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Defination Of Irrigation System.

An irrigation system is a set of components and techniques designed to deliver water to plants, crops, or landscapes to meet their water requirements. These systems are essential in agriculture, gardening, landscaping, and even for maintaining sports fields and golf courses. Irrigation systems help ensure a consistent and controlled water supply, which can improve crop yields, maintain healthy plants, and conserve water resources.

Components of a typical irrigation system include:

This Article Covers About Hydrographic Survey like Applications, Uses, Instruments And Procedure Of Hydrographic Surveying.

Hydrographic Survey

Hydrographic survey is an exploration of water-bound areas using sonar equipment.It can used to find underwater objects or map out land. This survey used to get information about the bottom of the sea. This information can used to create maps and charts for safe navigation. Instruments Used In Hydrographic Surveying The ship's officer who carries out a hydrographic survey will use a sounding machine to measure the depth of the water and collect samples of material from the sea bed. A sound speed meter used to calculate the depth of water by measuring the time it takes for sound waves to travel between two points. The accuracy of this instrument is affected by the depth of water and the temperature. A bathymetric chart displays the measured depth of water as cont

Procedure Of Hydrographic Survey Hydrographic surveys conducted for a wide range of purposes, but they all have the same general procedure. Once the survey designed and planned, you will need a suitable watercraft to carry out the survey. A hydrographic vessel required for open water work, while a low power boat will suffice for nearshore surveying. We've found that a rigid inflatable boat or even an inflatable kayak can used, provided it has sufficient capacity to carry the necessary equipment.

This article Covers Classification Of Surveys Based On Field And Instrument One By One. Surveying Defined As The Science Of Making Measurements Of The Earth Specially Surface Of Earth, This Being carried Out By Finding Spatial Location Of Points On Or Near Surface Of The Earth.

Classification Of Surveys

Before Going With Classification Of Surveys Let's See Objectives Objectives Of Surveying - To Collect Field Data - To Prepare Plan Or Map of The Area Surveyed - Analyse And To Calculate The Field Parameters For Setting Out Operation Of Actual Engineering Work. - To Set Out Field Parameters At The Site For Further Engineering Works. Lets Classification Of Surveys, According To Use And Purpose Of The Final Maps, Surveys May Be Classified, Under The Following Different Heads, Classification Based Upon Nature Of The Field/Purpose Topographical Survey:- These Survey Used To Obtained Maps Which Shows Details Of Natural And Man-Made Features On The Earth Surface Including Elevation.

Scale = (1:25000 To 1:10 Lakh) Engineering Survey:- These Surveys Used For Engineering Works Like Railway, Highway, Canal, Bridge, Etc Scale, - Building:- 1:50 To 1:200 - Bridge And Other Civil Engineering Work:- 1:500 To 1:2500 - Highway:- 1:1250 To 1:50000 Cadastral Survey:- The Surveys Which Generally Plotted To A Larger Scale Then Topographical Surveys And Carried Out For Fixing The Property Lines.

Scale 1:1000 To 1:5000 Hydrographic Survey:- The Survey Which Deals With Mapping Of Large Water Bodies For The Purpose Of Navigation, Construction Of Harbour Works, Prediction Of Tides And Determination Of mean Sea Level Called Hydrographic Survey.

Hydrographic Survey Consists Of Preparation Of Topographical Maps Of The Shore And Banks, By Taking Soundings End Determining The Depth Of Water At A Number Of Places And Ultimately Surveying Bathymetric Contours Under Water. Astronomical Survey:- With The Help Of This Survey We Can Determine Latitude, Longitude And LMT At Any Place On The Earth Surface. Geological Survey:- It Done To Determine Information About Various Strata Of Earth Surface. Classification Based On Instrument Chain Survey:- Chain Survey Simplest Type Of Surveying In which Only Linear Measurements Done With The Help Of Chain Or Tape And No Angular Measurements Done.

Compass Surveying:- It Is A Branching Of Surveying In Which Horizontal Angles And Direction Of Lines Are Measured With Compass And Length Of Line Are Measured With Chain And Tape.

Theodolite Surveying:- In This Surveying Horizontal And Vertical Angles Measured With Theodolite And Distance Measured With Chain Or Tape.

Levelling:- In This Type Of Surveying Elevations Of Various Points Measured With Levelling Instrument And Vertical Staff. Plane Table Survey:- In Plane Table Surveying Plan Or Map Is Produced By Determining Direction Of Various Points And Taking Linear Measurement With Chain Or Tape.

Tacheometric Surveying:- In This Surveying Horizontal And Vertical Distances Are Measured With A Instrument Called Tacheometer.

Photogrammetric Surveying:- In This Surveying Photographs Taken For An Area Which Are Inaccessible Or Time Available Is less And Area To Be Survey Large.

This Article Covers About Track Drainage In Railway Like Need, Requirements And Track Drainage System One By One.

