Road Margins - Highway Engineering

Hi,
Road margins are the various cross sectional elements of the road except the carriageway or pavement width. 
Various road margins are shoulders, foot-paths, cycle-tracks, frontage paths, driveways, lay byes, side slopes and guide rails. I will discuss each, one by one.

• Shoulders: Shoulders are the parts of the formation width except carriage ways. In other words, shoulder is the part of the pavement which is non-surfaced. 

They are used by the vehicular traffic as the emergency lanes or sometimes as the service lanes for the repairing of the non-expected problems. IRC recommends a minimum value 2.5 m for the shoulders for two lane rural roads. A width of 4.6 m is recommended so that a truck can be accommodated without interfering with the adjacent lane. 

• Footpaths: Foot paths or pedestrian paths are the smoothly paved paths used by the pedestrians to walk parallel to the pavements. Footpaths are smoothly surfaced in order to attract the pedestrians to walk over them. Footpaths are necessary where the pedestrian traffic is considerable.

• Cycle-tracks: Cycle tracks are provided to carry the cyclists. They are generally provided in the urban roads where the design speed is very high and it becomes necessary to separate the high speed traffic from the low speed traffic. Minimum of 2 m width is recommended for single lane and 1 m is added for constructing the extra lanes of the cycle tracks.

• Frontage Paths: They are provided in front of the commercial buildings where it becomes a necessity. In urban areas they are provided with the dividers to separate from the vehicular lanes.

• Drive-ways: Drive ways are provided to reach the buildings like fuel pumps or service centers. Drive ways should have a less width as much as possible because they are hindrance to the pedestrian traffic travelling along the foot-paths.

• Lay Byes: Lay Byes are the paved areas provided at some places on the sides of the lanes for providing a stoppage for the vehicles. 

• Parking Lanes: They are provided for parking the vehicular traffic generally needed in the market centers or the urban areas. Parallel parking is recommended in order to avoid the hindrance to the traffic and a minimum of 3 m parking lane is recommended.

• Side Slopes: A proper, flatter/gentle side slopes are necessary in case of filling or cutting for the stability of the pavements. If possible they must be provided with the landscaping so making them a pleasant and aesthetic appearance and making more stable.

• Guide Rails: Guide rails are provided on the roads on filling generally on the hills, on the outer edges, for the psychological as well as physical protection to the driver. 

Thanks!

Solution- GATE 2014 -Civil Engineering- set -I

Hi,
I hope GATE 2014 was a good experience for you. I don't remember values and figures but language of the questions can make you remind the question so, I will post here the manner in which the question was to be solved.This post contains the questions asked in set I(9:00AM to 12:00PM).

 I will keep updating this post. I will give you the possible manner in which question was to be solved. Questions are not in exact serial number because it is difficult to remember.

Surveying:

Q.1 Match group I with Group II.

GroupI                                                        Group II
P. Alidade                                               A. Chaining
Q. Arrow                                                B. Plane Table
R.

Solution:  P-B, Q-A,

Q.2 Following staff readings were taken using a level. Find the R.L. of station S.

Station           B.S.     F.S.        R.L.(m)
P                                           100
Q.
R.
S.
Solution: In this question first you have to add the B.S. to the R.L. of bench mark(P), to get the Height of instrument and then minus the F.S. at Q, then add the B.S. at Q, then minus the F.S. at R, then add up the B.S. at R and minus the for sight at S and you will get the R.L. of the S.
Remember, the Fore sights were given with the negative signs at some stations, so automatically two negative signs will produce a positive sign.

Structural Engineering:

Q.1 The influence line diagram for the shear force at point P at a distance of L/4 from end A in a simply supported beam AB will be.

Solution: Remember, there were four diagrams. The diagram which has a negative linear variation of shear force on the left of the section from a value of 0 at A to 0.25 units just on left of P and then 0.75 when just on right of P and then varying linearly to a value of 0 at B, is the right diagram for the influence line of shear force at P.

