Highway Engineering

In general, kerbs are essential in road pavements due to the following reasons (based on Arthur Wignall, Peter S. Kendrick and Roy Ancil):

(i) They provide strength to the sides of road pavements and avoid lateral displacement of carriageway due to traffic loads.

(ii) In terms of road safety, they serve as a separation line between footway and carriageway and aid car drivers in driving safely.

(iii) They act as a vertical barrier to guide the surface runoff collected in road pavements to the gullies.

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.

A sag gully is a gully installed at a low point in roads and stormwater would pond up the gully. An on-grade gully is a gully installed in a sloping road where any excess flows may bypass the inlet and flow to another one downstream. Generally speaking, the entry capacity of sag gully can be estimated from hydraulic design. But for on-grade gully, owing to complicated hydraulic behaviour, the entry capacity can hardly be predicted in accuracy by mere calculation.

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.

Overflow weirs should be provided for steep roads (longitudinal gradient>5%) , flat roads (longitudinal gradient<0.5%), sag points and blockage blackspots. For steep roads, flow is rapid and overflow weirs should be provided to accommodate the excess flow. For flat roads, the probability of accumulation of rubbish increases. Therefore, overflow weirs should be provided in these locations to bypass the stormwater flow in case of blockage of gullies caused by trapping of rubbish. [wp_ad_camp_1] Basically, kerb overflow weirs suffer from the drawback that it provides another passage for debris to enter the gullies and therefore bars (either horizontal or vertical) should be provided to prevent the entry of debris into the weirs. For steep roads, as the main concern is to provide an alternative route for excess flow, horizontal bars should be provided in this case to maintain better drainage efficiency. For flat roads, the purpose of overflow weirs is to trap rubbish and therefore, vertical bars should be provided because it is more effective in prevention of entry of debris. 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.

Grease and oils are commonly found in stormwater runoff from catchments. They come from the leakage and spillage of lubricants, fuels, vehicle coolants etc. Since oils and grease are hydrocarbons which are lighter than water, they form films and emulsions on water and generate odorous smell. In particular, these hydrocarbons tend to stick to the particulates in water and settle with them. Hence, they should be trapped prior to discharging into stormwater system. Oil interceptors are installed to trap these oil loads coming from stormwater. In commercial areas, car parks and areas where construction works are likely. It is recommended to establish oil-trapping systems in these locations.

Typical oil interceptors usually contain following compartments:

(i) The first inlet compartment serves mainly for the settlement of grits and for the trapping of floatable debris and rubbish.

(ii) The second middle compartment is used for separating oils from runoff.

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.

The basic mechanism of noise absorptive material is to change the acoustic energy into heat energy. The amount of heat generated is normally very small due to the limited energy in sound waves (e.g. less than 0.01watts). The two common ways for energy transformation are:

(i) Viscous flow loss
The absorptive material contains interconnected voids and pores into which the sound energy will propagate. As sound waves pass through the material, the wave energy causes relative motion between the air particles and the absorbing material and consequently energy losses are incurred.

(ii) Internal fiction
The absorptive materials have some elastic fibrous or porous structures which would be extended and compressed during sound wave propagation. Other than energy loss due to viscous flow loss, dissipation of energy also results from the internal friction during its flex and squeezing movement.

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.