Foundation Engineering – engineeringbrother

Plate Load Test-How Calculate Bearing Capacity and Settlement of Soil ?

ssorthiya58@gmail.com — Fri, 17 Apr 2020 11:02:00 +0000

Plate Load Test

How Calculate Bearing Capacity and Settlement of Soil ?

Plate Load Test by Gravity Loading Method

Plate load test is a field test to determine the ultimate bearing capacity of soil, and the probable settlement under a given loading. The test essentially consists in loading a rigid plate at the foundation level, and determining the settlements corresponding to each load increment.

Plan and section of plate load test pit

The size of square bearing plate may be 30 cm x 30 cm or 75 cm x 75 cm. The thickness of steel plate should not be less than 25 mm.

The test pit width is made five times the width of the base plate Bp

Bf = 5Bp

At the centre of the pit, a small square hole is dug whose size is equal to the size of the plate. The depth of hole (Dp)should be such that,

where,

Dp = Depth of hole

Bp = Width of plate

Df = Depth of foundation

Bf= Width of foundation

The loading to the test plate may be applied with the help of a hydraulic jack.

The reaction of the hydraulic jack may be borne by either of the following two methods.

(1) Gravity loading platform method

(2) Reaction truss method

1. Gravity Loading Platform Method

In case of gravity loading method, a platform is constructed over a vertical column resting on the test plate. the loading is done with the help of sand bags, stones or concrete blocks.


Gravity Loading Method For Plate Load Test

As per I. S. 1888-1962, a seating load of 0.7 t/m2 is applied and then released. The load is applied with the help of hydraulic jack, in convenient increments, say of about one-fifth of the expected safe bearing capacity or one-tenth of the ultimate bearing capacity.

Settlement of the plate is observed by two dial gauges fixed diametrically opposite ends, with sensitivity of 0.02 mm .

Settlement should be observed for each increment of load after an internal of 1, 4, 10, 20, 40 and 60 minutes and thereafter at hourly intervals until the rate of settlement becomes less than 0.02 mm per hour.

The maximum load that is to be applied corresponding to 1.5 times the estimated ultimate load or to 3 times the proposed allowable bearing pressure.

Interpretation of Results

The load intensity and settlement observations of the plate load test are plotted in the form of load settlement curve.

Settlement Curve from Plate Load Test

Fig shows four typical curves applied to different soils.

Curve Iis typical for loose to medium cohesionless soil. It can be seen that initially this curve is a straight line, but as the load increases it flattens out. There is no clear point of shear failure.

Curve IIis typical for cohesive soils. This may not be quite straight in the initial stages and leans towards settlement exist as the settlement increases.

Curve IIIis typical for partially cohesive soils.

Curve IV is typical for dense cohesionless soils.

Curves II and IV have well defined points of failure (yield points) and as such there is no difficulty in arriving at the value of ultimate bearing capacity of soil in case of cohesive soil and dense cohesionless soils The load corresponding to yield point is taken as the ultimate bearing capacity of plate (qp).

In case of curve I and II where yield point is not well defined, the ultimate bearing capacity of plate may be calculated as discussed below

A load-settlement curve is plotted as shown in Figure, The ultimate load for the plate qp, is indicated by a break on log-log plot.

If the break is not well-defined, the ultimate load is taken as that corresponding to a settlement of one-fifth of the plate width (Bp). On the natural plot, the ultimate load for the plate qp is obtained from the intersection of the forward and backward tangents as shown in figure.

How To Determine Ultimate Bearing Capacity From PLT Observation ?

The ultimate bearing capacity of the proposed foundation q(f) can be obtained from the following relations

(a) For clayey soils :

q(f)= q(p)

i.e. Bearing capacity of plate is taken as the bearing capacity of foundation.

(b) For sandy soils :

How To Determine Settlement From PLT Observation ?

The plate load test can also be used to determine the settlement for a given intensity of loading.

(A) for clayey soil

where,

Sp = Settlement of plate obtained from graph

Sf= Settlement of foundation.

