Seive Analysis weight of dry soil = a b Sieve No. Sieve Opening (mm) 4.75 2 0.85 0.425 0.25 0.106 0.075 n/a 4 10 20 40 60 100 200 Pan 506.66 g c d Sieve Sieve Mass Mass Full Empty (g) 750.51 759.63 673.53 702.92 608.12 668.47 568.45 630.26 544.89 598.12 521.15 567.78 512.95 591.85 484.75 647.89 e Soil Retained, Wn (g) f g Cumulative Cumulative Percent Weight Retained, Retained, ∑ Rn Rn h Percent Finer, 100 - ∑ Rn SOUTHERN ILLINOIS UNIVERSITY CARBONDALE DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING ASSIGNMENT 4: CE423 UNCONFINED COMPRESSION TEST SUBMITTED BY: SANJEEV REGMI DATE PERFORMED: 11/06/18 DATE SUBMITTED: 11/13/18 SUBMITTED TO: Dr. SANJEEV KUMAR Table of Contents Section Page No. Objective & Scope 1 Description 1 List of Equipment, Specimen, & Photographs 1 Procedure 3 Results 4 Graphs and Charts 9 Discussion & Conclusion 11 References 13 Objective & Scope Objective The purpose of the Unconfined Compression Test is to determine the unconfined compressive strength of a cohesive soil sample. This can then be used to calculate the undrained (with water present) shear strength of a clay or silty soil. Scope The main goal of the Unconfined Compression Test is to quickly obtain a measure of the compressive strength of soils (qu ) that possess enough cohesion. This test helps to determine the unconsolidated and undrained shear strength of soils. In the experiment, the unconfined compressive strength is the stress at which the specimen will fail due to shear. The compressive strain will be found as the maximum load applied at failure, or the maximum load achieved at 15% strain, whichever occurs first during the laboratory. The undrained shear strength, or S u , is necessary for the determination of load capacity for structure foundations. Furthermore, the scope of this experiment also includes calculation of dry unit weight of each sample before the test (γd ), Degree of saturation (S) of each sample before the test, Initial tangent modulus of the soil and Secant modulus of the soil at 25, 50, and 75% of q u . Description The Unconfined Compression Test is usually performed on undisturbed samples. This experiment is relatively simple to perform and usually takes no longer than 15 to 20 minutes once the sample is available. An undisturbed sample of cohesive soil (silt or clay) is obtained from field boreholes using a Shelby tube sample extractor. Once the sample is obtained, it can be used immediately to run the test. If the test is to be done in a later date, then the sample is kept in air tight bags and dipped in water until the test date arrives. Then, the test may begin, and a slow and steady load may be applied until failure of the specimen occurs—either by bulging or by vertical cracks seen in the sample. This experiment gives a good measure of the shear strength of fine-grained cohesive soils. In this experiment, 4 undisturbed soil samples from two different boreholes were taken to determine the unconfined compression strength and calculating undrained shear strength of the soil. The ASTM designation for the Unconfined Compression Test is ASTM D-2166. List of Equipment & Photographs List of Equipment 1. Unconfined Compression Testing Machine (1) 2. Undisturbed Soil Samples with length to diameter ratio being 2-2.5 (4) 3. Specimen Trimmer (1) 4. Evaporating Dish (1) 5. Balance (1) 1 Photographs Photo 1: Unconfined Testing Machine Photo 2: Failed Soil Specimen Note: Photo 1 shows the testing machine used to perform this experiment. The soil sample was placed between the two plates seen in the picture so that it was secure and the plate was perpendicular to the height of the soil. This allowed the specimen to be compressed with only axial loading via the machine. Note: Photo 2 shows the result of the Unconfined Compression test. One may easily see that the sample failed due to shear. Cracks and bulging may be seen in the sample. 