Model Test Study On Controlling Concrete Overfilling Of Cast-in-place Piles Based On Resistivity Method

With the rapid development of construction industry,pile foundation has become an important foundation form in high-rise buildings,heavy industrial buildings,bridges and other construction projects.Among all pile foundation types,cast-in-place pile is the most widely used.With the continuous development of economy and technological progress,the diameter and length of cast-in-place piles are increasing,and the bearing capacity of single pile is getting higher and higher.However,because the construction process of cast-in-place piles can not be directly observed and the amount of concrete pouring can not be effectively controlled,the control of concrete overfilling has become a very important part of cost control.Based on the above problems,a non-destructive testing method,resistivity method,which can effectively control the over-grouting of concrete and monitor the grouting process in real time,is put forward in this paper.Through establishing the grouting model test of cast-in-place pile concrete,a model experimental device and a testing system are made.The resistivity method is used to make use of the resistivity difference between concrete and mud and other different mediums to test the grouting process of concrete.The research and analysis are carried out.The resistivity of the interface material at the top elevation of cast-in-place pile is measured by installing a test probe at the top elevation part of the pile,so as to judge whether it is concrete or not,and record the filling process of the cast-in-place pile,so as to control the over-filling quantity of concrete.The main results are as follows:1.Comparing the records of model test and field test by resistivity method,the similarity of resistivity change characteristics between model test and field test of cast-in-place pile concrete filling verifies the reliability of simulation experiment,and restores the concrete filling process of field test by model test.2.The resistivity variation law of the medium-stable stage,the medium-concrete transition stage and the concrete stable stage in the concrete simulation grouting process under different media is analyzed.The resistivity variation of the top elevation of the cast-in-place pile is studied in detail.It is concluded that the resistivity variation of the medium-stable stage in the grouting process conforms to the linear law,and the concrete stable stage also conforms to the law.According to the linear law,the resistivity decreases sharply in the medium mixing stage in the medium-air perfusion simulation test,while in the medium-water perfusion simulation test,the resistivity decreases stepwise in the medium mixing stage.3.By studying the variation trend of resistivity of top elevation of cast-in-situ piles under different media,when the medium is air,it corresponds to dry cast-in-situ piles,and when the medium is tap water,it corresponds to underwater cast-in-situ piles.According to the variation characteristics of resistivity,the grouting process of cast-in-situ piles can be guided,so as to effectively control the excess grouting4.The feasibility of using resistivity method to control over-filling of concrete is verified by the above tests.