Effect of degree of saturation on pullout resistance of soil nailing in lateritic soil

Abstract

Soil nailing is a technique used to reinforce and strengthen the existing ground conditions. This is done by installing closely spaced, passive, structural inclusions known as nails into the soil, and these nails help to improve the overall shear strength of the soil. The nail pullout resistance is the shear stress at the grout-soil interface. The soil nail pullout resistance depends on many parameters. Among the factors influencing the soil nail pullout resistance, the degree of saturation of the soil is an important factor. The pullout resistance may decrease during intense rainfall as the degree of saturation of soil mass changes with the moisture content of the soil. However, verification of pullout tests on soil nail is not conducted under extreme conditions. Hence, the measured pullout resistance may not be a safe parameter for design. As such, in this research study, the effect of the degree of saturation on pullout resistance was studied by conducting a series of laboratory tests using a laboratory pullout box. A specially designed waterproof cap was used to apply back pressure to saturate the soil within the pullout box. Variations of earth pressures close to the grouted nail were observed during the tests. It is evident from the results that the higher the degree of saturation, the lower the pullout resistance. Maximum pullout resistance was observed when the degree of saturation was near the optimum moisture of the soil. When the soil is sufficiently dry, lower pullout resistance was observed due to low bond strength between the grout surface and surrounding dry soil.