Showing posts with label Field Tips. Show all posts
Showing posts with label Field Tips. Show all posts

Sunday, December 14, 2014

How to Remove, Eject a stuck Tremie pipe for Concreting Pile

“Site is a battle field for civil engineers”, this sentence is once wisely said by a workman. We as civil engineers while working see many poor labors losing their lives. We face the conditions one can’t even dream of.

Working in the field brings a lot of unforeseeable circumstances and challenges, I am writing this article today to just share with you a trouble I have recently faced while working as a Project Engineer here at your site in Metro Bus Project.



We here were working on one of the flyover which have 12 piers having on average 9 piles underneath. We here are using Cast-in place friction piles and for concreting we were using the tremie method of concreting.
Mostly while working for piles in underwater level we use the tremie method.  For tremie method after boring with auger upto required dia and depth. We lower the tremie pipe having conical top at the upper end. After attaching suitable no. of tremie pipes with the help of threads at the end. We just lowers the schut of the transit mixture to pour concrete through the upper conical portion into tremie pipe and then into bore hole. The concrete through pressure and weight displaces the water at the top and with this procedure the concreting of pile is done.

For lowering the tremie pipe we use mechanical crane rather than hydraulic crane the reason being that we in the concreting requires to shake the tremie pipe after few and while so that tremie pipe can’t stuck in. While concreting we removes the tremie pipe one by one and requires only the top portion to be dipped in the top of the concrete.

Tomorrow we faced a problem in which the tremie pipe got stuck in and as it is very costly pipe we don’t want to loose our pile as well as our tremie.

Following are some of the procedures we adopted and must be adopted in order to get out of such trouble.
1) Make sure to give shake the tremie pipe after few and while.
2) If the tremie pipe got stuck with crane use the excavator of crawler mounted type it will help
3) Use few liters of retarder admixture to increase the setting time it will help as well.
4) You can also use the concrete pump negative suction method, while the pump runs inversely it will help to create suction within the tremie pipe  that will help the concrete to come up in the tremie pipe and thus loosen concrete a bit.
5) Above all make sure to use safety precautions on the spot.

Sunday, November 16, 2014

Concept of Reinforced Earth

Reinforcement in the form of steel or synthetic strips called geo-strips are placed within an embankment, containing soil in various layers compacted mechanically; the granular material of embankment is linked by means of friction. The embankment becomes a self supporting structure, such a structure is called reinforced earth structure.

Earth Reinforced with Geo-strips and Reinforced Earth Panels



Concept

Construction of reinforced earth is a very simple process. The principle concept of reinforced earth is similar to that of a reinforced concrete that contains steel, aggregates and fines. In reinforcing earth process we reinforce the earth by means of steel or synthetic geo-strips.

Stresses that are generated within the embankment is transferred and resisted by these reinforcing strips. 
Concept of Reinforced Earth Works (REW)


History

Constructions using these techniques are known to have existed in the 5th and 4th millenniums B.C. Since early civilizations, man has attempted to use soil with other materials to enable it for being used for his necessities. Typical early use includes us of branches of tree etc. to support tracks over marshy areas and to build hutments. Structures are also built by insects and birds using mud and leaves.  These are all familiar sights even today. This kind of principle is also used in building parts of Great Wall of China and the Babylonian Ziggurats i.e. temples.
Great Wall of China

In the 19th Century Passel used tree branches to reinforce back fills in order to reduce the earth pressure and thereby economize the retaining walls. 

Textile material was perhaps first used in road construction in south Carolina in the early 1930s. The first use of a woven synthetic fabrics for erosion control was made in 1958 by Barrett.

Construction

Reinforced earth system consists of following items;

a) Facing or the skin of the embankment
b) Reinforcing geo-synthetic strips
c) Soil in lifts or layers

During the construction phase we first do a lean within the boundary of embankment upon which the reinforced earth panels or skin of the reinforcement is placed. In this boundary of panels we place the selected material containing fines and gravels in lifts or layers. Each lift is mechanically stabilized by using a roller. We in this case don’t use sheep foot roller or vibratory roller, we use simple steel drum roller to do the compaction as well as ensuring stability of the structure.

The skin or reinforced earth panels have a path or passage for geo-synthetic strips which is called connectors mostly they are in C shape so they are called C-Connectors.
A bridge Abutment



These strips after passing through C-Connector is jointed with a reinforced steel bars placed at center in a specified distance. With each lift the process repeats and as a result we get a well compacted reinforced earth embankment. Water sealant foam is applied between each panels to ensure it as a water tight structure.

