A drainage cell (10) comprises a backing plate (12) defining a plurality of holes (16a, 16b), a series of conical tubular structures (18) having side walls and a base extending from the backing layer, the tubular structures being in fluid communication with at least some of the holes (16a, 16b) in the backing plate (12) thereby allowing fluid to pass through the holes into a generally tubular structure. The sides of the tubular structures define apertures (109) permitting fluid flow out of the tubular structures through the walls of the tubular portions. Typically, the perforated or open area of the tubular structures is at least 20% of the area of the side walls of the tubular structures, more preferably at least 40%, more preferably 50% or greater and most preferably of the order of 70 to 75%. Providing apertures (109) in the side walls of the tubular structures significantly improves not only the rate of flow of the water through the cell but also creates a higher internal drain void volume area as the water can occupy the interior of the tubular structures and not just the volume in between the tubular structures.L’invention concerne une cellule de drainage (10) comprenant une plaque de support(12) définissant une pluralité d’orifices (16a, 16b), une série de structures tubulaires coniques (18) possédant des parois latérales et une base s’étendant à partir de la couche de support, les structures tubulaires étant en communication fluidique avec au moins certains desdits orifices (16a, 16b) de la plaque de support (12), permettant ainsi à un fluide de traverser les orifices jusqu’à une structure généralement tubulaire. Les côtés des structures tubulaires définissent des ouvertures (109) permettant au fluide de s’écouler hors des structures tubulaires à travers les parois des parties tubulaires. Typiquement, la zone perforée ou ouverte des structures tubulaires couvre au moins 20 % de la zone correspondant aux parois latérales des structures tubulaires, de préféren
