Geotechnical aspects of mud eruption disaster In East Java

Abstract

Mud eruption occured in East Java, 3 days after the Jogyakarta Earthquake in May 26, 2006 where at the site, deep drilling was being conducted. The mechanism of the causes of the eruptions are still in debate, whether trigerred by the drilling or pressurised fluid reactivated by the quake. However the objectives of this paper is to discuss mainly on the geotechnical aspects of the mud eruption which spread in larger area until today. In the early days of eruption, as much as 150,000 cubic meters discharge per day was reported, although presently only less than 5000 cubic meters of the discharge is estimated. Due to unknown characteristics of the mud, dykes were constructed to contain the mud and the areas being much larger to reach 450 hectares in 2006 and becoming larger in 2007. The location of the disaster is just in the middle of the town of Porong in the district of Sidoardjo, where the Surabaya International airport is located and has block the major arterial roads from north to south of east Java. The soil condition of the site is deep soft clays which causes instability of the dykes. Some dyke failures occured which endangered the residential areas due to the flow of the mud. This paper desscribe the characterics of the soil conditions from a number of drillings and CPTu conducted by the author for design of the replacement of the arterial road, west of the site. The paper discuss the geotechnical problems of land subsidence in large areas and differential settlement that causes damages of the infrastructures, including the roads, gas pipes, railways, the bridges and the buildings. The mud has been discharged through the Porong river, and the sedimentation is being part of the problems.