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Florida International University
Department of Civil and Environmental Engineering
CEG 4011 L Geotechnical Engineering I Laboratory
Prof. Luis A. Prieto-Portar PhD, PE, SE.
Lab Report
Atterberg Limits of Plasticity (ASTM D-4318)
Performed on 25 February 2009
Team Members:
Member Attendance Writing Assignment Completed
04 -The Atterberg Limits
1) Introduction: The theory behind the experiment.
When a cohesive soil is mixed with an excessive amount of water, it is in a somewhat liquid state and flows like a viscous liquid. However, when this viscous liquid is gradually dried, with the loss of moisture it passes into a plastic state. With further reduction of moisture, the soil passes into a semisolid, and then into a solid state. The moisture content (as a percentage) at which the cohesive soil passes from a liquid state to a plastic state is called the liquid limit of the soil. Similarly, the moisture content (also as a percentage) at which the soil changes from a plastic to a semisolid state, and from a semisolid state to a solid state, are referred as to the plastic limit and the shrinkage limit, respectively (Fig. 4.1). These three limits are collectively referred to as the Atterberg limits, named after Albert Atterberg, the scientist who initially developed them in 1911 to evaluate the relationship between soil moisture content and soil consistency. Albert Atterberg.
2) Equipment.
- Casagrande liquid limit device
- Casagrande grooving tool
- Moisture cans
- Spatula
- Oven
- Mass balance
- Plastic squeeze bottle
- Paper towels Figure 4.2. Casagrande Liquid Limit device. Figure 4.3. Moisture cans.
Figure 4.4. Grooved soil before and after the groove has closed. Figure 4.5. Lean clay soil at the Plastic Limit. Figure 4.6. Oven.
Figure 4.7. Adding water soil sample. Figure 4.8. Clearly defined groove. Figure 4.9. Closed grove. Figure 4.10. Schematic diagram of soil pat in the cup of the liquid limit device at (a) beginning of test, (b) end of test.
Figure 4.11. Kneading the soil. 4) Sample Data. Description of soil: Sand, cohesionless soil Weight of oven dry specimen: 300 g Table 4.1: Liquid Limit Test Can No. W 1 (g) W 2 (g) W 3 (g) m (g) w (%) N log N LL 1 15.45 31.60 29.12 2.48 18.14 60 1.78 20. 2 15.25 26.31 24.75 1.56 16.42 40 1.60 17. 3 15.51 48.31 43.39 4.92 17.65 37 1.57 18. 4 15.55 28.51 26.34 2.17 20.11 20 1.30 19. 5 15.41 27.51 25.33 2.18 21.98 10 1.00 19.
2 1 1 2 1 logN -logN w (%)-w (%) F slopeofgraph(MoistureContent vslog N) ……….………Eqn 3
- 121 N (^25) N LL w (%) ………………………… ……………….…………………...Eqn 4 PL (%) = 100 W - W
W - W
3 1
……………..………………………………………………Eqn 5 PI = LL – PL………………………………………………………………………….Eqn 6 5) Calculations. W = W 2 – W3.…….…………...………………………………………...……………Eqn 1 w (%)= 100 W - W
W - W
3 1
………………………………………………..……………Eqn 2 2 1 1 2 1 logN -logN w (%)-w (%) F slopeofgraph(MoistureContent vslog N) ……….………Eqn 3
- 121 N (^25) N LL w (%) ………………………… ………………..………………...Eqn 4 PL (%) = 100 W - W
W - W
3 1
……………..………………………………………………Eqn 5 PI = LL – PL………………………………………………………………………….Eqn 6 where: W 1 = weight of moisture can W 2 = weight of can + moist soil W 3 = weight of can + dry soil
N = number of blows w = moisture content LL = Liquid Limit F = Flow Index PL = Plastic Limit PI = Plasticity Index 6) Possible Sources of Error. In an Atterberg Limits Test the soil sample has to be properly prepared. That is the soil sample must be thoroughly mixed and permitted to cure for a sufficient period before testing. During the performance of this experiment careful analyses of factors that would affect the final results were done. There were factors that would affect the Liquid Limit (LL) as well as different factors that would affect the outcome of the Plastic Limit (PL). For the Liquid Limit, the possibilities of errors are:
- Width of grove
- Depth of groove
- Soil not uniformly mixed
- Handle turned too fast or too slow
- Height of fall adjusted improperly
- Length of closure not ½ in
- Air drying of soil between trials
- Worn out parts of liquid limit device especially at point of contact between the cup and base
- Loss of material during the test
- Temperature at which the test is perform For the Plastic Limit, the possibilities of errors are:
- Improper technique in rolling thread
7) Conclusion. The conclusion should answer the following questions:
- What is the liquid limit, plastic limit, and plasticity index of this soil?
