Study On The Influence Factors Of Face Slab Void Of CFRD

With the construction of concrete face rockfill dam(CFRD)getting higher and higher,the phenomenon of slab void becomes more and more common.For the CFRD,once the face slab appears void phenomenon,it will have a very adverse impact on the safe operation of the face slab.If it is serious,it may cause the face slab to appear through cracks,directly endangering the safety of the dam.The research shows that the direct cause of the face slab void is the disharmony of the deformation between the slab and the dam body,and the cyclic rise and fall of the valley topography,overburden and water level in front of the reservoir are the important external factors that affect the slab void.Therefore,the research on the influence of these three factors on the slab void of the rockfill dam will provide some theoretical basis and reference value for the design and safe operation of the CFRD.Firstly,this paper systematically summarizes the causes of the panel void,expounds the adverse effects of the panel void on the dam and the factors affecting the panel void,and analyzes the prevention and control measures of the panel void from the mechanism of the panel void.Then,several methods of simulating panel void are compared and analyzed,and sub model method is used to simulate panel void in finite element software ABAQUS.Secondly,taking a CFRD project as an example,the CFRD model with Valley width height ratio of 1.0,2.0 and 3.0 is established respectively.The stress and deformation of different models in the completion period and storage period are calculated and analyzed.On this basis,the relative deformation between the dam body and the concrete face is mainly calculated and analyzed,and the extreme value and range of the concrete face void of CFRD with different Valley width height ratio are calculated.Through the comparison of the calculation results,the maximum value of the width,length and depth of the panel void increases with the increase of the width height ratio of the river valley,and when the width height ratio of the river valley is lower than 2.0,the change rate of the stress deformation of the panel is very large,which may have a certain adverse impact on the safety of the panelThirdly,taking a CFRD on the overburden as the research object,the finite element models of the CFRD with the overburden thickness of 20 m,30 m and 40 m are established respectively,and the extreme value and range of the face void of different dams in the completion period and water storage period are calculated and analyzed.It is concluded that with the increase of the overburden thickness,the extreme value and range of the face void increase in different degrees,It can be seen that the influence of overburden on slab void can not be ignored.The overburden foundation should be strengthened to improve the bearing capacity of the foundation and play a positive role in preventing the concrete slab void on the overburden foundationFinally,combined with a CFRD,the stress and deformation of the dam are calculated after the cyclic rise and fall of reservoir water level once,four times,eight times and 16 times respectively.Then,the relative deformation of the concrete face slab and the dam body is analyzed,the extreme value and range of the face slab void under different conditions are calculated,and the influence of the cyclic rise and fall of the water level in front of the dam on the face slab void is analyzed.The results show that the maximum value of the length,depth and width of the slab void increases with the increase of the number of times of the water level rise and fall in front of the dam.It can be seen that the cyclic rise and fall of the water level aggravates the phenomenon of the face slab void,which is extremely unfavorable to the safe operation of the slab.Therefore,the cyclic rise and fall of the reservoir water level should be considered as an important factor in the design of the concrete face slab.