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Bc.ppt METHOD OF IMPROVING SOIL BEARING CAPPACITY

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METHOD OF IMPROVING SOIL BEARING CAPPACITY

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Bc.ppt METHOD OF IMPROVING SOIL BEARING CAPPACITY

  1. 1. TOPIC: METHOD OF IMPROVING SOIL BEARING CAPPACITY )
  2. 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. 3. 1> Mechanical Compaction 2>Dynamic Compaction 3> Preloading 4> Sand Compaction Piles 5> Grouting 6> Electric Methods 7> Thermal Methods 8> Vibroflotation
  4. 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. 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. 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. 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. 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. 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.
  10. 10.  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.
  11. 11.  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.
  12. 12.  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.

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