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Highway Engineering Common Laboratory Tests.pdf

  1. 1. Highway Engineering Common Laboratory Tests Materials Research and Testing Centre (MRTC)
  2. 2. Before we start ◉ All students and staff shall wear a face mask, covering their nose and mouth at all times. ◉ All students shall sanitize/disinfect/wash their when entering the lab. hands ◉ All students and staff shall abide to social distancing limit close contact guidelines; if not possible, . ◉ All students and staff should inform the responsible body if they have flu like symptoms. 2
  3. 3. Before we start ◉ Do not eat or drink in the laboratory. ◉ Footwear must have enclosed toes and heals (no sandals); especially, in the Materials laboratory. ◉ Confine long hair, loose clothing or jewelry when in laboratory. ◉ Report any and all accidents immediately to laboratory staff. 3
  4. 4. Before we start ◉ Make sure to obtain the appropriate training and/or authorization before operating any equipment or utilize any material. ◉ Use laboratory equipment only for its intended purpose. ◉ Place tools and equipment in proper place after use. 4
  5. 5. Before we start ◉ Keep the workbench clear of all but the required materials. ◉ Keep pathways free of obstruction. ◉ Clean up spills immediately. ◉ If you are uncertain about anything, ASK! 5
  6. 6. Instruction Soil related ◉ is divided in to two, and Material related. ◉ Each Experiment will take 2- 3 hrs. ◉ Groups of 10 – 12students ◉ All data should be collected on the provided sheets 6
  7. 7. Objectives ◉ limited review fundamental laboratory testing used in highway construction ◉ To understand and recall Apparatus and procedures used in testing ◉ To perform the test according to the procedures ◉ To perform computation on test data and present results ◉ Interpret and discuss test result 7
  8. 8. Contents ◉ Experiment-1: Moisture Content – Density Relationship (Soil Compaction) ◉ Experiment-2: In-place Density measurement by sand cone method ◉ Experiment- 3: California Bearing Ratio (CBR) 8
  9. 9. This laboratory instruction is given by ◉ Mathewos Endeshaw ◉ Wondwessen Tassew ◉ Shewagergesh Tadesse ◉ Abiy Fanta ◉ Workineh Kenenisa ◉ Saron Getachew ◉ Omedela Tadesse Hello! 9
  10. 10. Experiment-1 Moisture-Density Relationship (Soil Compaction) 1 gqNtZGzNAw2jcnBszQii Number of slides: 26 Duration: 20 min https://www.geospatialworld.net/news/trimble-komatsu-collaborate-to-improve-mixed-fleet- earthworks/? cf chl_managed_tk =pmd_6d9fa9fe224a5381f2144462ea38d7c10e690542-1628749586-0-
  11. 11. Background 2 • Soil compaction is the process of densification of soil through the reduction of air void by the application of mechanical energy. • The purpose of compaction is to improve the engineering property of the soil by increasing its strength, reducing its compressibility and reducing its hydraulic conductivity. • The degree of compaction is dependent on multiple factors, including • the moisture content at which the soil is compacted • the amount of energy applied per unit volume of soil • the type of compaction effort: impact, static, vibratory, kneading • The effect of moisture content on compaction for a given soil at a given energy input and type is represented by a moisture - density relationship.
  12. 12. Background • The water in the pore space of the soil can be thought of as a lubricant. • When the water content is low the soil particles will require a higher amount of energy to move relative to each other during compaction. • As the water content increase, the water, acting as a lubricant, will aid the relative displacement of the particles resulting in reduction of air voids and an increase the density of soil. • But too much water will interfere with the compaction • Hence, their is an optimum moisture content (OMC) which results in a maximum dry density (MDD) 3
  13. 13. Background • At a constant water content and for a given type of compaction effort, the more energy applied the higher the dry density. • For the same type compaction effort, a higher maximum dry density can be achieved at a lower optimum moisture content for a higher energy input. 4 Braja M. Das, Principles of Geotechnical Engineering , 2010
  14. 14. Background 5 • In the 1930s, R. R. Proctor developed a laboratory test method which involves fixing the compaction effort to a value that is practicable and relevant to construction equipment and the effort type to impact compaction. • The method was called standard effort compaction (or the standard Proctor compaction) the compaction effort proposed was 600 KJ/m3 • U.S. Army Corps of Engineers during construction of air bases developed a similar method that set the energy input at 2700 KJ/m3. This method is called modified effort compaction (or modified proctor compaction) • By using such forms of laboratory compaction testing the moisture-density relationship can be plotted.
