Page - 1094 - in Book of Full Papers - Symposium Hydro Engineering

The structural response of, for instance, the uplift pressure, is strongly related to the corresponding variation of the reservoir water level. The manual measurements presented in Fig. 4 were used for the computation of the Hydrostatic Season Time (HST) models [3,4,5] presented in this work. In this case study, the HST model with the best performance for the uplift pressure regarding the manual readings of the piezometer yHST, PZ14 (126.6m) was obtained as the sum of the hydrostatic pressure term β1 × h 4 (where h is the reservoir water level height and can vary between 0 and 123 m) and the temperature terms β2 × cos(d) + β3 × sin(d) to represent the effect of the annual thermal variation of the temperature (where d = 2π•j/365 and j represents the number of days between the beginning of the year, January 1, until the date of observation, 0 ≤ j ≤ 365). The time effect did not seem to have a significant importance in the period examined by this study. The regression coefficients of the quantitative models obtained are β1 = 1.342 × 10 -7, β2 = 1.2512 and β3 = 1.3459, with k=-6.049; being the HST model represented through the Eq. (1). YHST, PZ14 (126.6m) = β1 × h 4+ β2 × cos(d) + β3 × sin(d)+k (1) The effects of hydrostatic pressure variation based on the reservoir water level variation, the thermal effect due to temperature variations (considered as a proportional attenuation of the air temperature changes with a phase shift), the residuals* (k), the HST model prediction and the confidence intervals (based on 3 and 6 standard deviation, corresponding to 99.73% and 99.99% confidence levels, respectively) are presented in Fig. 5. The regression parameter estimates for the HST models, regarding to the uplift pressures, for the piezometers PZ8, PZ12, PZ14 and PZJ1, are presented in Table 3. Table 3 Regression parameter estimates for the HST models regarding to the uplift pressure obtained through the piezometers Designation  1  2  3 k   (m H2O) PZ8 (169,0m) 1.107X10-7 1.218 1.305 6.852 2.15 PZ12 (138,9m) 8.504X10-8 -0.084 1.996 -5.774 2.47 PZ14 (126,6m) 1.342X10-7 1.251 1.346 -6.049 1.71 PZJ1 (125,9m) 8.395X10-8 0.941 1.127 -2.111 1.39 * Besides the information related to any possible anomalous phenomena, the residuals contain information related to errors (measurements and model) and other unknown effects. 1094