Advantages

Following are some of few positivity in Reinforced Earth Works

Reinforced Earth Panels Facing
a) Easy Placement

Construction is repetitive and simple, panels, strips, granular fill and then compaction

b) Positive Connection

Galvanized reinforcing strips are connected to concrete panels with structural bolts

c)    Engineered Backfill

Alternating layer of reinforcing strips and backfill are applied and compacted.

d)   Structural Facing

TerraClass facing panels are easily handled by placement crew.

Wednesday, September 17, 2014

Defects in Brick Work and their Remedies

"sulphate attack on mortars, unsound materials, frost action, corrosion of iron and steel, crystallization of salts, linear changes resulting from variation in moisture content"
While doing brickwork and after the brick is completed there are certain defects which has to be faced, these defects they must be avoided and remedial measure must be taken. These defects not only ruins the physical quality and aesthetics of the project but also ruins its structural strength. So to avoid any mishap and loss we must know what are certain defects in brick work and how to avoid them. 

Common defects occurring in Brick work are; sulphate attack on mortars, unsound materials, frost action, corrosion of iron and steel, crystallization of salts, linear changes resulting from variation in moisture content. 


Sulphate attack on mortars

Sulphate attack leads to expansion of mortar, thereby causing cracking of brickwork, spalling of brick edges, deterioration of mortar, wide horizontal and vertical cracks in the plaster and falling of the plastered surface. 

The cause of this attack is the chemical action between the sulphate salts in bricks and constituents of Portland cement. 
Sulphate Attack on Bricks
This action is rapid in the presence of water and hence wherever moisture penetrates, excessive dampness occurs. This type of defect may be prevented by preventing moisture penetration. It will avoid the defect to a large extent. Bricks of low sulphate content and the sulphate resisting cement should be used. 

Unsound Materials

Unsound materials cause the formation of small pits at the mortar joints. General expansion and cracking of brick work is visible. Unsoundness in lime is caused by the presence of un-slaked particles of lime. Similarly un-slaked lime particles may be present in the bricks also. 
Unsound Material

Frost action

Defects due to frost action would cause cracking in brickwork. Prevention of water accumulation would prevent this defect.

Corrosion of Metals

Brickwork may get opened or cracked or stained due to corrosion of metals lying adjacent to it. Unprotected iron and steel are liable to get corroded when acted upon by moisture and they increase in bulk, thereby causing cracks in masonry. 
Corrosion of Bricks due to Metals
Protecting the metal surface with cement mortar up to a layer of 1 to 2 cm thick is essential to prevent corrosion.  Partially embedded steel or iron members should be surrounded with bituminous compound for portions not embedded in mortar. 
Metal Corrosion 

Crystallization of Salt and Efflorescence 

This is a prominent defect in brick masonry. In moist climate, in damp places, like basements or under leaky gutter, masonry often gets disfigured by the formation of a white deposit called efflorescence. Deposit originates from the mortar and frequently spreads over a part or entire face of the wall. 
Efflorescence 
Absorbed water dissolves the salts of sodium, potassium and evaporating, forms a crystalline deposit on the surface. In addition to unsightly appearance, the crystallization of salts in the pores of the bricks or mortar may cause disruptive expansion resulting in disintegration due to cracking. 
To avoid Efflorescence do not use porous bricks in contact with limestone. Protect brickwork against contamination of salt-bearing materials during building operations. Bricks should be thoroughly soaked during construction. Correct design of DPC should be used. 

Shrinkage Effects

Brick work may crack due to the shrinkage movements arising from changes in moisture content. This defect is more common with concrete and lime mortars. 
Shrinkage Effects
Good quality bricks should be used in dry condition. All of work should be protected from rain. 

Saturday, August 23, 2014

15+ Essential Tips for Civil Engineers regarding quality of construction

Do you know what? in the field site engineer is acting like a soldier fighting for the betterment of the construction quality. Ensuring construction quality is like ensuring good taste in food to make it tasty for the ones who are going to eat it. Quality of construction has many diversified aspects that has to be ensured and remembered by civil engineers working in the site. 

15+ Essential Tips for civil engineers regarding quality of construction

How to Define Quality in Construction?

In this particular state you might be wondering what do we mean by quality in construction. So hang on there here comes the genuine definition;
Quality can be defined as meeting the legal, aesthetic and functional requirements of a project. Requirements may be simple or complex, or they may be stated in terms of the end result required or as a detailed description of what is to be done. But, however expressed, quality is obtained if the stated requirements are adequate, and if the completed project conforms to the requirements. 
the Construction Industry Defines Quality as;
In the construction industry, quality can be defined as meeting the requirements of the designer, constructor and regulatory agencies as well as the owner. 
Civil Engineers Working on site 

Legal Definition of Quality

You know what, quality is not just meant for betterment of the construction, it has a legal existence that bounds both the parties to ensure it; here is how law defines importance of quality in construction; 

Law defines quality in terms of professional liability, a legal concept that requires all professionals to know their trade and practice it responsibly. Every architect and engineer who offers his or her expertise to owners is subject to professional liability laws. 

