LABORATORY II. PLASTICITY - Atterberg limits. w L - Cone test, Cassagrande test

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1 LABORATORY II. PLASTICITY - Atterberg limits w L - Cone test, Cassagrande test

2 Consistency - limits I P w L w P

3 Is plasticity important?

4 Smectite Structure Tetrahedral layer Octahedral layer Tetrahedral layer Interlayer (Gallery) exchangeable cations neutral molecules (H2O) d 001 Tetrahedral layer O OH Si, Al Al, Fe, Mg Li < Na < K < Ca < Mg < NH 4 Dietrich Koch, S&B, ABM Projectmeeting, Äspö,

5 Different forms of water in the interlayer space of Montmorillonite Flake surface + - M M M Flake surface Bonded Water Free Porewater Dietrich Koch, S&B, ABM Projectmeeting, Äspö,

6 Examples of Atterberg limits for several types of smectite soils

7 MX80 Na bentonite: w P = 53%, w L = 450%

8 Effect of sieving, natrification and mixing

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10 SKB TR-02-12: 108

11 Sample w L [%] 80 C /24h 110 C / 9 months w P [%] I P [%] w L [%] w P [%] I P [%] Locality Stránce Locality Skalná Locality Dnešice Locality Rokle Bentonite MX CEG

12 Impact of thermal loading

13 wl % Results of 2 methods? BI FEBEX RMN B 75 G Sab 65 MX wl % casagrande kužel

14 Is it easy to prepare sample?

15 WL [%] Is it easy to prepare sample? Compaction nelisovaný lisovaný

16 Task for today: To determine: 1/ Plasticity index I P w L w P 2/ Consistency index 3/ Liquid index (sample natural water content w = 7%)

17 Indexes Characteristics of cohesive soils: Plasticity index I p I P w L w P Consistency index I c Liquid index I L Index of colloidal activity of clay I A. I I C L w w L L L w w w w w w I A P P P I c I L amount of 1 I P grains smaller than 0,002 mm Regarded usage of the material as sealing layer the range of plasticity stage is very important. Plasticity is determined by plasticity index. It is range of water content in which soils behave as plastic. Material with high plasticity will be able to fill in and seal cracks and joints in the structure of engineering barrier.

18 Atterberg limits Since April Czech standard ČSN CEN ISO/TS Geotechnical investigation and testing Laboratory testing of soil Part 12. Determination of Atterberg limits

19 Methods w L One point method - based on equation faster method, BUT It is required, however, that the water content of the sample is not too different from the liquid limit. Useful / applicable on known material. wn log n tan w w n L n 25 tan = inclination of the flow curve SKB TR-02-20: 157

20 water content w [%] Methods Multi-point method no equation avoiding possible mistakes, needed more time Liquid limit w L = 101 % Number of blows

21 Liquid limit w L Czech standard ČSN CEN ISO/TS The behaviour of cohesive soil depends on its water content. A clay soil becomes pasty till liquid at high water content. The liquid stage corresponds to stage, when soil does not put up any resistance against shearing strain. Water content on the boundary between plastic and liquid stage is indicated as liquid limit wl. Unit: % Cone penetration preffered method Casagrande dish (Percussion liquid limit) SKB TR-02-20:

22 Liquid limit w L Sample preparation The air-dried sample is crushed in the mortar by means of the rubber-coated pestle and sieved through the 0.40 mm sieve. About 100 g of the material that has passed is mixed with distilled water in the cup until the soil obtains plastic consistency. The sample should then be left for a couple of hours, or preferably till the next day, to let the sample homogenize before the determination of the liquid limit is made. In the meantime, the cup must be covered in order to prevent water evaporation.

23 Liquid limit w L - Cassagrande method A prepared dry sample is placed on a glass plate, watered by distilled water and kneaded thoroughly. The water is added gradually, and with each dose of water the soil must be kneaded for 5 minutes. For clayey soils, it is necessary to leave the watered sample for 24 hours to enable good homogenisation. A part of the prepared sample is placed into the cup. Its surface is levelled, and no air bubbles are allowed inside the soil. The layer of the soil in the cup can be maximally 1 cm. A groove normal to the axis of the apparatus is made in the soil by means of a grooving tool, which is held perpendicularly to the spherical surface of the cup. The cup with the soil falls down from a height of 1 cm. The crank of the apparatus is rotated at a rate of 2 rounds per second until the soil surfaces separated by the groove touch each other along an uninterrupted length of 12.5 mm ( 0.5 mm). The number of blows which are necessary for putting the soil together is recorded. The sample for the water content determination is taken from both halves of the soil. The procedure is repeated for at least 4 different water contents (in certain limit of blows ).

