Damage of buried water pipelines due to an earthquake in Dhaka city

Abstract

Earthquakes can cause extensive damage to buried water supply pipelines which is one of six categories of infrastructure grouped under the heading 'lifelines', resulting in disruption of essential services for the whole community. This thesis focuses on the damage analysis of buried water supply pipelines of Dhaka city subject to earthquake effects. The water pipeline network is essential for daily life. It provides household using as well as industry and firefighting using. Damage prediction of water supply 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 water supply pipeline network of Dhaka WASA 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.kIn is (29%) of intensity IX and remaining 9 sq.km is (6%) of intensity X. From the digitized pipeline network, based on 1993 DWASA data, the length of 100mm, 200mm, 300mm and 450mm diameter pipe is found to be 916 km, 259 kIn, 170 kIn and 53 kIn respectively. But these lengths according to DWASA 2008 data are 1693 km, 419 kIn, 190 km and 54 kIn for 100mm, 200mm, 300mm and 450mm diameter pipe respectively. Again from the intensity based pipeline network it is found that 1043 kIn pipe falls in the zone of intensity VIII, 274 km falls in the zone of intensity IX and 81 kIn falls in the zone of intensity X irrespective of pipe diameter. A selection step is followed to estimate peak ground acceleration (PGA) to determine the pipeline damage rate. Existing empirical relations such as Katayama (1975), O'Rourke (1982), Isoyama and Katayama (1998) and Isoyama (2000) for the prediction of earthquake induced pipeline damage are reviewed. Finally using above four relations and selected peak ground acceleration damage rate of pipelines is determined and an estimation of financial loss is presented. Pipeline damage rate is expressed in number of repairs per unit length of pipe. Total number of repairs for all intensities are 587 within a total pipe length of 2356 km. Out of which 42 I number of repairs required for 1693 km pipelines of I00 mm diameter, 109 number of repairs required for 4 19 km pipelines of 200mm diameter, 42 number of repairs for 190 km pipeline of300mm diameter and 15 number of repairs for 54 km pipeline of 450mm diameter.