B) For sandy soils :

where, Bf and Bp are in metres.

(2) Reaction Truss Method

In this method basically truss are made for supporting load. and with help of truss loading is applied.

Reaction Truss Method

Limitations of Plate Load Test:

The plate load test has the following limitations:

(1) Size effect : The results of the plate load test reflect the strength and the settlement characteristics of the soil within the pressure bulbs. As the pressure bulb depends upon the size of the loaded area, it is much deeper for the actual foundation as compared to that of the plate. The plate load test does not truly represent the actual conditions.

(2) Scale effect:

The ultimate B.C. of saturated clays is independent of the size of the plate but for cohesionless soils, it increases with the size of the plate.

To reduce scale effect, it is desirable to repeat the plate Load test with two or three different sizes of plates and take the average

(3) Time effect: A plate load test is a test of short duration. For clays, it does not give the ultimate settlement. The load- settlement curve is not truly representative.

(4) Reaction load: It is not practicable to provide a reaction of more than 250 kN. Hence, the test on a plate size larger than 0.6 m width is difficult.

(5) Water table : The level of W. T. affects the bearing capacity of the sandy soils. If W.T is above the level of the footing, it has to be lowered by pumping before placing the plate.

(6) Interpretation of failure load: The failure load is not well-defined except in the case of a general shear failure. An error of personal interpretation may be involved in other types of failure.

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which type of foundation used in residental building ?

ssorthiya58@gmail.com — Fri, 03 Apr 2020 06:02:00 +0000

Which type of foundation used in residential building ?

Hello guys today we will discuss which type of foundation we will used in construction of resident building and which will more economical and durable. We learnt various type of foundation but we have to use that foundation which will safe and economical.

As we know we mostly cant used deep foundation in residential building because it cause too much cost and our structure does not contain that much of loading. But when soil contain expansive nature and too much low bearing capacity than we have to go with deep foundations.

Lets first see various type of shallow foundations according uses

In Load bearing residential building

In load bearing structure we generally use strip footing as a foundation.

Strip footing is the simplest footing in shallow foundation in this footing masonary wall laid on plain cement concrete or brick bat cement concrete.

Strip Footing

This type of shallow footing only used in load bearing residential building where numbers of stories are less.

In frame structures residential building

In frame structure we go for following footing.

1. Spread or isolated footing

2. Combined footing

3. Strap or cantilever footing

4. Mat or raft Foundation

1.Spread or isolated footing

Spreadfooting consists wide base below column. This type of foundation widely used in construction of residential building.

There are two type of spread footing.

1.pad footing

2.slope footing

1.1.pad footing

In pad footing slope is not provided only rectangular Reinforced cement concrete slab is provided below RCC column.

In this type of footing design and analysis is simple compare to slope footing.

1.2.slope footing

In slope footing slope is provided at 45 degree with respect to horizontal. The main function of this slope is to avoid punching failure. The design and analysis is time consuming.

2.Combined footing

Combinedfooting are provided when ,

1. Centre to centre distance is more between column

2. Very high load

3. Eccentric loading on column

4. Property line of building near to building

In combine footing two or more column are join with one slab.

Combine footing has a two type

2.1.Rectangularcombine footing

2.2.Trapezoidalcombine footing

Trapezoidal combine footing provided where there is very large difference between loading in column.

3. Strap or cantilever footing

Strap or cantilever footing

In strap footing RCC beam(strap) is provided to join two or more column with each other. This type of footing are not generally used in residential building because of less loading.

4.Mat or raft foundation

In mat or raft foundation, RCC slab is provided below all column. Whole area is excavated , then RCC slab is provided in entire area and column are place above that slab. This type of foundation is provided where there is heavy loading or bearing capacity is too low.

Mat or raft Foundation

This type of foundation are generally not provided in residential houses, this type of foundation are provided in 3-4 or above four stories complex’s or hotels.

