Assessing the applicability of sub-bottom profiling towards identification of the bedrock level - a case study in Colombo harbor, Sri Lanka

Abstract

Numerous studies have been conducted on seabed classification using various methods such as echo sounders, side scan sonars, and sub-bottom profilers. Identification of the bedrock level underneath the seafloor is crucial, especially for safe and effective underwater constructions. The bedrock is stratified into layers, due to differential weathering. In order to accurately establish whether the reflection signatures produced from sub-bottom profiling match the fresh or weathered rock layer in the bedrock, an accurate interpretation of the signatures is necessary. This study employed a boomer profiler as the seismic sound source with a frequency of 1kHz to survey the west side of Colombo Port in Sri Lanka. Sub-bottom profiling data were interpreted using the SonarWiz software based on the principle of the trends of the reflected signal. The interpretation mainly focused on identifying the bedrock layer from the sub-bottom profile data and it includes 8 survey lines. 12 Borehole data was used to validate the interpreted results, along with the Standard Penetration Test (SPT) values. After conducting processing and validation procedures, the researchers concluded that the bedrock reflection signature was mostly derived from the sediment layers with SPT-50 level which has high stiffness in this study.