1、Standard Method of Test for Determining Expansive Soils AASHTO Designation: T 258-81 (2013) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1a T 258-1 AASHTO Standard Method of Test for Determining Expansive Soils
2、AASHTO Designation: T 258-81 (2013) 1. SCOPE 1.1. This standard covers a method to determine if a soil is expansive and methods to predict the amount of swell. Note 1Methods that are being used by various agencies to control the amount of swell are given in the appendix. 2. REFERENCED DOCUMENTS 2.1.
3、 AASHTO Standards: R 58, Dry Preparation of Disturbed Soil and Soil-Aggregate Samples for Test T 89, Determining the Liquid Limit of Soils T 90, Determining the Plastic Limit and Plasticity Index of Soils T 99, Moisture-Density Relations of Soils Using a 2.5-kg (5.5-lb) Rammer and a 305-mm (12-in.)
4、Drop T 100, Specific Gravity of Soils T 216, One-Dimensional Consolidation Properties of Soils T 273, Soil Suction 3. DETECTING EXPANSIVE SOILS 3.1. The potential expansiveness of a soil may be determined by using the Atterberg Limits of the soil and the natural soil suction. 3.2. From Table 1, dete
5、rmine how potentially expansive the soil is using AASHTO Test Methods for the Liquid Limit (LL), the Plasticity Index (PI), and the soil suction at natural water content (nat). Table 1Determining Degree of Expansion in Soil Degree of Expansion LL PI natkPa , High 60 35 383 kPa Marginal 5060 2535 144
6、 to 383 kPa Low 50 25 144 kPa 4. DETERMINING THE AMOUNT OF SWELL 4.1. The amount of swell to be expected in a stratum is determined by one of the following described methods. Where more exacting determination of the amount of swell is needed, the Overburden Swell Test Procedure should be used. Due t
7、o the length of time and costs required to perform the 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 258-2 AASHTO Overburden Swell Test, an empirical procedure called the Potential Vertical Ris
8、e Method may be used to estimate the swell where conditions do not require the more exact determination. 4.2. Overburden Swell Test and Prediction Procedure: 4.2.1. Method 1Prepare an undisturbed sample for consolidation testing according to the procedure in T 216. Extreme care should be taken to pr
9、event moisture loss during the preparation stage. From the sample trimmings, determine the field moisture content and the specific gravity of the soil. The field moisture is determined as a percentage of the mass of oven-dried soil and shall be calculated as follows: mass of waterpercentage of moist
10、ure 100mass of oven-dried soil= (1) The specific gravity of the soil is determined as outlined in T 100. After the sample has been placed in the consolidometer, a load equal to the existing overburden pressure is applied on the sample. This load shall be maintained until the dial gage of the extenso
11、meter indicates that all adjustment to the applied load has ceased. During the application of this load and adjustment period, extreme care must be exercised to prevent desiccation. It is extremely important not to lose any moisture from this sample. This may be accomplished by covering the consolid
12、ometer with moist cotton. This loading procedure returns the sample, as closely as possible, to the actual field void ratio and field condition since extrusion allows undisturbed samples to immediately rebound elastically. Actual field conditions are defined as Point One (1) in Figure 1. The sample
13、is then inundated and allowed to reach an equilibrium as indicated by the dial gage of the extensometer. This condition then is defined as Point Two (2) in Figure 1. The sample then is unloaded to the desired pressure, in decrements of load that a laboratory normally uses, thus producing a swell cur
14、ve from Point Two (2) to Point Three (3) in Figure 1. From this point (Point 3, Figure 1), a normal consolidation-rebound test is conducted as outlined in T 216. The swell-curves form approximately straight lines on a semilog plot; therefore, the No-Volume Change pressure is determined by extrapolat
15、ing the swell curves between Points 2 and 3 until it intersects the Field Void Ratio as Point Four (4). The Field Void Ratio (ef) is determined as follows: percent field moisture specific gravitypercent saturationfe= (2) 4.2.2. Method IIThis method is presented because there may be a need to expedit
16、e the work and the existing overburden load may be so small that obtaining swell curves directly may be meaningless. This method may be used only after running several tests by Method I and finding that the slope of the rebound curve, Points Five (5) and Six (6), is substantially the same as the slo
