REDUCING RISK AND UNCERTAINTY IN CSO TUNNEL CONSTRUCTION

1. Accurate Geotechnical Data

A primary risk factor in tunnel construction is inaccurate geotechnical data. This data is gathered during the planning stages of the project and later refined during the design stage. Information is gathered by drilling borings; deep, vertical and inclined, into the bedrock to gather soil and rock samples that are utilized in laboratory testing while also creating an opportunity to perform down-hole in-situ testing to aid in obtaining the following critical data:

  • The consistency of the soil and rock strata to determine the optimal vertical and horizontal locations for tunnel alignment
  • By drilling inclined and vertical borings, rock fractures themselves as well as the rock fracture orientation can be defined
  • While soil sampling and rock coring, voids and other inconsistencies in the soil and rock strata can be determined
  • By timing rock core runs during geotechnical drilling, the drilling progress can aid in determining the TBM’s projected production rates
  • Proper core runs provide quality samples to be tested for critical properties more accurately (abrasivity, moduli, drillability, hardness)
  • Performing Hydraulic Conductivity Testing (Packer Testing) determines water movement within the rock
  • Installing both standpipe and/or vibrating wire piezometers records long term seasonal groundwater conditions
  • The major goal of the geotechnical drilling and testing is to gain as much ACCURATE data of the soil, rock and water as possible. The more accurate the data, the less risk the Owner will bear during construction.

Decisions regarding the expenditure of hundreds of millions of dollars are made based on the data gathered by the drilling firm. While the Owner will often spend significant resources in evaluating and selecting the Prime Design Firm, the drilling firm is usually hired for local, political and low cost reasons. This is ill-advised. Most drilling firms do not have the specialized experience needed to perform this work accurately.

SELECTION OF THE DRILLING FIRM SHOULD GET THE SAME LEVEL OF ATTENTION AS SELECTION OF THE PRIME DESIGN FIRM.

2. Highly Specialized Experience

7NT has highly specialized experience in conducting deep borings related to CSO projects. We have developed proprietary systems and procedures to accurately gather the data specified above. Key elements of our experience are as follows:

Over 500 deep borings since 2008 in diverse locations & geological conditions around the country.

Successful investigations on major tunneling projects in Indianapolis, Ft. Wayne, Louisville, St. Louis, Cleveland, Cincinnati and Hartford.

Specialized equipment and trained personnel specifically geared towards deep CSO projects.

Deep tunnel CSO projects are high risk projects as 9-figure decisions are often made based on limited geotechnical investigation. Even small inaccuracies in this data have resulted in change orders in the tens of millions of dollars.

Retaining 7NT to perform the drilling is a low/no cost way of insuring against this risk.

7NT’s track record on CSO tunneling projects includes the following:

DRTC project in Indianapolis set world records for mining in a day, a week and a month.

DRTC project in Indianapolis is $80 million under budget, while the remaining 18 miles of the Indianapolis system are currently projected to come in $70 million under engineer’s estimate.

South Hartford Conveyance Tunnel had multiple bids come in $30 million to $50 million under engineer’s estimate.

3. No Cost Insurance

Deep tunnel CSO projects are high risk projects as 9-figure decisions are often made based on limited geotechnical investigation. Even small inaccuracies in this data have resulted in change orders in the tens of millions of dollars.

Retaining 7NT to perform the drilling is a low/no cost way of insuring against this risk.

For little or no additional cost, the owner can hire the best drilling firm and reduce the substantial risk associated with inaccurate data gathering.

7NT’s track record on CSO tunneling projects includes the following:

  • DRTC project in Indianapolis set world records for mining in a day, a week and a month.
  • DRTC project in Indianapolis is $80 million under budget, while the remaining 18 miles of the Indianapolis system are currently projected to come in $70 million under engineer’s estimate.
  • South Hartford Conveyance Tunnel had multiple bids come in $30 million to $50 million under engineer’s estimate.

Drilling Equipment

Equipment is another area that distinguishes 7NT from other drilling firms.  The equipment is the means by which the experienced and knowledgeable personnel carry out their responsibilities effectively and efficiently.  7NT has made significant investments in its equipment for our personnel to be the most effective.  A condensed listing of the 7NT owned and leased equipment includes the following:

Drill Rigs:

  • (2) CME 550 X ATV w/ angle capacity
  • CME 750 ATV w/ angle capacity
  • CME 75 Truck Mount w/ angle capacity
  • Mobile B58 Truck Mount

Support Trucks:

  • GMC C-7500 Water Truck
  • Chevy 3500 1 Ton Box Truck
  • (5) 2015 Dodge 3500 Pick Up
  • 2016 GMC 3500 HD
  • (10) Various smaller support trucks

Barge:

  • 36’ x 20’ Spud Barge and Support Boat

Tools:

  • 100’ of 2.25” HSA, 300’ of 3.25” HSA
  • 400’ of 3.25” HSA
  • 600’ of 4.25” HSA
  • 150’ of 6.25” HSA
  • 200’ of 3” NW Casing
  • 1,100’ of 4” HW Casing
  • 6 Casing Advancers
  • 2 10’ NW Core Barrels
  • 4 10’ NQ3 Core Barrels (Wireline)
  • 9 10’ HQ3 Core Barrels (Wireline)
  • 2 5’ PQ Core Barrels (Wireline)
  • 8 HQ3 Double Packer Systems w/ Transducers
  • 3 NQ3 Double Packer Systems w/ Transducers
  • 8 Deck Over Trailers
  • 4 Troll Systems

Drilling Capabilities

  • Drilling to 400’ on land and in water
  • Packer Testing
  • Rock coring
  • Hollow stem auger drilling
  • Solid flight auger drilling
  • Mud rotary drilling
  • Air rotary drilling
  • Rock core drilling/extraction
  • SPT soil sampling
  • Shelby tube sampling
  • Boring logs
  • Field Classification (ASTM D2488)
  • Hand penetrometer testing
  • Inclinometer casing installation
  • Test pit excavation

7NT owns and operates a fleet of 5 rigs that are all newer and well maintained.  This minimizes mechanical breakdowns and delays.

Rigs are equipped with fluted Kelly bars.  This allows for using up to 15’ long casing and core barrels for higher quality sampling and faster production.

Rigs are equipped with calibrated automatic hammers for accurate SPT counts.

For deep drilling, wireline split inner triple barrels are used to maximize recovery and mechanical breaks in the rock core sample.

The core barrels are manufactured by Boart Longyear.

A double packer system is used with a vibrating wire transducer for water pressure testing.  This allows for actual readings within the 10-foot section from the transducer; the calculated values from the surface gauges are used as backup confirmation.

Ability to install nested standpipe and vibrating wire piezometers.  A grout mixer with moyno pump is also used during the piezometer installation that allows for accurate quantities and correct mix proportions/slump to be used.

Use a mole system for slug testing that contain a variety of transducers allowing pressures up to 1,500 psi ranges.  Furthermore, software for the slug testing is continually upgraded.

The support trucks are equipped with trailer systems that have been specifically designed and stocked by 7NT drilling crews for deep drilling work.  This allows for all equipment to be present at the drill site and organized in a manner to maintain high quality and increased production.