  15. 15. Purpose 6 The reasons for conducting laboratory compaction include • To provide a water content value that will achieve the maximum dry density for the given energy input and soil type (optimum moisture content) for construction operations. • The maximum dry density achieved by the laboratory compaction test is used in compaction control operations in the field. • Most earthwork specifications will set a minimum limit on the degree of compaction, which is the ratio of dry density achieved on site to the maximum dry density obtained from laboratory testing.
  16. 16. Apparatus 7 1. Compaction Mold Assembly: Cylindrical molds where the compaction occurs • There are two types of molds • 4-in mold: having a height of about 116.4mm and an inside diameter of about 101.6mm • 6-in mold: having the same height but an inside diameter of about 152.4 mm • The 4−in mold has a volume of about 944cm3 while the 6−in mold has about 2124cm3 • The reason for having two types of molds is to accommodate both fine grained and coarse grained soils • The assembly also consists of an extension collar, which is used in assisting the compaction process and a base plate where the assembly seats. https://civiconcepts.com/blog/standard-proctor-test
  17. 17. Apparatus • Rammers involve a cylindrical sleeve housing a weight that can move freely in the sleeve. • The weight is attached to a rod at the top and the sleeve is open at the bottom. • The rammer is pulled up by the rod to the top of the sleeve and allowed to free fall to the bottom where it will impact the soil surface. • There are two types of rammers: • The first has a weight of 24.5 N and can free fall from a height of 30.5cm • The second has a weight of 44.5N and can free fall from a height of 45.7cm 2. Compaction Rammers : Impact devices to exert the required amount of energy for compaction. sleeve 8 Weight https://www.ele.com/product/bs-compaction-rammer-4-5kg-wt- rod • The reason for having two rammers is to account for the standard effort compaction and modified effort compaction methods
  18. 18. Apparatus 3. Drying oven: Thermostatically controlled oven, capable of maintaining a uniform temperature of 110±5°C throughout the drying chamber. 4. Balance 5. Straight edge: A stiff metal straight edge of any convenient length but not less than 250 mm. 6. Sieves: The following sieves are required Sieve opening size 9 Alternative designation 4.75mm No. 4 9.5mm 3/8 in 19.0 mm 3/4 in 7. Moisture Specimen Containers 8. Mixing Tools: Miscellaneous tools such as mixing pan, spoon, trowel, spatula, graduated cylinders, water bottles.