2 Procedure This experiment was carried out for 4 different undisturbed samples taken from a Shelby Tube from two different boreholes. 1. The sample kept in air tight bags and stored in water until test time arrives. 2. The sample is taken out on test day. The top and bottom of the sample is trimmed so that it can properly fit between the bottom plate and top plate of the testing machine. 3. While trimming it is made sure that the length to diameter ratio of the sample is kept between 2-2.5. 4. Measure the diameter of the trimmed specimen at the top, bottom, and middle. Then measure the length in three places. This should be done so that you rotate approximately 120 degrees between each measurement. Record each value and find the average length and diameter. 5. Place the specimen on the bottom plate of the Testing Machine. Make sure that the specimen is centered on the plate and that the length of the sample is perpendicular to the plate of the machine. This allows the load applied during the experiment to be only axial in nature. 6. Slowly move the bottom plate of the machine in upward direction until the top of the specimen touches the top plate so that the specimen is secure but not yet carrying any load. If necessary, zero out any loads that may be showing or any indicators. 7. Turn the machine on and adjust the strain rate (the rate at which the load is applied) to a desired amount between 0.05%. 8. Record the load at a beginning increment of 0.01 inches of strain, and then continue to record the load at each 0.01-inch increment following (0.01, 0.02, 0.03 inches, etc.). Once the strain reaches a value of 0.10 inches, begin taking readings at 0.02 in increments of strain (1.20, 1.40, 1.60 inches, etc.). 9. Once the load begins to decrease, take an additional 2 to 3 measurements. The decrease in load indicates that the specimen has failed. 10. Turn off the machine and remove the specimen. Use an evaporating dish to collect a portion of the sample and determine its moisture content. 3 Results The following measurements and calculations were done before the start of the tests. Sample 1 Sample 2 Sample 3 Sample 4 Diameter (in) length (in) Diameter (in) length (in) Diameter (in) length (in) Diameter (in) length (in) 1st read. 2nd read. 2.846 2.886 4.864 4.884 2.712 2.709 5.616 5.651 2.865 2.869 5.358 5.341 2.842 2.862 5.52 5.531 3rd read. 2.879 4.89 2.735 5.634 2.876 5.311 2.844 5.51 Average 2.870 4.879 2.719 5.634 2.870 5.337 2.849 5.520 The tables containing the measurements and calculations from the unconfined compression tests are shown in the following pages. 4 Unconfined Compression Test Results DATA SHEET (Sample 1) Specimen Deformation, DL (inches) Column (1) 0.00 0.01 0.02 Vertical Strain, e = DL/L Column (2) 0 0.00204499 0.00408998 Proving Ring dial reading Column (3) 0 1 2 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.14 0.16 0.18 0.20 0.24 0.28 0.32 0.36 0.40 0.44 0.48 0.00613497 0.00817996 0.01022495 0.01226994 0.01431493 0.01635992 0.01840491 0.0204499 0.02249489 0.02453988 0.02862986 0.03271984 0.03680982 0.0408998 0.04907975 0.05725971 0.06543967 0.07361963 0.08179959 0.08997955 3 4 5 6 7 8 12 16 21 25 34 41 47 53 61 65 69 69 70 70 Can # S19 Load = Column (3) x Corrected Calibration Factor(2.04)(lb) Area (A c) Column Column (4) (5) 0 6.471 2.04 6.484 4.08 6.497 6.12 8.16 10.2 12.24 14.28 16.32 24.48 32.64 42.84 51 69.36 83.64 95.88 108.12 124.44 132.6 140.76 140.76 142.8 142.8 6.511 6.524 6.538 6.551 6.565 6.578 6.592 6.606 6.620 6.634 6.661 6.690 6.718 6.747 6.805 6.864 6.924 6.985 7.047 7.111 Moisture Content Calculations Can + Dry Can Dry Water Weight Weight 20.5700 58.3100 10.07 37.74 5 Stress = Column 4/Column 5 Column (6) 0.000 0.315 0.628 0.940 1.251 1.560 1.868 2.175 2.481 3.714 4.941 6.472 7.688 10.412 12.503 14.272 16.026 18.287 19.319 20.330 20.152 20.263 20.083 Water % 0.27 DATA SHEET (Sample 2) Specimen Deformation, DL (inches) Column (1) 0.00 0.01 Vertical Strain, e = DL/L Column (2) 0 0.00177504 Proving Ring dial reading Column (3) 0 1 Load = Column (3) x Calibration Factor(2.04)(lb) Column (4) 0 2.04 Corrected Area (A c) Column (5) 5.805 5.815 Stress = Column 4/Column 5 Column (6) 0.000 0.351 0.02 0.00355009 2 4.08 5.826 0.700 0.03 0.04 0.00532513 0.00710017 3 4 6.12 8.16 5.836 5.847 1.049 1.396 0.05 0.06 0.07 0.08 0.09 0.10 0.12 0.00887521 0.01065026 0.0124253 0.01420034 0.01597539 0.01775043 0.02130051 5 6 7 8 10 11 12 10.2 12.24 14.28 16.32 20.4 22.44 24.48 5.857 5.867 5.878 5.889 5.899 5.910 5.931 1.742 2.086 2.429 2.771 3.458 3.797 4.127 0.14 0.16 0.0248506 0.02840069 14 15 28.56 30.6 5.953 5.975 4.798 5.122 0.18 0.20 0.24 0.28 0.32 0.36 0.40 0.44 0.48 0.52 0.56 0.60 0.64 0.68 0.03195077 0.03550086 0.04260103 0.0497012 0.05680137 0.06390154 0.07100172 0.07810189 0.08520206 0.09230223 0.0994024 0.10650257 0.11360275 17 19 21 23 26 28 30 32 34 36 36 33 28 34.68 38.76 42.84 46.92 53.04 57.12 61.2 65.28 69.36 73.44 73.44 67.32 57.12 5.997 6.019 6.063 6.109 6.155 6.201 6.249 6.297 6.346 6.395 6.446 6.497 6.549 5.783 6.440 7.065 7.681 8.618 9.211 9.794 10.367 10.930 11.483 11.394 10.362 8.722 Dry Weight 46.59 Water % 0.27 Can # P22 Moisture Content Calculations Can + Can Dry Water Weight 31.3300 77.9200 12.79 6 DATA SHEET (Sample 3) Specimen Deformation, DL (inches) Column (1) 0.00 0.01 0.02 Vertical Strain, e = DL/L Column (2) 0 0.00187383 0.00374766 Proving Ring dial reading Column (3) 0 3 6 Load = Column (3) x Calibration Factor(2.04)(lb) Column (4) 0 6.12 12.24 Corrected Area (A c) Column (5) 6.469 6.481 6.494 Stress = Column 4/Column 5 Column (6) 0.000 0.944 1.885 0.03 0.04 0.00562149 0.00749532 10 14 20.4 28.56 6.506 6.518 3.136 4.382 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.00936914 0.01124297 0.0131168 0.01499063 0.01686446 0.01873829 0.02061212 16 20 22 25 28 29 32 32.64 40.8 44.88 51 57.12 59.16 65.28 6.530 6.543 6.555 6.568 6.580 6.593 6.605 4.998 6.236 6.846 7.765 8.681 8.973 9.883 0.12 0.14 0.02248595 0.0262336 34 38 69.36 77.52 6.618 6.644 10.480 11.668 0.16 0.18 0.20 0.24 0.28 0.32 0.36 0.02998126 0.03372892 0.03747658 0.04497189 0.05246721 0.05996252 40 42 43 42 38 34 81.6 85.68 87.72 85.68 77.52 69.36 6.669 6.695 6.721 6.774 6.827 6.882 12.235 12.797 13.051 12.649 11.354 10.079 Dry Weight Water % 34.62 0.21 Can # Can P-7 20.8800 Moisture Content Calculations Can + Dry Water Weight 55.5000 7.19 7 DATA SHEET (Sample 4) Specimen Deformation, DL (inches) Column (1) 0.00 0.01 Vertical Strain, e = DL/L Column (2) 0 0.00181148 Proving Ring dial reading Column (3) 0 6 Load = Column (3) x Calibration Factor(2.04)(lb) Column (4) 0 12.24 Corrected Area (A c) Column (5) 6.376 6.388 Stress = Column 4/Column 5 Column (6) 0.000 1.916 0.02 0.00362297 9 18.36 6.400 2.869 0.03 0.00543445 13 26.52 6.411 4.136 0.04 0.05 0.06 0.07 0.08 0.00724594 0.00905742 0.01086891 0.01268039 0.01449188 16 20 24 27 31 32.64 