What is Local Attraction, and How Does it Affect the Readings of Compass.

Hi,

Local Attraction: 

A compass shows the direction of the magnetic meridian on the principle of magnetism. 
Now whenever you bring any magnet attracting material(Ferrous metals), needle will show deflection. Please note that in its undisturbed condition, needle is always pointed towards magnetic north. 

So when that ferrous material is near to it, needle will not longer be in north south alignment, so that is how the error is introduced into your readings. This error is known as the local attraction.

Materials which are most likely to be present there, while you are doing the compass surveying, are such as an iron chain, metallic wrist band or ear rings(metallic) that one might be wearing.

Other things such as an electric pole or electric wires may also produce local attraction. The needle is attracted to these objects, so this will deviate from the true direction of the magnetic meridian.

If local attraction is available at a station then all the readings taken from that station will have the same amount of the error, and we have to correct the readings to get the true results.

There are methods to get the corrections to be applied on the erroneous readings in the traversing. The two methods which are used in general will be discussed here briefly.

(1) In first method we have to find out the stations where no local attraction exists. To find out this we have to look for a line where the difference between the fore bearing and the back bearing is exactly equal to 180 degrees. If we find such line then that means the two end stations of that line are free from any local attraction. After finding that line we apply the correction to the bearings of the other lines.

(2) In the second method we find the line where there is no local attraction. We know that even if the local attraction is present at every station the measured included angles will not be incorrect and we can calculate them correctly. With the help of the  readings from the stations which are free from local attraction and the correct included angles we can find out the bearings of all the lines.

If we do not find any line where the both stations are free from the local attraction, we have to take the line where the error is minimum and then apply the mean correction to both the stations and then take them as the correct readings. After that start as usual.

If you want further assistance with the topic, please leave a comment.

Thanks for your kind visit!

       

Solved- Traffic Flow Distribution among Routes at Equilibrium

Hi,

Prob: There are two routes, such that the time consumed is given by the following. 
t1 = 15 + 0.005q1 , t2 = 12 + 0.003q2, 
in peak hour the traffic flow is 6600 veh/hr, estimate the traffic flow distribution among the two routes at the equilibrium.

Solution:

Question Paper 2014- Highway Engineering (CE - 6004) - HPU

[Total No. of Questions -9]                                                         [Total No. of Printed Pages - 3]

  14706

 B.Tech. 6th Semester Examination

Highway Engineering

CE- 6004

Time: 3 Hours                                                                                      Max Marks:  100
The Candidate shall limit their answer precisely within the answer-sheet(40 pages) issued to them and no supplementary/continuation sheet will be issued.

Note: Attempt five questions in all, selecting one question from each of the sections A, B, C and D and all the sub-parts of question in section E.

SECTION - A

1. (a) Write down the construction steps of Macadam's construction along with a typical cross-section.              (10)                                                                                                        (b) What are the various surveys to be carried out before planning a highway system for a given area? Explain briefly.             (10)
2.  (a) Compare Nagpur Road Plan and the second twenty year road plan, discuss the merits of each.                      (10)                                                                                                    (b) Explain how the road lengths of different categories for a state are determined for the year 2001, using the third road development plan concept.          (10)                                                                                     SECTION - B
3. (a) Write down the various factors affection friction offered by pavement surface.  (5)           (b)  Draw a typical cross-section of a divided highway in urban area including the width of pavement, roadway and land.                                                                           (7)              14706/1900                                                                                                  [P.T.O.]                                                                   2                                                                      (c) Derive and expression for finding the stopping sight distance of a vehicle at level.  (8)
4. (a) Enumerate the various steps for practical design of super-elevation.               (10)             (b) A vertical summit curve is formed when an ascending gradient of 1 in 25 meet another ascending gradient of 1 in 100. Find the length of the summit curve to provide the required stopping sight distance for a design speed of 80 kmph.                                       (10)                                                           SECTION - C
5. (a) Indicate how the spot speed data are presented and the results used in Traffic engineering?          (10)                                                                                                      (b) Explain various patterns of kerb parking with diagram.                 (10)
6. (a) Explain briefly the various design factors that are to be considered in rotary intersection design.                                                                                         (12)                              (b) What are the advantages and disadvantages of Traffic signals?       (8)                                                                            SECTION - D
7. (a) What are the various tests for judging the suitability of road aggregates? Discuss the objectives, their advantages and limitations?                                      (12)                            (b) Define the term 'Group Index' of soils. How it is obtained?           (8)
8. (a) Discuss the desirable properties of bitumen. Compare tar and bitumen.    (10)                    (b) Write down the desirable properties of bituminous mixer in brief.            (10)                                                                         3                                                          14706                                                                                                                                                                                              SECTION - E
9. Write short notes on the following:

