Standard Test Procedures Manual

Transcription

1 STP Standard Test Procedures Manual Section: 1. SCOPE 1.1. Description of Test This method describes the quantitative determination of the distribution of particle sizes in soils. The distribution of particle sizes larger than 71 um is determined by a sedimentation process, using a hydrometer to secure the necessary data. 2. APPARATUS AND MATERIALS 2.1. Equipment Required Balance - sensitive to 0.01 g. Stirring apparatus - mechanically operated, with an electrical motor able to turn a vertical shaft at a speed of not less than 10,000 r.p.m. without load. The shaft shall have a stirring paddle made of metal, plastic, or hard rubber. The paddle shall be not less than 19.0 mm or more than 38.1 mm above the bottom of the dispersion cup. For details of the paddle and dispersion cup see Figure Hydrometer - graduated to read in grams per litre of suspension and conforming to requirements for hydrometer 152 H in ASTM Specification E 100. Sedimentation Cylinder - glass, 457 mm in height, 63.5 mm in diameter and marked for 1000 ml volume. Thermometer - accurate to 0.5 o C. Sieves - full set of Canadian metric sieves. Water bath or constant temperature room - to maintain the soil suspension at or near 20 o C during the analysis. If a room can be controlled at a constant temperature no water bath is necessary. Beaker ml. Timing device - a watch or clock with a second hand. Oven or hot plate. Date: Page 1 of 8

2 Standard Test Procedures Manual STP Materials Required Dispersing agent - prepare a solution of sodium hexametaphosphate (sometimes called sodium metaphosphate) in distilled or demineralized water. Use 40 g of sodium hexametaphosphate/litre of solution. Make new solutions at least once a month as it will slowly revert to the orthophosphate form causing a decrease in dispersive action. Water - either distilled or demineralized water. It should be kept at the same temperature as the test is to be run. The basic temperature for the hydrometer test is 20 o C. Page: 2 of 8 Date:

3 Standard Test Procedures Manual STP PROCEDURE 3.1. Test Procedure Obtain about 500 g of representative material to be tested as described in method STP 104. Air dry the sample thoroughly and weigh it. Break up aggregations in a mortar using a rubber covered pestle. Screen over a 2.00 mm sieve, then re-grind the coarser fraction and re-sieve. Combine the finer fractions for use in the hydrometer test. Wash the coarse fraction over a 2.00 mm sieve, then dry and weigh it for use in calculating the percentage of coarse material. Determine the hydroscopic moisture content of the air-dry fine fraction by method STP (oven drying). Weigh out a sample of the air-dry fine fraction for the hydrometer test. If the soil is predominately clay and silt, use approximately 50 g, but if the soil is mostly sand, use approximately 100 g. Place sample in 250 ml beaker, cover with 125 ml of sodium hexametaphosphate. Stir by hand until thoroughly wet and allow to soak at least 16 hours. At the end of the soaking period, disperse the sample further by transferring the complete sample to the dispersion cup. Use distilled or demineralized water to wash out beaker into cup so all the sample is transferred. Add water, if necessary, so cup is more than half full. Stir for a period of 1 minute using stirring apparatus. Immediately transfer the solution to the sedimentation cylinder and add distilled or demineralized water to the 1000 ml mark. Cover the end of the cylinder with the palm of the hand (or a rubber stopper), turn the cylinder upside down and back 30 times for a period of 1 minute. Loosen any soil remaining in the bottom of the cylinder during the first few turns by shaking the cylinder the inverted position. At the end of the 1 minute shaking period, set the cylinder on a stable surface, free from vibrations. Take hydrometer readings at the following intervals (measured from the beginning of sedimentation): 2, 5, 15, 30, 60, 250, and 1,440 minutes. Other times may be used if desired to obtain more or less data. Date: Page: 3 of 8

4 Standard Test Procedures Manual STP To take a hydrometer reading, carefully insert the hydrometer about 20 s before the reading is due. Insert it to the approximately depth for the reading. Take reading at the top of the meniscus formed by the suspension around the stem. Carefully remove the hydrometer immediately after the reading and place it with a spinning motion in a beaker of distilled or demineralized water. Enter the data on Form MR-8 Figure (Mechanical Analysis of Soil), in the columns "TIME", "TEMPERATURE", and "HYDROMETER READING ORIGINAL." Sieve Analysis of 71 mm Material After the final hydrometer reading, was the suspension through a 71 mm sieve with tap water. Dry the retained material in an oven at 110 o ± 5 o C. Sieve the material on the following sieves: 71 mm, 160 mm, 250 mm, 400 mm, 900 mm. Enter the cumulative weights to the left side of the column marked "WEIGHT PASSING" on Form MR-8 (Figure ) Composite Correlation for Hydrometer Hydrometer reading corrections are required to compensate for temperature and density changed in the dispersing fluid. Corrections are determined by doing a "blank" test without soil, as described below. At the same time as the test is being run on the soil, prepare a second sedimentation cylinder with 125 ml of the dispersing solution but no soil. Fill the cylinder to the 100 ml mark with water and mix well by shaking. Place the cylinder in the same area or in a water bath with the soil test cylinder. Take hydrometer readings periodically in the same manner as for the soil test. Because the readings do not vary much, take only 3 or 4 readings over the sedimentation period. condition. Enter the corrected readings in the column marked "CORRECTED FOR CALGON & TEMPERATURE." Page: 4 of 8 Date:

