Efforts have been made to estimate permeability coefficient of soil using cone penetration test with pore pressure measurement (CPTU) in recent years. However

there are large deviations for the current approaches. Moreover

the mechanism of permeability coefficient determined by CPTU can not be explained explicitly. In order to directly determine the permeability coefficient of soil by CPTU in the field

two assumptions are proposed: i) the flow surface area for pore water is assumed to be a spherical crown covered the tip of the cone; ii) negative exponent distribution of initial excess pore water pressure during CPTU is assumed. Based on these two assumptions and the previous approaches for evaluating the permeability coefficient of soil using CPTU

the equation to calculate the permeability coefficient of soil is derived. According to the measured data in the field

the comparison is made between the proposed approach and the existing one. The results show that the proposed modified approach extends the range of the application of existing approaches. The permeability coefficient of soil is influenced by the degree of the tip of the cone greatly

which increases with the increasing of the degree of the tip. For a cone penetrometer with 60 degrees accepted as the reference and specified in the international reference test procedure

the permeability coefficient determined by the proposed approach is larger than that of previous approaches and more close to that of lab and field tests.