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25 water content w [%] On the beginning, the soil has the lowest water content. The number of blows must be in a range of 15 to 35. It is not allowed to add dry soil into the prepared sample. The dependence of the water content on the number of blows is made. On the horizontal axis, there is the number of blows in a logarithmic scale, while on the vertical axis there is the water content in a linear scale. The water content which corresponds to 25 blows is the liquid limit w L. Liquid limit w L = 101 % Number of blows

26 Liquid limit w L Cone penetration method PROCEDURE Remould the soil sample in the mixing cup carefully by means of the spatula. The sample (part of the total amount) should fill the cup completely. Smoothen the sample flush with the edge of the cup by means of the spatula. Move the excess soil to an empty cup. Mount the cone in the stand of the fall-cone apparatus and place the mixing cup centrally under the cone. Bring the stand arm down so that the tip of the cone just touches the surface of the soil sample. Check that the index line on the cone shaft coincides with the zero line of the millimetre-graded scale. Release the cone. Read the cone penetration within 0.1 mm. The cone-point method is valid for 15-20mm (resp mm) cone penetration. SKB TR-02-20

27 Tab g/ g/60 First penetration approx. 15mm approx. 7mm Penetration range 15 20mm 7 15mm (BS ) Max. diff. between two succesful tests 0,5mm 0,4mm w L depth of penetration 20mm 10mm

28 Before the water content is adjusted, two 20g specimens are extracted for determination of the original water content. If the water content has to be increased, the sample in the cup is transferred back to the mixing cup and the entire sample is then diluted with distilled water and carefully remoulded with the spatula. If the water content has to be reduced, the whole sample is spread on the paper, which absorbs water relatively fast. The sample is then moved back to the mixing cup and carefully remoulded with the spatula. Before further trials are carried out, the cup must be cleaned. Read and record the cone penetration and extract a 20g specimen from the central part of the sample in the mixing cup. Transfer it to a drying can for water content determination. For soils with a very high liquid limit, such as smectite clay, the specimen should preferably be more than 20g to give an accurate determination of the water content. Replenish the mixing cup with excess soil and then remould the soil and repeat the determination. Repeat the determination by using the second sample. If the two determinations do not give almost the same cone penetrations, further determinations should be made. The water content is evaluated. SKB TR-02-20

29 water content [%] 210,00 Cone liquid limit w L 200,00 190,00 180,00 170,00 160,00 10,0 100,0 penetration [mm] test / figure according to BS 1377

30 Plasticity limit w P Czech standard ČSN CEN ISO/TS The water content on the boundary between the plastic and solid stage is indicated as the plasticity limit w P. Unit: % Sample preparation: Air-dried sample is cut into pieces and sieved through a 0.5 mm sieve. After that the soil is watered by distilled water and is kneaded thoroughly. At least 20g of soil is needed.

31 Plasticity limit w P Knead the sample together until fine cracks on the surface occur. Divide the sample into two approximately equal parts. Each part is tested separately. Each part is divided into four specimens (part-samples).

32 Plasticity limit w P Knead the specimen together again and form the cylinder with a diameter approx. 6mm. Roll each of the cylinders by hand to a thread, approximately 3mm thick, on the unglazed paper placed on a plane and hard base. In the case of silt use glazed paper. The rolling should be carried out with even motions of the hand, backwards and forwards, in such a way that the thread gets an even thickness. Furthermore, the pressure should be adjusted so as to successively reduce the thickness of the thread while keeping the cross section circular. Knead the sample together and roll it again and repeat this procedure until the thread breaks into several crumbles along its full length. Collect the crumbled sample, place it in a drying can and put the lid on. Handle the remaining (3) part-samples in the same way. Place all partsamples in one can. Repeat all procedure on the second part of basic sample. Determine the water content of the two samples.

33 What else? Calculation of w L, w P Calculation of I P, I c, I L All data and results to protocol Next laboratory Swelling pressure, swell index

34 It s your business now