| In China,bored piles with slurry wall protection are widely used in construction,railway and highway bridge construction.However,it has several obvious disadvantages: the disturbance of drilling to the surrounding strata and the stress release after drilling are easy to form a soft disturbed soil layer at the side and bottom of the pile;The use of slurry is easy to form the mud skin around the pile and the sedimentation layer and sludge layer at the pile tip;The erosion of clean water is easy to cause the erosion of soil around the pile and hole wall,and play the role of disturbance and damage;The concrete solidifies and shrinks,which is easy to form a shrinkage gap between the pile and soil.Post grouting technology of pile foundation can significantly overcome the above shortcomings.High pressure grouting is used to treat ordinary bored pile,effectively improve the boundary conditions of pile,expand the bearing area of pile,significantly improve the side friction and tip resistance of pile body,greatly improve the bearing capacity of pile and reduce the settlement and deformation of pile foundation.In the existing research and practical projects,the "open" and "closed" technologies are mainly used for post grouting.There is little research on the new "composite" pile foundation post grouting technology,which combines the advantages of the two post grouting technologies and largely avoids the disadvantages of the two post grouting technologies.In this paper,through the indoor vertical compression model test of three single piles with a length of 1m and a diameter of 0.1m,the open and composite post grouting of cast-in-place piles are simulated in the sandy soil layer,and compared with non grouting piles,and verified by numerical simulation results.The load settlement law of vertically loaded piles,the transmission characteristics of pile shaft axial force and pile side friction are analyzed.At the same time,with the help of finite element numerical simulation,the effects of length diameter ratio and grouting amount on the bearing capacity are discussed.The following conclusions are obtained:(1)According to the model test results,under the same grouting pressure and grouting volume,the ultimate bearing capacity of composite post grouting pile is significantly higher than that of non grouting pile by 101.6% and that of open post grouting pile by 20.6%;Under the same level of load,the settlement is only 18.8% ～ 29.0% of that of non grouting pile and 30.4% ～ 52.7% of that of open post grouting pile.(2)Through the excavation analysis of post grouting effect,it is found that the composite post grouting pile forms an enlarged head with a diameter of about 23 cm and a height of about 16 cm at the pile tip,which realizes the compaction and reinforcement of the soil within the specific range of the pile tip,and the integrity and uniform distribution of the reinforcement area are better,which reveals the interaction principle of pile-soil and slurry;(3)Composite post grouting technology can effectively improve the bearing ratio of tip resistance and give full play to the role of pile tip resistance;At the same time,it effectively improves the side friction of the pile body and strengthens the soil within 0.6m above the pile bottom;(4)According to the numerical simulation results,the displacement value of each test pile under the same level load is slightly less than the measured value,the change trend of side friction is consistent.Changing the pile diameter can improve the bearing capacity of the pile more than changing the pile length.There is a critical point that the enlarged head diameter is equal to 3 times the pile diameter.(5)Combined with the comparison of numerical simulation,compared with the open post grouting,the composite post grouting technology has obvious advantages in improving the bearing capacity of pile,reducing the settlement of pile foundation and controlling the grouting area. |
PDF Full Text Request