Section 1 Sieve analysis method

　　1. purpose

Determine the percentage of particles or grain groups smaller than a certain particle size in the mass of sand in order to understand the particle size composition of the soil and serve as the basis for sand classification and geotechnical construction material selection.

　　Fundamentals of 2.

The sieve analysis method is to use a set of standard sieves with different aperture to separate a certain amount of sand and the corresponding particle group of the sieve aperture, and then weigh, calculate the relative content of each particle group, determine the particle size of the sand composition. This method is suitable for separating particle groups with particle size greater than 0.075mm.

　　3. instruments and equipment

1. One set of standard sieve (Fig. 1-1);

2. Ordinary balance: weighing 500g, minimum dividing value 0.1g;

3. Magnetic bowl and rubber head grinding rod;

4, brush, white paper, ruler, etc.

　　4. operation steps

1. Preparation of soil sample

(1) Air-dry the soil sample, spread the soil sample into a thin layer, and put it in the air for 1 to 2 days to evaporate the water in the soil. If the soil sample has been dried, it can be used directly.

(2) If there are agglomerates in the sample, the sample can be poured into a magnetic bowl and ground with a rubber head grinding rod to make the agglomerates become individual particles. However, it should be noted that the grinding force should be appropriate and the particles should not be crushed.

(3) Take representative samples from the prepared soil samples, and the number is as follows:

If the maximum particle size is less than 2mm, take 100~300g;

If the maximum particle size is 2~10mm, take 300~1000g;

If the maximum particle size is 10~20mm, take 1000~2000g;

If the maximum particle size is 20~40mm, take 2000~4000g;

The maximum particle size is greater than 40mm, take more than 4000g.

The quartering method is used to select the sample. The method is as follows: mix the soil sample evenly, pour it on the paper to form a cone (Figure 1-2.1), and then use a ruler to rotate the cone with the cone vertex as the center in a certain direction (Figure 1-2.2), so that the cone becomes a round cake with a thickness of 1~2cm. Then draw two straight lines perpendicular to each other with a ruler, divide the soil sample into four equal parts, take away the same two parts (Figure 1-2.3, Figure 1-2.4), and mix the remaining two parts of the soil sample evenly; Repeat the above steps until the remaining soil sample is approximately equal to the required amount.

2. Sieving and weighing

(1) Weigh a certain amount of sample with an ordinary balance, accurate to 0.1g;

(2) Check whether the stacking sequence of standard sieves is correct (large aperture is on the top and small aperture is on the bottom), and whether the sieve holes are clean. If there are soil particles, they need to be brushed. Pour the weighed sample into the top sieve tray, cover well, shake it by hand or sieve shaker for 10~15min, then remove the sieve tray from top to bottom, tap the sieve tray on the white paper by hand, and shake it until it is sieved. Pour the soil particles leaking on the white paper into the next layer of sieve tray, in this order, until the last layer of sieve tray is sieved.

(3) Weigh the mass of soil particles left on each sieve tray, accurate to 0.1g, and measure the diameter of the largest particle in the sample. If the particles larger than 2mm exceed 50%, then analyze with a coarse sieve.

　　5. results collation

1. The difference between the sum of the mass of soil particles on each sieve tray and the mass of the sample before the sieve shall not be greater than 1%, otherwise the test shall be repeated. If the difference between the two is less than 1%, the cause of the error during the test should be analyzed and assigned to some grain groups.

2. Soil inspection

If the content of particle size less than 0.075mm is greater than 50%, the soil is not sandy soil, but fine-grained soil, and this part is analyzed by densitometer method (see section 2).

3. Draw the particle size distribution curve on the single logarithmic coordinates, find the uneven coefficient and curvature coefficient, explain the uniformity of the soil, and determine the name of the soil.

4. Fill in the test report.

　　6. considerations

1. In the sieve analysis, especially when the sample is poured from one vessel to another, the flying of tiny particles should be avoided.

2. After sieving, check whether there are particles in the sieve hole. If there are particles, brush the particles gently, put them into the soil sample on the sieve tray, and weigh them together.

