Showing posts from February, 2014

Critical Stress Combination for Rigid Pavements

Hi, How you doing?
As we know that the design of a pavement is governed by the analysis so, this is very important to know the various combinations of stresses that will be induced in the slab. There are two kinds of loading:

Traffic LoadingTemperature variation. Traffic loading will induce the compressive or tensile stresses in the pavement and temperature variation results in to kinds of stresses. One is known as warping stress and another is frictional stress.

That makes total of three kinds of stresses that will be induced in the pavement slab. Now, we have to find out the critical combination of these three.

In Summer Season: In summer season the average temperature is higher and it results in the overall expansion of the slab. This induces the frictional stresses which will be compressive so as to restrict the expansion. Remember friction will always act in the opposite direction of the movement of the bottom of the slab. That means when it tries to expand, friction will try to c…

Flash(Open cup) and Fire point Test - Highway Engineering Lab

Hi, I am going to explain flash(open) and Fire point test.

AIM: To find out the flash and fire point of a given bitumen sample using open cup.APPARATUS: Flash and Fire point apparatus (Open Cup). This apparatus consist of the a test cup, heating plate, heater, test flame applicator and supports.Thermometer (range -6 to 400 degrees Celsius).

THEORY: Bitumen is a volatile material and when temperature is increased, vapors are formed. In order to work safely with the bitumen at the site, one must know the temperature at which bitumen may become hazardous to work with. Flash and Fire points are the lowest temperature at which, sufficient amount of vapors are formed to catch the flash and fire respectively when a flame is brought near to it. At flash point sufficient amount of vapors are formed so as to catch a momentarily flash. Flash and fire point vary for different variety of Bitumen. 

PROCEDURE:Heat up the bitumen sample to a pouring temperature and then pour it down into the cup up to t…

Factors affecting the Stopping sight distance

Factors effecting the Stopping sight distance As per IRC(Indian Roads Congress), Stopping sight distance is such a distance along the center line of the road that if there is an obstruction of 0.15 m at the other end, it must become visible to the eye of a driver at a height of 1.2 m from the road surface .

In order to analyse the stopping sight distance which is required to design a given highway we have to consider the following factors which, effect the sight distance.

The total reaction time of the driverSpeed of the vehicleFriction between the Tyre and the pavement surfaceBreak efficiencyGradient of the road The total reaction time of the driver: Total reaction time of a driver is the time from the instance the obstruction is visible to the driver to the instance when he effectively applies the break.  In the total reaction time vehicle moves at the speed at which the driver is moving or taken as the design speed. So, if the total reaction time of the driver is more, more will…

Tri-axial method of flexible pavement design


In this method of pavement design we use the Tri-axial shear test to determine the Elastic modulus of the sub-grade material or those of the other layers. Boussinesq's equation is used to determine the thickness of the pavement.In order to include the factors, amount of traffic and rain-fall 'X' and 'Y' are multiplied to the equation which gives us the pavement thickness. More the traffic and amount of rainfall higher will be the values of 'X' and 'Y'.A stiffness factor is introduced when the Elastic modulii are different for the sub-grade and pavement layers. This factor (Es/Ep)^(1/3) is multiplied to the former value of thickness in which, the moduli are considered equal.In order to find out the thickness for the different layers we simply use the stiffness factor according to which, thickness is inversely proportional to the Elastic modulus raised to a power of 1/3. Thanks!

Road Margins - Highway Engineering

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, drive-ways, 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. Foot-paths: 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. Foot-paths are…

Solution- GATE 2014 -Civil Engineering- set -I

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.


Q.1 Match group I with Group II.

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

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
Solution: In this question first you have to add the B.S. …

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:
Find out the Group Index Value(GI) of the soil.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 …