40.8 48.96 55.08 63.24 6.423 6.435 6.446 6.458 6.470 5.082 6.341 7.595 8.529 9.774 0.09 0.10 0.11 0.12 0.01630336 0.01811485 0.01992633 0.02173782 34 37 40 41 69.36 75.48 81.6 83.64 6.482 6.494 6.506 6.518 10.700 11.623 12.542 12.832 0.14 0.02536079 44 89.76 6.542 13.720 0.16 0.18 0.20 0.24 0.28 0.32 0.02898376 0.03260673 0.0362297 0.04347564 0.05072157 45 39 37 31 24 91.8 79.56 75.48 63.24 48.96 6.567 6.591 6.616 6.666 6.717 13.980 12.070 11.409 9.487 7.289 Dry Weight Water % 49.65 0.20 Can # Can P-4 20.4900 Moisture Content Calculations Can + Dry Water Weight 70.1400 10.17 8 Additional Calculations The following calculations to fulfill the additional scope of the experiment were done after completion of the test. Specific Gravity (Gs ) = 2.7 Area (in2 ) Sample Length (in) Volume (in3 ) Weight (lb) Moist Unit Weight (lb/in3 ) Water Content (w) Dry Unit Weight (lb/ft3 ) Void Ratio 1 2 6.4707 5.8050 4.8793 5.6337 31.5729 32.7034 2.1640 2.3630 0.0685 0.0723 0.2668 0.2745 93.4908 97.9641 0.8021 0.7198 0.8982 1.0297 3 6.4692 5.3367 34.5242 2.5280 0.0732 0.2077 104.7717 0.6081 0.9222 4 6.3764 5.5203 35.1999 2.6070 0.0741 0.2048 106.2224 0.5861 0.9436 Graphs and Charts Legend: Initial Tangent Modulus Secant Modulus at 50% of qu Secant Modulus at 25% of q u Secant Modulus at 75% of q u Stress vs Strain Curve(Sample 1) 30.000 25.000 20.000 Stress (lb/in2) Degree of Saturation (Sr) 15.000 10.000 5.000 0.000 0 0.01 0.02 0.03 0.04 0.05 Strain 9 0.06 0.07 0.08 0.09 0.1 Stress vs Strain Curve (Sample 2) 14.000 12.000 Stress (lb/in2) 10.000 8.000 6.000 4.000 2.000 0.000 0 0.02 0.04 0.06 -2.000 0.08 0.1 0.12 Strain Stress vs Strain Curve (Sample 3) 14.000 12.000 Stress (lb/in2) 10.000 8.000 6.000 4.000 2.000 0.000 0 -2.000 0.01 0.02 0.03 0.04 Strain 10 0.05 0.06 0.07 Stress vs Strain Curve (Sample 4) 16.000 14.000 Stress (lb/in2) 12.000 10.000 8.000 6.000 4.000 2.000 0.000 0 0.01 0.02 0.03 Strain 0.04 0.05 0.06 From the plotted graphs following information can be deduced: Sample Unconfined Compressive Strength (lb/in2 ) (qu) Undrained shear strength (lb/in2 ) (su ) Initial tangent Modulus (lb/in2 ) (E t ) Secant Modulus (lb/in2 ) 25% of qu 50% of qu 75% of qu 1 2 3 20.33 11.49 13.05 10.165 5.745 6.525 150 252.5 620 242.0238 239.375 652.5 350.5172 191.5 543.75 390.9615 172.35 489.375 4 14 7 1000 875 777.7778 700 Discussion & Conclusion Based on the results from the Unconfined Compression Test, the objectives of the experiment were met. As seen from our Stress v. Strain Graphs the unconfined compressive strength of the soil samples 1 through 4 were found to be 20.33, 11.49, 13.05 and 14.00 lb/in2 respectively. The undrained shear strength of the soil samples 1 through 4 were calculated to be 10.165, 5.745, 6.525 and 7.00 lb/in2 respectively. The dry unit weight, void ratio and degree of saturation were also calculated after the completion of the test which are shown in the table in 11 results section. However, the degree of saturation of sample 2 was calculated to be greater than 1 which is an error. The degree of saturation of a soil cannot be more than 1. This error might have caused due to error in measurement done for moisture content calculation. Based on the results, Sample 1 to 4 can be classified as: stiff clay, soft clay, medium stiff clay and medium stiff clay respectively. Test of sample 2 yield in failure by bulging. The initial tangent modulus and secant modulus at 25%, 50% and 75% of qu were also calculated from the stress vs strain plots for each sample(tabulated above). These values come in handy during design purposes depending on