Track Drainage In Railway

Track drainage can defined as the interception, collection, and disposal of water from, upon, or under the track. It accomplished by installing a proper surface and sub-surface drainage system. Need for Proper Track Drainage Water is the greatest threat to a railway track, and the most prominent factor that adversely affects track maintenance is improper drainage. Excess water affects the stability of the embankment, and the bearing capacity of the soil and its resilience to shear gets considerably reduced. Railway engineers give maximum importance to the proper drainage of the track and the need to do so is felt because of the following concerns Settlement of embankment - Excess water may cause the embankment to settle. - An unequal settlement may lead to variation in cross levels as well as longitudinal levels thereby affecting the safety and riding quality of the track. Reduction in bearing capacity - The bearing capacity of the soil as well as its resistance to shear diminishes due to excess water in the soil. - This in turn leads to numerous problems and finally affects the safety and stability of the track. Failure of embankment - The percolation of water in the embankment increases the weight of the soil on the one hand and reduces its bearing capacity and shear resistance on the other. - This makes the formation unstable. - This is a common reason for the failure of embankments, which occurs in the form of slips. Formation of ballast pockets - Excess moisture leads to punctures in the formation. - The constant hammering action of running trains causes the sleepers to move up and down, resulting in ballast pockets, pumping sleepers, and other such problems. - All these factors lead to poor riding quality. Shrinkage and cracking of banks - The embankment soil cracks and shrinks once excess water dries up. - The problem becomes acute in the case of poor soils. - This in turn leads to many problems such as the loss of ballast in the cracks and uneven settlement, which have an adverse effect on track maintenance. Adverse effects of black cotton soil - There are certain soils, such as black cotton soil, which become plastic in nature due to the accumulation of excess water. - The formation shrinks due to change in moisture content. - The bearing capacity of the soil greatly reduced due to the excess water. - These problems imperil the safety of the track. Formation of slush - Slush formed due to the dynamic load of running trains. - It forced out, thus badly clogging the ballast. - This makes the maintenance of the track very difficult. Sources of Percolated Water in the Track Water can percolate to the formation of the track through any of the following methods. By gravity This includes water that collects due to rains, etc., moving into the subgrade because of the effect of gravity. This movement resisted by the permeability of the soil. The effective ways of reducing the progress of water by this method are the following. - Provision for drainage on the top of the embankment in the form of cross fall, side drains, lowering of cess, etc. - Turfing of side slopes of the embankment By capillary action At times water rises into the subgrade by way of capillary action. The capillary rise of water can prevented by providing a pervious layer in the embankment which serves a capillary break. From adjacent areas In this case, water from some nearby source seeps into the subgrade. Water seepage can reduced by taking the following steps. - Diverting the original source of water - Providing effective paved catch water drains - Providing inverted filters and underground drains By hydroscopic action from atmosphere The moisture present in the atmosphere is comparatively very small and has very little effect on the total moisture content of the soil. Requirements of a Good Track Drainage Railway System A good drainage system should satisfy the following requirements. Surface water should not percolate to track One of the basic requirements of a good track drainage system is that surface water from rains and adjacent areas should not percolate and seep into the formation of the track. Effective side drains The size of the side drains should be adequate with a proper slope, so that they effectively carry all the surface water away. Longitudinal drains to saucer-shaped The longitudinal drains provided between two tracks should preferably have a saucer-shaped cross section so that they can collect water from both sides. Provision for clearing and inspection The drains provided for drainage should be such that they can inspected and cleared periodically. Drain top to be below cess level Normally, the drain top should not be above the cess level for the effective drainage of the ballast bed. No erosion of banks The flow of water along the slope and across the track should not cause erosion of the banks or the slopes of the banks. Formation to be of good soil Ideally, the formation and subgrade should made of a pervious, coarse-textured soil. Such soils are more permeable, retain less capillary water, and respond more favourably to a surface drainage system. Proper sub-surface drainage Arrangements should made for a good sub-surface drainage system to drain off the water retained the track. This is more relevant in the case of defective formations. Proper outfall Longitudinal drains should designed so as to provide a proper outfall, from where the water can eventually drain off. Special arrangements for waterlogged areas and other difficult situations A good track drainage system should have special arrangements for the drainage of waterlogged areas and for all other related perennial problems. Practical Tips for Good Surface Drainage The following measures will ensure that the track drainage system gives a good performance. Maintain proper cess level Tracks on embankments get drained as long as the proper cess levels maintained and the ballast is clean. However, in cuttings and in yards, where water cannot recede freely and quickly from the track, a well planned drainage system must be provided. No vegetation There should be no growth of vegetation in the track, as this indicates clogging of the ballast and a lack of adequate track drainage. Such stretches of tracks should overhauled or deep screened. The ballast should be clean so that rainwater can easily flow out of the track. Area below rail foot to be clear About 25 to 50 mm of the area below the rail foot should kept clear of any ballast, earth, or cinder on all lines inside and outside the yards. This would enable good surface flow as well as avoid corrosion and failure of track circuits. Cleaning and repair of drains All drains should cleaned and repaired as a part of annual through packing, not only on run-through lines but also on all other running lines in yards. Track Drainage Railway Systems As mentioned earlier, a good track drainage system should essentially ensure that no water percolates into the track at either the surface or the sub-surface levels, And the arrangements for the drainage of sub-surface water should be good and effective wherever required. Track drainage should handled in two distinctive phases. Surface drainage Surface water due to rain or snow, or from adjacent areas should drained off properly by designing well-planned and effective surface drains. Sub-surface drainage In case water percolates into the formation due to bad soil or such other reasons, the formation gets adversely affected and this has a bearing on the safety and stability of the track. Surface drainage Surface drainage is dealt with in three different stages covering the entire length of the track. - Drainage in mid-sections between railway stations - Drainage in station yards - And Drainage of station platforms Drainage in Mid-sections Between Railway Stations A drainage system between two railway stations consists of the following features. Side drains Side drains should be provided along the track in cuttings and zero fill locations, where the cess level is not above the ground level. The typical cross section of a side drain is shown below. All drains must have an adequate gradient to enable the free flow of the collected water.

Lining of drains Side drain lining is imperative on Group A routes and preferable on other routes, except those routes where the drains are in rocky strata. Adequate opening under level crossing In order for all the water to flow out of the side drains in cuttings, adequate openings should be provided under level crossings, around trolley refuges, and around the overhead electric masts. Catch water drain Catch water drains should be provided wherever necessary, in cuttings. Their size should be worked out according to the volume of the water the drain is expected to carry. No surplus ballast Surplus ballast in the shoulders of the track retards drainage and encourages vegetation growth. All extra ballast should be taken out of the track and stacked in small heaps beside the track. Drainage in Station Yards When planning the drainage of station yards, the following guidelines should be kept in mind. Open surface drains Surface drains should generally be left open to make cleaning and inspection convenient. When designing in-yard drains, a velocity range of 0.5 to 1.0 m/s may be allotted for earthen drains and 1.0 to 2.0 m/s for lined (or masonry). Saucer-shaped drains As mentioned earlier, the longitudinal drains that lie between two tracks should be saucer-shaped with curved sides. However, drains with vertical sides may be provided wherever saucer-shaped drains are not practicable. Drain top not to be above cess level Normally, the drain top should not be above the cess level for the effective drainage of the ballast bed. However, if it is essential that a drain with a higher top level be provided in order to retain the ballast, weep holes must also be provided at the assumed cess level and the drain so designed that the water it carrier does not flow the base level of the weep holes. Outflow and slope Wherever there is a proper outfall available at either end of a yard, the longitudinal drains provided should have their slopes facing in the direction opposite to the middle of the yard. This will ensure the minimum size and depth of the drains. Position of ballast sections The ballast section in station yards should be the same as that on the main line. Network of cross and longitudinal drains Every station yard should have a network of cross and longitudinal drains, whether earthen or masonry, which allows water collected due to storms to be carried away in the least possible time. The arrangements for surface drainage at water columns and carriage watering points with washing hydrants should be efficiently maintained. At these locations, Water must be adequately trapped and borne away in a pipe or a lined drain. Open drain section Figure shows a detailed sketch of the open drains that are provided between two tracks on a railway line.

Drainage of Station Platforms The following points should taken into account when planning the drainage system of a platform. Slopes away from track Normally, all end platforms should sloped away from the track. The details of the drainage system of a platform illustrated in Fig.

This Article Covers Various Types Of Runway Configurations And Their Combinations One By One.

Types Of Runway

Before Going With Types Of Runway Configurations Let Us See What Is Runway? Runway A runway is a rectangular area on the airport surface prepared for the takeoff and landing of aircraft. An airport may have one runway or several runways which sited, oriented, and configured in a manner to provide for the safe and efficient use of the airport under a variety of conditions. Several of the factors which affect the location, orientation, and number of runways at an airport include local weather conditions, particularly wind distribution and visibility, the topography of the airport and surrounding area, the type and amount of air traffic to serviced at the airport, aircraft performance requirements, and aircraft noise.

