Comparison between the in situ and laboratory water retention curves for a silty sand

Abstract

After an extreme rainfall event in May 2002 a series of landslides occurred in Ruedlingen in Canton Schaffhausen, North Switzerland. A 38° steep slope has been chosen in this area beside the river Rhine to carry out an artificial rainfall experiment to investigate the dependence between rainfall, suction, saturation and shear resistance. Two sprinkling experiments were conducted to represent an extreme rainfall event, the second of which resulted in failure of 130 m 3 of the slope. Several cycles of wetting and drying were applied to the soil and suction and volumetric water content were measured at different depths in three locations of the slope, by which in-situ Water Retention Curves (WRC) can be derived. The WRC of an undisturbed sample was also determined from laboratory test. The in situ and laboratory WRCs are compared in this paper and the differences will be discussed.

Infiltration-induced Slope Instability: a multi-scale approach

“…This can be attributed to increase in volume during wetting and to the heterogeneity in the flow paths [8]. Similar trend are reported for different depths (see [8]). …”

“…The first wetting branch (W1) shows higher values of suction at the same VWC compared with first drying curve (D1), which is in contrast with the literature data and theory on hysteretic behaviour [18]. This can be attributed to increase in volume during wetting and to the heterogeneity in the flow paths [8]. Similar trend are reported for different depths (see [8]).…”

“…The point representative of instability in the slopes under different water content and stress ratio at consolidation fits the trend of increasing  IL with decreasing e csl -e IL well. The bonding induced by partial saturation and different void ratios at the end of the consolidation phase explains the higher instability ratio exhibited by the samples with  = 0 at decreasing water content (more details in [8]). …”

“…The investigation includes tests on both undisturbed and reconstituted soil samples, in saturated and unsaturated conditions. Water retention curves and hydraulic conductivity functions have been obtained in the laboratory at different scales [12] and in situ [8]. Mobilised shear strength has been investigated at multi-scale, with standard and modified shear box apparatuses in saturated and unsaturated conditions [13,14,15].…”

“…These factors are affected by the hydraulic properties of unsaturated soils, such as the water retention curve and the hydraulic conductivity function [e.g. [7][8].…”