| With the improvement of economic level and the development of transportation industry,the construction process of Chinese transportation network is accelerated,and the distribution scope of traffic road is more and more extensive.When facing the complicated terrain such as rivers,gullies or artificial obstacles,bridge construction is applied more and more in practical projects.The impact load generated by the drilling process of bridge pile foundation will cause vibration deformation,stress damage and other adverse effects on the adjacent building structure,especially for the ancient building built in a long time,its vibration damage is more significant.Based on the actual project of Xida No.1 Bridge,the finite element numerical simulation method is used to analyze the influence law of punching load on adjacent underground cavern under different influence parameters.At the same time,BP neural network model and multiple linear regression model are used to predict the maximum vibration velocity of underground caverns.The research is of great significance in the prevention of mechanical vibration and the protection of cultural relics.The main research contents of this thesis are as follows:(1)Combined with the relevant theory,the dynamic load action form of pile foundation impact hole is studied,the impact load characteristics of punching are analyzed,and the calculation model of impact load on underground cavitations is established.The mathematical expression of impact load is introduced and it is confirmed that the punching load acts on the soil in the way of triangle function in the simulation.(2)The Midas GTS NX finite element analysis software is used to establish the three-dimensional numerical model of soil and underground caving.The analysis shows that the most prone to failure location of caving is the joint of caving and the closest to the pile hole.Monitoring points are selected and set at dangerous locations,and the variation rules of maximum shear stress,displacement and velocity of underground caverns under different design parameters are analyzed.Through the analysis of the sensitivity of the design parameters through the orthogonal test,it is concluded that the influence of the three parameters on the cavity from large to small is the loading depth,stroke and hammer weight.(3)Combined with the safety vibration evaluation standards of various structures under the influence of dynamic load at home and abroad,the maximum vibration velocity of particles is selected as the evaluation index.It is suggested that the safe permissible control standard value of vibration speed for underground caverns in this project is 3mm/s.The Back Propagation neural network model and multiple linear regression model were used to predict the maximum vibration velocity of particle in underground caverns,and the predicted value of the two models was compared with the simulated measured value.The results show that the multiple linear regression model fits the actual value better.The calculation formula for predicting the maximum vibration velocity of particle with respect to loading depth,stroke and weight is obtained by fitting. |
