Variation over time of excavated soil properties treated with surfactants

Abstract

Foaming agents are frequently used to dig tunnels in soft ground. These additives are often considered to be biodegradable. However, the soil fine material of excavated treated soils is generally classified as waste, stored, and not used again. The foaming agent addition affects the hydromechanical property of the soil, and the resulting evolution of the soil remains poorly understood. This study evaluated the impact of surfactants on the potential of reuse of excavated soil. For this purpose, the degradation mechanisms of the treatment were first analyzed and quantified. Standard geotechnical tests were then used to characterize the evolution of hydromechanical properties of the treated soil. The foam state of surfactant was the driving force of the observed physical property changes. The half-life of this altered state was quite short on the order of days, and the material recovered its initial mechanical properties. On the other hand, the presence of surfactant in liquid form affected the hydraulic and viscous properties over longer time periods. Concerning the mechanical behavior variation, the compressibility index of the argillaceous soil passed from 0.12 to 0.24 after treatment; the friction angle of treated soil decreased to 19° and recovered the initial value of 23° after 20 days. The viscosity of more sandy soil was reduced by approximately 100-fold after treatment. This viscosity was recovered much longer after the mechanical one after about 2 months. The hydraulic permeability decreased with the introduction of the foam from 3.4 × 10−9 to 9.6 × 10−10 m/s. After 1 month, the total recovery had not yet occurred. The statistical analysis using PCA on mechanical, hydraulic, and rheological parameters measured as a function of time after the addition of the surfactant demonstrated that the surfactant was degraded over time and the initial conditions were approached.