Effect of Gradation on the Permeability of Foam-conditioned Soils in Mechanized Excavation

Abstract

Tunnel excavation in a soft ground is often conducted utilizing excavation machines, including earth pressure balance (EPB) boring machines. A safe and economical excavation using this method requires adding materials such as foam and polymer to the soil inside the chamber and the tunnel face to control parameters like permeability, plasticity, shear resistance, and compressibility. Using an experimental method, the present study investigates the effects of granulation, soil moisture content, and pressure on the permeability of a soil conditioned with foam. According to the results, as the effective grain size (d₁₀) increased from 0.1 to 0.4 mm, the permeability of the conditioned soil grew from 2.28 × 10⁻⁵ m/s to 12.3 × 10⁻⁵ m/s. A rise in the coefficient of curvature (C_c), while the percentage of the materials passing through the sieve No. 200 was kept constant, increased the permeability coefficient (k_i) of the specimens since the medium-grained particles (d₃₀) became coarser. A rise in C_c and the percentage of materials passing through sieve No. 200 resulted in an initial rise in the k_i due to the lack of contribution of d₃₀ and a subsequent reduction in it caused by the rise in fine-grained materials. The k_i was also found to have inverse relationships with the uniformity coefficient (C_u) and pressure. As C_u increased from 3 to 20, the k_i declined from 1.23 × 10⁻⁵ m/s to 0.71 × 10⁻⁵ m/s.