Middlebury Micro Tunnel Launch, Shaft, Drape

Scope of Work

Drill, blast, and stabilize a tunnel boring machine launch shaft. This included a 40-foot diameter x 37 feet deep rock excavation in a congested downtown city setting. The work was executed in a repeated sequence of line drilling, blasting, and slope stabilization. Bottom was made after the sequence was repeated 5 times (and ahead of schedule). After each sequence the vertical rock faces were inspected and stabilized by means of scaling, rock bolting, and high strength steel mesh to protect the equipment and crew.

Challenges

On this very unique project, MD&B was working in a 60-foot diameter "postage stamp" in downtown Middlebury, with an active railroad 10 feet away, pedestrian traffic 15 feet away, an active roadway and driveways within 20 feet, and buildings as close as 48 feet. Drilling and blasting occurred in an extremely confined hole 40 feet wide x almost 40 feet deep below the existing road level. All equipment and blasting mats had to be flown in and lowered with a 100-ton crane. Planning for this was on an hourly basis. The project necessitated very thorough daily planning with all parties and in the community, communicating with a Railroad liaison daily, and holding daily safety meetings with the contractor to secure the work areas. Utilization of fall protection, air circulation pumps and water mists were essential.

Outcome

This very difficult project was completed safely and successfully within all tolerances, specifications, and schedules. Personnel safety and awareness was maintained throughout the project. There was no breach with Railroad traffic, no property damage with vehicles or equipment, and no personnel injuries or exposure to unsafe air quality.

Customer Comment

Kubricky Construction has been under contract with Maine Drilling & Blasting for our Middlebury EWP3(2) contract in Middlebury, VT. Our project consists of construction of a launching pit for a Small Boring Unit for construction of new drainage system. The Launch Pit is a 40' diameter x 37' deep hole that was blasted into the existing rock in downtown Middlebury. The launch pit location is in extreme close proximity to existing structures including the Bank of Middlebury, the Middlebury Post Office and the St. Stephens Episcopal Church that was built in 1827. The face of the closest building was only 48' away from perimeter of the shaft. The rock was removed over the course of 18 blasts in four vertical lifts that were about 9' tall each. The location for the perimeter of the 40' diameter hole was extremely accurate, within 6". MD&B installed 17 rock dowels on the vertical face as we proceeded with our blasting to the finish grade. Once the blasting was completed, MD&B then installed more than 4,500 SF of rock netting around the perimeter for safety protection. The MD&B team was extremely safety conscious and very professional to deal with. Their hard work and attention to detail made this project a success for the traveling public, KCC and MD&B. We look forward to working with you and your team again in the near future for another successful project."

Michael Martin | Project Manager, Kubricky Construction Corp.