Sealing veil
A sealing veil (also: sealing screen ) is a subsurface sealing of dam structures ( dams , weirs ) or construction pits. He is injection of cement produced in the underground. Occasionally, bentonite is also used or mixed in. Alternatives for sealing to a sealing curtain are sheet piling , diaphragm walls , or (during construction) soil stabilization by freezing.
A sealing curtain in the subsurface reduces the seepage or flow through the subsoil and thus the circumference and underneath the structure.
The impermeability of the subsurface usually increases with depth. The sealing curtain must extend into the subsurface until the less permeable layers are reached. The depth of a sealing curtain can reach 30 m or more below the foundation level .
Sealing veils are often put on from hearth walls or control corridors. First, holes are drilled and cement milk is pressed into them under pressure. The injection of the cement suspension has, depending on the pressure, pore space, gap width, etc., only a limited range in the vicinity of the borehole. The distance between the drill holes must therefore be chosen so that there are no gaps. A second row of boreholes is often staggered so that a two-row sealing curtain is created.
The sealing / injection success is checked, for example, by water pressure tests in control wells, the Lugeon test . Detected flaws can be closed later with further targeted drilling.