Research On Lateral Bearing Behavior Of Large-diameter Steel Pipe Pile With Post Side Grouting

Compared with the traditional single pile,the steel pipe pile has the advantages of material performance,weight,bearing capacity,flexibility and construction speed,therefore,it is widely used in marine engineering.However,under long-term lateral loads such as waves,tides and hurricanes,the soil around the pile experiences lateral relaxation deformation,which weakens the lateral bearing capacity of the pile foundation.As one of the reliable means to improve the bearing capacity of pile foundation,the post side grouting technology has the advantages of simple process and low cost,which can make up for the shortboard of lateral bearing capacity of steel pipe pile.However,it is still challenging to develop a post-grouting device and process with a high bonding degree with steel pipe piles and convenient for practical construction.The research on the lateral bearing behavior of post grouting steel pipe piles under a complex marine environment needs to be further deepened.Therefore,on the basis of a set of distributed post grouting device for large diameter steel pipe pile developed by the research group,this paper adopts the method of combining model test,numerical simulation and theoretical analysis to study the lateral bearing behavior of steel pipe piles with different foundation soils and different post grouting methods,the main results are as follows:(1)Through model tests,it is proved that the self-designed and modified distributed post grouting device can be effectively applied to steel pipe piles and have obvious reinforcement effect.(2)Based on the model test in the clay foundation,the influence of different grouting methods on the lateral bearing behavior of steel pipe piles in clay is studied.The results show that: compared with the non-grouted pile,the lateral critical load of common post grouting pile and distributed post grouting pile is increased by 20.0% and 80.0% respectively,the lateral ultimate bearing capacity increased by 57.1% and 85.7% respectively,the lateral displacement of the pile under the same load decreases,and the improvement of the lateral bearing capacity of the steel pipe pile by the distributed post grouting is greater than that by the common post grouting.(3)Based on the model test in the sand foundation,the influence of different grouting methods on the lateral bearing behavior of steel pipe piles in sand is studied.The results show that: compared with the non-grouted pile,the initial stiffness of common post grouting pile and distributed post grouting pile increased by 42.4 % and 122.1 % respectively,the lateral critical load increased by 34.5% and 73.2% respectively,the lateral ultimate bearing capacity increased by 65.0% and 115.0% respectively,the side post grouting greatly improves the lateral bearing capacity of steel pipe piles in sand foundation,while the distributed post grouting can further improve the lateral bearing capacity of single pile on the basis of common post grouting.(4)The m values of different pile types in clay and sand are compared and analyzed.The results show that the m values of the non-grouted pile,common post grouting pile and distributed post grouting pile increase in turn under the same load.According to the test results,the recommended range of m value of post-grouting steel pipe pile in soft clay and medium coarse sand is given.(5)Through the comparison of internal forces of different piles,in clay foundation and sand foundation,distributed post grouting can solve the problem of excessive concentration and mutation of bending moment and shear force caused by common post grouting to a certain extent,and improve the distribution of the internal force of steel pipe pile.(6)Based on excavation,the diffusion mechanism of cement slurry in clay and sand is studied,and the mechanism of the pile-consolidation-soil system as a whole is analyzed.The results show that the main diffusion form of cement slurry in clay is splitting,with a small amount of compaction and filling along the outside of the pile.The cement slurry spreads mainly in the form of compaction in the sand,forming an irregular consolidation with a maximum diameter of about 8～10 cm near the grouting hole,and form a certain thickness of consolidation along the pile.Compared with common post grouting,distributed post grouting has a wider distribution range in the soil and is more closely integrated with the pile and soil,forming a more stable cement stabilized soil structure.