Research On Force Mechanism And Control Measures Of Reinforced Cage Floating In Bored Pile

With the rapid development of urban construction and highway and railway construction in our country,bored piles have been widely applied.During the construction of bored pile,the floating of reinforcement cage is one of the main factors affecting the pile foundation engineering,and the reinforcement cage floatation is a complicated problem.There is not a complete set of theoretical and calculation models at present,which brings a new topic to the scientific research personnel.Based on the predecessors' research,based on the project of the urban and rural integrated resettlement project in Xiaoshan District of Hangzhou City,and combining with the indoor drawing test,the mechanism of the reinforcement cage floatation is studied,the influence rules of the main factors are obtained,and the preventive measures for the reinforcement of the reinforcement cage are put forward in the project.The following main work has been done:(1)In order to overcome the effect of concrete solidification on the test results during the test,the similar material can be used to simulate the new mixed cement mortar and fresh concrete according to the similarity theory,and the indoor drawing test is carried out with the similar material.The characteristics of similar material,new mixed cement mortar and new concrete are 1,and the characteristics of the new mixed mortar include consistency,severity and the force to the specimen.The characteristics of the new concrete include the heavy,the collapse and the force of the test.The test shows that the sand,901 glue and barite powder can be configured to meet the requirements of the mortar similar material,and the sand and other heavy stones can be added to simulate the new mixed concrete.(2)When pouring concrete in engineering,there is a relative movement between the reinforced concrete cage and the concrete cage during the rising of the concrete level,resulting in the upward force and the reinforcement cage floating up.In the laboratory test,the problem is simplified.Through the relative motion of the reinforced bar specimen and the similar concrete,the interaction force of the two is deeply researched,so the drawing test of the thin iron sheet,steel bar and stirrup is carried out.Through the pulling test and stress analysis ofthin iron sheet,a calculation model of lateral resistance is established,and the lateral resistance is composed of friction force and lateral force.The calculation model of end resistance is derived through the pulling test of steel bar and the calculation model of lateral resistance.The calculation model of stirrup resistance is deduced through the stirrup test of stirrups.Through the analysis and research of large amounts of data in indoor lift test,we have got the influence rule of speed,surface area and depth on resistance.(3)Combined with the above 3 calculation models,the 3 stages of the reinforcement cage floating in the project are analyzed and studied.The essence of the reinforcement cage floating is that the upward resultant force of the reinforcement cage is greater than the downward resultant force,and the most important force in the upward resultant force comes from the friction between the concrete and the reinforcement cage when the concrete level rises.Therefore,in pile foundation construction,we can reduce the friction force to prevent the reinforcement cage from floating up.