Calculation of required tensile strength of geosynthetic, used as reinforcement underneath a soil layer on a slope, without toe abutment

Density of the soil (ɣ) in kN/m3
Thickness of the soil layer (t) in m
Slope angle with horizontal (β) in degrees
Length of the slope, measured on the incline (L) in m
Most critical angle of internal friction in the multi-layer structure in degrees(δ)
Safety factor over all (F), without dimension
Safety factor installation damage F(installation), without dimension
Safety factor durability F(durability), without dimension
Safety factor against creep F(creep), without dimension
Required strength of geosynthetic in kN/m

Calculation method

The stability of veneer cover soil on a slope should be checked against sliding. Especially when preferential sliding surfaces are present, e.g. a geomembrane, a bentonite geocomposite, a layer of clay. Due to typical low shear strength between the cover soil and the layer(s), the soil mass of the capping could slide down. The most important driving force, creating the instability, is the gravitational force (W). As an example for calculation of the required tensile strength (T) for geosynthetic reinforcement, the situation is considered where the veneer cover soil is installed on a geomembrane (GMB). The driving force (T1) is calculated and as a result of this, the necessary restoring force (>T1) is defined. The approach of design consists in taking into account the most critical (lowest) friction angle (δ) in the multi-layer structure. The veneer cover soil is considered as ridged block (l x t x 1m), mobilising friction between the different layers, thus a restoring force (T2). The lack of restoring force has to be compensated by the tensile strength of the geosynthetic (T) to be anchored at the top. In the design method used, the stabilising force of a toe at the bottom of the slope is not taken into account. Attention should be given to the internal friction angle (φ) of the cover soil itself, indicating the upper limit for all values of friction as well as for the angle (β) of the slope.

Function of the geosynthetics

The geosynthetic used to assure the stability will have the necessary specifications in terms of tensile strength, creep properties, permeability and friction with adjacent materials. Texion offers a wide variety of geotextiles and geogrids that will fulfil the design requirements. The geosynthetic used for reinforcement should be supplied in one piece, without overlap, nor stitching in the length (warp) direction.