The efficiency of drainage installed in clay soils using ditch backfill of soil mixed with lime is presented in this paper. The drainage
ditch backfill was mixed with lime where 0.6% of soil matter consists of active CaO. The paper proposes a methodology that
determines an optimal amount of lime. The experimental site was set in Kalnujai, Raseiniai district, Lithuania. The measurement of
filtration in drainage trench, the arable layer and the soil between drains was performed using a double ring infiltrometer. The mean
values of the hydraulic conductivity of the arable layer, the soil between drains, the pilot backfill and drainage ditches backfill with
a lime additive were respectively 1.66 ± 0.24, 0.65 ± 0.09, 0.94 ± 0.13 m/d and 2.47 ± 0.12 m/d under reliability of 95%. Dispersion
analysis on pilot drainage backfill and drainage ditch backfill with lime additive under ditch backfill containing 0.6 % of CaO in
soil matter showed that they significantly differ at a reliability of 95%. Thus, the effect of lime on the conductivity of the backfill
of the drainage ditch for the following 30-year period of drainage operation in clay soils has remained critical.