What to do in quality of construction?

Meeting the requirements of the owner as to functional adequacy; completion on time and within budget; life-cycle costs; and operation and maintenance. 

Quality of Construction
Meeting the requirements of the design professional as to provision of well-defined scope of work; budget to assemble and use a qualified, trained and experienced staff; budget to obtain adequate field information prior to design; provisions for timely decisions by owner and design professional; and contract to perform necessary work at a fair fee with adequate time allowance. 


Meeting the requirements of the constructor as to provision of contract plans, specification and other documents prepared in sufficient detail to permit the constructor to prepare priced proposal or competitive bid; timely decisions by the owner and design professional on authorization and processing of change order; fair and timely interpretation of contract requirements from field design and inspection staff; and contract for performance of work on a reasonable schedule which permits a reasonable profit.
Maintaining the quality of construction during working

Meeting the requirements of regulatory agencies as to public safety and health; environmental considerations; protection of public property including utilities and conformance with applicable laws, regulations codes and policies. 


1. Lapping is not allowed for the bars having diameters more than 36 mm.
2. Chair Spacing maximum spacing is 1.00 m or 1 No per 1 square meter
3. For dowels rod minimum of 12 mm diameter should be used
4. Chairs minimum of 12 mm diameter bars to be used.
5. Longitudinal reinforcement not less than 0.85 and more then 6% of Gross cross sectional area.
6. Minimum bars for square column is 4 No’s and 6 No’s for circular column.
7. Main bars in the slabs shall not be less than 8 mm High Yield Strength Deformed Steel or 10 mm (Plain Bars) and the distributors not less than 8 mm and not more than 1/8 of slab thickness.
8. Minimum thickness of slab is 125 mm.
9. Dimension tolerance for cubes + 2 mm.
10. Free fall of concrete is allowed maximum to 1.50 m.
11. Lap slices not be used for bar larger than 36 mm.
12. Water absorption of bricks should not be more than 15 %.
13. PH value of the what should not e less than 6
14. Compression strength of Bricks is 3.5N / square millimeter
15. In Steel reinforcement binding wire required is 8 kg Per MT.
16. In Soil filling as per IS Code, 3 samples should be taken for core cutting test for every 100 square meter.

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Friday, July 4, 2014

What is Liquidated damages? What are its clauses

Monetary compensation for a loss, detriment, or injury to a person or a person's rights or property, awarded by a court judgment or by a contract stipulation regarding violation of contract.

Definition

Cash compensation, agreed to by signed, written contract for breach of contract, payable to the aggrieved party. {Law Dictionary: (Black's Law Dictionary}

Generally, contracts that involve the exchange of money or the promise of performance have a liquidated damages stipulation. The purpose of this stipulation is to establish a predetermined sum that must be paid if a party fails to perform as promised.

Conditions when Liquidated damages are imposed:

Damages can be liquidated in a contract only if
1)    First, the amount of the damages identified must roughly approximate the damages likely to fall upon the party seeking the benefit of the term.

2)        Second, the damages must be sufficiently uncertain at the time the contract is made that such a clause will likely save both parties the future difficulty of estimating damages.

Difference between liquidated damages and un-liquidated damages (penalty)

At common law, a liquidated damages clause will not be enforced if its purpose is to punish the wrongdoer/party in breach rather than to compensate the injured party (in which case it is referred to as a penal or penalty clause).

A penalty will be imposed if the loss or damage is reasonably certain if it’s uncertain then liquidated damages clause will be imposed.

Examples of liquidated damage

For example, suppose Saad Iqbal agrees to lease a store-front to Zubair Saleem, from which Zubair intends to sell jewelry. If Saad breaches the contract by refusing to lease the store-front at the appointed time, it will be difficult to determine what profits Zubair will have lost because the success of newly created small businesses is highly uncertain. This, therefore, would be an appropriate circumstance for Zubair to insist upon a liquidated damages clause in case Saad fails to perform.

Undisclosed source code has value as a trade secret. Openly publishing the source code destroys the trade secret value. The trade secret value of source code is difficult or impossible to prove. There is no open market for "secret source code".

In the case of construction contracts, courts have occasionally refused to enforce liquidated damages provisions when both parties have contributed to the overall delay of the project.

Sunday, February 2, 2014

12+ Skills civil engineering students must have

Throughout the four years I have spent in an engineering college I have gone through various challenges and difficult situations where your survival sometimes look difficult for you and you think
“Now it’s the time to leave this world”. Don’t take engineering as easy as sciences or arts, although not any work in this world is easy but civil engineering by no means is easy.

