This is the excavation and installation of tunnel supports at the tunnel face by miners. Hand tunneling allows for any size, length, and shape of tunnel. While the method may seem dated the tools, engineering, and tunnel support materials are all 21st century. Hand tunneling is effective in soils above and below the water table.
It is generally the slowest and more costly tunneling method but it is the least risk option to the client when potential unknowns are a factor. Hand tunneling allows for flexibility when faced with an unknown condition such as buried utilities or difficult soil conditions. The miners use pneumatic hand tools to excavate the soil and then install wood and/or steel supports. Hand tunnels can be square, circular, elliptical, or horseshoe in shape. Soil removal is done using rail cars or track loaders.
Hand tunneling can deal with cobbles, boulders, and hard rock, quicker and more efficiently than other modern tunnel boring machines. Even with all the new technology offered sometimes it is most cost efficient for us to get in and get our hands dirty.
Tunnel Bore Machine
Tunnel Boring Machines (TBM) are used as an alternative to drilling and blasting methods and hand tunneling. They only minimally disturb the surrounding ground and effectively produce a smooth tunnel wall, which reduces the cost of lining the tunnel and makes them optimal for urbanized areas.
They are used for circular cross section tunnels through a variety of soil and rock and also used in micro tunneling. They can move through anything from sand to hard rock. HDD Willco uses these for tunnels with a 48” to 72” diameter.
Tunnel boring machines are cheaper than other methods because of their efficiency and shorter completion times. Tunnel boring machines consist of the revolving cutting wheel, called a cutter head, followed by the main bearing, a thrust system and trailing support mechanisms. There are Hard Rock TBMs and Soft Ground TBMs.
There are two types of Hard Rock TBMs, either shielded or open-type. There are three main types of Soft Ground TBMs: Earth Pressure Balance Machines (EPB), Slurry Shield (SS), and Open Face Type. The type of machine used depends on the geology of the project area, the amount ground water, and other factors.
This is a technique used to construct small tunnels that do not allow for an operator to be in the tunnel itself and the Micro-Tunneling Bore Machine (MTBM) must be operated remotely. MTBMs are similar to TBMs just on a smaller scale. HDD Willco uses these for a tunnel with a diameter between 24” and 54”.
Usually the machine is operated from a control room on the surface. The operator is given constant information about the machine’s location, orientation, and hydraulic devices via computer console or CCTV camera. The machine starts at the entry eye and pipes are shoved from behind the machine. The soil is infused with slurry at the face of the tunnel which then enter slurry inlet holes in the MTBMs crushing cone for circulation to and from a separation plant through a closed system.
This process is repeated until the MTBM reaches the reception shaft. The speed at which the machine moves is determined by the speed at which the pipe is inserted by the jacking frame. These machines can accurately install pipe in almost any kind of soil conditions. They are also capable of counter-balancing earth and hydrostatic pressures independently.