  19. 19. Procedure • First we will discuss the standard effort compaction test. • There are three method, associated with the standard effort compaction test designated as A, B and C. • The three methods defer by the type of soil gradation used in the test. Method Usage Method A used if 25 % or less by mass of the material is retained on the 4.75-mm sieve Method B used if 25 % or less by mass of the material is retained on the 9.5-mm sieve Method C used if 30 % or less by mass of the material is retained on the 19.0-mm sieve The test method discussed here are only applicable for material with less the 30% passing the 19mm sieve The procedures discussed here are based on ASTM D698 and D1557 10
  20. 20. Procedure 1. Identify which method to use based on the grain size distribution of the soil 2. Identify the apparatus to be used based on the method identified. Method Mold Method A 4-in Method B 4-in Method C 6-in 3. Sample preparation a. Air dry the sample b. Select at least 5 representative subsamples as the fraction of air dried sample passing the sieve specified by the method Generally, a sample size of about 3000g for each subsample is required for Method A & B and 5000g for Method C Method Sample passing sieve Method A 4.75 mm Method B 9.5 mm Method C 19 mm For the standard effort compaction the 24.5 N rammer is used 11
  21. 21. Procedure 12 4. Prepare each of the 5 subsamples by adding water and mixing • The water added should be in such a way that the five preparations bracket an estimated OMC • One way to do this is to prepare one of the subsamples to be at OMC through trial addition of water, The OMC may be estimated based on the following considerations • Typically, cohesive soils at the optimum water content can be squeezed into a lump that barely sticks together when hand pressure is released, but will break cleanly into two sections when “bent.” • Cohesive soils tend to crumble at molding water contents dry of optimum; they tend to stick together in a sticky cohesive mass wet of optimum. • For cohesive soils, the optimum water content is typically slightly less than the plastic limit. • For cohesion less soils, the optimum water content is typically close to zero or at the point where bleeding occurs. • For the rest of subsample, at least two of which should be prepared on the dry of optimum at about 2% interval, the other two wet of optimum at 2% interval. • If the samples are cohesive let the prepared subsamples stand for at least 16hrs in water tight containers
  22. 22. Procedure 13 5. Compaction (After standing time is over) a. Determine and recorded mass of mold and base plate (without the extension collar) [Mmb] b. Assemble the mold, base plate and extension collar c. Take one of the five subsample d. Compaction is to be done is layers of 3; hence, take about 1/3 of the sample and place it in the mold. e. Compact this layer by applying impact blows using the rammer (24.5N). The number of blows per layer depends on the method Method Number of Blows per layer Method A 25 Method B 25 Method C 56
  23. 23. Procedure f. Once you have compacted the 1st layer, repeat the compaction for the next two. • when compacting the rammer must be raised fully and allowed to free fall. • the rammer must be held perpendicular to the soil surface. • When compacting one may follow a circular pattern as shown below The top surface of the third layer after compaction must extended in to the extension collar above the mold 14 ASTM D698-12
  24. 24. Procedure 6. Slowly detach the extension collar and using a straight edge, trim the excess soil above the mold, until it is flush with the mold edges. 7. Clean the exterior of mold and base plate from any excess soil 8. Determine and record the mass of mold, compacted soil and base plate, [Mmbs] 9. Disassemble the mold and base plate. Extrude the compacted soil 10.Determine the water content of the compacted soil [w], making sure to take representative samples from each of the three layers for moisture content determination. 11.Repeat steps 5-11 for the remaining subsample. For the specific procedure involved in water content/moisture content measurement refer to previous notes. 15
  25. 25. Procedure 16 • For the case of Modified effort compaction, the procedure is similar to the standard effort • The modified effort compaction also has three methods • But note the following exceptions • The 44.5 N rammer with a free fall height of 45.7 cm is used • Compaction of each subsample is done in 5 layers instead of 3
