TOPIC: METHOD OF IMPROVING SOIL BEARING CAPPACITY

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It is ability of soil to safety carry the pressure placed on the soil from any engineered structure without undergoing a sher failure with accompanying large settlement.

WHAT IS SOIL BEARING CAPACITY OF SOIL

METHOD OF IMPROVING SOIL BEARING CAPACITY OF SOIL1> Mechanical Compaction2>Dynamic Compaction3> Preloading4> Sand Compaction Piles5> Grouting6> Electric Methods7> Thermal Methods8> Vibroflotation

This method is the cheapest method. The procedure is to remove first the weak soil up to the

depth required. & replace the same in layers with compaction. If the soil is sand-clay mixture the same can be replaced

suitably in layers & compacted. If soil is only sand it is not advisable to replace The compaction is done by rollers & Vibrators.

MECHENICAL COMPACTION

The method uses a crane to lift a steel block weighting upto 500kN & upto heights 40 to 50 m which height is allowed to fall freely on the ground surface.

The weight after iit is drooped leaves a dip pit at the surface. Then the process the reapeted either the same location over the

other parts of area to be compacted. Depth of recompaction can be calculated by “LEONARDS

EQUATION” as :-

W= Weight of falling mass in tons ½ h=heighht of drop in metres D=1/2(Wh) D= Depth of recompaction in metre

DYNAMIC COMPACTION

Preloading is a technique that can successfully be used to densify soft to very soft cohesive soils.

Preloading compress the soil. Compression takes place when the water of the is removed

which amounts to artificial consolidation of soil in the field. The process of consolidation can be checked by providing

suitable settlement plates.

PRELOADING

Sand compaction piles construction consists of driving a hollow steel pipe with the bottom closed with a collapasable plate down to the required depth, filling it with sand and withdrawing the pipe.

The bottom plate opens during withdrawal and the sand pile is created.

The in-situ soil is densified due to formation of large number of sand piles.

SAND COMPACTION PILES

GROUTING Grouting is a process in which fluid like materials, either in suspension or solution form are injected into the subsurface soil or rock.

The purpose of grouting:- To decrease permeabilityTo increase shear strengthTo decrease compressibility

GROUTING

Grouting is suitable in the following cases: When there is difficult access to the foundation level.When the adjacent structures require that the soil of the foundation strata should not be excavated. To control ground water flow under earth and masonry dams.

This method is also known as electro-osmosis. This method is used to density in the situ cohesive soils. The electric current induces a flow of water from the

anode(+ve) to the cathode (-ve). The cathode is generally a perforated metal pipe which is

use as a well-point for removing the water. The anode can be any type of metal rod. Both the anodes and cathode should be placed about be

2m apart beneath the lowest elevation to be stabilized.

ELECTRICAL METHOD

Heat is very rarely used to stabilize soils. At temperature of 100 C causes drying and increase in the

strength of clays. At 500 C temperatures, there is permanent change in the

structure of clays. At 1000 C temperature , clay is converted into a solid

substance like brick. Ground freezing appears to be gaining popularity in some

cases. This technique is useful in sinking tunnel shafts, advancing

tunnels in running ground etc.

THERMAL METHODS

Vibro floatation is a technique in which a granular soil is vibrated, extra granular soil is added and density of soil is increased.

This method was invented in Germany in 1930 and first used in USA in 1940.

Compactor produces centrifugal force of 10 tons to vibrate granular soils like sand and gravels.

10% of extra soil is added. Weight of vibrator is about 2 tons, 17inch diameter and 6

feet long.

VIBRO FLOTATION