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Objectives v Be able to use basic volume weight equations v Understand principal of soil compaction. v Explain how the compaction test is used in design.

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Presentation on theme: "Objectives v Be able to use basic volume weight equations v Understand principal of soil compaction. v Explain how the compaction test is used in design."— Presentation transcript:

1 Objectives v Be able to use basic volume weight equations v Understand principal of soil compaction. v Explain how the compaction test is used in design and quality control v Be able to perform basic compaction test (LAB EXERCISE) v plot compaction data and evaluate for accuracy v Understand procedure for Atterberg Limit Tests (LAB EXERCISE)

2 Review of Compaction Principles v Compaction Tests are not suitable for soils with more than 30 % by weight of the sample being larger than a ¾” sieve. v Compaction tests are not usually performed on soils with 12 % or fewer fines

3 Review of Compaction Principles v Relative Density testing is used for clean sands and gravels – covered later in class v Standard Procedures for testing are available for soils with some gravel (less than the maximum allowable content)

4 Principle of compaction v Theory developed by R.R. Proctor in 1930’s in California v Three Factors determine the density that results from soil compaction

5 Proctor Developed Principle v Three variables determine the density of a compacted soil –The energy used in compaction –The water content of the soil –The properties of the soil

6 State Diagram Water content, % Dry Density, pcf 100 % saturation curve

7 State Diagram Water content, % Dry Density, pcf

8 Energy Used in Compaction v Assume you have some clay soil that is at a water content of 16 percent. v Look at the effect different compaction energy has on the density of the soil. v Energy expressed as number of passes of a sheepsfoot roller on a lift of soil

9 Water content, % Dry Density, pcf 1 pass of equipment 2 passes of equipment 3 passes of equipment 4 passes of equipment 10 passes of equipment At this water content, energy has a large effect on compacted density

10 Water content, % Dry Density, pcf 10 passes of equipment At this point, the sample has had most of its air driven out by the compaction 100 % saturation line

11 Water content, % Dry Density, pcf 1 pass of equipment 2 passes of equipment 3 passes of equipment 4 passes of equipment 10 passes of equipment At a lower water content, energy has little effect on the compacted density of a clay soil

12 Compacting at low water contents v At low water contents, insufficient water is available to lubricate the particles and allow them to be rearranged into a dense structure. v The frictional resistance of dry particles is high

13 Water content, % Dry Density, pcf 1 pass of equipment 2 passes of equipment 3 passes of equipment 4 passes of equipment 10 passes of equipment At a very high water content, energy has little effect on the compacted density of a clay soil because the water is incompressible and takes the applied force without densifying the soil This results in a term called pumping

14 Compacting Very Wet Soil At this point, few air pockets remain – compaction forces are carried by water in soil which is incompressible

15 Water has Zero Shear Strength

16

17 Effect of Water Content v Now examine the effect of just changing the water content on a clay soil, using the same energy each time the soil is compacted. v For example, assume soil is spread and compacted with 4 passes of a sheepsfoot roller each time. v Examine using State Diagram

18 Effect of Water Content Dry density, pcf Water content, % Sample 1 compacted at 12 % water – Dry Density is 99.0 pcf 12 % 99.0 pcf

19 Effect of Water Content Dry density, pcf Water content, % Sample 2 compacted at 14 % water – Dry Density is pcf 14 % pcf

20 Effect of Water Content Dry density, pcf Water content, % Sample 3 compacted at 16 % water – Dry Density is pcf 16 % pcf

21 Effect of Water Content Dry density, pcf Water content, % Sample 4 compacted at 18 % water – Dry Density is 98.5 pcf 18 % 98.5 pcf

22 Effect of Water constant energy Dry density, pcf Water content, % Maximum dry density, pcf Optimum water content, %

23 Now, perform the same test at a different (Higher energy) on the soil Dry density, pcf Water content, % 4 passes of sheepsfoot roller 10 passes of sheepsfoot roller

24 Effect of Soil Type on Curves Dry density, pcf Water content, % Plastic Clay Soils have Low Values of Maximum Dry Density pcf

25 Effect of Soil Type on Curves Dry density, pcf Water content, % % Plastic Clay Soils have high values for optimum water content (20-40 %)

26 Effect of Soil Type on Curves Dry density, pcf Water content, % Plastic Clay Soils have a Flat Curve for Lower Energies Density

27 Effect of Soil Type on Curves Dry density, pcf Water content, % Sandy Soils with Lower PI’s have High Values of Maximum Dry Density pcf

28 8-15 % Effect of Soil Type on Curves Dry density, pcf Water content, % Sandy Soils with Lower PI’s have Low Values of Optimum Water Content

