EFFECT OF FINE CONTENT ON COMPACTION CHARACTERISTICS OF SAND. Nurul Wahida Azmi

Transcription

1 EFFECT OF FINE CONTENT ON COMPACTION CHARACTERISTICS OF SAND Nurul Wahida Azmi This project is submitted in partial of fulfillment of the requirements for the Degree of Bachelor of Engineering with Honours (Civil Engineering) Faculty of Engineering UNIVERSITI MALAYSIA SARAWAK 2005

2 To my abah & ma, family, and friends.

3 ACKNOWLEDGEMENT In the name of Allah s. w. t, the Almighty and Merciful, I am so grateful for the strength in accomplishment of this study. My appreciation goes much to my supervisors, Prof. Zoynul Abedin and Dr. Prabir Kumar Kolay for their expertise, guidance and opinion that help me to complete this study. I particularly thank all technicians that very cooperative and keeping my lab under control. Thanks to my friends, for supportive and problems shared during this study. I'll keep it in mind. Lastly, most important person, my parent and family, thank you for your support and staying beside me for my entire life, as usual. Thanks much.

4 ABSTRACT Normally sandy soils are used as fill material in construction and their engineering properties can be improved by compaction. Generally, study on compaction concentrates on the energy of compactive effort and water content. However, study of the effect of fine content in sandy soils on compaction characteristics seems to be limited. The present study deals with two riverbed sand and one quarry sand sample collected from different location of Sarawak, to investigate the effect of fine (i. e., sample passing 75 µm) content on the compaction characteristics. Those three sand samples were reconstituted with various proportions of fine content (5%, 10%, 20%, and 30%) for the tests. The compaction test has been carried out, by using standard Proctor test. Results shows that for riverbed sand samples, with the increase of 30% fines, maximum dry density increases by 9.36% & 4.12% and optimum moisture content decreases by 18.88% & 24.6%. While for quarry sand, with the increase of 30% fines, maximum dry density increases by 9.67% and optimum moisture content decreases by 43.5%. These results may be useful to simulate the insitu compaction methods. ii

5 ABSTRAK Kebiasaannya, pasir selalu digunakan sebagai tanah isian dalam pembinaan dan sifat- sifat kejuruteraannya boleh ditingkatkan dengan kaedah pemadatan. Umumnya, kajian berkaitan dengan pemadatan bertumpu kepada berapa banyak usaha memadat yang dikenakan dan kandungan air. Walaubagaimanapun, kajian mengenai kesan kandungan pasir halus di dalam pasir, ke atas ciri-ciri pemadatan didapati adalah terhad. Oleh itu, kajian ini telah melibatkan dua sampel pasir dasar sungai dan satu sampel pasir kuari yang telah dikumpul dari lokasi yang berbeza di Sarawak. Kajian ini bertujuan untuk mengkaji kesan kandungan pasir halus (sampel yang melepasi ayak bersaiz 75 µm) terhadap ciri-ciri pemadatan. Ketiga-tiga sampel pasir kemudiannya diadun semula dengan nisbah kandungan pasir halus yang berbeza (5%, 10%, 20% dan 30%) sebagai sampel untuk ujian. Ujian pemadatan telah dijalankan menggunakan ujian piawai Proctor. Keputusan yang diperoleh daripada ujian menunjukkan bagi sampel pasir dasar sungai, dengan peningkatan kandungan pasir halus sebanyak 30%, ketumpatan kering maksimum bartambah sebanyak 9.36% & 4.12%, dan kandungan air optimum berkurang sebanyak 18.88% & 24.6%. Sementara itu bagi sampel pasir kuari, dengan peningkatan kandungan pasir halus sebanyak 30%, ketumpatan kering maksimum bartambah sebanyak 9.67%, dan kandungan air optimum berkurang sebanyak 43.5%. Keputusan yang diperolehi mungkin boleh digunakan sebagai simulasi kepada langkah-langkah pemadatan yang dilakukan di tapak pembinaan. iii

