Lab _2 - UNIVERSITY OF CALIFORNIA DAVIS Department of Civil...

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UNIVERSITY OF CALIFORNIA DAVIS Department of Civil and Environmental Engineering ECI 171L Soil Mechanics Laboratory Laboratory Assignment # 2 MEMORANDUM To: ECI 171L Students Date: April 13 -1 6 , 200 9 From: ECI 171L TAs Subject: Grain Size Analysis (Hydrometer Analysis) and Index Properties (Atterberg Limits) of Fine Grained Soils . Purpose: The purpose of this laboratory exercise is to learn how to perform grain size analysis and Atterberg limits of fine grained soils. These results are used together with the grain size distribution information determined in Laboratory #1 to classify the test soils using the Unified Soil Classification System. Standard Test Methods: The experiments are performed as follows in general accordance to ASTM Standards D4318: Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils and D422: Standard Test Method for Particle Size Analysis of Soils Theory and Definitions: Hydrometer Analysis: As learned in Laboratory #1, the grain size distribution of coarse grained soils is determined by using a series of sieves ranging in aperture size. The lower limit of this method is fixed by the #200 sieve (75 μ m opening size). An alternative method, the hydrometer test, is an indirect technique used to determine the grain size distribution for the fine grained particle size range. It is based on the theory of Stoke's Law for the terminal velocity of spheres falling through a viscous medium. To obtain the velocity of fall of soil particles, a hydrometer is used. This instrument consists of a lead weighted glass tube, which is calibrated to read either the specific gravity (151H) or grams/liter (152H) of a soil-water suspension. The suspension is formed by mixing a given quality of soil with water and a small amount of dispersing agent to form a 1000 ml quantity of suspension. A dispersing agent is usually added to neutralize the particle charges on the smaller soil particles. Charged particles can form larger particles called flocs which settle out of suspension faster than true particle sizes.
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During the test readings are taken at specified times by placing the hydrometer in the soil-water suspension. Atterberg Limits: The liquid limit of a soil is defined as the water content at which a soil possesses a small, but measurable shear strength. This limit separates the viscous and plastic states of a soil. The plastic limit of a soil is defined as the water content at which a soil rolled into a 1/8" diameter just begins to crumble. This limit separates the plastic and semi-solid states of a soil. Equipments: For Hydrometer Analysis: Electronic Balance Hydrometer Cylinders Mixer Hydrometer Thermometer Mixing cup Beakers Distilled Water Sodium Hexametaphosphate (Dispersing Agent) Wash Bottles For Atterberg Limits: Casagrande Cup Grooving Tool Plexiglass Plate 1/8” Reference Rod Moisture Content Containers Electronic Balance Convectional Oven or Microwave Procedure: For Hydrometer Analysis (Note that the TA will have performed tasks 1-6 for you). As a class you are going to perform the hydrometer analysis for two soil samples.
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Lab _2 - UNIVERSITY OF CALIFORNIA DAVIS Department of Civil...

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