Elin Bergliv

Large shearing device

In large civil engineering constructions like embankments for roads and railways and dams in the hydro power and mining industry, it is possible to use large grained soil material. In the case of high-speed railways the settlement requirements are strict for safety reasons. The mechanical properties of a large grained material has to be known to be used in an embankment for high-speed railways. Also, for other types of constructions, strength and deformation investigations become more important as advanced numerical models are used for design. High quality data for this type of modelling is required for a useful result.

To investigate the mechanical behaviour of large grained granular material you also need large scale laboratory equipment. The large shearing device is a direct simple shearing device capable of investigating material with grain size up to 200 mm.

Crushed material in dams – Internal erosion of crushed filter material at natural stresses

Internal erosion can be defined as the migration of soil particles with water seepage. It is an important topic for any soil construction where there is water seepage, for example hydro power embankment dams and tailings dams in the mining industry. For construction of new dams in Sweden it is prohibited to use naturally occurring glacial till in favour of manmade crushed soil materials. A crushed material has angular grains. Suffusion tests has shown that using a material with more angular grains could improve the resistance to internal erosion. Angular grains are on the contrary more prone to crushing compared to the more rounded grains of the glacial till. Crushing of grains changes the shape of the grains and the particle size distribution of the material, which in turn could alter permeability, porosity, fines content, etc of the material. These changes of the material could reduce the internal stability.

At some depth in a dam there are stresses caused by overburden, coupled with water seepage. It has become more common in recent years to perform suffusion tests under stress conditions related to those in the field. Adding confining stress has been shown to add internal stability to a material. At higher stress states, the risk of grains breakage increases. This project will perform suffusion tests of crushed filter materials coupled with added confining stresses. The grain breakage will be investigated during suffusion and post-test sieving will be performed. The goal is to evaluate if the grain breakage at occurring stress levels is enough to impact the internal stability of dam.