Assessment of materials used in land drainage systems

Byrne, Ian Richard
Agricultural land drainage is one of a number of critical components to sustaining food production on poorly drained mineral soils. The key to efficient and consistent drainage system performance is an appropriate type and size of envelope material to surround the in-field drainage pipe that matches soil characteristics. The drain envelope must offer proficiency in a number of functions, such as protecting the pipe from excessive sedimentation and reducing water entry resistance around the pipe and surrounding soil. An efficient drainage envelope must perform well from both filtration and hydraulic perspectives. In Ireland, guidelines on aggregate size ranges that perform well from both filtration and hydraulic perspectives were never formally tested under scientific conditions. Such guidelines were based on the local availability of aggregates and stemmed from practical experience and localised field observations. In addition, alternative envelope materials (e.g., synthetic) are coming to market in Ireland. These have been used by landowners but remain untested in heavy-textured mineral soil. Indeed, there have been no experiments that compare filtration and hydraulic performance together with costs for various envelope types in Ireland. Therefore, the aims of this study were to: (1) quantify the size, type and popularity of aggregates supplied for use in agricultural land drainage systems, and to evaluate their suitability for use in mineral soils (2) provide guidance for contractors and farmers on the selection of suitable aggregate material, taking cognisance of performance, cost and lifespan (3) assess the hydraulic and filter performance of different drainage stone aggregates to elucidate an optimum size range for use in clay-textured soils, and (4) investigate the suitability of synthetic envelopes as an alternative to, or used in conjunction with, stone aggregate in clay-textured soils. Before the experimental phase of the work, the availability of stone aggregate used for land drainage works was established. A national survey was conducted across eighty-six quarries throughout Ireland to gather data on quarry distribution, aggregate type, sizes, popularity, and availability, and determine their suitability based on existing filter design criteria. The results indicated that limestone and river-run gravel (80% of all lithologies available at quarries) are widespread throughout the country. The quarry aggregate sizes changed across lithology and region and were, in most cases, larger than what is currently recommended by Ireland’s national agricultural research and advisory agency, Teagasc, (10 to 40 mm) for agricultural land drainage. The suitability of these aggregates as drainage envelopes in five soils of different textures was evaluated using three established design criteria. It was found that most of the aggregate in use is too large for heavy soil textures and is therefore unsuitable as drainage envelope material. Laboratory experiments were designed and conducted to quantify aggregate and synthetic envelope filter and hydraulic performance in clay-textured mineral soils using various aggregate and synthetic envelope configurations. The results indicated that only aggregates in the 0.7 to 19 mm size range performed adequately from both the filtration and hydraulic perspectives and were deemed suitable for use with a clay-textured soil. Based on this study, the use of synthetic envelopes, either alone or in combination with stone aggregate, is not recommended in Ireland, from both performance and cost perspectives.
NUI Galway
Publisher DOI
Attribution-NonCommercial-NoDerivs 3.0 Ireland