17、pe of the swell curve, Points Two (2) and Three (3). Method II is the same as Method I to the point where the sample is inundated and the total swell is recorded. At this point, a normal consolidation-rebound load sequence is followed to produce the desired curves. Since the slope of the rebound and
18、 swell curves is substantially the same, the swell curve can be produced by passing a curve through Point Two (2), Figure 1 that is parallel to the rebound curve. The intersection of this curve with the Field Void Ratio gives the point of No-Volume Change or maximum swell pressure potential. 2015 by
19、 the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 258-3 AASHTO Figure 1Design Example of Void Ratio Versus Log of Pressure 2015 by the American Association of State Highway and Transportation Officials.Al
20、l rights reserved. Duplication is a violation of applicable law.TS-1a T 258-4 AASHTO 4.2.3. CalculationsCalculation for the amount of swell to be expected in a stratum can be made as follows: 1feHSe=+(3) where: S = amount of swell in mm (in.), e = difference in void ratio between existing overburden
21、 pressure (no-volume change load) and the desired overburden pressure, H = thickness of stratum in mm (in.), and ef= field void ratio. 4.3. Potential Vertical Rise (PVR) Test and Prediction Procedure: 4.3.1. For this procedure, it is necessary to know the moisture content of each layer sampled. It i
22、s preferable that moisture samples be taken at the time of sampling. These moisture samples can be taken from cores that have been moisture sealed. 4.3.2. When cores have been taken, determine the wet density by trimming the cores to make right circular cylinders, measuring height and diameter, to t
23、he nearest 0.25 mm, determining the mass to the nearest estimated 0.5 g and calculating. When cuttings only are taken during sampling, use a wet density of 2002 kg/m3, which is usually a reasonable value. 4.3.3. From representative portions of the cuttings or cores, determine the Liquid Limit, Plast
24、icity Index, and percent soil binder minus 0.425-mm (No. 40) sieve in the soil layers. Record these results on Table 3 at the appropriate layer. 4.3.4. Beginning with the top layer at the surface of the ground from the drilling log (Table 2), start compilation of Table 3. Determine whether the layer
25、s are “wet,” “dry,” or “average.” Note 2It has been determined that 0.2 LL + 9 is the “dry” condition from which little shrinkage is experienced, but where volumetric swell potential is greatest. It is the minimum moisture content that swelling clays usually dry to. 0.47 LL + 2, or the “wet” conditi
26、on, corresponds to the maximum capillary absorption by laboratory tests on specimens molded at optimum moisture and surcharged with a 7-kPa load. This is also analogous to moisture contents found beneath old pavements and other lightweight structures. This is the “optimum” condition. 2015 by the Ame
27、rican Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 258-5 AASHTO Table 2Sample of Drilling Log Form 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is
28、 a violation of applicable law.Table 3Determining the Liquid Limit, Plasticity Index at the Appropriate Layer PVR, mm Depth, m Avg. load, kPa LL Dry 0.2 LL+9 Wet 0.47 LL+2 Percent Moisture Dry Avg. Wet Percent 0.425 mm PI Percent Vol. Swell (Fig 1) Percent Free Swell Top of Layer Bottom of Layer Dif
29、f. Mod 0.425 mm Factor Mod Density Factor PVR in Layer mm 00.6 6.9 21 3.1 Dry 100 4 0.0 0.0 0.0 0.0 0.0 1.00 1.00 0.0 0.61.2 21 60 21.0 30.2 29.7 Wet 100 38 5.5 8.5 10.4 22.3 11.9 1.00 1.00 11.9 1.21.8 34 60 21.0 30.2 20.9 Dry 100 38 11.0 14.5 39.4 55.9 16.5 1.00 1.00 16.5 1.82.4 48 75 24.0 37.3 24.
30、4 Dry 100 45 13.5 17.0 71.4 86.6 15.2c1.00 1.00 15.2 2.43.0 62 75 24.0 37.3 36.5 Wet 100 45 7.0 10.0 42.9 47.0 4.1 1.00 1.00 4.1 3.03.6 76 65 22.0 32.6 8.5 Wet 15 40 Less than 25% 0.425 mm 1.00 1.00 0.0 3.64.2 90 65 22.0 32.6 8.5 Wet 15 40 Less than 25% 0.425 mm 1.00 1.00 0.0 4.24.8 103 65 22.0 32.6
31、 8.5 Wet 15 40 Less than 25% 0.425 mm 1.00 1.00 0.0 4.85.4 117 65 22.0 32.6 8.5 Wet 15 40 Less than 25% 0.425 mm 1.00 1.00 0.0 5.46.0 131 85 26.0 42.0 41.5 Wet 100 60 10.2 13.5 89.9 91.9 2.0 1.00 1.00 2.0 6.06.6 145 80 25.0 39.6 33.9 Avg 100 60 12.6 16.0 123.9 127.9 3.1 1.00 1.00 3.1 6.67.2 159 80 2
32、5.0 39.6 33.9 Avg 100 54 12.6 16.0 127.0 129.8 2.8 1.00 1.00 2.8 7.27.8 172 80 25.0 39.6 33.9 Avg 100 54 12.6 16.0 129.8 132.1 2.3 1.00 1.00 2.3 7.88.4 186 80 25.0 39.6 33.9 Avg 100 54 12.6 16.0 132.1 133.9 1.8 1.00 1.00 1.8 8.49.0 200 80 25.0 39.6 33.9 Avg 100 54 12.6 16.0 133.9 135.4 1.5 1.00 1.00
33、 1.5 9.09.6 214 80 25.0 39.6 33.9 Avg 100 54 12.6 16.0 135.4 135.6 0.2 1.00 1.00 0.2 Total PVR = 61.4ab6.09.6 131 to 214 80 25.0 39.6 33.9 Avg 100 54 12.6 16.0 123.9 135.6 11.7 1.00 1.00 11.7 a2002 kilograms per cubic meter wet density assumed for all layers. When greater accuracy is desired, use 32
