On the problem of durability of underground drainage in the natural and climatic conditions of the Novgorod region

The article deals with the problem of stable operation of various structures of drainage systems on heavy soils in the natural and climatic conditions of the Novgorod region during the first years after construction and after 30 years of operation. The experiment examines the effectiveness of drainage using shallow drainage structures with the depth of 70 cm and two variants of medium-deep drainage (110 cm) with filling the drainage trench with sand-gravel mixture (PGS) and wood chips to the arable horizon. Analysis of groundwater dynamics showed that the rate of groundwater decline in the early spring period in the first years of operation on all experimental variants was approximately the same: 2.0-2.4 cm/day. In recent years in the shallow drainage variant, the decrease in ground water levels occurred more slowly (2.3 cm/day) compared to the standard drainage variants (3.8-3.9 cm/day). The average humidity of the root layer of the soil during the growing season in experimental closed drainage systems has not increased for 30 years. The average moisture reserves for the growing season in the experimental systems were: 177 mm in the shallow drainage variant in 1991, 168 mm in 2018; 165 and 154 mm for the standard drainage with drainage chips backfill, respectively; 164 and 123 mm in the PGS backfill variant, respectively. The highest reliability and durability were shown by collectors with PGS backfill of the drainage trench, which have maintained a consistently high efficiency over a thirty-year period. During the drought period, shallow drainage systems provided more favorable conditions according to the degree of moisture in the root layer: in 2018, the shortest period of moisture lack in the root layer of the soil (10 days) was observed in shallow drainage systems, and the longest (1 month) - in systems with backfill of the drainage trench with PGS.