Q.2 Central singly concentrated collapse load for the given propped cantilever beam of length L will be:
(A) 2Mp/L  (B) 4Mp/L   (C) 6Mp/L  (D) 8Mp/L

Solution:  (C) 6.Mp/L
Given beam is a propped cantilever so, there will be two hinges, one at the fixed end and one at the center, where the load is acting.
Equating the external work done to the internal work done,
Wp.L/2.O= Mp.O + 2.Mp.O
=> Wp = 6.Mp/L

Q.3 Find out the static indeterminacy:

(A) Two (B) One  (C) Zero   (D) Three.

Solution: (C) Zero
You were given a rigid frame with two pinned end supports and one internal hinge. Two pinned supports produce 4 external support reactions and also with one internal hinge our number of equations of static equilibrium gets increased by one so, total is four.
So, static indeterminacy = 4-4 = 0.

Q.4 A given reinforced concrete beam of M25, has a neutral axis at a distance of y  from the top face. If the maximum stress developed in the top fiber is x, find out the curvature of the beam. (If you remember the exact values, please post in comment box).

Solution: Here you have to use the flexure formula,
f/y = E/R    => 1/R = f/(E.y)

where, f= flexural stress in the top fiber, y = distance of the neutral axis from the top fiber
E is Thomas Young's modulus of elasticity = 5000(fck)^(1/2)  here, fck = 25 Mpa

Q.5 Find out the value of force P and its angle of application, in order to lift the given body of weight 'W' without any swing.

Solution: There were numbers of forces acting on the body with their respective angles mentioned. In order to lift up the body without any swing we had to use the following two equations:
Algebraic sum of all the horizontal forces = 0
Algebraic sum of all the vertical forces = W
We have two unknowns, P and its angle and also have two equations, so can be easily found.

Transportation Engineering:

Q.1 The design speed of a road is V km, and the co-efficient of longitudinal friction for the road and tyre is f, if the stopping sight distance of the vehicle is 's' find out the total reaction time of the driver.

Solution: In this question we need to use the equation  V.t + V^2/ (2gf) = s
here, all the values are given except t, which can be easily found.

Q.2 Equation of the velocity(Km/Hr) for a given traffic flow is u= 70+0.7k, where k(Veh/Km) is the density of the flow, the capacity of the flow is:
(A)..   (B)   .. (C) ..   (D)..
Solution:

Hydraulics and water resource Engineering

Q.1 Two parallel pipes diverges from a single pipe and after same length again converge at the another end. If the diameter of the first pipe is four times the diameter of the second pipe, the velocity ratio in first first pipe to that in second pipe will be
(A) 1  (B) 2  (C) 4  (D) 3

Solution: (B)
As the head loss in two pipes will be same,
we can equate the head loss equations of the two. given d1=4.d2.
use Hl= f.l.v^2/(2gd).

Q.2 A1 and V1 are area of cross section and velocity at section 1, and A2 is the area of the section at section two of a section of a continuous flow. What is the velocity at section 2?

Solution: Continuity equation can be applied to get the velocity at section 2.
Note: Values were given in the question and it was a subjective question)

Q.3 Diameter of the Venturimeter and of a section are given, velocity head difference at the throat of Venturimeter and section is given also, velocity at the section is given. Find out the co-efficient of discharge for the Venturimeter.

Solution:  Here first you have to calculate the velocity at the Venturimeter throat which, can be calculated from the given velocity head difference between the section and the throat.
The discharge at the section is calculated by the given data of the area and velocity,
finally equate the discharge to the formula of the discharge for the Venturimeter.
Final equation will give the value of co-efficient of discharge.

To be continued...

Group Index Method of Pavement Design

Hi,

Group Index method of flexible pavement design is an empirical method which is based on the physical properties of the soil sub-grade.  To design the thickness of the pavement you have to go through the following steps:

1. Find out the Group Index Value(GI) of the soil.
2. Use the design charts to find out the thickness of the pavement and layers.

Finding GI Value : Now let's discuss Group Index(GI) first. Group Index is a number assigned to the soil based on its physical properties like particle size, Liquid limit and plastic limit. It varies from a value of 0 to 20, lower the value higher is the quality of the sub-grade and greater the value, poor is the sub-grade.