• (a) CRRI
• (b) Obligatory points
• (c) Cross slope
• (d) Ovetaking zones
• (e) Three E's
• (f) Level of service
• (g) Grade Separated Intersections
• (h) Uses of rubber modified bitumen in bituminous mixer.
• (i) Emulsions uses in road construction.
• (j) Grade compensation on curves.                                                         (10*2)

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Failures in Rigid Pavements

Hi,

With the reference of the book titled as 'Highway Engineering,'  by S.K.Khanna and C.E.G.Justo, I created this post, which covers the failures in rigid pavements. If you have the book, please consult the book, because that would be a better option. Failures in cement concrete pavements are recognized mainly by the formation of the structural cracking. Failures occur due to two factors:

(a) Deficiency of pavement materials.

(b) Structural in-adequacy of the pavement system.

• Deficiency of the Pavement Materials:

1. Soft aggregates
2. Poor workmanship in joint construction
3. Poor joint filler or sealer material
4. Poor surface finish
5. Improper and insufficient curing.

Here are the various defects that creep in due to the causes above:

1. Dis-integration of the cement concrete
2. Formation of cracking
3. Spalling of joints.
4. Poor riding surface
5. Slippery surface
6. Formation of shrinkage cracks
7. Ingress of surface water and further progressive failures.

• Structural in-adequacy of Pavement System:

Inadequate sub-grade support, less pavement thickness would be the major cause of developing the structural cracking in pavements. Following are the causes and types of failure which develop:

1. Inadequate pavement thickness
2. In-adequate sub-grade support and poor subgrade soil
3. The incorrect spacing of joints.

Above would give rise to the failures of the following types:

1. Cracking of the slab corners
2. Cracking of the pavement longitudinally
3. Settlement of slabs
4. Widening of joints
5. Mud Pumping.

Now here are the typical pavement failures which occur in the rigid pavements and will be discussed here are details:

1. Scaling of the cement concrete
2. Shrinkage cracks
3. Spalling of joints
4. Warping cracks
5. Mud Pumping
6. Structural cracking

• Scaling of Cement Concrete:

Whenever there are deficiencies in the concrete mix or presence of some chemical impurities may result in the scaling of the cement concrete. Also when excessive vibrations are given to the mix, cement mortar will come on top during the construction and thus with use the cement mortar gets abraded exposing the aggregates of the mix. This makes the pavement surface rough and shabby in appearance.

• Shrinkage Cracks: During the curing operation of cement concrete pavement immediately after the construction, the shrinkage cracks normally develop. The placement of cracks is in longitudinal as well in the transverse direction.

• Spalling of Joints:

Sometimes when pre-formed filler materials are placed during the casting of pavement slabs, the placement is somehow dislocated and filler is thus placed at an angle. The concreting is completed without noticing this faulty alignment of the filler material. Thus, this forms an overhang of a concrete layer on the top side and the joint, later on, shows excessive cracking and subsidence.

• Warping Cracks:

If the joints are not well designed to accommodate the warping of slabs at edges, this results in the development of excessive stresses due to warping and the slab develops cracking at the edges in an irregular pattern. Hinge joints are generally provided for relieving the slabs of warping stresses. There is no structural defect due to warping cracks if proper reinforcement is provided at the longitudinal and transverse joints as it takes care of the structural in-adequacy.

Thanks!!

Reference:  

Traffic Capacity Studies (Highway Engineering)

Traffic volume refers to the number of vehicles passing a specific point on a highway, typically on a particular lane and in a specific direction, over a defined time interval, usually measured in vehicles per hour.

