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The composition of good brick earth:

1) Silica

• Good brick earth should contain 50 – 60% of silica.
• It prevents cracking, shrinking and wrapping of raw bricks.
• Silica imparts uniform shape to the bricks.
• Excess of silica makes the bricks brittle.

2) Alumina

• Good brick earth should contain 20 – 30% of Alumina.
• Alumina imparts plasticity to the earth so that it can be moulded.
• If it is excess raw bricks shrink and warp during drying and burning.

3) Lime

• It should not be greater than 5% for good bricks

4) Iron oxides

• It should be in the range of 5 – 6% for the good bricks.
• It imparts colour to the brick.

5) Magnesia

• It imparts color to the brick.
• It also decreases shrinkage in the bricks.

Concept:

Bowditch Rule is used when length and bearing both are equally precise. In this method, total error in Latitude and Departure is distributed as per the ratio of length of lines i.e.

Correction in Latitude is:

\({C_L} = ;\frac{l}{{{\rm{\Sigma }}l}} \times {\rm{\Sigma }}L\)

Correction in Departure is:

\({C_D} = ;\frac{l}{{{\rm{\Sigma }}l}} \times {\rm{\Sigma }}D\)

Where ΣL and ΣD are total error in latitude and departure respectively.

Σl is the summation of length of all lines involved in closed traverse.

Note:

Transit rule is used when bearings are more precise then length of line.

Concept

Measurement of Horizontal Angles

a) Repetition Method:

• This method is used for very accurate work.
• In this method, the same angle is added several times mechanically and the correct value of the angle is obtained by dividing the accumulated reading by the no. of repetitions.
• The angle should be measured clockwise in the face left to face right positions, with three repetitions at each face.
• The final reading of the first observation will be the initial reading of the second observation and so on.

b) Reiteration Method. 

• This method is another precise and comparatively less tedious method of measuring horizontal angles.
• It is generally preferred when several angles are to be measured at a particular station.
• This method consists of measuring several angles successively and finally closing the horizon at the starting point.

Additional Information The method of repetition eliminates different errors present in the measurement of a horizontal angle as follows:

• The errors due to the eccentricity of Vernier’s and centers get eliminated as readings from both the Vernier’s are taken
• The errors due to inaccurate graduations get eliminated as the readings are observed at different parts of the circle
• The errors due to lack in the adjustment of the line of collimation and the horizontal axis of the instrument get eliminated for considering both face readings
• Errors due to the inaccurate bisection of the object, eccentric centering, etc are eliminated partially as these get counter-balanced in different observations

Note: The errors due to slip, due to the displacement of the station or its signal do not get eliminated and moreover, these errors are cumulative in nature.

Explanation:

Line of sight: 

• It is the imaginary line passing through the intersection of the crosshair on the diaphragm and the optical center of the objective lens.
• when a line of sight comes in a horizontal plane, it is called a line of collimation.
• The line of sight generates a vertical plane when the horizontal axis is perpendicular to the vertical axis.

Line of collimation: 

• It is an imaginary line passing through the intersection of the crosshairs at the diaphragm and the optical center of the object-glass and its continuation.

Axis of Bubble tube: 

• It is an imaginary line tangential to the longitudinal curve of the bubble tube at its midpoint.

Axis of a telescope: 

• This axis is an imaginary passing through the optical center of the object-glass and the optical center of the eye-piece.

Concept:

Ranging is the process of aligning the chain in a straight line between two extremities.

In order to measure the length of the survey/chain line greater than the chain length, we are required to fix or establish some intermediate points. This process is known as Ranging.

Different types of ranging based on intervisibility between two stations are:

1. Direct ranging: It is applicable when the two ends of the survey lines are intervisible.

2. Indirect ranging: It is applicable when both the ends of the survey line are not intervisible either due to the high intervening ground or due to the long distance between them.

Explanation:

• In whole to part, the error is localized as it prevents accumulation of error and,
• In part to whole, the error is expanded.

The fundamental principles of plane surveying are:

1. Location of a point by measurement from two point of reference: Two control points are selected in an area and the distance between them is measured accurately.
2. Working from whole to the part: Major control points are selected and measured first with high degree of precision, minor details can be collected later on even with less degree of precision. In this manner, errors involved in minor detailing will be compensating and will not affect the major dimensions.

Note:

• The main idea of working from whole to part is to localise errors and prevent their accumulation.
• On the contrary, working from part to whole, the errors accumulate and expand to a greater magnitude and the survey work becomes uncontrollable at the end.

Explantion:

To achieve the similarity between the flow in the model and its prototype, every dimensionless parameter for certain conditions in the model must have the same value as the corresponding parameter referring to the prototype.

Types of similarity:

Geometric Similarity: 

• It is the similarity of shape i.e. geometric similarity exists if the ratio of all the corresponding linear dimensions is equal in the model and prototype. Geometrical parameters are Length, Width, Height, Area, and Volume.

Length Ratio: \(L_{r}=\frac{L_{m}}{L_{p}}=\frac{B_{m}}{B_{p}}=\frac{H_{m}}{H_{p}}\)

Area Ratio: \(A_{r}=\frac{A_{m}}{A_{p}}\)

Volume Ratio: \(V_{r}=\frac{V_{m}}{V_{p}}\)

Kinematic similarity: It is similarity of motion i.e. Kinematic similarity exist if ratio of all the kinematic parameters in model and the prototype is same.

Kinematic parameters includes velocity, acceleration, discharge etc.

Velocity Ratio: \(v_{r}=\frac{v_{m}}{v_{p}}\)

Acceleration Ratio: \(a_{r}=\frac{a_{m}}{a_{p}}\)

Discharge Ratio: \(Q_{r}=\frac{Q_{m}}{Q_{p}}\)

Dynamic Similarity: It is similarity of forces i.e. Dynamic similarity exist if identical force and its ratio at all corresponding points is same in model and prototype.

Force Ratio: \(F_{r}=\frac{F_{m}}{F_{p}}\)

Pressure ratio: \(P_{r}=\frac{P_{m}}{P_{p}}\)

Note:

• For kinematic similarity, geometric similarity must exist and for dynamic similarity both geometric and kinematic similarity must exist. These are necessary but not sufficient conditions.
• For complete similarity Geometric, Kinematic and Dynamic similarity must exist.

Explanation:

Pumps

• The hydraulic machines which convert the mechanical energy into hydraulic energy are called pumps.

Explanation:

• A section is said to be most efficient, if, for a given cross-section area, the discharge carrying capacity is maximum.
• The highest component of total construction cost is lining & if the perimeter is kept minimum the cost of lining will be minimum, hence it will be the most economical section.
• There are some important sections and conditions to be most efficient;

Concept:

Soils are generally classified in two types:

• Cohesive and
• Cohesion less soils.

Cohesive soils are soils having strong intermolecular force of attraction when water is added into them. This type of behaviour is shown by clays and silt. So, any soil having very high content of clay can be considered as cohesive soils. Cohesive soil does not crumble and can be excavated with vertical side slopes. The shear strength of these type of soils depends on inherent cohesion, friction in between them and normal stress acting on them.

Examples:  Clayey silt, Sandy clay, Silty clay, clay and organic clay.

Cohesionless soils are having no cohesion i.e. no intermolecular force of attraction when water is added into them. The shear strength of these type of soils depends on friction between particles and also normal stress acting on them.

Examples: Sand and Gravel.