Shear Strength Characteristics of Sand‐Polymer Interfaces

The results are summarized for an experimental program involving over 450 direct shear tests of sand‐polymer interfaces. The interface frictional strength was found to increase with soil density and decrease with the Shore D Hardness of the polymer. The shear strength characteristics were found to vary as a function of the type of sand, but were independent of repeated loading, at least insofar as polyethylene piping and linings are concerned. The shear strength characteristics of a polymer interface can be expressed conveniently as the ratio of the interface angle of friction and the direct shear angle of soil friction, $\delta /{\varphi }_{\mathrm{ds}}^{\prime }\text{.}$ This ratio was relatively constant at 0.55–0.65 along high‐ and medium‐density polyethylene surfaces for different types of sands at various densities. A general model for interface frictional resistance is developed, in which $\delta /{\varphi }_{\mathrm{ds}}^{\prime }$ is related to the Shore D Hardness, $H_D\text{,}$ of the polymer. Limiting conditions for $\delta /{\varphi }_{\mathrm{ds}}^{\prime }$ are defined on the basis of theoretical considerations involving the critical state angle of shear resistance, ${\varphi }_{\mathrm{cv}}^{\prime }\text{.}$ This model allows for rapid evaluation of interface frictional strength and applies to plastic piping, linings, soil strip reinforcement, and a variety of other soil‐polymer systems.