Question No. 01
In terms of pumping performance, how should engineers determine the use of radial flow pumps and axial flow pumps?
Answer: Specific speed is usually defined for a pump operating at its maximum efficiency. In order to minimize the cost of future operation, it is desirable to operate the pumps as close to the maximum efficiency point as possible. The specific speed for radial flow pumps is relatively small when compared with that of axial flow pumps. This implies that radial flow pumps tend to give higher head with lower discharge while axial flow pumps tend to give higher discharge with lower head.
Question No. 02
What is difference in purpose for conducting surface regularity test and sand patch test (test on texture depth)?
Answer: The purpose of surface regularity test is to measure the riding quality of pavements and the same requirement and standard is applied to both concrete and bituminous carriageway. On the other hand, sand patch test is used for checking the skid resistance of road pavements. Moreover, it is related to traffic noise because the intensity of noise generated from road traffic is related to texture depth of carriageway.
Question No. 03
For typical pile bents in marine piers, how is vertical loads related to horizontal capacity of the pile bents?
Answer: Let’s consider a pile bent with a top slab supported by two ranking piles, each incling at an equal angle to the pier slab. In designing such a system, truss action is normally adopted to analyze the pile bent. When the reaction forces of these piles, horizontal forces (e.g. due to berthing and de-berthing of vessels) and vertical forces (e.g. superimposed deck loads) are analyzed by drawing a force polygon, it is noted that lateral resistance of the pile bent is dependent on the vertical load, i.e. lateral resistance is small when vertical loads are high.
Question No. 04
In determining the effective stress parameters of a soil sample, which test is preferable, consolidated un-drained test or consolidated drained test?
Answer: The effective stresses parameters of a soil sample can be obtained from both consolidate dun-drained test and consolidated drained test. However, consolidated un-drained test is normally selected because of the following reasons:
(i) Time taken for consolidated un-drained test is shorter than that of consolidated drained test. It is because consolidated drained test requires the full dissipation of excess pore water pressure of the soil during testing and it takes long time when soils of low permeability are tested.
(ii) Useful information can be obtained from the stress path of consolidated un-drained test.
(iii) Failure occurs in lower stress level when compared with consolidated drained test.
Question No. 05
What is kn measurement?
Answer: kn (both letters lowercase) is knots, which is a speed nautical miles per hour.
Question No. 06
What are the design considerations for dowel bars in joints of concrete carriageway?
Answer: The behavior of dowel bars resembles that of piles in soils subject to lateral loads. Failure of the joint occurs by yielding of steel under bending action or by crushing of concrete due to bearing stresses.
In general, the spacing of dowel bars should not be too close which may pose problems during construction. However, it should be not too wide to allow the occurrence of bending between the dowel bars. On the other hand, regarding the length of dowel bars, it should not be too long because the induced stress at the end of long dowel bars is insignificant and is not effective in transferring loads between adjacent concrete panels. However, if the dowel bars are too short, the stress at the face of joint is increased resulting in concrete crushing. Reference is made to Ministry of Transport (1955).
Question No. 07
What is the function of a sand layer underlying paving slab/interlocking blocks?
Answer: Normally after the laying of sub-base layer of the paving slab/interlocking blocks, a 30 mm thick sand bedding is screeded and tamped over the pavement area. Then paving slabs are laid horizontally with joints of 2-3 mm wide and are laid in uphill direction. After completing the laying of paving slabs, sand used for filling joints is spread over the surface of the units and brushed into the joints such that all joints are completely filled. The paving slabs are then bedded into final position by using plate vibrators. The sand layer serves the same purpose of normal blinding layer under concrete structure:
(i) Provide a level and flat surface for the paving slab/interlocking blocks to lay on;
(ii) Protect the foundation (i.e. underground sub-grade and sub-base layer) against adverse outside conditions (e.g. bad weather) during construction of the laying work of paving slab/interlocking blocks.
Question No. 08
How do we calculate absolute pressure?
Answer: Absolute is equal to gauge pressure plus atmospheric.
Question No. 09
What is the origin of name Railway Sleepers?
Answer: When sleepers were added below the railway, lines the trains ran more smoothly and people fell asleep on their journeys.
Question No. 10
What is the relation of bearing pressure on soil nail head to the ratio La /Lb, where La is the length of soil nail before the potential slip circle while Lb is the length of soil nail beyond the potential slip circle?
Answer: The unstable soil mass before the potential circular slip is resisted by two components: soil nail head bearing pressure and friction of soil nail in the unstable soil mass. Therefore, the longer is the length of soil nail before potential slip circle La, the higher is the proportion of forces being resisted by frictional forces and hence the smaller amount is to be resisted by soil nail head. Hence, the smaller the ratio La/Lb, the greater is the resistance provided by soil nail head.