METHOD OF IMPROVING SOIL BEARING CAPPACITY

1. TOPIC: METHOD OF IMPROVING SOIL BEARING
CAPPACITY
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2.  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.

3. 1> Mechanical Compaction
2>Dynamic Compaction
3> Preloading
4> Sand Compaction Piles
5> Grouting
6> Electric Methods
7> Thermal Methods
8> Vibroflotation

4.  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.

5. 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

6. 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.

7.  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.

8. 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 permeability
To increase shear strength
To decrease compressibility

9. 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.

11.  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.

13.  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.

14.  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.