Murphy Oil Clean Fuels Project, Meraux, Louisiana: A Case Study of Design Build Foundations
Many challenges faced the design team when considering the foundations for the proposed Clean Fuels project at the Murphy Oil plant in Meraux, Louisiana. Exacting load-deflection criteria, deep normally consolidated soft soils, residential neighbors, and a tight schedule required a number of foundations options to be evaluated.
ABB Lummus Global worked with Morris-Shea Bridge Company to look at variety of options, including H-piles, pipe piles, precast piles and Augercast piles, before deciding on the DeWaal pile as the most cost effective, and environmentally sensitive pile system, with the advantage of considerable schedule efficiencies. Extensive load testing, quality assurance and rig instrumentation resulted in a successful project for all parties.
The Clean Fuels project at Murphy Oil’s Meraux, Louisiana facility comprises a series of process structures, hydrocrackers, heaters, cooling towers, reactors, flare drums and pipe racks. Static and dynamic load analysis disclosed a relatively complex range of compression, tension and shear load conditions on foundation piles.
The site specific geotechnical study comprised a total of 3 Standard Penetration Test (SPT) Borings and 2 Cone Penetration Tests (CPT’s). Typically fill soils, comprising very loose to loose silty sand and medium stiff clay and sandy clay were encountered in the upper 6 feet. Very soft to soft clay and silty clay underlie the fill to depths of approximately 25 feet. Loose silty sand, clayey sand and clayey silt generally occur between 25 to 40 feet, although occasionally appeared to continue deeper. Medium stiff silty clay and clay interbedded with loose silty sand and sandy clay were disclosed to the top of the Pleistocene contact at 78 feet. Silt and clay layers with shear strengths of less than 500 psf were disclosed over much of the site.
The Pleistocene deposits generally comprised interbedded sands and clays and extend to boring termination depths at 120 feet below grade.
Foundation options in the geotechnical report included H-piles, pipe piles, precast piles and Augercast piles.
After reviewing cost, schedule and technical issues, ABB Lummas Global considered Morris-Shea’s DeWaal pile option to be superior in all three areas.
To supplement the very sparse existing geotechnical information, Morris-Shea performed an extensive program of cone testing to allow a better evaluation of the soft soils, and variability of the intermittent sand layers.
A total of 54 cone soundings were performed across the site. Capacity analyses were performed at each location, and the depth required to achieve the design capacities of 25 and 40 tons profiled across the site.
Measurement of cone tip resistance, sleeve friction, pore water pressure, and friction ratio allowed classification of soil type, as shown above. The cone data was also used to accurately predict pile capacity. As shown above, high pore pressures were evident in the fine grained soils. The quality and quantity of Morris-Shea’s CPT data allowed a comprehensive understanding of subsurface soil variability.
To assess excess pore pressure dissipation with time, a series of dissipation tests were performed, as shown above. This data enables assessment of wait times prior to static load testing to ensure long term capacities are being determined. Pore pressure dissipation testing also helps set production pile installation spacing.
A series of cross sections across the site were compiled to allow typical soil profiles to be established and used for capacity modeling. Such characterization is not possible with conventional SPT borings due to cost, time and poor data quality.
Morris-Shea uses a variation on the LCPC pile capacity calculations developed by Bustamonte an Gianesalli. Coefficients used to scale tip resistance and skin friction are based on the Robertson soil classification system. Coefficients have been refined by calibrating our model to extensive load test data over the past 10 years. Application of this pile capacity model to an accurately mapped subsurface through the use of CPT allows us to confidently predict pile capacity, and recognize areas that may fall outside of the pile design specifications.
Test Pile Program:
A total of six compression, two tension and two lateral static load tests were performed to optimize pile length diameter and reinforcement for the various load conditions. Strain gauge instrumentation was used to determine unit shaft and end bearing in the various soil strata.
A total of approximately 1730 piles were installed at a rate of approximately 25 to 42 piles per day using one rig.
A Hitachi base machine with a high torque mast and hydraulic turntable was used for pile installation. Over most of the site, mats were required to provide a safe work platform. In some structures, high lateral loads required the use of battered piles.
The use of rig instrumentation to monitor drilling parameters such as depth, torque, drill rate, and pull-down force allowed verification of soil stratigraphy and adequate penetration in to sand bearing layers. In addition, measurement of concrete volume pumped, together with field verification of sufficient concrete head during tool withdrawal helped ensure no integrity issues.
Approximately 1% of production piles were subject to high strain dynamic load testing using a drop weight and Pile Driving Analyzer.
In addition, approximately 20% of production piles were integrity tested using PIT equipment. No integrity defects were disclosed.
Production piles were dipped to cut off elevation, up to 5 feet below grade. The vibration-less installation process allowed concrete work to follow closely behind pile installation, which when combined with the high pile production resulted in two months of schedule acceleration.
The use of the low-noise, vibration-less DeWaal piles also reduced the impact to adjacent residential areas. In addition, the elimination of pile deliveries avoided the potential for traffic congestion in the adjacent roads as well as eliminating significant on-site stockpile concerns.
The use of DeWaal piles resulted in a cost effective foundation solution at the Murphy Oil Clean Fuels project. A comprehensive program of supplemental CPT soundings, load tests, and production piling quality assurance resulted in a successful project while providing significant cost savings to the Owner.