Numerical modelling of RCC dam with special consideration on lift joints under earthquake conditions

The performance of roller compacted concrete (RCC) rely on horizontal lift joint and to act as monolithic structure requires good bond and contact between successive layers. Analysis of cracking and potential failure mechanism of RCC concrete gravity dam with consideration on lift joint is indispensable. Plane strain 2D numerical modelling is used to predict the response of the dam subjected to Loma prieta earthquake. Linear analysis, push over static non linear analysis and time history non linear analysis method is used with total strain based and discrete cracking model. These analysis is performed for intact concrete and with lift joint inclusion to point out what would be the effect of horizontal joints. Response spectrum of RCC gravity dam under earthquake loading and prediction of how cracks develop and propagate, principal tensile and compressive stress and also deformation is detected. The result indicates that principal stress created in the dam structure at a certain time steps exceed the tensile capacity of the concrete under 0.46g seismic excitation. Maximum displacement occur at the crest and also slight sliding of the base at the interface of the dam structure and foundation. The effect of lift joint as compared to intact concrete significantly reduce the base slide by about 47%. However, it increases the crest displacement by 33% and 60% in a horizontal and vertical direction respectively. Minimum and maximum principal stress created for the intact concrete model is higher when the lift joint are included. Total strain based model with tension softening model can predict crack propagation in koyna dam. The crack development starts at the base of the dam and at location where there is a change in slope from upstream and downstream face and then starts to propagate. In general, cracking along the neck, heel, central part and on places with the slope change are dominant for the occurrence of the failure. Relative displacement along the lift joint interface can be one of failure mechanism. These effect is considered using discrete cracking model by defining the interface using Mohr coulomb criteria. It indicates that the relative displacement of interface occurs starting from one cm to seven cm which can cause a permanent slip. Additionally, another phenomena observed is opening and closing of joints along the interface. Also, stress distribution and pattern is changed which shows that the stress concentration moves to the location of the interface. Furthermore, modelling for lift joints having relatively weak stiffness that may occur due to construction imperfection indicates that stress distribution is changed by concentrating to the weaker joints and becomes the reason for failure of the system. In conclusion, lift joint have significant influence by changing stress distribution, deformation and cracking. In this study failure modes for RCC dam can be cracking, crushing, overturning to upstream or downstream, sliding to upstream or downstream, topling down of crest and combination of the above