Research On Differential Settlement Control Technology Of Pile Foundation Used In Widenned Beam Bridge For Expressway Widenning Project

Control of settlement difference between new and old bridge pile foundations for widening bridges is a very important link of expressway.At present,most scholars only carry out relevant technical research on bridge splicing of new and old bridges.Little research is on the control technology of settlement difference between new and old bridge pile foundation,but the difference in settlement between the old and new bridge pile foundations is likely to cause disease in the joints of the old and new bridges.Therefore,this paper combines with the reconstruction and expansion project of Binlai Expressway in Shandong Province,based on numerical simulation,field test and theoretical prediction,the mechanical properties of pile foundations of new and old bridges are studied.Based on the research results,the control technology of widening settlement difference of bridge pile foundation in expressway reconstruction and extension project is put forward.The main results were shown as followings:(1)The change of stress distribution in foundation soil caused by bridge widening construction will obviously reduce the bearing capacity of nearby foundation,make the friction resistance and pile tip resistance decrease,and with the increase of the upper load of pile foundation,especially when the foundation soil enters the stage of plastic deformation,the influence degree will further increase.(2)The mechanical characteristics of the foundation of the new and old bridge piles are analyzed,and the control techniques of increasing pile length,increasing pile diameter and increasing pile number settlement are proposed,the reinforcement effect is as follows: increase the number of piles > increase the diameter of piles > increase the length of piles > pile side grouting.Increasing the number of piles is the most obvious effect of settlement control,and its bearing characteristics gradually increase with the increase of the number of piles,but the increase of bearing capacity gradually decreases due to the existence of pile group effect.Increasing the diameter of piles and increasing the length of piles have the same effect of settlement control.The reasonable pile length of Fanyang River Bridge and Daxing Zhong Bridgeis 20 m and 15 m respectively,the diameter of pile is 1.5m.(3)The law of settlement variation of widened bridge pile foundation is proved,and the differential settlement of new and old bridge pile foundations is faster in 60 days before observation,and reaches about 1 mm in 60 days;then the settlement rate slows down gradually and reaches 1.8 mm in 140 days,and the settlement tends to be stable gradually.(4)Based on the previous field test data,the GM(1,1)grey theory model for predicting differential settlement of widened bridge foundation is constructed,and the development trend of differential settlement of widened bridge pile foundation is predicted.The results of field test data and grey theory model prediction are compared and the results show that the two results are consistent.The observation results can be applied to similar reconstruction and expansion projects to provide reliable theoretical support.The results in this paper can provide reasonable guide for the design and construction of bridge pile foundation widening in highway reconstruction and extension,and can reduce or avoid the joint defects caused by settlement difference between new and old bridge pile foundation widening in beam bridge.It has important engineering application value.