2B03-Lab1-Particle Size Analysis 2022

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ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 1 LAB #1 PARTICLE SIZE ANALYSIS Assigned: week of 3 Oct, Due begging of lab 2, week of October 24 INTRODUCTION In any given soil, grain size can range from extremely small clay particles to large stones and gravel. The grain size distribution of a soil can be determined by calculating the percentages of sand, silt and clay present in the sample. This particle size analysis can be used to assign a textural class to the soil, which controls the general physical properties of the soil. As mentioned in class, if there is ONE soil property that governs the rest, it is soil texture. There are several methods of particle size analysis, two of which will be performed in this lab: mechanical sieving and sedimentation by the hydrometer method. Mechanical Sieving involves measuring the mass of soil caught in each sieve against the original total weight of the sample; in order to calculate the percent of the soil that passed through each sieve. A plot of percent passing vs. grain size diameter can be obtained, representing the grain size distribution of the soil sample. This method of particle size analysis can be used for a large range of particle sizes (0.02 mm to 2.00 mm in diameter). However, the probability of a particle passing through a sieve depends on the nature of the particle, the number of particles of that size, and the properties of the sieve. As a result, this method often requires pretreatment of the sample in order to achieve good results. Pretreatment can involve the removal of moisture, carbonates, soluble salts and organic matter by heating and chemical reactions. In addition, further preparation could involve physically removing all visible organic material, including grass clumps, roots, branches etc, and breaking up hard soil chunks with a rubber mallet. However, due to time restrictions, it is not possible to perform these treatments in the lab, thus it can be assumed that these substances have already been removed. Sedimentation analysis is based on the principle that soil particles are denser than water, so they typically sink, settling at a velocity proportional to their size. Meaning the bigger the soil particles, the faster they fall through the solution. Therefore, sedimentation analysis relies on the relationship between settling velocity and particle diameter as described by Stokes Law: v = d 2 g(r s – r 1 ) 18h v = terminal velocity r s = particle density d = particle diameter r 1 = water density g = gravitational force h = water viscosity
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 2 By applying Stokes Law to particle analysis it is assumed that 1) the terminal velocity of settling particles is attained instantaneously; 2) settling and resistance are entirely due to the viscosity of the fluid; 3) the particles are smooth and spherical; and 4) there are no interaction between individual particles in the solution. These assumptions are met for soil particles that are less than 80 μ m in diameter. In addition, no pre-treatment of the soil samples is necessary in the sedimentation process; however there can be some associated error with this assumption depending on the composition of the soil samples. For example, the presence of soluble salts or gypsum may cause the flocculation or clumping of clay particles which will affect the particle settling velocity. In this case, a significant amount of the dispersion agent, such as Calgon ® can be used to prevent such an occurrence. Sedimentation analysis can be conducted following the Hydrometer Method ; which involves placing a soil sample in a cylinder of water and measuring the density of water that is displaced by the soil particles as they settle out of suspension with a hydrometer. As soil particles settle out of suspension past the depth of the hydrometer, the density of the solution drops. Large particles settle out first, thus the decreasing hydrometer readings correspond to a decrease in particle size over time. There are two types of hydrometers used in this lab: ASTM 152H and ASTM 151H, discernable from the labelled paper inside the bulb of the hydrometer. The ASTM 152H measures the concentration of soil in suspension in g/L and the ASTM 151H measures the specific gravity of the solution (dimensionless). Reading the hydrometers can be tricky. The ASTM 152H ranges from 0 g/L to 60 g/L and increases by increments of 1 g/L. Whereas, the ASTM 151H hydrometer is a little more difficult to read, because it increases by increments of 0.0010 as seen in Figure 1. 0.9900 1.000 1.010 1.020 1.030 1.040 Figure 1: ASTM 151H hydrometer scale. All measurements must be recorded in g/L, thus a graph converting specific gravity to g/L is provided in Figure 2. Once the hydrometer reading is in units of g/L, then this value can be used in a series of equations to determine its particle size equivalent.
