Module - CE 2042 Soil Mechanics and Geology-1 Assignment Plasticity Characteristics of Soils Marks 10% Learning Outcome

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1 Module - CE 2042 Soil Mechanics and Geology-1 Assignment Plasticity Characteristics of Soils Marks 10% Learning Outcome Ability to conduct Atterberg Limits tests and determine liquid limit and plastic limit of fine grained soils Ability to interpret the plasticity characteristics of soils obtained by Atterberg limits tests Ability to discuss the applications of Atterberg limits in geotechnical Programme Outcomes engineering 1. Application of knowledge of mathematics, science, and engineering 1 2. Effective communication 1 3. In-depth technical competence in at least one engineering discipline 2 4. Ability to undertake problem identification, formulation and solution 2 5. Ability to utilize a systems approach to design and operational 2 performance 6. Individual and team work 1 7. Understanding of the social, cultural, global and environmental responsibilities of the professional engineer, and the need for sustainable 0 development 8. Understanding of the principles of sustainable design and development 0 9. Understanding of professional and ethical responsibilities and commitment to them Expectation of the need to undertake life-long learning and capacity to do so 0 0 not covered under this 1 covered to some extent 2 covered to a greater extent 3 one of the main themes of the subject Lecturer Prof. S. A. S. Kulathilaka Student Name Registration Number: Date of Assignment: Initial Submission Date: Assessed By: Signature Date Due: Re Submission Date: Date Lecturers Remarks B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 1 of 14

2 Important 1. Please note that plagiarism is treated as a serious offence and therefore the work you produce must be individual and original. 2. All sources of information must be referenced using Harvard Referencing where a reference list/bibliography should be included at the end of the assignment. (You may refer the information given in 3. Please note that the submission date given for the assignment (14 days after the date of performance for the laboratory session) is the final date that you can submit the assignment. If the given submission date is a public holiday, redefined submission deadline will be at 1300 hr of the immediate following working day. Late submissions will be graded lower. 4. Assignments returned to students for corrections must be re-submitted within 10 days 5. Failure to re-submit the previously marked assignment with the re-submitted assignment will mean that results cannot be released for the respective unit. Plagiarism Although research and discussion form an essential part of the assignment, deliberate copying of the work of others or unacknowledged copying from printed or electronic sources is NOT permitted. Disciplinary actions will be taken against those who are found guilty of plagiarism. Signing of this sheet is required to indicate your compliance with the above regulations. Student s Signature:.. Date:. Student s Comments, (Prior to the submission) if any: Student s feedback, (After the the submission) if any: B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 2 of 14

3 DETERMINATION OF PLASTICITY CHARACTERISTICS OF SOILS SOIL MECHANICS SOIL MECHANICS LABORATORY DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF MORATUWA SRI LANKA B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 3 of 14

4 Tests for Determination of Plasticity Characteristics 1 General Determination of the Liquid Limit, Plastic Limit and the Plasticity Index of soils are covered here. In recognition of their formulation by the Swedish soil scientist A. Atterberg, Liquid limit and plastic limit (along with the Shrinkage limit) are often referred to as Atterberg Limits. These limits are a basic measure of the nature of a fine grained soil. 2 Scope These limits distinguish the boundaries of the several consistency states of a plastic soil and are performed on the soil which passes the 0.425mm - (425µm) sieve. Liquid limit can either be determined using a multipoint test or a one point test. Plasticity limit test is performed on materials prepared for the liquid limit test. In some soils Liquid limit and Plastic limit can be considerably different when they are dried before the test. In such cases "Wet preparation method" described here should be adopted. Otherwise soil sample shall be prepared by the "Dry preparation method". Plasticity characteristics are used as an integral part of several engineering classification systems to characterise the fine grained fraction of the soil. 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 behaviour such as compressibility, permeability, compact ability, shrink, swell and shear strength. 3 Apparatus Liquid Limit Device (Casagrande s Apparatus) This is a. mechanical device consisting of a brass cup suspended from a carriage, which is designed to control its drop on to a hard rubber base. Figure 1 depicts the essential features of the device and provides the critical dimensions. The device may be operated either by a hand crank or by an electric motor. Different parts of the Liquid limit device should confirm to the standards listed below. Base The base shall be hard rubber having a Durometer hardness of 80 to 90, and resilience that an 8mm diameter polished steel ball, when dropped from a height of 25 cm will have an average rebounce of at least 80% but not more than 90%. The test shall be conducted on the finished base with feet attached. B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 4 of 14

