What are the main cross-sectional shapes?

The most common cross sectional shapes, also called sewer profiles, are the circular, the standard ovoid and the standard arch cross sections. They are summarised under the term standard shapes

The circular cross section has been and still is preferred in use because of its structural and hydraulic advantages in the nominal size range 100 ≤ DN/ID ≤ 500.

Since the development of reinforced- and prestressed concrete technology and, consequently, a continuous improvement of the pipeline manufacturing and pipeline construction/engineering methods, pre-fabricated pipes with a circular cross section up to DN 4000 are also used for main collectors.

The ovoid cross section has been used for the first time in London in 1846 and arrived in Germany about 1870 [Frühl10].

Hydraulically, the ovoid cross section has particular advantages in the drainage of larger, erratic drain flows, as e.g. in combined sewers with small dry weather flows Q_t/Q_v =0.22. Additionally, this special shape allows great cleansing effect and high flow velocity even with low water level in the pipeline. Just like the arch cross …

Arch cross sections offer advantages for large flows and a restricted construction height. Although the hydraulic efficiency for partial filling is poor, yet the shape is structurally advantageous because it approximates the course of the pressure line.

In the past, two more cross sectional shapes have been in use that have been derived from the standard arch cross section, namely the “extended arch cross section” and the “squashed arch cross section”.

In particular cases, e.g. in the construction of stormwater sewers, stormwater retention tanks or for defined location collecting points, rectangular cross sections have been and are still used. DIN 4263 in its edition of 1991 recommended about 800 mm as the smallest clear axial dimensions. The invert has a cross-slope to the low point at the centre of the cross-section.

[DIN4263:2011]

In addition to these standard cross sections there are numerous other cross sectional shapes and -sizes, that, partly, have also been standardised in the past and that are still used today in individual cases.

Examples for non-standardised cross sections in practice:

The minimum depth of cover for surface water sewers in a separate system results from being laid below gas and water pipes and the need frost-free operation of the water pipes and sewers. This results in a typical minimum depth of 1.5 m for the surface water sewer with connections of rainfall downpipes to the sewers from 1.5 to 1.7 m

Consequently, in a separate system, the wastewater sewers are installed deeper than the surface water sewers. When …

The gradient of a sewer in its total course up to a main collector, sewage treatment plant or pumping station is normally selected such that the upper sections with the smaller nominal sizes and the smaller flows are laid with a larger gradient than the middle and lower sections, as in these areas, larger and more constant flows, and thus, a larger wall shear stress of the sewage are very likely.

Since the middle of the 19th century sewer systems have been constructed according to plan in Europe. The ancient Romans’ high standard of knowledge served as a basis for German sewer systems, as the Romans had constructed large brick sewers (Image ) and often used “clay pipes” for small nominal sizes that were cone-shaped at one end, so that the pipes could be inserted into each other and thus connected.

For over a century, the accessible sewer systems …

The materials used in construction (common designation of all materials) are also called building materials [Meyer81].

The types of building materials used in sewer systems are divided into metallic, organic, non-metallic-inorganic and multi-component building materials. The latter are again subdivided into binding bound materials, reinforced materials and strengthened materials [Schor].

However, the greater part of sewers consists of prefabricated pipes of various materials, especially of concrete and reinforced concrete or vitrified clay. Plastic piping and pipes made of asbestos cement have been used since about 1930, pipes made of ductile cast iron since the second half of the 20th century, fibre cement since about 1990 and polymerised concrete since the 1980s.

The distribution of materials in sewers in the Federal Republic of …

Flexible pipes deform so much under external loading that the lateral bedding reaction is activated and thus used to take part of the loads. The flexible pipe and the bedding jointly take over the external loads

Rigid pipes deform only slightly. Since the pipe is stiffer than the surrounding soil, the loads are concentrated on the pipe, i.e., the lateral bedding soil is unburdened.