Particle Size Analysis (Sieves and Hydrometer)

Summary

In this educational video, Dave Whinger from Missouri S&T Geotechnical Labs demonstrates particle size analysis procedures essential for geotechnical engineers to classify soils. The video covers two main methods: the mechanical sieve analysis for coarse-grained soil and the hydrometer analysis for fine-grained material. These tests help characterize soil for engineering applications, such as soil description and permeability correlations. The lab uses various equipment like sieves, a mechanical shaker, and a hydrometer, and follows specific standards for accurate results. The process involves soil sample preparation, mechanical sieving, and hydrometer readings over time to determine the soil's grain size distribution.

Takeaways

• 🔬 Particle size analysis is crucial for geotechnical engineers to classify soils and ensure they are suitable for engineering applications.
• 📐 The process involves two main procedures: mechanical sieve analysis for coarse grain fraction and hydrometer analysis for fine grain fraction.
• 🏗️ Mechanical sieve analysis uses a series of sieves to determine grain size distribution, while hydrometer analysis measures the specific gravity change of a soil-water mixture over time.
• 📏 For mechanical sieve analysis, a stack of sieves with different mesh sizes (from number 4 to number 200), a pan, a lid, a mechanical shaker, a digital balance, and a weighing pull are required.
• 🧪 The hydrometer analysis requires a 1000ml sedimentation jar, a control jar, a hydrometer, a soil dispersion device, sodium hexametaphosphate, a squirt bottle with water, an evaporation dish, a rubber stopper, and a thermometer.
• 🌊 The soil sample used in the video is a silt from the Mississippi River Valley, which has been mechanically pulverized and had coarse material added for the lab.
• 📋 The lab documents, including standards and data sheets, are available on Blackboard for reference, and the particle size analysis is part of a combination lab handout.
• ⏱️ The mechanical sieve analysis involves shaking a 500g sample of air-dried soil through a series of sieves and then determining the mass retained on each sieve.
• 📊 The percentage of soil particles finer than a specific sieve size is calculated, and the results are plotted to create a particle size distribution curve.
• 🕒 The hydrometer analysis involves soaking the soil in a sodium hexametaphosphate solution, dispersing it, and then measuring the specific gravity changes at various time intervals up to 24 hours.
• 📈 The final results from both tests provide a comprehensive grain size distribution of the soil, which is essential for soil classification and engineering applications.

Q & A

What is the purpose of particle size analysis in geotechnical engineering?

Particle size analysis is used by geotechnical engineers to classify soils and determine the grain size distribution within the soil, which is essential for soil description, quantitative soil classification, and correlations to permeability based on the Hazen equation.

What are the two procedures involved in particle size analysis?

The two procedures involved in particle size analysis are the mechanical sieve analysis and the hydrometer analysis. The mechanical sieve analysis is used for the coarse grain fraction, while the hydrometer analysis is conducted on the fine grain fraction of the soil.

What materials are considered fine grain according to the script?

Material that passes the number 200 sieve is considered fine grain material.

What are the required devices for conducting a mechanical sieve analysis?

The required devices for a mechanical sieve analysis include a stack of sieves ranging from number four to number 200, a pan, a lid, a mechanical shaker, a digital balance, and a weighing pull.

What is the role of sodium hexametaphosphate in the hydrometer analysis?

Sodium hexametaphosphate is used as a soil dispersion agent to break down the cohesion between soil particles, preventing them from sticking together during the hydrometer analysis.

How long should the soil be allowed to soak in sodium hexametaphosphate solution before the hydrometer analysis?

The soil should be allowed to soak in the sodium hexametaphosphate solution for 15 minutes before proceeding with the hydrometer analysis.

What is the significance of the zero correction factor in hydrometer analysis?

The zero correction factor is used to calibrate the hydrometer by determining the distance from the zero mark to the top of the meniscus on the hydrometer staff, ensuring accurate readings during the analysis.

How is the soil sample prepared for the hydrometer analysis after the soaking period?

After the 15-minute soaking period, the soil is transferred into a dispersion cup, mixed with water, and then poured into a clean sedimentation jar. The jar is then filled to the 1000ml mark and capped with a rubber stopper.

What is the duration for which the sedimentation jar should be left undisturbed during the hydrometer analysis?

The sedimentation jar should be left undisturbed for 24 hours during the hydrometer analysis.

At what time intervals should the hydrometer and temperature readings be recorded during the sedimentation process?

The hydrometer and temperature readings should be recorded at approximate intervals of 2, 4, 8, 16, 30 minutes, and then at 1, 2, 4, 8, and 24 hours.

How is the total retained mass computed after the mechanical sieve analysis?

The total retained mass is computed by adding the individual masses retained on each sieve and the pan. The total mass should be within plus or minus 2% of the original mass.