what design and analysis is being performed: design of shallow foundations, deep foundations, slope stability and retaining structures, pavements etc. In each case the importance of each modulus may vary. Depending on the anticipated loading pattern and settlement pattern appropriate modulus is used for design purposes. In practice, initial tangent modulus is mostly used. 12 References Das, Braja M. Soil Mechanics Laboratory Manual. Oxford University Press, 2016. Sobhan, Khaled, and Braja M. Das. Principles of Geotechnical Engineering. Cengage Learning 2018. Jean-Louis Briaud, Introduction to Soil Moduli. 2001 Das, Bajra M., Principles of Foundation Engineering. Cengage Learning 2018. 13 SOIL MECHANICS LABORATORY MANUAL Sixth Edition Braja M. Das Dean, College of Engineering and Computer Science California State University, Sacramento New York Oxford OXFORD UNIVERSITY PRESS 2002 CONTENTS I. 2. 3. 4. 5. 6. 7. B. 9. 10. . II. 12. 13. 14. 15. 16. 17. lB. Laboratory Test and Report Preparation Determination of Water Content 5 Specific Gravity 9 Sieve Analysis 15 Hydrometer Analysis 23 Liquid Limit Test 35 Plastic Limit Test 41 Shrinkage Limit Test 45 Engineering Classification of Soils 51 Constant Head Permeability Test in Sand 69 Falling Head Permeability Test in Sand 75 Standard Proctor Compaction Test 81 Modified Proctor Compaction Test 89 Determination of Field Unit Weight of Compaction by Sand Cone Method 93 Direct Shear Test on Sand 99 Unconfined Compression Test 109 Consolidation Test I 17 Triaxial Tests in Clay 129 References 145 Appendices A. Weight-Volume Relationships· 147 B. Data Sheets for Laboratory Experiments 151 C. Data Sheets for Preparation of Laborat~ry Reports 215 PREFACE Since the early 1940's the study of soil mechanics has made great progress all over the world. A course in soil mechanics is presently required for undergraduate students in most four- year civil engineering and civil engineering technology programs. It usually includes some laboratory procedures that are essential in understanding the properties of soils and their behavior under stress and strain; the present laboratory manual is prepared for classroom use by undergraduate students taking such a course. The procedures and equipment described in this manual are fairly common. For a few tests such as permeability, direct shear, and unconfined compression, the existing equipment in a given laboratory may differ slightly. In those cases, it is necessary that the instructor familiarize students with the operation of the equipment. Triaxial test assemblies are costly, and the equipment varies widely. For that reason, only general outlines for triaxial tests are presented. For each laboratory test procedure described, sample calculation(s) and graph(s) are inCluded. Also, blank tables for each test are provided at the end of the manual for student use in the laboratory and in preparing the final report. The accompanying diskette contains the Soil Mechanics LaboratoryTest Software, a stand-alone program that students can use to collect and evaluate the data for each of the 18 labs presented in the book. For this new edition, Microsoft Excel templates have also been provided for those students who prefer working with this popular spreadsheet program. Professor William Neuman of the Department of Civil Engineering at California State University, Sacramento, took inost of the photographs used in this edition. Thanks are due to Professor Cyrus Aryarti of the Department of Civil Engineering at Califoruia State UnIversity, Sacramento, for his assistance in taking the photographs. Last, I would like to thank my wife, Janice F. Das, who apparently possesses endless energy and enthusiasm. Not· only did she type the manuscript, she also prepared all of the tables, graphs, and other line drawings. BrajaM Das dasb@csus.edu I Laboratory Test and Preparation of Report .