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How Under Reamed Piles are Constructed ?

ssorthiya58@gmail.com — Sat, 29 Feb 2020 05:31:00 +0000

How Under Reamed Piles are Constructed ?

What is under reamed pile ?

Under Reamed pile is a special type of pile manufactured by the Central Building Research Institute (CBRI). The Pile Is made of R.C.C. Near the bottom end of the pile is a spherical enlarged part called the under rim or bulb.

Under reamed pile

The diameter of the pile is 20 cm to 50 cm and the diameter of the bulb is 2 to 3 times the diameter of the pile. The length of the pile varies from 3m to 8m, the spacing between the two piles is 2m to 4m. The safe load on the pile is between 20 and 40 tonnes. Vertical spacing between two bulbs is 1.25 to 1.5 times of diameter of the bulb. If the load on the pile is high then more than one bulbs are provided.

Construction of under reamed piles.

The construction of under reamed Pile is done by manually. C.B.R.I developed tool for carried out Construction of under reamed.

The tool are simple and lightweight.

Following tools are used.

1)Spiral Auger
2)Under – reamer
3)Boring guide

1)Spiral Auger

Spiral auger

The under reamed pile uses a spiral auger to hole in the ground, with special cutter blade is use to dig the soil at the lower end of the auger. And a bucket is hang to fill the excavated soil beneath the two cutters.

Spiral auger and under reamer

2)Under reamer

Under reamer

Special types of cutters are used to prepare the bulbs, the diameter of which can be increased by applying pressure on the handle of the auger so that the bulbs are Constructed.

3)Boring Guides

Boring guides are provided to dig vertical. They are provided at ground level. Three leg tripod are used as a boring guided. Auger handle is pass trough this guide and then augering is done.

Placing of cage and pouring concrete

Reinforcement

Concreting

After digging the pile hole and the bulb to the required depth, the auger is taken out and the reinforcement cage are place into the hole and hole is poured by concrete. All the piles are joined together by forming a cap at the head of the pile and structure is constructed over a cap.

How to increase load bearing capacity of under reamed pile ?

1)By increasing numbers of bulbs.
2)By increasing Diameter of bulbs.
3)By increasing Lengh of pile.
4)By proper design of pile.

Advantages of under reamed pile

1.Under reamed pile is 15 to 20% cheaper than Strip Tooting.
2) Material is is less needed for such piles.
3) No need of heavy dig. Therefore, the operation can also be done in the rainy season.
4)No need for shoring
5)No dewatering is required.

Application of under reamed pile

1)Black cotton soil

This type of soil is expand when it come in contact with water and contract when water is removed, so that the cracks are formed in structure. Under Reamed Pile is used as a foundation in black cotton soil.

2)Less soil bearing capacity.
3)High water table in ground.
4)High uplift forces in soil.

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Deep Foundation|Type of Deep Foundation In Civil Engineering |2021|

ssorthiya58@gmail.com — Sat, 21 Dec 2019 17:34:00 +0000

let’s first discuss what is deep foundation ?

When depth of footing is larger then width of footing then this type of foundation are called deep foundation.

basically, there are three types of deep foundation,

pile foundation
cassions
cofferdams

In this article, we will study about pile Foundation in detail.

PILE FOUNDATION :

It is the type of deep foundation in which a long cylinder of different material like concrete,steel,timber etc are used.

Pile Foundation

Why we use Pile Foundation?

When safe bearing capacity of soil is not good.
When water table is at higher depth.
When there are no hard strata available at a lower depth.
When the dewatering for shallow footing is higher.
When their is very heavy load.
When foundation carrying nonuniform load.
When anchoring of structure is required.
To construct structure in marine area.

basically their are two type of pile base on load-bearing.

load-bearing pile
nonload bearing pile

1.Load bearing pile

this type of pile are used for transmit vertical load which is coming from above structure.

2.Non load-bearing pile

this type of pile are not designed for transmit vertical load . but it is used for another purpose like compaction of soil strata below ground.