　　7. Thinking Questions

1. What is the difference between the terms "particle group" and "particle size composition?

2. Try to analyze the causes of errors in the test process and how to distribute them.

　　Section 2 Density Meter Method

　　Purpose of 1. Test

Determine the percentage of particles smaller than a certain particle size in the mass of fine-grained soil in order to understand the composition of soil particles; and be used for the classification of silt and cohesive soil and the selection of building materials.

　　Fundamentals of 2.

The densitometer method is measured according to Stokes law. When the soil particles sink in the liquid by their own weight, the larger particles sink faster, while the smaller particles sink slower. It is generally believed that for particles with a particle size of 0.2~0.002mm, when they sink by their own weight in the liquid, they will move at a constant speed, which is in line with Stokes's law. The density meter method is a kind of hydrostatic sedimentation analysis method, which is only applicable to soil samples with particle size less than 0.075mm.

The densitometer method is to place a certain amount of soil sample (particle size <0.075mm) in a measuring cylinder, then add pure water, and after stirring, the size of the soil particles are evenly distributed in the water to make a certain amount of uniform concentration of soil suspension (1000mL). Static suspension, let the soil particles settle, in the process of soil particle subsidence, with the density meter measured in the suspension corresponding to different time of the different suspension density, according to the density meter reading and soil particle subsidence time, you can calculate the particle size is less than a certain particle size d(mm) of the percentage of soil particles.

The following three assumptions must be made for particle analysis using a density meter:

1, Stokes law can be applied to the suspension composed of soil particles.

2. At the beginning of the test, the size of the soil particles are evenly distributed in the suspension.

3. The diameter of the measuring cylinder used is much larger than the diameter of the gravity meter.

　　3. instruments and equipment

1. Density meter

At present, there are two kinds of density meters commonly used: A and B. The manufacturing principle and use method of these two kinds of density meters are basically the same, but the meaning indicated by the reading of the density meter is different. The reading of A kind of density meter indicates the quality of dry soil in a certain amount of suspension. The reading of B kind of density meter indicates the specific gravity of suspension.

(1) Type A density meter, the scale unit is expressed in grams of soil mass per 1000mL of suspension at 20°C, the scale is -5~50, and the minimum scale value is 0.5.

(2) Type B density meter, the scale unit is expressed by the specific gravity of the suspension at 20°C, the scale is 0.995~1.020, and the minimum scale value is 0.0002.

2. Measuring cylinder: volume 1000mL;

3. funnel-type washing screen: aperture 0.075mm;

4. Agitator: wheel diameter 50mm, aperture 3mm;

5. Boiling equipment: electric heater, conical flask;

6. Dispersant: 4% sodium hexametaphosphate or other dispersants;

7. Others: thermometer, mortar, stopwatch, beaker, porcelain dish, balance, etc.

　　4. operation steps

1. Calibration of density meter

In the manufacturing process of the density meter, the bubble volume and scale are often not easy to be accurate. Moreover, the scale of the density meter is 20 ° C pure water as the standard. Due to the influence of many factors in the laboratory, the density meter should be corrected for the influence of scale, meniscus, soil particle settlement distance, temperature, dispersant, etc. before use.

(1) Soil particle settlement distance correction

① Determination of bubble volume of density meter

Pour about 130mL of pure water into a 250mL measuring cylinder, keep the water temperature at 20°C, take the upper edge of the meniscus as the standard, measure and mark the reading of the water surface on the measuring cylinder, then slowly put the densitometer into the measuring cylinder, and when the water surface reaches the lowest scale of the densitometer (take the upper edge of the meniscus as the standard), measure and mark the reading of the water surface on the measuring cylinder again, the difference between the two readings of the water surface on the measuring cylinder is the bubble volume of the densitometer, and the reading is accurate to 1mL.

② Determination of the bubble volume center of the density meter

After measuring the bubble volume of the densitometer, slowly lift the densitometer vertically upward and make the water surface fall in the middle of the two marks. At this time, the tangent between the water surface and the bubble (the upper edge of the meniscus shall prevail) is the center of the bubble. Fix the densitometer on a tripod and measure the vertical distance from the center of the bubble to the lowest scale of the densitometer with a ruler.