Runway Configurations The term runway configuration refers to the number and relative orientations of one or more runways on an airfield. Many runway configurations exist. Most configurations are combinations of several basic configurations. The basic configurations are - Single runways, - Parallel runways, - Intersecting runways, and - Open-V runways. Single Runway It has estimated that the hourly capacity of a single runway in VFR (visual flight rules) conditions is somewhere between 50 and 100 operations per hour, while in IFR (instrument flight rules) conditions this capacity reduced to 50 to 70 operations per hour, depending on the composition of the aircraft mix and navigational aids available. Parallel Runways The capacities of parallel runway systems depend on the number of runways and on the spacing between the runways. Two, three, and four parallel runways are common. The spacing between parallel runways varies widely. For the purpose of this discussion, the spacing is classified as close, intermediate, and far, depending on the centreline separation between two parallel runways. Close parallel runways spaced from a minimum of 700 ft (for air carrier airports) to less than 2500 ft. In IFR conditions an operation of one runway is dependent on the operation of other runway. Intermediate parallel runways spaced between 2500 ft to less than 4300 ft. IFR Condition In IFR conditions an arrival on one runway is independent of a departure on the other runway. Far parallel runways spaced at least 4300 ft apart. If the terminal buildings placed between parallel runways, runways always spaced far enough apart to allow room for the buildings, the adjoining apron, and the appropriate taxiways. When there are four parallel runways, each pair spaced close, but the pairs spaced far apart to provide space for terminal buildings. In VFR conditions, close parallel runways allow simultaneous arrivals and departures, that is, arrivals may occur on one runway while departures are occurring on the other runway. Aircraft operating on the runways must have wingspans less than 171 ft for centreline spacing at the minimum of 700 ft. The hourly capacity of a pair of parallel runways in VFR conditions varies greatly from 60 to 200 operations per hour depending on the aircraft mix and the manner in which arrivals and departures processed on these runways. Similarly, in IFR conditions the hourly capacity of a pair of closely spaced parallel runways ranges from 50 to 60 operations per hour, of a pair of intermediate parallel runways from 60 to 75 operations per hour, and for a pair of far parallel runways from 100 to 125 operations per hour. Intersecting Runways Many airports have two or more runways in different directions crossing each other. These are referred to as intersecting runways. Intersecting runways are necessary when relatively strong winds occur from more than one direction, resulting in excessive crosswinds when only one runway is provided. When the winds strong, only one runway of a pair of intersecting runways can used, reducing the capacity of the airfield substantially. If the winds relatively light, both runways can used simultaneously. The capacity of two intersecting runways depends on the location of the intersection (i.e., midway or near the ends), the manner in which the runways operated for takeoffs and landings, referred to as the runway use strategy, and the aircraft mix. The farther the intersection is from the takeoff end of the runway and the landing threshold, the lower is the capacity. The highest capacity achieved when the intersection is close to the takeoff and landing threshold. Open-V Runways Runways in different directions which do not intersect are referred to as open-V runways. Like intersecting runways, open-V runways revert to a single runway when winds are strong from one direction. When the winds light, both runways may used simultaneously. The strategy which yields the highest capacity is when operations are away from the V and this is referred to as a diverging pattern. In VFR the hourly capacity for this strategy ranges from 60 to 180 operations per hour, and in IFR the corresponding capacity is from 50 to 80 operations per hour. When operations toward the V it is referred to as a converging pattern and the capacity is reduced to 50 to 100 operations per hour in VFR and to between 50 and 60 operations per hour in IFR. Combinations of Runway Configurations From the standpoint of capacity and air traffic control, a single-direction runway configuration is most desirable. All other things being equal, this configuration will yield the highest capacity compared with other configurations. For air traffic control the routing of aircraft in a single direction is less complex than routing in multiple directions. Comparing the divergent configurations, the open-V runway pattern is more desirable than an intersecting runway configuration. In the open-V configuration an operating strategy that routes aircraft away from the V will yield higher capacities than if the operations reversed. If intersecting runways cannot avoided, every effort should made to place the intersections of both runways as close as possible to their thresholds and to operate the aircraft away from the intersection rather than toward the intersection. Naming Of Runway Runway are named by a number between 01 and 36, which generally the magnetic azimuth of the runways heading in decadegrees. This heading differs from true north by the local magnetic declination. A runway can normally used in both directions and named for each direction separately. Runway Marking The area marked with yellow chevrons (V shapes) are the blast pads, also referred to as overrun areas or stop ways. These areas often constructed before start of a runway to reduce the erosion of earth by the jet blast produced by large planes when they power up for take-off. Blast pads often not as strong as the main paved surface of the runway and aircraft not allowed to use it except in extreme emergencies. The threshold essentially the start or end of the actual runway itself. the touch down zone is the target area for pilots to stick the wheels of their aircraft on the runway.

Runway Safety

Types of runway safety incidents include:- Runway Excursion- An Incident Involving only a single aircraft, where it makes an inappropriate exit from runway.

Runway Overrun- A type of excursion where the aircraft unable to stop before the end of runway.

And Runway Incursion- An incident involving incorrect presence of vehicle, person or another aircraft on the runway disaster.

This Article Covers About Principle Of Interlocking In Railway With Various Methods One by One.

Interlocking In Railway

Interlocking is a device or a system meant to ensure the safety of trains. With the increase in the number of points and the signals and introduction of high speeds it has become necessary to eliminate human error, which would otherwise lead to massive losses of life and property. The points and signals set in such a way that the cabin man cannot lower the signal for the reception of a train unless the corresponding points have set and locked. The signal thus interlocked with the points in a way that no conflicting movement is possible and the safety of trains ensured. Interlocking may therefore, defined as a technique, achieved through mechanical or electrical means by which it ensured that before a signal is taken 'off, the route which the signal controls properly set, locked and held till such time the entire route traversed by the train and at the same time all the signals and points, the operation of which would lead to conflicting movements, are locked against the feasibility of such conflicting movements. The signal and interlocking systems designed that the failure of any equipment results in the turning 'on' of the signal, thus ensuring train safety. Essentials of Interlocking Lever frames and other types of equipment provided for the operation and control of signals, points, etc, must interlocked and arranged as to comply with the following essential regulations - It should not possible to turn a signal off unless all points for the line on which the train is to received correctly set, all the facing points locked, and all interlocked level crossings closed and inaccessible to road traffic. - The line should fully isolated before the signal turned off, i.e., no loose wagons should be able to enter this line. - After the signal has taken off, it should not be possible to make adjustments in the points or locks on the route, including those in the isolated line. Also, no interlocked gates should, released until the signal replaced to the 'on' position - It should not be possible to turn any two signals off at the same time, which can lead to conflicting movements of the trains. - Wherever feasible, the points should interlocked as to avoid any conflicting movement. Standards of Interlocking The speed of a train depends on a number of factors such as the haulage capacity of the locomotive, the fitness of the track, the fitness of the rolling stock, the load of the train, the ruling gradient and standard to which the signalling system is provided. Signaling arrangements The signalling equipment, manner of locking points, and operation of signals and points differ in the different standards of interlocking. The types of signalling equipment provided at different interlocked stations and other requirements to met for each of the four categories do differ. Locking of points The method of locking of points is the key locking in Standard-I. It is an indirect method of interlocking between signals and points. In Standard-II, a plunger type facing point lock used. The plunger lock can operated from the cabin or from the site itself. In standard-Ill and IV, the points to centrally operated and the locking between points and signals required to be direct. Isolation of lines In Standard-I, isolation is optional. In Standards II, III, and IV, the main line must isolated from all the adjoining lines. Methods of Interlocking In Railway There are basically two methods of interlocking as explained below. Key Interlocking

