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An embankment dam can be damaged by internal erosion. During this process, the soil material erodes and is transported out of the dam structure. Some common types of damage due to internal erosion are piping, less dense soil zones, and zones where the fine material has been washed out. To prevent ongoing internal erosion from developing into a damage or a breach, injection grouting may be performed to replace the eroded soil material. In an embankment dam, injection grouting is usually performed vertically. A pipeline is drilled from the crest of the dam to the damaged zone, to which the grout material is delivered via a pump. The injection grouting methods suitable for embankment dams are compaction and permeation grouting. In compaction grouting, a lowmobility grout material is injected at high pressure, compacting the surrounding soil. In permeation grouting, the injection pressure is lower and the grout material flows more easily, allowing it to permeate the porous structure of the soil into which it is injected. A grout material for embankment dams should have properties, i.e., particle size distribution, water content, shear strength, and bulk density, similar to those of the original core soil after injection. A grout material with these properties will however be very stiff and difficult to pump, and permeation will be difficult to achieve. Therefore, a new type of non-hardening grout material has been developed and tested in the laboratory. The grout material is a low-mobility grout, but its viscosity and yield strength can be temporarily lowered by replacing the fine aggregates with a limestone filler and by adding a superplasticizer. After injection, the effect of the superplasticizer wears off, leaving a grouted zone with geotechnical characteristics similar to those of the original core soil. The grout material consists of 0–4 mm aggregates, limestone filler, dry bentonite powder, water, superplasticizer, and an air-release agent. The grout material pro

Research on embankment dam monitoring was recently carried out at a test site in Sweden, with the objectives of: testing geophysical meth-ods of locating defects in the structure; and, using geotechnical instruments to check the behaviour of the dam during first impounding, and subsequently during fluctuations of the reservoir level. The main purpose was to investigate if conventional geophysical methods can be used to detect embedded faults at a rockfill embankment dam in a blind test. Initially, a number of scientists with different specializations in geophysical methods were invited to perform a synthetic pre-simulation assessement to determine if their non-destructive methods would reveal the defects. The test facility is described, the embankment dam constructed for the study and some highlights of the results., QC 20231212

Embankment dams may be damaged by internal erosion, which ultimately may lead to a failure. During internal erosion, finer soil particles from the core soil are being washed out. To restore the core function, injection grouting may be undertaken. Grouting the core of an embankment dam should be performed with a grout with similar characteristics as the original core soil. This grout type is commonly used in compaction grouting, e.g., a low mobility grout. The grout is similar to a fine-grained moraine core soil, but given its stiffness, it is difficult to permeate a damaged core soil. A modified low mobility grout containing sand, limestone filler, bentonite, plasticizer, air release agent and water has been tested in the laboratory with focus on permeation. Grouting was done in different sized aggregates. Impact of paste-to-aggregate ratio, grout consistency, maximum grain size of grout, coarseness of grouted material, and grouting methodology was tested. Higher paste-to aggregate ratios and lower viscosity/yield strength in/of the grout improved the permeation. Initially pressurized grouting compared to only hydrostatic pressures followed by stepwise pressure increased grouting was furthermore identified as a factor to improve the permeation., Validerad;2024;Nivå 2;2024-03-15 (hanlid);Funder: Svenskt Vattenkraftcentrum (SVC);Full text license: CC BY

The core soil of an embankment dam can be exposed to deteriorating processes, i.e., different kinds of internal erosion due to high hydraulic gradients, disadvantageous particle size distribu-tion, too coarse-grained filters or built-in defects. During internal erosion, fines from the core soil are washed out by the seepage, decreasing the impervious properties of the core. If the internal erosion process is discovered in time, drilling and grouting can be performed to stop the erosion. During drilling and grouting, eroded material from the core soil is replaced. In this paper, the methodology: “Identification – Localization – Characterization – Remediation” has been proposed. The methodology was tested on a large-scale embankment dam in a laboratory environment. The dam had a central core of moraine and was built inside a watertight concrete structure so a reservoir of water could be created upstream the dam. The left abutment of the dam had higher seepage rates than the rest of the dam and therefore had to be remediated. During the identification and localization phase, a 10 x 10 cm horizontal, high hydraulic conduc-tivity zone through the core soil was identified and localized at the left abutment at 1 m depth. During drilling at the abutment, it was found that the core soil beneath the damage had become more wet compared to when built. The remedial method used was compaction grouting with a new developed type of non-hardening grout material. The grouting pressures equaled the height of the vertical grout material column with an additional pressure of ~50 kPa to compensate for frictional losses during injection. The grout material was delivered via a novel pipe system where water and air were allowed to be drained. The seepage was lowered by 44 % directly after grout-ing and 60% four months after grouting.

QC 20230825

QC 20120522