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Geotech -> CH 6 - Soil Compaction
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- 1CompactionDensification of an unsaturated soil by a reduction in the volume of
voids filled with air, while the volume of solid and water remain essentially the
same. - 2CosolidationThe process in which water is
squeezed out under the action of a continuous static load. - 3Objectives of Compaction1) Increase shear strength
2) Decrease compressibility
3) Decrease permeability
4) Control swelling and shrinkage
5) Reduce liquefaction potential
6) Prolong durability - 4Four factors affecting the extent of compaction:1. Compaction effort
2. Soil type and gradation
3. Moisture content
4. Dry unit weight (dry density). - 5Compaction –General Principlessee pg 6
- 6purpose of a laboratory compaction testis to determine the proper amount
of mixing water to use when compacting the soil in the field and the resulting
degree of denseness which can be expected from compaction. - 7Structure of Compacted Clay Soil‐ For a given compactive effort and dry density, the soil tends to be
more flocculated (random) for compaction on the dry side as
compared on the wet side.
‐ Increase in water content and compactive effort tends to disperse
(parallel oriented clay particle) the soil. - 8Effect of Compaction on Cohesive Soil PropertiesIncreasing the water content results in a decrease in permeability on the
dry side of the optimum moisture content and a slight increase in
permeability on the wet side of optimum. - 9Effect of Compaction on Cohesive Soil PropertiesIncreasing the compactive effort reduces the permeability since it increases
the dry density, thereby reducing the voids available for flow. - 10Effect of Compaction on Cohesive Soil Properties‐ Under lower pressure soil compacted on the wet side of the optimum is
more compressible than the sample compacted on the dry side of the
optimum.
‐ Under high pressure the trend is opposite. - 11Effect of Compaction on Cohesive Soil PropertiesStrength of compacted clayey soil generally decreasing with moisture
content. - 12Conventional Earthwork1. Clearing & Grubbing
2. Excavation
3. Transportation and Placement
4. Moisture conditioning – if soil is too dry spray water from a water truck and
mix thoroughly the soil using bulldozers or other equipment so that water
is uniformly distributed.
5. Compaction - 13Four common types of rollers:1. Smooth‐wheel rollers ‐
subgrade and finishing
operation with sandy
and clayey soil.
2. Pneumatic rubber‐tired rollers:
‐ Heavily loaded with several
rows (4‐6) of tires
‐ Suitable for sandy and clayey
soil
‐ Compaction is the combined
effect of pressure & kneading
3. Sheepsfoot rollers:
‐drums with a large number
of projections
‐ compact by pressure and
manipulation
‐Can be used for variety of
soils, but work best in silts
and clays
4. Vibratory rollers:
‐ suitable for granular soils (sand & gravel)
‐ could be attached to Smooth‐wheel, Pneumatic rubber‐tired, and
Sheepsfoot rollers
‐ compact by pressure, manipulation and vibration - 14A roadway section will include the following four courses in ascending order:• Subgrade
• Sub‐base course
• Base course
• Surface course - 15Three Methods to determine the Field Unit Weight of Compaction1. Sand cone method
2. Rubber balloon method
3. Nuclear method (often used) - 16Essential Points:1. Compaction is the densification of a soil by the expulsion of air and the
rearrangement of soil particles.
2. The Proctor test is used to determine the maximum dry unit weight and
the optimum water content and serves as the reference for field
specifications of compaction.
3. Higher compactive effort increases the maximum dry unit weight and
reduces the optimum water content.
4. Compaction increases strength, lowers compressibility, and reduces the
permeability of soils.
5. A variety of field equipment is used to check the dry unit weights
achieved in the field. Popular field equipment includes the sand cone
apparatus, the rubber balloon apparatus, and the nuclear density meter.
Información
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- Bachelor Geotech Fichas sobre Geotech -> CH 6 - Soil Compaction, creado por pdm800 el 09/07/2013.
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- pdm800
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