③ Measure the inner diameter of the 1000mL measuring cylinder (accurate to 1mm), and calculate the cross-sectional area of the measuring cylinder.

④ measure the distance from the lowest scale of the densitometer to each scale on the glass rod, once every 5 squares.

⑤ Calculate the effective settlement distance of soil particles

⑥ Calculate the corresponding effective settlement distance L value of soil particles, and draw the relationship curve between the density meter reading and the effective settlement distance of soil particles, so that the effective settlement distance of soil particles can be obtained according to the reading of the density meter.

(2) Calibration and meniscus correction

The reading of the densimeter during the test shall be based on the upper edge of the meniscus, while the scale of the densimeter shall be based on the lower edge of the meniscus when it is manufactured (Figure 1-3), so the scale of the densimeter and the meniscus shall be corrected. The densitometer is placed in pure water at 20°C, and the difference between the readings of the upper and lower edges of the upper meniscus of the densitometer at this time is the correction value of the meniscus. Since the upper edge scale of the meniscus is always greater than the lower edge scale, this value is always positive. Some density meters have been marked at the factory to the upper edge of the meniscus, that is, the correction value is zero.

(3) Temperature correction

The scale of the densitometer is made at 20°C, but the suspension temperature during the test is not necessarily exactly equal to 20°C, and the change of water density and the expansion of the volume of the densitometer bubble will affect the accurate reading of the densitometer, so temperature correction is required. The temperature correction value of the densitometer reading can be found in Table 1-1.

(4) Dispersant correction

In order to fully disperse the suspension, a certain amount of dispersant is often added, and the density of the suspension is larger than the original, so the effect of dispersant on the density meter reading should be considered. The specific method is as follows: keep 1000mL of pure water in the measuring cylinder at a constant temperature of 20°C, first measure the reading of the densitometer in pure water at 20°C, then add the dispersant used in the test, use a stirrer to stir evenly up and down along the whole depth in the measuring cylinder, and put the densitometer into the solution to measure the reading of the densitometer. The difference between the two is the correction value of the dispersant.

(5) Soil particle specific gravity correction

The scale of the density meter is made on the assumption that the specific gravity of the soil particles in the suspension is 2.65. If the specific gravity of the soil particles is not 2.65 during the test, it must be corrected. The specific gravity correction values of the two density meters A and B can be found in Table 1-2.

Table 1-1 Temperature Correction Value
Suspension Temperature (℃)	Temperature of Class A density meter Correction value	Temperature of Type B Density Meter Correction value	Suspension Temperature (℃)	Temperature of Class A density meter Correction value	Temperature of Type B Density Meter Correction value	Suspension Temperature (℃)	Temperature of Class A density meter Correction value	Temperature of Type B Density Meter Correction value
10.0	-2.0	-0.0012	17.0	-0.8	-0.0005	24.0	1.3	0.0008
10.5	-1.9	-0.0012	17.5	-0.7	-0.0004	24.5	1.5	0.0009
11.0	-1.9	-0.0012	18.0	-0.5	-0.0003	25.0	1.7	0.0010
11.5	-1.8	-0.0011	18.5	-0.4	-0.0003	25.5	1.9	0.0011
12.0	-1.8	-0.0011	19.0	-0.3	-0.0002	26.0	2.1	0.0013
12.5	-1.7	-0.0010	19.5	-0.1	-0.0001	26.5	2.2	0.0014
13.0	-1.6	-0.0010	20.0	0	0	27.0	2.5	0.0015
13.5	-1.5	-0.0009	20.5	0.1	0.0001	27.5	2.6	0.0016
14.0	-1.4	-0.0009	51.0	0.3	0.0002	28.0	2.9	0.0018
14.5	-1.3	-0.0008	21.5	0.5	0.0003	28.5	3.3	0.0019
15.0	-1.2	-0.0008	22.0	0.6	0.0004	29.0	3.3	0.0021
15.5	-1.1	-0.0007	22.5	0.8	0.0005	29.5	3.5	0.0022
16.0	-1.0	-0.0006	23.0	0.9	0.0006	30.0	3.7	0.0023
16.5	-0.9	-0.0006	23.5	1.1	0.0007