  26. 26. Procedure 17 Summary of Standard effort compaction Method A Method B Method C Sample Passing 4.75mm Passing 9.5mm Passing 19.0mm Mold 4-in 4-in 6-in Rammer 24.5 N@30.5cm 24.5 N@30.5cm 24.5 N@30.5cm Number of layers 3 3 3 Number of blows per 25 25 56 layer
  27. 27. Procedure 18 Summary of Modified effort compaction Method A Method B Method C Sample Passing 4.75mm Passing 9.5mm Passing 19.0mm Mold 4-in 4-in 6-in Rammer 44.5 N@45.7cm 44.5 N@45.7cm 44.5 N@45.7cm Number of layers 5 5 5 Number of blows per 25 25 56 layer
  28. 28. Computation • The test data set will involve at least 5 values of Mmb , Mmbs , w for each of the subsamples 1. Determine the bulk density (𝝆) 𝑀𝑚𝑏𝑠 − 𝑀𝑚𝑏 𝜌 = 𝑉 Where V is to the volume of mold 2. Determine the dry density (𝝆𝒅) 𝜌 𝜌𝑑 = 1 + 𝑤 19
  29. 29. Computation OMC • Plot the water content - dry density points, with the water content as abscissa and dry density as ordinate and connect the points with a smooth line. • From the plot read the OMC and MDD MDD OMC = 17.9% MDD = 1.78g/cm3 20
  30. 30. Discussion Additional Considerations • In presenting the results, the zero air-void line (100% saturation line) is also plotted • The zero-air void represents the state of the compacted soil, if all the aid void was removed (i.e. if the soil was saturated at the molding water content) • The zero air void line may be computed using the equation 𝜌𝑑,𝑠𝑎𝑡 = 𝑆 𝐺𝑠 𝑠 𝑤 𝐺 + 𝑆 𝜌 21 𝑤 Where, S is the degree of saturation (for the Zero air-void line, S = 1.0), Gs is the specific gravity of the soil solids and 𝜌𝑤 is the density of water. For the purpose of this experiment, it may be taken as 1.0 g/cm3
  31. 31. Discussion • The moisture-density relationship curve is always to the left of the zero air-void line and does not cross it. OMC MDD OMC = 17.9 % MDD = 1.78g/cm3 22
  32. 32. Discussion Expected results for standard effort compaction 23 Classification (USCS) OMC MDD Soil group Soil type (%) (g/cm3 ) GW Well graded clean gravel, gravel-sand mix 11 - 8 2.00 - 2.16 GP poorly graded clean gravel, gravel-sand mix 14 - 11 1.84 – 2.00 GM Silty gravel, poorly graded gravel-sand-silt mix 12 - 8 1.92 - 2.16 GC Clayey gravel, poorly graded gravel-sand-clay mix 14 - 9 1.84 - 2.08 SW Well graded clean sand, sand-gravel mix 16 - 9 1.76 - 2.08 SP poorly graded clean sand, sand-gravel mix 21 - 12 1.60 - 1.92 SM Silty sand, poorly graded sand-silt mix 16 - 11 1.76 – 2.00 SM-SC Silty sand clay mix with slightly plastic fines 15 - 11 1.76 - 2.08 SC clayey sand, poorly graded sand-clay mix 19 - 11 1.68 – 2.00 ML Inorganic silt 24 - 12 1.52 - 1.92 ML-CL Mix of inorganic silt and lean clay 22 - 12 1.60 - 1.92 CL Lean clay 24 - 12 1.52 - 1.92 OL low pastic organic fines, organic silt or silty clay 33 - 21 1.28 - 1.60 MH Inorganic plastic silt 40 - 24 1.12 - 1.52 CH Fat clay 36 - 19 1.20 - 1.68 OH high plastic organic fines, organic clays or clayey silt 45 - 21 1.04 - 1.60 Adopted from NAVFAC DM 7.02 1986
  33. 33. Discussion Energy input (compaction effort) [E] for laboratory compaction may be calculated as 𝐸 = 𝑚 𝑔 ℎ 𝑁𝐿 𝑁𝑏 𝑉 Where: m is the mass of the rammer weight, g is acceleration due to gravity (g = 9.81m/s2), h is the free fall height of the rammer weight, NL is the number of layers, Nb is the number of blows per layer, V is the volume of the mold Verify that the energy input for standard effort compaction is 600 KJ/m3 and for modified effort compaction is 2700 KJ/m3, using the formula above 24
  34. 34. Discussion 25 • Sources of Error: • The sample selected should be representative of the material under investigation. To ensure representativeness, techniques for field sampling and laboratory sample reduction (such as quartering) are used.(not discussed here). • Not allowing the subsample to stand after mixing incase of cohesive soils may result in non-uniform moisture distribution. • The volume of the mold needs to be calibrated to determine its “true” value and compared against standard values. Simply using a nominal volume provided in literature may cause errors. (not discussed here) • The test discussed here is only applicable for soils with less than 30% retained on the 19 mm sieve. For cases where this is not met correction factor may be used. (not discussed here) • During compaction, one needs to lift the weight to the top of the sleeve and let it free fall. The weight must impact the soil surface perpendicularly. • During water content determination the water content specimen must be representative of all layers.
