The Research On Bearing Mechanism And Test Method Of Bridge Pile Under Vehicle Cyclic Load In Sloping Ground

In order to assist the national poverty alleviation strategy and further promote the economic development of remote mountainous areas,it is imperative to strengthen the communication between mountainous areas and towns through the construction of railways or highways.When building bridges of railway or highway in mountainous areas,pile foundations sometimes have to be placed in sloping ground.Due to the existence of"slope effect",the bearing characteristics of pile in sloping ground are quite different from those of pile in ground.Many scholars have studied the bearing characteristics of pile under horizontal static load in sloping ground and that of pile under horizontal cyclic load in ground.However,there are few researches on bearing mechanism of pile under horizontal cyclic load in sloping ground.In addition,there are differences between pile in sloping ground and pile in ground,horizontal static load and horizontal cyclic load.To sum up,it is necessary to study the bearing characteristics of pile under horizontal cyclic load in sloping ground.The specific research work is as follows.(1)The analysis methods of vertical bearing mechanism and horizontal bearing mechanism of pile are summarized.The affecting factors and the waveform of the brake load are introduced.By analyzing horizontal cyclic load such as braking load,wind load and wave load,the difference between horizontal cyclic load and horizontal static load is mainly reflected in the period and waveform.(2)To explore the bearing mechanism of under horizontal cyclic load in sloping ground,model tests under different working conditions(30~o,45~oand 60~o)were carried out.It can be concluded that the number of cyclic loading of horizontal load n=100 is the cut-off point of whether the horizontal displacement of pile top is sensitive to the change of cyclic number.The bearing stability of pile is negatively correlated with the slope inclination and the amplitude of horizontal cyclic load.The soil in front of piles is weakened in the process of cyclic loading.The weakening of soil in front of piles leads to the increase of pile bending moment and the decrease of the bearing capacity of pile.The decreasing degree of the bearing capacity of pile is positively correlated with the slope inclination,the amplitude of horizontal load and the number of cycles.When the cyclic loading process ends,the soil in front of pile in each group heaves,cracks or even completely destroys.The larger the slope inclination is,the larger the amplitude of the horizontal cyclic load is,the more serious the uplift of soil in front of the pile is and the more obvious the"eight"shape crack on both sides of the pile.When the slope inclination is 60~o,the soil in front of the pile is even completely destroyed and some of the soil slides.The shape of the soil after shedding is similar to the ellipse and the failure occurs when the cycle number n<100.(3)Based on the measured data of model test and numerical model calculation results,a empirical formula for calculating horizontal displacement of pile top under horizontal cyclic load is proposed,which is based on the horizontal displacement of pile top under static load and can consider the influence of the slope inclination,the amplitude of horizontal load and the number of cycles.The method for strengthening soil in front of pile in sloping ground is proposed when the pile suddenly bears larger horizontal cyclic load due to river diversion or climate change.Finally,the horizontal displacement of a practical pile in sloping ground was calculated by using the proposed formula.The results show that the practical pile in the sloping ground can work safely under the design condition.