Permeability Characteristics and Mechanism of Silicone-Hydrophobic-Powder-Modified Compacted Loess

This paper proposes the addition of an environmentally friendly silicone hydrophobic powder (SHP) to compacted loess to enhance its impermeability and reduce the settlement caused by wetting deformation. A flexible wall permeability test was conducted to examine the permeability coefficient of compacted loess with different dry densities mixed with different proportions of the SHP. Water drop infiltration testing, low-temperature drying testing, low-field nuclear magnetic resonance testing, and scanning electron microscopy were performed to clarify the occurrence state and permeability reduction mechanism of the SHP between loess particles from the microscopic viewpoint of the loess structure. The permeability coefficient of the compacted loess decreases significantly after adding 1–3% SHP. Specifically, the permeability coefficient of the loess with low compaction degree (1.35 g/cm 3 ) decreases by 87% after the addition of 3% SHP. Moreover, the permeability coefficient of the loess with a compaction degree of 1.50 g/cm 3 decreases from 1.58 × 10 −6 to 7.9 × 10 −8 cm/s. When the SHP is added to compacted loess, filling and adsorption effects occur: The filling effect decreases the proportion of large pores in the loess. The adsorption effect allows the SHP to encapsulate the loess particles to form a hydrophobic film layer, which leads to the formation of a non-closed hydrophobic structure. This phenomenon decreases the water flow capacity while ensuring the water evaporation capacity inside the loess. The findings demonstrate the potential of adding SHP to enhance the loess impermeability and facilitate and optimize the anti-seepage treatment of various loess filling projects.