  35. 35. THE END Questions ? 26
  36. 36. Experiment-2 In-Place Density Measurement by Sand- Cone Method Number of slides: 14 Duration: 15 min https://www.geospatialworld.net/news/trimble-komatsu-collaborate-to-improve-mixed-fleet- earthworks/? cf_chl_managed_tk =pmd_6d9fa9fe224a5381f2144462ea38d7c10e690542-1628749586-0- gqNtZGzNAw2jcnBszQii
  37. 37. Background • Density is the measure of degree of packing of a material. • Mathematically, the mass density is defined as Where: M is mass V is Volume V 2 = M
  38. 38. Background • For soil one may define different types of density • Depending on the phase under consideration or the state of the soil mass • For the purpose of this test we will discuss the In-place measurement of bulk density by using the sand- cone method and indirectly dry density • Dry density can be related to bulk density by using water content (w) Bulk Density Dry Density Saturated Density Density of soil solids M V  = d  = Ms sat V  V = Msat s s V  = Ms Where: Ms is the mass of soil solids (Mass of soil in dry sate) Msat is the mass of soil in a saturated state Vs is the volume the soil solids  3 d = 1+ w
  39. 39. Purpose 4 • In place density measurement is primary used as for compaction control for a construction project. • Most construction specifications involve a statement on the relative degree of compaction between laboratory MDD and in-place density. • In place density measurement is also used for determination of the natural density of soil masses in cases where it may not be possible to collect undisturbed soil sample by traditional methods.
  40. 40. Apparatus 5 Base Plate 1. Sand-Cone Density Apparatus: consisting of sand container, sand cone and base plate. 2. Testing Sand: A clean dry sand, having a constant bulk density Sand Container Sand Cone https://www.ele.com/product/4-sand-density-cone
  41. 41. Apparatus 6 3. Chisel and hammer 4. Balance 5. Drying Oven 6. Moisture content specimen containers 7. Miscellaneous Equipment: Scoops, Brushes, Plastic bags and Nails
  42. 42. Procedure 1. Select a location that is representative of the area to be tested. 2. Inspect the cone apparatus for damage, free rotation of the valve, and properly matched baseplate. 3. Assemble the cone and container and fill the cone container with sand 4. Determine and record mass of sand, cone and container. [M1] 5. Prepare the surface of the location to be tested, so that it is a level plane. 6. Seat the base plate on the plane surface, secure the plate against movement using nails pushed into the soil adjacent to the edge of the plate 7. Dig the test hole through the center hole in the base plate. • The test hole should be deep enough to represent the layer of material being tested • Test hole volumes are to be as large as practical to minimize errors 8. Place all excavated soil, and any soil loosened during digging, in a moisture tight container • Take care to avoid losing any materials. • Protect this material from moisture loss The procedures discussed here are based on ASTM D1556 7
  43. 43. Procedure 8 9. Clean the flange of the base plate 10.Determine and Record the mass of the excavated material. [Mt ] 11.Mix the excavated material thoroughly and obtain a representative specimen for water content determination. [w] 12.Invert the sand-cone apparatus and seat the sand-cone funnel into the flanged hole 13.Open the valve and allow the sand to fill the hole, cone, and base plate • Take care to avoid jarring or vibrating the apparatus while the sand is running 14.When the sand stops flowing, close the valve 15.Determine and record mass of the remaining sand, cone and container. [M2]
