Cavitation of Water in Soil

Abstract

Despite increasing awareness that cavitation can be a potential mechanism for drainage of water from soil, comprehensive understanding of its effects on soil water retention (SWR) remains largely elusive. A major obstacle is that pore water pressure is commonly conceptualized and measured as a mean value spatially averaged over the entire representative soil volume, including solid, liquid, and gas phases. Water pressure defined as such does not represent the intermolecular pressure that dictates the cavitation phase change process. Classical theories for predicting water cavitation pressure are critically assessed using recent theory for soil sorptive potential and synthesized to determine cavitation of water in soil. Classical cavitation mechanisms of metastable nucleation that occur on a scale of less than tens of nanometers are unlikely to occur in soil water. Cavitation from entrapped bubbles on rough surfaces of soil particles on a scale of hundreds of nanometers, however, is identified as responsible for soil water cavitation. Specifically, cavitation can occur for soils with pore sizes ranging from 10−8 to 10−4 m with suction of 0.1–15 MPa but is most prominent in soils with pore sizes from 10−7 to 10−5 m and suction of 0.1–2.2 MPa (silty soils). A framework for soil water cavitation is proposed, parametrically analyzed, and experimentally validated against measured SWR data obtained using axis translation (AT) and hygrometer-based methods. Results indicate that AT can artificially suppress cavitation that otherwise may be a viable water drainage mechanism for soils in the natural environment.