The partial removal of an existing railroad tunnel and subsequent raising of pavement on North Main allowed pavement on Burnett Street to be lowered, meeting the revised elevation of North Main Street. This feat allowed traffic to proceed through the revised alignment and mass transit to proceed to the METRO Park & Ride without taking a circuitous route via a u-turn, saving transit time and improving operational efficiency of METRO transit system.
Avoiding damage to and stabilizing the section of tunnel that would remain was a chief concern, as no record drawings existed to assist in formulating the construction phase. During construction, it was discovered the tunnel walls were made of stair-stepped massive non-reinforced concrete with a seven foot wide base narrowing to a thickness of two feet near the tunnel ceiling. The walls were topped with a three foot thick concrete slab reinforced with two foot I-beams separated by 12″. Conventional concrete saw-cutting and jackhammering methods were not an option for the demolition phase of the tunnel improvement project. Instead, a high speed diamond wire cable saw used for marble mining was employed to cut the tunnel structure. This method resulted in a clean tunnel cut with limited vibration. To read the entire article, please click here.