A Geo-Physical Investigation into the Colombo Port Seabed using Sub Bottom Profiler

Abstract

Traditionally, seabed layers were determined by using conventional mechanical methods like boreholing, which retrieved the strata at a single point at one time. Later it was developed to various acoustic remote sensing techniques which can determine layers robustly, with less cost. Sub Bottom Profiler (SBP) is an effective method used to identify and describe the layers of sediments under the seabottom. SBP is almost similar to an echo sounder, but portion of the sound pulse is penetrating beneath the seafloor and reflected off of the strata layers. These refracted acoustic signals will show any sort of density disturbance. Sub bottom systems have been used to detect and measure the thickness of sediment deposits, identify buried objects, and define the bedrock layer of a basin. Transducer frequency and pulse length are the key aspects on the SBP system performance. Absorption losses are proportional to the transmitting frequency. Long sound pulse lengths required more energy and resulting deeper penetration but decreasing the system resolution. The Stratabox HD is a pinger type SBP having the capability of detecting the soft sediment layers in high resolution. The objective of this study was to carry out a geophysical investigation of the Colombo Port using the SBP. Data was collected at the Jaya Container Terminal (JCT) basin. Sub-bottom fence diagrams were generated with Hypack software and results were validated using the existing borehole samples. The initial sub bottom soft layers were closely matched with the borehole sample data.