Study On Parameters Of Post Grouting Of Bored Pile

Post grouting technology of bored pile can effectively improve the bearing capacity of pile foundation and reduce the settlement of pile foundation.It can properly reduce the length of pile,save the cost,and produce good economic benefits while meeting the design bearing capacity.Since its first application in 1961,post grouting technology of pile foundation has gradually been widely used in large-scale projects all over the world.The theoretical research and application analysis of post grouting technology by scholars in various countries have also made its theoretical system increasingly complete.However,the factors and conditions of soil formation in different areas are distinct,which lead to diverce geological conditions and soil properties in different areas.Due to the different grouting mechanism of virous soil layers,the relevant post grouting parameters will also show differences.At present,there is still a lack of sufficient theoretical research,a large number of engineering practice and detailed classification standards for post grouting parameters of pile foundations in different regions in China.In this paper,static load test is carried out in six test piles and two special engineering piles of the Grand Bridge engineering acrossing Beijing Hangzhou canal in Shandong flood detention area.The length of 5 test piles were cut with adopting the side-tip post grouting technology shall,while one pile is the original length without post grouting technology.After the completion of grouting,the ultimate bearing capacity of each test pile is measured by self balance method.Two special engineering piles are tested under traditional static load during the construction of post grouting engineering.The load transfer behavior of the post grouting pile foundation is analyzed and studied,and the strengthening mechanism and the action mechanism of the post grouting pile foundation are revealed,based on the static load test results of the test pile and the engineering pile.In the aspects of construction process,pile length reduction,grouting pipeline layout and grouting parameter design,an important guidance for the construction of piles in the later stage of the project is provided.As the key parameters in the process of post grouting,the grouting volume and grouting pressure directly affect the bearing capacity of post grouting pile foundation.Based on the grouting mechanism of each soil layer,this paper collects and arranges the test data of 6 piles and the construction data of 1715 engineering piles,uses the statistical analysis method to adjust and optimize the estimation method of the key parameters of post grouting,and gives the estimation formula of the grouting volume and grouting pressure of large-diameter cast-in-place piles suitable for various saturated soils in Shandong area.The range of the empirical coefficient of grouting resistance,which is used to estimate the grouting pressure in the current Technical Specification for Post-grouting of Cast-in-place Pile of Highway Bridges,is optimized regionally.Based on the actual engineering construction,the uncertainty of Engineering grouting parameters is analyzed and summarized from three aspects of natural factors,geological conditions and engineering construction.For pluralizing ways to carculate the grouting pressure,methods for estimating grouting pressure based on different soil layer parameters is proposed by the single factor analysis of grouting pressure and various soil layer parameters.Based on the Mohr Coulomb strength theory and the limit equilibrium condition of soil,the existing formula for estimating the end pressure of grouting is optimized by many factors,and the range of empirical coefficient of grouting resistance suitable for all kinds of saturated soil in Shandong area is given.The applicability of various kinds of pressure estimation formulas is verified by engineering examples,which can provide some guidance for the follow-up grouting work in Shandong area.