Design of Roadside Channels with Flexible Linings
Hydraulic Engineering Circular Number 15, Third Edition

Appendix F: Shear Stress Relationship for RECPS

The general relationship for the transmission of shear to soil surface beneath a manufactured unvegetated lining is given by (Cotton, 1993; Gharabaghi, et al., 2002; Robeson, et al., 2003):

(F.1)

where,

The critical shear value, τ_c, is for the soil type described in testing procedure ASTM D 6460.

Laboratory testing (McWhorter et al., 1968; Sanders, et al., 1990; Israelsen, et al., 1991; Northcutt, 1996; Robeson, et al. 2003) has shown that the rate of soil loss remains nearly constant and does not change with increasing shear stress over a wide range of applied shear stress. Data from Robeson, et al. (2003) is presented in Figure F.1 and shows this linear relationship for four lining types.

Figure F.1. Soil Shear versus Applied Shear to the Manufactured Lining

For a wide range of product types, the critical shear and the rate of shear transmission is directly related to the applied shear on the lining at cumulative soil erosion of 12.7 mm (0.5 in) over 30 minutes for a specified soil type in accordance with the ASTM D 6460. This shear value is referred to as the lining shear, τ_l. (Note, the lining shear should be determined by testing under the same conditions as recommended by the manufacturer, i.e. stapling pattern, check slots, etc.)

As would be expected the critical shear on the lining is just a linear extrapolation from τ_l.

(F.2)

where,

Likewise, the rate of shear transmission correlates to:

(F.3)

where,

Combining Equation F.2 and Equation F.3 with Equation F.1 gives:

(F.4)

Comparison to data presented in Robeson, et al. is shown in Figure F.2.

Figure F.2. Effective Shear on the Soil for Four RECP Linings

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