Traffic capacity, on the other hand, represents the maximum number of vehicles that can traverse a given point on a lane or roadway per unit time (commonly per hour). It is expressed in the same units as traffic volume—vehicles per hour per lane or roadway.

Although both traffic volume and traffic capacity share the same units, they convey different meanings:

• Traffic volume indicates the actual flow rate of vehicles at a given time and reflects fluctuations in traffic demand.

• Traffic capacity denotes the maximum possible flow rate that a roadway can sustain under specific operating conditions while maintaining an acceptable level of service.

---

Types of Traffic Capacity

Traffic capacity varies depending on roadway and traffic conditions. It can be classified into three major types:

1. Basic Capacity
   This is the maximum number of vehicles (in PCU - Passenger Car Units) that can pass a specific point on a lane or roadway in one hour under ideal traffic and roadway conditions.

   • Roads with identical physical characteristics will have the same basic capacity, regardless of current traffic behavior or conditions.

2. Possible Capacity
   This refers to the maximum number of vehicles that can traverse a point in one hour under actual (prevailing) traffic and roadway conditions.

   • It is always less than or equal to the basic capacity.

   • The value depends on how closely prevailing conditions resemble the ideal ones and can range from zero up to the basic capacity.

3. Practical Capacity (Design Capacity)
   This is the maximum number of vehicles that can pass a point on a lane or roadway per hour without causing unreasonable delays, hazards, or restrictions to drivers, under existing conditions.

   • As defined in "Highway Engineering" by S.K. Khanna, practical capacity is of primary importance to designers, as it directly influences the design of highway infrastructure.

   • For this reason, it is also known as the design capacity.

 

Center-to-center spacing of Vehicle (Traffic Capacity Studies)

• Vehicle Spacing and Traffic Capacity Studies

  Theoretical Maximum Capacity Calculation

  The theoretical maximum capacity (C) of a single lane can be determined using the formula:

  $$C = \frac{1000 \times V}{S}$$

  Where:

  • $C$ = Capacity of the lane, in vehicles per hour

  • $V$ = Speed of vehicles, in km/h

  • $S$ = Average center-to-center spacing between vehicles, in meters

  Capacity depends on both speed and spacing. Spacing is governed primarily by the safe stopping distance, ensuring that the rear vehicle has sufficient distance to stop if the vehicle ahead suddenly halts.

  ---

  Determining Vehicle Spacing

  The center-to-center spacing (S) between vehicles is given by:

  $$S = S_g + L$$

  Where:

  • $S_g$ = Space gap (distance from the front of one vehicle to the rear of the vehicle ahead), in meters

  • $L$ = Average length of a vehicle, in meters

  The space gap $S_g$ can be estimated using:

  $$S_g = 0.278 \times V \times t$$

  Where:

  • $V$ = Speed in km/h

  • $t$ = Driver’s reaction time, usually between 0.70 to 0.75 seconds.

  • For calculation purposes, assume $t = 0.70$ seconds.

  Substituting in the formula:

  $$S_g = 0.278 \times V \times 0.70 = 0.2 \times V$$

  So, the total center-to-center spacing becomes:

  $$S = 0.2 \times V + L \quad \text{(in meters)}$$

  By substituting this value of $S$ back into the capacity formula, one can compute the theoretical maximum capacity of the lane for a given design speed and vehicle length.

Failures of Flexible Pavements

Hi there,

Failures of flexible pavements can occur due to the failure of one of the four layers. Failure of Sub-grade will result in the failure of the pavement, because it will get reflected in the top surface. 

Similarly failure of the sub-base or base layer will also result in the failure of the pavement. There are various causes of the failure of the flexible pavement, I will post another article for this. 



Here we will talk about the general failures that occur in the flexible pavements.

