Hydro-Mechanical Properties of an Unsaturated Frictional Material

Chapter 8
New SWCC Model for Sand
including Scanning Curves
8.1 General
As a result of the present analysis 2D models for the soil-water characteristic curve are pro-
posed (Stoimenova et al. 2003b, 2005, 2006). The first model describes only the drainage
process in the investigated sand. The second model incorporates the hysteretic nature of the
relationship between volumetric water content θ and suction ψ including scanning imbibition
curves. The models are based on non-linear least squares estimation of the data derived from
experiments. Basic knowledge and theory for process modeling was given in Chapter 3.
For model building the available data of the transient state column tests I are used
(drainage and imbibition results). The data contain measurements of the volumetric wa-
ter content θ and the suction ψ at five different levels within the sand column. In this case,
the suction ψ and the initial imbibition suction s0 are used to obtain better estimates of
soil properties, such as soil-water characteristic curve. Incorporating this available informa-
tion about the suction-water content relation, a model is constructed that can be applied for
prediction of the volumetric water content (saturation, gravimetric water content) for any
position along the column. The uncertainty related to different measurement errors of TDR’s
is combined and used for estimating a global prediction error. The estimated error of the
model is valid in entire interval of suction-values and for arbitrary depth level. The variable
s0 represents the suction measured in the corresponding depth and gives the initial suction
distribution before each of the hydraulic loading test phases (imbibition process). Due to this
the proposed 2D regression models acquire the advantage that they: i) can be applied for
prediction of θ for any position along the column and thus any suction in the soil ii) give
the functional form for the scanning curves. The experimental results are an effort to access
based on statistical analysis the hysteretic form of the soil-water characteristic curve and to
model scanning curves applying 2D statistical model.
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