29 Effect of Soil Type on Curves Dry density, pcf Water content, % Sandy Soils have a Steep Curve – Short distance from plastic to liquid states of consistency

30 Summary Dry density, pcf Water content, % Lower PI – Sandier Soils in this Region Intermediate PI Soils in this Region Higher PI – Clayey Soils in this Region 75-95

31 Summary Dry density, pcf Water content, % Lower PI – Sandier Soils in this Region 8-14 Intermediate PI Soils in this Region Higher PI – Clayey Soils in this Region 20-40

32 Family of Curves (Covered Later)

33 Family of Curves water content, %  d, dry density, pcf Line of Optimums Zero air voids curve not parallel to line of optimums at upper end

34 v Using a standard energy, if a series of specimens of a soil are compacted at increasing water contents, the resultant dry density of the specimens will vary. The density will increase to a peak value, then decrease. Proctor’s principle of compaction

35 Principle of Compaction v A plot of the dry density versus the water content from a compaction test will be parabolic in shape. v The peak of the curve is termed the maximum dry density, and the water content at which the peak occurs is the optimum water content.

36 Standard Proctor Energies v Several standard energies are used for laboratory compaction tests –Standard – 12,400 ft-lbs/ft 3 –Modified – 56,000 ft-lbs/ft 3 –California – 20,300 ft-lbs/ft 3

37 Standard Proctor Compaction Test Summary v Uses 5.5 pound hammer v dropped 12 inches v mold filled in 3 lifts v 25 blows of hammer per lift v Total energy is  12,400 ft-lbs/ft 3 12”drop 3 lifts 5.5 # hammer

38 Modified Proctor Compaction Test Summary v Uses 10 pound hammer v dropped 12 inches v mold filled in 5 lifts v 25 blows of hammer per lift v Total energy is  12,400 ft-lbs/ft 3 18”drop 10 # hammer 5 lifts

39 Proctor Compaction Test Summary v Several Standard molds are used depending on maximum particle size in sample –4”diameter mold (1/30 ft 3 ) used for soils with low gravel contents –Method A for soils with < 20 % gravel –Method B for soils with > 20 % gravel and 20 % gravel and < 20 % larger than 3/8”

40 Proctor Compaction Test Summary v Several Standard molds are used depending on maximum particle size in sample –6”diameter mold (1/13.33 ft 3 ) used for soils with significant gravel contents –More than 20 % gravel larger than 3/8” –Must have less than 30 % larger than 3/4”

41 Proctor Compaction Test Summary v Standardized tests are not available for soils with more than 30 percent by weight of the total sample being larger than 3/4”in diameter gravels v ASTM Compaction Test Methods are –D698AD1557A –D698B D1557B –D698C D1557C

42 Proctor Compaction Test Summary v Prepare 4 to 5 specimens at increasing water contents about 2 % apart. Example - prepared samples at 14, 16, 18, and 20 percent. Use range of moistures based on feel and experience.

43 Proctor Compaction Test Summary v Then, compact each sample into a steel mold with standard procedures Compaction mold Cured soil Hammer

44 Proctor Compaction Test Summary v Then, strike off excess soil so the mold has a known volume of soil.

45 Proctor Compaction Test Summary v For each sample, measure the weight and the water content of the soil in the mold v The mold volume and weight are pre-measured. Don’t assume nominal volume of 1/30 ft 3 or 1/13.33 ft 3 v Calculate moist density v Calculate dry density v Plot dry density and water content for each point

46 Class Problem v Calculate Moist density, dry density

47 Class Problem Mold wt = 4.26 #, Mold Vol. = ft 3

48 Class Problem v Calculate Moist density, dry density v Plot curve of dry density versus water content v Determine Maximum dry density and optimum water content

49 { Set Up Plot – Form SCS pounds

50 Set Up Plot – Form SCS-352 Make each vertical division equal to 1 percent water content

51 Class Problem

52 Zero Air Voids Curve v After you plot a compaction test, plotting a zero air voids curve is very important. This curve is also called the 100 % saturation curve v This curve shows for a range of dry density values what the saturated water content is for any given value

53 Compaction Problem Zero air void equation Assume 3 values of  d and calculate w sat %

54 100 % Saturation Curve 75 % Saturation Curve 95 % Saturation Curve assumed Gs = 2.70 Unit wt. water = 62.4 Assumed dry density = 105 pcf wsat(%) = 22.1(%)

55 Zero Air Voids Curve

56 Plotted Class Problem

57 Zero Air Voids Curve v The 100 % saturation curve is used to judge the reliability of the compaction curve and of field measurements of compacted soil density and water content v Compacted soils for NRCS specifications are usually at a degree of saturation of about 75 to 95 percent

