Methods of Surveying

METHODS OF SURVEYING

Surveying means finding the position of any given point on, above or below the earth's surface with respect to a point and plotting it on a map using suitable scale. Surveying measurements are taken only in the horizontal plane. Surveying involves leveling which refers to the elevation of a point with respect to benchmark point. 

PRINCIPLES OF SURVEYING

There are 2 principles of surveying:

• Location of a point by measurement from 2 points of reference: This principle states that the relative position of a point should be located by measurement from at least 2 reference points whose positions have already been fixed. 
• Working from whole to part: This principle suggests that surveying should be carried out from whole to part meaning for an area to be surveyed, reference points should be setup which cover the whole area. From there other small details should be located. With this method the chances of error are reduced by a great amount. 

METHODS OF SURVEYING

There are 2 primary methods of surveying:

• Plane surveying: In this method the spherical shape of earth is neglected. Instead earth is assumed to be a plane surface and all the triangulations carried out are considered plane triangles. This is typically carried out for an area for 250 km sq.
• Geodetic surveying: This is a more precise method of surveying, reason being the earth is taken in it's original spherical shape and all respective calculations are carried out accordingly. This methods makes triangulation much more precise compared to plane surveying and is hence carried out for areas exceeding 250 km sq.

The secondary methods of surveying are as follows:

•  Chain surveying: Chain surveying is the oldest method in the books of civil engineering. The area to be surveyed is divided into smaller areas. The measurement of each divided area is carried out separately. The method is called chain surveying because the instrument used for taking measurements is a 20m chain. The chain has a brass ring at every meter and a tally at every 5 meters. The measurements are carried out accordingly and the individual areas are summed up in the end. Condition for this type of surveying is that the area to be surveyed should be small.
• Compass surveying: Compass surveying employs the use of triangulation and internal angles for carrying out the calculations. In this we use a prismatic compass for measuring the bearing of a line. With respect to that bearing we find the angles of the respective triangle and lengths are measured with chain. 
• Plane Table surveying: Idea behind plane table is that the entire area is divided into stations. These stations are separately worked on by drawing rays on paper as a reference line and carrying out measurements from that line. The results are plotted on paper with a suitable scale. Condition for this method is that every other station should be parallel to the previous one. 
• Theodolite surveying: In this we used theodolite which is an instrument used to measure horizontal angles, vertical angles, deflection angle and difference in elevation. Theodolite is accurate between 10" - 20". With theodolite we find the desired elevations and angles and then carry out the necessary calculations. 
• Tacheometric surveying: In this we make use of an instrument called tacheometer which works similar to theodolite, difference being the tacheometer has a different lens as compared to theodolite. Working is carried out the same way with tacheometer finding the horizontal and vertical distances by taking angular observations. 

Types of Loads acting on a structure

 TYPES OF LOADS ACTING ON A STRUCTURE 

Any type of structure is subjected to different types of loads. These loads can be vertical, horizontal or even longitudinal loads. 

According to IS: 875 - 1987 The different types of loads are:

1. Dead load: Dead loads compose of those loads which are stationary. They are also called permanent loads because they are applied on the structure throughout it's lifetime. Mostly these comprise of structure's self -  weight, fittings, partitions, etc. 

2. Live load: Live loads are also referred as imposing or sudden loads meaning they can change with respect to time. These loads comprise of furniture, equipment, people.

3. Wind load: As the name suggests, this load is imposed due to the wind movement and the direction and intensity with which it moves. Factors taken during calculation of wind loads are wind speed, direction of wind and height of building.

4. Earthquake load: This load is taken in consideration for the case of an earthquake striking the structure. During an earthquake there is lateral ground movement, hence the load applied on the structure is horizontal according to the force exerted by the ground. Vertical component is also taken into consideration but that is mostly due to structure's own weight.

5. Snow load: This load is not typically taken into consideration while designing a building. This is exclusive for structures which receive snowfall. Calculation are done with respect to height of building, shape and size of the roof. 

Types of Soil Testing for Construction

TYPES OF SOIL TESTING FOR CONSTRUCTION  

Soil tests are carried out to ensure optimum conditions for the soil hence making sure the working conditions are as per requirements for a smooth construction. Technically it is the first step in any construction activity as the entire load of a structure is transferred to the soil and if the soil conditions are not optimum, chances of structure failure are quite high. 

Different types of soil tests are carried out accordingly.

1. Core cutter method:

This method is used to find the in-situ dry density of soil. 

