MICROTUNNELING

Definition and History

Microtunneling is a process that uses a remotely controlled Microtunnel Boring Machine (MTBM) combined with the pipe jacking technique to directly install product pipelines underground in a single pass. This process avoids the need to have long stretches of open trench for pipe laying, which causes extreme disruption to the community. In the U.S., microtunneling has been used to install pipe from twelve inches to twelve feet in diameter. Therefore, the definition for microtunneling in the U.S. does not necessarily include size. Microtunneling has evolved in the US to describe a tunneling process where the workforce does not routinely work in the tunnel. Microtunneling is currently the most accurate pipeline installation method. Line and grade tolerances of one inch are the microtunneling industry standard. This can be extremely important when trying to install a new pipeline in an area where a maze of underground utility lines already exists.

Microtunneling was developed by the Japanese in the early 1970’s to replace open sewers in urban areas with underground gravity sewers. The first microtunneling project in the U.S. occurred in south Florida in 1984.This was a 600 foot crossing with 72" pipe under I 95 and the FEC Railroad. Although originally designed for gravity sewer construction, microtunneling installations include underground crossings of highways, railroads, runways, rivers, and environmentally sensitive areas for a variety of utilities. This process has also been used to install plant intakes and outfalls. Microtunneling is also used in the pipe arch technique of supporting large underground openings with an arch or roof made up of small tunnels.

Below: 96" Iseki Crunchingmole entering the receiving shaft. This microtunnel was 490 LF under the Florida Turnpike at SW 104th Street in Miami, Florida.

Equipment:

A typical microtunnel equipment spread consists of a MTBM matched to the expected subsurface conditions and the pipe diameter to be installed; a hydraulic jacking system to pipejack the pipeline; a closed loop slurry system to remove the excavated tunnel spoil; a slurry cleaning system to remove the spoil from the slurry water; a lubrication system to lubricate the exterior of the pipeline during installation; a guidance system to provide installation accuracy; an electrical supply and distribution system to power all of the above equipment. Top side equipment used to support the tunneling operation usually includes a crane; pile driving and dewatering equipment for shaft construction; backhoe and front end loader for shaft excavation and spoil handling; and truck transport for equipment moves.

In 1992, company owner Dwayne Huxted, traveled to Europe to speak directly with microtunnel equipment owners and manufacturers. " The unique subsurface conditions here in Florida are ideal for microtunneling," said Mr. Huxted. "After assessing the available microtunnel equipment, I chose the Iseki Unclemole™ . In my opinion, this is the best microtunnel boring machine on the market". We now own two complete microtunnel equipment spreads which enable us to install pipe from 30" to 120" in diameter. Our first microtunnel job was an 88" steel casing installation crossing the Palmetto Expressway in Miami. Although most contractors get their first microtunneling experience installing small diameter pipe, our initial experiences were with large diameter pipe." This machinery can efficiently push steel casing, fiberglass, concrete, clay, or composite jacking pipe. We can provide a turn-key project from installation of jacking/receiving shafts to installation of the tunnel (including carrier pipe if required). Huxted Tunneling is equipped to solid sheet or shore shafts as necessary.

Pictured Above: 88" Jacking Pit and Spacer