Session: 06-06-03 Pipe/Soil Interactions

Paper Number: 134046

134046 - Effect of Longwall Mining on Exposed Pipelines: FEA Vs Measured Stresses 

Abstract: 

With coal and natural gas extraction often occurring in similar regions, and the overwhelming legal support of coal rights over subsidence hazards, pipeline operators are often forced to navigate the complexities of mine subsidence beneath their pipelines. Coal or other mined mineral seam thickness and its related mine subsidence often exceeds several feet. The longwall mining operation through its subsidence can cause high soil strains with the potential to compromise the integrity of buried pipelines. Mitigation measures often include pipeline excavation and a strategic pipeline strain monitoring program to ensure that stresses on pipelines do no exceed allowable limits. Numerical analysis is often used to help develop a mitigation and a monitoring plan while remaining sensitive to overall mitigation project costs. In this research a comparison is made between the finite element analysis versus measured strains in two exposed pipelines subjected to longwall mining subsidence in the Appalachian and Midwest regions. Strain gauges were attached to the exposed pipelines before subsidence was experienced to monitor changes in the strain throughout the duration of the subsidence event. Simultaneously, ground displacements were monitored by performing regular ground surveys. Soil-pipe interaction finite element models were developed to calculate pipeline strains based on measured ground displacements.

This paper establishes a comparison between calculated strains from finite element analysis and the actual strains measured by the strain monitoring system. To further expose the root of any deviations, comparisons will be made on both expected subsidence and expected pipeline stress. Subsidence amounts will compare survey data to the predicted subsidence. While pipeline stress will compare strain gauge data to the predicted model stresses.  Data from two case studies are presented and compared. The first case study is on a transmission pipeline on relatively flat terrain, while the second case study is on a high-pressure gathering line in foothill terrain. These case studies highlight the accuracy of the model and help provide operators with the confidence to leverage soil spring models to determine optimal mitigation plans. This paper will also analyze potential errors between the finite element analysis model and measured stresses provide a plan for improvement for the model or for monitoring strategies. Highlighting the accuracy of soil spring models and the continued effort for model optimization will prove the value of modeling strains before monitoring as compared to visually selecting stress concentration points in mine subsidence mitigation efforts and continue to improve pipeline safety in mineral rich geographic areas.

Presenting Author: Benjamin Zand RSI Pipeline Solutions

Presenting Author Biography: Dr. Zand has 24 years of experience in various engineering areas including geotechnical and geohazard assessment, analytical and numerical (FEA) pipeline stress analysis, pipeline integrity assessment, mechanics of composite material, and mathematical modeling. He has analyzed numerous pipelines under geohazard loadings such as longwall mine subsidence, ground movement, sinkhole, earthquake and fault crossing. He has performed fatigue life assessment for buried and above ground pipelines subjected to vibration and cyclic loading including vortex induced vibration (VIV). He has developed mitigation and monitoring programs for pipelines subjected to various geohazard conditions. He previously worked with Kiefner & Associates for 6 years. He earned a Bachelor of Science in Engineering from the University of Tehran (1996) and a PhD from the Ohio State University (2007).

Authors:

Benjamin Zand RSI Pipeline Solutions
Brett Dugan Pillar Innovations, LLC