| In the strong seismic zone of Western China,more and more high rockfill dams have been built or designed,and some of these high dams are located in the near-fault region.The near-fault zone is typically assumed to be within a distance of approximately 20 km from the ruptured fault,which has relatively long velocity and displacement pulse periods,and a dynamic directivity effect could result in dam failure.Therefore,the seismic response of dams subjected to near-field ground motions urgent to be studied.However,there are few seismic analysis of high rockfill dams consider the effects of pulse-like ground motions.Therefore,it is necessary to investigate the dynamic response of high rockfill dams subjected to the near-fault ground motions.Hence,the main objective of this paper is to investigate the dynamic behavior of rockfill dam subjected to near-fault ground motions.Meanwhile,a suggested acceleration distribution figure of the rockfill dam in the near-fault region is proposed,which offers a reference for the modifying specification,and the prediction model for the rockfill dam slope sliding is established.Furthermore,the plastic failure of a concrete face rockfill dam(CFRD)subjected to near-fault ground motions is investigated.The results show that when analyzing the dam failure under near-fault ground motions,the asymmetry of earthquake should be taken into account.The main work of this paper is as follows:(1)The numerical results of the 200m high dam under two types(pulse-like and non-pulse)earthquake records are compared.It is pointed that although the near-fault pulse-like ground motion has a moderate impact on dam acceleration,it has a remarkable impact on horizontal displacement of the rockfill and lop-direction tensile stresses of slab.Therefore,the especially research should be done on the seismic response of a concrete-faced rockfill dam to pulse-like ground mitons.The tensile stresses of the slabs in the lower position for pulse-like ground motions are greater than those for non-pulse records,which may bring some disadvantageous influences on the anti-seepage of dams.(2)The finite element analysis is performed for different height CFRDs to compare the dynamic acceleration responses of the dams subjected to the near-fault ground motions and the artificial waves generated by a standard spectrum.A suggested acceleration distribution figure of the rockfill dam in the near-fault region is proposed,which offers a reference for the aseismatic design.That is,a,m is 3.5,3.0,2.5(H<150m)and 3.5,3.0,2.0(H≥150m)in the erthquake intensity 7,8 and 9 respectively.(3)An approach for the real-time slip deformation coupled strain with softening is used to analyze a 300 m-high core-wall rockfill dam subjected to pulse-like and non-pulse ground motions.The results show that the pulse-like ground motion has a remarkable effect on the soil softening.it is unreasonable that dynamic stability of the slope is only evaluated by a safety factor.Meanwhile,due to bidirectional pulse,the near-fault pulse-like ground motions with forward directivity have more negative on the stability of the upstream and downstream dam.(4)The dynamic behaviors and nonlinear stability of different high CFRDs have been studied.The results show that the relationships between the slip displacements of dam are highly related to PGV/PGA,Arias and PGD,which are used to build the prediction model for the rockfill dam slope sliding.The model can be used to preliminarily evaluate and forecast the dam slope stability.And the effective anti-seismic can be taken to reducing the losses caused by near-fault ground motions.(5)The plastic failure of a CFRD subjected to pulse-like and non-pulse ground motions is investigated and compared.The rockfill materials are described using a generalized plasticity model,while a plastic damage model that considers stiffness degradation and strain softening is used to simulate the face slab.The result show that the tensile damage factor and area in the slabs for pulse-like ground motions are greater than those for non-pulse records,which increases with an increasing ratio of the peak ground velocity to the peak ground acceleration(PGV/PGA).Meanwhile,the influence of asymmetry of near-fault ground motion on displacement response of CFRD is studied.The results show that the dam displacement produced by positive and negative input of seismic wave is different,especially horizontal displacement of dam.Thus,when a core-wall dam is constructed in a near-fault zone,the asymmetry of near-fault ground motions should be considered,ignoring this factor may lead to underestimate the destruction level of dam. |