To find out the value of GI we, can either use the following equation, or we can use the charts

GI = 0.2a + 0.005 a.c. + 0.01b.d

where,

a= percentage of soil passing 0.074 mm sieve in excess of 35 percent, not exceeding 75.

b= percentage of soil passing 0.074 mm sieve in excess of 15 percent, not exceeding 55.

c= Liquid limit in percent in excess of 40.

d= Plasticity index in excess of 10.

The second method to find out the GI value is to use two charts whose numerical values added together to get the GI value.

Using design charts to find the thickness: 

Once the GI value is found next we can use the design charts given by IRC(Indian Roads Congress) to find out the thickness of the pavement and its thickness of various layers. Charts are prepared based on the GI value and one can find the thickness of the pavement to be designed for different traffic volume. 

Traffic volume is classified in three categories as Light, Medium and Heavy. When nos. of vehicles per day is less than 50, this is light traffic, greater then 50 and less than 300 is medium and greater than 300 is classified as heavy traffic. 

You have follow the corresponding curve for the given traffic and for the one among the three different curves you can find the total value of the thickness of the pavement. Then there are two other curves, one to find out the thickness of the sub-base and one to find the thickness of the base course.

Limitation of Group Index method: Limitation of this method is that this is based only on the physical properties of the soil and does not consider the strength parameters.

Thank you!

Factors affecting design of pavements

Hi,
Design of pavement consist of two parts:

1. Design of the mix to be used as the material for different layers.
2. Design of the thickness of the different pavement layers.

In this post I will discuss here the various factors which are considered while designing the pavement thickness.

1. Design Wheel Load
2. Type of sub-grade
3. Climatic conditions
4. Properties of the pavement layers
5. Environmental conditions
6. Other special conditions.

• Design Wheel Load: Design wheel load is the main factor which decides the thickness of the pavement. Of course higher the design wheel load larger will be the pavement thickness. There are other factors related with the design wheel load. 

         Total Design wheel load, Magnitude of contact pressure, repetition of load and dynamics of load is analyzed. Total thickness is governed by the total design wheel load and the quality of         the surface material is governed by the magnitude of the contact pressure. 

Higher speed of the load will result in lesser contact time and thus the deflection of the pavement will be less but if the pavement is undulated then the impact will be higher when speed is higher so, dynamics plays an important role.

• Type of Subgrade : Subgrade quality is determined by various tests such as CBR test, Tri-axial test, plate load test etc. When this possess high strength the thickness required will be less and vice verse.

• Climatic conditions: Amount of rainfall and subsequently the moisture affects the moisture in the sub-grade. The daily and seasonal variation of the temperature also affect the design of flexible and rigid pavements. 

If freezing occurs in the winter then there are chances of frost action on the subgrade soil and so this should be considered while the design of the pavement.

• Properties of the pavement layers: Performance of the pavement layers depends on the properties of the materials used in the layers. The fatigue and their performance under the adverse environmental conditions should be tested beforehand and should be given due considerations.

• Environmental Conditions: Environmental factors such as, height of the embankment,  foundation details, depth of cutting and the level of the water table affects the design of pavements. Variation in temperature daily or seasonal induces the warping stresses in case of rigid pavements.

• In case of semi-rigid pavement materials, the formation of the hair cracks, their propagation has to studied before arriving at a specific method of design of the semi-rigid pavement.

Sight Distance at Intersections

Hello there,
Stopping site distance, Overtaking sight distance and Sight distance at intersections  are important to study and check for the design of the highways.

Sight distance at the intersections:

IRC recommends that at non-controlled intersections, sufficient visibility should be provided such that sight distance on each road is at-least equal to SSD corresponding to the design speed of the road.

IRC recommends that a minimum visibility distance of 15 m along the minor road and a distance of 220, 180, 145 and 110 m along the major road corresponding to design speeds of 100, 80, 65 and 60 kmph. respectively may be provided.

Apart from three situations above, following sight distances are considered by IRC in highway design.