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 3 Hydrometers, ASTM 152H and ASTM 151H are calibrated at 20°C. Correction of hydrometer readings for other temperatures, solution viscosity and density effects are made by taking a hydrometer reading in a blank (no soil) solution (R ). This Figure 2: Hydrometer Conversion Chart PURPOSE To determine the unknown grain size distributions of two soil samples using two different techniques. OBJECTIVES To become familiar with the methods commonly employed to determine the composition of a soil sample. To determine the limitations of each procedure. To determine the textural class of the soil samples based on their particle distribution. 0.0 10.0 20.0 30.0 40.0 50.0 60.0 1.000 1.005 1.010 1.015 1.020 1.025 1.030 1.035 Specific Gravity (151H Model) g/L (152H Model)
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ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 4 PROCEDURE Part 1: Mechanical Sieving Due to time constraints and the destructive nature of this grain size distribution test, you will only sieve a sample of the provided sand , which has been oven dried at 105°C for approximately 24 hours. Equipment 6 sieves, sieve pan, cover weighing dishes/ paper towel soil shaker rubber mallet & brush scale Method 1. Weigh a large crucible weighing dish (W 1 ) ( Table 1 ). 2. Place approximately 75 g of pre-treated soil in the weighing dish and record total weight (W 2 ) ( Table 1 ). 3. Retrieve a bottom pan, a lid and the appropriate sieves. Each sieve is labelled with the pore size in mm. Choose 6 sieves between the pore sizes ( i ) 0.07 mm to 2.00 mm. Brush all sieves to remove any stray particles from previous experiments. Also, check to make sure none of the sieves are damaged. 4. Assemble the sieves in a size-ordered stack, with the coarsest (largest) sieve at the top and the finest at the bottom. Place the sieve pan on the bottom and a sieve cover on the top of the stack. Record the pore sizes in Table 1 . 5. Remove the cover and pour the pre-weighed sample into the top sieve. Replace the sieve cover, place the stack on the sieve shaker, secure it and pre- test for stability. Turn the shaker on for 10 minutes. If you are unsure, ask the T.A. for assistance. 6. Record mass of emptied weigh dish (W 3 ) in Table 1 . 7. Turn off the shaker and carefully remove the sieve stack. 8. Weigh a series of weighing dishes (W di ) ( Table 1 ). Be sure to label each dish with the intended pore size ( i ) that will be emptied on it. Can use any type of dish. 9. Remove the top sieve and pour its contents into the pre-weighed weighing dish and weigh the sample + dish (W dsi ) ( Table 1 ). Be sure to brush out all the soil
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 5 from the sieve into the weighing dish. 10. Remove the next sieve from the stack and pour its contents into another weighing dish and weigh the sample + dish. Repeat this step until you have measured the weight of the soil caught in each sieve tray and the bottom pan. Record all values in Table 1. 11. Brush the sieves clean and return the sieves to the proper storage area. Part 2: Hydrometer Method for Sedimentation Analysis Use the same sand soil in Part I . Equipment hydrometer 1.5-2.0g of dispersing agent (Calgon ® ) 1L graduated cylinder stopwatch, second hand watch, or clock distilled water stirring device soil plastic weighing boats Method 1. Record weight of empty plastic weighing dish (W d ) in Table 3 . 2. Accurately weigh out approximately 80 g of dry loam soil, using a plastic weighing boat. Record weight of dish and sample (W ds ) in Table 3 . 3. Place the soil sample into a beaker, gently break up any harden chunks of soil with a rubber mallet. Then add some water to the beaker and mix into a slurry. This will ensure that you measure the sedimentological properties of the sample only. 4. Fill a 1L graduated cylinder to the 1L line with distilled water. 5. Weigh out approximately 1.5 - 2.0 g of dispersing agent in a plastic weighing boat. 6. Add the dispersing agent to the graduate cylinder and mix vigorously with provided stirring device. 7. Check the scale of the hydrometer to determine the type of model: the 152H model is in g/L and the 151H model uses the dimensionless scale of specific gravity. Reminder: if you’re using the 151H hydrometer, you must convert your values to g/L using the conversion graph provided in the Introduction (Figure 2).
