The Fall cone test, also called the cone penetrometer test or the Vasiljev cone test, is an alternative method to the Casagrande method for measuring the
Liquid Limit
The Atterberg limits are a basic measure of the critical water contents of a fine-grained soil: its shrinkage limit, plastic limit, and liquid limit.
Depending on its water content, soil may appear in one of four states: solid, semi-solid, plastic ...
of a
soil sample proposed in 1942 by the russian researcher Piotr Vasiljev (russian: Пё́тр Васи́льев) and first mentioned in the russian standard GOST 5184 from 1949. It is often preferred to the Casagrande method because it is more
repeatable and less variable with different operators. Other advantages of the fall cone test include the alternative to estimate the undrained
shear strength
In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a materia ...
of a soil based on the fall cone factor K.
In the Fall cone test, A
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
cone of a standardized weight and tip angle is positioned so that its tip just touches a soil sample. The cone is released for a determined period of time, usually 5s, so that it may penetrate the soil. Several standards around the globe exist. Main differences are related to the cone tip angle and cone mass. The liquid limit is defined as the
water content
Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as ...
of the soil which allows the cone to penetrate a determined depth during that period of time. The penetration depth at which the liquid limit is measured depends on the standard and method adopted. For example, one of the most recognized standards is the BS 1377. The British standard defines the liquid limit as the water content of a soil at which a 80g, 30º cone penetrates 20mm. Because it is difficult to obtain a test with exactly 20 mm penetration, the procedure is performed multiple times for a range of water contents and the results are
interpolated
In the mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points.
In engineering and science, one often has a n ...
.
[Powrie, W., Spon Press, 2004, ''Soil Mechanics - 2nd ed'' ] Furthermore, the undrained
shear strength
In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a materia ...
for each one of those measured water content can be computed as proposed by Hansbo:
where,
''c
u = U''ndrained
shear strength
In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a materia ...
;
''K'' = Fall cone factor;
''Q'' = Cone weight;
''h'' = Penetration depth.
The fall cone factor can vary between 0.5 and 1.33. It can be estimated as proposed by Llano-Serna and Contreras:
where,
''
='' Equivalent rate of rotation when measuring the undrained shear strength using the mini
shear vane test.
A summary of different existing standards is shown in the table below:
References
{{DEFAULTSORT:Fall Cone Test
Soil shear strength tests