Geotechnical Engineering: Practical Size Analysis Mr. Rohan Dashupta, Asst. Professor Department: B.E. Civil Engineering Subject: Geotechnical Engineering - I Semester: V eCourseware@AIKTC Teaching Aids Service by KRRC Information Section

Particle Size or grain size refers to the diameter of a grain of soil. INTRODUCTION Particle Size or grain size refers to the diameter of a grain of soil.

INTRODUCTION Particle Size Analysis or Mechanical Analysis is the determination percentage of various sizes of particles in a given dry soil sample. It is the separation of soil into different size fractions.

Sedimentation Analysis or Wet Mechanical Analysis TYPES OF PARTICLE SIZE ANALYSIS There are 2 types of Particle Size Analysis: Sieve Analysis Sedimentation Analysis or Wet Mechanical Analysis

Sieves used for Sieve Analysis Mechanical Sieve Shaker

SIEVE ANALYSIS Course Analysis The portion of soil retained on 4.75 mm sieve is termed as gravel fraction and is kept for the course analysis. Fine Analysis The portion of soil passing through 4.75 mm sieve is termed subjected to fine analysis. 4.75 mm sieve

SIEVE ANALYSIS: INDIAN STANDARDS Indian Standard Specification for Test Sieves Course Sieve Analysis Fine Sieve Analysis 100 mm 2 mm 63 mm 1 mm 20 mm 600 micron 10 mm 425 micron 4.75 mm 300 micron - 212 micron 150 micron 75 microns

SIEVE ANALYSIS: OBSERVATION TABLE Sr. No. IS Sieve Particle Size D (mm) Mass Retained (gm) % Retained Cumulative % Retained % Finer (N)

SIEVE ANALYSIS: CALCULATION % Retained = (Mass Retained / Total Mass of Dry Soil Sample) x 100 Cumulative % Retained = Current % Retained + Previous % Retained Cumulative % Finer = 100 – Cumulative % Retained

Total Mass of Dry Soil Sample = 1000 gm Example Total Mass of Dry Soil Sample = 1000 gm Mass of Soil passing through 75 micron = 77 gm Sr. No. IS Sieve Particle Size D (mm) Mass Retained (gm) % Retained Cumulative % Retained % Finer (N) 1. 100 mm - 100 2. 63 mm 3. 20 mm 33 3.3 96.7 4. 10 mm 49 4.9 8.2 91.8 5. 4.75 mm 85 8.5 16.7 83.3 6. 2 mm 140 14 30.7 69.3 7. 1 mm 160 16 46.7 53.3 8. 600 μm 0.6 mm 142 14.2 60.9 39.1 9. 425 μm 0.425 mm 118 11.8 72.7 27.3 10. 300 μm 0.3 mm 82 80.9 19.1 11. 212 μm 0.212 mm 56 5.6 86.5 13.5 12. 150 μm 0.15 mm 35 3.5 90 10.0 13. 75 μm 0.075 mm 23 2.3 92.3 7.7

PARTICLE SIZE DISTRIBUTION CURVE The results of the mechanical analysis are plotted to get a particle size distribution curve with the percentage finer N on the Y-axis and particle diameter on the X-axis, the diameter being plotted on a logarithmic scale. The particle size diameter curve gives us an idea about the type and gradation of the soil. A curve situated higher up or to the left represents a relatively fine grained soil. A curve situated to the right represents a course grained soil. continued...

PARTICLE SIZE DISTRIBUTION CURVE Well Graded Soil = good representation of particles of all sizes Poorly Graded Soil = excess of certain particles and deficiency of other. Uniformly Graded Soil = most of the particles of the same size Gap Graded or Skip Graded Soil = intermediate particle sizes are missing

PARTICLE SIZE DISTRIBUTION CURVE For coarse grained soil, certain particle sizes such as D10, D30 and D60 are important. D10 represents a size, in mm such that 10% of the particles are finer than this size. The size D10 is sometimes called the effective size or effective diameter. D30 represents a size, in mm such that 30% of the particles are finer than this size. D60 represents a size, in mm such that 60% of the particles are finer than this size.