Laboratory permeability test with two soils in series, Find the Head loss - Solved Example(Soil Mechanics)

Hi,

With this solved example you will learn how to find the head loss in soil stratas stacked in series(linearly).

Problem: 
In a laboratory, a permeability test is as indicated in the figure below. The cross sectional area of the sand is 200 cm2, and the permeability coefficients of sand I and sand II are 0.2 cm/s and 0.1 cm/s, respectively. The total hydraulic head loss is 30 cm. It is assumed that the seepage velocity in sand I is same as in sand II. Determine the height of the water in the standpipe as shown in figure below.

P.S. Assume that the initial water height in the standpipe is equal to total hydraulic head loss + the hydraulic head loss for Sand I.



Solution:


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Head Loss in a Sharp Edged Pipe Entrance - Solved Example (Hydraulics)

Hi,
With this example problem, you will understand how to find the head loss at the sharp edged pipe entrance, where water enters at a given flow rate.

Problem:
A 150 mm diameter pipe conveys water at a flow rate Q = 0.2 m3/sec from a reservoir using a sharp edged exit as shown below. What is the head loss at the point where water leaves the reservoir?


Solution:


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Deflection and Forces in Cantilever Beam propped with a Spring - solved Example.

With this example you will learn how to find the deflection in an indeterminate propped cantilever beam using the equations of compatibility.

Problem: 
Before the Load P was applied to the beam shown, the beam was straight and spring was unstretched. Find the deflection under the load P in terms of EI, L, and spring constant k.


Solution: 


If you have any doubt, please ask in the comment box.

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I Beam Shear Flow - Solved Example

From this example, you will understand how to calculate the moment of inertia of I-beam, Moment of Area, and Shear Flow.


Problem: 
An I beam has a flange width b=400 mm, height h = 400 mm, web thickness tw = 13 mm, and flange thickness tf = 21 mm. Calculate the shear flow at a point shown, where x = 55 mm.


Solution: 


 If you have any doubt, please comment below.
Thank you!

Drying, Burning of Bricks- Continuous, Intermittent, Bull's Trench Kiln, Hoffman's kiln

The Manufacturing of bricks consists of  following processes:

1.  Preparation of brick clay
2.  Moulding of Bricks
3.  Drying
4. Burning of bricks

First two operations are already discussed in the previous two parts of the article in the same blog. In this blog I am going to discuss with you the Drying and the Burning of the bricks:

• Drying Of Bricks: 

Drying of the bricks at lower temperature is done to strengthen the bricks to have sufficient strength so that they do not crack or crumble while holding and carrying them in hand.

Finally bricks are to be stacked in the kiln, but they must possess the sufficient strength to maintain their shape while the transportation and loading operations, so drying of the bricks is important process. Drying of the bricks can be done in two ways:

(a) Natural Drying: Natural drying is done by putting the bricks in the under the air circulation, generally avoided to direct Sun-light.

(b) Artificial Drying: In artificial burning bricks are put under a temperature of about 120 degrees Celsius in a tunnel like structure where arrangements are there to maintain the temperature.

 These tunnel kilns can be period or continuous. In periodic kilns the bricks are dried periodically but in the continuous they are put continuously at one end and dried bricks are taken out at the other end.

• Burning of Bricks: 

Bricks are burned at high temperature to gain the strength, durability, density and red color appearance.

All the water is removed at the temperature of 650 degrees but they are burnt at an temperature of about 1100 degrees because the fusing of sand and lime takes place at this temperature and chemical bonding takes between these materials after the temperature is cooled down resulting in the hard and dense mass.

 Bricks are not burnt above this temperature because it will result in the melting of the bricks and will result in a distorted shape and a very hard mass when cooled which will not be workable while brickwork. Bricks can be burnt using the following methods:

(a) Clamp Burning

(b) Kiln Burning

•   Clamp Burning: 

Clamp is a temporary structure generally constructed over the ground with a height of about 4 to 6 m. It is employed when the demand of the bricks is lower scale and when it is not a monsoon season.

 This is generally trapezoidal in plan whose shorter edge among the parallel sides is below the ground and then the surface raising constantly at about 15 degrees to reach the other parallel edge over the ground.