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 6 8. Carefully place the hydrometer slowly into the water in the graduate cylinder (do not bang it against the side of the cylinder or drop it in the water). Release it as close to its natural floating point as possible. If necessary, use your finger to stop any oscillations of the hydrometer. *Use extra caution when using the hydrometers as they are fragile and very expensive. 9. Take a blank (no soil) hydrometer reading (R L ). Record this value in Table 3 . 10. Remove approximately 200 mL of water from cylinder. 11. Add the soil slurry to the graduated cylinder, rinse beaker with distilled water to ensure that all of sample is added to the graduated cylinder. 12. Top cylinder back up to the 1 L line. * Note, the exact volume of solution in cylinder must be known (V T ) and recorded in Table 3 . 13. Using the provided stirring device, drag the stirring disk up and down several times to disperse the soil evenly throughout the water column. 14. As soon as you finish mixing, start the stopwatch. 15. Take hydrometer readings at 30-second intervals for two minutes (R t ). Then take readings at 3, 5, 10, 30, 60, 90 and 120 minutes. Record these values in Table 3 . *Note, this is the minimum number of data points required. 16. Once you are finished, carefully remove from the hydrometer. Clean and return all equipment to the proper storage areas. Use appropriate waste bins for Calgon ® solution/ soil slurry. FINAL LAB REPORT Part 1: Sieving Analysis 1. Calculate the initial weight of the soil sample using the values recorded in Table 1. Initial mass of sample = (mass of weighing dish + soil) – (mass of empty dish) W S = W 2 - W 1 2. Calculate the weight of soil caught in each sieve tray using values recorded in Table 1 as follows: Weight of soil in sieve i = (weight of dish + soil from sieve i ) – (weight of empty dish) W si = W dsi - W di
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ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 7 3. Find the total weight that passed through the sieve stack (W t ) by totalling the values in the W si column in Table 1 . This value should be close to the initial sample weight (W s ) (before sieving) otherwise some of your soil sample was lost. 4. Calculate the percentage of soil caught by each sieve tray, including the bottom pan using the following equation: % caught = (W si / W t ) x 100 W s = weight of soil in sieve i (g) W t = total weight that passed through sieve stack (g) 5. Calculate the % cumulative passing value for the top sieve: % cum. passing in top sieve = 100 – (% caught in top sieve) 6. Calculate the % cumulative passing value for each remaining sieve as follows: % cum. passing = (% cum. passing from above sieve) – (% caught from current sieve) 7. Plot the percent cumulative passing vs. grain size diameter (sieve pore size) on the semi-log, grain size distribution graph paper provided. 8. Repeat the above steps for the provided dataset for the loam soil ( Table 2 ). Include on your grain size distribution results for the loam soil on the same graph paper as the sand. ** Sample Calculation of Grain Size Distribution Chart from Mechanical Sieving** Sieve Pore Size (i) (mm) Mass of Empty Weighing Dish, W di (g) Mass of Weighing Dish + Soil Caught in Sieve i, W dsi (g) Mass of Soil Caught in Sieve i , W si (g) (W dsi -W di ) % Caught Cumulative % passing 0.7 1.5 23.5 22 23.0 77.0 0.5 2.0 58.0 56 58.3 18.7 0.2 1.0 14.0 13 13.5 5.2 Bottom Pan 1.5 6.5 5 5.2 0.0 W t (g) = 96
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 8 Example Calculations: W t = 22 + 56 + 13 + 5 = 96 g % caught (0.7mm) = (W S0.7 / W t ) x 100 = (22g/ 96g) x 100 = 22.9% % cumulative passing (0.7mm) = 100 - 23.0 = 77.1% % cumulative passing (0.5mm ) = 77 - 58.3 = 18.7% Part 2: Hydrometer Analysis 1. Calculate the actual weight of the soil sample using the values recorded in Table 3 . Actual mass of sample = (mass of weighing dish + soil) – (mass of empty dish) W T = W dT - W d 2. Calculate total concentration of soil in suspension at time 0 (C T ) using total mass of sample (W T ) and known volume of solution in graduated cylinder (V T ). 3. Correct the hydrometer readings (concentration of soil in suspension at time t ) in Table 3 for each time interval as follows: Corrected Reading = (Actual Hydrometer Reading) – (Blank Hydrometer Reading) C t = R t - R L 4. Calculate the summation percentage (P) for each hydrometer reading as follows: P = C t /C T * 100 C T = total concentration of soil sample in solution (g/L) C t = corrected hydrometer concentration (g/L) 5. Calculate the effective hydrometer depth (h) for hydrometer reading (R t ) – related to specific design and shape of hydrometer. h = the effective hydrometer depth (cm) for a standard 152H hydrometer = (-0.164 cm·L·g -1 ) ·R t + 16.3cm R t = the hydrometer reading at time t (g/L) 6. Find the Sedimentation Parameter (q) in units of cm·sec ½ for each time
