TORVANE ®

TORVANE ®

Description

The TORVANE is a hand-held vane shear device for rapid determination of shear strength in cohesive soils either in the laboratory or the field. The TORVANE allows shear strength to be measured in the sides of test pits, trenches or excavations. It may also be used on the ends of thin wall or split spoon samples and soil chunks removed from test pits, etc.

What type of soils can it be used for?

The TORVANE has a stress range of from zero to 1.0 TSP. This is also the approximate range of torque that can be easily applied by the fingers. It should be used only for fully saturated cohesive soils whose undrained strength is independent of normal pressure. The stress range permits it to be used for clays varying in consistency from very soft to stiff.

What is its accuracy?

The shear strength of a cohesive soil is dependent upon many factors, including rate of loading, progressive failure, orientation of the failure plane, pore water migration during testing, etc. The TORVANE does not eliminate the effects of any of these variables. However, it does give repeatable values in a homogeneous clay and extensive laboratory testing indicates excellent agreement between the unconfined compression test and the TORVANE. The smallest division on the dial is in units of 0.05 TSF, permitting visual interpolation to the nearest 0.01 TSF

What are the advantages?

The TORVANE permits the rapid determination of a large number of strength values with different orientation of failure planes. It is simple to use and sample trimming is eliminated. All that is required is a reasonably flat surface one inch in diameter.

Typical applications in the field
The TORVANE, ideally suited to field usage, is an invaluable addition to the Boring Inspector's kit or to the Consulting Engineer. Suggested applications for evaluation of shear strength are:

1. Sides of Test Pits
2. Ends of Shelby Tube Samples
3. Standard Penetration Samples
4. Split Spoon Samples
5. Chunk Samples from Test Pits and Backhoe Excavations

Typical applications in the laboratory

The TORVANE is a precision testing device for the rapid determination of shear strength. Ten or more TORVANE tests can be performed in the same length of time as one unconfined compression test. Suggested applications on undisturbed thin-wall tube samples are:

1. Slit the sample lengthwise, using a wire saw, and at intervals of 1 to 6 inches perform a TORVANE test, thus obtaining quickly a more detailed strength profile than is possible by conventional methods.
2. Cut the sample into segments ½ inch longer than the desired length for a triaxial or consolidation test. Perform a TORVANE test on each end, then trim material disturbed by TORVANE.
3. Use the TORVANE as a control test to determine the shear strength prior to other testing.
4. In consolidation testing, after the specimen has been consolidated under a desired normal stress, remove the upper stone and determine, using the TORVANE, the consolidated strength of the specimen.

The TORVANE features:

• Three vane sizes to permit testing in a variety of clay consistencies.
• Calibrated dial converts torque directly into shear stress in kg/cm². The maximum reading obtained on the dial is the shear strength.
• High strength thermoplastic case.

The TORVANE set includes three vanes with conversion dial and carrying case.

Regular vane (0 to 1 kg/cm²): used for fully saturated cohesive soils with undrained strength independent of normal pressure. The stress range permits it to be used for clays varying in consistency from very soft to stiff

Large vane (0.2 kg/cm²): use with remolded samples.

Small vane (2.5 kg/cm²): for stiffer clays.

The TORVANE is 1-5/8 inches in diameter by 2-3/4 inches high.

TORVANE® is a registered tardemark of Durham Geo Slope Indicator.

TORVANE© Instructions:

Three sizes of vanes are supplied with each TORVANE. The standard vane has a stress range from 0 to 1 kg/cm²  (Approx. 1 ton/ft² ). This is also the approximate range of torque that can be easily applied by finger pressure. It is used for fully saturated cohesive soils with undrained strength independent of normal pressure. The stress range permits it to be used for clays varying in consistency from very soft to stiff. A large vane is provided for use with remolded samples, and has a ratio of 0.2. A smaller vane with a ratio of 2.5 is used with stiffer clays.

1. Select desired vane size and fit to vane driver.
2. Make sure zero on dial is aligned with index mark on knob. A counter-clockwise rotation of the dial face, (while holding onto the vane) brings the zero mark on the dial face back to the index mark.
3. Test surface should be reasonably flat and at least two inches in diameter. Press TORVANE into soil to depth of blades and maintain a constant vertical pressure while turning the knob. A rate of rotation such that failure develops in five to ten seconds is recommended.
4. After failure develops, release the remaining spring tension slowly and the index mark on the knob will indicate the maximum shear value.