5 Feet The base shall be supported by rubber feet designed to provide isolation of the rubber base from the work surface. When the finished feet is attached to the base it should provide Durometer hardness less than 60. Cup The cup should be brass and have a weight (inclusive of cup hanger) of g. Cam The cam shall raise the cup smoothly and continuously to its maximum height, over a distance of at least of cam rotation. The preferred cam motion is a uniformly accelerated lift curve. The design of the cam and follower combination shall be such that there is no upward or downward velocity of the cup when the cam follower leaves the cam. Carriage The cup carriage shall be constructed in a way that allows convenient but secure adjustment of the height of drop of the cup to 10 mm. The cup hanger shall be attached to the carriage by means of a pin which allows removal of the cup and cup hanger for cleaning and inspection. Optional motor drive As an alternative to the hand crank, the drive may be equipped with a motor to turn the earn at 2 revolutions per second Other Accessories Grooving Tool A grooving tool having dimensions as shown in Figure 2. The tool shall be made of plastic or non corroding metal. The design of the tool may vary as long as essential dimensions are maintained. Gauge A metal gauge block for adjusting the height of drop of the cup having dimensions shown in Figure A (The gauge could have been incorporated in the cutting tool itself). Containers Small containers for moisture content determination. Balance A balance readable to at least 0.01 g Storage Containers A container in which to store the prepared soil sample so that contamination or moisture loss is prevented. A porcelain, glass or plastic dish about 11.5 cm in diameter and a plastic bag large enough to enclose the dish and be folded over is adequate. B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 5 of 14

6 Ground Glass Plate A ground glass plate at least 30 cm square by 1cm thick for mixing soil and rolling plastic limit threads. Spatulas A spatula having a blade about 2 cm wide by 10 cm long and another having a blade 2.5cm wide and 15 cm long. Sieve A 425µm sieve. Wash bottle Wash bottle or a smaller container for adding controlled amounts of water to the soil and washing fines from coarser particles. Drying Oven A thermostatically controlled oven capable of continuously maintaining a temperature of C o, throughout the drying chamber. The oven shall be equipped with a thermometer of suitable range and accuracy for monitoring the oven temperature. Rod A metal or plastic rod or tube 3.2 mm (1/8 inch) diameter and about 10 cm long for judging the size of plastic limit threads. 4 Procedure 4. 1 Preparation of the Sample Soil used in the test should be finer than 425 µm. A representative portion of from the total sample sufficient to provide 150 g to 250 g of material passing 425 µm sieve should be obtained. Preparation of the sample may be done either by "Dry Preparation Method" or "Wet Preparation Method". Dry Preparation Method In the dry preparation method, soil sample received in the laboratory shall be air dried or oven dried (at a temperature less than 60 deg) and a portion finer than 425 µm shall be obtained by dry sieving. With some soils Liquid Limit and Plastic Limit obtained after drying in the above manner would be different from the LL and PL obtained on undried samples. In such instances wet preparation method shall be used. B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 6 of 14

