Shear viscosity of clays using the fall cone test

Abstract

A knowledge of shear viscosity is important in understanding the viscous resistance in the dynamic penetration of soils for geotechnical applications such as jacked piles and cone penetrometers. Viscosities of soils with water contents greater than the liquid limit have been investigated using viscometers. There is, however, no standard method to determine shear viscosities of clays at water contents lower than the liquid limit. In this paper, the post failure (critical state) response of finegrained soils is modelled as if they were visco-plastic fluids. In addition, the theory of the fall cone test, currently used to interpret the index and strength properties of fine-grained soils, is re-evaluated to discern the viscous drag as the cone penetrates the soil. This reevaluation shows that the shear viscosities of clays at liquidity indices less than 1 . 5 can be estimated from a continuous record of time-cone penetration depth data. Fall cone test results on kaolin show that the shear viscosity decreases exponentially with increase in liquidity indices.

Methods

“…Fall cone factor is a constant that is influenced by cone geometry, cone roughness, surrounding soil or sediment, and dynamic effects (Houlsby, 1982;Wood, 1985;Koumoto and Houlsby, 2001;Mahajan and Budhu, 2009). In empirical fall cone experi-ments performed with cones of different angles, Wood (1985) showed that the average cone factor value for the 30° cone is K = 0.85.…”

A comparative study of different model families for the constitutive simulation of viscous clays

“…Most clays show a rate-dependent mechanical behavior as presented in many experimental works. [1][2][3][4][5][6][7][8][9][10][11] Experience has shown that rate dependency influences many geotechnical problems, for example, long-term settlement of structures, [12][13][14][15][16][17] slope creep, 18,19 pile shafts penetration, 20,21 and ground anchor relaxation. [22][23][24][25][26] Clearly, the study of the soil's viscous behavior is of relevant importance.…”

Development of Laboratory Methodologies for the Determination of Viscosity and Yield Stress of Mass-Flowing Soils

“…No standards are available to evaluate rheological soil parameters from single geotechnical tests. Nguyen & Boger (1983 Mahajan & Budhu (2009) proposed the use of the laboratory fall cone test to estimate the viscosity of soils at low liquidity indexes (LI < 1.5), finding that, for kaolin samples, shear viscosity decreases exponentially with LI. These authors assumed a theoretical simulation of the fall cone test (Houlsby, 1982) to backanalyse the shear viscosity while taking into account a given rheological model and a modified cone factor, K (Koumoto & Houlsby, 2001).…”