( condition: it is only used in case of fine grained soil )

This method involves,

• a cylindrical core cutter ( 130mm in length and 100mm in diameter )
• a steel dolly ( 25mm high and 100mm in diameter )
• steel rammer ( 9kg mass and 900mm length )
• weighing balance

PROCEDURE:

• Determine the volume of core cutter by measuring the internal dimensions.
• Calculate the weight of core cutter without dolly.
• Drive the cutter into the soil by placing dolly over the cutter.
• Remove the cutter containing soil.
• Remove the dolly and trim off the excess soil.
• Calculate the weight of cutter filled with soil.
• Take the representative sample and repeat the test three/four times and calculate the average density.

2. Sand Replacement Method:

This method is also used for dry density testing of soil.

This method involves,

• sand pouring cylinder
• calibrating container
• tray with circular hole
• chisel

PROCEDURE:

• Fill the cylinder with uniformly graded sand up to a height of 10mm below the top.
• sand is made to pass through 600 micron sieve and retained on 300mm sieve.
• This weight is recorded as M1.
• Place the sand pouring cylinder over a plane surface and open the shutter to allow the sand to fill the cone.
• This weight is recorded as M2.
• Collect the sand on the plane surface and transfer it back to the pouring cylinder.
• Place the sand pouring cylinder over the cylindrical can and allow the sand to fall into the cylindrical can till it is full. 
• Once the sand is filled, close the shutter.
• Measure the weight of pouring cylinder again and this is noted as M3.
• Calculate the unit weight of sand.

3. Calculation of Liquid Limit using Casagrande's apparatus:

Liquid limit refers to the moisture content at which the soil sample can flow and close a groove of standard width.

This method involves,

• Casagrande's apparatus
• Grooving tool
• Wash bottle 
• Palette knives

PROCEDURE:

• Pass approximately 120g of soil sample through a 425 micron IS sieve and mix it with distilled water.
• Take into consideration that the paste should be consistent.
• Place the sample in the cup and with the help of a spatula, spread it across the entire cup to be uniform.
• With the help of a grooving tool, make a sharp groove along the diameter from the center.
• Drop the cup from a height of 10mm by cranking it at a rate of 2 revolutions/sec until the two halves of the soil cake come in contact with the bottom of the groove at a distance of 12mm.
• Make a note of the number of drops required to close the gap of 12mm.
• Repeat the procedure about 4 times and record the observations.
• Plot a graph of the recordings and the moisture content corresponding to 25 drops is taken as the liquid limit of the soil.

4. Shrinkage limit test on soil:

When the water content is sufficient enough to fill all the pores of the soil and the soil is saturated, that is known as shrinkage limit. It is defined as the lowest water content at which the soil is completely saturated.

This method involves,

• Shrinkage dish
• Evaporating dish
• Glass cup
• Spatula
• 425 micron IS sieve
• Balance
• Mercury

PROCEDURE:

• Pass 100g of soil sample through 425 micron IS sieve.
• Mix 30g of soil sample with distilled water in an evaporating dish till the voids are completely filled.
• Weigh an empty shrinkage dish. This weight is taken as W1.
• Grease the inside of the dish to prevent adhesion and fill the shrinkage dish in 3 equal layers.
• Weigh the shrinkage dish with wet soil. This weight is taken as W2.
• First the sample is dried at room temperature for approx. 24 hours and then shifted to oven at 105 - 110 degree celsius. 
• Note the weight of oven dried shrinkage dish. This weight is taken as W3.
• Remove the soil cake from the shrinkage dish. 
• Remove the excess mercury from the paste by placing sponge on top of the soil cake. Gently transfer this over a dry container and make a note of the weight as Ws.
• Carry out the necessary calculations.

5. Proctor's Compaction Test:

Compaction refers to the mechanical effort applied over a soil in order to rid it of the void space between particles. 

This method involves,

• Rammer of mass 2.6kg
• Compaction mould of capacity 1000ml
• IS sieve ( 4.75mm )
• Oven 
• Weighing balance 
• Mixing pan
• Spatula
• Mixing tools

PROCEDURE:

• Pass 20kg soil through 4.75mm IS sieve.
• Calculate the percentage retaining on sieve and the percentage passing the sieve.
• 100mm of mould is used for this procedure. Mix both the soil percentages.
• Grease the mould and base plate and weigh them to the nearest accuracy.
• Add water to the soil and keep it in an air tight container for about 18 - 20 hours for maturing and mix it thoroughly.
• Divide the sample into 6 parts.
• Take 3kg of soil and place it in the mould in 3 equal layers.
• Take one third of the sample and compact it by giving 25 blows of the rammer. Distribute the blows uniformly over the soil layer. Repeat it for the second and third layer.
• Trim the excess soil and remove the mould. Weigh the sample.
• Determine the water content for the top, middle and bottom layer and carry out the necessary calculations.

