Pipe Jacking Trenchless Construction Technology
Today, after 60 years, pipe jacking technology has provided not only provides the solution to construction of underground services with minimal traffic disruption, but also minimal environment impact. Current technology has allow pipe jacking to be carry out from size 150mm to 3000mm diameter and the length of several meters to few hundred meters. Semantra No-Dig Engineering Sdn. Bhd. as one of the major players in the industry in Malaysia has the technology, expertise and experience to provide the pipe-jacking solution for installation of any underground services i.e sewerage, water pipe and utilities services. Our 30 years of experience has given us knowledge to not only overcome but also provide solutions to almost any pipe-jacking problems in Malaysia.
In today world, there are currently 2 types of pipe jacking method:
Manshield/ Handshield, Open Face Excavation Method
Open face excavation method is the oldest form of pipe jacking method. This method provides an open excavation face access and the ability for the removal of man made obstacles and boulders. The spoil is removed by the conveyor and spoil trolleys which are winched out. The hydraulic jacks pushing the pipes are held by the main jacking frame and are part of the jacking rig. The jacking rig, jacking shield & other hydraulic equipment is powered by portable diesel hydraulic power-pack situated outside of the launch pit. The jacking frame transfers the horizontal loads from the jacks back to the thrust wall. Open face excavation involves the usage of hydraulic jacks, which provides the necessary driving force for thrusting specially designed pipes and / or culverts directly into the ground while excavation of soil is taking place from within manually or mechanically depending on the type of machine used. This jacking method provides a structurally flexible and watertight finished conduit.
Like other pipe jacking method, this method requires the construction of just two pits – the thrust/launch and reception pits. The size of the pits are determine by the size of the pipes and sites conditions. The launch pit is where by the jacking rig, shield and other hydraulic equipment are situated. Jacking pipes are lowered into the launch pit.
SNDE in the past has had the privileged to jack pipes using this method from to several meters to approximately 70 metres using pipe diameters ranging from 900mm to 3 metres.
Microtunnelling / MTBM / Close Face Method
As the name implies, microtunneling is used to construct small tunnels. These small diameter tunnels make it impossible to have an operator in the machine itself. Instead, the microtunnel boring machine or MTBM must be operated remotely. Usually the operator controls the machine from a control room on the surface of the ground. The operator is given constant feedback about the machine’s location, orientation and hydraulic devices via a computer console. Most machines also have video cameras set up to give the operator more information. The operator can then control the MTBM and the jacking frame from the safety of the control room.
In most microtunneling operations the pipe is inserted from the entry and pushed behind the machine. This is a process often called Pipe Jacking. As the machine advances, more tunnel liner is pushed from the entrance. Thus, the speed of the advancing machine is controlled by the speed at which the pipe is inserted into the entrance.
As the length of tunnel increases, the friction of the ground around the pipe increases as well. Usually, two practices are used to minimize this friction. First, over-cutting is used to give a slight gap between the inner edge of the tunnel and the outer edge of the liner. Usually this is achieved by using a cutter wheel with a diameter ½ inch (12mm) to 4 inches (100mm) larger than the outside diameter of the liner. Secondly, an economical and ecologically friendly lubricant, often bentonite slurry, is injected into this gap. In addition to lubrication, the pressure of the lubricant prevents the gap from collapsing.
While friction can be reduced, it can never be eliminated, and so hundreds of tons of force are required to push the machine and liner into the ground. A large “jacking frame” is required to produce these forces. In most cases the entrance must be modified to support this frame and the forces it generates.
In addition to the jacking frame, smaller jacks, called “interjacks”, may be inserted between sections of tunnel liner. These push the two sections of liner apart. Friction on the liner sections between the interjack and the tunnel entrance helps to prevent the liner from sliding out backwards. So while the liner behind the interjack does not move, those sections in front of it receive additional pushing force.