Key interlocking is the simplest method of interlocking and still exists on branch lines of small stations on Indian Railways. The method involves the manipulation of keys in one form or the other. This type of interlocking is normally provided with standard interlocking with a speed limit below 50 km per hour. The simplest arrangement of key interlocking accomplished in the following manner. - Take the example of a station with a main line and a loop line, the point can set either for the main line or branch line. - The point has two keys, the first is key A, which can taken out when the point set and locked for the main line. Similarly, key B can taken out when the point set and locked for the loop line. At any given time either key A or key B can taken out, depending upon whether the route set for the main line or the loop line. - The lever frame operating the signals is provided with two levers. The lever concerning the main line signal can operated only by key A and similarly the loop line signal lever can operated only by key B. - If the train received on the main line, the points set and locked for the main line and key A released. This key used for interlocking the main line signal lever, thus lowering the signal for the main line. Since key A cannot used for interlocking and lowering the loop line signal, only the appropriate signal can taken off. This type of interlocking called indirect locking. Mechanical system of interlocking in railway Almost 70 per cent of railway stations in the country work with the mechanical system of signalling. The interlocking arrangements for mechanical signalling system have to mechanically oriented. Two systems of mechanically designed signals: - Single-wire system and the - Double-wire system. A mechanically structured signal has (i) spectacle with an arm; (ii) signal post, which may be tubular or lattice. Longer posts chosen to be lattice; and (iii) a counterweight to help pull the wire back to allow the signal to go back to its on/normal position. Such mechanical structures of signals are: (i) two-aspect semaphore signal and (ii) multiple aspect semaphore signal. Mechanical interlocking or interlocking on lever frames is an improved form of interlocking compered to key locking. Electrical system of interlocking in railway As the signal displays fixed light illuminated by incandescent lamp or a light emitting diode (LED) signal, The operation of such system may through mechanically operated levers or by push buttons provided on the yard layout depicted on the top of panel box to be termed as the control cum indication panel. Under the electrical signalling system the colour light signals used in any case operated by lever, points - operated by wrought iron solid 33 mm rod; - operated by electric point machines or operated by Control cum Indication Panel operating points by an electric point machine with signals coloured light. The system of operation of electrically operated signals by levers is hybrid and invariable an interim measure to suit 25 kV ac traction, to subsequently converted to operation by control-cum indication panel. Typical Cases of Interlocking In Railway The following typical cases of interlocking usually encountered. Normal Locking Normal locking In this case, pulling one lever locks the other lever in its normal position. Such locking shall required in situation like the signal lever locking a point lever, when the signal requires the point to moved for train movement. Back Locking or Release Locking

This Article Covers About Track Junction With Various Types Of Junctions One By One.

Track Junction

Track junctions are formed by the combination of points and crossings. Their main objective is to transfer rail vehicles from one track to another or to enable them to cross from one track to another. Depending upon the requirements of traffic, there can be several types of track junctions with simple track layouts. The most commonly used layouts Or Track Junction Types discussed in the following. Turnout Of Similar Flexure A turnout of similar flexure (Below Fig.) continues to run in the same direction as the main line curve even after branching off from it. The degree of the turnout curve will be higher than that of the main line curve. The degree and radius of the turnout curve given by the formulae

- Where Ds is the degree of the outer rail of the turnout curve from the straight track, - Dm is the degree of the rail of the main track on which the crossing lies, i.e., the inner rail in Fig. above, - Dt is the degree of the rail of the turnout curve on which the crossing lies, i.e., the outer rail, - Rs is the radius of the outer rail of the turnout curve from the straight track, and - ft, is the radius of the rail of the turnout curve on which the crossing lies, i.e., the outer rail. Turnout Of Contrary Flexure A turnout of contrary flexure takes off towards the direction opposite to that of the main line curve. In this case, the degree and radius of the turnout curve given by the following formulae Dt = Ds-Dm Rt = Rs Rm /(Rm –Rs) Here, Dm is the degree of the rail of the main track on which the crossing lies, i.e., the outer rail in Fig. below.

Symmetrical Split "Alien a straight track splits up in two different directions with equal radii, the layout known as a symmetrical split (Fig. below). In other words, a symmetrical spat is a contrary flexure in which the radii of the two curves are the same.

Three-Throw Switch In a three-throw arrangement, two turnouts take off from the same point of a main line track. Three-throw switches used in congested goods yards and at entry points to locomotive yards, where there is much limitation of space.

A three-throw switch has two switches and each switch has two tongue rails placed side by side. There is a combined heel block for both the tongue rails of the switch. The switches can operated in such a way that movement is possible in three different directions, that is, straight, to the right, and to the left. Three-throw switches are obsolete now as they may prove to be hazardous, particularly at higher speeds, because the use of double switches may lead to derailments.

Double Turnout A double turnout or tandem is an improvement over a three-throw switch. In a double turnout, turnouts staggered and take off from the main line at two different places. This eliminates the defects of a three-throw switch, as the heels of the two switches kept at a certain distance from each other. The distance between the two sets of switches should be adequate to allow room for the usual throw of the point.

Double turnouts mostly used in congested areas, particularly where traffic is heavy, so as to economize on space. Diamond Crossing

A diamond crossing is provided when two tracks of either the same gauge or of different gauges cross each other. It consists of two acute crossings (A and C) and two obtuse crossings (B and D).

Single Slip and Double Slip In a diamond crossing, the tracks cross each other, but the trains from either track cannot change track. Slips are provided to allow vehicles to change track. The slip arrangement can be either single slip or double slip. In single slips, there are two sets of joints, the vehicle from only one direction can change tracks. And In single slip shown in Fig, the train on track A can change to track D, whereas the train on track C remains on the same track, continuing onto track D.

In case of double slips, there are four sets of points, and trains from both directions can change tracks. In the double slip shown in Fig. the trains on both tracks A and C can move onto either track B or D.

Scissors Crossover A scissors crossover enables transferring a vehicle from one track to another track and vice versa. It is provided where lack of space does not permit the provision of two separate crossovers. It consists of four pairs of switches, six acute crossings, two obtuse crossings, check rails, etc.

Gauntletted Track Gauntleted track is a temporary diversion provided on a double-line track to allow one of the tracks to shift and pass through the other track. Both the tracks run together on the same sleepers. It proves to a useful connection when one side of a bridge on a double-line section is required to be blocked for major repairs or rebuilding. The speciality of this layout is that there are two crossings at the ends and no switches .

Gauntletted tracks also used on sections where trains have to operate on mixed gauges, say, both BG and MG, for short stretches. In such cases, both the tracks are laid on the same set of wooden sleepers .

Gathering Line

Triangle

Double Junctions

A double junction (Fig. below) required when two or more main line tracks are running and other tracks are branching off from these main line tracks in the same direction. The layout of a double junction consists of ordinary turnouts with one or more diamond crossings depending upon the number of parallel tracks.

This Article Covers Rail Wear Their Types, Measurements And Method To Reduce Wear One By One.