 A vertical brick and mud wall is constructed at the lower edge to support the stack of the brick. First layer of fuel is laid as the bottom most layer with the coal, wood and other locally available material like cow dung and husk.

Another layer of about 4 to 5 rows of bricks is laid and then again a fuel layer is laid over it. The thickness of the fuel layer goes on with the height of the clamp.

After these alternate layers of the bricks and fuel the top surface is covered with the mud so as to preserve the heat.

Fire is ignited at the bottom, once fire is started it is kept under fire by itself for one or two months and same time period is needed for the cooling of the bricks. 

• Disadvantages of Clamp burning: 

1. Bricks at the bottom are over-burnt while at the top are under-burnt. 
2. Bricks loose their shape, and reason may be their descending downward once the fuel layer is burnt.
3. This method can not employed for the manufacturing of large number of bricks and it is costly in terms of fuel because large amount of heat is wasted.
4.  It can not be employed in monsoon season.

• Kiln Burning: 

Kiln is a large oven used for the burning of bricks. Generally coal and other locally available materials like wood, cow dung etc can be used as fuel. They are of two types:

(a) Intermittent  Kilns.

(b) Continuous Kilns.

• Intermittent Kilns 

are also the periodic kind of kilns, because in such kilns only one process can take place at one time. Various major processes which takes place in the kilns are:

Intermittent Kiln

Loading, unloading, Cooling, and Burning of bricks.

There are two kind of intermittent kilns:

(i) Up-draught Intermittent Kilns

(ii) Down draught Intermittent Kilns

Down draught kilns are more efficient, because the heat is utilized more by moving the hot gases in the larger area of the kiln. In up draught kilns the hot gases are released after they rise up to chimney entrance.

• Continuous Kilns: 

These kilns are called continuous because all the processes of loading, unloading, cooling,  Heating, preheating take place simultaneously. 

Continuous Kiln

They are used when the bricks are demanded in larger scale and in short time. Bricks burning is completed in one day, so it is a fast method of burning.

There are two well known continuous kilns:

• Bull's Trench Kiln: 

Bull's trench kiln consist of a rectangular, circular or oval plan shape. They are constructed below the ground level by excavating a trench of the required width for the given capacity of brick manufacturing.

This Trench is divided generally in 12 chambers so that 2 numbers of cycles of brick burning can take place at the same time for the larger production of the bricks. Or it may happen that one cycle is carried out at one time in all the 12 chambers by using a single process in the 2-3 chambers at the same time.

Bull's Trench Kiln

The structure is under-ground so the heat is conserved to a large extent so it is more efficient.  Once fire is started it constantly travels from one chamber to the other chamber, while other operations like loading, unloading, cooling, burning and preheating taking place simultaneously.

Such kilns are generally constructed to have a manufacturing capacity of about 20,000 bricks per day. The drawback of this kiln is that there is not a permanent roof, so it is not easy to manufacture the bricks in the monsoon seasons.

• Hoffman's Kiln:

The main difference between the Bull's trench kiln and the Hoffman kilns are:

1.  Hoffman's kiln is an over the ground structure while Bull's Trench Kiln is an underground structure.
2. Hoffman's kiln have a permanent roof while Bull's trench Kiln do not have so it former can be used in 12 months a year to manufacture bricks but later is stopped in the monsoon season.

courtesy: http://www.llanymynech.org.uk/html/hoffman_kiln.html

Hoffman Kiln Layout

Hoffman's kiln is generally circular in plan, and is constructed over the ground. The whole structure is divided into the 12 chambers and all the processes takes place simultaneously like in Bull's trench Kiln.

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(IS-1077:1992) Classification and Specification of Bricks

Hi,

According to Indian standard(IS: 1077: 1992) bricks are classified into the following categories:

Classes of common burnt clay bricks:

  Class Designation             Average compressive strength not                                            less than[ (N/mm2)     (kg/cm2)

1. 35                                              35                350
2. 30                                              30                300
3. 25                                              25                250
4. 20                                              20                200
5. 17.5                                           17.5             175
6. 15                                              15                150
7. 12.5                                           12.5             125
8. 10                                              10                100
9. 7.5                                              7.5                75
10.  5                                                5                   50
11.  3.5                                             3.5                35

General Quality

• Bricks shall be hand moulded or machine moulded and shall be made from suitable soils. They shall be from from cracks and flaws and nodules of free lime. 
• Bricks with height of 90 mm or 70 mm will be moulded with a frog of  10 mm to 20 mm deep on one of its flat sides. Bricks with height of 40 mm or less, and as well those made by extrusion process  may not be provided with frogs.
• The bricks shall have smooth rectangular faces with sharp corners and shall be uniform in colour.