6 TABLE OF CONTENTS CONTENTS PAGE Title page Dedication ACKNOWLEDGEMENT 1 ABSTRACT 11 ABSTRAK 111 TABLE OF CONTENT iv LIST OF TABLES vi LIST OF FIGURES vii LIST OF NOMENCLATURES xi CHAPTER 1 INTRODUCTION 1.1 General 1.2 Statement of problem 1.3 Objectives of present research 1.4 Organization of the project report CHAPTER 2 LITERATURE REVIEW 2.1 General 2.2 Mechanism of soil compaction 2.3 Compaction characteristics 2.4 Concluding remarks iv

7 CHAPTER 3 METHODOLOGY 3.1 General Test material Test programme Test procedure Separation of materials Determination of physical properties Determination of engineering properties 31 CHAPTER 4 EXPERIMENTAL RESULT AND DISCUSSION 4.1 General Sieve Analysis (Original sample) Sieve analysis (Reconstitute sample) Specific gravity tests Compaction tests 39 CHAPTER 5 CONCLUSION AND RECOMMENDATION 5.1 Conclusion Recommendation 47 REFERENCES 48 APPENDIX A 52 APPENDIX B 71 APPENDIX C 75

8 LIST OF TABLES TABLES PAGE Table 3.1. Designation for the original and fine samples 28 collected from different locations Table 3.2. Details of test programme 29 Table 4.1. Physical (index) properties of original sand samples 34 Table 4.2. Physical (index) properties of reconstitute sample 1, 37 sample 2 and sample 3 Table 4.3. Specific gravity values of reconstitute sample 1,39 Table 4.5. Maximum dry density [ Yd(,,, ax)] with increase of fine 43 contents Table 4.6. Optimum moisture content (w %) with increase of 43 fine contents vi

9 LIST OF FIGURES FIGURES PAGE Fig Weight volume relationship 8 Fig Mechanism of soil compaction 9 Fig Typical moisture content - dry density relationship 15 Fig Typical compaction test curves 18 Fig Moisture-density relationships of seven soils 20 Fig Grain size distribution curve for three original samples 33 Fig Grain size distribution curves for sample I with various 35 proportions of fines Fig Grain size distribution curves for sample 2 with various 36 proportions of tines Fig Grain size distribution curves for sample 3 with various 36 proportions of fines Fig Compaction test result for sample 1 41 Fig Compaction test result for sample 2 41 Fig Compaction test result for sample 3 42 Fig Response of tine content percentage with maximum dry density 44 Fig Response of fine content percentage with optimum 44 moisture content Fig. A. 1. Grain size distribution curve for sample 1 53 \ü

10 Fig. A. 2. Grain size distribution curve for sample 2 54 Fig. A. 3. Grain size distribution curve for sample 3 55 Fig. A. 4. Grain size distribution curve for sample I with 0% fine content 56 Fig. A. 5. Grain size distribution curve for sample I 57 with 5% fine content Fig. A. 6. Grain size distribution curve for sample I 58 with 10% fine content Fig. A. 7. Grain size distribution curve for sample 1 59 with 20% fine content Fig. A. 8. Grain size distribution curve for sample 1 60 with 30% fine content Fig. A. 9. Grain size distribution curve for sample 2 61 with 0% fine content Fig. A. 10. Grain size distribution curve for sample 2 62 with 5% fine content Fig. A. 11. Grain size distribution curve for sample 2 63 with 10% fine content Fig. A. 12. Grain size distribution curve for sample 2 64 with 20% fine content Fig. A. 13. Grain size distribution curve for sample 2 65 with 30% fine content Fig. A. 14. Grain size distribution curve for sample 3 66 with 0% fine content Fig. A. 15. Grain size distribution curve for sample 3 67 with 5% fine content Fig. A. 16. Grain size distribution curve for sample 3 68 with 10% tine content viii

