In pipe jacking/microtunneling, it is commonly accepted that cover depths of jacking pipes cannot be too shallow (i.e. less than 2D where D is the diameter of jacking pipes). Why?
Answer: For pipe jacking/microtunneling, the causes of large settlement are loss of face stability, failure to stabilize ground around shafts, presence of annular space around pipes and shield, drag along pipe joints, etc. The settlement mechanism of shallow depths of pipe jacking/microtunneling is the formation of a settlement trough on top of the jacking pipes. The width of the trough depends on soil properties; the larger is the cover depth of jacking pipes, the larger is the width of settlement trough. For the same soil volume loss due to pipe jacking/microtunneling, the width of settlement trough for shallow cover depth is smaller and therefore it results in a larger vertical maximum settlement.
Question No. 02
What is the force exerted by the Tacoma narrows bridge?
Answer: The force exerted to the Tacoma narrows bridge was initially the wind resistance. The wind resistance caused the whole bridge to act as a system with forced vibration with damping.
Question No. 03
What is the mechanism of protection by hot dip galvanizing?
Answer: Hot dip galvanizing protects steel/iron from corrosion by:
(i) It forms a metallic zinc and zinc-iron alloy coating on top of steel surface. This zinc coating reacts with moisture in atmosphere to from zinc salts which act as an insulating layer for steel/iron.
(ii) Zinc is higher than steel/iron in the galvanic series and when these dissimilar metals with different electrical potential are in contact, the zinc anode corrodes and offers sacrificial protection to steel/iron and hence steel/iron is protected from corrosion.
Question No. 04
In pre-stressing work, if more than one wire or strand is included in the same duct, why should all wires/strands be stressed at the same time?
Answer: If wires/strands are stressed individually inside the same duct, then those stressed strand/wires will bear against those unstressed ones and trap them. Therefore, the friction of the trapped wires is high and is undesirable.
Question No. 05
What is a kip?
Answer: 1 kip = 1000 lbs
Question No. 06
What is the difference between fasteners, bolts and screws?
Answer: Fastener is a general term to describe something which is used as a restraint for holding things together or attaching to other things.
The main physical distinction between screws and bolts is that screws are entirely full of threads while bolts contain shanks without threads. However, a better interpretation of the differences between the two is that bolts are always fitted with nuts. On the contrary, screws are normally used with tapped holes.
Question No. 08
How do you measure concrete?
Answer: Cubic feet, Cubic yards, Cubic Meter
What are the advantages of piers constructed monolithically with the bridge deck over usage of bearings?
Answer: Basically, piers constructed monolithically with the bridge deck are advantageous in the following ways:
(i) Movement of the bridge deck is achieved by the bending deformation of long and slender piers. In this way, it saves the construction cost of bearings by using monolithic construction between bridge deck and piers. Moreover, it is not necessary to spend extra effort to design for drainage details and access for bearing replacement. On the other hand, in maintenance aspect substantial cost and time savings could be obtained by using monolithic construction instead of using bearings as bridge articulation.
(ii) Monolithic construction possesses the shortest effective Euler buckling length for piers
because they are fixed supports at the interface between bridge deck and piers. Note: Monolithic construction means that piers are connected to bridge decks without any joints and bearings.
Question No. 10
What is braced excavation all about?
Answer: Excavations are braced to prevent the cavein of surrounding unstable soil.