Rail Wear

Due to the passage of moving loads and friction between the rail and wheel, the rail head gets worn out in the course of service. The impact of moving loads, the effect of the forces of acceleration, deceleration, and braking of wheels, the abrasion due to rail-wheel interaction, the effects of weather conditions such as changes in temperature, snow, and rains, the presence of materials such as sand, the standard of maintenance of the track, and such allied factors cause considerable wear and tear of the vertical and lateral planes of the rail head. Lateral wear occurs more on curves because of the lateral thrust exerted on the outer rail by centrifugal force. A lot of the metal of the rail head gets worn out, causing the weight of the rail to decrease. This loss of weight of the rail section should not be such that the stresses exceed their permissible values. When such a stage is reached, rail renewal is called for. In addition, the rail head should not wear to such an extent that there is the possibility of a worn flange of the wheel hitting the fish plate. Types of Wear on Rails A rail may face wear and tear in the following positions (a) On top of the rail head (vertical wear) (b) On the sides of the rail head (lateral wear) (c) On the ends of the rail (battering of rail ends) Wear is more prominent at some special locations of the track. These locations are normally the following - On sharp curves, due to centrifugal forces - On steep gradients, due to the extra force applied by the engine - And On approaches to railway stations, possibly due to acceleration and deceleration - In tunnels and coastal areas, due to humidity and weather effects Measurement of Wear Wear on rails can measured using any of the following methods - By weighing the rail - By profiling the rail section with the help of lead strips - And By profiling the rail section with the help of needles - By using special instruments designed to measure the profile of the rail and record it simultaneously on graph paper Methods to Reduce Wear Based on field experience, some of the methods adopted to reduce vertical wear and lateral wear in straight paths and curves are as follows - Better maintenance of the track to ensure good packing as well as proper alignment and use of the correct gauge - Reduction in the number of joints by welding - Use of heavier and higher UTS rails, which are more wear resistant - Use of bearing plates and proper adzing in case of wooden sleepers - Lubricating the gauge face of the outer rail in case of curves - Providing check rails in the case of sharp curves - Interchanging the inner and outer rails - Changing the rail by carrying out track renewal Rail End Batter The hammering action of moving loads on rail joints batters the rail ends in due course of time. Due to the impact of the blows, the contact surfaces between the rails and sleepers also get worn out, the ballast at places where the sleepers are joined gets shaken up, the fish bolts become loose, and all these factors further worsen the situation, thereby increasing rail end batter. Rail end batter measured as the difference between the height of the rail at the end and at a point 30 cm away from the end. If the batter is up to 2 mm, it is classified 'average', and if it is between 2 and 3 mm, it is classified as 'severe'. When rail end batter excessive and the rail is otherwise alright, the ends can cropped and the rail reused. Other Effects In Rail Rail wear and battering of rail ends are the two major defects in rails. However some other types of defects may also develop in a rail and necessitate its removal in extreme cases. These as follows: Hogging of rails

Rail ends get hogged due to poor maintenance of the rail joint, yielding format, loose and faulty fastenings, and other such reasons. Hogging of rails causes the quality of the track to deteriorate. This defect can be remedied by measured she packing. Scabbing of rails The scabbing of rails occurs due to the falling of patches or chunks of metal from the rail table. Scabbing generally seen in the shape of an elliptical depression; whose surface reveals a progressive fracture with numerous cracks around it. Wheel burns

Wheel burns caused by the slipping of the driving wheel of locomotives on the rail surface. As a consequence, extra heat is generated and the surface of the rail gets affected, resulting in a depression on the rail table. Wheel burns generally noticed on steep gradients or where there are heavy incidences of braking or near water columns. Shelling and black spots Shelling is the progressive horizontal separation of metal that occurs on the gauge side, generally at the upper gauge corner. It is primarily caused by heavy bearing pressure on a small area of contact, which produces heavy internal shear stress. Corrugation of rail

This Article Covers Gradient In Railway Tracks Their Types And Geometric Design One By One.

Gradient In Railway

Geometric design of a railway track discusses all those parameters which affect the geometry of the track. These parameters are as follows: - Gradients in the track, including grade compensation, rising gradient, and falling gradient - Curvature of the track, including horizontal and vertical curves, transition curves, sharpness of the curve in terms of radius or degree of the curve, cant or superelevation on curves, etc. - Alignment of the track, including straight as well as curved alignment It is very important for tracks to have proper geometric design in order to ensure the safe and smooth running of trains at maximum permissible speeds, carrying the heaviest axle loads. The speed and axle load of the train are very important and sometimes also included as parameters to considered while arriving at the geometric design of the track. Necessity For Geometric Design The need for proper geometric design of a track arises because of the following considerations - To ensure the smooth and safe running of trains - To achieve maximum speeds - And To carry heavy axle loads - To avoid accidents and derailments due to a defective permanent way - To ensure that the track requires least maintenance - For good aesthetics Details Of Geometric Design Of Track The geometric design of the track deals with alignment of railway track and Curves Details regarding curves and their various aspects. Gradients Gradients are provided to negotiate the rise or fall in the level of the railway track. A rising gradient is one in which the track rises in the direction of movement of traffic and in a down or falling gradient the track loses elevation the direction of movement of traffic. A gradient normally represented by the distance travelled for a rise or fall of one unit. Sometimes the gradient indicated as per cent rise or fall. For example, if there is a rise of 1 m in 400 m, the gradient is 1 in 400 or 0.25 per cent. Gradients are provided to meet the following objectives - To reach various stations at different elevations - To follow the natural contours of the ground to the extent possible - And To reduce the cost of earthwork Types Of Gradients The following types of gradients used on the railways - Ruling gradient - Pusher or helper gradient - Momentum gradient - Gradients in station yards Ruling Gradient

Gradient In Railway-Ruling The ruling gradient is the steepest gradient that exists in a section. It determines the maximum load that can hauled by a locomotive on that section. While deciding the ruling gradient of a section, it is not only the severity of the gradient, but also its length as well as its position with respect to the gradients on both sides that have to taken into consideration. The power of the locomotive to put into service on the track also plays an important role in taking this decision, as the locomotive should have adequate power to haul the entire load over the ruling gradient at the maximum permissible speed. In plain terrain: 1 in 150 to 1 in 250 In hilly terrain: 1 in 100 to 1 in 150 Once a ruling gradient has been specified for a section, all other gradients provided in that section should be flatter than the ruling gradient after making due compensation for curvature. Pusher or Helper Gradient

Pusher or Helper Gradient In hilly areas, the rate of rise of the terrain becomes very important when trying to reduce the length of the railway line and, therefore, sometimes, gradients steeper than the ruling gradient are provided to reduce the overall cost. In such situations, one locomotive not adequate to pull the entire load, and an extra locomotive required. When the gradient of the ensuing section so steep as to necessitate the use of an extra engine for pushing the train, it known as a pusher or helper gradient. Examples of pusher gradients are the Budni-Barkhera section of Central Railway and the Darjeeling Himalayan Railway section. Momentum Gradient

This Article Covers Various Types Of Joint And Their Ideal Requirements One By One.