11 Fig. A. 17. Grain size distribution curve for sample 3 69 with 20% fine content Fig. A. 18. Grain size distribution curve for sample 3 70 with 30% fine content Fig. C. l. Compaction test result for Sample I with 0% fine content 77 Fig. C. 2. Compaction test result for Sample 1 with 5% fine content 79 Fig. C. 3. Compaction test result for Sample I with 81 10% fine content Fig. C. 4. Compaction test result for Sample I with 83 20% fine content Fig. C. 5. Compaction test result for Sample I with 30% fine content 85 Fig. C. 6. Compaction test result for Sample 2 with 87 0% fine content Fig. C. 7. Compaction test result for Sample 2 with 89 5% fine content Fig. C. S. Compaction test result for Sample 2 with 91 10% fine content Fig. C. 9. Compaction test result for Sample 2 with 93 20% fine content Fig. C. 10. Compaction test result for Sample 2 with 95 30% fine content Fig. C Compaction test result for Sample 3 with 97 0% fine content Fig. C. 12. Compaction test result for Sample 3 with 99 5% fine content ix

12 Fig. C. 13. Compaction test result for Sample 3 with % fine content Fig. C. 14. Compaction test result for Sample 3 with % fine content Fig. C. 15. Compaction test result for Sample 3 with % fine content r

13 LIST OF NOMENCLATURES %- Percentage µm - micron cc - Coefficient of curvature C - Coefficient of uniformity D) - Grain diameter at 10% passing D3, ) - Grain diameter at 30% passing D60 - Grain diameter at 60% passing Dr - Relative density gcm3 - Gram per centimeter cubic G, - Specific gravity OMC - Optimum moisture content SM Silty sand - SP - Poorly graded sand SW - Well graded sand USCS - Unified Soil Classification System w- Water content y- Unit weight ydr\ - Dry unit weight 'fdr iiiar) - Maximum dry unit weight xi

14 CHAPTER 1 INTRODUCTION 1.1 General As a construction material, soil has been used since antiquity with both success and failure. The widespread availability and relative economy of earth material continue to make it attractive for use in foundations, embankments, and as backfill. It has long been recognized, first empirically and then scientifically, that compaction changes the physical properties of soils- in some cases tremendously. But, it also may result in a change of workability of the soil that will ease handling during construction. For example, properly compacted, well- graded gravel may be 15 times as resistant to deformation under a bearing load as the same material in the loose state (Hilf, 1991). To be used effectively, compaction must be tailored to the soil type, moisture condition, and subsequent environment of the compacted product. Thus, the ability of the engineer or job superintendent to identify the soil type accurately takes on prime importance. Wasted effort, such as that in attempting to compact clean sand with sheepfoot rollers, can result from inattention to the recognition of soil type. The fallacy of making twice as many passes of the roller

15 in an attempt to compensate for overly thick layers or overly wet soil can be avoided by an understanding of the compaction process. Compaction is the process by which a mass of soil consisting of solid soil particles, air, and water is reduced in volume by the momentary application of loads, such as rolling tamping or vibration. Compaction involves an expulsion of air without significantly changing the amount of water in the soil mass. Thus, the moisture content of the soil is normally the same for a loose, uncompacted soil as for the same soil after compaction to a denser state. Since the amount of air is reduced without change in the amount of water in the soil mass, the degree of saturation increases. In most soils, however, the expulsion of all the air cannot be achieved by compaction; hence 100 percent saturation does not occur. Compaction of the soil generally increases its density thus shear strength, decreases its compressibility, and its permeability. When considering the compaction of soils, two broad classifications of soils can be considered separately, cohesive and cohesionless soils. An important characteristic of cohesive soils is the fact that compaction improves their engineering properties of shear strength and compressibility. Studies of compacted soil at microlevel have shown that soils compacted on the dry side of optimum moisture content have a flocculent structural arrangement of particles. On the wet side of optimum moisture content, the structure is dispersed. Although there are several laboratory compaction standards and many different types of compactive efforts used in construction of compacted fills of cohesive 7

16 soils, the effect of the water content of the soil on the resulting dry density (dry unit weight) is similar for all methods. For each compaction procedure there is optimum moisture content that results in the greatest dry density or state of compactness with a peaked curve relationship between water content and dry density. Cohesionless soils are relatively pervious even when compacted. They are not affected significantly by water content during the compaction process. Instead, cohesionless soil is a function of relative density. With this type of structure, no important difference noted out between a natural deposit or fill provide both at same density. Consequently, the peaked curved relationship between dry density and water content may be ill defined or nonexistent for clean sands and gravels. Most obviously it is evident that greater energy input results in greater densification. But, logically, as higher energies are used, greater compaction results and further densification becomes increasingly difficult. Thus, for these soils the Proctor density curve concept may be questionable; though in practice engineers and professionals still using the Proctor concept on the ground that the till materials normally contain some fine materials. 3

