The freeboard is defined as the vertical distance from water surface to the top of channel bank. The selection of freeboard is dependent on the consequence should overflow out of channel bank occurs. Other than that,consideration should also be given to prevent waves, superelevation and fluctuations in water surface from overflowing the channel banks.

Generally, a 300mm freeboard is generally considered acceptable. For steep channels, it is preferably to have the height of freeboard equal to the flow depth to account for high variations in swift flow induced by waves, surges and splashes.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.

A penstock is commonly used to control the flow and water level and for isolation of fluid. It mainly consists of a sliding door which is controlled by mechanical spindle moving through a hole in a frame built onto a structure. Penstock is the term used in UK while sluice gate is more commonly adopted outside UK. In the design of penstock, it is important to identify if it would take on-seating head or off-seating head.

On-seating head refers to the water pressure forcing the penstock into the wall while off-seating head refers to the water pressure forcing the penstock out of the wall as shown below.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.

During the construction of new pavement, vibratory roller and heavy equipment are needed to compact the filling material and bituminous material. These heavy equipment could generate very high impact load with short duration on the concrete pipes. It requires an extremely even and uniform support in order to safely support these loads. Therefore, it is not uncommon that construction vehicles are primary source of crack-producer and it usually results in the formation of circumferential cracks.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.

Concrete pipes are designed to be uniformly supported along the length to carry vertical loads on its top. They are normally not intended to serve as a beam to carry loads in longitudinal direction under poor ground supports (i.e. high and low spots in bedding). Under cantilever beam action and simply support beam action as shown in the diagram below, circumferential cracks would develop in concrete pipes. Circumferential cracking develops in concrete pipes only when pipe bedding becomes non-uniform. Therefore in unstable ground conditions such as soft spot and hard foundations, care should be taken to provide firm and even support to concrete pipes.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.

Higher porosity of recycled aggregate compared to natural aggregate leads to a higher absorption. Moreover, recycled aggregate has lower specific gravity than natural aggregate and will make concrete with higher drying shrinkage and creep. Such differences become more significant when there is an increasing amount of recycled fine aggregates. Recycled aggregates also contain more chloride than normal aggregates which may affect the durability of concrete. Moreover, excessive recycled fine aggregates can also generate a harsh concrete mix with low workability.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.