Abstract
An overview of the commonly used materials used for drain and sewer construction across the world.
Author
Steve Peregrine BEng Hons, Senior Technical Manager
Page Contents
Introduction
The materials used for constructing for the transportation of water have evolved over a very long period of time from the most basic ditches and stone channels in the years BC through hollowed out wooden logs to labour intensively constructed large scale brick sewers in Victorian times to the most modern of composite and manmade materials we see today.
The stresses placed on these conduits have increased as time has marched on as we as a human race have also evolved and engineering solutions and developments have given us more and more abrasive and generally offensive things in our lives that we all simply tip down the drain during modern life without giving it a 2nd thought.
This page shows some of the more common materials seen today by CCTV surveyors during pipe inspections.
Material Classes
Drainage materials are generally classed into two types, with two additional sub types:
Modular - sewer conduits that are constructed from small building blocks without any discrete joints, like brick sewers.
Piped - sewers and drains that are constructed from discrete jointed manufactured pipes:
Rigid pipes - pipes that have no capacity to bend when stressed under load, they just break.
Flexible Pipes - pipes that can absorb a degree of deformation without any loss of structural integrity as a result of their design and manufacturing process.
Modular Sewer Construction
Modular sewers, usually referred to as ‘Brick’ or ‘Masonry’ are constructed using building blocks and mortar and are always rigid, but there is a distinct difference between the materials ‘Brick’ and ‘Masonry’ although the construction methods are basically the same:
Bricks are man made and usually have clean edges from the manufacturing process. Brown bricks are fired from clay, but there also blue bricks, sometimes known as ‘Engineering Bricks’. Brick sewers are still used these days in some areas of the world, particularly where there are very fast flowing sewers due to their wear resistance, and it is common to see bricks not fired from clay, but cut from Basalt rock, also with hard clean edges.
Masonry is used to define modular construction where the unit objects are either irregular sizes, have rounded edges, or are simply modular and not bricks. Masonry is more of a 'catch-all generic term for non-piped, non-brick sewers. Masonry can be regularly coursed (in neat rows of similar sized elements) or irregularly coursed.
Brick sewers usually have two skins of bricks, sometimes three, so it is not uncommon to see the inner skin of bricks has fallen away in the structure of the sewer, but the basic construction of the conduit is still in tact, albeit damaged.
Brick sewers can be almost any shape due to the way that they are constructed, the most common shapes being egg shape and circular.
Egg Shaped Brick Sewer
Notice the clay channel at the bottom (know as the invert) which is hollow. This is because most sewers were originally constructed along the lines of streams, rivers and ditches, so the hollow channel was used to carry the water of the original stream and keep it away from the waste water inside the sewer.
Circular Brick Culvert
A culvert is a ‘Covered Watercourse’, so is seen on rain water systems, often going under roads and railway lines, or carrying a river underneath the streets of a city.
Open Mouth Profile
A fantastic piece of engineering. When originally built often in the 19th Century, these large dimension below ground water ways were used as canals for transporting goods underneath cities, and the walkways along the sides of the main channel were for the ponies to walk along, towing barges.
Arch Shaped, with Engineering ‘Blue’ Bricks
A common mistake in deciding on sewer shapes is confusing ‘Arch’ shape with ‘Horseshoe’ but the differences are subtle. The first is usually a wide, low structure with a slightly convex curved base, like the example above. Horseshoe shape is usually a taller construction where the sides of the sewer near the invert actually start to curve back in on themselves again. ‘Open Mouth’ profile is either of these where there is a clearly defined separate channel at the bottom.
Masonry Construction
See that the blocks are more rounded than bricks with much less well defined edges, and the sizes of the blocks is not consistent. This would be ‘Regularly Coursed Masonry’.
Tiled Construction
Where there is no option in a material list for tiled constructions, we would use ‘Other’ with a comment. Here, the sewer is constructed from manufactured interlocking clay tile segments creating a smooth internal surface that is hard wearing. If you look in the distance, you can see the design of the tiles where the sewer has failed and there were often two layers of interlocking tile skins in the construction.