טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentShoshana Hermann
SubjectLeakage-Induced Pipeline Stressing
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Klar Assaf
Professor Linker Raphael
Full Thesis textFull thesis text - English Version


Abstract



This research aims to develop an analytical solution to model the bending moment profile in a buried pipeline which occurs as a result of a leak.  The solution begins by describing the displacements incurred due to a buried point source, and then incorporates the pipe-soil interaction to form a comprehensive semi-coupled model of the underground pipeline stressing.  The final model was tested using COMSOL Multiphysics to simulate a buried pipeline with a leak.  COMSOL is an equation-based modeling system which uses predefined sets of equations - in this case, for unsaturated flow and solid mechanics - to show the resulting stresses and strains, as well as other parameters, as calculated based on user-defined initial and boundary conditions.  In this way, the particular problem at hand could be described in terms of already-existing theories, such as Darcy’s Law or Richards’ Equation.  The results from COMSOL were used to confirm the analytical solution, and ensure that the calculated strain profile during a leak is reliable.  The analytical solution required the use of an approximation of the pressure distribution which occurs along the radial axis moving further from the point of the leak.  Two different approximations were considered: Green and Ampt and a steady state assumption.  The former proved less accurate, and the steady state assumption was used in the final solution.  By comparing the two sets of results, one derived analytically and the other solved numerically using COMSOL, it can be shown that the analytical solution described in this work can be used to calculate the resulting stresses and strains in an underground pipeline caused by a leak.  The volume of leakage associated with a particular amount of strain depends on the configuration of the pipeline in the soil, and on the soil and pipe material parameters.  If only a small amount of liquid has leaked, the level of strain will not be detectable by fiber optic cables, but once a significant amount of liquid has been lost the strain reaches detectable levels and the solution presented can be used to develop a strain-based detection system to determine if and where a leak occurs.