  44. 44. Computation 1. Determine the amount of sand in the hole [Msh] Msh = M1 − M2 −Mscb Where: Mscb is the mass of sand the is above the hole and retained in the inverted cone and base plate This value is determined by calibration in the lab (not discussed here, one will be provided) Mass of sand above the hole b/n the cone and base plate (Mscb) Mass of sand in hole (Msh) 9 https://mocivilengineering.com/field-density-test-sand-cone-method/
  45. 45. Computation Where: ρsand is density of the sand used for testing This value is determined by calibration in the lab (not discussed here, one will be provided) 3. Determine the Bulk Density of the material at the test point [ρ] h sand  2. Determine Volume of test hole [Vh] V = Msh Vh 10 = Mt
  46. 46. Computation 4. Determine the Moisture Content [w] Refer to previous notes 5. Determine the Dry Density of the material at the test point [ρd] 1+ w 11 d   =
  47. 47. Discussion • Most construction contract specify a minimum degree of compaction for earth work as a means of performance specification. MDD 12 • Degree of compaction is the ratio of the laboratory MDD obtained from a specific compaction effort to the in-place dry density, expressed as a percentage. Degree of Compaction =  d,on−site 100
  48. 48. Discussion 13 Sources of Error • Existence of moisture and fine material in the testing sand will affect results; hence, the sand must be placed in air tight containers • The sand used for testing must be uniformly graded and able to flow freely • The sand and equipment should be calibrated regularly to determine the mass of sand b/n the cone and base plate and the density of sand • During calibration, if there is large variation b/n successive measurements of the density of sand, the sand may not be viable for testing purposes and may require adjustment or replacement. • Loss of excavated material or addition of foreign substance to the excavated material will cause errors • Vibration or disturbance of sand and container during the pouring of sand in to the hole will cause errors.
  49. 49. THE END Questions ? 14
  50. 50. Experiment-3 California Bearing Ratio (CBR) Number of slides: 18 Duration: 15 min https://www.geospatialworld.net/news/trimble-komatsu-collaborate-to-improve-mixed-fleet- earthworks/? cf_chl_managed_tk =pmd_6d9fa9fe224a5381f2144462ea38d7c10e690542-1628749586-0- gqNtZGzNAw2jcnBszQii
  51. 51. Background 2 • The California bearing ratio is used to evaluate the potential strength of subgrade, subbase, and base course material. • It is the normalized ratio of the penetration resistance of a material at a specified penetration. • The CBR value forms an integral part of several flexible pavement design methods. • The CBR value is determined on a compacted specimen • Factors that affect CBR value for a given soil include: • Moisture content and • Density
  52. 52. Background • Depending on whether or not the effects of moisture content and density on CBR are required, three type of CBR test may exist • One-point test • Three-point test • CBR at a range of water content • In this experiment we will only be discussing about One-point CBR testing • One-point CBR test is used to determine the CBR value at the OMC and MDD of a soil sample • One-point CBR can not be used to study the effects of compaction moisture content and density on CBR value. This two are also called CBR at OMC 3
  53. 53. Purpose 4 • The CBR value is one of the primary parameter for flexible pavement design. It characterizes the strength (resistance) of the pavement to traffic loads. • Most design method make use of CBR for determining the thickness of the various pavement layers • Further, subgrade, subbase, and base course material are classified according to their CBR values.
