Tengizchevroil (TCO), a joint venture partnership of Chevron, ExxonMobil, KazMunaiGas and LukArco, decided to upgrade and expand the Crude Tank Farm (CTF) at its Tengiz field facilities. The Tengiz field is one of the world’s 10 largest oilfields. The existing tank farm is largely composed of decades-old smaller tanks built during the former Soviet era. The proposed CTF facilities consisted of two very large crude oil storage tanks, the largest of which has a diameter of 200 feet and is 60 feet high, two smaller crude tanks, a firewater tank, and associated facilities such as manifolds, pump stations, and piping. The site’s major geotechnical challenge was the 10- to 15-foot thick shallow layer of soft, compressible marine deposits that are prone to large settlement under applied load. TCO’s goal is to significantly expand its crude exports from the Caspian Sea area by creating a larger, more reliable crude oil storage complex that can be constructed with local expertise.
Geosyntec’s Scope of Work
Geosyntec was selected to develop recommendations for foundation design of the CTF structures. Because of TCO’s commitment to implementing construction with local expertise in geological settings unique to the country (compressible soft soils near the ground surface), Geosyntec conducted an extensive site reconnaissance as part of the first phase. Our senior geotechnical engineer on site performed an extensive review of existing area-wide subsurface data during meetings with local contractors. Geosyntec provided both oversight of the contractor’s subsurface investigation program and, concurrently, developed conceptual foundation alternatives for large tanks. Geosyntec observed the contractor’s soil mechanics testing laboratory to understand the similarities and differences in soil testing procedures and results between local and Western standards (e.g., ASTM and British Standards). Working with TCO and other stakeholders, Geosyntec developed tank foundation alternatives that included piles, ground improvement/deep soil mixing, and excavate-and-replace approaches. Based on preliminary findings developed during the ongoing geotechnical investigation, the tank foundation alternatives were screened and a soil excavate-and-replace approach was selected. Geosyntec prepared a comprehensive geotechnical engineering report for TCO that included geotechnical design recommendations for foundations and earthwork. Our on-site senior geotechnical engineer worked with the owner’s general civil/structural designer throughout the design process. After the project’s first phase was completed, TCO altered the CTF layout requiring an expanded geotechnical investigation. The combined investigations included 58 soil borings, 100 CPTs, and 23 test pits.
Geosyntec’s on-site presence during the first phase of this project resulted in a comprehensive geotechnical investigation program. The investigation program provided data of sufficient quality that the drilling, sampling, and testing results developed using local practices and standards could be interpreted and applied to Western methods of foundation engineering. Geosyntec’s conceptual engineering designs provided tank foundation alternatives that allowed the client to choose a foundation type that considered local technical, cost, and institutional factors such as the availability of specialized construction equipment and skilled local labor, regulatory approval processes, degree of comfort with ground improvement and construction technologies. Geosyntec’s recommendation of a foundation type and associated design considerations allowed the project to forego the use of expensive pile foundations and minimized the use of expensive pipeline hanger systems. The recommended design met Kazakhstan requirements for settlement performance of large storage tanks, which are generally more conservative than standard Western engineering practice requires. Our ongoing oversight and foundation design recommendations allowed a less costly but still prudent tank foundation type in this geological setting that achieved substantial construction costs savings when compared to previous tanks that have been constructed in Tengiz.