Skills civil engineering students must have

Firstly entering in an engineering college itself is a challenge and if your are among those few lucky ones who have got this change – then be happy now fellow because you have got that potential and you have those solid nerves and patience that is needed ultimately.

Now let me state here the worlds of my heart. “Among the other entire tough engineering disciplines civil engineering is toughest and the most difficult one”; you might laugh at me once, but after you have grinded in the crusher for four years your heart will speak the same sentence. The truth of this sentence can also be observed after counting the number of female students you have with you in your class. :P

One of the very irritating thing you will observe in your starting years is people making statements like
“Civil is chill”
“They have nothing to do except staring at girls”
“They are the poor masons without instruments.”
“They are the only ones…always single……”
And bla bla.

Why you have to face these statements? Answer is simple it is because apparently it feels to others that civil engineering is very easy and one might say “Oh! Yeah! Those poor illiterate contractors can also build a house for me very easily, I dn’t need you!” but the only one standing alone within the fighting ring knows how those punches and kicks feel.
In this post I will be sharing with you the skills and abilities a civil engineering students must have so as to be a successful professional civil engineer for this world.


Patience and Control on Anger

 

Now you have already listened to those statements, results of those statements would only be anger in you; lets first know the reason why patience is needed, listening to teachers for continuous hours without break, listening to the statements of your parents and specially father, bearing the cold irritating behavior of your class fellows, seeing no beauty and colors in your life, and a lot more others. These all factors will make your brain hot, you will easily lose your temper, so you must have some patience and control over it otherwise the results will be problems, fights, more statements, and more anger.
So try to develop an ignoring attitude to what others say, always keeps a smile on your face, remain positive and let other do what they are doing and only thing you can change is yourself, develop yourself as a calm and cool engineer.

Confidence 

 

It is a basic need for being a successful human on this planet. Confidence will cover your inabilities and your weaknesses. It is like if we have a black ball with sun, we will not see it. So if you have confidence you will shine along with all of your weakness. Confidence is needed because you constantly have to give presentations, even in examinations you might have to give vivas; and it is like a short interview in which your instructor will judge and mark you on the basis of your confidence. Similarly to make new friends and to have a healthy communication with them you need confidence. Because it is a professional study where every one might have his/her own opinion and own designs you must have confidence on your abilities and skills to prove yourself right.
You can develop confidence by self-motivating yourself, set an aim and goal for yourself and when you will achieve it you will feel confident, participate in extra-curricular activities, sports and games it will boost up your confidence.

Physically Strong

 

It is the very important requirement and is needed because you in your education have to handle stones, aggregates, crush, heavy manual testing equipment, heavy machines, buckets and so on.
Similarly you have to stand while doing manual drawing for hours, and if on computer using structural and drawing softwares you need have that strong back-bone and strong mental skills to remain active and remain confident.

You in survey might have to handle equipment in rough and tough environment, might be too cold or 
might be too hot, but you have to handle, you must have strong immunity to fight with those extreme weathers and those extreme laboratory environment having smell of burning sulfurs, dusting cement, soil, blasting sounds of breaking steel bars and so much more.
You have to eat well, stay healthy, sleep as required, do exercise, take fruits and juices, protect yourself from unhealthy activities and drugs etc.

Absorb Pressure

It is already being explained why pressure is there, your family might not be that much strong 
economically they might be trusting you to get educated and earn a good livelihood for you and for them and thus they would be trusting you and they will have dozens of expectations for you. You at the other end are facing the odds and difficulties as a front war fighter.  You have to learn skills, softwares, remembers countless figures and countless points in your mind, thick chubby books of hundreds of pages and so on.

Thus you have stay calm, because if you take tension you might not be able to solve questions you will lose hope and will ultimately caught in that fear hole. Try to practice your religion and get those superficial powers in yourself and take help from that motivation.

Good Communication Skills

Civil engineering starts by communication, you in field have to satisfy your clients, you must have 
ability to say what your mind imagines and thinks, you have to constantly stay in touch with contractor and consultant and architects and thus you have to make your point and tell them what is feasible and what not.
In class you might not understand a thing and to ask a question from your instructor you will have to have that strong edge in communication skills, any one even not that much strong technically can excel if he/she has strong communication skills.
Try to talk as much as you can with your friends on facebook, on calls, in real life as well. You in start might have a fear calling a stranger like some service stations or some companies, you must have to overcome that fear to be successful.

Good Drawing skills 

 

Drawing is the language of engineers. You can’t communicate that much with words and writings as 
you can with drawings. You must have strong imagination as what a thing will look like in a different perspective view. You might have to draw elevations, sections and so much. You must be able to use manual drawing tools like T-Square, Set Square. Even if you use AutoCAD, you must have that skill because softwares just helps you they don’t have brain.