 

 TYPES OF PILE FOUNDATION

• SHEET PILES: Equipped with a vertical interlocking system, sheet piles are long structural sections that create a continuous wall which is used to retain soil or water. The dependency of a sheet pile's ability to perform is on the geometry and the type of soil it is driven into. The pile transfers pressure from the high side of the wall to the soil in front of the wall.

• LOAD BEARING PILES: Load bearing pile are used to transmit the load of a structure through a soil layer which is too weak to support the structure. Pile acts as a column to transfer the load through the weak layer to a stronger layer. This type of pile is designed similar to a reinforced concrete column except the buckling is not considered in the design. 

• FRICTION PILES: Also called floating piles, friction piles receive their bearing capacity through shear stresses along the sides of the pile. They are best used in places where the hard layers of the soil are too deep to reach. Friction piles transfer the load from the topsoil to the bottom with the help of adhesion between pile surface and soil. 

• TIMBER PILES: Like the name suggests, this type of pile is made from timber obtained from teak, sal, deodar, etc. They can be square or circular in shape. 

Pile foundation

 PILE FOUNDATION

In case where the shallow foundation has adequate capacity to support the load of the superstructure then shallow foundation is provided but if the soil is poor, the depth of foundation has to be increased in order to safely transmit the load. Because of this increased depth the foundation is known as deep foundation and pile foundation is one such type of deep foundation along with piers and wells.

TYPES OF PILE FOUNDATION

Pile foundations can be classified into different types based on certain criteria. 

1. BASED ON FUNCTION OR USE

A. Sheet piles

B. Load bearing piles 

C. End bearing piles

D. Friction piles 

E. Soil compactor piles

2. BASED ON MATERIAL AND CONSTRUCTION METHOD 

A. Timber piles

B. Concrete piles

C. Steel piles 

D. Composite piles

These can be further classified into the following:

• Timber piles: Untreated and Treated with Preservative 
• Concrete piles: Pre cast piles and Cast in-place piles 
• Steel piles: I - section piles and Hollow piles

But the best way of classifying pile foundation is on the basis of effect of installment of pile on the soil. Based on this pile foundation is divided into 2 types:

• Displacement piles
• Non - displacement piles

USES OF PILE FOUNDATION

• Piles provide load transfer in cases of poor/weak soil.
• In foundations for retaining walls, bridge abutments piles are used to resist horizontal loads.
• Loose sand deposits which get densified by the vibration set up on driving are compacted using piles.
• Piles are useful in resisting uplift loads.

MACHINE FOUNDATION

Machine foundations are heavily specialized foundations for machines, machine tools, and heavy equipment that operate at a variety of speeds, weights, circumstances.

These foundations are built to withstand the shocks and vibrations ( dynamic forces ) caused by machine operation.

The various types of machine foundations are as follows:

1. BLOCK MACHINE FOUNDATION

This foundation is made up of a pedestal that rests on a footing with a big mass and low natural frequency.

2. BOX OR CAISSON TYPE MACHINE FOUNDATION

A box type foundation is made of hollow concrete blocks. Because it is hollow, this foundation has a lower mass than a block type machine foundation. The natural frequency of the foundation of the box type machine is increased.

3. WALL TYPE MACHINE FOUNDATION

A pair of walls with a slab laying on top make up this form of machine foundation. This foundation is made up of the same elements throughout. The machine rests on the top slab and is utilized for tiny machines. 

4. FRAMED TYPE MACHINE FOUNDATION

Vertical columns with horizontal frames at their summit make up for this form of machine foundation. It is used for machines which are bigger in size. Machines are positioned on top of frames. Different materials can be used to construct the foundation's vertical and horizontal elements. 

Foundation selection based on soil types

FOUNDATION SELECTION BASED ON SOIL TYPES

Foundations are selected based on the type of soil reason being not every foundation can be supported on every soil type because of their varying textures and properties.

Foundations are selected based on the following types of soils: - 

1. Rocks

2. Uniform, firm and stiff clay 

3. Soft clay

4. Peat

1. Rocks: - Rocks, hard sound chalk, sand, and gravel with limited clay content and dense silty sand all fall under this group.

