LAB MANUAL 6StandardProctorCompaction

LAB MANUAL - CIVE 310 Soil Mechanics Standard Proctor Compaction Section Before Lab Read this Handout Assigned Due 60 COMPACTION What is Compaction

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CIVE 310 Soil Mechanics Standard Proctor Compaction Section Assigned Due Before Lab: Read this Handout 60
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COMPACTION What is Compaction? Compaction is the densification of soil by the removal of air (using mechanical energy). How do we compact soil? We can use a variety of methods and machinery: Method Machinery Used Used on what soil? Static Pressure Steel Drum Roller Rubber Tired Roller All Soils Vibration Vibratory Rollers Vibratory Plate Tampers Usually Cohesionless Tamping Jumping Jack Tampers Usually Cohesionless Kneading Sheepsfoot Roller Cohesive Why do we compact soil? To improve soil properties and behavior: strength compressibility permeability shrink/swell behavior reduce liquefaction potential compression due to wetting How do we compact soils (in fills)? 1) Spread the soil in layers (also called lifts) of a specified thickness. 2) Bring the moisture content close to optimum (by drying or wetting the soil as necessary). 3) Compact the soil to the proper density using appropriate equipment. How do we know how much to compact a soil? We can correlate a soil’s properties from lab testing. In this case we perform a Proctor test on the soil - we compact a soil at different moisture contents (but using the same effort each time) to determine the moisture-density relationship for that soil. If we draw a curve between the points, we can determine the maximum dry density and optimum water content for a soil at a certain effort. Moisture-density relationships are different for different types of soil. Coarse sands and gravels are less sensitive to moisture changes than are fine-grained soils. 61
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What is the Zero Air Voids Line? e G eV V V G V V W V W w s s s s w s v s d + = + = + = = 1 γγ γ Recall that , where S=1 if the saturation is 100%. So our final formula is: Se w G s = w G G s w s d + = 1 This is the theoretical maximum density obtained when there is no air in the void spaces. It is usually not reached when soils are compacted. If your points plot above this line, there is an error in your data somewhere. ) ( d Remember that the values of water content, wet unit weight and specific gravity are not constant throughout a soil formation. There could also be variability in the test results. These variabilities can result in points on the compaction curve above the ZAV line (S>100%). These data points should not be thrown out. Throwing them out could give an accurate analysis of the soil. What effect does the amount of compactive effort (i.e. energy) have on compaction? Increasing the amount of compactive effort (energy imparted to the soil) will increase the maximum dry density and lower the optimum water content of a particular soil. How do we know how much compaction is enough? How do we determine if soils have been
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This note was uploaded on 04/03/2008 for the course CIVE 310 taught by Professor Iforget during the Spring '08 term at Drexel.

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LAB MANUAL - CIVE 310 Soil Mechanics Standard Proctor Compaction Section Before Lab Read this Handout Assigned Due 60 COMPACTION What is Compaction

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