Advanced solutions for sustainable assessment of existing gravity dams (Stable Dams)

According to NVEs official database over 4002 dams are registered in Norway today. It is believed that about 2000 small and old dams are undocumented. Concrete is the most common construction material used, more than half of the dams are made out of this material. Almost 90% of the concrete dams in Norway are Small Dams. Therefore, Stable Dams is focused on these types of dams. The construction of hydropower plants in Norway took place in the large hydropower era stretching from 1945 to 1975, when about 55% of the concrete dams were built. Nevertheless, the construction of concrete dams is still ongoing today; over 200 concrete dams have been built each decade since the 80s. The safety requirements have been increased by 50% compared to the original design. Consequently, a large number of such dams must be upgraded and strengthened. These decisions are made based on the so-called reassessment process. The reassessment process follows the same principles as the design process of new dams. This means that the uncertainties and potential errors before and during construction time, collectively incorporated in the design partial safety factors, are treated identically. This is not true for a built structure, where almost any parameter can be measured with todays technology. The efforts in Stable Dams is focusing on identifying new methods, tools and technologies dedicated to understanding better the real condition of the dams. Because this requires multidisciplinary approach, it was created a framework of a multilevel assessment with increasing level of complexity, were these methods can be introduced gradually depending on the needs of a dam. Some examples of measurable achievements are given below. In 2018 an e experimental program on four-model concrete pillars has been performed. The aim of the tests has been to investigate the influence of the topographical profile at the interface on the shear stability of plate dams. The pillar has been scaled with a ratio 1:5 according to specific scaling laws. Scaled materials have been designed and pre-tested prior to manufacturing the model samples. Numerical modeling of the test setup has been conducted prior to testing to determine a best fit loading configuration that would replicate the hydrostatic pressure. Preliminary results from the tests show that the topological profile greatly will influence the shear stability and that it could multiply the capacity. Results from the tests are now being analyzed and together with parametric studies performed by numerical modelling it will form the basis for recommendations for calculating shear stability incorporating topological profiles. In connection with the tests, a 2-day workshop was held gathering around 20 participants from Norway and Sweden. Since September 2017, a monitoring system has been operating at Kalhovd dam. The objective has been to measure the displacement in discrete points and crack openings within a full cycle of loading, typically one year. Besides classic measuring instruments, a new system of full field optical displacement measurements has been also deployed. Data has been remotely transmitted to a server making it possible to do real time verification. The system has now been working for a full year, providing unique data of the behavior of the pillar showing that the movement of the pillar is cyclic, with no signs of propagating failure. As such, the method has proven that it can act as alarm triggering system in case of potential failure. Results have been disseminated via different channels including, publications, workshops, meetings and internet based outlets. The main deliverables from the project are summerized in 4 report: 1. A literature review, which identifies tools, methods and procedures with potential use in the assessment process of small concrete dams. 2. Condition assessment and inspection; describes the development and implementation of new technologies to achieve a data-driven assessment of existing concrete dams. It investigates possibilities to use non-destructive as well as semi-destructive techniques able to characterize the structural condition of existing concrete dams. 3. Capacity and resistance - The document gives in depth presentation of several methods within three main areas; theoretical models, model tests and numerical methods for investigation of the resistance and capacity of small concrete dams. 4. Demonstration; In this document it is shown how the key findings in the project can be applied in the assessment process of a concrete dam.

The main outcome of Stabledams is a set of four reports which enables dam owners to introduce a holistic strategy that enables a more accurate assessment of concrete dams safety. The impacts of the project will be visible within the coming years as results will be applied by the dam owners and their consultants. Alongside reducing, or removing, the costs and CO2 footprint directly linked to the physical interventions, the methods introduced by StableDams will greatly reduce production loss costs normally associated physical interventions. Another outcome of the project is increased research within an area that is of great importance for Norway. The project has involved an international research team, two Norwegian PhD candidates and several master students both in Norway and Sweden. Implementation of StableDams results will allow dam owners to increase their profitability ensuring better safety, increased dividend and more development of our most important renewable energy source.

The methods used today for verifying the structural safety of the dams were developed over 100 years ago and could be updated in accordance to the technologies used now. Mostly the verification consist of simple hand calculations carried out using these methods. The results of these assessments are not always accurate and many cases they yield to high costs for rehabilitation. This project aims to mitigate the impact of the increased safety requirements for existing gravity dams. The overall objective is to propose new assessment steps for calculating more accurately the structural safety of existing concrete gravity dams. The concept behind this management system is to utilize efficiently the information from an existing structure. Because of the advances in technology today it is possible to collect information that were not available, or tested, during design of the structures, hence to remove many of the uncertainties built in the safety factors. The project introduces evaluation steps based on methods such as material testing, statistical tools and numerical modelling. For demonstration purposes during this project a full scale test to failure will be conducted on a section of a concrete gravity dam. It is believed that using these methodologies and approaches answers can be found to research questions on how the stability is affected by: contribution of cohesion, elastic deformation, discontinuous nature of the potential failure plane or stress redistribution in materials and structural parts. Fundamental research will be carried out within two PhD projects guided by an international research group, where senior researchers have an active role in all activities. Master projects will be also defined for several sub-tasks of the project. Besides the scientific relevance of this work, it is sought during this project to strengthen the collaborations with dam owners, regulating bodies and consulting companies working in the hydro-power industry.