Study On Bearing Features Of Shallow-buried Gravity Anchorage Foundation In Suspension Bridge

With the wider application of suspension bridges,gravity anchorage is also developing,and its geological conditions are becoming more and more complex.When the rock layers at the bottom of the anchorage foundation are deep,deep foundation burial will encounter difficulties in foundation pit support,dewatering and drainage,and it has a great disadvantage in engineering cost and construction period,so shallow foundation burial is a better choice.Combining with the south bank anchorage of Wujiagang Yangtze River Bridge in Yichang,this paper studies the displacement characteristics,stability and bearing capacity of shallow-buried gravity anchorage of suspension bridge by means of theoretical analysis,field test and numerical simulation.The main contents and conclusions are as follows:(1)This paper presents that gravity anchorage can be divided into deep-buried type and shallow-buried type.The difference is that the foundation of deep-buried anchorage is located on rock foundation,while the foundation of shallow-buried anchorage is located on non-rock foundation and the rock foundation is deeply buried.The characteristics of shallow-buried gravity anchorage in cost and time limit,strength and displacement,and model analysis are summarized.On this basis,it is concluded that shallow-buried gravity anchorage should be mainly controlled by displacement and supplemented by strength control.The calculation methods of vertical settlement and horizontal displacement of anchorage on inhomogeneous soil are given.According to the calculation of the code,the safety factor of anti-slip of shallowburied gravity anchorage is much smaller than that of anti-overturning,so the anchorage is more prone to slip damage.(2)The vertical bearing capacity and horizontal bearing capacity of the south bank anchorage of Wujiagang Yangtze River Bridge are tested and studied.Through plate load test,the allowable bearing capacity of the foundation of undisturbed soil without grouting and reinforced soil after grouting is compared,which verifies that the foundation after grouting can meet the bearing capacity requirements.It indicates that the bearing capacity of shallow-buried gravity anchorage can be satisfied by grouting and other foundation treatment methods.Through direct shear test,the shear friction coefficient of concrete and reinforced soil after grouting is obtained,and the safety factor of anti-sliding under the most unfavorable conditions still meets the requirements of the code.This verifies that the horizontal bearing capacity of the anchorage foundation on the south bank meets the requirements and there will be no sliding damage.(3)Comparing the numerical simulation results of the whole process of the south bank anchorage under grouting and no-grouting,the results show that grouting effectively reduces the maximum settlement of the foundation and reduces the increment of horizontal displacement during the operation period of the anchorage.Sensitivity analysis of factors affecting bearing characteristics of shallow-buried gravity anchorage shows that the safety factor of anti-sliding of circular foundation is increased by 2.4%~6.9% compared with rectangular foundation,which is slightly better in anti-sliding stability.Under the condition of grouting at the bottom of the pit,the maximum settlement of the foundation is the smallest during the construction and operation of the anchorage.Foundation reinforcement can effectively reduce the maximum settlement and the maximum horizontal displacement increment of the anchorage foundation during construction and operation period,and with the improvement of reinforcement soil parameters,the reduction effect is more obvious,which has a very positive effect on the safe and normal use of the entire suspension bridge.