Experimental Investigation of the Interaction Mechanism at the EPS Geofoam-Sand Interface by Direct Shear Testing

Abstract

The results of laboratory direct shear tests conducted at the expanded polystyrene (EPS) geofoam-sand interface are presented in this paper. The sands used in the tests were composed of rounded to subangular particles with values of mean particle size ranging from 0.28 to 2.17 mm and void ratios ranging from 0.51 to 0.72. The EPS geofoam was of two different densities: 10 and 20 kg/m 3 . The test results are expressed in the form of shear stress versus normal stress in direct shear failure envelopes, which were found to be nonlinear. The curved interface failure envelopes were approximated by piecewise linear envelopes composed of three linear segments corresponding to three types of phenomenological interaction mechanism, which develop successively for increasing values of normal interface stress: purely frictional, frictional-adhesional, and purely adhesional. A simple conceptual framework is proposed that qualitatively explains the observed interface behavior in terms of the normal interface stress, EPS geofoam hardness (or density), interface relative roughness (which incorporates the mean particle size), shape of sand particles, and void ratio of sand. The experimental results are compared to similar results reported in the literature for HDPE geomembrane-sand interfaces. Apparent values of interface friction angle, δ, and adhesion, c a , are proposed in the paper for the tested sands and for specific ranges of normal interface stresses and the two EPS geofoam densities.

The Role of Expanded Polystyrene and Geocell in Enhancing the Behavior of Buried HDPE Pipes under Trench Loading Using Numerical Analyses

“…The pipe was modeled with a total of 2730 elements with linear four-node shell elements (S4R), and EPS blocks, like the soil, were modeled by hexahedral linear elements with reduced integration formulation (C3D8R). The frictional coefficient between the EPS block with trench soils was considered to be 0.6 [35]. The friction angle value between the pipe and the soil was set to half of the peak frictional angle of the soil [36].…”

Numerical Analysis of Earthquake Load Mitigation on Rigid Retaining Walls Using EPS Geofoam

“…not observed in the physical models. An interface friction angle of 15º was assumed based on recommendations by [8].…”

Cooperative Performance of Sandwich Insulation Walls With Expanded Polystyrene Under Static Loads

“…In previous numerical analysis, the EPS plates are assumed to tie with interior walls and exterior walls.Since these contact surface may not tie closely, the interface between EPS plate and concrete hollow blocks shall be friction surface. An friction angle of 15º is assumed based on recommendations by [6]. Table 4 indicates the difference between results of models with tie and with friction interface.…”