Study On The Treatment Technology Of Cave Under Bridge Pile Foundation

With the large-scale construction and expansion of the highway in our country,it is necessary to build a bridge in the karst area to leap over obstacle and meet the requirements of linearity.The pile foundation is widely used in the construction of bridge because of its unique advantages.The karst area has a hidden cave,many bridges did not find the cave in the stage of pile foundation engineering geological survey,and found that the existence of the cave during construction or after completion of the project,in order to ensure the normal use of the bridge and the stability of the bridge structure,It is necessary to evaluate the stability of the roof of the pile foundation at the bottom of the pile foundation and put forward the corresponding measures according to the evaluation results.Based on the highway engineering of 319 Zuoquan County,this paper makes use of the field investigation,field test and numerical simulation method to research,and gets the following conclusions:(1)Based on the understanding of engineering geological characteristics of the region,the high density electrical method,the geological radar method and the geological drilling are used for the karst detection of the project area,and obtained the basic characteristics of the cave.The generalization model of geological structure is established based on the spatial position relation between pile foundation and cave;(2)This paper analyzes the influencing factors of the stability of karst roof and the evaluation method,and studies the safe thickness range of cave roof under the conditions of the actual engineering by using numerical simulation software FLAC 3D.The results show that the safety thickness of the pile foundation roof under the condition of the project is 2.4 meters;(3)According to the engineering conditions,the paper puts forward the application of grouting method to reinforce the existing cave of pile foundation.Based on the existing engineering experience,according to the test results of field slurry ratio,the technical parameters of grouting reinforcement And grouting process parameters.After the completion of the grouting reinforcement project,the grouting effect was tested by three methods: mass inspection hole(borehole core),hole velocity logging and cross hole electromagnetic wave CT detection.The results showed that the grouting treatment effect was good.The results can provide some reference for similar projects.