TITLE Sieve Analysis OBJECTIVES
To determine the particle-size distribution curve for a given soil sample. To determine the coefficient of uniformity (Cu) and coefficient of concavity (Cc) of soil.
INTRODUCTION In the sieve analysis process, soil is basically shaken through a set of sieves that have progressively smaller openings. Sieves that are taken for the process are U.S. standard sieves. Sieve analysis of soil is categorized under mechanical analysis of soil which determines the size range of particles present in a soil expressed as a percentage of the total dry weight. Sieve analysis can only be implemented for the soils with particle sizes larger than 0.075 mm in diameter (passing through No. 200 sieve). Where a large portion of the soil particles is smaller than 0.075 mm, hydrometer analysis is used to define the particle – size distribution.
THEORY Weight of soil retained = (weight of soil +sieve) – (weight of sieve) Percentage retained on any sieve = (Weight of soil retained/Total soil weight) x 100 Cumulative percentage retained on any sieve = sum of the percentages retained on the sieve Coefficient of uniformity (Cu); an indication of the spread of particle size which is calculated as, Cu = D60/D10 Coefficient of concavity (Cc); a measure of the shape of the curve between D60 and D10 grain size and is defined as; Cc = D230/ (D10 x D60) where D10, D30 and D60 are the soil diameters, at which 10%, 30%, and 60% soil weights are finer, respectively.
APPARATUS
Set of sieves (2.36mm, 1.18mm, 0.85mm, 0.6mm, 0.425mm, 0.25mm and 0.075mm) – U.S Standard Sieve shaker Sample splitter Larger evaporation dishes Spatula Brush Balance sensitive to 0.1 g Mortar and pestle
Figure 1: Set of sieves and the shaker (www.TheConstructor.org )
PROCEDURES Preparation of soil sample The air dried soil was used and aggregation of lumps were thoroughly broken up with the fingers. Large soil samples to be divided by using the sample splitter to preserve their grain size distribution. Testing procedure 1) 2) 3) 4)
Soil sample was oven dried and allowed it to cool. Weight of the sample was measured. Weight of the each sieve was recorded. Stack of sieves was arranged so that the largest mesh opening is at the top and the smallest is at the bottom. 5) Pan was attached to the bottom of sieves.
6) Sample was poured on the top sieve and cover plate was added to avoid and loss of particles while shaking. 7) Stack of sieve was placed on the mechanical shaker and stack was shaken horizontally for about 10 min.
REFERENCES Das, B. &. (2014). Principles of Geotechnical Engineering. Delhi: Cengage Learning. Shukla, R. L. (2005). Principles of Soil Physics. New York: Taylor & Francis. CE 281 – Geotechnical Engineering I– laboratory assignment, Sieve Analysis, (2 October 2016), http://courseweb.sliit.lk/mod/resource/view.php?id=53205 Particle Size Analysis of Soils AASHTO Designation T 88 (Mn/DOT Modified) viewed 2 October 2016, http://www.dot.state.mn.us/materials/manuals/laboratory/1302.pdf Mechanical Analysis of Soil, viewed 3 October 2016, http://www.ce.memphis.edu/1101/notes/filtration/filtration-2.html
TITLE Hydrometer Analysis OBJECTIVES
To determine the particle-size distribution of a soil sample where the particle size is smaller than 0.075 mm in size.
INTRODUCTION Hydrometer analysis is governed by the principal of sedimentation of soil grains in water. The settlement of a diffused soil sample in water depends on the shape, size, and weight of the soil particles and the viscosity of the water. Throughout the analysis soil particles are assumed to be spheres and the velocity of soil particles is expressed by Stoke’s law. THEORY “Stokes Law” provides the relationship among the terminal velocity of fall of sphere in a fluid, the diameter of a sphere, the weights of the sphere, and the viscosity of the fluid.
Hydrometer reading is a measure of soil mass in suspension at the level of the bulb. The grams of soil still in suspension after elapsed time t can be obtained from the actual hydrometer reading (Ra). To determine the correction (Cd) due to the dispersing agent on hydrometer readings, readings should be obtained within a sedimentation cylinder with distilled water and same amount dispersing agent as that used in soil-water suspension. Meniscus error (Cm) is usually occurred while readings are taken to the top of the meniscus due to the invincibility of bottom of the meniscus as it is surrounded by colored water. Hence, correction of meniscus (Cm) is applied to the hydrometer readings prior calculating the percentage finer of soil. Corrected hydrometer reading (Rc) = Ra – (Cd – Cm) hydrometer. Percentage finer (P) = (Rc x a x 100)/W % of a = 1.
where, Ra is the actual reading of the
where, W is the weight of soil in suspension and value
Weight of soil finer than a particular particle size in given soil fraction (W1) passing through No 200 sieve = (W1 x P) g Percentage finer than particular particle size of the soil sample used in sieve analysis; = ((W1 x P)/W2) x 100 where, W2 is the total weight of the sample used for sieve analysis.
APPARATUS
Hydrometer Mixer Dispersing agent Two graduated cylinders (1000 ml) Thermometer Balance sensitive to 0.1 g Timer Measuring cylinder Distilled water Drying oven Desiccator Syringe Large evaporation dishes Spatula
Figure 1: Reading a Hydrometer (www.bartech-co.com )
PROCEDURES Preparation of soil sample for Hydrometer Analysis. 50g of soil was accurately weighted. Weighted soil was placed in a beaker and 125 ml of the Sodium Hexametaphosphate solution (40g/litre) was added. Mixture was stirred using a mixture and kept to soak for 16 hours. Base solution of 1000ml and the same amount of dispersing agent was prepared in a separate measuring cylinder.
Soaked soil sample was transferred to the cup of mixer. Water was added to half fill the cup and it was stirred for 3 minutes. Soil water slurry was transferred to the glass sedimentation cylinder, and distilled water was added until the total water is 1000 ml. Cylinder was shaken vigorously by turning it upside down and back using the palm of the hand over the open end of the cylinder, for a period of 1 min or more, until a uniform suspension is formed. Hydrometer was inserted carefully into the soil-water suspension. Hydrometer readings were taken at following time intervals. ½ min, 1min, 2min, 4min, 8min, 15min, 30min, 1hr, 1.5 hrs and 24 hrs.
REFERENCES CE 281 – Geotechnical Engineering I– laboratory assignment, Hydrometer Analysis, (2 October 2016), http://courseweb.sliit.lk/mod/resource/view.php?id=23811 CIVILBLOG.ORG 2015, Hydrometer Analysis of soil – what, why & how? viewed 2 October 2016, http://civilblog.org/2015/11/18/hydrometer-analysis-of-soil-what-why-how/# Das, B. &. (2014). Principles of Geotechnical Engineering. Delhi: Cengage Learning. Dr. George Mylonakis 2005, ‘Hydrometer Analysis', The Lab Manual, The City College of New York. Importance of Particle Size Distribution Emphasized in Proposed ASTM Soil and Rock Standards, Shukla, R. L. (2005). Principles of Soil Physics. New York: Taylor & Francis.