- Does your plot of blow count from the liquid limit machine look reasonable?
- What would be the single greatest source of error in the liquid and plastic limit tests that was performed? Here is an example: “After analyzing and calculating the previous data, we were able to find the Atterberg limits which it illustrates three different states. These three states define the water content borders between viscous fluid, plastic and non-plastic states. For this lab report the final value for the Atterberg limits is as follows, The Liquid limit (LL) is 27.14, the Plastic Limit (PL) is 7.20 and the Plasticity index (PI) is 5.81. The Plasticity Index point and the Liquid Limit point of the soil meets above the A-line. The A-line is the border line which allows one to classify Clay, Silt and Organics according to the Unified Soil Classification System (USCS). On the chart the Clay would fall above the A-line while the Silts and Organics fall below. The soil is further divided into subgroups above or below the A-line. Any group which has a liquid limit greater than 50 is considered to have a high plasticity and the letter “H” is carried beside the soil name to indicate this. Also any group which has a liquid limit less than 50 is considered to have a low plasticity and the letter “L” is carried beside the soil name to indicate this. Plasticity Index (PI) in our lab example is 5.81 and the Liquid limit (LL) is 27.14 which falls just above the A-line of the chart (Plasticity index Vs Liquid limit). This means that the soil is inorganic clay of low plasticity. The plot of blow count from the apparatus looks very reasonable since it decrease and chart value for LL and Liquid limit value calculated are similar. The Liquid Limit (LL) is 21.25, the Plastic Limit (PL) is 12.5 and the Plasticity Index (PI) is 8.75. The Plasticity Index was plotted against the Liquid Limit on the Liquid Limit and Plasticity Chart. The Plasticity Index point and the Liquid Limit point of the soil meets above the A-line. The A-line is the border line which allows one to classify Clay, Silt and Organics according to the Unified Soil Classification System (USCS). On the chart the Clay would fall above the A-line while the Silts and Organics fall below. The soil is further divided into subgroups above or below the A-line. Any group which has a liquid limit greater than 50 is considered to have a high plasticity and the letter “H” is carried beside the soil name to indicate this. Also any group which has a liquid limit less than 50 is considered to have a low plasticity and the letter “L” is carried beside the soil name to indicate this. The value of our Plasticity Index (PI) “8.75” and Liquid Limit (LL) “21.25” falls above the A-line of the chart and in the below 50 subgroup. This means that the soil is Clay because it falls above the A-line and it has a low plasticity because it fall in the below 50 subgroup. This means that the soil is an Inorganic Clay of low plasticity with reference to the USCS. This testing method is used as an integral part of several engineering classifications systems to characterize the fine-grained fractions of soils and to specify the fine-grained fraction of construction materials. The liquid limit, plastic limit and plasticity index of soils are also used extensively, either individually or together, with other soil properties
to correlate with engineering behavior such as compressibility, permeability, compactibility, shrink-swell and shear strength.” 8) References.
- Coduto, P. Donald. Geotechnical Engineering: Principles and Practices. New Jersey: Pearson Education, Inc., 1999.
- L. A. Prieto-Portar, “Geotechnical Laboratory Notes”, Miami, 2009. http://web.engfiu.edu/~prieto/SoilandRockMechanics
- L.A. Prieto-Portar, The Atterberg Limits of Clay, 2009.
- L. A. Prieto-Portar, Eleven (11) Solved Problems in Soil Classification_._ 2008. http://web.eng.fiu.edu/~prieto/geo1/P10-SoilClassificationProblems/Classify-02.pdf http://en.wikipedia.org/wiki/Atterberg_limits http://www.keystonewalls.com/media/technote.pdfs/atterb.pdf http://www.engr.uconn.edu/~lanbo/CE240LectW031consistencyAtterberglinmits.pdf
