Rehabilitation and Maintenance of Drains and Sewers / Prof. Dr.-Ing. D. Stein, Dipl.-Ing. R. Stein (2004)

Local Restoration of Defective Areas in Manholes

Because the structures of drain and sewer systems, and especially the manholes, are mostly constructed of concrete, reinforced concrete or brickwork, the following will deal exclusively with the local restoration of missing portions of these materials.

Such defective areas that can occur in the manhole walls, joints, connection regions, as well as in the benching and the channels, are, for instance:

  • Partial surface corrosion;
  • Ejection of the cover layer as a result of corrosion of the reinforcement;
  • Mechanical damage;
  • Leakiness.

The restoration of brick masonry is specially dealt with in (Abschnitt 5.2.1.4).

The restoration of defective areas in concrete and reinforced concrete manholes is carried out by means of pointing. This is understood to mean the sealing and localised replacement of concrete as well as the filling of cavities [NN81] [NN84c].

Before carrying out any repairs in manholes, measures must be taken to maintain the drainage flow and must be strictly adhered to due to the often-changing water levels (Abschnitt 5.5).

Repairs to the manhole base unit - benching and channels - are carried out by means of methods similar to pointing, assuming that there is no corrosion protection and that none is required.

Missing or loose protective coverings such as sewer tiles, vitrified clay shells or plates, are replaced or placed flush into a new layer of grout (Abschnitt 5.3.2.4). As regards new pointing, see (Abschnitt 5.2.1.4).

Under certain circumstances, greater damage can also be repaired economically within the scope of the repairs as shown in (Image 5.2.2.2.5-1).

image
Image 5.2.2.2.5-1: 

Repair of a masonry entry manhole damaged by underground work (H. Schaefer, Geldern, Germany)

In this case, the strongly damaged parts caused by tunnelling were removed from inside one after another; a shuttering was placed into position and replaced by a swelling liquid concrete.

Pre-conditions for the application of this process include the existence an externally stable temporarily hard soil without groundwater inflow and corresponding safety precautions for the protection of the workers.

For larger points of damage in the region of the manhole that cannot be carried out economically as a repair work, renovation and replacement measures must be undertaken. These will be dealt with in more detail in (Abschnitt 5.3.3) and (Abschnitt 5.4).

Rehabilitation and Maintenance of Drains and Sewers / Prof. Dr.-Ing. D. Stein, Dipl.-Ing. R. Stein (2004)