A distribution model of permeability derived from undisturbed gravelly samples in alluvial fan

Abstract

Permeability of alluvial fan deposit is variable with how fully matrix is packed, matrix packing level. In this study, undisturbed gravelly samples are divided into two parts by optimum calculation based on matrix packing levels.Matrix part is one part in which matrix is fully or almost fully packed, and water passage part is the other part in which matrix isn't packed enough. A distribution model of permeability is induced by the arithmetic mean of the permeability of matrix and water passage parts weighted by their thickness. In the Toyohira-gawa river Alluvial fan, especially on Sapporo-surface, the optimum equation by setting four matrix packing levelsⅠto Ⅳ can calculate the permeability to be nearly equal, ranged between half and double, to the measured one. This model is effective to estimate in-situ permeability of alluvial fan deposit. In addition, this model is expected to be applied to estimate heterogeneity by inferring the detailed distribution of permeability. The vertical distribution of permeability in the Toyohira-gawa river Alluvial fan indicates strong heterogeneity between adjacent points. The variogram of log(K') reveals that the macroscopic heterogeneity occurs at observation distance in excess of 5 to 10 meters.

Dépendance à la profondeur et modèles exponentiels de perméabilité dans des cônes de déjection graveleux

“…The authors' previous studies (Sakata et al 2011;Sakata and Ikeda 2012b) established the following relations between the 32 slug test results and core properties found at the same depth.…”

“…The dataset is composed of previous data on BW1-6 taken from Sakata et al (2011), as well as new data on BW7. A scatter plot of estimated K versus measured K values is given in Fig.…”

“…Therefore, the packing in the gravel cores is considered to be related to the sampling depth, and the obvious absence of fine sediment corresponds to the natural openings that form water passages. The authors' previous study (Sakata et al 2011) designated this packing difference as the matrix packing level, and packing was qualitatively categorized into four levels ( Fig. 3): level I (full), level II (almost full), level III (loose) and level IV (very loose).…”

“…Discrepancies in indirect methods are considered to be caused by the simplification of equations to only a few variables (or even a single variable, for example, effective grain size diameter). A previous study by the authors (Sakata et al 2011) suggested that when applying an indirect method for unconsolidated gravel deposits, other variables are needed that reflect the packing in openings between the gravel grains. Consequently, an additional "matrix packing level" index was proposed using relatively undisturbed gravel cores obtained from the Toyohira River alluvial fan, Sapporo, Japan.…”