TRANSPORTATION ENGINEERING - Superelevation on Highways

Dear readers, today I am going to discuss about the term 'Superelevation' that is frequently used in Transportation Engineering.
Transportation Engineering is the branch of Civil Engineering that mainly deals with design, construction and analysis of highways. That is why it is sometimes also known as Highway Engineering.
While designing the highways the safety of passengers is of utmost importance followed by comfort of passengers while travelling at high speeds. For designing the highways many different studies are carried out like speed study, traffic volume study, accident study etc. The main problem lies in designing the highway on curves when it should be designed such that no skidding of vehicle should take place. Skid is the term that is used when longitudinal movement of vehicles is more than circumferential movement of the tires. Slip is the term that refers to the condition when circumferential movement is more than longitudinal movement of vehicle. So skidding is the main problem that can occur on the curves when vehicle is moving in circular motion at high speed due to centrifugal force. To clear your doubts regarding circular motion there is a video below that will explain the circular motion and basic terms related to it.

(Clip showing basics of Circular Motion)

So now we will continue to the technical part that is involved in providing superelevation on highways. Superelevation is the rise provided to the outer part of the road on curves to prevent skidding of vehicle due to centrifugal force. The figure shown below represents various forces that are involved while vehicle is moving along the curve on highway.

Figure 1.1 : Showing direction of frictional force along the tires

Figure 1.2 : Showing various forces and their components

As shown in the figure 1.1 "e" is the superelevation provided. e multiplied by total width of road will give you total rise "E" required on highways. W=m×g and P=mv²/r 

where W - Weight, m - Mass, g - Acceleration due to gravity, P - Centrifugal force, v - Velocity of vehicle, r - Radius of curve.

Now as depicted from figure Pcosθ=Wsinθ+F_b, where F_b is frictional force and is equal to 

f(Wcosθ+Psinθ).

Therefore Pcosθ=Wsinθ+f(Wcosθ+Psinθ), where f is frictional coefficient. Putting values of W and P we get,

(mv²/r)cosθ-(mg×sinθ)=f(mg×cosθ)+f(mv²/r)sinθ. 

Reducing the equation after dividing by gcosθ  we get,

v²/gr - tanθ = f + f(v²/gr)tanθ, from figure 1.2 tanθ= E/B= e

v²/gr(1-fe)= f+e. Since f i.e frictional factor's maximum value is 0.14 and maximum value of e i.e. superelevation 0.07 so f×e being very small can be neglected. Hence we get

v²/gr=f+e.

Where v is design velocity

g is acceleration due to gravity

r is radius of curve

f is frictional coefficient subject to maximum of 0.14

e is superelevation provided subject to maximum of 0.07

From the above equation we can decide superelevation or we can determine new design velocity if value of superelevation is exceeding its maximum value i.e 0.07.

Therefore while designing highway on curves we should provide designed superelevation so that vehicles can take turn at design speed without skidding. The rise so provided is introduced by different methods that will be discussed in other post. Hope the topic was helpful to you.

Please do share your valuable views in comments...!!!

ENVIRONMENTAL ENGINEERING - Finding Eco-friendly ingenious ways of disposing wastewater

Dear readers today i am going to discuss some basic aspects of waste water treatment plant as to how and why it is carried out.
Environmental Engineering is the branch of Engineering that deals with the contemporary issues of society related to water resources.
Infrastructure development ensues huge harm to the environment due to increasing levels of Air Pollution, Noise Pollution and Water Pollution that is affecting the health of living organisms in one way or another. To antagonize this effect environmentalists, scientists, scholars, engineers are contemplating on this subject so as to coin various methods that can reduce the harm caused by pollution. As an initiative step towards reducing water pollution environmental engineers have designed various techniques to treat the waste water generated from houses and industries so that it can be disposed off effectively in water bodies or can be used for fulfilling other purposes like watering the gardens, medians etc.
To accomplish the above cited task water treatment is divided into three main categories namely:

1. Primary Treatment
2. Secondary Treatment
3. Tertiary Treatment

In the first step waste water is passed through primary treatment units where any solid matter present in it is filtered out by making use of screenings, filters etc. In the next step water is allowed to pass through various units like sedimentation tanks, grit chambers etc. where heavy suspended solids are settled down during detention period. Then finally primary treated water is passed through various units involving chemical and biological treatment of water that is known as tertiary treatment. After water is passed through all the three stages of treatment, it is disposed off in the water bodies without altering oxygen demand.
Oxygen Demand is the amount of oxygen required for the aquatic life to survive. As the pollution in water body increases, the living organisms in the form of bacteria, microorganisms etc. As a result those bacteria and various flora and fauna present in the water body will consume oxygen already present in the water body for their survival resulting in increased oxygen demand. This amount of oxygen required for the survival of living organisms is known as Biochemical Oxygen Demand (BOD). The high values of BOD in water sample indicates high degree of pollution due to larger number of bacteria present in water.
So 5-day BOD value of the sample is determined before disposing off the water in water body because if BOD value is higher it will pose danger to aquatic life. That is why it is necessary that before disposing off the waste water in the streams or rivers it should be properly treated in Waste Water Treatment Plant.
Following video will help in understanding the process of water treatment more effectively.

Please do leave your valuable remarks in the comments...!!!!