Helston, Cornwall, U.K., April 9, 2002 -- Seacore Ltd. and joint venture partner Fugro West Inc. of California have successfully completed an $800,000 site investigation on Lake Michigan near Chicago, Illinois.
The environmentally stringent geotechnical marine site investigation was performed to help evaluate the proposed Jardine fresh water intake tunnel project for the City of Chicago's Department of Water.
The new tunnel, designed by consulting engineer Montgomery Watson Harza, is currently conceived as a bedrock TBM bore within carbonate bedrock extending beneath Lake Michigan.
The alignment investigation area extends up to 9.5 miles beyond the Chicago shoreline. Ancillary near-shore facilities may include additional filled land at the shoreline, new head house intake and pumping facilities, and large diameter vertical intake and construction access shafts.
Working from Seacore's Skate III jack-up, 8 boreholes were drilled to depths of up to 410 feet to evaluate the subsurface conditions along the proposed tunnel alignment. Three of the boreholes were performed at an angle of 25 degrees from vertical to assess additional bedrock properties.
The Geobor-S triple wireline system was used to penetrate up to 69 feet of lacustrian clays, sand, and glacial till soil materials overlying the dolomite bedrock at the locations explored. Geobor-S core recovery averaged about 83%. The underlying dolomite bedrock, along the tunnel alignment, was cored to depth using the HQ triple tube wireline system, which achieved excellent average core recovery of about 95%.
Fifteen boreholes were also drilled to appraise the subsurface conditions in the vicinity of the proposed cofferdam and head house facilities. The holes were drilled to depths of about 128 feet using Geobor-S and NQ coring systems. Extensive soil sampling was performed during the drilling process using a variety of methods. These included piston samples in the softer lake sediments, pushed Shelby tubes (using the Geobor-S), and driven standard penetration test (SPT) samples in the harder clays and dense sands.
Bedrock permeability/fluid migration was evaluated using a combination of single and double packer tests performed at specified depth intervals. A total of 117 packer tests were performed for the project. The single packer tests were typically performed at about 49-foot intervals during borehole advancement, while the double packer tests, at about 23-foot intervals, were performed after total depth was achieved. Following the packer tests, borehole deviation and inclination were recorded with a Tropari downhole survey tool in the deeper boreholes.
Drilling parameters, such as mud pressure, torque, depth, penetration rate, and rpm were recorded during drilling using the Jean Lutz system. This system, while developed to monitor equipment parameters and performance, has been proven to be very beneficial as a tool to aide the evaluation of the subsurface conditions.
Seacore's versatile Skate III jack-up was ideally suited to the Chicago project. The jack-up, designed and built by Seacore for rapid assembly and containerised transportation, safely operates in water depths up to 98 feet with a jacking capacity of 100 tons at elevations of 105 feet above seabed level. All pontoons, components and associated equipment are designed around the container freight concept. The pontoons double as containers and house the jack-up legs, power units and all other ancillary equipment, allowing cost-effective international transportation by road, rail or container ship. A Skate III jack-up can be assembled and commissioned within 4 days of arriving on location.
At Chicago several modifications were made to Skate III to ensure the project went smoothly. Lake Michigan waters can be severe at times, with wave heights exceeding 11.5 feet. Due to the jack-up leg penetrations of up to 32.8 feet into the lakebed and water depths of up to 79 feet, the total leg length was increased to 136 feet to ensure a safe working environment. The drill mast was also modified to provide the ability to convert from vertical to angled drilling efficiently, with minimal time and effort.
Strict environmental conditions on Lake Michigan required Seacore to operate a "zero discharge" policy. This was achieved by using an efficient drilling fluid recirculation and separation system designed by Seacore. Drill cuttings were removed from the drilling fluid during recirculation, containerised onboard Skate III, and later removed and properly disposed of onshore by a local authorized waste contractor. Seacore operated 24 hours a day on two 12-hour shifts. A 20-foot RIB, with twin 75hp outboard engines, provided quick and efficient crew changes and doubled as a safety boat. The outer-most borehole was 9.5 miles from shore.
"We at MWH have been favourably impressed by Seacore and Fugro's drilling operation," says MWH Energy & Infrastructure Senior Vice President James E. Lindell. "Their jack-up rig, Skate III, was well suited for work in the 23 to 82 foot water depths and 11.5 foot waves and exploration of our proposed tunnel alignment in Lake Michigan. Coring equipment for soil and rock was exceptional and was used successfully in vertical and inclined holes to depths of 410 feet. The drill crews and supervisory personnel, from site manager to driller's helpers, were all professional, helpful, and enthusiastic for the assignment. We have found Seacore and Fugro to be top line firms and have no hesitation in recommending them for offshore geotechnical work."
Seacore, based in Cornwall, England is one Europe's largest marine construction and geotechnical contractors. Fugro West is a member of the worldwide Fugro group, a leading geotechnical and survey services provider for onshore and offshore projects.
For further information visit the companies web sites at www.seacore.co.uk or www.fugro.com.
