Sieve Analysis and Hydrometer Tests on Soil

Grain Size Distribution Test: Sieve Analysis and Hydrometer Test

Overview of the Grain Size Distribution Test

• The grain size distribution test consists of two main parts: testing coarse soil particles and fine grain portions.

• The sieve analysis test is used for coarse particles, while the hydrometer test is employed for fine grains.

Sample Preparation

• A bulk sample of approximately one kilogram of soil is collected for testing, which includes both coarse and fine particles.

• The first step involves a wash analysis to separate fine contents from coarse particles by rinsing with water. Fine materials that pass through a number 200 sieve (75 micrometers) are targeted for separation.

Soil Composition Insights

• The soil sample contains various particle sizes, including gravel (>4.75 mm), coarse sand, medium sand, and fine sand, resembling beach sand in texture.

• Finer particles such as silt and clay are also present but harder to distinguish visually within the mixture.

Washing Process

• During washing, fines are collected in a bucket using a number 200 sieve while ensuring minimal water flow to avoid losing material. This process helps clarify the water as fines are removed from the soil mixture.

• Continuous monitoring of water clarity indicates when sufficient fines have been washed out; clear water suggests effective separation of fine materials from coarser ones.

Final Steps in Sample Processing

• After washing, all coarse particles are placed in an oven to dry completely before conducting the sieve analysis test; this ensures accurate measurement without moisture interference.

• The remaining mixture containing fine particles will settle over several days, allowing clear water to form on top before further processing for hydrometer testing once dried out completely.

Hydrometer and Sieve Analysis Process

Overview of Testing Procedures

• The hydrometer test will be conducted alongside a sieve analysis to determine grain size distribution. Coarse particles are tested using a sieve shaker, while results from both tests will be combined for analysis.

• A stack of sieves is prepared for testing, with finer sieves at the bottom and coarser ones at the top. The arrangement includes number 4, 10, 20, 40, 60, 100, and 200 sieves.

• A pan collects fines that were not fully washed during the initial washing process. This mass will contribute to the hydrometer test analysis later.

Preparing for Sieve Analysis

• Before running the sieve shaker, each sieve must be cleaned and weighed to establish a baseline weight. This allows for accurate measurement of soil retained after shaking.

• The weight difference before and after shaking provides data necessary for constructing the grain size distribution curve.

Demonstration of Sieve Types

• An example of a coarse sieve (number four with openings of 4.75 mm) is shown alongside a finer sieve (number thirty-five with openings of 0.0164 inches), illustrating differences in particle retention capabilities.

• After placing soil on top of the coarser sieve and covering it with a lid, it is prepared for placement in the shaker to begin sorting by size.

Operating the Sieve Shaker

• The shaker's collar is secured tightly to prevent movement during operation. After approximately ten minutes in the shaker, it's time to disassemble and weigh each sieve.

• Each sieve is removed one by one; weights are recorded based on how much soil has been retained on them post-shaking.

Final Steps in Grain Size Distribution Analysis

• As finer materials are collected through various sieves down to number two hundred, any remaining fines indicate incomplete washing during preparation.

• Following this step, water from the wash containing clay and silt must be siphoned off carefully before drying all collected soil samples in an oven.

Conducting Hydrometer Test

• Once dried, fine particles are analyzed using a hydrometer—a glass tube designed to float within liquid mixtures—allowing measurement based on specific markings known as r sub t values.

• Calibration involves weighing the hydrometer first and measuring key height values (h1 value), which assists in accurately reading measurements against tick marks during testing.

Soil Testing Procedure Overview

Calibration and Preparation

• The calibration process is essential before starting the actual soil test, ensuring accurate measurements.

• A mixture of approximately 50 grams of dried soil, water, and a deflocculating agent (about five grams) is prepared to break up soil particles.

Mixing Process

• The soil-water mixture is blended using an automatic mixer until it forms a smooth paste before transferring it into a mixing cup.

• After adding the deflocculating agent, the mixture needs to be thoroughly mixed for 10 minutes to ensure all particles are well-separated.

Graduated Cylinder Setup

• The mixed solution is transferred into a graduated cylinder, rinsing with distilled water to ensure no residue remains in the mixing cup. The goal is to fill the cylinder up to the 1000 milliliter mark.

• Once filled, the mixture must be agitated for 30 seconds using an end-over-end method to prevent any soil from settling at either end of the cylinder.

Hydrometer Readings

• Hydrometer readings are taken at intervals (every quarter minute), starting from one minute after mixing begins; initial readings show gradual changes in density over time.

• After two minutes, further hydrometer readings indicate continued sedimentation and density changes as observed through repeated measurements every few minutes.

Final Observations

• After approximately 40 hours of allowing clay and silt to settle out of suspension in water, significant sediment accumulation can be observed at the bottom of the graduated cylinder. This indicates successful separation of soil components based on density differences.