Pipe jacking is a trenchless method of new pipe installation Factory made pipe sections are jacked or pushed behind the tunnel boring machine or other tunnel excavation methods. Jacking force is transmitted from thrust wall installed in the drive shaft. Pipe jacking is used for the following cases.
1.Heavy traffic roads and crossing s of railways, rivers, and massive structures
2.Sensitive environment & neighborhood
This kind of pipe is able to bear huge jacking pressure. As well owns enough intensity to endure internal and external pressure. It also possesses perfect characteristic of anti-corrosion and durability. In addition, the inherent flexibility enables it to adapt ground displacement.
The followings need to be considered when jacking is adopted.
1.High water table and difficult soil condition may require special work.
2.Jacked pipe may subside in soft ground.
3.Handling unexpected subsurface obstacles may face difficulties while jacking.
4.Experience d operators and well organized construction work are necessary.
5.Location of shafts is important . Drive shaft may affect surrounding grounds.
QA and QC for Jacking for Small Diameters
In the same way as the jacking method for medium to large diameter, controls for progress, material and equipment, work, safety and pollution are highlighted for QA and QC for small diameters jacking. Small diameter jacking have some specific problems such as: impossible jacking, zigzag line, pipe break, surface settling, groundwater inflow, damage to other utility lines. Man-entry is not possible for small diameters. So the excavation face cannot be checked directly visually. Furthermore, even in case of emergency, human operation is impossible in the tunnel. For this reason, it is expensive to control the emerging situation. Therefore, QA and QC requires special attention.
Earth Pressure Balance
In closed earth pressure balance shield jacking, separation wall is placed behind the cutter head of boring machine. Excavated soil with or without plasticizer is filled between separation wall and excavation face to stabilize the face. By controlling the amount of excavated soil removed from the tunnel face, excavation and jacking are operated.
Classification of Pipe Jacking
Classification can be made by several aspects such as methods of excavation, tunnel face support, jacking force transmission, spoil removal and so on. The nominal diameter of jacking pipe is also used for classification of pipe installation. In Japan, the diameters from 800 to 3000mm are defined as medium to large. The diameters correspond to man-entry size. The diameters from 150 to 700mm are defined as small. An example of classification is shown.
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