Soil Mechanic Laboratory Lect Muhannd Waleed Majeed Grain

Soil Mechanic Laboratory Lect. Muhannd Waleed Majeed Grain Size Analysis Sources: Soil Mechanics – Laboratory Manual, B. M. DAS (Chapters 4 & 5) Soil Properties, Testing, Measurement, and Evaluation, C. Liu, J. Evett

Class Outlines n Grain size Analysis n n Chapter 4: Mechanical Method (Sieve Analysis) Chapter 5: Hydrometer Method

2 - Grain size Analysis n The knowledge of sizes of solid particles comprising a certain soil type and their relative proportion is useful because it is used in; Soils classification n Soil filter design n Predictions the behavior of a soil with respect to shear strength, settlement and permeability n

Grain size Analysis (Continue) n Two types of grain size analyses are typically performed Mechanical analysis also know as sieve analysis n Hydrometer analysis n

Sieve Analysis n ASTM D 421 n Applicable for soils that are mostly granular with some or no fines n The U. S. No. 200 sieve (0. 074 mm or 0. 0029 in) is the smallest sieve size typically used in practice n Small size is 500 g (why? )

Sieve Analysis (Cont. )

Sieve Analysis (Cont. ) n 3/8”, ¼” sieves is the size of the opening n No. 10 sieve …. has 10 apertures per linear inch n Use sieves No. 3/8”, No. 4, No. 10, No. 40, No. 140 & No. 200

Grain Size Distribution Curves D 60 D 30 D 10 0. 15 mm 0. 4 mm 0. 8 mm 0. 15 mm Civil Engineering - Texas Tech University 5. 3 0. 4 0. 15 0. 8 1. 33

Sieve Analysis (Cont. ) n D 60 - the diameter corresponding to 60% finer in the particle-size distribution curve n D 10 – effective size n Cu – coefficient of gradation, n Cc – coefficient of curvature, Note: If cu is relatively large, it indicates a well graded soil. Cu = 1 indicates that the soil grains are of approximately equal sizes.

Hydrometer Analysis n ASTM D 422 n This method is generally used to determine the particle- size distribution for soils with small grain sizes < 0. 075 mm (No. 200) n The lower limit of the particle size determined by this procedure is about 0. 001 mm n In the lab we will use ASTM 152 -H Hydrometer (? ) n This method is based on Stoke’s law “The larger the grain size, the greater its settling velocity in a fluid” n The sample size is 50 g passing #10 (why? )

Hydrometer Analysis (Cont. ) L =30

Hydrometer Test (Cont. ) n A Hydrometer reading of 30 means that there are 30 g of soil solids in suspension per 1000 cc of soil-water mixture at a temperature of 200 C n Take reading at 15, 30, 60 seconds then at 2, 5, 15, 30 and 60 minutes

Composite Corrections n Fm – Meniscus Correction Fm n Zero Correction, Fz Accounts for the effect of using a deflocculating agent n Temperature Correction, FT FT = - 4. 85 + 0. 25 T (T between 15 – 280 C) n Composite Correction = Fm + Fz + FT

Hydrometer Test (Procedure) 1. Prepare a deflocculating (dispersing) agent n n Use a 4% solution of Sodium hexametaphophate (Calgon) Add the 40 g of Calgon in 1000 cc of distilled water and mix thoroughly 2. Use 45± 5 g of soil passing #10 3. Take 125 cc of the mixture prepared in (1) and add it to the soil in (2) and let it soak for about 8 – 12 hours

Hydrometer Test (Calculation - pp 30) n R – Hydrometer reading (col 2) n Rcp – corrected hydrometer reading for calculation of percent finer (col 3) Rcp = R + FT – Fz n Percent finer (col 4) = a = correction for Gs see Table 5 -3 pp 30 Assume Gs = 2. 65 n Rc. L - Corrected reading for determination of effective length (col 5) & Find L from Table 5 -1 pp 26 Rc. L = R + Fm n Determine D =