  54. 54. Apparatus 1. CBR Mold Assembly: Cylindrical molds where the compaction and then penetration occurs • Having a height of about 177.8mm and an inside diameter of about 152.4mm 5 • The assembly also consists of • extension collar, which is used in assisting the compaction process, • spacer disk used as a place holder during compaction; having a height of 61.4mm and • Perforated base plate where the assembly seats. http://civil-instruments-com.sell.everychina.com/p-106461489-astm-aashto-california-bearing-ratio-cbr-mold-and- components-soil-test-equipment.html https://myerstest.com/product/2-part-surcharge-weight-10lb/ When the spacer disk is placed inside the mold the height is reduced to 116.4. The remaining volume is 2124 cm3, equal to the 6-in compaction mold Straight Edge Tripod Spacer Disk swell Plate Perforated Base Plate Displacement Gauge Surcharge weight
  55. 55. Apparatus 2. Tripod, Swell plate and Displacement gauge: for measurement of swelling 3. Surcharge weights: to simulate over burden pressure. Each surcharge has mass of 2.27 Kg 4. Compaction Rammers: identical to the ones used for compaction 5. CBR loading Machine: used for applying penetration load • Consists of a loading mechanism, a frame, load measuring device, displacement gauge and penetration piston • The penetration piston has an penetration area of 1935cm2 6 https://www.ele.com/product/cbr-test-50-machine
  56. 56. Apparatus 6. Drying oven: Thermostatically controlled oven, capable of maintaining a uniform temperature of 110±5°C throughout the drying chamber. 7. Balance 8. Straight edge: A stiff metal straightedge of any convenient length but not less than 250 mm. 9. Sieves: The following sieves are required Sieve opening size 7 Alternative designation 4.75mm No. 4 9.5mm 3/8 in 19.0 mm 3/4 in 7. Moisture Specimen Containers 8. Soaking tank 9. Miscellaneous tools such as mixing pan, spoon, trowel, spatula, graduated cylinders, water bottles, filter paper
  57. 57. Procedure 1. Sample Preparation: a. Air dry the sample b. Select one representative subsample (about 6000 g) • If all of the subsample pass 19mm sieve use the subsample as is • Otherwise remove the fraction retained the 19mm sieve and replace by by an equal amount of material passing the 19.0mm sieve and retained on the 4.75mm. c. Take a small fraction (about 1000g) of the prepared subsample and determine its moisture content 2. Prepare the subsample by adding water to bring it’s moisture content to OMC. To bring the water content, w, of a subsample of mass M, to OMC, the amount of water that needs to be added can be found as 𝑂𝑀𝐶 − 𝑤 𝑀 1 + 𝑤 Before one-point CBR test is conducted, the OMC and MDD of the soil sample must be known. The procedures discussed here are based on AASHTO T193 Similar to compaction, it is necessary to let the soil-water mix stand for at least 16 hrs. in the case of plastic soils 8
  58. 58. Procedure 9 3. Compaction a. Determine and recorded mass of mold and base plate (without the extension collar and spacer disk) [Mmb] b. Assemble the mold, base plate and extension collar c. Place the spacer disk in to the mold and place a filter paper on top of the disk d. Compact the sample according to the selected compaction method (Expriment-1) 4. Remove the extension collar, and using a straightedge, trim the compacted soil even with the top of the mold 5. Remove the base plate and spacer disk 6. Place a filter paper on the perforated base plate 7. Invert the mold and compacted soil and place on the filter paper, so the compacted soil is in contact with the filter paper 8. Reassemble the plate and mold.
  59. 59. Procedure 10 9. Clean the exterior of mold and base plate from any excess soil 10. Determine and record the mass of mold, compacted soil and base plate, [Mmbs] 11. Collect the trimming and determine the water content [w] 12. Soaking a. Place the swell plate in the mold b. Apply sufficient weights to produce an intensity of loading equal to the mass of the subbase and base courses and surfacing above the material. A minimum of 4.45 Kg (2 weights) is required. c. Place the tripod with dial indicator on top of the mold and make an initial dial reading [H0]. d. Immerse the mold in water, make sure to allow free access of water at top and bottom of the specimen. e. Soak the specimen for 96 hours (4 days) f. At the end of 96 hrs, make a final dial reading on the soaked specimens, [Hf]. g. Remove the specimens from the soaking tank, pour the water off the top and allow to drain h. downward for 15 min
  60. 60. Procedure 11 13.Penetration a. Place one annular weight on the specimen. Seat the penetration piston with a load of no more than 44 N b. After seating the penetration piston, place the remainder of the surcharge weights around the piston. c. Set the penetration dial indicator and the load indicator to zero. d. Apply the loads to the penetration piston so the rate of penetration is uniform at 1.3mm/min e. Record the load when the penetration is 0.64, 1.27, 1.91, 2.54, 3.81, 5.08, and 7.62, 10.16 and 12.70mm. The last two are optional.
