Recycled drain envelopes for problematic calcareous soils

In soils with low cohesion, using envelopes can help reduce the entry of soil particles into drainpipes (filter function) and reduce entrance resistance by creating a more permeable zone around drains (hydraulic function). Calcareous soils with calcium carbonate (CaCO3) content of more than 15% are considered hazardous problematic soils that cause envelope clogging and sedimentation in the subsurface drainage network. Synthetic envelopes have been proposed as a relatively cheaper accessible alternative to replace gravel envelopes, besides better-quality control. However, earlier testing of synthetic drain envelopes in calcareous soils has revealed poor performance. Therefore, the main objective of this study is to investigate new granular envelope materials (GEM), derived from recycling industries, as drain-envelope alternatives to the traditionally used, hence enhancing the subsurface drainage performance in calcareous soil. Theoretical and experimental lab and field investigations were conducted to assess the performance of the recycled GEM, considering different calcareous soil characteristics. The theoretical assessment revealed that the particle size distribution of the obtained recycled GEM is compatible with calcareous soil gradation, hence they would satisfy the desired hydraulic and filtration performance. Moreover, the lab investigations proved that the proposed recycled GEM satisfy no clogging conditions, and give a distinguished filter and hydraulic functions; with a permeability comparable to that of the natural gravel. The field investigations assure lab deductions, since the utilized recycled GEM revealed a promising hydraulic performance similar to or better than the currently used gravel envelopes.