 

Table 1-2 Corrected value of soil particle specific gravity
Specific gravity of soil particles		2.50	2.52	2.54	2.56	2.58	2.60	2.62	2.64	2.66
Correction value	A type density meter	1.038	1.032	1.027	1.022	1.017	1.012	1.007	1.002	0.998
	Type B density meter	1.666	1.658	1.649	1.641	1.632	1.625	1.617	1.609	1.603
Specific gravity of soil particles		2.68	2.70	2.72	2.74	2.76	2.78	2.80	2.82	2.84
Correction value	A type density meter	0.993	0.989	0.985	0.981	0.977	0.973	0.969	0.965	0.961
	Type B density meter	1.595	1.588	1.581	1.575	1.568	1.562	1.556	1.549	1.543

2. Treatment of soil samples and preparation of suspension

(1) Take 200~300g of representative sample, air-dry and measure the air-dry moisture content of the sample, put it in a mortar, and grind it with a grinding rod with a rubber head.

(2) weigh 30g of air-dried sample, pour into 500mL conical flask, inject 200ml of pure water, and soak overnight.

(3) Shake the conical flask containing the soil liquid slightly and then put it on the boiling equipment for boiling. The boiling time should be 40min.

(4) Flush all the cooled suspension into a beaker and grind it with a rubber head grinding rod; After standing for about 1min, pour the upper suspension onto a 0.075mm washing sieve, inject it into a 1000mL large measuring cylinder through a funnel, grind the remaining sediment at the bottom of the cup with a rubber head grinding rod, stir with an appropriate amount of pure water, pour out the upper suspension and sieve it into the measuring cylinder. This is repeated until the suspension is clarified and all the samples in the beaker are sieved and rinsed; the sand particles on the sieve are moved into the evaporating dish, and after drying, the sieve is weighed according to Step 2 of Test 1, and the percentage content of each grain group is calculated.

(5) Add 10mL of 4% sodium hexametaphosphate into a large cylinder, and then inject 1000mL of pure water.

3. Determine the density and temperature of suspension on time

(1) Put the agitator into the measuring cylinder, and stir up and down along the depth of the suspension for 1min, so that the soil particles are completely evenly distributed in the whole suspension. Pay attention not to splash the suspension out of the cylinder during mixing.

(2) Take out the stirrer, start the stopwatch immediately at the same time, put the densitometer into the suspension, measure and record the densitometer readings at 0.5, 1, 2, 5, 15, 30, 60, 120 and 1440min, and measure the corresponding suspension temperature. According to the test situation or actual needs, the number of densimeter readings can be increased, or the last reading time can be shortened.

(3) During each reading, the densitometer shall be slowly placed in the middle of the suspension 10~20s before the predetermined time, not close to the cylinder wall, and the densitometer shall be vertical. The densitometer shall also be released at the scale similar to the density of the suspension to avoid stirring the suspension.

(4) The densitometer reading is based on the upper edge of the meniscus. Type A density meter should be accurate to 0.5 and estimated to 0.1. Type B density meter should be accurate to 0.0002 and estimated to 0.0001. After each reading, immediately take out the density meter and put it into the measuring cylinder with clear water.

(5) Determination of suspension temperature should be accurate to 0.5°C.

