Viscous effects on penetrating shafts in clays

Abstract

The penetration of rigid objects such as piles and penetrometers into soils creates a zone of soil disturbance around them. The extent of this disturbed zone influences the resistance of the moving rigid body. This paper presents a theoretical framework to analyze the resistance in the disturbed zone created by a shaft penetrating a clay soil. The soil is modeled as a viscous material after it reaches failure [critical state (CS)]. The results of this analysis show that the viscous drag stress component on the shaft surface is influenced by the size of disturbed zone that has reached CS around the shaft, the shear viscosity of the soil and the velocity profile (or strain rate) in the CS zone around the shaft. The size of CS zone, the velocity profile and the viscosity of soil are interdependent. Large variation in viscous drag occurs when the size of the CS soil zone is less than four times the shaft's radius. Limiting drag occurs when the size of the CS soil zone exceeds six times the shaft's radius. The theoretical velocity distribution of the movement of soil in the CS zone shows that the soil is dragged along with shaft in the near field (close to the shaft surface) and moves upwards in the far field.

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.…”

Shear viscosity of clays using the fall cone test

“…Studies concerning the dynamic penetration of plates, probes and cone penetrometers in clays (Turnage, 1973;Murff & Coyle, 1973;Berry, 1988;Mahajan & Budhu, 2006) show that viscous resistance is an important component of the total resistance offered by the soil during penetration.…”