Only the minimum amount of ground is removed, and its place is immediately filled by the pipe. Settlement and ground falls need never occur as the shield can be advanced millimetres at a time. Nominal overbreak will occur in rocky grounds.

1. The boom digger handles a wide variety of ground conditions and still allows full access to the face. Obstacles and abandoned services can be carefully removed. A minimum diameter of 1200mm is required to accommodate the boom digger. Tunnel Boring Australia has developed other face cutting methods which can be installed to suit the prevalent ground conditions.

2. The jacking shield provides full safety at the front of the tunnel. Face support can be increased with shelves, hoods or baffles for very soft grounds. Temporary tunnel shoring is not required. Normally the ground is excavated 600mm ahead before the jacks force the cutting edge into the ground. The operator works inside the shield which provides protection at all times, and also supports the ground above - preventing cave-ins.
PLEASE NOTE: We have various face excavation methods depending upon site ground conditions.

3. The steering jacks are controlled by the shield operator to keep the laser target central around the laser beam as the pipes move forward. As shield design and survey techniques improve, the standard accuracy tolerance has reduced from 75mm, to 25mm, to 10mm.

Ground loads imposed on pipes that have been tunnelled into position are less than loads imposed by backfilled trenches. Jacking loads are usually the critical factor in pipe-jack situations. Tunnel Boring Australia are able to specify the required pipe class for a project, based on jacking loads, vertical loads and experience.

Intermediate Jacking Stations are used to increase the overall jacking distance and to reduce the forces on the main jacks. Sections of the pipeline are independently advanced. Lubricants such as bentonite are used to reduce jacking loads.

4.Pipe joints must be designed to suit the actual ground conditions, the jacking loads and pipe usage. Shown here is a typical steel band with timber cushioning ring. Waterproof seals can be obtained with in-wall rubber rings or twin rubber rings.

5. The front of the working pit is normally behind any services running along the main road. Jacking under such services ensures their perfect safety.

6. Service lines supplying the tunnel face are in suitable modular lengths with easy connections for quick extensions.

7.The main jacking frame holds the jacking pipes accurately in position as they are advanced into the ground. The frame transfers the horizontal loads back to the thrust wall.

8.Portable diesel power-pack provides hydraulic power to the jacking rig, jacking shield and other hydraulic equipment.

Spoil trolley is winched out on rails and tipped.

9.The laser beam provides constant survey control, is mounted securely and is regularly checked by a surveyor.

The size and type of thrust wall is determined by Tunnel Boring Australia from geotechnical information, frictional jacking records, and experience.