Experimental review on the effective stress equation in sand–EPS mixtures

ABSTRACT

Employing Expanded PolyStyrene, EPS has become common in the construction industry, however, their compressibility creates complexities in effective stress analysis. In this paper, the compressibility of EPS beads and the overall compressibility of sand–EPS beads mixtures have been evaluated. Drained and undrained one-dimensional compression tests along with CD and CU triaxial tests were performed on the mixtures to evaluate the classic effective stress equation. Modified versions of the effective stress equation were applied to results and pore pressure correction factors were obtained from both data series based on two different effective stress analysis approaches (volume change and shear strength related) and compared. Results showed that the two sets of correction factors are consistent. Therefore, correction factors obtained based on the compressibility parameters of the mixtures can be used in the effective stress analysis of CU triaxial tests. Pore pressure factors obtained from the oedometer data were used to analyze results of CU triaxial tests. It is shown that a better agreement between CD and CU stress path results is obtained when the EPS compressibility is considered, leading to similar effective strength parameters in both conditions.

KEYWORDS:

• Compressibility
• effective stress analysis
• expanded polystyrene
• oedometer
• triaxial testing

Notation

The following symbols are used in this paper:

A = pore water pressure reduction factor;

A_g= gross area;

A_s = area of contact between particles;

a = area of contact between particles per unit total area of the material;

k = intrinsic cohesion;

K₀ = coefficient of at-rest lateral earth pressure;

C = compressibility of porous material;

C_c = coefficient of curvature;

C_s = compressibility of solid material;

C_u = uniformity coefficient;

cʹ = cohesion intercept;

D_r = relative density;

e_max = maximum void ratio;

e_min = minimum void ratio;

G_s = specific gravity of solid material;

p = mean normal stress;

pʹ = effective mean normal stress;

P = force normal to the contact plane;

P_s = normal force acting between the particles;

q = deviatoric stress;

u_w = pore water pressure;

V = volume of solid material;

V_p = volume of solid particles;

V_t = total volume of samples;

W = weight of solid material;

γ_d,sand = dry unit weight of sand;

γ_w = unit weight of water;

ΔV_p = variation in volume of solid particles;

ΔV_t = variation in total volume of samples;

ε_v,drained= volumetric strain in drained compression tests;

ε_v,undrained = volumetric strain in undrained compression tests;

η = EPS dry mass ratio;

σ = total stress;

σʹ = effective stress;

σ₃ = confining stress;

σ_v = vertical stress;

τ = shear stress;

τ_s = shear stress acting between the particles;

φʹ = angle of shearing resistance;

ψ = angle of intrinsic friction for solid material.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data Availability Statement

All data, models and code generated or used during the study appear in the submitted article [https://onedrive.live.com/edit.aspx?resid=FCBEC33525065D2!1514&ithint=file%2cxlsx].

Additional information

Funding

This research did not receive any grant from funding agencies in the public, commercial or not-for-profit sectors.