AASHTO T 223-1996 Standard Method of Test for Field Vane Shear Test in Cohesive Soil《粘性土风向标测试的标准测试方法》.pdf

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1、Standard Method of Test for Field Vane Shear Test in Cohesive Soil AASHTO Designation: T 223-96 (2012) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1b T 223-1 AASHTO Standard Method of Test for Field Vane Shear

2、Test in Cohesive Soil AASHTO Designation: T 223-96 (2012) 1. SCOPE 1.1. This method covers the field vane test in soft, saturated, cohesive soils. Knowledge of the nature of the soil in which each vane test is to be made is necessary for assessment of the applicability and interpretation of the test

3、. 1.2. The values stated in SI units are to be regarded as the standard. 2. SUMMARY OF METHOD 2.1. The vane shear test basically consists of placing a four-bladed vane in the undisturbed soil and rotating it from the surface to determine the torsional force required to cause a cylindrical surface to

4、 be sheared by the vane; this force is then converted to a unit shearing resistance of the cylindrical surface. It is of basic importance that the friction of the vane rod and instrument be accounted for; otherwise, the friction would be improperly recorded as soil strength. Friction measurements un

5、der no-load conditions (such as the use of a blank stem in place of the vanes, or a vane that allows some free rotation of the rod prior to loading) are satisfactory only provided that the torque is applied by a balanced moment that does not result in a side thrust. As torsional forces become greate

6、r during a test, a side thrust in the instrument will result in an increase in friction that is not accounted for by initial no-load readings. Instruments involving side thrust are not recommended. The vane rod may be of sufficient rigidity that it does not twist under full-load conditions; otherwis

7、e, a correction must be made for plotting torque-rotation curves. 3. APPARATUS 3.1. The vane shall consist of a four-bladed vane, as illustrated in Figure 1. Vane dimensions shall be as specified in Table 1. Sizes other than those specified in Table 1 shall be used only with the permission of the en

8、gineer in charge of the boring program. The ends of the vane may be tapered (Figure 1). The penetrating edge of the vane blade shall be sharpened having an included angle of 90 degrees. 3.2. The vane shall be connected to the surface by means of steel torque rods. These rods shall have sufficient di

9、ameter such that their elastic limit is not exceeded when the vane is stressed to its capacity (Note 1). They shall be so coupled that the shoulders of the male and female ends shall meet to prevent any possibility of the coupling tightening when the torque is applied during the test. If a vane hous

10、ing is used, the torque rods shall be equipped with well-lubricated bearings where they pass through the housing. These bearings shall be provided with seals to prevent soil from entering them. The torque rods shall be guided so as to prevent friction from developing between the torque rods and the

11、walls of casing or boring. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 223-2 AASHTO Figure 1Geometry of Field Vane Table 1Recommended Dimensions of Field Vanesa Minimum Casting Requirement Di

12、ameter Height Thickness of Blade Diameter of Vane Rod mm in. mm in. mm in. mm in. A 38.1 1.5 76.2 3 1.59 0.0625 12.7 0.5 Acker B 50.8 2 102 4 1.59 0.0625 12.7 0.5 Type N 63.5 2.5 127 5 3.18 0.125 12.7 0.5 H 92.1 3.625 184 7.25 3.18 0.125 12.7 0.5 SGIbH 55 2.17 110 4.33 2 0.078 11 0.43 Type H 65 2.56

13、 130 5.12 2 0.078 11 0.43 B 50 1.97 110 4.33 2d0.078 20 0.79 NilconcN 65 2.56 130 5.12 2 0.078 20 0.79 Type H 80 3.15 172 6.77 2 0.078 20 0.79 aSelection of the vane size is directly related to the consistency of the soil being tested; that is, the softer the soil, the larger the vane diameter. bThi

14、s is a totally self-contained, portable vane shear unit, which is capable of providing its own cased hole. Where overburden is too stiff, casing is required for the 77-OD mm vane housing. cThis is a totally self-contained, portable shear unit, which is capable of being pushed directly into the soil.

15、 The vane is followed by a slip coupling during penetration, which provides for rod friction calibration before each test. Where overburden is too stiff, casing is required. dThis is the average thickness. Vane blades are tapered 2.5 mm (0.098 in.) at the shaft to 1.5 mm (0.059 in.) at the edge. 3.3

16、. Torque shall be applied to the torque rods, thence to the vane. The accuracy of the torque reading should be such that it will produce a variation not to exceed 1.2 kPa (25 lb/ft2) shear strength. 3.4. It is preferable to apply torque to the vane with a geared drive. In the absence of a geared dri

17、ve, it is acceptable to apply the torque directly by hand with a torque wrench or equivalent. The duration of the test should be controlled by the requirements of Section 4.3. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violati

18、on of applicable law.TS-1b T 223-3 AASHTO Note 1If torque versus rotation curves are to be determined, it is essential that the torque rods be calibrated (prior to use in the field). The amount of rod twist (if any) must be established in degrees per meter (foot) per unit torque. This correction bec

