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Soil Compaction. Compaction Compaction is the method of mechanically increasing the density of soil by removal of air. Dry density (  d ) is the measure.

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Presentation on theme: "Soil Compaction. Compaction Compaction is the method of mechanically increasing the density of soil by removal of air. Dry density (  d ) is the measure."— Presentation transcript:

1 Soil Compaction

2 Compaction Compaction is the method of mechanically increasing the density of soil by removal of air. Dry density (  d ) is the measure of the degree of compaction.

3 Why Compaction? Increase bearing capacity Increase stability of slopes of embankments Reduce compressibility Reduce permeability Reduce volume changes Prevent frost damage

4 Laboratory Compaction Tests Why Test? Provide moisture density curve identifying optimum moisture. Compare the degree of compaction vs. specs (Relative Compaction, R.C.).

5 Compaction Laboratory Tests Standard Proctor Test Modified Proctor Test

6 Standard Proctor Test V = 1/30 ft 3 (944 cc)

7 Standard Vs. Modified Proctor Compaction Standard Proctor Modified Proctor

8 Zero Air Voids Line S = 100% Dry side of optimum w opt Wet side of optimum Moisture-Density Curve Test 1234 w tt dd  ZAV

9 Allowable Moisture Allowable Moisture = (OMC – 3%) to (OMC + 2%)

10 Factors affecting Compaction Compactive Effort Moisture Content Soil Type

11 Compactive Effort Zero air void Water content w (%) Dry density  d (Mg/m 3 ) Dry density  d (lb/ft 3 ) Line of optimums Modified Proctor Standard Proctor Holtz and Kovacs, 1981  d max w opt

12 Soil Type Grain size distribution. Shape of soil grains. Specific gravity of soil solids. Amount and type of clay minerals.

13 Soil Type (cont ’ d) Zero air voids line Sand, some fines Clay Dry Density Moisture content  d max OMC Constant compaction energy

14 Check Point Method Water content w % w opt Dry density,  d  d max 100% saturation Line of optimums A B M C X Y (No) 1 point Proctor test Known compaction curves A, B, C Field check point X (it should be on the dry side of optimum) Holtz and Kovacs, 1981 X M

15 Relative Compaction Correlation between relative compaction (R.C.) and the relative density Dr Typical required R.C. = 90% ~ 100%

16 Field Compaction

17 Elephant and Compaction Heavy Weight Question? The compaction result is not good. Why? He He! I’m smart.

18 Types of Compaction Vibration Impact Kneading Pressure Static or Vibratory

19 Compaction Equipments and Techniques Smooth Wheel rollers Sheepsfoot Rollers Pad Rollers Pneumatic (Rubber-Tired) Rollers Grid Rollers Vibratory Rollers

20 Smooth-wheel roller (drum) 100% coverage under the wheel All soil types except for rocky soils. Contact pressure up to 380 kPa Compactive effort: static weight Most common use is for proof- rolling subgrades and compacting asphalt pavement. Holtz and Kovacs, 1981

21 Sheepsfoot Rollers 8% ~ 12 % coverage Best for clayey soils. Contact pressure from 1400 to 7000 kPa Compactive effort: static weight and kneading.

22 Pad Roller About 40% coverage Best for compacting fine- grained soils (silt and clay). Contact pressure is from 1400 to 8400 kPa Compactive effort: static weight and kneading.

23 Pneumatic Rollers 80% coverage under the wheel. Bet for Granular and fine-grained soils. Contact pressure up to 700 kPa. Compactive effort: static weight and kneading.

24 Grid Rollers About 40% coverage Contact pressure is from 1400 to 8400 kPa Best for compacting fine-grained soils (silt and clay). Compactive effort: static weight and kneading.

25 Vibratory Compactors Compactive effort: static weight and vibration. Suitable for granular soils

26 Compaction Type Vs. Soil Type Materials Vibrating Sheepsf oot Rollers Static Sheepsfoot Grid Roller Scraper Vibrating Plate Compactor Vibrating Roller Vibrating Sheepsfoot Scraper Rubber-tired Roller Loader Grid Roller Lift Thickn ess Impact Pressure (with kneading) Vibration Kneading (with pressure) Gravel12+PoorNoGoodVery Good Sand10+/-PoorNoExcellentGood Silt6+/-Good PoorExcellent Clay6+/-ExcellentVery GoodNoGood

27 Compaction Difficulty Vs. Soil Type Fill Materials Permeability Foundation Support Pavement Subgrade Expansive Compaction Difficulty Gravel Very HighExcellent NoVery Easy Sand MediumGood NoEasy Silt Medium LowPoor Some Clay None+ModeratePoorDifficultVery Difficult Organic LowVery PoorNot AcceptableSomeVery Difficult

28 Field Density Destructive Testing:  Sand Cone  Core Cutter  Rubber Balloon Nondestructive Testing:  Nuclear Density

29 Sand Cone Test W1= mass of sand cone before test W2 = mass of sand cone after test W3 = mass of sand filling cone and hole (W3 = W1-W2) W4 = mass of sand filling the cone =  sand *V cone W5 = mass of sand filling the hole = W3-W4 V hole = W5 /  sand W6 = mass of soil extracted from the whole w = moisture content of soil W1 W2 Standard Sand with known Gs W4 W5

30 Sand Cone Test Procedure A small hole (6" x 6" deep) is dug in the compacted material to be tested. The soil is removed and weighed, then dried and weighed again to determine its moisture content. The specific volume of the hole is determined by filling it with calibrated dry sand from a jar and cone device. The dry weight of the soil removed is divided by the volume of sand needed to fill the hole. This gives the density of the compacted soil.

31 Core Cutter Static Load 4 in 5 in Suitable for cohesive soils only

32 Rubber Balloon

33 Nuclear Density Nuclear Density meters are a quick and fairly accurate way of determining density and moisture content. The meter uses a radioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (direct transmission). The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottom of the unit. Dense soil absorbs more radiation than loose soil and the readings reflect overall density. Water content can also be read, all within a few minutes.

34 Nuclear Density


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