7 Wet preparation Method If by appearance it is determined that no material coarser than 425 µm is present in the sample a sample of 150 g g shall be prepared by mixing thoroughly with distilled or demineralised water on a glass plate using a spatula. Before mixing soil may be softened by soaking it in a storage disk for a while. If a small percentage of material coarser than 425 µm is encountered during mixing they shall be removed by hand. If it is impractical to remove the coarse material by hand coarse material may be removed by working the specimen through 425 µm sieve. If a larger percentage of coarse material is encountered during mixing, or if it is impractical to remove the coarse material by the methods described above sample may be washed through the 425 µm sieve. Prior to the washing process any obviously large particles may be removed by sieving through a 2mm sieve. Thereafter 425 µm sieve shall be kept on the bottom of a clear pan and water should be added to bring to a level of about 13 mm above the surface of the 425 µm sieve. The slurry shall be washed through the 425 µm sieve by taking not more than 500 g of soil at a time on to it. Material retained on 425 µm sieve shall be discarded and the water content of the soil in the pan shall be reduced till it approaches the Liquid Limit. Water content may be reduced by Exposing it to air currents at room temperature, exposing it to warm air currents of a hair drier, filtering through a funnel or colander with the help of a high wet strength filter paper or by decantering clear water from the surface of the suspension. Soil sample of about 250 g finer than 425 µm obtained through one of the procedures above should then be thoroughly mixed using a. spatula. Mixed soil should then be returned to the mixing dish, covered to prevent loss of moisture and allowed to stand for at least 16 hrs. After the standing period and immediately before starting the test, sample shall be remixed thoroughly Test Procedure for the Liquid Limit (Casagrande s Apparatus) A portion of the prepared soil shall be placed in the cup of the liquid limit device and spread in the cup to a depth of 10 mm at its deepest point, to form an approximately horizontal surface. Care should be taken to eliminate air bubbles from the soil pat. But the pat should be made with as few strokes as possible. Unused soil on the glass plate should be kept covered by a wet towel or an inverted dish. A groove should be made in the soil pat by drawing the tool, beveled edge through the soil on a line joining the highest point to the lowest point on the rim of the cup. When cutting the groove, grooving tool should be held against the surface of the 'cup and be maintained perpendicular to the surface throughout its movement. In soils where a groove cannot be, made in one stroke without tearing the soil, groove may be cut with several strokes of the grooving tool. Alternatively the groove may be cut with a spatula initially to a slightly less width and made to -the final dimensions B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 7 of 14

8 by the grooving tool. Extreme care should be exercised to prevent any sliding of the soil relative to the surface of the cup. Cup shall be lifted and dropped by turning the crank at a rate of 2 drops per second until the two halves of the soil pat come in contact at the bottom of the groove along a distance of 13 mm. The number of drops, N, required to close the groove should be recorded and a slice of the soil be removed for the determination of moisture content. Sample should be taken from edge to edge of the cup to include the portion of the groove in which the soil flowed together. A spatula may be used for this purpose. The soil remaining in the cup shall be returned to the glass plate, and the cup and grooving tool shall be washed and dried. Cup shall then be reattached to the carriage in preparation for the next trial. The entire soil specimen on the glass plate shall be remixed adding more water to increase the moisture content so that the number of blows required for the closure of the groove will be less. In the trials number of blows required should be between 15 and 50. Liquid limit is the water content of the soil when the grove closes with 25 blows Test Procedure for the Liquid Limit (Penetration Method) The apparatus for the liquid limit test in this method consists of a penetrometer fitted with a 30 cone of stainless steel, 35 mm long; the cone and the sliding shaft to which it is attached have a mass of 80 g. The soil to be tested is mixed with water to form a thick homogeneous paste and stored for 24 hrs. Some of the paste is then placed in a cylindrical metal cup, 55 mm internal diameter by 40 mm deep, and leveled off at the rim of the cup to give a smooth surface. The cone is lowered so that it just touches the surface of the soil in the cup, the cone being locked in its support at this stage. The cone is then released for a period of 5 sec and its depth of penetration into the soil is measured. A little more of the soil paste is added to the cup and the test is repeated until a consistent value of penetration has been obtained. (i.e. the average of the two values within 0.5 mm or three values within 1.0 mm is obtained). The entire test procedure is repeated at least four times using the same soil sample but increasing the water content. The penetration values should cover the range of approximately 15mm to 25mm. Cone penetration is plotted against water content and the best straight line fitting the points in drawn. Liquid limit is defined as the water content corresponding to a cone penetration of 20 mm. B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 8 of 14