34、002actual wet density of soil, kg/mas the modifier. bNote: Since the 3.6-m layer from 6.09.6 m is uniform, the PVR may be determined in one reading by using the “top of the layer” as 131 kPa (as in 0.6-m layers) and reading the bottom of the layer at 214 kPa load as in the 9.09.6m layer. Readings of
35、 123.9 mm and of 135.6 mm, respectively, or a difference of 11.7 mm will be obtained, which is the summation of increments (differences) as shown above for the bottom 3.6 m. When layers of expansive clays of less than 0.6 m exist (example 1.21.4), it is preferable to enter the abscissa on the proper
36、 swell curve at 1.2 and 1.4 curve and use the difference in the respective ordinate readings as the unmodified swell in the 0.2-m-thick layer. cSee example in Figure 2. TS-1aT258-6AASHTO 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication i
37、s a violation of applicable law.TS-1a T 258-7 AASHTO 4.3.5. Using Figure 2 and the wet, dry, or average moisture condition, find the PI of the first soil layer on the abscissa. Move vertically upward to the appropriate swell curve (dry, average, or wet) and read the percent volumetric change on the
38、ordinate. This percent volumetric change was determined for 7-kPa surcharge. Figure 2Interrelationship of Plasticity Index and Volume Change Note 3The PVR versus Load Curves in Figures 3 and 4 are for free swelling clays under no load and are based on a wet density of soil of 2002 kg/m3. In order to
39、 use the curves in Figures 3 and 4, it has been determined that under the conditions of free swell and the percent volumetric swell at 7-kPa surcharge given in Figure 2, the following relationship exists: Percent volumetric swell No load = percent volumetric swell 7 kPa (1 psi) (1.07) + 2.6 Example:
40、 From Figure 2, the swell 7 kPa = 10 Percent at no load or free swell = 10 (1.07) + 2.6 = 10.7 + 2.6 = 13.3 These curves may have to be penciled in on Figures 3 or 4 for accurate readings. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication
41、 is a violation of applicable law.TS-1a T 258-8 AASHTO Figure 3Potential Vertical Rise Versus Load Curves for Free Swelling Clays 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 258-9 AASHTO Figu
42、re 4Potential Vertical Rise Versus Load Curves for Free Swelling Clays 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 258-10 AASHTO 4.3.6. In calculating the potential vertical rise, it is conve
43、nient or preferable to use 0.6-m elements or layers, provided the moisture contents and the log of the hole will permit. The use of 0.6-m layers and the assumption of 2002 kg/m3wet density, which is usually a reasonable wet density, make the tabulation simpler. The modification caused by using 2002
44、kg/m3rather than 2307 kg/m3for 7 kPa per meter has already been incorporated into the curves on Figures 3 and 4. Where wet densities vary from 2002 kg/m3and greater accuracy is desired, a modification factor should be applied to that layer equivalent to 2002 divided by the actual wet density. Note 4
45、In the 0.6-m layer at the surface, the “average” load in the layer is 7 kPa; likewise, in the 0.6 to 1.2-m layer, the kPa load is 14 kPa for the top 0.6 m plus one half of the 0.6 to 1.2-m layer, or 21 kPa total. Therefore, the average load in any 0.6-m layer is the average depth of the layer (subje
46、ct to the correction factor as described above). 4.3.7. Using the percent minus 0.425-mm (No. 40) sieve column, PVR subsequently determined shall be modified as follows: Use zero swell where the percent minus 0.425 mm is less than 25 percent. Multiply the swell obtained for the layer by the percent
47、minus 0.425 mm when the percentage exceeds 25 percent. 4.3.8. Then using Figure 2, determine the percent Volumetric Swell in the first layer (0 to 0.6 m). Since this swell is determined using 7-kPa surcharge, it must be modified for free swell, or no surcharge, as given in Note 3. Using Figures 3 an
48、d 4, and the percent free swell curve, just determined, begin to compile the swell in the layer as follows: 4.3.8.1. In the 0 to 0.6-m layer, read the ordinate (PVR) at the 7-kPa load from the swell curve and record on Table 3 as “bottom of layer.” 4.3.8.2. From the curve, read the “top of the layer
49、” load of zero in the case of this layer, and record on Table 3. 4.3.8.3. The difference in these two readings is the PVR in the first 0.6-m layer, subject to modification for density correction from Section 4.3.6 and for soil binder (minus 0.425-mm) correction from Section 4.3.7. 4.3.9. Take the 0.6 to 1.2-m layer and determine the percent Volumetric Swell by modifying the value determined from Figure 2. On this percent Volumetric Swell curve, or a sketched-in pencil curve if the line i