  61. 61. Computation 1. Determine the actual moisture content and dry density of the compacted sample (in the CBR mold) using data from steps 3a, 8 and 9 (refer to Experiment-1 on the computation) • This intended to check that the CBR value obtained is actually at OMC and MDD 2. Determine the Percent swell as 𝐿𝑓 − 𝐿0 𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑠𝑤𝑒𝑙𝑙 = 3. Compute penetration resistance 116.4 𝑚𝑚 a. For each of the readings load value: 𝑙𝑜𝑎𝑑 = 𝑙𝑜𝑎𝑑 𝑟𝑒𝑎𝑑𝑖𝑛𝑔 × 𝑝𝑟𝑜𝑣𝑖𝑛𝑔 𝑟𝑖𝑛𝑔 𝑓𝑎𝑐𝑡𝑜𝑟 Where the proving ring factor (N/div) is determined by calibration (one will be provided during the testing) b. For each load computed, determine the resistance 𝑙𝑜𝑎𝑑 𝑙𝑜𝑎𝑑 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = = × 10 (𝐾𝑃𝑎) 𝑝𝑖𝑠𝑡𝑜𝑛 𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑎𝑟𝑒𝑎 1935 𝑐𝑚2 12
  62. 62. Computation 13 4. Plot the penetration vs. resistance curve. Penetration as the abscissa and resistance as the ordinate. 5. Load correction: in some cases the initial penetration takes place without a proportional increase in the resistance to penetration and the curve may be concave upward. If this happens, the location of the origin must be adjusted as follows • Extend the straight line portion of the pen. Vs res. curve downward until it intersects the abscissa • Use this intersection point as the new origin
  63. 63. Computation 14 AASHTO T193-13 Curve 1 does not require correction but curve 2 and 3 do due to the concave upward shape of the curve near the origin. Consider Curve 3: Before this adjustment the resistance at 2.5mm was 689KPa The correction shift the origin by 1.25mm. Now to find the corrected resistance at 2.5mm read from the original curve the resistance at 3.75mm (2.5mm + 1.25mm) which is about 1300KPa. 1 2 3 1.25
  64. 64. Computation 6. Determine CBR value: • First read the correct resistance value at penetrations of 2.54mm and 5.08mm (after correction, if necessary) • Then CBR is 𝐶𝐵𝑅 = 𝑐𝑜𝑟𝑟𝑒𝑐𝑡𝑒𝑑 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 × 100 15 Where: corrected resistance are the loads at 2.54mm and 5.08 mm read from the plot by considering the adjusted origin and standard loads are 6900KPa and 10300KPa for the 2.54mm penetration and 5.08mm penetration, respectively. Note that you have 2 values (lets call me them CBR2.54 and CBR5.08). The CBR is then selected as • If CBR2.54 > CBR5.08, CBR = CBR2.54 • If CBR5.08 > CBR2.54, rerun the test, if the condition repeats, CBR = CBR5.08
  65. 65. Discussion 16 • Soaking of the specimen may not be conducted for cases where the proposed project is in an arid environment. • The one-point method has limited practical application since it dose not account for the effect of variation of compacting moisture content and dry density. • The three-point CBR method takes in to consideration the effect of density, this is done by determining CBR values for 3 different subsamples compacted at different energy but at the same OMC • The CBR at a range of water content method takes in to consideration both compaction water content and density; hence, this method is the most general. • The compaction mold for the CBR is equivalent to the 6-in mold (after consideration for the spacer disk is made) • For soils where the OMC and MDD was determined using the 4-in mold, the density obtained by compacting in the CBR mold (computation step 1) may be slightly smaller than the MDD.
  66. 66. Discussion 17 • Sources of Error • Errors in compaction (refer to Experiment 1) • One needs to check if the actual density and water content are equivalent to the OMC and MDD • One needs to make sure that there is free access for water to enter the compacted specimen during soaking • The CBE loading machine and measurement instruments must be regularly checked • The penetration piston must be properly placed on the specimen
  67. 67. THE END Questions ? 18