m-method is a widely used method for pile-soil interaction analysis. The main shortcoming of traditional m-method is ignoring the non-linear of soil. The actual relationship between the m and the displacement of pile (y) caused by loads is non-linear; however, it is unreasonable to used a linear curve and a fixed value of m during the calculation. Two methods for getting the m-y curve based on the p-y curve and the NL method are given. Linear spring is used and the m is dynamic modified based on the m-y curve by iteration. A test problem of a large-diameter monopile for offshore wind turbine is given and the dynamic modification of m of the full-range, the shallow and the deep-seated soil are carried out. It reveals that the dynamic modification of m by iteration made it possible to consider the non-linear of soil; the difference between the traditional m-method and the p-y curve method or NL method is caused by the way that using one and fixed m value and it is reasonable to use the non-linear m-y curve obtained by in-situ test; the lateral load-bearing capacity of the pile is influenced mainly by the soil between the mud-line and the depth of 3~5D (pile diameter), so that the dynamic modification of the m can be carried out for this part of soil to raise efficiency.

According to the characteristics of installation about the penetrometer of seismic piezocone penetration tests (SCPTu) and the pile, a theoretical relationship between ultimate bearing capacity of single pile, time-effect of shaft bearing capacity of single pile, excess pore water pressure around the pile during pile driven and the data measured from SCPTu is developed based on the cavity expanded theory, the Terzaghi one-dimensional consolidation theory and effective stress theory. The result of field test in KunShan and the calculated result which used the theoretical relationship mentioned above are compared. The results indicate that the analytical solutions agree well with the in-situ tests, which show that the application of seismic piezocone penetration tests have wide range in the pile foundation.