Pipe Jacking (Manned Techniques)
Hydraulic pipe jacking (see ATV-A 125E or DVGW-W 304 [ATVA125a]) [Stein85a] [Conra84b] [Hornu89] [Scher77b] [Stein85e] has been available since the turn of the 20th Century as an alternative to the gallery techniques (heading) and the shield tunnelling with segment lining. This method for the case under consideration consists of "pipe eating" the existing sewer from a starting excavation by jacking pipes or jacking elements through the ground up to a target excavation by means of hydraulic jacks. Thus, the ground is removed and the old sewer is disassembled under the protection of a cutting shoe or shield and moved through the jacked section to the surface. The jacking pipes or elements at the same time also take on the task of supporting the ground. This double function - supporting the space excavated out on the one hand and finished construction on the other - is the essential difference and the particular advantage of the hydraulic pipe jacking (Image 188.8.131.52-1) and the processes discussed in the (Abschnitt 184.108.40.206) and (Abschnitt 220.127.116.11).
The most important functional parts of hydraulic pipe jacking are:
- Cutting shoe or shield;
- Jacking element or jacking pipe;
- Intermediate jacking station;
- Main jacking station.
The technical and economic success of this process depends in no small measure on the interaction of the whole system. Thus, the various parts must be coordinated in their dimensions, forces and speeds. The breaking, loading and transport equipment are usually integrated into the primary functional parts of the pipe jacking.
An important item of the steerable pipe jacking is the cutting shoe or shield that must be placed in front of every pipeline to be installed. In this case, besides that described in (Abschnitt 18.104.22.168), it must also carry out the following functions:
- It must cut out the soil (also called the ground) surrounding the old sewer in such a manner that the following continuous pipe can be jacked through with the least amount of settling and the lowest possible amount of friction on the pipe skin;
- It must support the breakout space against the collapsing force of the ground until the pipes jacked in behind can finally accept all loads and forces.
As a rule, the cutting shoe, analogous to the shield in shield tunnelling with segment lining, is designed as for tunnelling. As the driving of the shield is achieved with the aid of the main jacking station with possible support from the intermediate jacking stations, the jacking cylinders usually integrated in the shield are not required (Abschnitt 22.214.171.124) (Animation 126.96.36.199-1).
In the case under consideration, as in the shield tunnelling with segment lining, hand mining shields and mechanical partial excavation shields with a minimum diameter of 1.2 m (Image 188.8.131.52-1) are usually used. Support of the working face and the lowering of the groundwater level could be necessary under certain circumstances.
- Variant 1: Single-stage pipe jacking (Animation 184.108.40.206-2).
In this variant, the product pipe, in this case the sewer is driven in one working step following immediately behind the cutting shoe.
- Variant 2: Two-stage Pipe jacking (Image 220.127.116.11-2) (Image 18.104.22.168-3).
Phase 1: Drive of a liner pipe (corresponds to a protective pipe in the sense of ATV-A 161E or DVGW-GW 312).
Phase 2: Installation of a product pipe by insertion or pulling it through the protective pipe left in the ground. The gap between the product pipe and the protective pipe is usually grouted.
The application of variant 2 can be particularly useful for sewers running through or crossing water catchment areas. In these areas, the placing of sewers in sealed lining pipes (double wall system) is already being partly promoted, whereby the gap remains free (Abschnitt 6.1).
Because of the special method of introducing the piping, it is necessary in both variants to maintain the flow of sewage by measures outside the sewer to be replaced (Abschnitt 5.5).
The laterals must be separated from the section of the sewer with the open cut method both to protect them and to ensure the flow of sewage (Abschnitt 5.5) usually before the start of the pipe jacking. Reconnection is carried out after the ending of the pipe jacking, e.g. after reaching the final position of the pipe, which, during the driving, is constantly moving and following the shield.
Depending on the amount of space available and the type of the shield, the sewer to be replaced can either be immediately destroyed and removed or can be disassembled after ending the driving.
Although the pipe jacking, because of its controllability [Stein88c] [Stein86b] is, in principle, also suitable for curves, in the case under consideration, the run should be kept as much as possible in a straight line.
The process requires the start and target excavations to be arranged in the run of the pipe so that, if the position is in a road, interruption of traffic cannot be avoided.
The advantages and disadvantages of the gallery techniques (heading) apply also to the manned working pipe jacking method.
Compared to all other pipe methods of construction mentioned, the degree of mechanisation is highest and the safety risk is the lowest.
In contrast to the segment method of the Mini Tunnel system, the amount of grooving is greatly reduced; an advantage that is especially important in the direct use of the jacking pipe as a product pipe.
- The cutting and reconnecting of laterals;
- The required placing of the start and target excavations in the run of the sewer and the possibility of traffic interruption resulting from this;
- The necessity of having to design the starting excavation to absorb the jacking forces.
The proposal request for the construction can be according to the "Standardleistungsbuch LB 085" (standard service record) [LB085] [Schaa98] and the structural calculations of the jacking pipes according to ATV-A 161E or DVGW-W 312 [ATVA161] [Körke98]. The drive is to be carried out in accordance with ATV-A 125E or DVGW-GW 304 [ATVA125a] and the protective measures for work safety. Pipes for the laterals that are laid by the open cut method must be sized according to ATV-A 127E [ATVA127a] and laid in accordance with EN 1610 [DINEN1610a].
During the drive work the "jacking forces of the main and intermediate jacking stations must be continuously recorded and compared to the calculated values. Reasons for deviations must be given. A protocol must be kept of the condition of the piping. For this purpose, the height and side position of the cutting shoe and the first pipe piece must be controlled every 2 metres or at least after each installed pipe: the result must be depicted on a diagram. Additional controls of the measuring system must be carried out regularly at suitable intervals. When using lubricants, their pressure must be measured. The employer must be notified immediately that contamination is suspected. The records must contain the date as well as the position of the construction site, the soil and groundwater conditions" [ATVA125a].
After the piping has been laid, the laterals are reconnected if they are not being rehabilitated themselves. Subsequently, sight and leaktightness tests are to be carried out according to ATV-A 125E (Abschnitt 4.5.1).