Types Of Rail Joint

Rail joint has always been an integral part of the railway track, it is looked upon as a necessary evil because of the various problems that it presents. Earlier, rails were rolled in short lengths due to difficulties in rolling and the problem of transportation. With increase in temperature, rails expand and this expansion needs to be considered at the joints. It was, therefore, felt that the longer the rail, the larger the required expansion gap, and this too limited the length of the rail. A rail joint is thus an inevitable feature of railway tracks, even though it presents a lot of problems in the maintenance of the permanent way. Before Going With Types Of Rail Joint Will Cover ILL Effect And Ideal Requirements. ILL Effects Of a Rail Joint A rail joint is the weakest link in the track. At a joint, there is a break in the continuity of the rail in both the horizontal and the vertical planes because of the presence of the expansion gap and imperfection in the levels of rail heads. A severe jolt is also experienced at the rail joint when the wheels of vehicles negotiate the expansion gap. This jolt loosens the ballast under the sleeper bed, making the maintenance of the joint difficult. The fittings at the joint also become loose, causing heavy wear and tear of the track material. Some of the problems associated with the rail joint are as follows. Maintenance effort Due to the impact of moving loads on the joint, the packing under the sleeper loosens and the geometry of the track gets distorted very quickly because of which the joint requires frequent attention. It is generally seen that about 30 per cent extra labour is required for maintenance of a joint. Bonded main line 6-bolt rail joint on a segment of 76.9 kg/m rail. Note how bolts are oppositely oriented to prevent complete separation of the joint in the event of being struck by a wheel during a derailment.

Lifespan The life of rails, sleepers, and fastenings gets adversely affected due to the extra stresses created by the impact of moving loads on the rail joint. The rail ends particularly get battered and hogged and chances of rail fracture at joints are considerably high due to fatigue stresses in the rail ends. Noise effect A lot of noise pollution is created due to rail joints, making rail travel uncomfortable. Sabotage chances Wherever there is a rail joint, there is a potential danger of the removal of fish plates and rails by miscreants and greater susceptibility to sabotage. Impact on quality The quality of the track suffers because of excessive wear and tear of track components and rolling stock caused by rail joints. Fuel consumption The presence of rail joints results in increased fuel consumption because of the extra effort required by the locomotive to haul the train over these joints. Requirements Of An Ideal Rail Joint An ideal rail joint provides the same strength and stiffness as the parent rail. The characteristics of an ideal rail joint are briefly summarized here. Holding the rail ends An ideal rail joint should hold both the rail ends in their precise location in the horizontal as well as the vertical planes to provide as much continuity in the track as possible. This helps in avoiding wheel jumping or the deviation of the wheel from its normal path of movement. Strength An ideal rail joint should have the same strength and stiffness as the parent rails it joins. Expansion gap The joint should provide an adequate expansion gap for the free expansion and contraction of rails caused by changes in temperature. Flexibility It should provide flexibility for the easy replacement of rails, whenever required. Provision for wear It should provide for the wear of the rail ends, which is likely to occur under normal operating conditions. Elasticity It should provide adequate elasticity as well as resistance to longitudinal forces so as to ensure a trouble-free track. Cost The initial as well as maintenance costs of an ideal rail joint should be minimal. RAIL JOINTS The nomenclature of rail joints depends upon the position of the sleepers or the joints. Classification According to Position of Sleepers Three types of rail joint come under this category. Supported joint In this type of joint, the ends of the rails are supported directly on the sleeper. It was expected that supporting the joint would reduce the wear and tear of the rails, as there would be no cantilever action. In practice, however, the support tends to slightly raise the height of the rail ends. As such, the run on a supported joint is normally hard. There is also wear and tear of the sleeper supporting the joint and its maintenance presents quite a problem. The duplex sleeper is an example of a supported joint (Fig. below).

Suspended joint In this type of joint, the ends of the rails are suspended between two sleepers and some portion of the rail is cantilevered at the joint. As a result of cantilever action, the packing under the sleepers of the joint becomes loose particularly due to the hammering action of the moving train loads. Suspended joints are the most common type of joints adopted by railway systems worldwide, including India.

Bridge joints The bridge joint is similar to the suspended joint except that the two sleepers on either side of a bridge joint are connected by means of a metal flat or a corrugated plate known as a bridge plate . This type of joint is generally not used on Indian Railways.

Classification Based on the Position of the Joint Two types of rail joint fall in this category. Square joint In this case, the joints in one rail are exactly opposite to the joints in the other rail. This type of joint is most common on Indian Railways (Fig. below).

Staggered joint In this case, the joints in one rail are somewhat staggered and are not opposite the joints in the other rail. Staggered joints are normally preferred on curved tracks because they hinder the centrifugal force that pushes the track outward (Fig. below).

This Article Covers Creep Of Rail Their Causes, Effect, Adjustment And Measurements One By One.

Creep Of Rail

Creep defined as the longitudinal movement of the rail with respect to the sleepers. Rails have a tendency to gradually move in the direction of dominant traffic. Creep is common to all railway tracks, but its magnitude varies considerably from place to place; the rail may move by several centimetres in a month at few places, while at other locations the movement may be almost negligible. THEORIES FOR THE DEVELOPMENT OF CREEP Various theories have put forward to explain the phenomenon of creep and its causes, but none of them have proved to be satisfactory. The important theories briefly discussed in the following sections. Wave Motion Theory According to wave motion theory, wave motion is set up in the resilient track because of moving loads, causing a deflection in the rail under the load. The portion of the rail immediately under the wheel gets slightly depressed due to the wheel load. Therefore, the rails generally have a wavy formation.

Percussion Theory According to percussion theory, creep developed due to the impact of wheels at the rail end ahead of a joint. As the wheels of the moving train leave the trailing rail at the joint, the rail gets pushed forward causing it to move longitudinally in the direction of traffic, and that's how creep develops. Though the impact of a single wheel may be nominal, the continuous movement of several wheels passing over the joint pushes the facing or landing rail forward, thereby causing creep.

This Article Covers Various Types Of Ballast, Sizes, Design And Functions Of Ballast One By One. Ballast is a layer of broken stones, gravel, moorum, or any other granular material placed and packed below and around sleepers for distributing load from the sleepers to the formation. It provides drainage as well as longitudinal and lateral stability to the track. Different types of ballast materials and their specifications are discussed.

Types Of Ballast

The different types of ballast used on Indian Railways are described here. Sand ballast Sand ballast is used primarily for cast iron (CI) pots. It is also used with wooden iron steel trough sleepers in areas where traffic density is very low. Coarse sand is preferred in comparison to fine sand. It has good drainage properties, but has the drawback of blowing off because of being light. It also causes excessive wear of the rail top and the moving parts of the rolling stock.

Moorum ballast The decomposition of laterite results in the formation of moorum. It is red, and sometimes yellow, in colour. The moorum ballast is normally used as the initial ballast in new constructions and also as sub-ballast. As it prevents water from percolating into the formation, it is also used as a blanketing material for black cotton soil.

Coal ash or cinder This type of ballast is normally used in yards and sidings or as the initial ballast in new constructions since it is very cheap and easily available. It is harmful for steel sleepers and fittings because of its corrosive action.

Broken stone ballast This type of ballast is used the most on Indian Railways. Good stone ballast is generally procured from hard stones such as granite, quartzite, and hard trap. The quality of stone should be such that neither it should be porous nor it flake off due to the weathering. Good quality hard stone is normally used for high-speed tracks. This type of ballast works out to be economical in the long run.

