Research On Bearing Mechanism Of Split Grouting Pile Composite Foundation In Loess Area

The composite foundation of split grouting pile is composed of pile-branch-soil,and the composite foundation of split grouting pile composed of the three components bears the load together through the linkage effect between pile and soil,and between pile and pile.Significantly improve the bearing capacity of the foundation.Its construction is simple and low in cost,and it has significant advantages as a composite foundation for low-rise buildings in the loess area.However,the current research on the bearing characteristics of split grouting pile composite foundation in loess area is not mature enough,and its load transfer mechanism is not clear.Based on this,the thesis takes the split grouting pile composite foundation in the loess area as the research object,and uses the method of indoor geotechnical test,theoretical analysis and field test to carry out the research on the bearing mechanism of the split grouting pile composite foundation in the loess area.The specific research work and main results are as follows:(1)Through the systematic analysis of pile diameter,pile length and pile-soil modulus ratio,it is determined that the split grouting pile composite foundation belongs to the flexible pile composite foundation;based on the pile-soil displacement coordination,the pile side friction resistance is triangularly distributed and vertical The assumption that the vertical displacement of the pile body and the horizontal branch vein is consistent,the effective pile length of the pile body is determined,the distribution of the pile body stress and the pile side friction resistance along the pile body is revealed,and the pile body’s performance under a certain vertical load is calculated.The amount of compression.(2)Carry out the directional controllable split grouting test in the loess area,and realize the controllability of split grouting by controlling the grouting volume and segmented grouting.Plot the grouting quantity Q,grouting pressure P and grouting time T in the grouting process into a PQT relationship curve diagram.Through the relationship curve diagram,it is concluded that when the grouting pressure is below 0.4MPa,the soil does not significantly split.In order to realize the directional controllability of the split grouting pile branches in the loess area,a grouting pipe suitable for the directional split grouting technology in the loess area is designed.(3)Carry out indoor geotechnical tests and stone body performance test research systematically to determine the water content,density,liquid plastic limit,degree of consolidation and compressive modulus of the soil,to calculate the amount of split grouting and pile body The calculation of effective pile length,friction resistance,etc.provides basic parameters.After the split grouting is completed for a period of time,the on-site split grouting pile is excavated,and the spacing,number,length,etc.of the branch veins formed by the split grouting are measured and analyzed,and the design value is compared and analyzed.Controllability of crack grouting.The results show that the deviations are all within ±30%,which can realize the controllable orientation of the split grouting pile branches in the loess area.(4)Using the test results of soil performance and stone performance,the effective pile length of split grouting pile and the relationship between pile side friction and pile depth were calculated,and the relationship between branch depth and branch friction was drawn.When the depth of branch veins is obtained from the relationship curve,the friction resistance of branch veins is the largest.(5)Using the concrete block counterweight as the counter-force device,the composite static load test of the split grouting pile composite foundation single pile was carried out.The test results are drawn into a graph of the relationship between the load P and the settlement S,and the P-S relationship graph determines the ultimate load of the composite foundation of split-grouting piles with different branch depths.The pile compression is calculated using parameters such as ultimate load and effective pile length.The calculation results show that the difference between the pile compression and the settlement of the pile top is within 15% of the pile compression.It is concluded that the load transfer mechanism deduced by the coordination of pile-soil displacement under rigid foundation can be used as a reference for engineering design.