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 9 interval using the following formula: q = (Bh) 1/2 B = constant describing particle movement in a solution = 9.9x10 -5 cm·sec h = the effective hydrometer depth (cm) 7. Convert q to units of µm·min ½ since X and t are reported in µm and minutes. cm·sec ½ x (10 mm/ 1 cm) x (1000 µm/ 1 mm) x (1 min ½ / √60 sec ½ ) 8. Calculate the particle diameter (X) in units of µm using the following equation: X = qt -1/2 q = the sedimentation parameter (µm·min 1/2 ) t = the time of the hydrometer reading (min) 9. Using the hydrometer data, a fine particle distribution curve can be obtained by plotting the summation percentage (P) vs. the particle diameter (X). This graph should be plotted on the same semi-log paper as the sieving data. The curve from the sieving method and the hydrometer method can be joined to produce a complete grain size distribution for the loam soil. *Note, grain diameter (scale on x-axis) on provided semi-log graph paper is in mm; thus all calculated X values will need to be converted from µm to mm. *Sample Calculation of Grain Size Distribution Chart from Sedimentation Analysis* Time, t (min) Concentration of soil in suspension at time t (hydrometer reading) R t (g/L) Corrected Concentration C t (g/L) (R-R L ) Summation Percentage, P (%) Effective Hydrometer Depth, h (cm) Sedimentation Parameter, q (µm·min ½ ) Particle Diameter, X (µm) 0.5 11 9 21.8 14.5 48.9 69.2 1 10 8 19.4 14.7 49.2 49.2 1.5 9 7 17.0 14.8 49.5 40.4 2 8 6 12.5 15.0 49.7 35.2 R L = 2 g/L C T =41.2 g/L
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ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 10 Example Calculations: C T = total mass of soil in 1 L of water = 41.23 g/L P (0.5min) = (C t / C T ) x 100 = (9g/ 41.2g) x 100 = 21.8% h (0.5min) = -0.164 R t + 16.3 = -0.164 (11) + 16.3 = 14.5 cm q (0.5min) = (Bh) 1/2 = ((9.9x10 -5 )·14.5) 1/2 = 0.0379 cm·sec ½ = (0.0379cm·sec ½ )(10mm/1cm)(1000µm/1mm)(1min ½ /√60sec ½ ) = 48.9 µm·min ½ X (0.5min) = qt = (48.9)(0.5) = 69.2 µm or 0.0692 mm QUESTIONS 1. Describe some of the disadvantages and advantages of each particle size method. List some possible sources of error associated with each method. 2. In a few words, what is the difference between the particle size distribution curve obtained by the hydrometer method compare to the curve obtained by the sieving method? 3. Compare the grain size distribution curves for the sand and loam soil. Is there a lot of difference in the data? Is one of the soils more or less coarse than the other? Is one soil more or less well graded than the other? 4. Use the particle distribution curves to determine the percent of sand, silt and clay in the soil. Classify the soil (e.g. silty-loam, sandy-clay, etc.) by referring to a textural triangle - The major soil textural classes are defined by the percentages of sand, silt and clay according to the heavy boundary lines shown of the textural triangle provided on the last page.
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 11 DATA Table 1: Sieving Data for the Sand Group Members: Sample Weight before Sieving Parameter Description Recorded Value W 1 (g) Mass of empty weighing dish W 2 (g) Mass of dish + soil sample W 3 (g) Mass of emptied dish Sieving Data Sieve Pore Size (i) (mm) Mass of Empty Weigh Dishes W di , (g) Mass of Dish + Mass of Caught Sample in Sieve W dsi , (g) bottom pan
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 12 Table 2: Sieving Data for the Loam Soil Sample Weight before Sieving Parameter Description Recorded Value W 1 (g) Mass of weighing dish (g) 158.55 W 2 (g) Mass of dish + soil sample (g) 254.04 W 3 (g) Mass of emptied dish (g) 158.56 Sieving Data Sieve Pore Size (i) (mm) Mass of Empty Weigh Dishes W di (g) Mass of Dish + Mass of Caught Sample in Sieve W dsi (g) 2.00 1.30 3.218 1.40 1.31 3.953 1.00 1.32 5.395 0.500 1.30 15.025 0.125 1.30 49.418 0.065 1.33 7.994 bottom pan 1.33 19.397
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ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 13 Table 3: Hydrometer Method Data for Sand Soil Data before Test Parameter Recorded Value Mass of empty weighing dish (W d ) (g) Mass of dish + soil sample (W dT ) (g) Blank Hydrometer Reading (R L ) (g/L) Total Volume of Solution (V T ) (L) Hydrometer Test Data Time, t (min) Concentration of Soil in Suspension (Hydrometer Reading) R t (g/L) 0.5 1 1.5 2 3 5 10 30 60 90 120
ENVIRSC 2B03 Soils and the Environment S.K. Carey, 2022 14 Figure 3 USDA Soil Texture Triangle

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