mekanika tanah - sieve analysis

SIEVE TESTUji Ayakan

Mektan Kuliah 2

Out Line Slide

• 1.Engineering consideration of soil particles• 2.Sieve test• 3.Hydrometer test• 4.Particle distribution• 5.Shape of soil particles

Definitions for SOIL

• Engineering definitions:Civil Engineering:• Soil is the earth material that can be disaggregated in water

by gentle agitation.Construction:• Soil is material that can be removed by conventional means

without blasting. similar to the definition of regolith in geological terms.

Agronomy definition:• Soil consists of the thin layers of the earth’s crust formed

by surface weathering that are able to support plant life.

Soil particles

• The description of the grain size distribution of soil particles according to their texture (particle size, shape, and gradation).Major textural classes include:– gravel (>2 mm);– sand (0.1 – 2 mm);– silt (0.01 – 0.1 mm);– clay (< 0.01 mm).

• Furthermore, gravel and sand can be roughly classified as coarse textured soils, wile silt and claycan be classified as fine textures soils.

• For engineering purposes, soils can also be divided into cohesive and non-cohesive soils. Non-cohesive means the soil has no shear strength if no confinement. Cohesive soil contains clay minerals and posses plasticity.

• In engineering practice, plasticity is defined as the ability to be rolled into thin thread before breaking into pieces. Clay is cohesive and plastic. For example, mud sticking on shoes in a rainy day when one walk in a field. Sand is non-cohesive and non-plastic.

Procedure for grain sizedetermination

• Sieving - used for particles > 75 µm• Hydrometer test - used for smaller particles

(f< 75 µm)– Analysis based on Stoke’s Law, velocity

proportional to diameter

• A sieve test apparatus in a soil mechanics laboratory, (Das, Fig. 2.15)

Sieve Test

First of all, let’s discuss the sieve that is the essential tool to study particle size distribution for the grain size greater than 0.075 mm (75 microns).U.S. Standard Sieve Sizessieve # Sieve opening (mm)4 4.7510 2.0020 0.85040 0.42560 0.250100 0.150200 0.074

Sieve test procedure:

the total mass of the soil sample (SM) under sieve test;1, determine the mass of soil retained on each sieve and the pan at last (i.e.,

M 1 , M 2 , M 3 , …. M n , and M p ).2, the sum of soil mass retained on each sieve plus the mass in the pan

should be equal to the total mass (SM=M 1 +M 2 +M 3 +…. +M n +M p ).3, determine the cumulative mass of soil retained above each sieve, for the

ith sieve we have SM i= M 1 +M 2+M 3 +…. +M i.4, the mass of soil passing the ith sieve is SM - SM i= SM – (M 1 +M 2+M 3 +….

+M i ) .5, the percent of soil passing the ith sieve (percent finer) is 100

Example: If you have a soil sample with a weight of 150 g, afterthorough sieving you get the following result.

sieve# size(mm) W(g) % accum% 100-accum%4 4.750 30.0 20 20 8020 0.850 40.0 26.7 46.7 53.360 0.250 50.0 33.3 79 21100 0.150 20.0 13.3 92 8200 0.074 10.0 6.67 98 2

• The last column shows the percentage of material finer than that particular sieve size by weight.

No Ayakan Lubang

Masa Tanah Tertinggal tiap ayakan %Tertinggal % lolos

4 4.75 0 0.0% 100.00%

10 2 21.6 4.8% 95.20%

20 0.85 49.5 11.0% 84.20%

40 0.425 102.6 22.8% 61.40%

60 0.25 89.1 19.8% 41.60%

100 0.15 95.6 21.2% 20.36%

200 0.106 60.4 13.4% 6.93%

PAN 31.2 6.9% 0.00%

Cu = D60 = 0.4= 3.33D10 0.12

Cc = (D30)2 = (0,19)2 = 0.75D60 x D10 0,4 x 0,12

Gradation:Gradation is a measure of the distribution of a particular soil sample. Larger gradation means a wider particle size distribution.Well graded poorly sorted (e.g., glacial till)Poorly graded well sorted (e.g., beach sand)The range of grain size distribution is enormous for natural soils. E.g., boulder can be ~1 m in diameter, and the colloidal mineral can be as small as 0.00001 mm = 0.01 micron

=> It has a tremendous range of 8 orders of magnitude.

Fine-grained soilThe hydrometer test uses Stokes equation (for the velocity of a free falling sphere in suspension) to determine grain size distribution smaller than #200 sieve.

The grain size distributions of soils are commonly determined by sieve (smallest being #200) and hydrometer procedures. In the hydrometer analysis the soil smaller than #200 sieve is placed in suspension and by use of Stokes' equation for the velocity of a free falling sphere the equivalent particle size and percent of soilin suspension are computed.

For soils with both fine and coarse grained materials a combined analysis is made using both the sieve and hydrometer procedures.


• Hydrometer test - used for smaller particles– Analysis based on Stoke’s Law, velocity

proportional to diameter

Stokes Law

• A sphere falling freely through a liquid of infinite extent will accelerate rapidly to a certain maximum velocity and will continue at that velocity as long as conditions remain the same.

• The relationship of the terminal velocity to the physical properties of the sphere and the liquid are expressed by Stokes' Equation as shown in the following page.

wherev: velocity of the particle settlementρs : density of soil particlesρw : density of waterη: viscosity of waterD: diameter of soil particles

However, by proper sample and laboratory technique all except Item 1 (soil particles are not always spherical) in the 7 factors can be controlled or minimized so that the resulting inaccuracies can be ignored in normal testing.

The shape of soil particles will vary from cubes to flakes with each of the shapes between these limits having different influence. Nevertheless, the results of the hydrometer analysis are valid if they are considered equivalent grain diameter rather than actual grain diameter.

• The particle distribution curves for 3 soil samples (West, Fig. 7.1)

LatihanHasil uji Ayakan (Sieve Test) Sample tanah seberat 500 gr

No Ayakan Lubang

Masa Tanah Tertinggal tiap ayakan

4 4.75 06 3.35 30

10 2 48.720 0.85 127.340 0.425 96.860 0.25 76.6

100 0.15 55.2200 0.075 43.4PAN 22

1. Tentukan Prosentase Masa tanah tertinggal

2. Gambarkan Kurva Distribusi Ukuran Butirnya

3. Tentukan D10, D30, D60 4. Hitung Koefisien

Keseragaman Cu 5. Hitung Koefisien Gradasi Cc

No Ayakan Lubang

Masa Tanah Tertinggal tiap

ayakan %Tertinggal % lolos

4 4.75 0 0% 100%

6 3.35 30 6% 94%

10 2 48.7 10% 84%

20 0.85 127.3 25% 59%

40 0.425 96.8 19% 39%

60 0.25 76.6 15% 24%

100 0.15 55.2 11% 13%

200 0.075 43.4 9% 4%

PAN 22 4% 0%

500 100%

Cu = D60 = 0.9= 7.50D10 0.12

Cc = D302 = (0,3)2 = 0.83D60 x D10 0,9 x 0,12

2. Un tuk Suatu Tanah diberikan Diberikan D10 = 0.08 mmD30 = 0.22 mmD60 = 0.41 mm

Hitung Koefisian Keseragaman dan Koefisien Gradasinya

Cu= 5.13Cc = 1.48

Latihan 3