In a paper by O.E. Gouda from 2010, nine artificial samples of soil were investigated and tested for determination of their thermal properties. Sand mixed with differnt ratios of lime as artificial backfill materials were tested.

Symbol
$M_{\mathrm{soil}}$
Unit
-
Related
$\rho_{\mathrm{4}}$
Choices
Soil sample
 
Gravel
%
Sand
%
Silt
%
Clay
%
Lime
%
ρ4 (wet)
K.m/W
ρ4d (dry)
K.m/W
Sand1.588.510.00.00.00.962.036
Lime1.51.57.00.090.00.9412.35
Clay3.06.02.089.00.00.6271.568
25% Sand + 75% Lime0.324.01.70.074.00.8222.156
50% Sand + 50% Lime0.548.52.50.048.50.7841.911
75% Sand + 25% Lime0.00.02.024.074.00.5221.304
75% Clay + 25% Lime1.474.00.60.024.00.881.792
Silt + Sand10.060.030.00.00.00.7561.9
Clay + Salt + Sand3.037.030.030.00.00.831.65