Presentation on theme: "Objectives Be able to use basic volume weight equations"— Presentation transcript:
1Objectives Be able to use basic volume weight equations Understand principal of soil compaction.Explain how the compaction test is used in design and quality controlBe able to perform basic compaction test (LAB EXERCISE)plot compaction data and evaluate for accuracyUnderstand procedure for Atterberg Limit Tests (LAB EXERCISE)
2Review of Compaction Principles Compaction Tests are not suitable for soils with more than 30 % by weight of the sample being larger than a ¾” sieve.Compaction tests are not usually performed on soils with 12 % or fewer fines
3Review of Compaction Principles Relative Density testing is used for clean sands and gravels – covered later in classStandard Procedures for testing are available for soils with some gravel (less than the maximum allowable content)
4Principle of compaction Theory developed by R.R. Proctor in 1930’s in CaliforniaThree Factors determine the density that results from soil compaction
5Proctor Developed Principle Three variables determine the density of a compacted soilThe energy used in compactionThe water content of the soilThe properties of the soil
8Energy Used in Compaction Assume you have some clay soil that is at a water content of 16 percent.Look at the effect different compaction energy has on the density of the soil.Energy expressed as number of passes of a sheepsfoot roller on a lift of soil
9At this water content, energy has a large effect on compacted density 10 passes of equipmentDry Density, pcf4 passes of equipment3 passes of equipment2 passes of equipment1 pass of equipmentWater content, %
10At this point, the sample has had most of its air driven out by the compaction 10 passes of equipmentDry Density, pcf100 % saturation lineWater content, %
11At a lower water content, energy has little effect on the compacted density of a clay soil Dry Density, pcf10 passes of equipment4 passes of equipment3 passes of equipment2 passes of equipment1 pass of equipmentWater content, %
12Compacting at low water contents At low water contents, insufficient water is available to lubricate the particles and allow them to be rearranged into a dense structure.The frictional resistance of dry particles is high
13At 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 soilDry Density, pcf10 passes of equipment4 passes of equipment3 passes of equipmentThis results in a term called pumping2 passes of equipment1 pass of equipmentWater content, %
14Compacting Very Wet Soil At this point, few air pockets remain – compaction forces are carried by water in soil which is incompressible
17Effect of Water Content Now examine the effect of just changing the water content on a clay soil, using the same energy each time the soil is compacted.For example, assume soil is spread and compacted with 4 passes of a sheepsfoot roller each time.Examine using State Diagram
18Effect of Water Content Dry density, pcf99.0 pcfSample 1 compacted at 12 % water – Dry Density is 99.0 pcf12 %Water content, %
19Effect of Water Content Dry density, pcfSample 2 compacted at 14 % water – Dry Density is pcf104.5pcf14 %Water content, %
20Effect of Water Content Dry density, pcf105.5pcfSample 3 compacted at 16 % water – Dry Density is pcf16 %Water content, %
21Effect of Water Content Dry density, pcfSample 4 compacted at 18 % water – Dry Density is 98.5 pcf98.5 pcfWater content, %18 %
22Effect of Water Content @ constant energy Dry density, pcfMaximum dry density, pcfOptimum water content, %Water content, %
23Now, perform the same test at a different (Higher energy) on the soil Dry density, pcf10 passes of sheepsfoot roller4 passes of sheepsfoot rollerWater content, %
24Effect of Soil Type on Curves Dry density, pcfPlastic Clay Soils have Low Values of Maximum Dry Density80-95 pcfWater content, %
25Effect of Soil Type on Curves Dry density, pcf20-40 %Plastic Clay Soils have high values for optimum water content (20-40 %)Water content, %
26Effect of Soil Type on Curves Dry density, pcfPlastic Clay Soils have a Flat Curve for Lower Energies DensityWater content, %
27Effect of Soil Type on Curves Dry density, pcfpcfSandy Soils with Lower PI’s have High Values of Maximum Dry DensityWater content, %
28Effect of Soil Type on Curves Dry density, pcfSandy Soils with Lower PI’s have Low Values of Optimum Water Content8-15 %Water content, %
29Effect of Soil Type on Curves Dry density, pcfSandy Soils have a Steep Curve – Short distance from plastic to liquid states of consistencyWater content, %
30Summary Lower PI – Sandier Soils in this Region 110-135 Dry density, pcfIntermediate PI Soils in this Region95-120Higher PI – Clayey Soils in this Region75-95Water content, %
31Lower PI – Sandier Soils in this Region SummaryLower PI – Sandier Soils in this Region8-14Dry density, pcfIntermediate PI Soils in this RegionHigher PI – Clayey Soils in this Region20-4012-20Water content, %
33Zero air voids curve not parallel to line of optimums at upper end Family of CurvesZero air voids curve not parallel to line of optimums at upper endgd, dry density, pcfLine of Optimumswater content, %
34Proctor’s principle of compaction 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.
35Principle of Compaction A plot of the dry density versus the water content from a compaction test will be parabolic in shape.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.
36Standard Proctor Energies Several standard energies are used for laboratory compaction testsStandard – 12,400 ft-lbs/ft3Modified – 56,000 ft-lbs/ft3California – 20,300 ft-lbs/ft3
37Standard Proctor Compaction Test Summary 5.5 # hammerUses 5.5 pound hammerdropped 12 inchesmold filled in 3 lifts25 blows of hammer per liftTotal energy is 12,400 ft-lbs/ft312”drop3 lifts
38Modified Proctor Compaction Test Summary 10 # hammerUses 10 pound hammerdropped 12 inchesmold filled in 5 lifts25 blows of hammer per liftTotal energy is 12,400 ft-lbs/ft318”drop5 lifts
39Proctor Compaction Test Summary Several Standard molds are used depending on maximum particle size in sample4”diameter mold (1/30 ft3) used for soils with low gravel contentsMethod A for soils with < 20 % gravelMethod B for soils with > 20 % gravel and < 20 % larger than 3/8”
40Proctor Compaction Test Summary Several Standard molds are used depending on maximum particle size in sample6”diameter mold (1/13.33 ft3) used for soils with significant gravel contentsMore than 20 % gravel larger than 3/8”Must have less than 30 % larger than 3/4”
41Proctor Compaction Test Summary 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 gravelsASTM Compaction Test Methods areD698A D1557AD698B D1557BD698C D1557C
42Proctor Compaction Test Summary 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.
