假设条件：

If we assume, to first order, a soil porosity of 40% and a frozen active layer with saturated ice before thawing, then the thaw settlement causedby volume contraction (corresponding to a density changefrom 0.9 g/cm3of ice to 1 g/cm3of water) is 1.2–2.8 cmwithin one thawing season. the ALT=30cm。

估计：以1cm3为基准算，1g/cm3冰-0.9g/cm3冰，沉降为0.1cm；孔隙度为40%的话（孔隙全部冻结），沉降为0.1*40%=0.04cm，那么ALT=30cm，沉降为1.2cm。