~ Introduction Proper laboratory testing of soils to detennine their physical properties is an integral part in the design and construction of structural foundations, the placement and improvement of soil properties, and the specification and quality control of soil compaction works. It needs to be kept in mind that natural soil deposits often exhibit a high degree of nonhomogenity. The physical properties of a soil deposit can change to a great extent even within a few hundred feet. The fundamental theoretical and empirical equations that are developed in soil mechanics can be properly used in practice if, and only if, the physical parameters used in those equations are properly evaluated in the laboratory. So, learning to perfonn laboratory tests of soils plays an important role in the geotechnical engineering profession. Use of Equipment Laboratory equipment is never cheap, but the cost may vary widely. For accurate experimental results, the equipment should be properly maintained. The calibration of certain equipment, such as balances and proving rings, should be checked from time to time. It is always necessary to see that all equipment is clean both before and after use. Better results will be obtained when the equipment being used is clean, so alwa);'s maintain the equipment as if it were your own. Recording the Data ," J " . ' b In any experiment, it is always a good habit to record all data in the proper table immediately after it has been taken. Oftentimes, scribbles on scratch paper may later be illegible or even misplaced, which may result in having to conduct the experiment over, or in obtaining inaccurate results. 1 2 Soil Mechanics Laboratory Manual Report Preparation In the classroom laboratory, most experiments described herein will probably be conducted in small groups. However, the laboratory report should be written by each. student individually. This is one way for students to improve their technical writing skills. Each report should contain: 1. Cover page-This page should include the title of the experiment, name, and date on which the experiment was performed. 2. Following the cover page, the items listed below should be included in the body of the report: a. Purpose of the experiment b. Equipment used c. A schematic diagram of the main equipment used d. A brief description of the test procedure 3. Results-This should include the data sheet(s), sample calculations(s), and the required graph(s). 4. Conclusion-A discussion of the accuracy of the test procedure should be included in the conclusion, along with any possible sources of error. 120r---~~---r-----' 120 0!:----''----'-~1;':5,--.-L-.,!25 (a) Figure 1-1. (a) A poorly drawn graph for dry unit weight of soil vs. moisture content 80 0!;----'--!c-5-----:;1';;-0--~15 Moisture content, w (%) (b) (b) The results'given in (a), drawn in a more presentable manner Soil Mechanics Laboratory Manual 3 Graphs and Tables Prepared for the Report Graphs and tables should be prepared as neatly as possible. Always give the units. Graphs should be made as large as possible, and they should be properly labeled. Examples of a poorly-drawn graph and an acceptable graph are shown in Fig. 1-1. When necessary, French curves and a straight edge should be used in preparing graphs. Table 1-1. Conversion Factors Length .,, _1 in. 1ft ~ 25.4 mm 0.3048 m 304.8 mm 1 mm 1m , .!