17 1.2 Statement of the problem Comprehensive studies on the effect of fine content on laboratory maximum density and optimum moisture content of sandy soils appeared to be very limited. Most of the past studies were concentrated on the effect of compaction energies and moisture content on the dry density of soils. It seemed important, for practical purposes, to know the effects of fine content on both the dry density and necessary water content for a minimum compacting effort. With this view, the present study is concentrating at the investigating of some physical and compaction characteristics (maximum dry density and optimum moisture content) of sandy soil. Sand samples from several selected locations are to be collected and fractions be separated to remix them in desired proportions to prepare sand samples having various proportions of fine contents. Standard laboratory compaction tests are to be done to obtain maximum dry density and optimum moisture content. Some other physical properties of the collected and reconstituted samples and the consistency properties of the fines are also to be performed. The findings of the study may be used in any sand fill project by performing simple test like grain size analysis instead of more complicated and expensive laboratory tests for the determination of maximum dry density and optimum moisture content. 4

18 1.3 Objectives of the present research The present study is aimed at correlating the properties like grain size, maximum dry density, optimum moisture, and consistency limits of fine materials of sandy soils with fines. The objectives of the present study may be summarized as under; (i) To study the effects of fine contents on the compaction characteristics like maximum dry density and optimum moisture content of sandy soils with fines. (ii) To investigate the effect of soil fineness (fineness modulus as used in material science) on such compaction properties. 1.4 Organization of the project report The investigation scheme is presented in this report with five chapters. The introduction of the study is contained in chapter 1. The second chapter includes the review of related literatures. Chapter three covers test programme, procedure and testing materials. Chapter four is the experimental results and discussion. Chapter five presents the conclusion of the study and suggests the recommendations for future research.

19 CHAPTER 2 LITERATURE REVIEW 2.1 General Construction like earth fill dam, roadways and embankments really apply compaction effort for construction. Original soil may not perfectly tough or fix the criteria needed to protect the construction. Thus, the critical condition of soil or the fill (termed as 'borrow') is improved by increasing their density in order to stabilize the soil. An earth fill dam is constructed of compacted uniformly and intensively in relatively thin layers and at controlled moisture content, so that it function like tank carries water. As air void is expelled in compaction, it is the greatest determining factor in dense graded for pavement performance that carry heavy traffics. Thus, compaction is significant and being a part of construction. In spite of this, however, the compaction performance depends much on the physical properties of soil, where the appearances of the particles in soil mass influence the result of compaction. The aim of the present study is, thus, to investigate the effect of fine content on the compaction characteristics like maximum dry density and optimum moisture content (OMC) of sandy soil. In the following articles the related literature are briefly presented.

20 2.2 Mechanism of soil compaction Discrete particles that form whole soil mass are not strongly bonded together, hence they can still move freely with respect to one another once disturbing energy is applied. However, it is not as easy when compared to elements that accompany by fluid. Thus, soil is inherently a particulate system. Generally, when load is transmitted to soil, contact forces developed between adjacent particles. It can be said that deformation of soil mass is controlled by interactions between individual particles, especially sliding between particles. The interparticle forces, in conjunction with the external forces at the time of formation of the soil and the stress history, are responsible for the structure of a compacted cohesive soil (Seed et al., 1961). Leroueil and Vaughan (1990) states that the effects of structure are as important in determining engineering behavior, as are the effects of initial porosity and stress history'. Existence of spaces (voids) among the soil particles, called pore space usually filled with air or water (with or without dissolved materials). Thus, the soil is naturally a multiphase system, as shown in Fig. 2.1, that consists a mineral phase and fluid phase (both water and air), called pore fluid. In case of very tiny soil particles, the pore fluid may intrude between the particles. Although particles are no longer in contact in usual way, they still remain in close proximity can transmit the load, also tangential force. The pore space between particles tends to decrease or increase as the transmitted compressive forces decrease or increase. 7

