Standards (abstract)

abstract from the SIA 272 (Swiss Society of Engineers and Architects) waterproofing and drainage-systems of underground buildings.

5.4.1 Effects of sintering

Hard deposits (sinter) in the drainage system can destroy their function. This causes that the the water pressure around the building, rises up and subsequently water enters into the building. In addition, buoyancy can adjust with unpredictable consequences like, damage to the building and costly repairs.

5.4.2 Causes of sintering

5.4.2.1 In the drainage system sinter is produced (hard deposits) if:

  • type and quantity of liquid and non liquid substances in the water are favorable for the formation of hard deposits.
  • pressure, heat, pH and carbon dioxide content in the resulting ground or underground water predominates,
  • or when entering (water) these values are changed in the drainage system,
  • the water gets in contact with parts of the building, for example, excavation safety,
  • injections, hydraulic binder, are used

5.4.2.2 The balance between the lime and the carbonic acid of ground or underground water change during the inflows and the entry into the drainage system. The dissolved carbon dioxide may be precipitated in contact with air. As result we see calcification and hard deposits.

5.4.2.3 The sintering potential can be calculated by the amount of water, the composition of the water (devided in the liquid and non-liquid substances) and the water temperature. The results of this calculation is one of the bases for the design of the drainage system and for the assessment of the necessary drainage and sintering cavity.Sintering increases the cleaning – / maintenance effort and causing a large tear in the drainage system.

5.4.3 Measures to reduce and prevent sintering

5.4.3.3 The addition of a hardness stabilizer to the water in the drainage line affects the crystallization behavior of the lime in the precipitation. A large proportion of the calcium crystals will result in suspension and will be removed with the water.

5.4.3.6 In the so-called feedback system a hardness stabilizers are used as well. A portion of the already conditioned water is removed from the inner drainage system to the outer drainage system (seepage water drain). From there, it is added at regular intervals to the mountain and groundwater. In this way, the inflowing water can already be conditioned outside the drainage system. This feedback system depends on water quantity and sintering potential. It is already set in the project. If a high sintering potential is already known in the project phase or at start of construction, the injection line must be laid in the seepage water drain. But it must be done in any case outside the drainage pipe. Number and size of the outlet openings in the injection line depend on the length and pump power. Only when sintering occurs, the recovery system will be put into operation – equipped with pump and control.