Moisture Accumulation and Pore Water Pressures at Base of Pavements

Abstract

A unique mechanism based on extensive field and laboratory studies is presented to account for certain premature failures of flexible pavements in cold areas like those in Scandinavia and in northern parts of Canada and the United States. Water condensing at the interface between pavement and granular base accumulates at subzero temperatures resulting in excess moisture in this zone. During the thaw period of the uppermost base layer, the excess water in the aggregate is trapped between impervious layers of frozen ground to the sides and below as well as an impervious layer of asphalt pavement above. Because of this containment, high pore water pressures can occur, leading to loss in shear strength of the base material and thus to failure of the pavement structure itself. It was found that under special conditions, excess moisture can accumulate in granular base with a silt content greater than 20 percent and very high pore water pressures can develop during initial thaw at the pavement-soil interface. With silt contents of less than 2 percent, excess pore water pressures can be avoided during thaw. It was also shown that when a clean open gravel is placed below the pavement on top of a silty base material, moisture accumulation near the pavement-base interface can be prevented, and thus also the development of high pore water pressures.

Numerical investigation on vapor transfer in unsaturated soil during freezing

“…As a matter of fact, water vapor flow can represent a major part of overall water flow especially in the case that temperature gradient is remarkable. The recent experimental evidences also proved that vapor flow in freezing soil could lead to large amount of ice formation, even dominate the moisture migration (Eigenbrod and Kennepohl, 1996;Guthrie et al, 2006;Wang et al, 2012). Additionally, water vapor flow significantly affects the movement of heat, since it drives a substantial amount of energy as the latent heat of vaporization (Sakai et al, 2006).…”

The effects of urban impervious surfaces on eco-physiological characteristics of Ginkgo biloba: A case study from Beijing, China

“…Morgenroth and Buchan (2009) found that the soil moisture differences are insignificant between pervious and impervious paving, while other studies have reported that soil moisture is generally greater in soil beneath paved rather than unpaved soil (Morgenroth et al, 2013;Qian et al, 2010). Some other researches have shown that soil moisture is not necessarily lower beneath impervious pavements (Eigenbrod and Kennepohl, 1996;Oh et al, 2010;Hedayati et al, 2014;Grabosky et al, 2009). Clearly more research is needed in this research field.…”

A New Mechanism of Canopy Effect in Unsaturated Freezing Soils

“…The case reported by Li et al (2014) [1] refers to profile A 2 in Figure 1. Eigenbrod and Kennepohl (1996) [2] also reported that significant moisture accumulation due to vapour transfer occurred underneath a road pavement and led to significant frost heave damage to the pavement. As profile A 2 represents a deep groundwater table and a dry foundation soil, issues associated with high moisture content are more likely to be ignored in geotechnical design.…”

“…We first note that the two cases reported in the literature with significant moisture accumulation underneath impervious covers are both related to frozen soils (Li et al (2014) [1] ; Eigenbrod and Kennepohl (1996) [2] ). Another inspirational example is that ice tends to grow continuously inside an old type freezer (the non-frost-free type) as long as warm and humid air enters the freezer.…”