Remedial Injection Grouting of Embankment Dams with Non-Hardening Grouts
Abstract (Summary)The focus of this thesis is to study the possibility of injection grouting of embankment dams affected by internal erosion. Internal erosion is a process where certain soil material from an embankment dam is removed. This phenomenon occurs in the central core of the embankment dam. If the internal erosion is allowed to continue over a longer period of time, the dam might face a fatal situation. Since the dam core is washed out, larger voids are created, thus lowering the geotechnical stability of the dam. If the voids become larger, more seepage is allowed to pass and if more seepage passes, the internal erosion process is accelerated. The central core in an embankment dam is preferably constructed with till. Till is a natural soil that origins from the ice age. The till contains a wide range of grain sizes, basically anything from clay to blocs. The mixture of grain sizes does however give the till characteristics that are highly desirable for a water retaining construction. It is cohesive, has a low permeability, a high angle of internal friction and can be found practically anywhere in Sweden. In an embankment dam the core is the water barrier. The core alone is however weak and cannot withstand the large external forces put on a dam construction. Because of this, several zones are constructed on both sides of the core. The first zone outside the core is the filter. The filter has no cohesion and is constructed with a coarser material than the core. Outside the filter, the shell is found. The shell is constructed with even coarser material than the filter and supports the entire dam structure. Outside the shell the riprap is found. The riprap protects the dam from erosive forces such as wave erosion, ice loads and heavy rainfalls. The filters main task is to protect the core from being washed out. Since the till in the core has a wide range of grain sizes, a constant rate of seepage may start to move its finer particles (clay, silt). If the filter doesn’t catch these moving particles, a loss of material will occur. This is the basis for internal erosion. If the till has a smooth particle size distribution curve it is less prone to internal erosion. The smoothness of the curve ensures that the different grain sizes involved are evenly distributed. The finer particles are mechanically locked in place by coarser particles, which in turn are mechanically locked by even coarser grains. Finally, the soil structure is more able to withstand the erosive forces provided by the seepage. If the finer particles aren’t mechanically locked and eroded by the seepage, the filter must be designed to catch them. Therefore, internal erosion occurs only if both the till and the filter flaws. If the internal erosion is continuous, the loss of material must be replaced. By doing so without dismantling the dam, injection grouting can be performed. The grout will replace the lost core material and restore the dam. The type of grout can basically be divided into two sub groups: 1. Hardening grouts; 2. Flexible grouts.
School:Kungliga Tekniska högskolan
Source Type:Master's Thesis
Date of Publication:01/01/2009