Peter Viklander

Stone movements and permeability changes in till caused by freezing and thawing

Vertical uplifting of boulders and stones is well known to take place in cold regions. Movements of stones in roads might lead to traffic danger, vehicle failures, and cause breakdown of the road surface with the need of expensive repair as a consequence. In addition, freeze/thaw and associated stone movements may cause an increase in permeability, which can lead to contamination of soils and ground water if used as soil liners in landfill areas or even dam failures if used as hydraulic barriers in earth dams. Freeze/thaw tests were carried out in the laboratory on a silty sandy soil in order to study movements of embedded stones and to measure how the overall permeability was influenced by freeze/thaw cycles. The soil samples were compacted at three different water contents, i.e. 11.5% (optimum), 14.5%, and 17.5%. Each sample contained one stone, placed at a predetermined depth. The soil samples were subjected to one-dimensional open system freeze/thaw. Soil temperatures, volume changes, and stone movements were measured. The results showed that upward stone movements took place due to freeze/thaw in the frost susceptible soil compacted at and 3% above the optimum water content. In addition, the permeability increased in samples with initial water contents of 11.5% and 14.5%. This permeability increase was as much as 81 times after six freeze/thaw cycles. For the samples with initial water contents of 17.5%, very small changes in permeability were measured.

Laboratory study of stone heave in till exposed to freezing and thawing

Cyclic freezing and thawing of soils affect the structure and might, under certain conditions, cause stones and particles to move and relocate. The movement of stones will influence the soil struct ...

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.

Experimental Investigation of Suffusion in Dam Core Soils of Glacial Till

The main objectives of this study were to determine the susceptibility to suffusion of widely graded, non-plastic glacial till; to identify potential factors influencing susceptibility; and convers ...

A unified-plot approach for the assessment of internal erosion in embankment dams

Surpassed only by overtopping as the larger contributor to the failure of embankment dams, internal erosion occurs when fine-grained particles are allowed to erode by the action of seepage. A dam may be susceptible to internal erosion if there are erodible surfaces not protected by filters. Signs of internal erosion of dams may be sinkhole formations, increased seepage, and muddy discharge. Most methods to assess potential susceptibility are empirically based with little or no comparison to field experience. Based on a database of 80 embankment dams that includes 23 dams reported to have experienced some form of internal erosion and exhibited signs of internal erosion, analysis indicates a correlation between dams with internal erosion and characteristics of the filter of a dam. From comparison with field experience, an approach to assessing existing dams and internal erosion is proposed in this paper by combining attributes of filter gradation in a unified plot, namely its internal stability and its capacity for soil retention. The unified plot may serve as a preliminary screening tool for the susceptibility of internal erosion of dams.

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.