The semi open cut method, also called the semi open pipe jacking, is characterized in that the new man-accessible sewer, as with hydraulic pipe jacking (Abschnitt 18.104.22.168), is pushed through from a starting excavation to the target excavation.
The removal of the soil and taking the sewer taken out of service is carried out from the surface with the protection of a bottom ring, open in the crown and with the assistance of a grab or excavator. For this purpose, a small, supported trench along the line of the drive and up to the jacking pipe is sufficient (Image 5.4.3-3) (Image 5.4.3-4). A bulkhead at the end of the bottom ring prevents the ingress of soil and groundwater into the jacking pipe so that, with groundwater levels up to the springing height, lowering of the groundwater will not be necessary. The width of the excavation and the small trench depends on the size of the grab and the depth of the excavation and is about 1.2 - 1.5 m.
The advantages of this patented process compared to the open cut method is primarily in the reduction of the space required for breaking open the road cover and its replacement, the earthworks (soil removal and refilling), the space required for the work, the water retention costs and the bad effects on neighbouring structures and planting. With professional work, the new sewer will have an ideal bedding.
The process can be applied to sewer sections up to 200 m. Curved jacking is basically possible. All laterals must first be cut off using the open cut method (Abschnitt 5.5). When laying new pipes with this method, laying speeds of 35 to 95 m per day have been achieved [Uffma87].
One example for replacement of a man-accessible masonry sewer 1750/2150 using the semi open cut method is shown in (Image 5.4.3-1), (Image 5.4.3-2), (Image 5.4.3-3) and (Image 5.4.3-4) [Karna94]. The average drive performance in this case, taking into account the shuttering time and that taken for breaking up the old sewer, was 6 to 7 m per day. The maximum performance in a 10-hour shift was 42 m.
All construction work with the open cut method must be carried out in accordance with EN 1610 [DINEN1610a] and the protective measures for works safety.
For the proposal request, structural calculations, execution and testing of the construction works with the trenchless method, reference should be made to the discussions in (Abschnitt 22.214.171.124).