# Capillary Rise in Layered Soils
## 1 Introduction  
The capillary rise of water is an important phenomenon, as it can enhance the soil freezing, thawing, and settlements of buildings. It can also cause damage to both concrete and steel if the water contains erosive ions, or influences the water balance and management in irrigated areas with shallow groundwater tables [1] To evaluate the water capillarity of the soil, the maximum capillary height, the water content profile, and the rate of capillary rise are the three keys. [PERSON] and [PERSON] [2] used the column test, which controlled the relative air humidity above sample surface and the temperature of the entire sample, to discuss the capillary height. [PERSON] and [PERSON] [3] proposed a model to predict the overall behavior of the capillary rise dynamics in a heated capillary tube. [PERSON] et al. [4] proposed a new theoretical solution for quick and easy estimation of the maximum height of the capillary rise in homogeneous soil. However, the soil deposit is usually layered. Soil texture has a decisive effect on the hydraulic properties of soil, such as unsaturated hydraulic conductivities (\(k(h)\)), soil water retention curve (SWRC), field capacity, air entry value, and capillary rise height and rate [5]. Typically, the finer the soil texture is, the greater the porosity, the water retention capacity, and the maximum capillary height, but the permeability and the capillary rise rate are slower. the capillary rise height can also be influenced by the concentration of iron in the water [6, 7] and the thermal conductivity [8].  
Layering in the soil can affect both the downward infiltration and the upward capillary rise. Vertical infiltration in layered soils has been studied by many researchers [9, 10, 11]. All of these studies have reported that the infiltration in layered soils is complex because of the high nonlinearity of SWRC, hydraulic conductivity, various boundary and initial conditions, the textural contrast, and the hysteresis of SWRC, which increases the complexity further [12]. Compared with extensive research on the infiltration, the related reports about capillary rise in layered soils are relatively less, particularly on the water capillary rise process without evaporation. In a study of the capillary height in layered soil, the steadystate capillary rise was strongly influenced by the depth of the water table, and soil with a finer layer overlying a coarser layer, a linear relationship was observed between the thickness of the coarser layer and the critical groundwater depth, below which capillary water could not enter into the upper finer layer [13]. In a study of the water content profile, [PERSON] et al. [14] demonstrated that a capillary pressure jump caused by the air invading the interface between the finer and the coarser layers, and that will significantly modify the water distribution as compared to the homogeneous soil profile.  
In the present study, laboratory column tests and numerical simulations were used to investigate the characteristics of the water capillary rise in layered soils. The results show that the soil suctions on the two sides of the interface, where is higher than the maximum capillary rise height of the coarser soil, are not same when water flow reaches the hydrostatic equilibrium condition.