Inverted siphons are designed at locations in which a sewer system is blocked by underground utilities or stormwater drains. They are sometimes called depressed sewers because it is claimed that there is no actual siphon action. They connect the upstream and downstream sewers with U-shaped vertical alignment such that they are always running full.

The drawbacks of inverted siphons are:
(i) They induce additional head loss to the sewer system which is undesirable in hydraulic performance;

(ii) U-shaped siphons create sediment accumulation problem and previous experience showed that inverted siphons were easily blocked due to siltation;

(iii) Maintenance of invert siphons is difficult due to its inaccessibility.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

CCTV is a well-established and prevalent method for pipe inspection. However, there are several limitations of CCTV technology:

(i) It could only provide the view of pipe internal surface above waterline.

(ii) It does not provide the view of soil conditions surrounding the pipe.

(iii) Most CCTV system is incapable of measuring pipe gradient.

(iv) It does not provide any structural data on the integrity of pipe wall.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

There are mainly three major effects of sediment deposition in sewers:

(i) The deposited sediment may cause initiate small blockage of flow. Later when larger solid builds up it may result in total blockage of sewers.

(ii) The deposited sewer restricts flows leading to the drop in hydraulic capacity.

(iii) The deposited sediment serves as a point of pollutant storage or generator. The pollutants are stored temporarily and be discharged in high flow conditions. Moreover, biomedical change in sediment deposition releases gases which are corrosive to sewers.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Vitrified clay pipe is capable of withstanding extreme temperatures. However, vitrified clay pipe is liable to damage by thermal shock – a swift change of temperature. Such rapid temperature variation induces thermal gradients inside the pipe wall which produces stresses which damage the pipe. To guard against possible damage of vitrified clay pipe by thermal shock, engineers should check in design about the temperature of sewage to be carried, rate of flow, temperature of pipe and soils and the wall thickness of clay pipes.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

In the manufacturing process of vitrified clay pipe, the clay material particles are fused into an inert and chemically stable compound. It is capable of carrying a wide range of commercial, industrial and domestic sewage. In fact, it is chemically resistant against sulfuric acid induced by hydrogen sulfide. Moreover, it is reported to be unaffected by the presence of solvents.

However, there are still some chemicals which are known to cause damage to vitrified clay pipe. For instance, vitrified clay pipe is not immune to attack by hydrofluoric acid and hot concentrated caustic wastes.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.