1. Parametrized PISA curves Figure 1. Parametrized PISA curves Figure 1 above shows how the shape of PISA curves is related to four parameters k, n, Xu and Yu. The curve is a normalized non-dimensional curve. The values, \({x}\) and \({y}\), are scaled with physical soil layer properties as defined in the soil layer profile, \(\bar{x}\) and \(\bar{y}\). The initial stiffness is given by k and ultimate values are given as Xu and Yu. The parameter n ranges from 0 to 1, where 0 gives a bilinear curve and 1 gives a straight line from (0,0) to (Xu,Yu), see Figure 1 for n=0 and n=1 respectively. The Parametrized PISA curve equation below is used to define the exact shape of the curve: \[-n (\frac{\bar y}{\bar{y}_u}-\frac{\bar x}{\bar{x}_u})^2+(1-n)(\frac{\bar y}{\bar{y}_u}-\frac{\bar x k}{\bar{y}_u})(\frac{\bar y}{\bar{y}_u}-1)=0\] The initial stiffness k must satisfy the requirement k > Yu/Xu. Pisa Soil Model Pisa Soil Layer Profile