• Intermediate sight distance(ISD) = 2.SSD

When overtaking sight distance cannot be provided, intermediate sight distance is provided to give limited overtaking opportunities to fast vehicles.

• Head light sight distance

This is the distance along the road, visible to a driver during the night driving under the illumination of the vehicle head lights. This sight distance is critical at up-gradients and at the ascending stretch of the valley curves.

Thank you for your visit.

Traffic signs and Rotary intersection - (Traffic Engineering)

Traffic Signs:

These should be mounted on sign posts pointed alternatively with 25 cm black and white band.

• Regulatory signs: These are used to inform road users of certain laws, regulations and prohibitions.

• Warning signs: These are used to warn the road users of certain hazardous conditions that exist on or adjacent to the roadway. Shape of these are equilateral triangles with its open pointing upwards.

• Informatory signs:  These signs are used to guide the road users along to make travel easier, safe and pleasant. Informative signs are grouped under following sub-heads:

1.  Direction and place identification signs.
2. Facility information signs.
3. Other useful information signs.
4. Parking signs.
5. Flood gauge.

Conditions when traffic rotary is justified:

American Association of State highway officials(AASHO) have suggested that lowest limit of traffic volume when a traffic rotary is justified is about 500 vehicles per hour or all intersecting roads put together and maximum limit beyond which the rotary may not efficiently function is about 5000 vehicles per hour. IRC suggests that maximum volume of traffic that a rotary can efficiently handle is 3000 vehicles per hour entering from all the legs of the intersection. Traffic rotary angles may be provided where intersecting motor traffic is about 50% or more of the total traffic or all intersecting roads or where the fast traffic turning right is at-least 30% of the total traffic.

What is traffic rotary?

Traffic rotary is an enlarged road intersections where all converging vehicles are forced to move round a large central island in one direction before they can weave out of traffic flow into their respective directions radiating from the central island.

One liners - Transportation Engineering for GATE, PSUs - Part 10

Hello there,
How have you been? Here is another round of one liners for your preparation for the GATE and PSUs examinations.

• Ratio of width of the car parking area required at kerb for 30 degree parking relative to 60 degree parking is approximately 0.5
• Load carrying capacity of rigid pavements depends more on the properties of concrete than strength of sub-grade.
• Compared to flexible pavements, rigid pavements are more affected by temperature variations.
• Collision diagrams are used to study accident pattern and determine remedial measures.
• Emergency escape ramp is provided in down grades of a highway.
• Plasticity index of the fraction passing 425 micron IS Sieve in case of sub-base or base course would be less than 6.
• If the CBR value obtained at 5 mm penetration is higher than that at 2.5 mm, then the test is repeated for checking; and if the check test reveals a similar trend, then the CBR value is to be reported as higher value obtained at 5 mm penetration.
• Road construction/design in chronological sequence : Tresaguet, Telford, Macadam & C.B.R.
• The general requirement in constructing a reinforced concrete road is to place a single layer of reinforcement near the top of the slab.
• It is a common practice to design a highway to accommodate the traffic volume corresponding to 30th hour.
• The amount of mechanical energy imposed on the aggregate during the aggregate impact test is of the order of (15*14*38 kg-cm) 7980 kg-cm.
• For wet and cold climates emulsions are recommended to be used as binders.
• With reference to Marshall mix design criteria for highways, Stability value = 340 min.; Flow value = 8-16 & % air voids = 3-5.
• For the design of valley vertical curve, the design criteria used are rider comfort, headlight sight distance and drainage.
• Bird baths may be formed as the deformations which may be caused by localized or variable sub-grade failure.
• Pot holes A steep sided, bow-shaped cavity caused by the loss of surfacing as well as base course erosion.
• Ravelling is the removal of larger surface aggregates leaving craters.
• Subsidence is abrupt lowering of the road surface due to poor drainage.
• For carrying out bituminous patch work during the rainy season, the most suitable binder is bituminous emulsion.
• The characteristic rebound deflection on a pavement, using Benkelman beam study is used by IRC to suggest the equivalent overlay design thickness.

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