Abstract
Good drainage is the most important design consideration for a road, both to miniaturize road maintenance costs and maximize the time the road is operational. The lack of good drainage lead to the structural damages and costly repairs. Many of roads are built in intensively drained agricultural land. The effective way to drain subgrades is reconstruction of existing agricultural drainage. The impact of cross-subsurface drainage system on water level fluctuation was measured using Plane geofiltration mathematical model, one of 3D geofiltration modelling programs. The hydraulic permeability characteristics were determined in field of Pikeliai, close to local road in Kėdainiai district, Lithuania. This object is composed of clay and loamy soils. Subsurface cross drains trenches spacing of 20 m, 30 m and 40 m were simulated. The hydraulic permeability of cross drain trenches and lateral trenches modelled was from 0.006 m/a day to 6 m/a day. The simulation of cross drains trenches showed that the most effective distance between them are 20 m. The highest water depression occurs when the permeability of cross drain trenches and lateral trenches is ~ 6 m/day, at the distance of 20 m. The water recession is 20 cm lower compared to the drainage systems without cross drains trenches. By installing cross drains trenches every 30 m, water recession is 10 cm lower when the trench permeability is about 6 m/day. When increasing the distance between the cross drains up to 40 m their influence disappears.
Highlights
The drainage system in road construction depends on factors such as: sensitivity of groundwater, importance of road, area, and intensity of traffic, density of streams, rivers and lakes
The hydraulic permeability of cross drain trenches and lateral trenches modelled was from 0.006 m/a day to 6 m/a day
Values obtained during modelling manifested that the selected technology allows to lower recession of ground water table in the area between the road and drainage system from 13% to 32%
Summary
The drainage system in road construction depends on factors such as: sensitivity of groundwater, importance of road, area (rural or populated), and intensity of traffic, density of streams, rivers and lakes. Heavy clay soils often have low hydraulic permeability that they require very narrow drain spacing (Ritzema et al 1994) As their permeability is dependent on the soilwater content and macro pores, it happens that their infiltration rate is too low for the water to enter the drain, that frequent surface water pond will occur. The most effective way to calculate the filtration value is based on water-table measurements, where lateral drains are already installed in the field (Moustafa 2000). The most effective way to calculate the filtration value is based on water-table measurements, where lateral drains are already installed in the field (Moustafa 2000; Oosterbaan 2002). The following 3D form of differential equation to calculate geofiltration is employed in the programme:
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