Development of Electronic Miniature Cone Penetrometer and Penetration Test in Silty Clay

A new kind of electronic miniature cone penetrometer is developed for miniature cone penetration test (MCPT), with which the cone penetration resistance and penetration depth can be acquired automatically. In order to form homogeneous soil specimens for MCPT, a new experimental facility is designed. A series of MCPTs in silty soil are carried out and it is found that, for silty soil, the curves of the penetration resistance vs. the depth have no correlation with the cone angles. For MCPTs in silty clay, the initial segment of the penetration curve is straight and the cone tip resistance tends to be stable when the cone is intruded into a certain depth, i.e. the critical depth. For silty clay, the critical depth effect of the cone tip resistance is related with the different failure mechanism of soil under different confining pressure. The relation between the characteristic values of the penetration curve and soil strength parameters is analyzed. The cone resistance factor is linear with the tangent of the internal friction angle of soil. The ultimate cone penetration resistance is found to be closely related to the critical depth.