Minimisation of leg-slot expansion in mole-drained sports surfaces

Mole drainage is an appropriate method for low-cost drainage of sports surfaces on clay soils. Its adoption as a solution in the sports surface–drainage industry has been limited, in part, because of concerns over player safety in the first 12–24 months post-installation due to excessive leg-slot expansion. Two experiments investigated the effect of mole-plough leg width and mole-drain spacing on mean leg-slot width for a 6-month period following installation of mole drains at two sites on clayey soils. The effect on leg-slot expansion of secondary slitting using a rotating knife soil-loosening implement, both parallel and perpendicular to the mole-drain direction, was also determined. Mole-plough leg width and mole-drain spacing had a significant effect on leg-slot width. The parameter t10 was defined as the time taken for leg-slot width to reach a safe value of 10 mm or less. Reducing mole-drain-spacing from 1.5 to 1.0 m significantly reduced t10 from 90 to 30 days. Secondary slitting parallel to the mole-drain direction significantly reduced t10 from 90 days to 32 days at 1.5 m and from 100 to 66 days at 2.0 m spacing. There was no significant effect of secondary slitting on t10 at 1.0 m. Practitioners should operate with a mole-plough leg width of 20 mm and reduce mole-drain spacing to 1.0 m to minimise leg-slot expansion and reduce the time between installation and commencement of play. For combined 1.5 m mole drain centres and slitting to be as economical as 1 m mole drains, requires a 78% reduction in current slitting costs.