• FEA is performed to study the 3D effects of voids on the earth pressure on the pipe.
• Initial earth pressures are first calculated and compared with field measurements.
• The effects of increasing the void length, depth and angle are examined.
• At the springline, voids resulted in earth pressure increase of more than 100%.

In this study, elasto-plastic finite element analyses are performed to investigate the three-dimensional effects of erosion voids developing behind the walls of an existing sewer pipe on the earth pressure distribution around the pipe and the stresses in the pipe wall. Initial earth pressures are first calculated and compared with field measurements. Erosion voids of different sizes are then introduced at the springline and invert of the pipe and the changes in pressure are evaluated and compared with the initial values. The effects of increasing the void length, depth and angle are examined. Results clearly reveal that the presence of erosion voids can have a significant impact on the earth pressure distribution around an existing pipe as well as on the pipe wall stresses. Increase in pressure is found to be mainly influenced by the void length and location with respect to the pipe circumference. Voids introduced at the springline resulted in earth pressure increase of more than 100% near the void boundaries whereas the pressure change was less significant when the void is introduced at the pipe invert. The findings of this study highlight the importance of locating voids behind pipe walls to prevent further deterioration and possibly sewer failure.