3. Terminology
3.1 Definitions:
3.1.1 For common definitions of terms in this standard, refer to Terminology D 653.
3.1.2 sensitivity—the effect of remolding on the consistency of cohesive soil.
3.1.3 vane shear test (VST)—an in-place shear test in which a rod with thin radial vanes at the end is forced into the soil and the resistance to rotation of the rod is determined.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 remolded undrained shear strength—shear strength of fine-grained soil in rapid loading with little or no drainage of pore water pressure after significant failure and remolding of the initial soil structure. (Also see D 2166 and D 4648). 3.2.2 undrained shear strength—shear strength of fine- grained soil (primarily clays and clayey silts) in rapid loading with essentially no drainage of porewater pressure. (Also see D 2166 and D 4648). 3.2.3 vane—a device with four, thin, flat metal blades or plates, fixed at an angle of 90 degrees to each other, which is inserted into the soil and then rotated about a vertical axis for shear testing (see Fig. 1). 3.2.4 vane shoe—a section of drill casing and cutting bit at the end in which the vane can be retracted while drilling or pushing
3.3 Symbols:
3.3.1 In accordance with ASTM D 653.
3.3.2 shear strength, su—the maximum (undrained) resis- tance of soil to shearing stresses.
3.4 Symbols Specific to This Standard:
3.4.1 peak undrained shear strength, (su)fv—the peak und- rained shearing resistance measured during the initial rotation of the vane in a vane shear test.
3.4.2 remolded undrained shear strength, (sur)fv—the re- molded undrained shear strength is measured after five to ten of vane rotations in a vane shear test.
3.4.3 sensitivity–ST fv—the ratio of peak undrained shear strength to remolded undrained shear strength measured in the field vane shear test: ST fv=( su)fv/(sur)fv. The remolded shear strength is measured after large shearing strains (see 8.7 and 9.3).
3.4.4 torque–T, (FL)—the measured torque (or moment) required to rotate the vane.
3.4.5 vane area ratio–VA–% —the ratio of the cross section area of the vane to the circular area of the rotated vane expressed as a percent (see Fig. 2).
3.5 Acronyms:
3.5.1 VST—vane shear test.
3.5.2 FV—field vane.
4. Summary of Test Method
4.1 The vane shear test consists of placing a four-bladed vane in the undisturbed soil and rotating it from the surface to determine the torque required to shear a cylindrical surface with the vane. This torque, or moment, is then converted to a the unit shearing resistance of the failure surface by limit equilibrium analysis. Friction of the vane rod and instrument are either minimized during readings by special casings or housing, or else accounted for and subtracted from the total torque to determine the torque applied to the vane.
5. Significance and Use
5.1 This test method provides an indication of in-situ undrained shear strength of fine- grained clays and silts or other fine geomaterials such as mine tailings, organic muck, and substances where undrained strength determination is required. The test is applicable to soils with undrained strengths of less than 200 kPa (2 tsf). Very sensitive soils can be remolded during vane insertion.
5.2 This test method is used extensively in a variety of geotechnical explorations to evaluate rapid loading strength for total stress analysis of saturated fine-grained clays and silts. The test is routinely performed in conjunction with other field and laboratory tests.
5.3 The peak undrained shear resistance of the vane test is commonly corrected to determine the undrained shear strength for geotechnical analysis. The agency requesting the testing must interpret these data to determine applicability for strength analysis. It is beyond the scope of this standard to recommend applicability of vane testing for geotechnical analysis. For information on the general use of these correction factors, consult Appendix X1.
5.4 This method is not applicable in sands, gravels, or other high permeability soils. With the shearing rates described in this standard, sand lenses, if present, will allow total or partial drainage. Soils with higher permeability, in rapid shear, can dilate or collapse and generate negative or positive pore pressures which may, or may not, dissipate in the shearing process. It is important to check the soil type being tested. It is very beneficial to sample the soil either before or after testing, to understand the drainage conditions (permeability) of the soil tested.
5.5 This test is often performed in drilled boreholes or with self-push or self-drilling or pushed (vane shoe) methods. This method also applies to hand held vane shear tests performed at shallow depths, however, hand held equipment may be less accurate, because it may be more difficult to maintain vane/rod stability and verticality.