A PARAMETRIC EVALUATION OF BURIED PIPELINE SUBJECTED TO SEISMIC EXCITATIONS

Abstract

Buried pipelines, usually carrying essential facilities, are generally known as lifeline facilities and are considered one of the most susceptible structures under seismic action. Considerable research has been conducted addressing the response of buried pipes under fault rupture and permanent ground deformation. However, research on the response of buried pipes under seismic action is seldom found in technical writings. A three-dimensional numerical analysis has been performed in this research using a FEM based software, Abaqus 6.14 to focus on the insight response of buried pipe considering potential parameters under real seismic excitation. Shell element has been used to define the pipe model, while soils have been modeled by solid elements. The interface between soil and pipeline has been modeled by penalty friction to ascertain a realistic soil-pipe interaction. The vertical time history of the 1940 El Centro Earthquake has been used for this study, and the model has been validated with an experimental study in a static case, and a similar response has been observed that implicitly justifies the accuracy of the model. The seismic response of buried ductile iron pipe under seismic excitation portrays higher displacement, and significant stress has been observed. The maximum pipe response due to seismic excitations was noticed at the mid-span along the crest line of the pipe. Accounting for the finite model, the response of pipes under different boundary conditions has been studied to clutch the overall response of pipelines under different constraints. Furthermore, a parametric study has been carried out to comprehensively examine the sensitivity of different parameters such as burial depth, and aspect ratio (D/t); embedment ratio (h/D), Soil-pipe interface friction co-efficient, pipe end-restraint conditions, soil characteristics (Dry density, Modulus of elasticity, Friction angle, Poisson’s ratio), Traffic load, operational water pressure, Unidirectional Seismic excitation on the seismic response of straight buried pipes. The observed maximum vertical spatial displacement, deformation, von Mises stress, plastic strain, etc., are graphically depicted to analyze the seismic behavior of the buried pipeline. Significant response has been noticed at shallow burial depths in the parametric analysis, and both the burial depth and boundary conditions have been found as critical parameters in the response of pipes under seismic action. The increase in embedment ratio (h/D) from 1 to 5 by up to 5 times, decreases pipe displacement, stress and strain by 28.7 %, 1.3 % and 23.2 % respectively. The maximum displacement and stress magnitude generated in thepipe increases by up to 2.87 % and 34.9 % respectively for hinge support; also, it increases by up to 2.83 % and 34.9 % respectively for fixed support with respect to roller support. The observed plastic strain in the pipe was 90.1% lower (roller); 53.1 % higher (hinge); 45.9 % higher (fixed) than the minimum elongation (10%) of DI pipe. In addition, soil properties and induced traffic load contribute substantially to the deformation of buried pipes. The maximum displacement, stress and strain developed in the pipe decreased by up to 59.2%, 84% and 100% respectively, due to an increase in soil density (from 1700 to 2160 kg/m3 by 1.27 times), the modulus of elasticity (from 19 to 96 MPa by ~5 times) of soil, the Poisson’s ratio (from 0.2 to 0.45 by 2.25 times) of soil and the friction angle (from 30º to 45º by 1.5 times) of the soil. The greatest displacement and stress values occurred in the pipe considering the traffic load (1100 kPa) on the soil significantly increased by 135.7% and dramatically increased by (1326 %) respectively compared to the no traffic load case. The observed plastic strain in the pipe due to traffic load was 90 % lower than the minimum elongation (10%) of DI pipe. Overall, numerical results demonstrate that these influencing factors can impact the seismic behaviors of the buried pipeline to different degrees and cannot be neglected in the seismic analysis. In a nutshell, this research can be used as a direction for further research to provide a comprehensive guideline for the design, safety evaluation, and protection of buried pipelines crossing seismic areas.