9 20mm Cone Penetration Water Content LL 4. 4 Test Procedure for the Plastic Limit About a 20 g portion of soil from the material prepared for the Liquid Limit test shall be used for this test. By spreading and continuously mixing on the glass plate or by rolling between the palms of hands the water content of the soil should be reduced to a consistency at which it can be rolled without sticking. Soil specimen may be exposed to air currents from an electric fan to expedite the process of drying. From the specimen about 2 g shall be taken and formed it to an ellipsoidal mass. This mass shall be rolled between the palms of hands and the ground glass plate. Mass should be rolled with just sufficient pressure to make it in to a thread of uniform diameter of about 3.2 mm. (Rod may be used to get a guidance about the size). Any crumbling of the thread should be observed. This should be done over and over again; thereby reducing the water content till the thread crumbles when rolled to a diameter of 3.2 mm. The portions of the crumbled thread should be gathered and place on a container to determine the moisture content. The procedure should be repeated for another 2 g portion of the soil from the original specimen. This should be continued until the container has at least about 9 g of soil. The process should be repeated to obtain another container of at least 9 g of soil. The moisture content from the two containers should be computed separately to determine the Plastic Limit of the soil. If the difference is greater than 2% the test should be repeated. B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 9 of 14

10 4. 5 Presentation of Results Liquid Limit Test The relationship between the water content and the number of blows shall be plotted in a semi log paper. Number of blows should be plotted on the X axis on the logarithmic scale and water content should be on the Y axis on the arithmetic scale. The water content corresponding to 25 blows should be taken as the Liquid Limit of the test. Plastic Limit Test The average moisture contents of the crumbled threads shall be reported as the Plastic Limit of the soil. Plasticity Index (PI) should also be reported. (PI = LL - PL). Also whether the sample is prepared using wet preparation method or dry preparation method shall be reported. If the Liquid Limit and Plastic Limit tests cannot be performed or if PL is equal to or greater than LL, the soil shall be reported as non plastic. Soil Mechanics Laboratory -University Of Moratuwa Atterberg Limit Test Results Client: Project: Sample Details : Depth: Liquid Limit Test Trial Number Number of Blows Moisture can No Mass of wet soil + can (g) Mass of dry soil + can(g) Mass of can (g) mc % cs12 28 cs41 b6 a Plastic Limit Test Data: LL %= 51.5 PL%=34.4 PI % =17.1 B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 10 of 14

11 Specimen Calculation - Taking data from Trial Number 1 Mass of moisture = = 4.19 g Mass of dry soil = = 9.31 g Moisture content = (4.19/9.31) x 100 = % Plot the moisture content against the number of blows. Note that the number of blows should be plotted on a log axis. Liquid limit is the moisture content corresponding to 25 blows. LL = 51.5 % Mass of dry soil shall be obtained after oven drying the sample for at least 24 hours at a temperature of around 106 C deg. B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 11 of 14

12 Soil Mechanics Laboratory -University Of Moratuwa Atterberg Limit Test Results Client: Project: Sample Details : Liquid Limit Test Depth: Trial Number Number of Blows Moisture can No Mass of wet soil + can (g) Mass of dry soil + can(g) Mass of can (g) mc % Penetration (mm) cs12 28 cs41 b6 a Plastic Limit Test Data: LL %= 52 PL%=34.4 PI % =17.6 For Penetration of 20mm LL = 52.0 % B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 12 of 14

13 Figure 1 : Liquid Limit Device B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 13 of 14

14 Figure 2: Grooving tool type B BS Standard B.Sc Engineering, Semester III, CE 2042 Soil Mechanics & Geology - 1 Page 14 of 14