After the hurricane - rebuilding New Orleans

Jan 19, 2011

In the aftermath of Hurricane Katrina, more stringent requirements resulted in the innovative use of Trenchless Technology for the installation of underground infrastructure. Here we learn about a successful project involving two crossings near levees.

Think of levees and you think of the catastrophic consequences of their failure when Hurricane Katrina came ashore and rocked New Orleans in August 2005. Over four years have passed since more than 80 per cent of metro New Orleans was left underwater when 53 of the levees protecting the city failed. But while the city has long since picked up the pieces and returned to its vibrant self, the message from the disaster has remained clear: bolstering and preserving the surrounding levee system is of the highest priority.
The images captured in the aftermath of Hurricane Katrina resonate with people around the world. For the underground construction industry, those disastrous results left a lasting impression, forever changing the methods and procedures associated with crossing a levee.
Michels Directional Crossings, a division of Brownsville, Wisconsin-based Michels Corporation, recently dealt with this firsthand after being awarded a contract by Chevron for work near New Orleans that began in September 2009. Michels signed on to complete two separate crossings within two miles of each other, both running beneath the Mississippi River and the extremely important protective levee system. The first crossing was the 20-inch Fourchon Pipeline, which consisted of 5,087 feet of steel pipe running through silts, sands and clay. The second crossing, the 4,708 foot Buras Bundle, ran through the same soil conditions and consisted of one 12 inch and one 4 inch steel pipe.
Engineering challenges
In the aftermath of Hurricane Katrina, the US Army Corps of Engineers (USACE) adopted more stringent requirements for construction around levees in hopes of better preserving their protective qualities. For Michels and Chevron, this meant meeting the USACE-established “Guidelines for Installing Pipeline by Nearsurface Directional Drilling under Levees,” which required that: “…the entry or exit points, when located land-side of a levee, should be set back sufficiently from the land side toe of the levee such that (a) the pipeline reaches its horizontal level (max depth), and/or (b) the pipeline contacts the substratum sands or some other significant horizon, at least 300-feet land side of the levee toe.”
To discuss the plans to meet these requirements, Chevron requested that Michels meet directly with the USACE in New Orleans several months prior to the project start date. Acting as a third-party engineer for Chevron, Geo-Engineers provided Annular Pressure Curve data based on representative soils and proposed drill geometry, which are just a few variables used for estimating hydraulic fracture potential. With this data, Geo-Engineers recommended that downhole mud pressure be limited to 92.7 psi in order to provide the required 1.5 safety factor against fracture within 300 feet on either side of the levee toe (critical monitoring zone).
Armed with this information, Michels developed and presented a comprehensive drill plan that reflected many innovative mitigative measures to reduce annular pressure. While this consisted of many specialised tactics, one particular method involved performing a pilot hole intersect just beyond the 700 foot long critical levee monitoring zone to reduce downhole pressures. Annular Pressure Monitoring was also conducted through this zone during both pilot hole drilling and reaming operations, and the depth of cover beneath the levee was also maximised to minimise fracture potential. The established target intersect zone was 1,800 to 2,200 feet from the levee side entry point.
Construction challenges
Serving as project manager for Chevron, Ralph Radomski oversaw the drilling, pipe stringing and marine operations conducted by the team of contractors. To support Michels’ drilling operations, Chevron hired a local contractor, Sunland, who are familiar with directional drilling procedures and have extensive experience in local marine construction. Sunland performed pipe string-out and welding operations for both crossings, and also provided marine support for the HDD operations. This included barging Michels’ resources to the exit sides and excavating a temporary false ditch for floating the pipe through a marsh area before finding suitable water to float the remaining section.
The first section of product pipe was floated into the false ditch up to the main canal, and the remaining pipe string was staged in a tributary on the other side of the canal, readied for attachment to the first string. Both pipe strings were sunk to the bottom and tied off for protection of the coating. Once pullback operations were initiated, the main canal was blocked off and the two pieces were dewatered and welded into one string. They were then floated on top of the water for the duration of pullback.
With the pieces in place and Tom Breunig and Ray Viator overseeing the project as managers for Michels, Michels Project Manager Louis Barber and drillers Paul Krings, Jeff Nehmer and Cale Mullenix went to work. The 20 inch crossing was conducted first, with the pilot hole started in late September. During vital drilling operations, the flood stage for the Mississippi River reached critical levels above eleven feet, which was the established flood level at the location. Because of this, the USACE criteria required Michels to shut down all drilling operations underneath the levee on 21 October. Hurricane Ida added more water to the mess when it bullied its way ashore on 10 November, and drilling operations were unable to continue until 23 November.
The brackish water carried from the Gulf of Mexico flooded the drill site equipment and washed out the access roads. To make matters worse, the floodwaters also brought in an abundance of dangerous reptiles, including snakes. Prior to re-mobilisation of the entire crew, it took a full week for mechanics to change out oil, fuel, filters and electric motors for all engines onsite, and for repairs to be made to the access roads.
Once the repairs and maintenance were complete, however, work on the crossing went off without a hitch. The crossing was designed to be 190 feet deep at the levee and 68 feet deep at the lowest point of the Mississippi River, and it was executed to perfection by the two drill rigs performing the pilot hole intersect. The crossing, which Michels monitored for annular pressure throughout pilot hole drilling and reaming operations, was completed by mid-December.
With that difficult stretch out of the way, Michels began drilling for the 12 inch and 4 inch bundled crossing in the first week of January. With the co-operation of the weather this time around, drilling and reaming operations endured only minor difficulties in maintaining the targeted pressure beneath the levee. This was mitigated by adding casing and thinning out drill fluids at various stages of the operation.
Once pressure was reduced to acceptable levels, Michels was able to successfully complete the drilling and reaming operations for the bundle, which was 180 feet deep at the levee and 60 feet deep at the lowest point of the Mississippi River. However, during pipe pullback, it was discovered that a portion of the 4 inch pipe was bent and in need of repairs. Pullback operations were temporarily delayed while the repair was made. Once repairs were made and X-ray, testing and coating was conducted, pullback on the crossing was complete by the end of January.
With the devastation wrought by Hurricane Katrina still fresh in many minds, any work on any levee near New Orleans is a sensitive endeavour with a lot of eyes watching. But thanks to close monitoring and the implementation of specialised pressure reducing methods, Michels was able to successfully install both crossings within the parameters set forth by the USACE and protect the levee – and therefore the city that has been billed as “The Big Easy” – from any adverse impacts.
>> This article is presented with permission of Trenchless International / Great Southern Press Pty Ltd. <<

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