Common Sections of a Sewer | Sewage | Sanitary Engineering

Following are the common sections of a sewer: 1. Old Rectangular 2. New Rectangular 3. Circular Brick-Sewer 4. Circular Pipes 5. Semi-Elliptical 6. Horse-Shoe Type 7. Basket Handle Type 8. Egg-Shaped Sewers.

Section # 1. Old Rectangular:

These were used in ancient times and are not used nowadays. It was constructed by laying concrete in the bottom and constructing sides with stone or brick masonry and then plastering.

Section # 2. New Rectangular:

This is constructed with R.C.C. which may be precast or cast-in-situ.

Section # 3. Circular Brick-Sewer:

This type of section is used under culverts and at such places where big diameter is required for short lengths. These sections are plastered from inside. In olden days these were common, but now-a-days these are not used due to their much wear and difficult centring.

Section # 4. Circular Pipes:

Precast asbestos cement concrete pipes reinforced with steel are mostly used now-a-days. Sometimes steel pipes with lining of cement concrete on inside and outside are used. Cast iron pipes are also used on large scale for branch sewers. Laying of these pipes is very simple.

This section gives the least perimeter for a given area; therefore it has the maximum hydraulic mean depth for running full and half full depth of the section. This section is also very economical as the quantity of materials required is less.

This section can be easily manufactured in the factories, transported and laid at the required places. But this section is useful in separate system of sewerage, where discharge is more or less uniform. It is not suitable for combined system, because in dry weather it is very difficult to develop the self-cleaning velocity.

Section # 5. Semi-Elliptical:

This section is suitable for sewers carrying large discharge throughout the year. These are usually constructed with R.C.C.

These sections are structurally more stable, because the arch thrust is vertical at the invert. The arch section can be varying type. This section has good hydraulic properties, except at low depths. The section is suitable for sewers of large size more than 1.8 m diameter.

Section # 6. Horse-Shoe Type:

This is constructed with R.C.C. and is used in case of heavy discharges. Usually it has semi-circular shape on the top with sides inclined or vertical. The invert may be flat, circular or paraboloid in section. Its height is less than the width.

Section # 7. Basket Handle Type:

The shape of this section is similar to that of basket-handle; therefore it is called as Basket-handle type. R.C.C. is used for the construction of this section. This section is designed in such a way that self-cleaning velocity is developed even in D. W.F. This section is not commonly used.

Section # 8. Egg-Shaped Sewers:

The depth of these sewers is one and half times of their width. In olden form it was used with greater radius at bottom, but in new shape smaller radius is used at the bottom. These types of sewer sections are mostly used because in dry weather, self-cleaning velocity is available due to greater depth of water as compared with other sections. These are mostly constructed with concrete and brick arch with special invert at bottom or of R.C.C. These section are always constructed at the site.

This section is most suitable for combined system, because it gives self-cleansing velocity even in D. W.F. This section can be equally suitable for separate system, because it will easily accommodate the flow of sewage with the development of the town.

It has good hyraulic properties, even better than circular section with low discharge. The only disadvantage is that its construction is difficult and it is less stable than circular section, hence it requires good masonry backing.