Overview
This lecture covers laboratory procedures for particle size analysis in soils, focusing on mechanical sieve analysis and hydrometer analysis, including equipment, steps, and key calculations.
Purpose of Particle Size Analysis
- Particle size analysis helps classify soils for geotechnical engineering applications.
- The results are used for soil description, quantitative classification, and permeability estimation using the Hazen equation.
Mechanical Sieve Analysis Procedure
- Separates coarse-grained soil fractions using stacked sieves (No. 4 to No. 200).
- Requires equipment: sieve stack, pan, lid, mechanical shaker, digital balance, and weighing tools.
- Weigh 500g of mixed, air-dried soil and record the mass.
- Pour the sample into the top sieve, assemble the stack, and secure with the lid.
- Place the stack in a mechanical shaker for 10 minutes.
- Remove and weigh material retained on each sieve and the pan.
- The soil passing the No. 200 sieve is the fine-grained fraction for hydrometer analysis.
- Total retained mass should be within ±2% of original mass; otherwise, repeat the test.
- Calculate percent passing each sieve as 100 minus the sum of percent retained on that sieve and all coarser sieves.
Hydrometer Analysis Procedure
- Used for fine-grained soil passing the No. 200 sieve.
- Equipment includes sedimentation jar, hydrometer, dispersion device, sodium hexametaphosphate, squirt bottle, evaporation dish, stopper, and thermometer.
- Weigh 60g of residual soil; mix with 125mL of 4% sodium hexametaphosphate, let stand 15 minutes.
- Calibrate the hydrometer in a control jar to determine zero and meniscus correction factors.
- Transfer soil to dispersion cup, fill halfway with water, mix for 2 minutes.
- Pour into sedimentation jar, fill to 1,000mL, cap, and agitate 30 times in 1 minute.
- Let settle undisturbed for 24 hours; take hydrometer and temperature readings at set times (2, 4, 8, 16, 30 min, 1, 2, 4, 8, 24 hr).
- Use hydrometer readings and time history to calculate grain size distribution of fine particles.
Key Terms & Definitions
- Mechanical Sieve Analysis — Lab method using stacked screens to separate and weigh soil fractions by size.
- Hydrometer Analysis — Measures suspension density over time to determine fine particle distribution.
- Percent Passing — Percentage of soil mass smaller than a given sieve size.
- Grain Size Distribution Curve — Graph of cumulative percent finer vs. particle diameter (log scale).
- Sodium Hexametaphosphate — Chemical dispersing agent to break soil particle cohesion.
- Meniscus Correction — Adjustment for reading hydrometer at the top of the liquid meniscus.
- Zero Correction — Calibration value specific to each hydrometer for accurate readings.
Action Items / Next Steps
- Download lab handout "CE 215 lab #3 and #4" and ASTM standards (ASTM C136, ASTM D422) from Blackboard.
- Complete data sheet for particle size analysis lab.
- Review plotted grain size distribution curves after analysis.