Correlation of Saturated Hydraulic Conductivity with Atterberg Limits and Soil Confined Compression Curve Parameters

In developing new pedotransfer functions, finding new input variables is a major challenge for improving the estimation of soil hydraulic properties. In this study, behavior of soils under compaction along with some basic soil properties were used as new inputs for the estimation of saturated hydraulic conductivity (Ks) of 120 soil samples from five provinces, namely, Mazandaran, West and East Azarbaijan, Kermanshah, and Hamadan. The Ks was estimated using Atterberg limits (liquid limit, plastic limit and shrinkage limit), confined compression curve parameters and basic soil properties (silt/sand, clay percentage and bulk density) as predictors, at 3 steps. At the first step, only the basic soil properties were used as predictors. Pedotransfer functions developed by regression method showed that step 2, with the inputs of confined compression curve parameters, and step 3, with the inputs of only Atterberg limits, both along with basic soil properties, led to relative improvement in the Ks estimates.The root mean square error (RMSE) values in training and testing of the steps 1, 2, and 3 were 0.624, 0.620, 0.584 and 0.887, 0.821, 0.829, respectively. According to RMSE criterion, relative improvement values for the training of the second and third steps were 0.64% and 6.35% and for the testing of the second and third steps were 7.55% and 6.33%, respectively. According to the R2adj entering confined compression curve parameters or Atterberg limits along with the basic soil properties could not improve the estimations. Accuracy of the third step (according to RMSE and Akaike’s information criterion) and reliability of the second and third steps (according to RMSE and Akaike’s information criterion) were improved in comparison with the first step.