Preface
Structure and Limiting Conditions of Sewer Systems - Historical Outline
Damage, its Causes and its Consequences
Deposits
According to [DIN4046], deposits are caused by gravitation of settled out materials (Image 2.4.3.2-1) (Image 2.4.3.2-3) (Image 2.4.3.2-4) (Image 2.4.3.2-2). If deposits are not regularly removed, they can become more or less strongly fixed due to their compositions and the course of time (Image 2.4.3.2-1) (Image 2.4.3.2-3) (Image 2.4.3.2-4).
Image 2.4.3.2-3:
Hardened deposits [Image: S&P GmbH] - Sewer filled with injected grout of an incorrectly set excavation anchor
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In all sewer systems, solids will occur that are introduced with
- the waste water from buildings and industry,
- the surface water, and/or
- the infiltrating groundwater,
and that possess a very heterogeneous composition (Abschnitt 2.2.3.2) [Billm84] [Schüt83].
These solids only first sink and form deposits when the flow falls below the limiting velocity of the mixed flow (Abschnitt 1.5). This is dependent on the following parameters [NN83] :
- Pipe diameter;
- Degree of filling;
- Operational roughness;
- Average particle diameter of the mineral solids.
- Gradient of the pipe.
On the other hand, numerous articles and materials enter the sewer systems that can either be conveyed only with a greater hydraulic effort or that cannot be conveyed at all. Just as flow obstacles, in the piping, they often represent the starting point for large area deposits (Abschnitt 2.3.2.2) (Abschnitt 2.3.2.3).
The causes can be [Schäf82] :
- Interiors of pipes, which are not smooth, e.g. through incrustation, corrosion, wear, gasket rings, which have been pressed out of the pipe joint, invert unevenness.
- Fragments falling out of the pipe walling, sewer tiles, joint mortar.
- Objects and materials that have fallen into the manhole (e.g., step irons) (Image 2.4.3.2-5) (Image 2.4.3.2-6).
- Introduction of concrete, mortar, cement suspensions, etc. from adjoining construction sites.
