DISPLACEMENT MONITORING IN CABRIL DAM USING GNSS


Figure 6a presents a theoretical example of a reservoir water level evolution over time, and its discretization for the aforementioned calculation. Figure 7 serves as an example of a typical HP creep effect evolution over time.


The temperature effect can be simulated with the air temperature values registered at the site (it is usual to apply a phase shift of approximately 20 to 30 days, which is roughly the dam response time to an air temperature variation), or by harmonic functions with annual or


annual and half annual periods[12]. Where b or b1 and b2 are the regression coefficients, Tair is the air temperature at the site and t is the time of year. Figure 7 serves as an example of a typical temperature effect evolution over time.


_


The SW creep effect is a viscoelastic dam response to the SW load. The SW is a constant action following gravity’s direction. It is applied to the whole structure, developing a creep effect that can be estimated by the elastic displacements predicted by the FEM for the SW based on the creep coefficients estimated by the creep function, and taking into account the structure’s concrete mean age from the end of the construction period. Figure 6b presents a theoretical example of the evolution over time of the two SW displacement


components. The grey colour represents the creep displacement component, uC (ue is the SW elastic response determined by the FEM). Figure 7 serves as an example of a typical SW creep effect evolution over time.


(a) (b)


Figure 6. Creep behaviour over time: (a) Reservoir level discretization in even intervals (the reference campaign for time counting is approximately coincident with the mean construction period date); (b) SW elastic creep component


The adjustment functions associated with the displacements created by the swelling effect are presented in Table 1, and an example of its development over time is presented in Figure 7.


In the presented formulation c or c1, c2 and c3 are the regression coefficients. Usually, the result is a sigmoid-type curve which slowly increases over time until half of its total displacement


Vol XXXI Issue 3 DAM ENGINEERING 157


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