What is the difference between absorption and adsorption ?

Absorption generally refers to two phenomena, which are largely unrelated. In one case, it refers to when atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. For instance, a sponge absorbs water when it is dry.
 Absorption also refers to the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electronic energy levels. The absorbed energy may be re-emitted as radiant energy or transformed into heat energy. The absorption of light during wave propagation is often called attenuation/ The tools of spectroscopy in chemistry are based on the absorption of photons by atoms and molecules.

Adsorption is similar, but refers to a surface rather than a volume; adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film(the adsorb-ate). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution. 

SW ROAD TUTORIALS

This is a tutorial of the road design software called SW-ROAD. This software is made in Nepal and it is one of the most used and most easy software for designing the road. In this tutorial series, you will learn following things:
1) SW Road Introduction
2) Importing Topo Map and fixing horizontal alignment
3) Profile Alignment
4) Data Input and Calculation
5) Cross Section Design
6) Drawing output
7) Quantity Output for estimation

FUNCTIONS OF INGREDIENTS OF CEMENT

1) Lime: It makes the cement sound and strong. The lime in excess quantity makes the cement unsound and cause the cement to expand and disintegrate.

2) Silica: It provides strength to the cement due to the formation of dicalcium and tricalcium silicates. The silica in excess quanity causes the cement to set slowly.

3) Alumina: It provides quick setting property to the cement and lowers the clinkering temperature.

4) Iron Oxide: It provides colour, hardness and strength to the cement. It also helps the fusion of raw materials during the manufacture of cement.

5) Magnesium Oxide: It provides hardness and colour to the cement, when present in small quantity. The magnesium oxide in excess quantity makes the cement unsound.

6) Sulphur trioxide: It makes the cement sound, when present in very small quantity. The sulphur trioxide in excess quantity makes the cement unsound.

7) Alkalies: These should be present in small quantities. The alkalies in excess quantity will cause efflorescence.

COFFER DAM

What is Coffer Dam? 

A temporary Structure concstructed in a river, lack etc. for ecvluding water from a gicen site to enable the building operation to be performed on the dry surface, is called a coffer dam. It may be made of earth materials, timber or steel sheet piling or a combination thereof.

Some of the common types of coffer dams are as follows:

1) Cantilever sheet pile Coffer Dams

2) Braces Coffer Dam

3) Embankment Protected Coffer Dams

4) Double Wall Coffer Dams

5) Cellular Coffer Dam

The cantilever sheet pile coffer dams are suitable for small heights. The braces coffer dams are economical for small to moderate heights. There us no height limitation for embanking type coffer dams. The double wall coffer dams are suitable for moderate heights while the cellular coffer dams are suitable for moderate and large heights. 

Figures:

Classification of Piles

The piles are classified as follows:

1) Classification based on the function

The piles based upon the function or use may be classified as follows:

a) Bearing Piles: The piles which do not support the load by themselves, but act as a medium to transmit the load from the foundation to the resisting sub-stratum are known as bearing piles.

b) Friction Piles: The piles which are driven in the type of soil whose strength does not increase with depth or where rate of increase in strength with depth is very slow, are known as friction piles.

c) Compaction Piles: The piles which are driven in granular soil with the aim of increasing the bearing capacity of the soil, are known as compaction piles.

d) Batter Piles: The piles which are driven at an inclination to resist large horizontal or inclined force, are known as batter piles.

e) Fender Pile: The piles used to protect concrete deck or other water front structures from the abrasion or impact are called fender piles.

f) Sheet piles: These piles are commonly used as bulk heads or as impervious cut off to reduce seepage and uplift under hydraulic structures. These piles are not meant for carrying any vertical load. The sheet piles are made of wood, steel or concrete.

2) Classification based on materials and composition

The piles based on the materials and composition are as follows:

a) Concrete Piles: They are made up of concrete and can be precast or cast-in-situ.

b) Steel Piles: A steel pipe can be rolled section, a fabricated shape or a piece of sheet pole.

c) Timber Piles: The timber piles are generally square or circular in cross section, having cast iron show at the bottom.

d) Composite Piles: The composite pile is made of two portions of two different materials driven on above the other. The two materials can be steel, timber or concrete.

e) Screw Piles: This is made of a hollow cast iron or steel shaft. The external diameter of the shaft may vary from 150 to 300 mm , which mat terminate into a helix or screw base at its base.

f) Disc Pile: A disc pile consists of hollow cast iron pipe with a disc or casing of enlarged size at the bottom, to enlarge area to very great extent. The diameter of dics pile may vary from 0.6 to 1.2m.

Types of levelling

levelling may be classified as under :

1. Differential levelling
2. Cross-sectioning levelling
3. Check levelling 
4. Reciprocal levelling 
5. Profile levelling 
6. Precision levelling

1. Differential levelling.

The operation of spirit levelling which is employed to determine the elevations of a number of points some distance apart to establish Bench Marks in the area is called differential levelling. It is done regardless of the horizontal positions of the points with respect to each other. It is also sometimes known as taking fly levels or simply fly levelling.

