Jan Laue

Experimental modelling of debris flow behaviour using a geotechnical centrifuge

Physical modelling of debris flows has been carried out in the geotechnical drum centrifuge at ETH Zurich. A new apparatus to model debris flows in the centrifuge is described. The apparatus permits the final reach of a typical debris flow to be modelled within the centrifuge, with unconsolidated material flowing down a slope to deposit as a fan around the drum. Experiments are described for both fixed base conditions and erodible bases. Tests to examine the verification (modelling) of models show that debris flow behaviour is governed mainly by friction and consolidation processes, although some resolution is required between flow behaviour downslope and flow arrest during runout. The results are compared with bulk parameters determined for field-scale debris flows. It is found that some important flow mechanisms, such as contact-dominated behaviour and high pore pressures, are developed that are closer to those developed at field-scale than tests conducted at 1g. Velocity profiles for erodible beds are ...

Mechanisms controlling the behaviour of double-porosity clay fills; in situ and centrifuge study

Abstract Two instrumented embankments built on a double-porosity landfill of clayey lumps were monitored in situ and modelled in a geotechnical drum centrifuge. Field measurements of hydrostatic levelling, depth reference points and pore pressure gauges showed high and variable compressibility of the landfills. Introductory modelling in a mini-centrifuge, combined with oedometer testing, demonstrated the key mechanisms in the double-porosity fills: irreversible deformation at low stress ranges as a result of rearrangement of the lumps, and reversible deformation (swelling) at higher stresses, similar to the behaviour of reconstituted material. Placing fill under water resulted in high initial void ratios followed by large deformations while loading. Dry filling followed by saturation may be recommended for further development of the landfills in future. Data from the geotechnical centrifuge models confirmed that permeability was controlled by the complex structure of the clay fills. Similarly to the field measurements, there were significant initial settlements on loading as a result of compression of open macro-voids. The double-porosity structure in the fresh fill allowed excess pore pressures to dissipate quickly, which accelerated the consolidation process initially. Thereafter, dissipation was controlled by the permeability of the intragranular pores in the clay, once the intergranular pores had closed.

MODELLING DEBRIS FLOW PROCESSES WITH A GEOTECHNICAL CENTRIFUGE

In this paper, we examine the effect of flow mass and moisture content on debris flow velocity, dis- charge, and runout using a series of smallscale flume tests in a geotechnical centrifuge. We found that an increase in mass and an increase in moisture content increased peak velocity during down-slope move- ment. However, the effect of increased moisture con- tent is much more pronounced than that of increased mass. The maximum cross-sectional area observed did not depend on mass or moisture content, although may have been affected by the flow rate entering the centrifuge. Consequently, flow velocity largely deter - mined the peak discharge of each flow. An increase in moisture content increased the mobility of the flow in terms of depositional area and runout. Further, the runout of the centre of mass of the flows appears to be linearly related to the momentum of flow material entering the flume.

Geothermal study to explain man-made permafrost in tailings with raised surface

Deposition of mine tailings in a cold climate requires precautions as temporary sub-zero temperatures can imply considerable consequences to the storage due to creation of permafrost. The risk of creating man-made permafrost lenses due to tailings deposition exists even in regions with no natural permafrost, as material being frozen during winter might not fully thaw by the following summer. When such frozen layers thaw during later longer warmer periods, excess pore water pressure and large settlements might develop. Such implications close to the dam structure have to be avoided and therefore the risk of generating permafrost should be reduced. This paper describes a geothermal model for one-dimensional heat conduction analysis. The model is able to simulate the temperature profile in tailings where the surface elevation is constantly increased due to deposition. At the tailings surface, the boundary condition is the air temperature changing over time during the year. Air temperatures, tailings deposition schedule and tailings properties are given as input to the model and can easily be changed and applied to specific facilities. The model can be used for tailings facilities in cold regions, where the effects of tailings deposition on the temperature regime are of interest. Findings can improve tailings management by explaining man-made permafrost generation. The model can also aid in setting up appropriate deposition schedules and to prevent generation of permafrost layers.

Soil Characteristics in Selected Landfill Sites in the Babylon Governorate, Iraq

The Babylon Governorate is situated in the middle of Iraq. It covers an area of 5,315 km2 and has 2,092,998 inhabitants distributed throughout its five major cities (Qadhaa). Presently, there is no ...

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.

Direct Simple Shear Tests on Swedish Tailings

Tailings is a waste stream produced by mining industry. It is often stored on the surface in a retaining structure, called tailing impoundment surrounded by tailing dams. Strength property of taili ...

Effects of Void Ratio and Hydraulic Gradient on Permeability and Suffusion of Glacial Till Cores

Dams with core of broadly graded glacial moraines (tills) exhibit signs of internal erosion by suffusion to a larger extent than dams constructed with other types of materials, as reported by Sherard (1979). Garner and Fannin (2010) indicated that internal erosion initiates when an unfavorable combination of soil material, stress conditions and hydraulic load occur. A laboratory program, carried out at Lulea University of Technology (LTU), aims to study the effects of void ratio and hydraulic gradient on the initiation of suffusion of glacial till. It consists of suffusion tests conducted in permeameters with an inner diameter 101.6 mm and a height of 115 mm. Results show, as expected, that the hydraulic conductivity is lower with lower void ratio. Nevertheless, as the hydraulic gradient increases, the hydraulic conductivity reaches steady values. Changes in the hydraulic conductivity suggest variation in the initial void ratio due to detachment of the finer particles from the soil matrix. These fine particles start clogging the lower layers, therefore the rate of water flow decreases and so does the hydraulic conductivity. The hydraulic gradient for which the hydraulic conductivity reaches steady values is considered as the upper limit without suffusion evolved.

Evaluation of Land Use & Land Cover Change Using Multi-Temporal Landsat Imagery: A Case Study Sulaimaniyah Governorate, Iraq

Land use & land cover change detection in rapid growth urbanized area have been studied by many researchers and there are many works on this topic. Commonly, settlement sprawl in area depends on many factors such as eco-nomic prosperity and population growth. Iraq is one of the countries which witnessed rapid development in the settlement area. Remote sensing and geographic information system (GIS) are analytical software technologies to evaluate this familiar worldwide phenomenon. This study illustrates settlement development in Sulaimaniyah Governorate from 2001 to 2017 using Landsat satellite imageries of different periods. All images had been classified using remote sensing software in order to proceed powerful mapping of land use classification. Maximum likelihood method is used in the accurately extracted solution information from geospatial imagery. Landsat images from the study area were categorized into four different classes. These are: forest, vegetation, soil, and settlement. Change detection analysis results illustrate that in the face of an explosive demographic shift in the settlement area where the record + 8.99 percent which is equivalent to 51.80 Km2 over a 16-year period and settlement area increasing from 3.87 percent in 2001 to 12.86 percent in 2017. Accuracy assessment model was used to evaluate (LULC) classified images. Accuracy results show an overall accuracy of 78.83% to 90.09% from 2001 to 2017 respectively while convincing results of Kappa coefficient given between substantial and almost perfect agreements. This study will help decision-makers in urban plan for future city development.

Risk Management Concepts in Dam Safety Evaluation:Mosul Dam as a Case Study

Gradual shift has been observed lately of dam safety procedures from the conventional technical based towards a widerscope of risk management procedure based on risk analysis. The new approach cons ...