5 Standard Test Procedures Manual STP RESULTS AND CALCULATIONS 4.1. Calculations Use the formulas given to calculate each of the following quantities: Hydroscopic Moist. = Air Dry Wt. - Oven Dry Wt. x 100 Oven Dry Wt. % Pass mm Sieve Total Sample Wt. - Wt. Ret x 100 Total Sample Wt. Oven dry wt. of dispersed sample W d = Air Dry Wt. x % Hydroscopic Moist. Wt. of Dispersed Sample Corrected to total sample basis = w W = Oven Dry Wt. x 100 % Pass mm Enter appropriate values in the columns marked "K" and "L" on Form MR-8. The required values are obtained from the tables on the form. K depends on temperature, while L depends on the original uncorrected hydrometer reading. Calculate grain diameter from each hydrometer reading using the formula following, and enter the data in the correct column on the form. Grain Diameter = K L T All the values required for the calculations are taken from the data previously recorded in the various columns. Calculated percentage (P) of total test sample in suspension for each hydrometer reading and enter the data in the final column on the form. Use the following formula to calculate P: P = R x 100 W Where R = corrected by hydrometer reading W = dispersed weight of sample corrected to total sample Date: Page: 5 of 8

6 Standard Test Procedures Manual basis, as previously calculated. STP Calculate the sieve analysis portion of the test and enter the values in the column on the form marked "PERCENTAGE PASSING." For the fraction retained on the 2.00 mm sieve, base calculations on the total air dry weight of sample. For the fraction passing the 2.00 mm sieve, adjust the cumulative weights passing each sieve to the "weight dispersed basis" or W d as previously calculated. First obtain the weight accumulated on the balance for the material from the 71 mm sieve to the 2.00 mm sieve. Subtract this weight from W d and use this difference as an adjustment to each sieve size as shown in the following example. Assume weight dispersed or W d = 49.5 g Weight after washing over 71 mm and drying = 15 Adjustment = 34.5 Sieve Cumulated Wt. Adjusted Wt mm 15.0 g 49.5 g 400 mm 20.5 g 45.0 g 71 mm 1.0 g 35.5 g Calculate percent passing each sieve using the formula: % Pass. = Adjusted Wt. x 100 W Enter the values for the percentages passing for both the coarse and fine fractions in the "SIEVE ANALYSIS" section of Form MR-8 (Figure ) Reporting Results Combine the results of the sieve analysis and hydrometer analysis and report on Form MR-38. The form includes a graphical presentation of data. 5. ADDED INFORMATION 5.1. References ASTM D Page: 6 of 8 Date:

7 Standard Test Procedures Manual STP General The hydrometer test is an application of Stokes Law, which in essence states that larger particles fall more quickly in a suspending fluid, while finer particles remain in suspension longer. The time at which the hydrometer readings are taken determines the size of particle remaining in suspension, while the reading on the hydrometer determines the amount of that size. Several assumptions are made about particles shape and other test conditions, so the results are somewhat approximate. The sieve portion and hydrometer portion of the test may not exactly line up. The method as presented, assumes a particle specific gravity of For most purposes this will be sufficiently accurate even though S.G.'s may be somewhat lower or higher. If further refinement is required, additional corrections may be found in the reference. Results are used to indicate whether the soil is frost susceptible and for comparing soils from different areas or strata. Because the sample size is small, take extra care to obtain representative material. Considerable care should also be taken in all weighing and liquid volume measurements. The sample must be completely dispersed and remain dispersed throughout the test. Be sure the dispersing agent is not more than one month old. Also make sure the stirring paddle is not badly worn. Some soil (like heavy clays) tend to coagulate and form curds and then settle quickly giving false readings. If you see any evidence of coagulation, you must re-run the test. Reducing the sample size to 25 g sometimes helps this problem. Date: Page: 7 of 8

8 Standard Test Procedures Manual STP MECHANICAL ANALYSIS OF SOIL VALUE OF L SEIVE ANALYSIS HYD RDG. L HYD RDG. L HYD RDG. L SIEVE WT % SAMPLE NO SIZE PASS PASS TESTED BY mm DATE mm SAMPLE WEIGHT mm mm mm um VALUE OF K um TEMP O C K TEMP O C K um um um DETERMINATION OF SIZE AND PERCENTAGE OF SOIL IN SUSPENSION HYDROMETRE READING MIN CORRECTION GRAIN % OF TOTAL TEST TIME TEMP ORIG. CORRECTED FOR COEFFICIENTS DIA. SAMPLE IN CALGON & TEMP T L K k L / T SUSPENSION FIGURE Page: 8 of 8 Date: