Lecture (4)

Mechanical Analysis of Soil Sieve Analysis Mechanical Analysis of Soil is the determination of the size range of soil particles, expressed as a percentage of total dry weight. The particle size distribution of soil can be fined by two methods. • The sieve analysis technique is applicable for soil grains larger than No. 200 (0.075 mm) sieve size. • For fine-grained soils the procedure used for determination of the grain-size distribution is hydrometer analysis. This is based on the principle of sedimentation of soil grains. • Particle Size Classification. (Amercian Association – (AASHTO ) 1/16

CLAY&SILT SAND % GRAVEL %PASSING SIEVE 200 COARSE MEDIUM FINE 4.75-75 mm 2.0-4.75 mm 0.42-2.0 mm 0.075-0.42 mm < (0.075 mm) For a basic understanding of the nature of soil, the distribution of the grain size present in a given soil mass must be known. The grain-size distribution of coarse-grained soils (gravelly and / or sandy) is determined by sieve analysis. the opening size of some U.S. sieves. Below, 2/16

U. S. standard sieves Sieve no. Opening size (mm) 4 4. 75 8 2. 38 10 2 3/16

Sieve Analysis consists of shaking the dried soil sample through a set of sieves having progressively smaller openings. • First the soil sample is oven dried. • All lumps are broken into small particles • The standard sets of sieves is placed in the sieve shaker and the sample is passed through the sieves. ( the duration of sieve shaker is about 10 minutes). • The portion of soil sample retained on each sieve is weighted. • Percentage passing are calculated, the resulting values are plotted on a semi-log. Scale. • The cumulative percent by Dry weight of a soil passing a given sieve is referred to as the percent finer 4/16

Figure below shows the results of a sieve analysis for a sandy soil Figure below shows the results of a sieve analysis for a sandy soil. The grain-size distribution can be used to determine some of the basic soil parameters, such as the effective size, the uniformity coefficient, and the coefficient of gradation. Grain-size distribution of a sandy soil. 5/16

• The effective size of a soil is the diameter through which 10% of the total soil mass is passing and is referred to as D10. Effective Diameter = D10 Cu Uniformity coeff. = D60 / D10 Cc Gradation coeff. = (D30 )2/ (D60 * D10 ) 6/16

A soil is called a well-graded soil if the distribution of the grain sizes extends over a rather large range. In that case, the value of the uniformity coefficient is large. Generally, a soil is referred to as well graded if Cu is larger than about 4–6 and Cc is between 1 and 3. When most of the grains in a soil mass are of approximately the same size—i.e., Cu is close to 1—the soil is called poorly graded. A soil might have a combination of two or more well graded soil fractions, and this type of soil is referred to as a gap-graded soil. 7/16

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I. Poor graded Soil – Most of the soil grains are the Same Size II I. Poor graded Soil – Most of the soil grains are the Same Size II. Well graded Soil - Soil particle sizes are distributed over a wide range. III. Gap graded Soil – Soil might have a combination of two or more uniformly graded fractions. 9/16

PARTICLE-SIZE ANALYSIS ASTM D 422 10/16

D10% = 0. 101 D30% = 0. 266 D60% = 0. 555 Effective Diameter = 0 D10% = 0.101 D30% = 0.266 D60% = 0.555 Effective Diameter = 0.101 cu uniformity coeff. = 5.471 Cc gradation coeff. = 1.260 Effective Diameter = D10 Cu Uniformity coeff. = D60 / D10 Cc Gradation coeff. = (D30 )2/ (D60 * D10 ) 11/16

PARTICLE-SIZE ANALYSIS ASTM D 422 12/16

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Pharos University Faculty of Engineering CV 256: Soil Mechanics Architectural Dept. Dr. Hassan Abd Ellatif     Sheet (2) Grain Size Analysis   Sieve analysis was made for four soil samples and the results are as shown in the following table:

Sieve (D) in mm Sample (A) Sample (B) Sample (C) Sample (D) (W retained) in gm 4.75 0.00 28 2.00 21.60 42 44 0.840 49.50 48 56 0.425 102.6 128 82 249.1 0.250 89.10 221 91 179.8 0.149 95.60 86 136 22.7 0.075 60.40 40 92 15.5 Pan 31.2 24 45 23.5

* Determine the percent finer than each sieve and plot a Grain -Size Distribution Curve for all the samples. * Calculate D10, D30 & D60 form the Grain -Size Distribution Curve for all the samples * Calculate the uniformity coefficient, Cu * Calculate the coefficient of gradation, Cc. * Comment about each sample gradation. * Classify each sample.