Month: October 2018
The following factors govern the choice of a different(particular) gauges:
1. Cost of construction and funds available for the railway project.
2. Volume and nature of traffic.
3. The intensity of population.
4. Industrial and commercial development of the locality.
5. Prospects of future development of the area.
6. Topographical and geological features of the country.
7. Speed of movement required.
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Creep of rails is defined as the longitudinal movement of rails with respect to sleepers in a track. Creep is common to all railway tracks but varies in magnitude considerably from place to place and from time to time. It is observed that the creep occurs in the direction of the dominant traffic.
The following are the principal causes of creep in rails.
According to this theory, wave motion is set up in a resilient track by moving loads of wheels which is the chief cause of creep.
This theory states that the creep in rail is due to the impact of wheels at the end of the rail ahead at joints.
This theory states that the backward thrust on the driving wheel pushes the rail in the backward direction(drag effect), while the other wheels push the rail in the direction of travel and they gave greater effects as compared to drag effect. This results in the creep of rail in the direction of movement of trains.
The amount and direction of creep depend upon starting, accelerating, slowing down, or stopping of the train.
Creep also occurs due to the variation in temperature.
Heavy traffic in one direction will cause creep.
In addition to the above main causes, the following minor causes are also responsible for the development of creep in rails.
1. Creep depends upon the alignment of the track, It is more on curves than on a straight railway track.
2. It also depends upon the grade of the track, type, and age of the rails.
3. Poor maintenance of track components and ill-design of superelevation, curves, joints, etc. will also maybe increase the creep.
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Following are the common methods adopted to prevent creep
1. When creep is distinctly visible, the best remedy is to pull back the rails to their original position by means of crowbars.
2. The creep of rail can be prevented by the use of anchors and sufficient crib ballast.
3. The creep of the track can be prevented by the use of steel sleepers which provide a good grip.
4. Increase in the number of sleepers per rail length helps to prevent creep.
5. Provision of a good drainage system and efficient maintenance of the track helps in minimizing the creep of rails.
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The common effects of the creep of rails are as follows:
1. Sleepers move out of position, This affects the gauge and alignment of the track.
2. The surface of the track gets disturbed. This results in uncomfortable riding.
3. At some places, excessive stresses may develop in fish plates and bolts due to creep. This results in breaking the bolts. The rails are also battered at the ends.
4. In some places, joints are jammed. This prevents the required expansion of rails.
5. The points and crossings get disturbed and the movement of switches becomes difficult.
6. If any rail is removed from the track for any purpose, it becomes difficult to fix it again at the proper position because the gap of this rail becomes either too short or too long due to creep.
7. The ballast is forced out of place.
8. Besides these effects, smashing of fish plates and fish bolts, bending of bars, and kinks at rail joints are common effects of creep.
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Welding of rails is done for the following purpose:
1. Welding is done to increase the rail length by joining two or more rails.
2. It reduces the number of joints and requirements of fish plates and thereby increases the strength joint and makes the track economical.
3. It is done to repair the damaged rails and thus increase their life.
4. The welding process is used to buildup the burnt portion of rail head.
The following four methods are employed for welding of rails.
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Following are the 8 advantages of welding of rails are described below:
1. It satisfies the condition of the perfect joint and thus increases the life of the rail and reduces maintenance costs.
2. It reduces the amount of creep.
3. Expansion effect due to temperature is reduced.
4. By eliminating joints, it provides a good riding quality.
5. It minimizes the wear of rails at joints.
6. Welding facilitates track circuiting on electrified tracks.
7. The cost of track construction by welding of rails decreases due to less the number of rail joints.
8. The welded rail offers more lateral, longitudinal and vertical stability to the track.
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In this type of privy, a pit of suitable size is excavated. The width of pit privies is about 20 cm to 25 cm and the depth varies from 60 to 250 cm.
Two planks are placed over the pit. A temporary shed with bamboo posts and the hedge is constructed over it.
To reduce the bad odour, lime and ash are thrown in the pit from time to time, When the pit is nearly filled up, it is closed by earth or ash and a new pit is excavated.
This type of latrine is of a very temporary nature and is widely adopted for small temporary camps.
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The settlement of the foundation can be defined as the vertical downward movement of the foundation base of a structure into the soil mass. The following common types of settlement are described below
The vertical downward movement of the base of a structure is called settlement. Settlements in soils are of two types:
The immediate settlement is caused by the elastic deformation of soil mass on the application of a load. The consolidation settlement is taking place over a long period of time due to the gradual expulsion of water from the soil pores. The sum of “immediate settlement” and “consolidation settlement” is termed as “total settlement(S)”.
Thus, S= Si +Sc
The relative settlement of the adjacent portions of a structure is termed differential settlement. In other words, when the different parts of the foundation settle at different rates, it is called differential settlement.
Differential settlement can lead to cracks in the walls, beams, floors, and other structural problems. It is most detrimental to the structure and should not be allowed to exceed the permissible limits.
This is the maximum limit of settlement which can be allowed for foundation soil without having any risk of danger to the structure.
As the name suggests, this type of settlement occurs uniformly i.e. the entire foundation settles evenly and at the same rate. The probability of structural damage in these cases is relatively low.
When the settlement occurs vertically in a downward direction, it is called vertical settlement. It can be caused by soil erosion, soil consolidation, or the weight of the building itself.
Unlike vertical settlement, lateral settlement refers to the horizontal movement of the foundation. It can happen for the expansion or contraction of soil, slope instability, the presence of a water body near the foundation, or the presence of underground water. Although it is more appropriate to call it a lateral movement of the foundation instead of a lateral settlement of the foundation.
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The settlement of the foundation can be defined as the reduction in the thickness of soil mass or as the vertical downward movement of the foundation base of a structure into the soil mass.
Settlement may be due to one or more following factors
1. Due to external static loads from structures.
2. Due to the self-weight of the soil such as recently placed fills.
3. Due to the lowering of the groundwater table.
4. Due to the flowing or slipping of soil particles.
5. Due to the excessive loading on the adjacent foundation.
6. Due to the excessive surrounding soils.
7. Due to the impact effect of vibration.
8. Due to the failure of base concrete etc.
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The term sludge volume index or sludge index is defined as the volume occupied in ml by one gm of solids in the mixed liquor after settling for 30 minutes.
It is used to indicate the physical state of the sludge produced in the biological aeration system.
It represents the degree of concentration of the sludge in the system, and it is determined experimentally.
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