-~ ~ 1 Area 1 em2 1 in 3 1 ft3 1ft' 16.387 em 3 0.028317 m3 28.3168 I I em3 1 ftls 304.8 m\ll/s 0.3048 m/s 5.08 mm/s 0.00508 m/s I em/s 1.969 ftlmin 1034643.6 ftlyear 1~ :~ x 10-2 in. x 10-3 ft in. ft 6.4516 x 10-4 m2 6.4516 em2 645.16 mm2 929 x 1O-4m 2 929.03 em2 92903 mm 2 1 in. 2 ~ ~ ,l' 3.937 3.281 39.37 3.281 .,, --.~ ,:l :1 1 m2 0.155 in 2 1.076 x 10-3 ~ 1550 in 2 10.76 ft2 ~ ·.~i Volume '1 ~ i I m3 .~ -Jb«n"'o"'w,u'n.... d""quvei,l!:,Y-"-sl""lt_ _ __ Sample No. Westwind Boulevard Location Tested by _ _ _ _ _ _..,,-_ _ _ _ _ _ __ Date I Mass of coated shrinkage limit dish, WI (g) /2.34 Mass of dish + wet soil, W2 (g) 40.43 Mass of dish + dry soil, W3 (g) 33.68 Wi (%) = (W, - W,) x 100 (W, - 31.63 w;) Mass of mercury to fill the dish, W4 (g) /98.83 Mass of mercury displaced by soil pat, W5 (g) /50.30 ~Wi (%) = (~ - W,) SL = Wi - X 100 (13.6)(W; - W;) (~- W,) 13.6(W, -W;) (100) /6.72 /4.91 8 Soil Mechanics Laboratory Manual 49 General Comments The ratio of the liquid limit to the shrinkage limit (LLI SL) of a soil gives a good idea about the shrinkage properties ofthe soil. If the ratio of LLISL is large, the soil in the field may undergo undesirable volume change due to change in moisture. New foundations constructed on these soils may show cracks due to shrinking and swelling of the soil that result from seasonal moisture change. Another parameter called shrinkage ratio (SR) may also be determined from the shrinkage limit test. Referring to Fig. 8-1 SR = _.'l_V_/~VI,­ .'lw /W, .'lV/VI =~ (.'lVpw)/w, P'YI (8.4) where Ws = weight of the dry soil pat =W3 -W\ If Ws is in grams, VI is in cm3 and Pw = 1 g/cm3 . So SR= W, VI (8.5) The shrinkage ratio gives an indication of the volume change with change in moisture content. 9 Engineering Classification of Soils Introduction Soils are widely varied in their grain-size distribution (Chapters 4 and 5). Also,depending on the type and quantity of clay minerals present, the plastic properties of soils (Chapters 6, 7 and 8) may be very different. Various types of engineering works require the identification and classification of soil in the field. In the design of foundations and earth-retaining struc- . tures, construction of highways, and so on, it is necessary for soils to be arranged in specific groups and/or subgroups based on their grain-size distribution.and plasticity. The process of placing soils into various groups and/or subgroups is called soil classification. For engineering purposes, there are two major systems that are presently used in the United States. They are: (i) the American Association ofState Highway and Transportation Officials (AASHTO) Classification System and (ii) the Unified Classification System. These two systems will be discussed in this chapter. American Association of State Highway and , Transportation Officials ,LL- 30=49- 30=19. So this soil isA-7-6. Soil Mechanics Laboratory Manual 4. 5. 57 From Equation (9-2) GI= (F200 - 35)[0.2 + 0.005(LL - 40)] + 0.01(F2oo - 15)(PJ - 10) = (58 - 35)[0.2 + 0.005(49 - 40)] + 0.01(58 - 15)(21 - 10) = 5.64 + 4.73 = 10.37 '" 10 So the soil is classified asA-7-6(JO). Unified Classification System This classification system was originally developed in 1942 by Arthur Casagrande for airfield construction during World War II. This work was conducted on behalf of the U.S. Anny Corps of Engineers. At a later date, with the cooperation of the United States Bureau of Reclamation, the classification was modified. More recently, the American Society