The Brunei Temburong Bridge (BTB) is an iconic project connecting Brunei Muara and Temburong districts in Brunei over a length of 30 km. The bridge crosses from Brunei Muara across Brunei Bay to Temburong. A key aim of the BTB project was the development of Temburong district, being prior the more isolated district, because of not having a direct land link to the other districts. This study reviews the geology of soil materials and sedimentary rocks along the bridge alignment based on 164 boreholes drilled for ground investigation. Standard Penetration Test, Rock Quality Designation and Fracture Index data were evaluated to interpret soil materials and sedimentary rocks along the alignment. Borehole data was used to generate lithological cross sections along the alignment providing an overview of geology. The geology encountered is extremely heterogenous, with low strength sediments encountered at depth of up to 80 m and more e.g., at the Temburong section. Rock quality designation vs. Fracture Index did not show a strong correlation likely due to the extreme heterogeneity in particular for the Brunei Bay and Temburong sections. The study demonstrates the importance of a closely spaced investigative drilling and sampling program for major construction programs which was successfully achieved for this project. Other investigative techniques such as geophysical methods could be highly useful for future projects. Considering economic and environmental reasons these techniques could be very useful to map the top of the bedrock even under highly heterogeneous ground conditions.

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