Try to sketch anything that interests you, you only need a paper and a pencil and a rubber to initiate creativity. Don’t hesitate that what others will say or how they comment. Just be confident and tell the world you have got skills. 

Strong in Mental Calculation

Calculation is what civil engineers mostly do after eating :P, as you might not have always a pocket calculator your brain must be that much fast in calculation that you might not need calculator very often.
You must be able to sum up or subtract or multiply or divide things on your finger tips. Because in calls your teacher might say “What is the dia of #4 bar” you will say ½” instantly but if you dn’t have that skill you will open up the calculator and say 4/8 = 1/2=0.5 and then say sir “0.5” and up to that time the class might be ended.

Must be rough and tough

 

That totally depends on what sort of field or major you select as your career, but if you hate extreme weathers, and harsh environments your chances for survival will be minimized.

Good Computer Skills

 

Because now a day’s computer has overcome all the calculations, manual drawing and manual structural calculations are now very rare and obsolete. Now engineers use ETABS, STAAD Pro and AutoCAD, and etc. etc. These all require from you a strong computer basic skills, you if have computer phobia that if will be difficult for you, you must start by just playing with it, do experiments, and see what happens. It will be a fun.

Good Convincing Skills


“No one is perfect” but if you have confidence you will say “NO ONE is perfect, and I am that NO ONE”. In civil engineering every field and every task has got variables that are obvious to have different answers for different humans. So you must have that convincing skills to tell others why you answer is more economical and more correct than others. Its like a marketing skills that are obviously required. Because you have to justify yourself.

Time Management

 

Time as we all know is money, you have to use it effectively and efficiently. Try to develop a schedule on daily basis follow it, set goals for each day and fight to achieve that goal.

Common Sense

 

“Civil engineering is an engineering of common sense”, this is the sentence that is being told by most of our teachers. Because in civil engineering whatever we build or whatever we develop it is physical, we don’t play with charges moving and we don’t see them. We play with bricks, aggregates, cement, sand, steel, you name it and we can touch that we can feel that and thus most laws and procedure are physical.
To understand and to imagine you must have a common sense. Like if you are a manager and you have to schedule a project activities, you must not set erecting walls before excavation and foundation design so there the common sense come.
But common sense is not very common :D

From Editor’s Desk

 

Civil engineering is a very interesting and very challenging field. But as it is rightly said, the more difficult the task is, the more beautiful the result will be. So don’t lose hope or don’t let yourself down, Your destiny is a few steps away.
I Hope you’d like the post, lets share it with your friends, there are many options available down there.

Saturday, January 11, 2014

Methods to find your coordinates on globe

A coordinate system that helps us finds the location on the Earth by using set of numbers and letters. Among these coordinates one of the number represents vertical position and other two numbers represent horizontal position. Commonly they are called latitude, longitude and elevation.
Finding Your Coordinates

Longitude

Longitude is that geographic coordinates that specifies the east-west position of a point on the Earth’s surface. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lamda. If we have points with the same longitude it means the points lies in line running from North Pole to the South Pole.

Prime Meridian is a point that passes through Greenwich England, and showing the position of zero longitude using this as a reference the longitude of other places is measured as an angle east or west from prime Meridian, ranging from zero degree at prime meridian to +180 degrees eastward and -180 degrees westward.

latitude

Latitude is a geographic coordinate that specifies the north-south position of a point on the earth’s surface. Latitude is an angle which ranges from zero degrees at the Equator to 90 degrees at the North and South poles.
Latitude is used together with longitude to specify the precise location of features on the surface of the earth.

Altitude

Coordinates on earth surface
Altitude or height or Elevation is defined generally as a distance measured in vertical or up direction, between a reference datum and a point or object. The reference datum is usually the datum sea level.
Methods to find out your location coordinates
Now days with the advancement in technology there are various ways with the help of which we can find out the coordinates of our location on the earth surface.


Using GPS – Global Positioning System

The most common and the most accurate is the GPS, GPS stands for Global Positioning System and as its name implies, it is used to tell you your exact position on the globe (world's surface) to an accuracy of about 5 meters.
 

People regularly use GPS technology in everyday life and in some cases they may be unaware that it is a modified GPS unit. A great example of this is satellite navigation systems in cars, these use GPS technology along with map information to give you road directions. SatNavs and GPS units utilize a network of satellites. These satellites transmit precise microwave signals to the GPS unit, which enables a GPS receiver to determine its’ location; speed and direction. A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites using a method called triangulation. In triangulation, a microwave signal is sent out from three or more satellites to the GPS receiver, the length of time it takes to receive a single signal relates to a distance measurement. These measurements allow the GPS unit to Make an accurate approximation of its location.
 

