A model tool in dam rehabilitation

Published: May 19, 2014

Bimont double-curved arch dam © Tractebel Engineering France

 

Creativity, as well as numerical modelling expertise, is essential in dam rehabilitation; as the development of an elastoplastic SCAS (Stress Controlled Anisotropic Swelling) module demonstrates. Christine Noret, Project Director – Dams & Hydroelectricity Schemes Tractebel Engineering (France), explains.

ONE DAM PROBLEM – ONE SMART SOLUTION

After 50 years or more exposure to the elements, even the most well constructed dams will be in need of some form of rehabilitation intervention to safely extend the life and commercial operability of the structure for years to come. But as all dams are different; in size, type, materials, purpose, location etc. the problems that surface are different too. Be it scour holes, concrete alkali swelling causing surface cracking, or distortion of sluice gates; lateral thinking and the ability to apply superior numerical modelling skills to dam monitoring and rehabilitation is needed both to accurately diagnose issues and formulate the right solutions. This was certainly the case with Bimont Dam in France. Read more

To be able to imagine something and then demonstrate it is something special for all engineers.
Christine Noret – Project Director – Dams & Hydroelectricity Schemes Tractebel Engineering (France)


  • Bimont dam-location of drilling and swelling zones © Tractebel Engineering France
  • Bimont arch dam-detail © Tractebel Engineering France
  • Bimont dam mesh with SCAS module © Tractebel Engineering France

 

SCAS & BIMONT DAM

Asked to design a rehabilitation programme for 60 year old Bimont Dam, near Marseille, (to regain the original arch dam behaviour allowing operation at a higher water level), the Tractebel Engineering (France) team realised there was more to the problem than first met the eye. This led to the development of a new tool SCAS – to help investigate the situation further.

COMBINED INVESTIGATION AND MODELLING IN THE ANALYSIS OF A LARGE-SCALE HYDRAULIC INFRASTRUCTURE

The Problem:
Concrete swelling and cracking is a widely observed phenomenon in dam reahabilitation. When a dam is affected by such  chemical reactions (Alakali Aggregate or sulfatic reaction), normally, the whole dam wall is affected by surface cracks. Because Bimont Dam had superficial cracks in just 4 zones it was clear that the deformation mechanism was different. This led to the suspicion that a larger internal crack network existed inside the wall. How to determine that was the trigger for SCAS development.

The Solution: SCAS (Stress Controlled Anisotropic Swelling) is an elastoplastic module developed in conventional finite elements software by the Tractebel Engineering dam rehabilitation team in France. It allows the simulation of concrete alkali or sulfatic reaction swelling (and potential of internal cracking) in a large-scale hydraulic structure. Similar but more sophisticated models exist; the drawback being the large number of parameters needed to run such complex models and the cost of the laboratory tests confirming these for each individual dam.

Where SCAS breaks new ground is that it is a much simpler more flexible model suited to our purpose in that it can be effectively applied to more than one dam; bringing benefits to more than one dam owner. We managed to prove that the results we got with SCAS were sufficiently reasonable to be able to reproduce and help understand the observed deformation behaviour, define the solution and prove it! Developing SCAS for Bimont took about 1 year; we know the software well, but had to adapt it to answer specific questions, then validate the adaptation, run the model and interpret the results.  But it was well worth it in terms of the final solution we could present on the Bimont issue.Christine Noret – Project Director

The Result: Based on SCAS readings, boreholes could be accurately drilled into the Bimont Dam wall to allow camera inspections, visual confirmation of the internal cracking and confirmation of the proposed solution. The combined modelling and investigation campaign provided superior information and understanding of internal crack networks; their existence, creation, size and potential evolution – everything needed to design a more complete and effective dam rehabilitation programme for the concerned client.

For more information on Tractebel Engineering expertise in dam monitoring and rehabilitation www.tractebel-engineering-gdfsuez.com

A Valued Tool

Kariba concrete arch dam-spillage © Tractebel Engineering France

A paper on SCAS was presented to ICOLD (International Congress of Large Dams) in Kiyoto, Japan after its successful Bimont Dam application. Tractebel Engineering (France) was congratulated both by supporters and competitors for its innovative thinking! To read the full presentation (in French & English) click here.

A Model Reference

Kariba dam-best option for emergency gate and gantry © Tractebel Engineering France

Since Bimont Dam, the SCAS application has also been used effectively on Kariba Dam in Southern Africa where Tractebel Engineering is working to resolve 2 rehabilitation issues:

  • rehabilitation of the spillway structure plus construction of a new emergency sluice gate system (click here to read a report on the subject)
  • mitigation of a deep erosion plunge pool (click here to read a report on the subject)

Tractebel Engineering have special expertise in dam monitoring and rehabilitation worldwide. Visit www.tractebel-engineering-gdfsuez.com for more references.

More information

Christine Noret-Duchene

Christine Noret – Project Director – Dams & Hydroelectricity Schemes Tractebel Engineering (France)

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