TM 5-852-4/AFM 88-19, Chap. 4
Table 4-7. Computation of Temperature Below Top of Permafrost.
NOTE: The temperature distribution in the silt layer is the same as if all the soil were silt and the temperature distribution
in the sand is obtained by first computing the temperature as if the layer were silt and then adjusting the depths
beneath the silt-sand interface, In this case:
X' =-1 (X-20) + 20 = Actual distance from top of permafrost to point in sand
U. S. Army Corps of Engineers