Structural safey of cracked concrete dams

Cracks and cracking in concrete dams can give a need to determine the current status from a dam safety perspective and an estimation on remaining service-life taking the cracks in to consideration. A comparison between the current status and the formal requirements should be made. Condition control is a prerequisite to define the current status and future development and to do this there is a need for knowledge on what type of cracks has occurred and the reason for cracking. To do this there is a need to combine observations, sampling, measurements and theoretical models/ analysis. A previous project within Dam Safety Interest Group (DSIG) resulted in a seven- step-method to analyse cracked concrete dams [1] and the current work is taking this forward to adapt the methodology to Swedish conditions. The goal has been to develop a Swedish guideline to define status and both current and future safety level for a cracked concrete dam with the purpose to create a uniform and reliable methodology for condition control and guidance for planning of measures. The disposition of the report is based on a management process with the parts REQUIREMENTS-INVESTIGATIONS-ANALYSIS-MEASURES and in the report also with REFERENCE PROJECTS exemplifying the recommendations given in the report. Recommended requirements for concrete dams can be found in the Swedish power industry guideline RIDAS [3], [4], with focus on water-tightness, stability, load-bearing capacity and limited deformations. Investigations is best performed stepwise from a visual inspection to a more or less detailed investigation with sampling depending on how unclear the conditions are regarding mechanical properties, crack extent, reason for cracks etc. The results are commonly used later when analysis is performed and therefore it is preferred to plan them in cooperation with the person that will do the analysis later.Analysis can be anything from simple behavior models via analytical calculations to advanced numerical simulations. The purpose with the analysis is to investigate if the dam fulfills the requirements. The results can also be used to suggest further investigations, monitoring or strengthening measures. Measures are taken when the deviation from the requirements are not acceptable (now or in the future). It is often a matter of reducing the load, slow down the development or increase/restore the performance. Surveillance with planned inspections, or monitoring, can be used for evaluating any crack propagation and is sometimes selected instead of a physical measure. The compilation of reference projects shows that a common reason for critical cracks often origins from movement due to seasonal temperature variations. Insulation of the dam body to minimize the impact from this is effective. Indoors also cracking from shrinkage is common. Many of the cases have the cause for cracking and damages from frost or ASR. Generally, it is also common with cracks from the time of construction that will not develop further.QC 20210517