Other types of ballast There are other types of ballast also such as the brickbat ballast, gravel ballast, kankar stone ballast, and even earth ballast. These types of ballast are used only in special circumstances. Functions Of Ballast The ballast serves the following functions in a railway track. - It provides a level and hard bed for the sleepers to rest on. - It holds the sleepers in position during the passage of trains. - And It transfers and distributes load from the sleepers to a large area of the formation. - It provides elasticity and resilience to the track for proper riding comfort. - It provides the necessary resistance to the track for longitudinal and lateral stability. - Also It provides effective drainage to the track. - It provides an effective means of maintaining the level and alignment of the track. Size Of Ballast Previously, 50 mm (2") ballasts were specified for flat-bottom sleepers such as concrete and wooden sleepers, and 40 mm (1.5") ballasts for metal sleepers such as CST-9 and trough sleepers. Now, to ensure uniformity, 50 mm (2") ballasts have been adopted universally for all types of sleepers. Points and crossings are subjected to heavy blows of moving loads and hence are maintained to a higher degree of precision. A small sized, 25 mm (1") ballasts. therefore, preferable because of its fineness for slight adjustments, better compaction, and increased frictional area of the ballast. For uniformity sake, the Indian Railways has adopted the same standard size of ballast for the main line as well as for points and crossings. This standard size of ballast should be as per Indian Railways specification. The specification provides grading of ballast from 25 mm to 65 mm, maximum quantity of ballast being in the range of 40 mm to 50 mm size. Requirements Of Good Ballast Ballast material should possess the following properties, - It should be tough and wear resistant. - It should be hard so that it does not get crushed under the moving loads, - Then It should be generally cubical with sharp edges. - It should be non-porous and should not absorb water. - It should resist both attrition and abrasion. - And It should be durable and should not get pulverized or disintegrated under adverse weather conditions. - It should allow for good drainage of water, - It should be cheap and economical. Design Of Ballast Section The design of the ballast section includes the determination of the depth of the ballast cushion below the sleeper and its profile. These aspects are discussed as follows. Minimum Depth of Ballast Cushion The load on the sleeper is transferred through the medium of the ballast to the formation. The pressure distribution in the ballast section depends upon the size and shape of the ballast and the degree of consolidation. Though the lines of equal pressure are in the shape of a bulb as discussed in, yet for simplicity, the dispersion of load can be assumed to be roughly 45° to the vertical. In order to ensure that the load is transferred evenly on the formation, the depth of the ballast should be such that the dispersion lines do not overlap each other. For the even distribution of load on the formation, the depth of the ballast is determined by the following formula: Sleeper spacing = width of the sleeper + 2 x depth of ballast.

This Article Covers Details About Railway Sleepers Like Function And Types Of Sleepers One By One.

Railway Sleepers

Sleepers are the transverse ties that are laid to support the rails. They have an important role in the track as they transmit the wheel load from the rails to the ballast. Several types of sleepers are used on Indian Railways. The characteristics of these sleepers and their suitability with respect to load conditions are, Functions And Requirements Of Sleepers The main functions of sleepers are as follows: - Holding the rails in their correct gauge and alignment - Giving a firm and even support to the rails - Transferring the load evenly from the rails to a wider area of the ballast - Acting as an elastic medium between the rails and the ballast to absorb the blows and vibrations caused by moving loads - Providing longitudinal and lateral stability to the permanent way - Providing the means to rectify the track geometry during their service life Apart from performing these functions the ideal sleeper should normally fulfill the following requirements. - Initial as well as maintenance cost should be minimum - Weight of the sleeper should be moderate so that it is convenient to handle - Designs of the sleeper and the fastenings should be such that it is possible to fix and remove the rails easily. - Sleeper should have sufficient bearing area so that the ballast under it is not crushed - Sleeper should be such that it is possible to maintain and adjust the gauge properly - Material of the sleeper and its design should be such that it does not break or get damaged during packing. - Design of the sleeper should be such that it is possible to have track circuiting. - Sleeper should be capable of resisting vibrations and shocks caused by the passage of fast moving trains. - Sleeper should have anti-sabotage and anti-theft features. Sleeper Density And Spacing Of Sleepers Sleeper density is the number of sleepers per rail length. It is specified as (M + x) or (N + x), where M or N is the length of the rail in metres and x is a number that varies according to factors such as - Axle load and speed, - Type and section of rails, - Type and strength of the sleepers, - Type of ballast and depth of ballast cushion, and - Nature of formation. If the sleeper density is M+ 7 on a broad gauge route and the length of the rail is 13 m, it implies that 13 + 7 = 20 sleepers will be used per rail length of the track on that route. The number of sleepers in a track can also be specified by indicating the number of sleepers per kilometre of the track, for example, 1540 sleepers/km. This specification becomes more relevant particularly in cases where rails are welded and the length of the rail does not have much bearing on the number of sleepers required. This system of specifying the number of sleepers per kilometre exists in many foreign countries and is now being adopted on Indian Railways as well. The spacing of sleepers is fixed depending upon the sleeper density. Spacing is not kept uniform throughout the rail length. It is closer near the joints because of the weakness of the joints and impact of moving loads on them. There is, however, a limitation to the close spacing of the sleepers, as enough space is required for working the beaters that are used to pack the joint sleepers.

Types Of Sleepers The sleepers mostly used on Indian Railways are - Wooden sleepers, - Cast iron (CI) sleepers, - Steel sleepers, and - Concrete sleepers. Wooden Sleepers Wooden sleeper, also called timber sleeper, is one kind of railway sleeper that is made of wood, also known as wooden railway sleeper or wood railroad tie. As a basic railway track components of railway track, wooden sleeper is used for carrying steel rail, it is fastened by common rail fasteners like rail clip, railroad spike, railroad tie plate and etc.

Steel Sleepers Steel sleepers are different to timber and concrete sleepers, mainly because they are relatively light in comparison to their rigidity. They rely on the ballast in the sleeper “pod” to provide vertical and lateral support.

Concrete Sleepers Concrete sleeper is a kind of railway sleeper made of steel reinforced concrete. With the characteristic of water resistant, sun resistant and corrosion resistant, concrete sleeper has been widely used.

Cast Iron Sleepers The Sleepers Made Of Cast iron Non As Cast iron Sleepers.

This Article Covers Types Of Rails Requirement Of An Ideal Rail And Length Of Rails One By One. Rails are the members of the track laid in two parallel lines to provide an unchanging, continuous, and level surface for the movement of trains. To be able to withstand stresses, they are made of high-carbon steel.

TYPES OF RAILS

Types Of Rails - DOUBLE HEADED RAIL - BULL HEADED RAIL - FLAT-FOOTED RAIL Double heading indicates the use of two locomotives at the front of a train, each operated individually by its own crew.

The rail section whose head dimensions are more than that of their foot called bullheaded rails. In this type of rail, the head made little thicker and stronger than the lower part by adding more metal to it. Bullheaded rails especially used for making points and crossings.

Rail sections having their foot rolled to flat are called flat-footed or Vignoles rails.

This Article Covers Various Stresses In Rigid Pavement Like Temperature Stresses And Combined Etc.

