Sunday, 24 January 2016

Different types of the soil samples


The soil samples can be of two types:-

1) A disturbed sample

2) Undisturbed sample

 

1) A disturbed sample is that in which the natural structure of soil get partly or fully modified and destroyed although with suitable precautions the natural water content may be get preserved.

such a sample however be representative of the natural soil by maintaining the original proportion of various soil particle impact.

it can be used to determine the  index properties of the soil. Such as grain size, plasticity characteristics specific gravity.

however it is impossible to get truly undisturbed sample. some disturbance is inevitable during sampling even when almost care is taken. even the removal of the sample from the ground produces a change in the stresses and cause disturbance. it is used for determining the compressibility shear strength permeability shrinkage limit etc. the smaller disturbance the greater would be the reliability of the result.

 

2) An undisturbed sample is that in which the natural structure and properties remain preserved.

Negative skin friction

Negative skin friction is a downward drag acting on the pile due to downward movement of the surrounding compressible soil relative to the pile.

This happens when the surrounding, compressible soil has been recently filled of formed.

 AS the soil consolidates the earth filed moves downward developing the friction forces on the perimeter of the pile which tends to carry the pile further into the ground.

The negative skin friction may also be developed by lowering of the ground water the increase in effective stress causing consolidation of the soil, with the resulting settlement and friction force being developed on the pile.

Permeability


1) Is the ease with which water can flow through any medium.

2) In soil mechanics, permeability of soil is a soil property which describes quantitatively, the ease with which water flows through soil.

3) Permeability is a very important engineering property of soil.

4) Knowledge of permeability is essential in a number of soil engineering problems, such as settlement of buildings yield of wells, seepage through and below the earth structures. it control the hydraulic stability of soil masses.

5) The permeability of soil is also required in the design f filter used to prevent piping in hydraulic structures and subgrade drainage, rate of consolidation of composition of compressible soils and many other aspects.

Index properties of soil


Those properties which helps to access the engineering behavior of soil and which assist in determining its classification accurately are termed as the index properties. index properties include indices which help in determining the engineering behavior such as

1_ strength

2_ load-bearing capacity

3_ swelling and shrinkage

4_ settlement etc.

 

these properties may be relating to

1. individual soil grain

2. aggregate soil mass

The properties of individuals particles can be determined from the  remoulded, disturbed sample.

These depend upon the individuals grains there mineralogical composition size and shape of grain and are independent of soil formation.

The soil aggregates properties depend upon the mode of soil formation, soil history and soil structure. these properties should be determined from the disturbed sample or preferably from in situ test.

Saturday, 2 January 2016

Grade of concrete

Characteristic strength is defined us the strength of material below which not more than 5% of test results are expected to full. 

The concrete grade M10, M15 and M20 are termed as ordinary concrete and those of M25 to M55 are termed as standard concrete and the concrete of grade 60 and above are termed as high strength concrete. 

 The selection of minimum grade of concrete is dictated by durability considerations which are based on kind of environment to which the structure is exposed, though the minimum grade of concrete for reinforced concrete is specified as M20 under mild exposure conditions, it is advisable to adopt a higher grade.  

 For moderate, severe, very severe and extreme exposure conditions, M25, M30, M35 & M40 grades respectively are recommended.

Types of constructions


1 load bearing structure

2 framed structure

1) load bearing structure:- 

 1. in load bearing structures the entire load of the superstructure is transmitted through the walls to the soil below the ground. 

2. these walls are supported on continuous foundation that resist on hard strata. thickness of such walls is too large.

3. if the number of storey is increased the thickness of the wall increases.

4. this type of construction reduces the carpet area

5. this type of construction cannot be used for multi-storeyed building.

2.) framed structure

1. framed structure consists of a series of frame made up of beams and columns.

2. walls are constructed within the frames which are known as a partition walls

3. thus the load of floor roofs and partition walls are supported by beams which in turn transmit the load to the column.

4. column transmit the load to the foundation, which rests on a hard soil below the ground

5. framed structure are suitable for medium and multi storeyed building.

Types of loads


The basis requirement of any structural member  of building is that should be strong enough to carry or support all the possible type of load which acts on it.

1 dead

2live or imposed

3 impact

4 wind load

5 snow

6 earthquake

 1. dead load :-   dead load are permanent loads which are transferred to structural throughout the life span. the dead load in a building comprise the weight of roofs, floors, beams, columns, walls, partition walls etc

2. live load:- the load which keep on changing on time to time are called live loads. common example of such moving loads in a building re the weight of the person, weight of movable partition , weight of furniture's, home appliances, equipment etc. these loads are to be suitably assumed by the designer. it is one of the major loads in the design.

3. impact load:- it is caused by vibration or acceleration thus impact loads is equal to imposed loads incremented by some %. for ex, vibration of moving vehicle or machines

4 wind loads:- when wind is obstructed by the structure, it exerts a pressure on the structure known as wind pressure. wind pressure acts horizontally on the exposed vertical faces of the structure. wind loads is effective in case of tall buildings.

5. earthquake load:- earth causes horizontal and vertical ground shaking. the  horizontal and verticle shaking is usually most critical on building. every building and its portions should be designed and constructed to resist  the effect of earth ground motions.

6 Snow loads:- it acts on the roofs. roofs should be designed loads due to snow, whichever is more severe. for the building to be located in the regions wherever snow is likely to falls, this loads is to be considered. mountainous regions in northern parts of India are subjected to snow fall.

Basic function of building.


1. it should be sufficiently strong to withstand the effects of the atmosphere and environment.

2. it should be durable and stable to take up the anticipated loads coming on it including the self weight live load and earthquake load.

3. it should be well ventilated and free from dampness.

4. it should be resist penetration of moisture

5. it should be provide maximum living and working comfort

6. it should be dimensionally stable

7. grouping of rooms should be so planned as to ensure circulation and optimum utilization of space and maximum efficiency fire hazards.

8. the building should be safe against fire hazards

9. the building should be safe against theft and burglary the external wals should be made so strong to resist any such attempt.

10. the building should be sound insulating so as to reduce sound passing through it.

SELECTION OF SITE




For good planning and designing of building, the site of the building is the most important aspect. the fallowing general guidelines should be kept in mind while selecting a site for a building.

1 . SITE plot must be of clear title along with clear ownership rights of the land.

2. the building site should be located on a fully developed or fat developing locality.

3. for happy living the neighborhood should be of equal status in society.

4. the shape of the plot shall not be irregular

5. as far as possible rectangular plot should be selected because maximum area of plot can be used for construction.

6. the site should be have general facilities such as a sewer line,  water line, power construction, street lights, and garbage disposal.

7. the site should be well connected by road by pass and service lines.

8. the site should be elevated land so as to have easy surface drainage  of rain water

9. the ground water table level at the site should be not too high not too low.

10.the soil condition of plot should be such that economical foundation should be possible, good compact soil, hard strata, rock or sand is desirable at minimum depth.

11. the site should have good view of landscape such as hills, gardens, rivers, lake, seashore as to promote healthy and peaceful living.

12. the site should away from kilns, quarries, congested and noisy localities and such other places.