The Fall Cone apparatus, first introduced in 1915, provides a rapid, simple and accurate method for determining empirically the undrained shear strength, the shear strength of remoulded samples and thus the sensitivity of clays. The equipment is also used for determination of liquid limit WL (or fineness number WF). Four cones of different weight and apex angle are provided. The diagram shows the relation of shear strengths in undrained and remoulded samples measured by cone test, vane tests and unconfined compression test (Norwegian Geotechnical Institute Publ. 41, Oslo).
The shear strength of a soil (s) is proportional to the weight of the cone (Q) and inversely proportional to the square of the penetration (h) of the cone into the sample: s= K•Q/h2 (Hansbo, see reference). The proportional constant (K) depends primarily on the angle of the cone and sensitivity of the clay. The shear strength is measured by placing the sample underneath the cone holder, with the tip of a cone touching the sample. After releasing the cone from the magnet holder and measuring the depth of penetration, the shear strength of the undisturbed or of the remoulded sample is given in tables accompanying the apparatus.
- Rapid, simple and accurate measurement of:
– Undrained shear strength
– Shear strength of remoulded samples and thereby sensitivity
– Liquid limit WL
- Testing capacity: Shear strengths of 0.01. to 200 kPa (0.001 to 20t/m2)
- Portable and easy to use
- Designed by the Norwegian Geotechnical Institute, NGI
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