DISPLACEMENT MONITORING IN CABRIL DAM USING GNSS 5.2. HSCT Module. Separation of effects models


The main purpose of the effect separation models is to isolate each load’s effect, which facilitates the study about the influence of each load on the observed displacement histories and, in particular, facilitates the detection of any anomalous or pathological components on the observed displacements.


Among the pathologies that dams can develop over time, swelling is becoming more


relevant, arousing interest in its evolution and subsequently studies of its effects. Many concrete dams have registered problems related to swelling due to chemical reactions occurring between the cement components and the aggregate, i.e. alkali-silica reactions (alkalis present in the cement and silica in the aggregate)[4-7]. The swelling reactions occur with relatively high humidity and temperature, producing a gel which fills the concrete’s internal microstructure pores. This process eventually generates cracking, the consequent concrete damage, and a global volume increase (swelling). Many dams have problems due to swelling reactions; the most serious cases in Portugal are Santa Luzia, Pracana and Alto Ceira. The case of Alto Ceira dam is an extreme example of concrete swelling pathological effect consequences, which ultimately led to decommissioning of the dam. A new dam – Alto Ceira II – was constructed immediately downstream, which is now in full operation. The HSCT-FEM model adopted in DamSafe 4.0 allows the integrated use of FEM and HSCT models. In the analysis of the observed displacement histories the HSCT models are able to separate the creep structural effect[8-10] from the other time effects[11] using the following regression model (also see Table 1):


(1)


This HSCT model is capable of making the time effect separation into one creep component related to the hydrostatic pressure (uC


HP (h,t)), one creep component associated with the


self-weight (uC (uswe


SW(t)), and one other time effects component (for example, swelling


(t)), foundation movements, etc.). In order to estimate the creep effect it is important to distinguish self-weight creep from hydrostatic pressure creep; for this purpose it is useful to estimate the elastic response component for both loads. This procedure can be executed more precisely by FEM.


The functions used to represent each separated effect correspondent to each term of the regression equation (Equation 1) are presented in Table 1.


Vol XXXI Issue 3


DAM ENGINEERING


155


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