Estimate of damage buried gas pipelines in Dhaka City due to an earthquake

Abstract

This thesis focuses on the damage analysis of buried gas supply pipeline of Dhaka City subject to earthquake effects. Damage prediction of gas pipelines due to earthquake involves seismic microzonation of Dhaka city and determination of the length of water supply pipeline. In this process already developed seismic microzonation map of Dhaka city is used and the available map of gas supply pipeline network of “TITAS gas Transmission and Distribution Company Ltd” is digitized to get the length of pipelines with the help of GIS software. On the basis of intensity the whole Dhaka city has been divided into three different zones. Out of total area of 135 sq.km 88 sq.km is (65%) of intensity VIII, 39 sq.km is (29%) of intensity IX and remaining 9 sq.km is (6%) of intensity X. From the digitized pipeline network, based on 1988 “TITAS gas Transmission and Distribution Company Ltd”, the length of 20mm, 25mm, 50mm, 75mm, 100mm, 150mm, 200mm, 250mm and 300mm diameter pipe is found to be 11.3 km, 121.28 km, 175.16 km, 40.69 km, 28.35 km, 28.52 km, 42 km, 1.5 km, and 3.49 km respectively. Again from the intensity based pipeline network it is found that 376 km pipe falls in the zone of intensity VIII, 67.31 km falls in the zone of intensity IX and 22.23 km falls in the zone of intensity X irrespective of pipe diameter. A selection step is followed to estimate peak ground acceleration (PGA) and peak ground velocity (PGV) to determine the pipeline damage rate. Existing empirical relations based on peak ground acceleration such as Katayama (1975), Isoyama and Katayama (1982), O’Rourke (1998) and Isoyama (2000) for the prediction of earthquake-induced pipeline damage are reviewed. Similarly empirical relations based on peak ground velocity such as Eidinger et al. (1995, 1998), O’Rourke and Ayla (1993), Isoyama (2000) and O’Rourke (2001) also reviewed. Finally using above relations and selected peak ground acceleration and peak ground velocity damage rate of pipelines is determined. Pipeline damage rate is expressed in number of repairs per unit length of pipe. In case of PGA based analysis total number of repairs for all intensities is 97 within a total pipe length of 465 km. Out of which 24 numbers of repairs required for 376 km pipelines, 28 numbers of repairs required for 67.31 km pipelines and 45 numbers of repairs for 22.23 km. For PGV base analysis total number of repairs for all intensities is 182 within total pipe length of 465 km. Out of which 87 numbers of repairs required for 376 km pipelines, 50 numbers of repairs required for 67.31 km pipelines and 45 numbers of repairs for 22.23 km.