Amin Askarinejad

Landslide triggering experiment in a steep forested slope in Switzerland

A landslide triggering experiment was carried out on a 37°- 40° steep forest slope in North-East Switzerland by sprinkling water artificially to represent an extreme rainfall event. This project is part of a multidisciplinary collaboration, which includes geotechnical engineering, hydrology, hydrogeology, forest engineering, geophysics and photogrammetry. A three dimensional model of the ground was developed from non-invasive geophysical surveys, insitu probing, combined sprinkling and dye tracer tests and shallow test pits. Laboratory tests were carried out on undisturbed samples under various degrees of saturation This paper mainly focuses on the characterisation of the site.

Numerical modelling of slope–vegetation–atmosphere interaction: An overview

The behaviour of natural and artificial slopes is controlled by their thermo-hydro-mechanical conditions and by soil–vegetation–atmosphere interaction. Porewater pressure changes within a slope related to variable meteorological settings have been shown to be able to induce soil erosion, shrinkage–swelling and cracking, thus leading to an overall decrease of the available soil strength with depth and, ultimately, to a progressive slope collapse. In terms of numerical modelling, the stability analysis of partially saturated slopes is a complex problem and a wide range of approaches from simple limit equilibrium solutions to advanced numerical analyses have been proposed in the literature. The more advanced approaches, although more rigorous, require input data such as the soil water retention curve and the hydraulic conductivity function, which are difficult to obtain in some cases. The quantification of the effects of future climate scenarios represents an additional challenge in forecasting slope–atmosphere interaction processes. This paper presents a review of real and ideal case histories regarding the numerical analysis of natural and artificial slopes subjected to different types of climatic perturbations. The limits and benefits of the different numerical approaches adopted are discussed and some general modelling recommendations are addressed.

Unsaturated Hydraulic Conductivity of a Silty Sand with the Instantaneous Profile Method

The unsaturated hydraulic conductivity of a silty sand at different initial void ratios is measured using the instantaneous profile method. The variation of the suction and volumetric water content is recorded during the infiltration process as a function of time. Accordingly, an infiltration column was developed with a height of 600 mm and an inner diameter of 170 mm. The suction and volumetric water content were measured simultaneously every 100 mm along the column by means of small tensiometers and TDRs, respectively. Hydraulic conductivity is calculated by dividing the water flow velocity by the hydraulic gradient. The soil is reconstituted from Ruedlingen (Canton Schaffhausen, Switzerland), where landslide triggering experiments were carried out in October 2008 and March 2009. The hydraulic conductivity functions are determined and the laboratory values are compared to the in-situ measurements of hydraulic conductivity carried out in the course of the landslide triggering experiments.

The Effects of Hydraulic Properties of Bedrock on the Stability of Slopes

The transient process of rain infiltration in the soil and the effect of geometry and drainage properties of the bedrock on the pore pressure distribution and the stability of a slope are investigated. The simulated slope is a test field in northern Switzerland, where landslide triggering experiments were carried out. From geological point of view, the experimental site is located in the Swiss Molasse basin. The lithological units in the area are composed of horizontally layered and fractured sandstones intersected by marlstone. The stability of the slope is monitored at different stages of the infiltration using the limit equilibrium method of slices. Several cases were compared to study the effect of the fissures in the shallow bedrock on the stability of the slope. The approximate location and size of the fissures in the bedrock were determined by monitoring of spatial and temporal changes of electrical resistivity during rainfall and also geological investigations of the bedrock before and after the failure.

On the Design of Ground Improvement for Embankments on Soft Ground

Constructing embankments on soft ground to adhere to the requirements of modern Codes of Practice is challenging without ground improvement. An overview on the types of columnar inclusions and embankment base reinforcement is presented in terms of load-settlement behaviour together with calculation procedures using partial safety factors, based on the Swisscode 267, Switzerland’s national annex to Eurocode 7. An approximate slip circle analysis is presented for analysis of the Ultimate Limit States, by incorporating additional stabilisation methods. Simple assumptions are validated against a physical model for the Serviceability Limit State with good agreement that permits first approximations to be calculated in this way.