SOIL COMPACTION AND ITS EFFECT ON PROPERTIES

soil compaction occurs when soil particles are pressed together so that reduction in pore space between them.soil compaction increases the shear strength of the soil.And soil compaction is much effective in earth dams.

1. Soil compaction and its effects on properties george p thampy roll no.40 civil.a

2. TOPICS INTRODUCTION TO COMPACTION. EFFECTS OF COMPACTION ON SOIL

3. INTRODUCTION Compaction means pressing of the soil particles close to each other by mechanical methods. Air is expelled from soil mass and mass density is increased. It is done to improve the engineering properties. Like shear strength,stability etc.. Reduces compressibility and permeability.

4. compaction

5. EFFECTS OF COMPACTION The following properties are effected. Soil structure. Permeability. Swelling. Pore water pressure. Shrinkage. Compressibility Stress strain relationship. Shear strength Shear strength at moulded water content. Shear strength after saturation.

6. Effects on soil structure The water content at which the soil is compacted plays an important role in soil structure Soil compacted at water content less than optimum water content have flocculated structure.

7. Effect on soil structure Soil compacted at water content more than optimum water content have dispersed structure .

8. Effects on soil structure

9. Effect on soil structure At a point A, the water content is low and attractive forces are predominant, so results n flocculated structure. As the water content is increased beyond optimum, the repulsive forces increase and particles get oriented into a dispersed structure.

10. Effect on permeability Permeability of soil depends on void size. As water content increases,there is an improved orientation of particles resulting in reduction of void size and permeability. Above optimum water content , the permeability slightly increases. if compactive effort is increased, the permeability decreases due to increased dry density.

11. Effect on swelling The effect of compaction is to reduce void space. Hence swelling is enormously reduced. Further soil compacted dry of optimum exhibits greater swell than compacted on wet side because of random orientation and deficiecy of water

12. Effect of pore water pressure It is defined as pressure of ground water held within a rock or soil , in gaps between particles(pores). The pore water pressure for soil compacted dry of optimum is therefore less than that for the same soil compacted wet of optimum.

13. Effect on compressibility The flocculated structure o the dry side of optimum offers greater resistance to compression than the dispersed structure on wet side. So, the soil compacted dry of optimum are less compressible.

14. Effects on stress-strain relationship The soil compacted dry of optimum have steeper stress-strain curve than those on wet side. The strength and modulus of elasticity of soil on dry side of optimum will be high. Soil compacted dry of optimum shows brittle failure. And soil compacted on wet side experience increased strain.

15. Effect on shear strength In general the soils compacted dry of optimum have a higher shear strength than wet of optimum at lower strains. However at large strains the flocculated structure of soil is broken and ultimate strength will be equal for both dry and wet sides.

16. Effect on shear strength

17. summary

18. Compaction grouting It is a the use of a mortar or concrete to laterally compact soils without vibration . The treatment involves the injection of a mortar, generally with high viscosity, under pressure and at controlled flow rate, which displaces the soil around the drilling tool and subsequently compacts it.   Compaction ratios for this technique can be quite high and are generally in the range of 6-10%.

19. Compaction grouting procedure First step is to install grout pipes using drilling. or driving techniques.

20. Compaction grouting procedure The mortar-like grout , injected through the pipes displaces the surrounding soil. The grout pipe is then lifted some distance(0.3 to 1.5),and the injection process is repeated.

21. Compaction grouting procedure Injection in stages continues until the target layer has been treated. Grouting can stiffen and strenghthen the soil layer by increasing its density, increasing the lateral stresses and acting as a reinforcement. Grouting may also be used for to produce controlled heaving of the ground surface to relevel a structure that has been damaged by the differential settlements.

22. Compaction grouting

23. Compaction grouting six different possible applications for compaction grouting.

24. Explosive compaction Explosive compaction is the ground modification technique where by the energy released from setting off explosives in subsoil inducing artificial earthquake effects. The efficiency depends on soil profile, grainsize , initial status and intensity of energy applied to the soil. The first successful application of EC method was the Franklin dam in New Hampshire in 1930.

25. Procedure for explosive compaction Series of boreholes are drilled and Pipe of 7.5 to 10 cm is driven to the required depth. The detonator and the dynamic sticks are both enclosed in a water proof bundle and is lowered through casings. Casing is withdrawn and a wad of paper or wood is placed against the charge of Explosive (To protect it from misfire). Boreholes are backfilled with sand to obtain full force of blast. The charge is fired in definite pattern.

26. Explosive compaction

27. Explosive compaction Blasting is more effective in loose sands that contain less than 20% silt and less than 5% clay .  The capillary action obstructs the densification tendency by preventing soil particles to come close. So this method is not useful for partial saturated soils. The top surface up to 1m gets disturbed and needs surface compaction. Although blasting is quite economical, it’s limited by several considerations as it produces strong vibrations that may damage nearbystructures  or produce significant ground movements .