The risk of failure of high concrete dam mainly involves two aspects: one is the instability of the dam body, that is, the stability condition;The second is the destruction of the dam body and dam foundation, that is, the strength condition. In order to ensure the safety of the dam, these two essential conditions must be met in the design. In fact, both of these conditions are related to the stress of the dam foundation or dam body, and once the stress exceeds the strength of the material or bedrock, it will lead to the instability or failure of the dam. Therefore, stress-strain monitoring of dams is essential to assess their safety.
Some scholars believe that dam deformation is more intuitive and effective in monitoring dam safety. However, in fact, dam deformation is the effect of multiple factors, among which the temperature effect accounts for a large proportion. For concrete gravity dams in long-term operation, the temperature of the dam body has reached or approached a stable temperature field, so the temperature deformation does not form temperature stress. In the case of arch dams, the temperature deformation of the dam body is constrained by the boundary and the concrete itself, resulting in temperature stress. However, even in the absence of constraints, temperature distortion can still account for a considerable proportion. Therefore, a large amount of deformation does not mean high stress, let alone a precursor to dam failure.
In the past, 47 arch dam models were tested for failure, and it was found that the displacement value of the arch dam overload reached the failure was 3 25 times that of the displacement value caused by the maximum hydrostatic pressure. In addition, after the collapse of the Malbasay arch dam in France, the displacement of the remaining part of the dam body reached 85cm, and the displacement of the gravity pier on the left bank reached 210cm. It can be seen that there is still a considerable process of change from large deformation to dam collapse, and this process is still difficult at present. In contrast, stress is a much more sensitive indicator. When the stress value is large, it is often a precursor to cracks or local failure, and this early warning often does not have much amplitude, so it is more important to monitor the stress of the key parts of the dam body.
Stress and strain monitoring is a systematic project, involving the whole process of design, construction, management and operation. Failure in any one of these areas can lead to the monitoring objectives not being achieved as expected. Because of this characteristic, many people feel that stress and strain monitoring is difficult, not easy to do well, and have a fear of difficulties. However, as long as we strictly control every link and ensure quality, we will be able to achieve the expected results.