GRAIN SIZE DISTRIBUTION

Posted by : Saurabh Gupta Monday, August 25, 2014

GRAIN SIZE DISTRIBUTION

I.SIEVE ANALYSIS

OBJECTIVE

(a). Select sieves as per I.S specifications and perform sieving.
(b). Obtain percentage of soil retained on each sieve.
(c). Draw graph between log grain size of soil and % finer.

NEED AND SCOPE OF EXPERIMEN
The grain size analysis is widely used in classification of soils. The data obtained from grain size distribution curves is used in the design of filters for earth dams and to determine suitability of soil for road construction, air field etc. Information obtained from grain size analysis can be used to predict soil water movement although permeability tests are more generally used.

PLANNING AND ORGANISATION

Apparatus

1.Balance

2.I.S sieves

�� 3.Rubber pestle and mortar.

�� 4.mechanical Sieve Shaker

�� The grain size analysis is an attempt to determine the relative proportions of different grain sizes which make up a given soil mass.

KNOWLEDGE OF EQUIPMENT

1.The balance to be used must be sensitive to the extent of 0.1% of total weight of sample taken.

2.I.S 460-1962 are to used. The sieves for soil tests: 4.75 mm to 75 microns.

PROCEDURE

1.For soil samples of soil retained on 75 micron I.S sieve

(a) The proportion of soil sample retained on 75 micron I.S sieve is weighed and recorded weight of soil sample is as per I.S 2720.

(b) I.S sieves are selected and arranged in the order as shown in the table.

(c) The soil sample is separated into various fractions by sieving through above sieves placed in the above mentioned order.

(d) The weight of soil retained on each sieve is recorded.

(e) The moisture content of soil if above 5% it is to be measured and recorded.

2.No particle of soil sample shall be pushed through the sieves.

OBSERVATIONS AND RECORDING

Weight of soil sample:

Moisture content:

I.S sieve number or size in mm	Wt. Retained in each sieve (gm)	Percentage on each sieve	Cumulative %age retained on each sieve	% finer	Remarks
4.75
4.00
3.36
2.40
1.46
1.20
0.60
0.30
0.15
0.075

GRAPH

Draw graph between log sieve size vs % finer. The graph is known as grading curve. Corresponding to 10%, 30% and 60% finer, obtain diameters from graph are designated as D_10, D_30,D_60.

CALCULATION

The percentage of soil retained on each sieve shall be calculated on the basis of total weight of soil sample taken.
Cumulative percentage of soil retained on successive sieve is found.

II.HYDROMETER ANALYSIS

OBJECTIVE

Grain size analysis of soils by hydrometer analysis test.

SPECIFIC OBJECTIVE

1. To determine the grain size distribution of soil sample containing appreciable amount of fines.

2. To draw a grain size distribution curve.

NEED AND SCOPE OF THE EXPERIMENT

For determining the grain size distribution of soil sample, usually mechanical analysis (sieve analysis) is carried out in which the finer sieve used is 63 micron or the nearer opening. If a soil contains appreciable quantities of fine fractions in (less than 63 micron) wet analysis is done. One form of the analysis is hydrometer analysis. It is very much helpful to classify the soil as per ISI classification. The properties of the soil are very much influenced by the amount of clay and other fractions.

APPARATUS

1. Hydrometer

2. Glass measuring cylinder-Two of 1000 ml capacity with ground glass or rubber stoppers�� about 7 cm diameter and 33 cm high marked at 1000 ml volume.

Thermometer- To cover the range 0 to 50^o C with an accuracy of�� 0.5 ^oC .
Water bath.
Stirring apparatus.
I.S sieves apparatus.
Balance-accurate to 0.01 gm.
Oven-105 to 110.
Stop watch.
Desiccators
Centimeter scale.
Porcelain evaporating dish.
Wide mouth conical flask or conical beaker of 1000 ml capacity.
Thick funnel-about 10 cm in diameter.
Filter flask-to take the funnel.
Measuring cylinder-100 ml capacity.
Wash bottle-containing distilled water.
Filter papers.
Glass rod-about 15 to 20 cm long and 4 to 5 mm in diameter.
Hydrogen peroxide-20 volume solution.
Hydrochloric acid N solution-89 ml of concentrated hydrochloric acid.(specific gravity 1.18) diluted with distilled water one litre of solution.
Sodium hexametaphosphate solution-dissolve 33 g of sodium hexametaphosphate and 7 gms of sodium carbonate in distilled water to make one litre of solution.

CALIBRATION OF HYDROMETER

Volume

(a) Volume of water displaced: Approximately 800 ml of water shall be poured in the 1000 ml measuring cylinder. The reading of the water level shall be observed and recorded.

The hydrometer shall be immersed in the water and the level shall again be observed and recorded as the volume of the hydrometer bulb in ml plus volume of that part of the stem that is submerged. For practical purposes the error to the inclusion of this stem volume may be neglected.

(b) From the weight of the hydrometer: The hydrometer shall be weighed to the nearest 0.1 gm.

The weight in gm shall be recorded as the volume of the bulb plus the volume of the stem below the 1000 ml graduation mark. For practical purposes the error due to the inclusion of this stem may be neglected.

Calibration

(a ) The sectional area of the 1000 ml measuring cylinder in which the hydrometer is to used shall be determined by measuring the distance between the graduations. The sectional area is equal to the volume include between the two graduations divided by the measured distance between them.

�Place the hydrometer on the paper and sketch it. On the sketch note the lowest and highest readings which are on the hydrometer and also mark the neck of the bulb. Mark the center of the bulb which is half of the distance between neck of the bulb and tip of the bulb.

(b) The distance from the lowest reading to the center of the bulb is (R_h) shall be recorded

(R_h�=H_L + L/2).

(d) Draw a graph hydrometer readings vs H_H and R_H. A straight line is obtained. This calibration curve is used to calibrate the hydrometer readings which are taken with in 2 minutes.

(e) From 4 minutes onwards the readings are to be taken by immersing the hydrometer each time. This makes the soil solution to rise, there by rising distance of free fall of the particle. So correction is applied to the hydrometer readings.

(f) Correction applied to the R_h and H_H

V_h= Volume of hydrometer bulb in ml.

A� =Area of measuring cylinder in cm².

From these two corrected readings draw graph (straight line)

Grain Size Distribution in Soil-Data and Calculation Chart

Date:

Sample No:

Total weight of dry soil taken, W =

Specific Gravity of soil, G =

Hydrometer No.��_____________ � Wt. Of soil gone into solution ,W_s =

Meniscus correction, C_n =�� Dispersion agent correction =

Reading in water RW�� =

Temperature correction�� =

% finer for wt. Of soil W_s gone into solution�� N=[(100G)/{W_s x (G �1)}] x R

Date	Time	Elapsed Time in Sec	Hydrometer reading upper Meniscus R_h � 1000	Corrected hydrometer Reading (1- lower meniscus C_m)	Z_r _or _Z^l_r	Velocity Cms/sec V=Z�r/K or _Z^l_r/ t	Equivalent dia. Of Particle D_�mm	R	N(%finer Thanfor soil)	REMARKS