Study On The Movement And Embedding Regularity Of Interlayer Aggregates Of Roller-compacted Concrete During Vibratory Compaction

The unique technique adopted by the construction of roller-compacted concrete(RCC)dams,where dam materials are extensively compacted by rollers in a layer-by-layer manner,easily forms relatively weak interfaces between layers while dramatically accelerating construction.Cracks and leakages would occur in RCC dams if the interlayer bonding quality has not been carefully controlled.Therefore,the interlayer bonding quality is the key factor for RCC dam safety.The interlayer strength grows with the meshing force between the embedding aggregate of upper layer and cementitious material of lower layer during the layer-by-layer vibratory compaction of RCC dams.The interlayer bonding quality and physical-mechanical property of RCC are directly determined by the movement and embedding process of interlayer aggregates(IAs)during RCC compaction and the embedding characteristics of IAs after RCC vibratory compaction.Therefore,how to reveal the interlayer bonding mechanism of RCC from the view of embedding movement of IA and how to monitoring the regularity of movement and embedding of IA,are two significant scientific problems need to be solved for controlling the interlayer bonding quality of RCC.However,previous researches mainly focused on the qualitative analysis and failed to propose an index for describing the overall embedding degree of IA and its relationship with the interlayer strength of RCC.Moreover,due to the invisibility of the RCC aggregate,it’s hardly possible to monitor the movement of IA by ordinary measures during vibratory compaction.Hence,it’s necessary to quantitively analyze the relationship between the embedding of IA and interlayer bonding quality of RCC with advanced techniques,which reveals the layer forming mechanism of RCC from the meso view of the embedding of IAs.Meanwhile,it’s also necessary to develop a smart aggregate technology for RCC which can simulate the real aggregate and monitor the movement of IA during RCC vibratory compaction.Taking IAs as the research objects and using the theory of embedding and meshing mechanism of IAs,the smart aggregates(SA)technology for RCC was studied and developed with emphasis.Using SA and discrete element method,the relationship between the embedding regularity of IAs,material characteristics,vibratory compaction parameters and particle size was analyzed,which provides a theoretical basis for the following evaluation and control of interlayer bonding quality by using SA for RCC.Main research results of this dissertation are as follows:(1)The embeddedness index was defined by the particle size and embedding value to characterize the interlayer bonding quality of RCC.The reason for the shear capacity of interlayer was analyzed from the view of IA embedding.An indoor test was conducted to build the 3D model of IAs based on CT scanning technology.The embedding values were collected of different size IAs;the relationship model between the shear strength and the embeddedness index was established.The interlayer bonding mechanism of RCC was explained from the view of aggregate movement and embedding,and a new index for characterizing the interlayer bonding quality of RCC was provided.(2)Smart aggregate(SA)technology for monitoring the movement of aggregates of RCC was proposed.A SA device and a 3D visualization system were developed.The geometry,equivalent relative density and transient contact stiffness of real aggregates were simulated by 3D scanning and 3D printing technology.Using the acceleration and angular velocity of aggregate movement collected by a high-precision MEMS inertial navigation module and based on a 3D visual integration model with plug-ins of Three.js and Tween.js,the calculation of movement displacement of IA and the 3D visualization of aggregate movement were realized.A technical means was provided for monitoring the embedding of IA.(3)The calculation method of settlement displacement from the monitoring acceleration based on empirical mode decomposition and Tikhonov regularization was proposed.Shaking table test with high-speed camera was conducted to collect the accumulated settlement displacement and acceleration of RCC during vibratory compaction.The time-frequency domain features of the displacement and acceleration of the RCC settlement were analyzed.Based on the characteristic,the method for calculating settlement displacement via acceleration was proposed,which converts the displacement calculation into the calculation of regularization parameter.The regularization parameter λwas inversed by measured displacement,and a gaussian process regression model was established between the regularization parameter λ and the acceleration noise index.The algorithm provides an effective technical route for the accurate solution of motion displacement of IAs during vibratory compaction.(4)Using the RCC SA technology,experiments of movement and embedding monitoring of IAs were conducted under different vibratory compaction parameters for RCC with various characteristics.The effects on the movement and embedding process of different parameters including vibrating-compacted(VC)value of dam material,the interval time between layers and compaction load were analyzed,according to which the construction suggestions were put forward combined with the actual situation.It provides a new technical method for the real-time evaluation and control of interlayer bonding quality of RCC in the rolling and compacting process from the meso perspective of aggregates embedding.(5)A discrete element modeling method was proposed,in which the real shape of aggregate,rheological properties of mortar and RCC double-layer vibration compaction process were simulated simultaneously;based on 3D scanning and shaking table test,the calibration method of meso parameters of contact model was given;the simulation of movement and embedding of IAs with different particle sizes was realized,and the embedding regularity of IAs with different particle sizes was analyzed from the meso perspective,which provides a theoretical basis for the follow-up study of RCC construction quality control based on the SA technology for RCC.