ABSTRACT
This study investigates the effectiveness of soil conditioning using permeability tests to enhance hydraulic performance. Evaluating the reduction in permeability is critical in the preliminary design phase for the definition of the suitability of Earth Pressure Balance (EPB) technology.
The research focuses on hydraulic improvements related to varying soil granulometry, with permeability tested under different pressures due to its significant influence on soil filtration processes. The impact of the Foam Injection Ratio (FIR) on permeability is also examined.
Laboratory tests to identify the appropriate conditioning method are essential for optimizing excavation performance. This study specifically analyses foam conditioning to assess the hydraulic performance of conditioned soils. The permeability tests measure the effects of conditioning on soil permeability. The experimental setup allows for parallel testing, reducing variability due to setup conditions, and an automatic acquisition system accurately captures the permeation process, even on small temporal scales.
Permeability is influenced by soil granulometric distribution, with a transitional phase observed as soil composition changes based on the ability to fill interstitial voids and close preferential filtration channels. The FIR affects permeability reduction, varying with the granulometry of the conditioned soil. Soils with higher fine content retain more foam, effectively hindering water filtration without significant differences in the range of pressures analyzed, while soils with lower fine content the achieved permeability is linked with the applied pressure.
Given the results obtained, this approach could represent a further step in the definition of soil conditioning parameters for situations in which the permeability constraints are relevant for the management of the tunnel excavation.