Finding your Sample Site Coordinate using GPS

Using Global Positioning System (GPS)

You could simply write down the location information that your receiver calculates and/or
you can store the waypoint in the receiver. You will need to save your sample site location
as a waypoint; this is useful as you can later use this point as a navigation guide and it also acts as a digital copy of your coordinate, which can be, used alternative non‐paper back up.

1)     In order to save your location you need to first make sure you are standing at your
sample site. Next navigate to the ‘map’ screen using the ‘page’ button.

2)    In the top right hand side of this screen there should be a box titled ‘accuracy’
you need to write the ‘accuracy’ value down on your data sheet (value in meters). THIIS VALUE MUST BE BELOW 5 METRES.

3)    Once you have an accuracy value at or below 5 meters you can make an accurate
waypoint. Press and hold the ‘Enter’ button on the map screen until a ‘waypoint’ screen appears. Once in this screen you can save and edit your waypoint coordinate information.

4)     First, before you edit your waypoint, you must write the location value onto your
data sheet. This value must be given in decimal degrees (will appear on you screen
as a number followed by a ‘°’ symbol).

5)     In the first large box you can edit the name of your waypoint  the name of the waypoint
is often set as a number by default,  you should change this to a name that is easily distinguishable as your sample site (for example use GLWW). Using the ‘rocker’ key highlight this box and click ‘Enter’, you can now use the ‘rocker’ to select letters using a pop up keypad, click ‘ok’ once you have selected all your desired letters. You can then repeat this same method in the comment box.

6)     After you have edited your waypoint data select ‘ok’ using the ‘rocker’ key and
press ‘enter’. This will save the waypoint coordinates into the internal memory of
the GPS unit.
 

Using Google earth



When you have the street address or the zip code you can easily calculate the latitude, longitude and altitude with the help of google maps or google earth.
1.    Open the google earth software – free to download from the google and then enter your location information in the search box
2.    Zoom in the Google earth as much as possible until you find the location exactly as required.
 
3.    Move the mouse cursor over the desired location as shown here in the picture with A.
4.    Then from the status bar read the coordinates of the desired location
 

The coordinates of the admin block as shown here is 33045’57.07’’ N and 72049’31.18’’ E and elevation is 1638 ft.


The coordinates of the Civil Department as shown here is;
330 46’ 00.13’’ N and 720 49’ 30.73’’ E and elevation is 1644 ft.
My location approx. on the day the assignment was given has coordinates of

330 46’00.66’’ N 720 49’ 29.68’’ E and elevation of 1646 ft from ground and as I was on the first floor it could be approximately 1646 ft + 11 ft = 1657 ft.

Sunday, December 1, 2013

What is scouring, Bridge Scouring? How to calculate Scour Depth?

Scouring can be defined as a process due to which the particles of the soil or rock around the periphery of the abutment or pier of the highway bridge spanning over a water body, gets eroded and removed over a certain depth called scour depth. Scouring usually occurs when the velocity of the flowing water increases or crosses the limiting value that the soil particles can easily handle.
Scour at bridge Pier and abutment

When Scouring Happens? Causes?

Scouring can be easily observed during the flood being passed through that water body. Scouring is initiated at the nose of the piers or at the sharp bends. Estimation of scour depth is very important for the design of foundation for abutment or pier. Scouring compromises the structural integrity and thus causes failure of the structure. It has been estimated that over 60 % of the highway bridges are being collapsed due to scouring.

When the discharge within the water body passes the allowed discharge; which is usually the case when flood is there; the scour is initiated; the scour depth can easily be obtained after the flood by finding the depth of the scour in reference with the surroundings or existing structures. If this is not possible the mean depth of scour may be easily obtained by a mathematical formula for natural streams in the alluvial depth.

How to Calculate or Estimate Scour Depth?

Hydraulic Engineering Circular (HEC) has published a manual in which the methods are mentioned some of which are empirical equations or graphs to estimate the scour depth based on the discharge, flow velocity or flow depth etc.

Zeller Equation for estimation of scour depth

If the bed is sand bed streams we can use the empirical Zeller Equation for estimation of scour depth;

Ygs = Ymax [(0.0685 Vm^0.8) / (Yh^0.4 Se ^0.3)-1]
Where Ygs = general scour depth (ft), Ymax is maximum depth of flow, Vm is the average velocity of flow(ft/sec), Yh is hydraulic depth of flow (ft) and Se is the energy slope (or bed slope for uniform flow), (ft)
From actual field measuring scour depth charts to estimate scour depth;
Estimate Scour Depth


This method is applicable only for coarser sands where the bed slope ranges from 0.004 ft to 0.008 ft.
Other empirical methods are also there like Neil, Blench and Lacey for estimation of the scour depth.

