Dynamic response of concrete face rockfill dam affected by polarity reversal of near-fault earthquake

In China,an increasing number of high concrete face rockfill dams(CFRDs)are located in high intensity earthquake zones,some of which are close to the seismic fault line.Recordings suggest that near-fault ground motions are characterized by large one-sided velocity pulses.The conventional dynamic analysis of dams,however,neglects the features of strong ground movements.In this study,under different ground motion levels some numerical dynamic studies considering the one-sided broadband pulses of near-fault earthquakes are presented for CFRDs based on a generalized plasticity model for rockfill materials.The results indicate that the displacements of dam crest corresponding to positive and reverse input of near-fault ground motion make a significant difference,while the displacements of the dam crest under artificial seismic waves are similar.Furthermore,using the horizontal and vertical components as simultaneous excitations near the faults,the displacements of the dam crest before and after reversing the motion produce a larger difference than that using a single component.More importantly,the difference of horizontal displacements of the dam crest caused by polarity reversal of near-fault ground motions increases with the increase of earthquake intensity.Due to the randomness and uncertainties of earthquakes,using a stochastic near-field motion input as excitation without considering the polarity(i.e.,positive vs reversed waveform),does not necessarily obtain a conservative result.

Fuzzy Earthwork Dynamic Allocation and Optimization for Construction of High Concrete Face Rockfill Dam

Due to the complexity of earthwork allocation system for the construction of high concrete face rockfill dam,traditional allocation and planning are not able to function properly in the construction process with strong randomness.In this paper,the working mechanism of earthwork dynamic allocation system is analyzed comprehensively and a solution to fuzzy earthwork dynamic allocation is proposed on the basis of uncertain factors in the earthwork allocation of a hydropower project.Under the premise of actual situation and the experience of the construction site,an all-coefficient-fuzzy linear programming mathematical model with fuzzy parameters and constraints for earthwork allocation is established according to the structure unit weighted ranking criteria.In this way,the deficiency of certain allocation model can be overcome.The application results indicate that the proposed method is more rational compared with traditional earthwork allocation.

Predicting crest settlement in concrete face rockfill dams using adaptive neuro-fuzzy inference system and gene expression programming intelligent methods

This paper deals with the estimation of crest settlement in a concrete face rockfill dam （CFRD）, utilizing intelligent methods. Following completion of dam construction, considerable movements of the crest and the body of the dam can develop during the first impoundment of the reservoir. Although there is vast experience worldwide in CFRD design and construction, few accurate experimental relationships are available to predict the settlement in CFRD. The goal is to advance the development of intelligent methods to estimate the subsidence of dams at the design stage. Due to dam zonifieation and uncertainties in material properties, these methods appear to be the appropriate choice. In this study, the crest settlement behavior of CFRDs is analyzed based on compiled data of 24 CFRDs constructed during recent years around the world, along with the utilization of gene ex- pression programming （GEP） and adaptive neuro-fuzzy inference system （ANFIS） methods. In addition, dam height （H）, shape factor （St）, and time （t, time after first operation） are also assessed, being considered major factors in predicting the settlement behavior. From the relationships proposed, the values ofR2 for both equations of GEP （with and without constant） were 0.9603 and 0.9734, and for the three approaches of ANFIS （grid partitioning （GP）, subtractive clustering method （SCM）, and fuzzy c-means clustering （FCM）） were 0.9693, 0.8657, and 0.8848, respectively. The obtained results indicate that the overall behavior evaluated by this approach is consistent with the measured data of other CFRDs.

Features of seismic hazard in large dam projects and strong motion monitoring of large dams

Earthquakes can affect large dam projects in many different ways.Usually,design engineers are focussing on ground shaking and neglect the other aspects.The May 12,2008 Wenchuan earthquake has damaged 1803 dams and reservoirs,and 403 hydropower plants with an installed capacity of 3.3GW.Among these dams were the 132-m-high Shapai RCC arch dam and the 156-m-high Zipingpu concrete face rockfill dam.These recently completed dams are dam types which,up to now,have not experienced strong ground shaking.The widespread mass movements have caused substantial damage to dams and surface powerhouses in Sichuan.The different features of earthquake hazard are presented,i.e.,ground shaking,faulting and mass movements.It is proposed to prepare project-specific safety plans for all dams,which consist of a matrix where the possible hazards and the corresponding countermeasures are listed.The earthquake behaviors of the Sefid Rud,Zipingpu and Shapai dams,which,in the past,have experienced strong ground shaking from nearby earthquakes,are discussed.Finally,the need for strong motion instrumentation of large dams is discussed.It is proposed that major dams with large damage potential,dams located in areas of high seismicity,and dams showing signs of abnormal behavior be equipped with strong motion instruments.