2. Check levelling.

The operation of running level line to check the accuracy of the bench marks previously fixed is called check levelling. The stability of the existing bench marks can only be ascertained if the difference in line of the sections between three bench marks agree with the observed differences obtained by check levelling.

3. Profile levelling.

The operation of levelling carried out to determine the elevations of the points at known distances apart and also other known features at a given straight line is called profile levelling. If we plot the elevations of different points as ordinates and the horizontal distances between the points as abscissa, then the line joining the ends of the ordinates, gives the profile of the surface of the earth. Profile levelling is also called Longitudinal !culling.

4. Cross-sectioning levelling

The operation of levelling which is carried out to provide levels on either side of the main line at right angles, in order to determine the vertical section of the earth surface on the ground, is called cross sectioning.

S. Reciprocal levelling.

The operation of levelling in which difference in elevations between the points is accurately determined by two sets of reciprocal observations. it called reciprocal levelling. Reciprocal levelling is employed when it is not possible to set up the level between two points due to an intervening structures such as large water bodies.

6. Precision levelling.

The operation of levelling in which further refinement of field technique, is made by using precise staves and levels, and special precautions are taken Turing observation, to eliminate all errors, is known as precision (evening. G.T.S. bench marks are established by carrying out precision levelling -

Principle of Levelling

The principle of levelling lies in furnishing a horizontal line of sight and finding the vertical distances of points above or below the line of sight.
The line of sight is provided with a level and a graduated levelling staff is used for measuring the height of the line of sight above the staff positions.

How to detect local attraction ?

The magnetic needle is seriously deflected from its normal position when it is under the influence of external attractive forces. Such a disturbing influence is known as local attraction. The term is also used to amount of deviation of the needle form its normal position.

Detection of local attraction
The presence of local attraction at any station may be detected by observing the fore and back bearing of the line. If the difference between fore and back bearing is 180 degree, both end stations are free from the local attraction. If not, the discrepancy may be due to :

a) An error in observation of either fore or back bearing or both.
b) Presence of local attraction at either station.
c) Presence of local attraction at both the stations.

Correcting method

1) Method of elimination of local attraction by included angles

- Compute the included angle at each station from the observed bearings .
- Starting from the unaffected line, rub down the correct bearing of the successive sides.

2) Method of elimination of local attraction by applying correction in bearing

- Calculate the magnitude and direction of the error due to local attraction at each affected station.
- Run down the bearings, starting from the bearing unaffected by local attraction.

Adjustment of Surveyor's Compass

The adjustment of surveying compass are:

a) Temporary Adjustment 

The adjustments which are required to be made at every set up of the instrument are known or stationary adjustment. It includes:

1) Centering
The process of centering the instruments i.e. making the pivot exactly vertically over the ground station mark is called centering. The compass is fixed on the top of a tripod. By adjusting the legs of the tripod, centering is achieved. A plumb bob may be hung from the center of the circular box, to check the cantering  of the compass. If the compass is centered perfectly, the pebble will fall exactly over the ground station mark.
If the bob is not provides, centering can be done by dropping the stone freely from the center of the bottom of the cylinder box.

2) Levelling 
The process of holding the compass in such a way that its graduated rings swings freely, is called levelling. The levelling is done by eye judgement. Generally the compass is provided with a ball and socket arrangement attached to the tripod for achieving quick levelling of the instrument.

3) Focusing the prism
The process of moving up and down the prism for obtaining the figures and graduations sharp and clear, is called focusing the prism. 

b) Permanent Adjustment
The adjustments which are made only if the fundamental relations between the various parts of a compass, are disturbed due to careless handling or otherwise are called permanent adjustments.

The following fundamental relationship between different parts of a compass, are established by making permanent adjustments:

1) when plate bubbles. if provided are at the centers of their run, the vertical axis of  the compass should be truly vertical.
2) When the instrument is perfectly levelled, sight vanes should be vertical.
3) The ends of the needle and the center of the picot should lie in the same vertical plane.
4) The center of the pivot should coincide with the geometrical center of the graduated ring.

Its main adjustments includes:
1) Adjustment of the plate levels
To make the vertical axis truly vertical when plate bubbles are at he center for their run.

2) Adjustment of sight vanes
To make sight vane and object vane vertical when the compass is level.

3) Adjustment of magnetic needdle
To straighten the magnetic needle

4) Adjustment of the pivot
To set the pivot point at the geometric center of the graduated ring 

Surveying Compass

Surveying Compass are of following two types:

1) Prismatic Compass
2) Surveyor's Compass

1) Prismatic Compass
It is most suitable type of surveying compass which consists of a circular box about 100mm in diameter. Prismatic compass can be used as a hand instrument or on a tripod. Prismatic compass can be accurately centered over the ground station mark.

2) Surveyor's Compass
Surveyor's compass is similar to the construction to the prismatic compass with a few modifications stated below:
a) The graduated ring is directly attached to the circular box and not wiht the megnetic needle.
b) The edge bar magnetic needle floats freely over the pivot.
c) The eye vane consists of a simple metal vane with a fine sight hole.
d) Readings are taken against the north end of the needle.
e) The ring is graduated in quadrilateral system having o degree at North and south ends, 90 degree at East and West Ends.