43Proctor Compaction Test Summary HammerThen, compact each sample into a steel mold with standard proceduresCured soilCompaction mold
44Proctor Compaction Test Summary Then, strike off excess soil so the mold has a known volume of soil.
45Proctor Compaction Test Summary For each sample, measure the weight and the water content of the soil in the moldThe mold volume and weight are pre-measured. Don’t assume nominal volume of 1/30 ft3 or 1/13.33 ft3Calculate moist densityCalculate dry densityPlot dry density and water content for each point
46Class ProblemCalculate Moist density, dry density
50Make each vertical division equal to 1 percent water content Set Up Plot – Form SCS-352Make each vertical division equal to 1 percent water content
51Class Problem Calculate Moist density, dry density Plot curve of dry density versus water contentDetermine Maximum dry density and optimum water contentPlot zero air voids ( 100 % saturation curve assuming specific gravity = 2.68
52Zero Air Voids CurveAfter you plot a compaction test, plotting a zero air voids curve is very important. This curve is also called the 100 % saturation curveThis curve shows for a range of dry density values what the saturated water content is for any given value
53Assume 3 values of gd and calculate wsat% Compaction ProblemZero air void equationAssume 3 values of gd and calculate wsat%
54Assumed dry density = 105 pcf Unit wt. water = 62.4Assumed dry density = 105 pcfassumed Gs = 2.7095 % Saturation Curve100 % Saturation Curve75 % Saturation Curvewsat(%) = 22.1(%)
57Zero Air Voids CurveThe 100 % saturation curve is used to judge the reliability of the compaction curve and of field measurements of compacted soil density and water contentCompacted soils for NRCS specifications are usually at a degree of saturation of about 75 to 95 percent
65Check a point on wet side at 98 pcf, w % on curve is 24.3% Review of CompactionWet side parallel to saturation curve at 90 % saturation ?% Sat = 24.3 ÷ 26.4 = 92.0 %gd, pcfCheck a point on wet side at 98 pcf, w % on curve is 24.3%w, %
66Plotted Class Problem wopt/wsat = 24.3/26.6 = 91 % pcf = (62.4/ /2.70) * 100 = 26.6 %
67dmax = 130.3 - 0.82 *LL + 0.3*PI wopt = 6.77 + 0.43 * LL - 0.21 * PI Review of CompactionEvaluating Compaction TestsTypical value for fine-grained soils compared to Navdocks equationsdmax = *LL + 0.3*PI wopt = * LL * PI
68Review of Compaction Evaluating Compaction Tests Typical value for fine-grained soils compared to Navdocks equationsdmax = * *30= pcf OK - test value was pcf wopt = * * 30= 19.6 % OK Test value was 21.0 %
69Purposes of compaction Soils are compacted to improve the engineering properties over those of loosely placed soils.The engineering properties are affected both by the density to which the soil is compacted and the water content at which it is compacted
70Role of compaction tests in earth fill projects Samples are obtained in site investigation and sent to laboratory for testingSoils are tested to determine reference density - as well as other index propertiesEngineering 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.
71Role of compaction tests in earth fill projects The engineering properties are used in analyses to determine a suitable designFor example, the shear strength is used in a slope stability analysesIf the engineering properties allow a satisfactory design, then the degree of compaction is used in a contract specification.
72Role of compaction tests in earth fill projects If an unsatisfactory design results, the soil is re-tested at a different degree of compaction to obtain better engineering propertiesThe design is re-analyzed and the process repeated until a final satisfactory degree of compaction is decidedThen the degree of compaction is used in a contract specification.
73Role of compaction tests in earth fill projects 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 contentsField compaction tests are performed to assure that the proper reference density is being used
74Compaction Tests as Used in Design of an Earth Fill
76Example of ProcessSample obtained to determine suitability as clay linerSample Sent to LaboratoryLaboratory performs Standard Proctor TestA Permeability Test is performed at 95 % of maximum Standard Proctor Dry Density
77Example of ProcessThe sample is remolded at 2 percent wet of optimum (for this sample, 85 % saturated)The permeability test measures an acceptably low permeabilityA recommendation is given to the field office that compaction to this combination of density and water content results in acceptably low permeability
78Example of ProcessDuring construction, measurements of dry density and water content are made during construction.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.
79Class Problem 2A compaction test measures a maximum dry density of pcf and an optimum water content of 18.0 %. The soil has an estimated Gs value of 2.68A contract requires compaction to 95 % of maximum dry density at a water content of optimum or greater
80Class Problem 2A field test measures a moist density of pcf and a water content of 23.4 %Does the compacted fill meet the contract requirement ?Use the values given for measured moist density and water content, calculate the dry densityAssume a Gs value of 2.68 and compute a wsat value
81Class ProblemCompare the reported compaction water content to theoretical saturated water contentCompacted soils are commonly in the range of percent saturatedWhat do the results tell you about the reliability of the field data?What would you look for to explain any problems?
82Conclusions of Class Problem The measured data appears to have problems.Possible errors are in the measurement of the dry density, the water content, or the specific gravity value used in computationsRecommend investigating most probable causes