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Friday, November 29, 2013

California Bearing Ratio (CBR) for determining Shear Strength of subgrade

California Bearing Ratio (CBR) test is a compressive nature penetration test. It was originally developed by Caltrans i.e. California Department of Transportation after World War II i.e. in the late 1930s. 
The test is specifically used to determine the mechanical strength as well as the potential strength of road subgrades and basecourses materials including the recycled material generally used for road and airfield pavements. CBR value is a percentage comparison with the standard crushed rock from California and thus this test is a comparison test.
The test is standardized by American Society Of Testing Materials (ASTM) as D1883-05 (this standard is used for laboratory prepared samples or re-molded samples) and D4429 (for on field soils); and by American Association of State Highway and Transportation officials (AASHTO) T193; and by British Standard as BS 1377; and by International Standard (IS) as 2720 (Part XVI).

Main components of Pavement design

The results obtained by CBR test are used with the empirical curves to determine the thickness of different layers of flexible pavement like subgrade, subbase, base courses. This is the most widely used method for the design of flexible pavement.
CBR value is used to quantify the response of the pavement foundation and subgrade to loading. CBR does not provide any data regarding the properties of the soil except as to compare its resistance to penetration to the base crushed rock’s resistance to penetration. Although CBR test is empirical and has some limitations but it is still used around the world due to its low equipment requirement, ease of performance prediction and history of use.
The two empirical methods for pavement design used now days are CBR method and Group Index Method. In CBR method beside many other steps one step is to determined the CBR value. This test allows the Engineer to design the Capping Layer and the sub-base layer by determining the strength of the underlying soil.
Flowchart for pavement design using CBR method
 

Scope and Objective of the CBR Test

The Objective of the California Bearing Ratio test is to determine the CBR value for a soil under consideration as a pavement foundation.
CBR is generally used for cohesive soils where effect of water content on CBR is more and generally CBR is determined for a range of water content but it can also be performed for cohesionless soils or coarse grained materials where the effect of water content on CBR is small and thus CBR is performed at Optimum Moisture Content (OMC).
According to ASTM; CBR is primarily intended for evaluating the strength of materials having maximum particle sizes less than ¾ inches or 19 mm, but this restriction is not strict one; if the sample has a material larger than 19 mm; equal amount of such material be replaced by material of size smaller than 19 mm but from the same representative sample.
If the sample to be tested contains much fraction of particles of sizes 3 in (Sieve No. 4), the CBR results will fluctuate and thus more trials are required to establish a reliable CBR; thus generally the sample to be tested consists of particles smaller than 19 mm but larger than 3 in.
CBR test can be performed for both in soaked conditions or un-soaked conditions; but mostly soaked conditions is preferred so as to evaluate the material strength in worst conditions. 

Description of Apparatus

Apparatus required to perform the CBR test is as follows;
  • Molds:  Cylindrical mold with an internal diameter of 6 in. and a height of 7 in. with an extension collar of 2 in. height and a perforated base plate.
  • Spacer Disk: A circular disk of metal 5 – 15/16 in. diameter and 2.416 in. height.
  • Rammer: A rammer of mass 4.54 kg (10 lbs)
  • Apparatus for measuring expansions. This consists of a swell plate with adjustable stem and a tripod support for a dial indicator.
  • Surcharge weights: Several slotted or split metal plates of 149.2 mm; diameter and 5 lb weight.
  • Penetration Piston: A metal Piston of circular cross – section having diameter of 1.954 in. Area = 3in2 and not less than 4 inches in length.
  • Loading Device: A compression type apparatus capable of applying a uniformly increasing load up to 10,000 lb at a rate of 1.3 mm/min.Soaking Tank: A tank suitable for maintaining the water level of 1 in, above the top of specimen.
  • Drying Oven: Oven Capable of maintaining a temperature of 110 + 5 0C for drying samples.
  • Moisture content Containers
  • Miscellaneous: Tools such as mixing pans, spoons, straightedge, filter paper, balances etc.