19、omes progressively more important as the depth of the test increases and the calibration must be made at least to the maximum depth of testing anticipated. 4. PROCEDURE 4.1. In the case where a vane housing is used, advance the housing to a depth that is at least five vane housing diameters less tha

20、n the desired depth of the vane tip. Where no vane housing is used, stop the hole in which the vane is lowered at a depth such that the vane tip may penetrate undisturbed soil for a depth of at least five times the diameter of the hole. 4.2. Advance the vane from the bottom of the hole or the vane h

21、ousing in a single thrust to the depth at which the test is to be conducted. Take precautions to make sure no torque is applied to the torque rods during the thrust. 4.3. With the vane in position, apply the torque to the vane at a rate that should not exceed 0.1 degrees per second. This generally r

22、equires a time to failure of from 2 to 5 min, except in very soft clays where the time to failure may be as much as 10 to 15 min. In stiffer materials, which reach failure at small deformations, it may be desirable to reduce the rate of angular displacement so that a reasonable determination of the

23、stressstrain properties can be obtained. During the rotation of the vane, hold it at a fixed elevation. Record the maximum torque. With apparatus with geared drives it is desirable to record intermediate values of torque at intervals of 15 s or at lesser frequency if conditions require. 4.4. Followi

24、ng the determination of the maximum torque, rotate the vane rapidly through a minimum of 10 revolutions; the determination of the remolded strength should be started immediately after completion of rapid rotation and in all cases within 60 s after the remolding process. 4.5. In the case where soil i

25、s in contact with the torque rods, determine the friction between the soil and the rod by means of torque tests conducted on similar rods at similar depths with no vane attached. Conduct the rod friction test at least once on each site; this shall consist of a series of torque tests at varying depth

26、s. 4.6. In apparatuses in which the torque rod is completely isolated from the soil, conduct a friction test with a blank rod (Note 2) at least once on each site to determine the magnitude of the friction of the bearings. In a properly functioning vane apparatus, this friction should be negligible.

27、4.7. Conduct undisturbed and remolded vane tests in cohesive soils only. Do not conduct the vane test in any soil that will permit drainage or dilates during the test period, such as sands or silts or in soils where stones or shells are encountered by the vane in such a manner as to influence the re

28、sults. Note 2In some cases, it is not necessary to remove the vane for the friction test. As long as the vane is not in contact with the soil, that is, where it is retracted into a casing, the friction measurements are not affected. 5. CALCULATION 5.1. Calculate the shear strength of the soil in the

29、 following manner: The turning moment required to shear the soil is as follows: T = s K (1) where: 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 223-4 AASHTO T = torque, kNm (or lbfft); s = she

30、ar strength of the clay kPa (or lbf/ft2); K = constant depending on dimensions and shape of the vane, m3(or ft3). 5.2. Assuming the distribution of the shear strength is uniform across the ends of a cylinder and around the perimeter, calculate the value of K as follows: SI Units: 2912310= +DH DKH(2)

31、 U.S. Customary Units: 211728 2 3= +DH DKH(3) where: D = measured diameter of vane, mm (in.); and H = measured height of vane, mm (in.). It is important that these dimensions are checked periodically to ensure the vane is not distorted or worn. 5.3. If the ratio of length to breadth of the vane is 2

32、:1, the value of K may be simplified in terms of the diameter so that it becomes the following: SI Units: 393.6610= KD (4) U.S. Customary Units: 332.1210= KD (5) 5.4. Because the value of s is required, it is more useful to write the equation as follows: = sTK (6) where: T = the torque, is measured

33、so that s can be calculated. 5.5. For the tapered vane of Figure 1, the following modified equation may be used for the vane constant: SI Units: ( )3 33910.37 210=+K D Dd (7) U.S. Customary Units: ( )3 3310.37 21728= +K D Dd (8) where: d = rod diameter, mm (in.). 2015 by the American Association of

34、State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 223-5 AASHTO 6. REPORT 6.1. For each vane test, record the following observations: 6.1.1. Date of test; 6.1.2. Boring number; 6.1.3. Size and shape of the vane (tapered or rectangular

35、); 6.1.4. Depth of the vane tip; 6.1.5. Depth of the vane tip below the housing or bottom of the hole; 6.1.6. Maximum torque reading, and intermediate readings if required for the undisturbed test; 6.1.7. Time to failure of the test; 6.1.8. Rate of remolding; 6.1.9. Maximum torque reading for the re

36、molded test; and 6.1.10. Notes on any deviations from standard test procedure. 6.2. In addition, record the following observations for the boring: 6.2.1. Boring number; 6.2.2. Location; 6.2.3. Location of the soil conditions; 6.2.4. Reference elevation; 6.2.5. Method of making the hole; 6.2.6. Descr

37、iption of the vane, that is, housed or not; 6.2.7. Description of the method of applying and measuring the torque; 6.2.8. Notes on the driving resistance; 6.2.9. Name of the drilling foreman; and 6.2.10. Name of the supervising engineer. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.