joined together to form the trench wall section application_number US 20287280 A description this invention relates to a method for constructing trench walls wherein a trench is excavated in the soil simultaneously filled with a shore up fluid and subsequently filled with in situ concrete displacing said shore up fluid trench walls are generally employed at sites whereat a building is to be erected within or above the ground in this application the trench wall enables the underground structure to be erected by shoring up the surrounding soil frequently the finished trench wall is employed as the peripheral wall of the building to this effect the soil is removed at one side of the finished trench wall so that the latter has then an exposed visible side facing towards the interior of the building and an outer side facing the surrounding ground under certain geological conditions of the soil for instance in the case of gravel or other loose components tending to slip or to cave in during excavation the introduction of the in situ concrete may not result in the formation of a smooth trench wall inasmuch as such slippage cavities will also be filled with the concrete a desired smooth surface at the exposed side of the wall will then require additional finishing work resulting in increased cost it is an object of the present invention to provide a method of the type defined in the introduction by the employ of which it is possible to erect trench walls having substantially smooth exposed surfaces even under difficult geological conditions in order to attain this object the invention provides that prior to introducing the in situ concrete at least one prefabricated.