Degree and Extent of Wetting Due to Capillary Rise in Soils

Abstract

Increased water content of subgrade soils can lead to degradation of their quality and result in pavement distress. Pavement performance depends on the modulus of the compacted unsaturated subgrade soil as well as that of the underlying natural soil deposits. The soil modulus is a strong function of water content; therefore, changes in water content over the life of the pavement must be understood. In this study, it has been found that for a relatively near-surface groundwater table, significant potential exists for capillary rise into subgrade soils. For fine-grained soils in particular, the height of this capillary rise can be quite substantial. Results from capillary rise column experiments have shown that soils wetted above the groundwater table through capillary rise remain at a degree of saturation averaging about 60 percent. It has also been found that soil suction within this capillary zone must be determined through the use of soil water characteristic curves or direct measurement. The conventional assumption that negative pore water pressures can be estimated by backward extrapolation above the groundwater table of a line of slope γ w is only appropriate in a very thin region above the groundwater table, where soils are wetted to a degree of saturation of 85 percent or more.

Measurement and Simulation of Soil Water Contents in an Experimental Field in Delta Plain

“…This was because the long period of rainfall before had allowed the water table to rise significantly and then began to fall with evaporation, despite this small rain. At the same time, the soil water content of the deep layers remained relatively stable for capillary rise [56,57]. When the rainfall increased to 17.5 mm ( Figure 5c) and 30.8 mm (Figure 5d), the water table rose by 0.065 m (5.2%) and 0.360 m (31.0%), respectively.…”

“…High values of soil water content were observed at the deeper soil layers and strong correlation between soil water content and the water table were found at a depth of around 100 cm. The capillary action is significant in this region and the height of this capillary rise can be quite substantial [56,57]. Table 3.…”

“…Soils were wetted to the degree of saturation from 26.6 to 56.3%. This was closely associated with the soil properties, soil hydraulic properties, capillary action and hydrologic characteristics of the plain river network in this region [57][58][59]. Therefore, it was significant to calculate or calibrate the values of the hydraulic parameters for the five soil zones separately in the model.…”

Experimental study on capillary water rise and influencing factors in silty soil

“…Capillary water is an important factor inducing silt site erosion and collapse (Ma and Liu 2020). When silty soil is used as subgrade filling material, if it is subjected to groundwater capillarity, the water content of subgrade soil will change significantly, which will lead to the decrease of subgrade strength, and then, settlement and collapse may occur (Al-Samahiji et al 2000). Therefore, it is of great theoretical and practical significance to study the rising law of capillary water in silty soil.…”

“…It was found that the pore structure and particle gradation had a significant effect on the rise of capillary water. Al-Samahiji et al (2000) studied the change law of soil water content and the characteristics of pore water pressure, suction, and soil strength in the range of capillary water infiltration. Li et al (2018) tested the capillary water rise of 8 kinds of soils by vertical pipe method, and found that the maximum rise height mainly depended on the distribution of large pores, and put forward a new method to calculate the maximum capillary water rise height by using soil pore distribution function.…”