The foundations recommended for this soil type are:

1. Raft foundation

2. Pad foundation

3. Strip foundation

2. Uniform, firm and stiff clay: - This type is divided into 3 cases:

•  If the foundation is adjacent to the vegetation or where the presence of vegetation is unimportant.

The foundations recommended for this case are: -

1. Raft foundation

2. Strip foundation

3. Pad foundation

•  Where there are trees, hedges and bushes near the foundation or where there is a proposal to plant these plants near the structure in the future.

The foundations recommended for this case are: -

1. Concrete piles supporting reinforced concrete ground beams and precast concrete floor.

2. Raft foundation.

3. Specially designed trench fills in certain clay soil based on the foundation location relative to trees. 

4. Concrete piles carrying in situ concrete slab.

• Where trees are felled just prior to the start of foundation construction

The foundations recommended for this case are: -

1. Strip foundation

2. Raft foundation

3. Reinforced concrete pile in previously tree root zone

3. Soft Clay: - soft clay, soft silty clay, soft sandy clay and soft silty sand all fall within this group. 

The foundations recommended for this case are: -

1. Pile to firmer strata below

2. Wide strip footing

3. Raft foundation

4. For smaller projects use pier and beam foundation to firm strata.

4. Peat: - The foundations recommended for this case are as follows:

1. Raft foundation for the case where firm strata is not available at reasonable depth but there is hard surface crust within 3-4mm thick of suitable bearing capacity.

2. Concrete piles extended to the firm soil layer below.

3. For small projects, pad and beam foundation are taken to the firm strata below.

USES OF DIFFERENT TYPES OF FOOTINGS

 USES OF DIFFERENT TYPES OF FOUNDATIONS/ FOOTINGS

The different types of foundations/footings serve uses in their own separate ways.

1. STRAP FOOTING:-When the distance between the column is so great that the combined trapezoidal footing becomes fairly narrow, with a strong bending moment, a strap footing may be employed.

2. ISOLATED FOOTING:- When single - columns are positioned at a great distance, an isolated footing is one of the most commonly utilized type of foundation. An isolated footing must be built to avoid exceeding its bearing capacity, offer safety from overturning or sliding, and keep the ground from setting.

3. SPREAD FOOTING:- When compared to a load bearing foundation, a spread footing/foundation has a wider bottom component; the wider bottom "spreads" the structure's weight across a larger area for greater stability. Spread footings are used to support a foundation or piers beneath a structure.

Spread foundation can also be used in the following ways: -

CONCRETE SPREAD FOOTINGS:- Spread footings are used to support a building's foundation or piers. Spread footings, which are made of concrete and reinforced with steel, provide additional support.

SPREAD FOOTING WITH PIER:- Spread footings are used to support a foundation or piers beneath a structure. Spread footings are made of concrete and reinforced with steel to provide additional support. 

4. RAFT FOOTING:- Raft foundations are commonly used to support structures such as residential or commercial buildings in poor soil conditions, storage tanks, silos, and large industrial equipment foundations, among other things.

5. COMBINED FOOTING:- When only a single column appears in the foundation plan of a project, this style of footing is preferred. The term "combined footing" refers to a foundation that can carry two or more column loads. These might be rectangular or trapezoidal in plan and can be continuous.

Types Of Foundation

TYPES OF FOUNDATION  

The types of foundations are provided depending upon the type of structure, distribution of loads, type and capacity of sub-soil, presence and level of water table etc. 

The foundation can be classified into the following types:-

1) Shallow Foundation- This type is provided if the depth is equal to or less than its width. Some examples of shallow foundation are spread footing, strap footing, combined footing, raft footing, isolated footing.

• Strap footing:- Strap footing is considered to be a type of combined footing since it consists of 2 or more column footings connected by a concrete beam
• Isolated footing:- Individual columns are supported by individual footings.
• Spread footing:-  Spread footing is a type of individual footing. It is described as the structural parts that support the columns and walls while also transmitting and distributing the load from structure to the soil underneath it. 
• Raft footing:- Raft foundations are made of a thick concrete slab resting on a huge area of soil that is reinforced with steel and serves to support columns or walls while transferring load from the structure to the soil. Mat foundation is often stretched across the full surface of the structure it supports.
• Combined footing:- When two or more columns are near each other and their foundations overlap then combined footings are built.

                                      

2) Deep Foundation- This type is provided if the the depth is greater than the width. Examples of deep foundation are pile, well, pier.