Until a few years ago, the sewers in the Federal Republic of Germany were laid almost exclusively by the open cut method, i.e. by means of digging a trench, laying the sewer with the protection of an embankment or a shoring and then covering up the trench again (trench sewer) (Image 126.96.36.199-1).
The most important regulations for the laying of sewers using the open cut method are DIN 4033 [DIN4033b] and the ATV-A 139E [ATVA139b], which have been replaced since October 1997 by EN 1610 "Construction and testing of drains and sewers" [DINEN1610a]. Further regulations and guidelines in this connection were promulgated by the individual cities [Hambu79b].
Depending on the requirements, different trench cross sections are possible ranging from embankment type trenches up to those with vertical walls [Stein88i]. Furthermore, combinations such as stepped trenches with vertical, embanked or partly embanked trench walls also occur (Image 188.8.131.52-2) (Image 184.108.40.206-3) (Image 220.127.116.11-4).
Different soil zones are found during the excavation of the trench and these are the native soil as well as disturbed soil in the area of the trench cross section or in the embankment. The dimensions of the disturbed soil area are determined by the depth of the trench and its width. The total width of the trench is thus calculated from the minimum width of the trench with the addition of the shoring, which, with panel profiles and stays for example, can amount to 0.4 m. In the cross section itself, one differentiates between the embedment and the main backfill.