(Atterberg Limits).pptx

Liquid Limit Plastic Limit

1. Geotechnical Engineering–I [CE-221] BSc Civil Engineering Atterberg Limits by Engr. Mudassar Munir Shah Qualification: MSc Geotechnical Engineering (2022) Institute: UET Lahore Teaching Exp : AUG-2018 to OCT-2019 at JCET Email: mudassarmunirshah461 @ gmail .com 1

2. SOIL CONSISTENCY Is a property of soil which… Indicates the degree of firmness of fine-grained soil . Soil g enerally expressed in terms of very soft , soft , stiff , very stiff , and hard . Soil behave like: 2 SOL ID L I QU ID at at v er y low mo i st u r e content v e ry h igh moisture content

3. ATTERBERG/CONSISTENCY LIMITS (Swedish Agriculturist, Define boundaries b/w states of soil) S o li d S emi - S o li d P l a sti c Viscous Liquid Moisture content, w (%) Soil volume, v or e Shrinkage Limit SL Plastic Limit PL Liquid Limit LL Plas t ici ty Index 3

4. Liquid Limit (LL) is defined as the moisture content at which soil begins to behave as a liquid material and begins to flow. ( LL of a fine-grained soil gives the moisture content at which the shear strength of the soil is approximately 2.5kN/m 2 ) LIQUID LIMIT ( LL or w LL ) 4

5. 250g air dry sample passing through No.40 sieve. Add some water to make paste of soil. Add water carefully not much more nor much less then LL. Place soil paste in pat of apparatus. Make a groove in soil. Repeat test three time for 3 point method & one time for one point method 5 LIQUID LIMIT DETERMINATION Ca s ag r a n de Apparatus , ASTM D-4318

6. LL is the moisture content required to close a 2-mm wide groove in a soil pat a distance of 12.7 mm (1/2”) along the bottom of the groove after 25 blows . 6 LIQUID LIMIT DETERMINATION A) Three-Point Method

7. 25 7      N  tan  LL  w N  number of blows w n  corresponding moisture content tan   0.121 Assumes a constant slope of the flow curve . The slope is a statistical result of 767 liquid limit tests (Norman, 1959). Limitations: tan  is an empirical coefficient , so it is not always 0.121. Good results can be obtained only for the blow number between 20 to 30 . n B) One-Point Method LIQUID LIMIT DETERMINATION

8. Flow Index N 2 =30 N 1 =20 w 1 =44 w 2 =39 FLOW INDEX ( I F ) (Rate at which soil mass loses its shear strength with an increase in moisture content) Larger the I F , smaller will be shear strength of soil. Soil Flows like liquid material I F =28.39 8

9. Plastic Limit (PL) is defined as the moisture content at which soil begins to behave as a plastic material. Plasticity Index ( PI or I P ) = LL - PL PLASTIC LIMIT ( PL or w PL ) 9 PI is a difference between numerical values of LL & PL PI gives a range of moisture content for which soil behaves like a Plastic Material.

10. Moisture content at which the soil when rolled into threads of 3.2mm (1/8 in) diameter, will crumble . PL = w% at 3.2 mm (1/8 in) dia. 10 PLASTIC LIMIT DETERMINATION ASTM D-4318 50g air dry sample passing through No.40 sieve. Add some water to make small ball of soil. Add water carefully not much more nor much less then PL. Make thread (1/8’’ dia) with the help of your palm Repeat test three time for better results

11. Shrinkage Limit (SL) is defined as the moisture content at which no further volume change occurs with further reduction in moisture content. SHRINKAGE LIMIT 11

12. SHRINKAGE LIMIT 12

13. PLASTICITY/A-LINE CHART 13

14. PLASTICITY/A-LINE CHART High plasticity Low plasticity LL=50% 14

15. PLASTICITY/A-LINE CHART High Plastic Silts Sil t s Coh e s i o n l ess Soils 15

16. w here, I L = Liquidity index w n = Natural moisture content PL = Plastic limit moisture content LL = Liquid limit moisture content 0< I L <1 → Soil is in plastic state I L < → Soil is in semi-plastic or solid state I L > 1 → Soil is in liquid state (quick clays or ultra sensitive clays) LIQUIDITY INDEX ( I L ) I L LL  PL  w n  PL 16 P I  w n  PL Also known as water plasticity ratio

17. Toughness index ( I t ) is useful to distinguish between soils (types) of different physical propertie s such as clays, silts etc. TOUGHNESS INDEX ( I t ) F 17 t Flow Ind e x I I  Plasticity Index  PI Soil Type I t Clayey soils 0-3 Soils which are friable at plastic limit (e.g. Silts) <1 it varies between 0 to 3

18. Helpful to predict the dominant clay type/mineral in soil sample. V of clay during shrinkage & swelling depends on A It measures water holding capacity of clay soil. High activity signifies large volume change when wetted and large shrinkage when dried. Clay Type Activity Inactive Clays < 0.75 Normal Clays 0.75 < A < 1.25 Active Clays > 1.25 ACTIVITY, A PI 18 % clay fraction smaller than  0.002 mm A 

19. The following data were recorded from a LL test on a silty clay; 19 If PL =23.4%, determine LL , flow index , and the toughness index . Practice Problem#1 No. of blows Water content (%) 35 41.1 29 41.8 21 43.5 15 44.9

20. LL = 42.8% PL = 23.4% PI = 42.8-23.4 PI = 19.4% Practice Problem 1 100 w (%) 10 No. of blows (N) N =25 20 48 47 46 45 44 43 LL =42.8% 42 41 40

21. I F = 10.22 Practice Problem 40 41 42 43 44 48 47 46 45 1 10 No. of blows (N) 100 w (%) 2  log   N 1   N  w 1  w 2 I  F  21  20   30  lo g   43.5  41.7 I t = I P /I F I = 19.4/10.22 t I t = 1.898 N 2 =30 N 1 =20 w 1 =43.5% w 2 =41.7%

22. CONCLUDED 22 REFERENCE MATERIAL An Introduction to Geotechnical Engineering (2 nd Edition) By R. D. Holtz, W. D. Kovacs and T. C. Sheahan Chapter #2 Principles of Geotechnical Engineering – (7 th Edition) Braja M. Das Chapter #4 Norman, L. E. J. (1959). The one-point method of determining the value of the liquid limit of a soil. Geotechnique , 9 (1), 1-8.