58 75 % Saturation Curve 100 % Saturation Curve 95 % Saturation Curve

59 v Evaluating Compaction Tests –Standard requirements - spread in water content about 2 % and at least two points above and below optimum –Typical shape - soil type ? Review of Compaction

60 Compaction Problem Other given information: LL = 47, PI = 30, classified as CL soil Gs = 2.68

61 Evaluating compaction test Are points about two percent apart ? 2.1 %2.7 %

62 Evaluating compaction test Are two points below and 2 above optimum ?

63 Optimum water content about 80 % saturated water content ? - Acceptable range is Review of Compaction Optimum w% = 21.0  % sat = 21.0÷23.6=89% pcf

64 Plotted Class Problem w pcf = (62.4/ /2.68) * 100 = 23.6 % wopt/wsat = 21.0/23.6 = 89 % 

65 Wet side parallel to saturation curve at  90 % saturation ?  d, pcf w, % Review of Compaction % Sat = 24.3 ÷ 26.4 = 92.0 % Check a point on wet side at 98 pcf, w % on curve is 24.3%

66 Plotted Class Problem wopt/wsat = 24.3/26.6 = 91 %  w 98.0 pcf = (62.4/ /2.70) * 100 = 26.6 %

67 Evaluating Compaction Tests Evaluating Compaction Tests u Typical value for fine-grained soils compared to Navdocks equations  dmax = *LL + 0.3*PI w opt = * LL * PI Review of Compaction

68 Evaluating Compaction Tests Evaluating Compaction Tests u Typical value for fine-grained soils compared to Navdocks equations  dmax = * *30 = pcf OK - test value was pcf w opt = * * 30 = 19.6 % OK Test value was 21.0 % Review of Compaction

69 v Soils are compacted to improve the engineering properties over those of loosely placed soils. v The engineering properties are affected both by the density to which the soil is compacted and the water content at which it is compacted Purposes of compaction

70 Role of compaction tests in earth fill projects v Samples are obtained in site investigation and sent to laboratory for testing v Soils are tested to determine reference density - as well as other index properties v Engineering properties are measured by testing at a percentage of the reference test density. For example, a shear test might be performed at 95 percent of the Standard Proctor maximum dry density of the soil.

71 v The engineering properties are used in analyses to determine a suitable design v For example, the shear strength is used in a slope stability analyses v If the engineering properties allow a satisfactory design, then the degree of compaction is used in a contract specification. Role of compaction tests in earth fill projects

72 v If an unsatisfactory design results, the soil is re- tested at a different degree of compaction to obtain better engineering properties v The design is re-analyzed and the process repeated until a final satisfactory degree of compaction is decided v Then the degree of compaction is used in a contract specification. Role of compaction tests in earth fill projects

73 v Quality control processes are used to ensure that the earth fill is compacted to the degree of compaction specified, within a range of specified water contents v Field compaction tests are performed to assure that the proper reference density is being used Role of compaction tests in earth fill projects

74 Compaction Tests as Used in Design of an Earth Fill

75

76 Example of Process v Sample obtained to determine suitability as clay liner v Sample Sent to Laboratory v Laboratory performs Standard Proctor Test v A Permeability Test is performed at 95 % of maximum Standard Proctor Dry Density

77 Example of Process v The sample is remolded at 2 percent wet of optimum (for this sample, 85 % saturated) v The permeability test measures an acceptably low permeability v A recommendation is given to the field office that compaction to this combination of density and water content results in acceptably low permeability

78 Example of Process v During construction, measurements of dry density and water content are made during construction. v If the degree of compaction and percent saturation are equal to or better than specified, the liner is judged to have a low permeability and is considered acceptable.

79 v A compaction test measures a maximum dry density of pcf and an optimum water content of 18.0 %. The soil has an estimated G s value of 2.68 v A contract requires compaction to 95 % of maximum dry density at a water content of optimum or greater Class Problem 2

80 v A field test measures a moist density of pcf and a water content of 23.4 % v Does the compacted fill meet the contract requirement ? v Use the values given for measured moist density and water content, calculate the dry density v Assume a Gs value of 2.68 and compute a wsat value Class Problem 2

81 Class Problem v Compare the reported compaction water content to theoretical saturated water content v Compacted soils are commonly in the range of percent saturated v What do the results tell you about the reliability of the field data? v What would you look for to explain any problems?

82 Conclusions of Class Problem v The measured data appears to have problems. v Possible errors are in the measurement of the dry density, the water content, or the specific gravity value used in computations v Recommend investigating most probable causes


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