For other detailed dimensions and tolerance criteria please visit the IS 1072 : 1992

In some books the classification of the bricks is given as below:

General classification:

(1) First Class Bricks

(2) Second Class Bricks

(3) Third Class Bricks

First class bricks: 

Specifications: 

(1) Plain surface, sharp edges and size with tolerance in dimensions +-3%

(2) Uniform red or brownish colored.

(3) High crushing strength, not less than 10.7 N/mm2

(4) Machine moulded

(5) Efflorescence- NIL

(6) Water absorption less than 15%.

USE: They are used for the exterior wall brick works, short columns and arches.

Second class bricks:

Specifications:

(1) Slightly uneven faces and edges with tolerance in dimensions +-8%

(2) Uniform colored but may be slightly over burnt.

(3) High crushing strength, not less than 7 N/mm2

(4) Hand moulded

(5) Efflorescence- Little

(6) Water absorption less than 20%.

USE: They are used for internal walls and compound walls.

Third class bricks:

Specifications:

(1) May be distorted with blunt edges.

(2) Over burnt or under burnt and non uniform color.

(3) High crushing strength, not less than 3.5N/mm2

(4) Hand moulded

(5) Efflorescence- Large

(6) Water absorption less than 25%.

USES: They are used for flooring, paving, small brick foundations and brick bat lime concrete(B.B.L.C.).

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Vicat's Apparatus - Initial and Final Setting Time of Cement - Test Theory

• Vicat's Apparatus 

is used to find out the consistency, initial setting time and final setting time of the cement. In the normal consistency test we have to find out the amount of water to be added to the cement to form a cement paste of normal consistency.

 Vicat's apparatus consists of an arrangement to hold the plunger of 10 mm diameter and two other needles which are made to freely fall into a mould filled with the cement paste and the amount of penetration of the needles of plunder can can be noted using the vertical graduations from 0 mm to 50 mm.

•   Consistency Test: 

To find out the consistency test you have to take a sample of dried cement of about 400 g weight which must pass through the 90 micron IS Sieve. Then mix in it about 25% of  water by weight a form a uniform paste withing 2 minutes of time.

 Fill the Vicat's mould with this paste and make the 10 mm plunger fixed to the arrangement to just touch the top surface of the cement paste. Make it freely fall and note the amount of penetration.

When the penetration is of about 42 to 45 mm or when the reading on the vertical graduation is about 5 mm to 7 mm that means cement is of normal consistency. Generally the water required to form a paste of normal consistency is 30%.

Vicat's Apparatus with all the accessories

• Initial Setting Time: 

Initial time of Cement is the time required by the cement for its early setting. Cement must be applied to the place of its use before its initial setting so it is necessary to find out the initial setting time that is available with us.

Vicat's apparatus is the standard apparatus used to find out this initial setting time. Look in the figure above, there is a needle of diameter 1 mm. This needle is fixed to the movable rod weight.

The cement paste of normal consistency is formed and is filled in the mould. Now the needle is made just touch the top surface of the cement paste and made freely fall in it. Initial setting time is the time from the mixing of the cement and the water to the time when the penetration of the needle is just above 5 mm from the bottom of the base plate or mold.

Generally the initial setting time of the ordinary Portland cement is 30 minutes. For Slow setting cement this time may be increased by adding the admixtures or Gypsum up to 60 minutes.

Similarly, for the final setting time we have to use the third needle which has a enlarged  5mm hollow cylindrical base. The final setting time is the time from the mixing of the water to the time when this needle just makes the impression on the surface of the cement but do not penetrate into it. Generally the final setting time of cement (OPC) is 10 hrs to 12 hrs.

 

Photograph of the Vicat's Apparatus

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