Question No. 1 What is the load transfer mechanism for paving blocks in pedestrian footway?
Answer: In Hong Kong, footway is normally designed with paving slabs/interlocking blocks instead of concrete because the extensive use of concrete in pavement is boring. Moreover, poor appearance will result in concrete pavement due to frequently trench openings for utility work. In addition, owing to the prolonged setting and curing time of concrete, the use of concrete pavement inevitably generates disturbance to the general public.
The pedestrian loads are taken up through the following ways:
(i) Load carrying capacity of paving slabs/interlocking blocks are derived from their individual strength;
(ii) Pedestrian loads are also supported by interlocking forces provided by friction transfer
through the sand in vertical joints (K. K. Tang & Robert P. Cooper (1986).
Question No. 02
What is the meaning of soil reinforcement?
Answer: Soil reinforcement is the act of improving soil strength to enable it support or carry more load.
Two common examples are:
a) Mixing a soil amendment such as lime into weak clayey soil and re-compacting to improve soil-bearing capacity (often done under the road base in highway construction)
b) Installing plastic or composite webbing layers (called geo-grid material) alternating with compacted soil to produce a stronger sloped soil structure (often done on steep roadway embankments to improve strength and stability)
Question No. 03
If the construction of concrete carriageway is carried out in summer, can expansion joints be omitted?
Answer: If the construction of concrete carriageway is carried out in summer, expansion joints may not be necessary as suggested by Arthur Wignall, Peter S. Kendrick and Roy Ancil. Expansion of concrete carriageway is mainly due to seasonal changes with an increase in temperature from that during construction to the ambient temperature (i.e. the temperature in summer). However, if the construction of concrete carriageway takes place in summer, the concrete carriageway will undergo contraction in the following winter, thus the space available in contraction joints can accommodate the future expansion in the next summer.
Question No. 04
Why are steel tubular marine piles often driven open-ended?
Answer: In marine structures where piles are constantly subject to significant lateral and uplift forces induced by berthing operation and wave action, it is necessary to drive the piles to much greater depth. To avoid premature refusal so that insufficient soil cover may develop which is incapable of providing the required lateral and uplift resistance, tubular piles are normally driven open-ended so that they are driving to greater depths than piles with closed ends.
Question No. 05
What is the difference between engineering stress and true stress?
Answer: In biology, Stress is something that disrupts homeostasis of an organism. In engineering, Stress is an external force that pushes, pulls, twists, or otherwise puts force on something. Engineering stress assumes that the area a force is acting upon remains constant, true stress takes into account the reduction in area caused by the force.
Question No. 06
Why are high and narrow beams not desirable in concrete piers?
Answer: Based on past experience in other countries (Carl A. Thoresen (1988)), high and narrow beams after several years of construction showed signs of serious deterioration at the bottom of the beams. However, the deterioration of pier slabs was not significant when compared with that of the deep beams. The main reason to account for this is due to the close proximity of the deep beams to the sea level. To avoid these problems, either beamless slab or wide with shallow beams are normally designed.
Question No. 07
Why does the pressure increase under soil?
Answer: Soil pressure increases with depth due to the overburden or self-weight of the soil and due to loads imposed upon the soil.
For example, the pressure variation below the depth of soil is linear and the relation is given by pressure = unit wt × depth. As depth increases, there will be a linear increase in the soil pressure.
Question No. 08
Geotechnical Instrumentation is frequently employed for monitoring the condition of reclamation. Sometimes two piezometers are installed inside the same borehole. What is the reason behind this?
Answer: For standpipes, they normally contain one plastic tube between its intention is to measure water level only. However, for piezometers, they are used for measuring pore water pressure in a certain depth below ground. For instance, if there are two clayey layers below ground at different depths, a multiple piezometer including two separate piezometers may be sunk at the same borehole to determine the pore water pressure at these layers respectively. This arrangement has the advantage that it saves the cost of installation of separate boreholes for several piezometers. However, the installation of multiple piezometers within the same borehole is affected by occurrence of leakage along the pipes as suggested by Marius Tremblay (1989).
Question No. 09
What do you mean by honeycomb in concrete?
Answer: Some people call it an air pocket in the concrete or a void.
Question No. 10
In the construction of pump troughs for accommodation of screw pumps, what is the construction method to ensure close contact between the screw pumps and the pump trough?
Answer: In the construction of screw pump troughs, trapezoidal-shaped troughs are usually formed by using normal formwork. In order to enhance close contact between screw pumps and troughs, upon lifting the screw pumps into the troughs screeding works is carried out. Screw pumps are set to blade and trapezoidal-shaped troughs during the rotating action of screw pumps. After the screed sets, it serves to prevent leakage of water during the pumping operation of screw pumps.