Terzaghi's three stability factors for pipeline burst-related ground stability

Abstract

A recent study on active trapdoor stability has been completed by the authors using Terzaghi's three stability factors approach. It was concluded that the superposition approach is an effective way to evaluate the stability of cohesive-frictional soils. This technical note aims to extend the previous active trapdoor study to perform a stability assessment of a passive planar trapdoor (i.e., a blowout condition) in cohesive-frictional soil. Note that this passive trapdoor problem represents the blowout stability of soils due to defective pipelines under high water main pressures, in spite of the frequent media news about the water main bursts which enlightens the relevance of the problem. Numerical solutions of upper and lower bound finite element limit analyses are presented in form of the three stability factors (Fc, Fs, and Fγ), which consider the effect of cohesion, surcharge, and soil unit weight respectively. In the event of passive trapdoor stability, this technique can be used to determine a critical blowout pressure due to a water mains leak. The study continues with a series of sensitivity analyses with a widely selected range of parameters including the cover-depth ratio (H/B) and the drained frictional angle (ϕ). The influence of these parameters on the three stability factors is discussed, and a practical example of adapting these approaches is also introduced. All numerical results are provided in the forms of design charts and tables that can be efficiently used with confidence in design practice.

Keywords

• Water mains
• Blowout
• Stability
• Trapdoor
• Limit analysis