Stresses in Rigid Pavement

Curvature and Stresses Caused by Bending. Relative Stiffness of Slabs. Modulus of Subgrade Reaction. Stresses due to Warping. Traffic loading will induce the compressive or tensile stresses in the pavement and temperature variation results in to kinds of stresses. One known as warping stress and another is frictional stress. That makes total of three kinds of stresses that will induced in the pavement slab. Now, we have to find out the critical combination of these three. As the name implies, rigid pavements are rigid i.e, they do not flex much under loading like flexible pavements. They constructed using cement concrete. In this case, the load carrying capacity is mainly due to the rigidity ad high modulus of elasticity of the slab (slab action). Modulus of Sub-Grade Reaction Westergaard considered the rigid pavement slab as a thin elastic plate resting on soil sub-grade, which assumed as a dense liquid. The upward reaction assumed to be proportional to the deflection. Relative Stiffness of Slab to Sub-Grade A certain degree of resistance to slab deflection offered by the sub-grade. The sub-grade deformation is same as the slab deflection. Hence the slab deflection is direct measurement of the magnitude of the sub-grade pressure. Critical Load Positions There are three typical locations namely the interior, edge and corner, where differing conditions of slab continuity exist. These locations are termed as critical load positions.

This Article Covers Bituminous Mix Design Their Requirements And Dry, Marshall Mix Design One By One.

Bituminous Mix Design

The bituminous mix design aims to determine the proportion of bitumen, filler, fine aggregates, and coarse aggregates to produce a mix which is workable, strong, durable and economical. The requirements of the mix design and the two major stages of the mix design, i.e dry mix design and wet mix design. Objectives of mix design - Sufficient bitumen to ensure a durable pavement, - Sufficient strength to resist shear deformation under traffic at higher temperature, - Then Sufficient air voids in the compacted bitumen to allow for additional compaction by traffic, - Sufficient workability to permit easy placement without segregation, - Sufficient flexibility to avoid premature cracking due to repeated bending by traffic,and - And Sufficient flexibility at low temperature to prevent shrinkage cracks. Constituents of a mix - Coarse aggregates - Fine aggregates - Filler - Binder Types of mix - Well-graded mix - Gap-graded mix - Open-graded mix - Unbounded Different layers in a pavement - Bituminous base course - Bituminous binder course - Asphaltic/Bituminous concrete

Requirements of Bituminous mixes

Stability Stability is defined as the resistance of the paving mix to deformation under traffic load. Two examples of failure are - Shoving - a transverse rigid deformation which occurs at areas subject to severe acceleration - Grooving - longitudinal ridging due to channelization of traffic. Stability depend on the inter-particle friction, primarily of the aggregates and the cohesion offered by the bitumen. Durability Durability is defined as the resistance of the mix against weathering and abrasive actions. - Pot-holes, - deterioration of pavements locally and - Stripping, lost of binder from the aggregates and aggregates are exposed. Flexibility Flexibility is a measure of the level of bending strength needed to counteract traffic load and prevent cracking of surface. Fracture is the cracks formed on the surface (hairline-cracks, alligator cracks), main reasons are shrinkage and brittleness of the binder. Skid resistance It is the resistance of the finished pavement against skidding which depends on the surface texture and bitumen content. It is an important factor in high speed traffic. Workability Workability is the ease with which the mix can be laid and compacted, and formed to the required condition and shape. Desirable properties From the above discussion, the desirable properties of a bituminous mix can be summarized as follows: - Stability to meet traffic demand - Bitumen content to ensure proper binding and water proofing - Voids to accommodate compaction due to traffic - Flexibility to meet traffic loads, esp. in cold season - Sufficient workability for construction - Economical mix Dry Mix Design The objective of dry mix design is to determine the amount of various sizes of mineral aggregates to use to get a mix of maximum density. The dry mix design involves three important steps, viz. selection of aggregates, aggregates gradation, and proportion of aggregates, which are Selection of aggregates The desirable qualities of a bituminous paving mixture are dependent to a considerable degree on the nature of the aggregates used. Aggregates are classified as coarse, fine, and filler. The function of the coarse aggregates in contributing to the stability of a bituminous paving mixture is largely due to interlocking and frictional resistance of adjacent particles. Aggregate gradation The properties of the bituminous mix including the density and stability are very much dependent on the aggregates and their grain size distribution. However, some minimum amount of void space is necessary to :- - Provide adequate volume for the binder to occupy, - Promote rapid drainage, and - Provide resistance to frost action for base and sub base courses. Proportioning of aggregates After selecting the aggregates and their gradation, proportioning of aggregates has to be done and following are the common methods of proportioning of aggregates: - Trial and error procedure - Graphical Methods - Analytical Method Marshall Mix Design The mix design (wetmix) determines the optimum bitumen content. This is preceded by the dry mix design. Marshall mix design The Marshall stability and flow test provides the performance prediction measure for the Marshall mix design method. The stability portion of the test measures the maximum load supported by the test specimen at a loading rate of 50.8 mm/minute. Specimen preparation Determine the properties of the mix

Theoretical specific gravity of the mix Gt

Bulk specific gravity of mix Gm

Air voids percent Vv

Voids in mineral aggregate VMA

Voids filled with bitumen VFB Determine Marshall stability and flow Marshall stability of a test specimen is the maximum load required to produce failure when the specimen is preheated to a prescribed temperature placed in a special test head and the load is applied at a constant strain (5 cm per minute). Apply stability correction

Prepare graphical plots The average value of the above properties are determined for each mix with different bitumen content and the following graphical plots are prepared: - Binder content versus corrected Marshall stability - Binder content versus Marshall flow - And Binder content versus percentage of void in the total mix v - Binder content versus voids filled with bitumen (V F B) 5. Binder content versus unit weight or bulk specific gravity Determine optimum bitumen content Determine the optimum binder content for the mix design by taking average value of the following three bitumen contents found form the graphs obtained in the previous step. - Binder content corresponding to maximum stability - Binder content corresponding to maximum bulk specific gravity - And Binder content corresponding to the median of designed limits of percent air voids in the total mix v (i.e. 4%)

This Article Covers Various Test On Bitumen Performed Before Used For Road Pavements One By One.

Test On Bitumen

There are a number of tests to assess the properties of bituminous materials. The following tests usually conducted to evaluate different properties of bituminous materials. - Penetration test - Ductility test - Softening point test - Specific gravity test - Viscosity test - Flash and Fire point test - Float test - Water content test - Loss on heating test Penetration Test It measures the hardness or softness of bitumen by measuring the depth in tenths of a millimetre to which a standard loaded needle will penetrate vertically in 5 seconds. BIS had standardized the equipment and test procedure. The penetrometer consists of a needle assembly with a total weight of 100g and a device for releasing and locking in any position.

Penetration Test Ductility Test A Ductility is the property of bitumen that permits it to undergo great deformation or elongation. And Ductility defined as the distance in cm, to which a standard sample or briquette of the material will elongated without breaking.

Ductility Test Softening Point Test Softening point denotes the temperature at which the bitumen attains a particular degree of softening under the specifications of test. The test conducted by using Ring and Ball apparatus.

Softening Point Test Specific Gravity Test In paving jobs, to classify a binder, density property is of great use. In most cases bitumen weighed, but when used with aggregates, the bitumen converted to volume using density values. The density of bitumen greatly influenced by its chemical composition. Increase in aromatic type mineral impurities cause an increase in specific gravity. Viscosity Test Viscosity denotes the fluid property of bituminous material and it is a measure of resistance to flow. At the application temperature, this characteristic greatly influences the strength of resulting paving mixes. Low or high viscosity during compaction or mixing has observed to result in lower stability values. At high viscosity, it resist the comp active effort and thereby resulting mix is heterogeneous, hence low stability values.