of Testing and Materials (ASTM) introduced a more definite system for group name of soils. In the pre-sent form, it is widely used by foundation engineers all over the world. Unlike the AASHTO system, the Unified system uses symbols to represent the soil types and the index properties of the soil. They are as follows: G Gravel S Sand W Well,-graded (for grain-size distribution) P Poorly-graded (for grain-size distribution) M Silt C Clay L Low to medium plasticity 0 Organic silts and clays H High plasticity Pt Highly organic soil and peat Soil groups are developed by combining symbols for two categories listed above, such as GW, SM, and so forth. Step-by-Step Procedure for Unified Classification System 1. 2. If it is peat (i.e., primarily organic matter, dark in color, and has organic odor), classifY it as Pt by visual observation. For all other soils, determine the percent of soil passing through U.S. No. 200 sieve (F200 ). Determine the percent retained on U.S. No, 200 sieve (R 200 ) as 58 Soil Mechanics Laboratory Manual (9.3) 3. 4. (nearest whole number) If R200 is greater than 50%, it is a coarse-grained soil. However, if ~oo is less than or equal to 50%, it is a fine-grained soil. For the case where R200 s 50% (i.e., finegrained soil), go to Step 4. If R200 > 50%, go to Step 5. For fine-grained soils (i.e., R 200 S 50%, determine if the soil is organic or inorganic in nature. a. If the soil is organic, the group symbol can be OH or OL. If the soil is inorganic, the group 'symbol can be CL, ML, CH, MH, or CL-ML. b. Determine the percent retained on U.S. No.4 sieve (R 4) as R4 = 100 - F4 (9.4) i (nearest whole number) where F4 ='percent finer than No.4 sieve Note that R4 is the percent of gravel fraction in the soil (OF), so (9.5) c. Determine the percent of sand. fraction in the soil (SF), or SF=R200 5. - OF (9.6) d. For inorganic soils, determine the liquid limit (LL) and the plasticity index (Pl). Go to Step 4e. For organic soils, determine the liquid limit (not oven dried), LLNOD ; the liquid limit (oven dried), LIoD; and the plasticity index (not oven dried), PINOD' Go to Step 4f. e. With known values of R 200, OF, SF, SF/OF, LL and PI, use Table 9-3 to obtain group symbols and group names of inorganic soils. f. With known values of LLNOD' LLoD , PINOD ' R200 , OF, SF and SF/OF, use Table 9-4 to obtain group symbols and group names of organic soils. Figure 9-2 shows a plasticity chart with group symbols for fine-grained soils. For coarse-grained soils: a. If R4 > 0.5R 200> it is a gravelly soil. These soUs may have the following group symbols: OW OW-OM OF OW-OC OM OP-OM OC OP-OC OC-OM Soil Mechanics Laboratory Manual 59 70 60 CH or 50 j OR 40 ~ s:: OL 20 10 00 y" . t-:'>$' or 30 --- "MI-_C;;hty' 10 20 30 ';' ."",0 .. CL .~ ~r,:jV V / MH or L ~ or OH OL 40 50 60 70 80 90 100 Liquid limit Figure 9-2_ Plasticity chart for group symbols of fine-grained soils. Detennine the following: (1) F zoo (2) Unifonnity coefficient, Cu = D601D1O (see Chapter 4) (3) Coefficient of gradation, Cc = Ii'jO/(D60 x D IO ) (4) LL (of minus No. 40 sieve) (5) PI (of minus No. 40 sieve) (6) SF [based on Equations (9.3), (9.4), (9.5) and (9.6)] Go to Table 9-5 to obtain group symbols and group names. b. If R4 ,;; 0.5Rzoo , it is a sandy soil. These soils may have the following group symbols: SW SP SM SC SW-SM SW-SC SP-SM SP-SC SM-SC 60 Soil Mechanics Laboratory Manual Table 9-3. Unified Classification of Fine·Grained Inorganic Soils (Note: The group names are based on ASTM D-2487.) LL < 50, CL PI> 7, 15' and PI ML 29
Purchase answer to see full attachment