Injection seal

from Wikipedia, the free encyclopedia

In the construction industry, an injection seal (by means of subsoil grouting ) is the pressing of hardening liquids or suspensions (especially fine-grained flow mortars, cement suspensions, polyurethanes, silicates, acrylates, epoxies or similar substances) into the pore space of the soil (mostly alluvial soils - hence the English "alluvial" grouting ", French" injection des Alluvions ") and in fissures, cracks, etc. of rock or concrete in building components , for the purpose of sealing or consolidating.

application

  • In dam construction , injections with (above all) cement suspensions are used to reduce / prevent seepage water losses, undesired pore water pressures, erosion, etc. under and next to the barrage - dam or dam, see: Sealing curtain .
  • In tunnel construction (e.g. for power plant tunnels, rail and road tunnels or underground railways), injections are used to reduce inflowing seepage water, to counter environmental damage by lowering the groundwater level, to prevent water ingress and to consolidate unused mountains.
  • In geological boreholes , the production probes or pipe tours are sealed against the borehole wall by means of cementation in order to avoid contact between the production fluids with the groundwater or possible migration paths between individual geological horizons .
  • Walls that are permeated by moisture can also be sealed with injections.

Injection wells, injection packers

DESOI steel packer 13 x 120mm for ground grouting

Injections are usually carried out via boreholes which are sunk into the rock (as uncased hammer-blow holes in stable rock) or the subsoil (as flushing boreholes or cased overlying boreholes, built with so-called sleeve pipes).

The aid for sealing defined borehole sections (or the borehole mouth) is the injection packer , simply called packer in technical jargon . This usually consists of an expandable hollow rubber cylinder - between screwable steel / plastic pipe elements. Alternatively, this hollow rubber part can be designed as an inflatable tube. These injection packers are firmly clamped in the component (or sleeve pipe) and thus enable the controlled delivery of the injection liquid to defined injection points in the building site / component. A distinction is also made between recoverable and so-called lost packers .

Materials used & processing parameters

  • Cement suspension (cements with a fineness of> 4,000 cm² / g; water + cement (+ possibly bentonite as stabilizer) = cement milk; suspensions of fine and superfine binders with grain sizes <12 μm are also used as injection material)
  • Mortars in various compositions, occasionally with fiber reinforcement
  • Polyurethane (PUR)
  • Hydro structure resin (acrylate gel)
  • Resin (epoxy resin, with special wetting properties, e.g. for tensile strength connection of the crack flanks)
  • Microemulsions (silicate gels; silica fume <2 μm)

The corresponding soil exploration of the subsoil to be treated (and ultimately also the examination of the success of the injection) are primarily carried out by means of permeability / conductivity / transmissivity tests in specially provided boreholes. The Lugeon test is used to measure the water absorption / min / running meter of the borehole in the rock at 10 bar overpressure and from this the transmissivity is obtained in [m² / s]. Tests according to Lefranc (lowering and rising again, or topping up with observation and measurement of the lowering of the water level in the cased borehole, in loose soil) are used to calculate the conductivity in [m / s].

The injection pressure at a defined injection rate and the injection quantity are observed and interpreted during the injection process (by means of electronic data acquisition, display and processing). Criteria for limiting the pressure and volume, such as the Grouting Intensity Number (Lombardi) or the interpretation of the pressure drop after borehole inclusion (TPA) have proven their worth. Further hydraulic interpretations of the process (see methods from the petroleum industry) are also particularly helpful.

literature

  • European standard EN 12715 (2000)
  • Injections ; ISRM (1996)
  • Wolfgang Hornich, Gert Stadler : Injections , in: Grundbau-Taschenbuch , 7th edition, Volume 2: Geotechnical processes (2009), Ed .: Karl Josef Witt, Ernst and Son, ISBN 978-3-433-01845-3 .
  • Henri Cambefort; Injection des Sols , Edition Eyrolles, Paris 1967
  • Alan Bell, Klaus Kirsch (editors): Ground Improvement , Spon-Pressl, 3rd edition 2012
  • KD Weaver, DA Bruce: Dam Foundation Grouting , ASCE Publications 2007
  • Heinrich Otto Buja: Handbook of drilling technology, shallow, deep, geothermal and horizontal drilling . 2nd edition, Books on Demand, Norderstedt 2012, ISBN 978-3-7357-3409-9 , pp. 255-264