The trenchless mode of construction
At the present time two remote steered methods for the construction of underground sewers are in use. These two methods are described below in accordance with ATV working sheet A 125 - microtunnelling:
Shield pipe jacking (slurry system)
Jacking of casing or media pipes with simultaneous full cross-section removal of the soil from the working face, counter balanced by mechanical and hydraulic loads. Surveying is carried out with a laser beam. Changes in direction are executed with the aid of a cutter head able to be swivelled hydraulically.
Removal of the soil is carried out continuously, as a rule by hydraulic means. The drive for the cutter head is located in the jacking shield. In general this method is used for pipes of external diameters up to 1850 mm and manhole to manhole lengths of up to 250 m in earth and rock with and without ground water, the particular manhole to manhole length possible depending on the nominal size of the pipes.
The cutting wheel to be used on the cutter head is selected on the basis of the composition of earth. Use of the correct tools selected in accordance with the consistency of the soil and the size of the stones enables the rate of microtunnelling to be optimised. Cutter heads for rock can be used from DN 500. The expert rep rts on the soil, which are essential for microtunnelling, can be prepared in accordance with DIN 18319, VOB part C. A reprint " Opportunities and limits for micro tunnelling taking into account the excavating tools" can be obtained from KERAMO-STEINZEUG.
Thrust boring pipe jacking (Auger system)
Jacking of casing or media pipes with simultaneous removal of the soil at the working face by a cutter head. Surveying is carried out with a laser beam. Changes in direction are executed with the aid of a cutter head able to be swivelled hydraulically.
Removal of the soil is carried out continuously with the aid of auger flights. Cutter head and auger flights are driven as a rule from the start shaft or pit. The area of application of this method covers in general pipes of external diameters up to 1300 mm and manhole to manhole lengths of up to 100 m. In the case of cohesive soils of firm consistency, excavating and conveying of the soil can be facilitated through the feeding of water at the working face.
In water bearing soils, additional measures, e.g. the use of compressed air, are necessary. A container is placed over the jacking pit or immediately adjacent to this. This enables the work to be carried out at the site more or less regardless of the weather even in winter months.
The width of the container is such that in general the site only occupies one traffic lane so that traffic can pass the site with relatively little disturbance on one half of the road or with the aid of traffic control signals.
Sewers can also be renewed by the pipe cracking or pipe eating methods with the aid of this method. Further information is available on request.