21 Soil Skeleton Phase Diagram Phase Diagram Phase Diagram Air Fully Saturated Dry Soil Fig Weight volume relationship Thus, soil is inherently multiphase, and the constituents of the pore phase will influence the nature of the mineral surfaces and hence affect the processes of force transfer at particles contact. This phenomenon is known as chemical interaction. By reducing the air voids, more soil can be added to the block. When moisture is added to the block (water content, w, is increasing) the soil particles will slip more on each other causing more reduction in the total volume, which will result in adding more soil and, hence, the dry density will increase accordingly. The phenomenon is illustrated in Fig

22 Add More App lying Load More Load Sail /`ý' ý. e Mack AJr Air 4s S ail Block Before Compaction 01 Block After C ompaction O1 Block After Mar e Compaction Increasing Dry Density of the Soil Fig Mechanism of soil compaction Soil can be perfectly dry (no water contents) and full saturated or partly saturated (with both water and air). Water flows in soil from high energy to low point of energy and relate to amount of pressure applied to soil. More permeable the soil, water movement get better for a given excess of pressure. The flow also altering the magnitude of forces at the contacts between particles and influences the compression and shear resistance of soil. Because the soil is multiphase system, it may in expectation that load given to soil mass would be carried in part by pore fluid. When load is applied to a soil is suddenly changed, this change is carried jointly by pore fluid and mineral skeleton. Changes in pore pressure will cause water to move through soil; hence the properties of soil essentially change with time. 9

23 2.3 Compaction characteristics Degree of compaction of soil is measured by dry unit weight, 7d, 1, and water content, w. Most important factors that affect the soil compaction are; type of soil, water content, compaction effort, and lift thickness. From the past experience, it shows that there is maximum density, at which a given soil can be compacted using a particular compaction effort. For each soil and given compactive effort, there is unique water content that produces maximum density and is called optimum moisture content. Normally, the soil to be used is compacted in laboratory over a range of water contents, using standard Proctor compaction procedures. The compaction effort used is selected on the basis of requirements of the structure. Discusser believes that estimating the laboratory maximum dry density unit weight is one of the major factors that lead to poor quality backfill and resulting lawsuits, Day (1999). Cohesionless soils are relatively pervious even when compacted; they are not affected significantly by their water content during the compaction process. Consequently, the peaked curved relationship between dry density and water content (Proctor curve) that is characteristic of all cohesive soils is ill defined or nonexistent for clean sands and gravels. For a given compactive effort on the later soils, the dry density obtained is high when the soil is completely saturated, with somewhat lower densities occurring when the soil has intermediate amounts of water. The explanation for this involves phenomenon of bulking in sands, where small capillary stresses in the partly saturated soil tend to resist the I()

24 compactive effort. This bulking phenomenon is not present in completely dry sand and disappears when the moist sand is saturated. For these soils, where the Proctor curve concept is not applicable, the normally used compaction criterion is relative density, introduced by Terzaghi (1925). Burmister (1948) showed that the relative density of noncohesive soils was a more significant parameter than dry density alone in so far as engineering properties of the soil are concerned. His work has been verified and extended by other investigators (D'Applonia, 1970). Tests were made in 1956 by the Bureau of Reclamation in the one-dimensional consolidation apparatus with the sand in wet condition. Tests showed that this sand is more than twice as compressible at a relative density of about 40% as it is at a relative density of 70 %. The effect of relative density on compressibility is accentuated at higher loads; for example, under 25-psi load the consolidation (volume change) is 0.86 % for a relative density of 73.1 % and 1.86 % for a relative density of 39.4 %, but under load of 200-psi, the consolidations are 1.7 and 5.1, respectively, for those relative densities. Terzaghi and Peck (1967) reported similar results for compressibility of confined layers of loose and dense sand and showed that the shape of particles affect volume change under load; sands with flat particles (sand-mica mixtures) are more compressible than sand alone. Crushing of sand grains appeared to occur at pressure of about 100 kg/cm2. Roberts and DeSouza (1959) conducted Ii