1. Alligator(Map) cracking
2. Shear Failure
3. Frost Heaving
4. Longitudinal cracking
5. Consolidation failure
6. Wearing of the Surface
7. Reflection cracks

• Alligator Cracking: 

Alligator or map cracking occurs on the surface of the flexible pavement due to the relative movement of the material or failure of the materials of the pavement layers. This may be caused by the repeated application of the heavy wheel loads resulting in fatigue failure due to the moisture variations resulting in swelling and shrinkage of sub-grade and other pavement materials. A localized weakness of the under-lying base course would also cause a cracking of the surface course in this pattern.

• Shear Failure: 

Shear failure of the flexible pavement occurs due to the weakness of the pavement mixtures, the shearing resistance being low due to in-adequate stability of excessive heavy loading. The shear failure causes upheaval of pavement material by forming a fracture or cracking. 

• Frost Heaving: 

Areas having cold climates, are prone to frost heaving. When the water present in the pores of the layers turns into ice, it causes swelling of the ice, and therefore results in the upheaval of the area affected by the frost. 

It must be remembered that the difference between the frost heaving and the shear failure is that in shear failure the depression is followed by the upheaval of the adjacent area but in case of the frost heaving, there is no depression.

• Longitudinal Cracking: 

Longitudinal cracking may occur due the differential settlement of the pavement due to the differential volume change. The area of the pavement near to the pavement edge is more prone to moisture and therefore it may swell more as compare to the interior region of the pavement sub-grade. 

This will cause a differential volume change of the pavement and therefore may lead to the longitudinal cracking of the pavement. Generally, these longitudinal cracks traverse through the full pavement thickness.

• Consolidation Failure: 

Consolidation of the subgrade due to the continuous action of the wheel load along the wheel path results in the formation of the ruts along the wheel path. 

• Wearing of the Surface: 

Generally wearing of the surface may be caused due to the use of inferior material or due to the lack of the inter-locking of the surface layer with the bottom layers. 

Lack of the interlocking may be a result of the non-use of the prime and tack coat. Specifically in case of the overlays over the existing cement concrete pavements or the soil cement roads have poor inter-locking.

• Reflection cracks: 

Reflection cracks are formed in the overlays laid over the existing cement concrete pavements. In such overlays, if any cracks are there in the existing cement concrete pavements, will get reflected in the surface layer also. These cracks are known as the reflection cracks.

REFERENCES:

Thanks for your kind visit!

Accident Studies- Causes and Prevention (Highway Engg.)

Hi there,
In the syllabus for Highway Engineering(HPU) , this topic is under the section C of Traffic Studies. I have discussed the parking studies in my previous article and in this post I am going to post about the Causes and Prevention of the accidents.

• Causes

Under the mixed traffic conditions and different types of man-oeuvres avoiding the accidents to 100% is not possible, but by studying the various causes and characteristics of the accidents we can provide some preventive measures or improvements to reduce the rates of the accidents.
In any accident there are four elements which take part in it:

1. Road User
2. Vehicle
3. Road
4. Environment.

Road user may be a driver or a pedestrian. Generally driver becomes the cause of the accidents when he is in drunken state, tired, sleepy or in some temporary state of anger or grief. Pedestrians becomes the cause of accident when they are careless while crossing the roads.
Vehicle may becomes the cause of accident when its dynamic characteristics such as braking, accelerator and steering are not working properly. A sudden tyre burst may also become a cause of accident.
Various Road geometric characteristics such as in-sufficient sight distance, excess gradient, less width and surface characteristics such as less friction or presence of pot holes or another failures may lead to accidents.
Environment factors also play sufficient role in the accidents. Heavy rain fall, presence of fog and very high temperature are some of the factors which may result in the accidents by causing in-convenience to the drivers.

• Prevention:

Prevention of the accidents can be done with the help of 3 E's:

1. Engineering
2. Enforcement
3. Education

By using the various engineering measures to construct the best road for the required traffic performance, it is possible to prevent the accidents to some extent.
Enforcement of the motor vehicle act to each and ever traffic may reduce the accidents. Various traffic laws must be enforced with proper guidelines.
Educating the road users about the traffic laws and the safe practices can play a big role in effective traffic performance. This can be done with the help of various medias such as TV and radio and also traffic safety weeks may be organised to educate the traffic.

This was a brief introduction to the Causes and prevention of the Accidents.
Thanks for your kind visit!