Test procedure

  1. Approximately 18 kg soil pass of 19mm sieve and retain of sieve no. 4 is taken.
  2. Moisture and dry density curve is obtained using the standard AASHTO T 99 or T 180.
  3. Optimum Moisture Content (OPC) is obtained from the graph between moisture content and dry density
  4. Prepare the sample by adding optimum moisture content and then compact the soil in five layers by applying 10,30 and 65 blows respectively in three CBR molds using 10 lb rammer having 18 in. height of fall. The compacted densities of the three specimens range from 95 percent to 100 % of the maximum dry density  already determined by the T 180 compaction test.
  5. Soaking: Place the swell plate with adjustable stem on the soil sample in the mold and apply sufficient annular weights to produce an intensity of loading equal to the mass of sub-base and base courses and surfacing above the tested material, but not less than 4.54 kg (10 lbs) . Place the tripod with dial indicator on top of the mold and make an initial dial reading.
  6. Immerse the mold in water to allow free access of water. Place the sample in water for 96 hours (4 days)
  7. Make a dial reading on soaked specimen and calculate swell as a percentage of initial sample height.
  8. Remove the sample from tank and allow to drain for 15 minutes.
  9. Penetration Test: Place the mold on the loading frame and adjust its potion until the piston is centered on the specimen.
  10. Seat the penetration piston with a 44 N (10 lb) load, and set both the load dial and the strain dial to zero. This initial load is considered as the zero load when determining the stress-penetration relationship.
  11. Place the surcharge weights on the specimens equal to that used during soaking. Apply load at a rate of 1.3 mm / min and record the load for penetration of 0.025 in, 0.05 in, 0.075 in, 0.10 in and so on up to 0.5 inches.
  12. Stress strain curve: Plot curves between load and penetration for each specimen. Apply the corrections to the curves if required. Take the readings of load for 0.1 in and 0.2 in. penetration and find CBR for both penetrations. The greater values is the required CBR for that specimen. Also find the dry density for each specimen.
  13. CBR = Test load value, divided by, the standard load, multiplied by 100.
  14. Design CBR: it is calculated by plotting a graph between CBR values and dry densities of all the three specimens and then calculating the design CBR against value of 85 % maximum dry density.

   Test results, table ,graphs and calculations

Step 1: Getting the relationship and graph between moisture content and dry density
Moisture Density Relationship

Dry Density (lb/cft)
Sample No.
Moisture Content (%)
Dry Density (lb/cft)
1


2


3


4


5



Step 2: Finding the density of the three samples each of 10 blows, 30 blows and 60 blows

Step 3: Load v/s Penetration Graph
Load Penetration Curve

For sample made with 10 blows
Sr.No
Load (lbs)
Penetration (mm)
1
0.5 mm

2
1.0 mm

3
1.5 mm

4
2.0 mm

5
2.5 mm

6
3.0 mm

7
3.5 mm

8
4.0 mm

9
4.5 mm

10
5.0 mm

11
5.5 mm

12
6.0 mm

13
6.5 mm

14
7.0 mm

15
7.5 mm

16
8.0 mm

17
8.5 mm

18
9.0 mm

19
9.5 mm

20
10 mm


For sample made with 30 blows
Sr.No
Load (lbs)
Penetration (mm)
1
0.5 mm

2
1.0 mm

3
1.5 mm

4
2.0 mm

5
2.5 mm

6
3.0 mm

7
3.5 mm

8
4.0 mm

9
4.5 mm

10
5.0 mm

11
5.5 mm

12
6.0 mm

13
6.5 mm

14
7.0 mm

15
7.5 mm

16
8.0 mm

17
8.5 mm

18
9.0 mm

19
9.5 mm

20
10 mm


For sample made with 60 blows
Sr.No
Load (lbs)
Penetration (mm)
1
0.5 mm

2
1.0 mm

3
1.5 mm

4
2.0 mm

5
2.5 mm

6
3.0 mm

7
3.5 mm

8
4.0 mm

9
4.5 mm

10
5.0 mm

11
5.5 mm

12
6.0 mm

13
6.5 mm

14
7.0 mm

15
7.5 mm

16
8.0 mm

17
8.5 mm

18
9.0 mm

19
9.5 mm

20
10 mm

Summary of CBR Test and conclusion

Sample No.
Compaction Effort
Dry Density (lb/cft)
CBR value (%)
1.
10
113
14.5
2.
30
121
28
3.
65
125
34.5

Maximum Dry density _____________________ (lb./cft)
95% of maximum dry density________________(lb/cft)
Resultant CBR or Designed CBR __________________ (lb/cft)
CBR - Density Relation

Limitations

The laboratory and field compaction methods are not identical, however, comparative tests indicate that reasonable correlation of results can be obtained from field compact materials and samples compacted under similar conditions in the laboratory.
Because added strength to highly stabilized surfaces such as asphaltic concrete is neglected, the assumption of a completely saturated subgrade condition sometimes results in a too conservative factor of safety.

Because many of the procedures are of an arbitrary nature, you must run the test to exact standards in order for the design tables to be valid.

Conclusion:

California bearing ratio is a widely used method to design the flexible pavements, beside all the limitations it is easy to perform and still does not need any big instruments etc. The value of the CBR test is then compared with the following table to get the quality of material from which the required thicknesses and other parameters are decided.
CBR VALUE
SUBGRADE STRENGTH
COMMENTS
3% and less
Poor
" Capping is required 
3% - 5%
Normal
Widely encountered CBR range capping considered according to road category
5% - 15%
Good
"Capping" normally unnecessary except on very heavily trafficked roads.