　　5. results collation

1. Calculation of particle size of sample:

Table 1-3 Calculation Coefficient of Particle SizeAvalue table
Temperature t (℃)	Specific gravity of soil particlesGs
	2.45	2.50	2.55	2.60	2.65	2.70	2.75	2.80	2.85
5	0.1385	0.1360	0.1399	0.1318	0.1298	0.1279	0.1261	0.1243	0.1226
6	0.1365	0.1342	0.1320	0.1299	0.1280	0.1261	0.1243	0.1225	0.1208
7	0.1344	0.1321	0.1300	0.1280	0.1260	0.1241	0.1224	0.1206	0.1189
8	0.1324	0.1302	0.1281	0.1260	0.1241	0.1223	0.1205	0.1188	0.1182
9	0.1305	0.1283	0.1262	0.1242	0.1224	0.1205	0.1187	0.1171	0.1164
10	0.1288	0.1267	0.1247	0.1227	0.1208	0.1189	0.1173	0.1156	0.1141
11	0.1270	0.1249	0.1229	0.1209	0.1190	0.1173	0.1156	0.1140	0.1124
12	0.1253	0.1232	0.1212	0.1193	0.1175	0.1157	0.1140	0.1124	0.1109
13	0.1235	0.1214	0.1195	0.1175	0.1158	0.1141	0.1124	0.1109	0.1094
14	0.1221	0.1200	0.1180	0.1162	0.1149	0.1127	0.1111	0.1095	0.1080
15	0.1205	0.1184	0.1165	0.1148	0.1130	0.1113	0.1096	0.1081	0.1067
16	0.1189	0.1169	0.1150	0.1132	0.1115	0.1098	0.1083	0.1067	0.1053
17	0.1173	0.1154	0.1135	0.1118	0.1100	0.1085	0.1069	0.1047	0.1039
18	0.1159	0.1140	0.1121	0.1103	0.1086	0.1071	0.1055	0.1040	0.1026
19	0.1145	0.1125	0.1108	0.1090	0.1073	0.1058	0.1031	0.1088	0.1014
20	0.1130	0.1111	0.1093	0.1075	0.1059	0.1043	0.1029	0.1014	0.1000
21	0.1118	0.1099	0.1081	0.1064	0.1043	0.1033	0.1018	0.1003	0.0990
22	0.1103	0.1085	0.1067	0.1050	0.1035	0.1019	0.1004	0.0990	0.0977
23	0.1091	0.1072	0.1055	0.1038	0.1023	0.1007	0.0993	0.0979	0.0966
24	0.1078	0.1061	0.1044	0.1028	0.1012	0.0997	0.0982	0.0960	0.0956
25	0.1065	0.1047	0.1031	0.1014	0.0999	0.0984	0.0970	0.0957	0.0943
26	0.1054	0.1035	0.1019	0.1003	0.0988	0.0973	0.0959	0.0945	0.0933
27	0.1041	0.1024	0.1007	0.0992	0.0977	0.0962	0.0948	0.0935	0.0923
28	0.1032	0.1014	0.0998	0.0982	0.0967	0.0953	0.0939	0.0926	0.0913
29	0.1019	0.1002	0.0986	0.0971	0.0956	0.0941	0.0928	0.0914	0.0903
30	0.1008	0.0991	0.0975	0.0960	0.0945	0.0931	0.0918	0.0905	0.0893

 

2. The percentage of the mass of the sample smaller than a certain particle size to the total mass of the sample can be calculated according to formula (1-4) or formula (1-5):

(1) Type A hydrometer

(2) Type B hydrometer

3. Draw the particle size distribution curve on the semi-logarithmic coordinates, and find the uneven coefficient Cu and the curvature coefficient Cc to illustrate the uniformity of the soil.

It must be pointed out that when there are both particles smaller than 0.075mm and particles larger than 0.075mm in the sample, when the combined analysis of density meter and sieve analysis is required, the percentage of the mass of the sample smaller than 0.075mm to the total mass of the sample should be considered, I .e. the calculation result obtained according to formula (1-4) or formula (1-5) should be multiplied by the percentage of the mass of the sample smaller than 0.075mm to the total mass of the sample, then draw the particle size distribution curves obtained by the density meter method and the sieve analysis method respectively, and connect the two curves into a smooth curve.

4. Fill in the test report.

　　6. considerations

1. After measuring the density of suspension each time, the density meter should be gently placed in the measuring cylinder containing water.

2, the reading should be rapid and accurate, it is not appropriate to place the density meter in the suspension for too long. Before the formal test, the accurate reading method of the density meter must be practiced several times.

3. Before the test, the measuring cylinder should be placed in a fixed and stable place, and it should not be moved during the test, and the temperature of the suspension should be kept stable.