Geotextile Transmissivity
Calculate a geosynthetic's transmissivity, θ = k_p·t, from the in-plane permeability k_p (m/s) and the thickness t (m); the result, in m²/s, is the transmissivity. Transmissivity characterizes the geosynthetic's ability to convey water WITHIN its own plane (longitudinally, like a planar drain), and is the key property in the DRAINAGE function. While permittivity measures flow THROUGH the geotextile (perpendicular), transmissivity measures flow ALONG it (parallel). It is the fundamental property of drainage geocomposites and geonets — products with a 3D open core (geonet) between filtering geotextiles, used to drain water replacing gravel layers: drainage behind retaining walls, under landfills (leachate and gas collection), in roads, sports fields and gardens (subsurface drainage), and in foundations. Transmissivity depends strongly on confining PRESSURE (the more compressed, the less space for water to flow and the lower θ) and on gradient, so it is specified at the work's real load conditions. Times the gradient and width, it gives the drained flow. Enter the in-plane permeability and the thickness.
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Transmissividade de geotêxtil
A transmissividade de um geossintético é θ = k_p·t, a partir da permeabilidade no plano k_p e da espessura t; o resultado, em m²/s, é a transmissividade. Ela caracteriza a capacidade do geossintético de conduzir água dentro do seu próprio plano (no sentido longitudinal, como um dreno laminar), e é a propriedade-chave na função de drenagem. Enquanto a permissividade mede o fluxo através do geotêxtil (perpendicular), a transmissividade mede o fluxo ao longo dele (paralelo). É a propriedade fundamental dos geocompostos drenantes e georredes — produtos com núcleo tridimensional vazado (georrede) entre geotêxteis filtrantes, usados para drenar água em substituição a camadas de brita: drenagem atrás de muros de arrimo, sob aterros sanitários (coleta de chorume e gases), em estradas, campos esportivos e jardins (drenagem subsuperficial), e em fundações. A transmissividade depende fortemente da pressão de confinamento (quanto mais comprimido o geocomposto, menor o espaço para a água fluir e menor θ) e do gradiente, por isso é especificada nas condições reais de carga da obra (e não em laboratório descarregado, o que superestimaria a drenagem). Multiplicada pelo gradiente e pela largura, dá a vazão drenada. Informe a permeabilidade no plano e a espessura.
Related Tools
Geocomposite Drain Flow
Calculate the drainage flow of a drainage geocomposite, q = θ·i·b, from the transmissivity θ (m²/s), the hydraulic gradient i (dimensionless) and the drain width b (m). This is the practical application of transmissivity: it estimates how much water a drainage geocomposite (geonet between geotextiles, or drainage geotextile) can convey in its plane, to check whether it adequately replaces a gravel layer or conventional drain. The flow is the product of transmissivity (the drain's in-plane 'conductivity' at the work's confining pressure), the hydraulic gradient (the head-line slope driving the flow) and the drain width (the drainage front). It is Darcy's law applied to in-plane flow in the geosynthetic. This calculation is essential to size drainage systems with geocomposites: gas and liquid drainage in landfills and mining, drains behind walls and cutoffs, green-roof and buried-structure drainage, and road and railway drains. The flow the geocomposite provides is compared with the design flow (the water to drain, with a safety factor); if insufficient, a higher-transmissivity geocomposite is chosen or the width increased. Enter the transmissivity, hydraulic gradient and width.
Geotextile Permittivity
Calculate a geotextile's permittivity, ψ = k_n ÷ t, from the cross-plane permeability k_n (m/s) and the geotextile thickness t (m); the result, in s⁻¹, is the permittivity. Permittivity characterizes the geotextile's ability to let water pass PERPENDICULAR to its plane (through the fabric), and is the key property in the FILTRATION and cross-plane DRAINAGE functions. It is defined as permittivity (not simply permeability) because a geotextile's thickness is small, variable and hard to measure precisely under load — so permeability is normalized by thickness, giving a property (ψ = k/t) measurable directly from flow per unit area and gradient, without knowing the thickness. In a geotextile filter (replacing the traditional graded sand filter in drains, behind retaining walls, under riprap), the geotextile must be permittive enough to let water pass freely (without damming and building pore pressure), but with pores small enough to RETAIN the soil particles (without clogging or letting soil escape — the retention criterion). The balance between permittivity and retention is the heart of geotextile filter design. Enter the cross-plane permeability and the thickness.
Reinforcement Tension per Layer (Geogrid)
Calculate the required tensile tension in a geosynthetic reinforcement layer in a reinforced-soil wall or slope, T_req = K_a·γ·z·S_v, from the active earth pressure coefficient K_a, the soil unit weight γ (kN/m³), the layer depth z (m) and the vertical spacing between layers S_v (m). In a reinforced-soil wall (geogrid walls, mechanically stabilized earth, reinforced steep slopes), each geosynthetic layer must resist the horizontal force the soil, under active pressure, tends to push out over that height band. The required tension grows with DEPTH (z), since lateral pressure increases with the vertical soil stress above — so the lower layers of a reinforced wall are the most stressed and sometimes get stronger geosynthetics or smaller spacing. The vertical spacing S_v sets each layer's 'influence area' (closer layers → less force each). Comparing T_req with the geosynthetic's allowable strength (and checking pullout), the reinforcement is designed: type, strength, spacing and length of each layer. It is the central calculation in reinforced-soil wall and slope design. Enter the active earth pressure coefficient, unit weight, depth and vertical spacing.
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