Marine Geotechnical & Geophysical Survey in Complex Geological Formations
Kedar C Birid1
1 Geotechnical Engineer
Resumo
The Western Freeway Sea Link (WFSL-Phase IIA) is an offshore bridge project connecting two major hubs from Worli to Haji Ali, running parallel to the western coastline of Mumbai, India. This bridge (shown in white line on the south) is an extension of the existing offshore bridge from Bandra to Worli. The main bridge will be connected to the mainland using two connector bridges at the Worli end and the Haji Ali end. The length of the proposed bridge is 5.5 km with eight lane carriageway connecting two areas viz. Worli at north and Haji Ali at south. Geotechnical and geophysical surveys were carried out along the proposed bridge alignment as a part of the detailed investigation program to gather complete information about sub soil stratification and seabed features. Detailed marine geotechnical investigation was carried out offshore of Mumbai (Bombay) coast to assess the foundation design parameters for the offshore bridge project. 52 boreholes were drilled using two jack up barges along the proposed bridge alignment and field & laboratory testing program was implemented at selected locations and on selected soil and rock samples. Geophysical survey using side scan sonar, sub bottom profiler and magnetometer was also carried out to reveal continuous seabed features along the bridge alignment. The results obtained through this study were analyzed and interpreted to arrive at foundation design parameters. This paper presents the details about marine geotechnical and geophysical investigation programs, thus carried out, interpreted field and lab test results and the subsurface material properties. The major challenge was carrying out the geotechnical and geophysical work within short time and in shallow water which was conducted using wireline drilling and special barge positioning technique in a planned manner. The decision to carry out geophysical survey was beneficial and provided the supplementary information on seabed stratification between the boreholes and buried objects along the proposed bridge alignment.
Palavras-chave: marine geotechnical investigation; jack up barge ; geophysical survey; rock; soil