Two Dimensional Analysis of Cone Penetration into the Ground

Abstract

Considering that the soil is a plastic-rigid material, the penetration of a cone or circular footing into the ground considered two-dimensionally as a wedge or footing is analysed under conditions of plane strain based on the theory of plasticity. An experiment was carried out in which the wedge and footing penetrated a clay sample contained in an acrylic box. Slip lines around the wedge or under the footing were photographed. The value of the bearing capacity factor for the wedge or footing N_cα were calculated and compared with the experimental values of the bearing capacity of the wedge or footing q/the undrained shear strength of the clay c_u. The results are summarized as follows:
(1) The analyses based on the theory of plasticity:
i) The weight of soil γ does not practically affect the shape of slip lines when γ/c_u≤0.1
ii) The smaller the value of the angle of internal friction φ, the larger the calculated value of β which is the inclination of the ground surface heaped around the wedge. The value of β is larger when the surface of the wedge is smooth than when it is rough.
iii) The bearing capacity factor for smooth wedges increases with increasing semi angle of the wedge α(α=0-90°), On the other hand, the value of N_cα for rough wedges decreases with decreasing α, reaches a minimum value at a certain α value and increases again with decreasing α. The larger the value of φ, the smaller the value of α at which the bearing capacity factor for th rough wedge is at a minimum.
iv) Generally, the value of N_cα is smaller when calculated considering the effect of β.
(2) The penetration experiment and photographic observation of the slip lines:
i) The analysis made by assuming the existence of slip lines is applicable to the case of clay. ii) The slip line field in Hill's solution occurs under the smooth footing and that in Prandtl's solution occurs under rough footing.
iii) The direction with which the soil mass moves around the wedge largely coincides with the direction predicted from the hodograph.
iv) The smaller cones such as those in common use should be considered to have rough surfaces compared with the wedge used in the present experiment.