Main Classification of Pile

base one function
base on material

1. Type of Pile Base On Function.

Pile are classified base on function as following manner,

Bearing Piles or End Bearing Piles
Friction Piles or Skin Friction Piles
Sheet Piles
Tension Piles or Uplift Piles
Anchor Piles
Batter Piles
Fender Piles
Compaction Piles

1. Bearing Piles or End Bearing Piles

End bearing piles are transmitting load by using the end component of the pile. in this type of pile, the base of the pile is rest on hard strata i.g. rock. the pile is driven up to hard strata. following are the pictures of end-bearing piles.

End Bearing Pile

2. Friction Piles or Skin Friction Piles

In this type of pile load is basically transform by skin friction of pile.

For increasing load-carrying capacity of pile follow things are follow

by increase diameter of pile.
by increase length of pile.
by reducing spacing between adjacent piles.
by making a pile of a rough surfaces.

Friction Pile

3. Sheet Piles

Sheet pile are not designed for taking vertical load but it is used retain soil/water as retraining wall.

Sheet piles

4. Tension pile/Uplift pile

This type of piles is used for anchoring structures with soil strata. This type of piles are used when their is high uplift pressure. When structure is tall due to wind pressure or earthquake or horizontal force structure try to overturn at ground level so it generates tensile stress in Foundation that why tension piles/Uplift piles are used for the resistance of the overturning of structure.

tension piles

5. Anchor piles

This type of piles are used for anchoring the structure against high lateral pulls.

Tension Pile/Anchor Pile

6. Batter piles

This type of piles are place inclide in ground to resist horizontal thrust which is product by structure.this type of piles are used in marine structures.

Batter Piles

7. Fender piles

This type of piles is used to protect waterfront structures or marine structures from the floating materials & impact of ships.

Fender Piles

8. Compaction pile

This type of pile are not used for carrying vertical load , but it is used for increasing bearing capacity of soil strata.

Compaction Piles

2. Type of pile Foundation base on materials

Following are the type of pile Foundation base on material of pile.

1.concrete pile
2.steel pile
3.timber pile
4.composite pile
5.sand pile

So lets we discuss one by one,

1. Concrete Pile

In this type of pile concrete/reinforced concrete is used as material. This type of piles are strong,durable and economical also. this type of piles are widely used in construction field.

Type of concrete piles
1.pre cast piles
2.prestress piles
3.cast in situ piles

1. Precast piles

This type of pile is casted on factories and they are transported on-site. this type of pile is readymade available. this type of piles are carried out on construction site and then using pile driving equipment this type of piles are driven.
The shape of the pile may be square, rectangular, circular.

Precast piles

2.Prestress piles

In this type of piles stressed reinforcement are used.stress in reinforcement is developed by applying opposite direction force on ends of reinforcements.
This type of piles are strong but costly also.

Prestress Piles

3. Cast in situ piles

This type of piles are also widely used. In this piles are made on construction site.

Following steps are carried out.
1.boring of pile hole.
2.making reinforcement cage.
3.lowering reinforcement cage.
4.concreting of pile hole.

Cast in situ Piles

Quality of this type of piles are depend open quality of concrete and quality of workers.

2. Steel piles

In this type of pile steel section are used for vertical load transportation. The following sections are widely used

1.box section
2.H section
3.Tube section

H-Steel Piles

Box Steel Piles

Tube Steel Piles

This type of section are penetrated by heavy load or driving equipment.

3. Timber piles

In this type of pile timber as a material is used. At the bottom of the pile steel shoe is provided to easily driving of pile.

Timber Piles

4. Composite piles

In this type of pile, two or more than two materials are used.
For example, concrete+timber…means the advantage of durable concrete and the cheapness of timber is taken.

Composite Pile

5. Sand Piles

In this pile, sand is used as basic material. And at the top of sand pile plug of concrete is provided. Sand is compacted by hammering.

Sand Piles

I will make saperate article on Cassions and Cofferdam because It’s been too long.

I hope you like our article ” deep foundation , types of deep foundation ” please don’t be cheap to share this article with your friends.