Pipe Jacking & Utility Tunneling
Pipe Jacking & Utility Tunneling can be synonymous, depending on the application. Both processes involve a manned tunnel excavation. Although hand tunneling is often viewed as archaic, it is a very effective way of creating an accurate bore. Operators always have an exact knowledge of the tunnel face geological conditions.
The pipe jacking and utility tunneling techniques have evolved quite a bit from the dawn of hand tunneling. Today, Tunnel Boring Machines have replaced the typical pick and shovel. Sometimes hand excavation is still found to be the best solution to a complicated bore.
Pipe Jacking Description:
One or more workers positioned at the bore face operate jack hammers, picks, and shovels in order to remove tightly packed material. The casing pipe is thrust forward with hydraulic rams located in the launching pit while the laborors work to extract the face. Theoretically, the face of the bore will crumble away as the jacking pipe is thrust forward, minimizing the need for hand tunneling. Spoils are removed in one of two ways.
1. The material is carried out by hand using a wheeled cart system (commonly referred to as a "tunnel buggy").
2. The spoils are directed from the boring face to the invert of the casing where a spoils tube is located. The spoils tube removes the sediment with a flighted auger transporting it to the launching pit.
Utility Tunneling Description:
Utility tunneling differs from pipe jacking in the fact that utility tunneling requires liner plates. Liner plates provide a shield for workers to install the designed utility. The process of utility tunneling involves several steps.
• Workers located at the face of the tunnel remove the encountered material while inside a protective shield.
• As the workers continue to dig, the shield is hydraulically thrust forward from the liner plates behind it.
• When the shield is completely advanced, the hydraulic cylinders are retracted and additional liner plates are installed.
• This process is then repeated for the duration of the bore.
Since the liner plates are installed without being thrust into place, skin friction is then considered to be negligible. This feature keeps the thrusting force fairly constant throughout the bore.
• Soil Conditions – Ground conditions are a very important when choosing either of these methods. In solid rock conditions for example, Aaron Enterprises may be faced with the need to use explosives or blast.
• Lubrication – Occasionally soil conditions require the use of a bentionite mud mixture in order to reduce the skin friction between the casing pipe and the material that surrounds it.
• Grade Control – This aspect becomes critical when tunneling around existing structures. Grade is also crucial when installing certain utilities such as gravity sewer systems.
• Ground Water Conditions – After the excavation of a launching pit, crews often find themselves below the water table. A well point can be installed to control the influx of water.
• Physical Restraints of Setup Area – Different job site constraints may require special attention during mobilization and pit excavation. Restraints at the job site are an important consideration when using any boring method.