Studies On The Characteristic Of Super-long Pile And Soil Improvement Of The Loess Foundation Of A Large-scale Engineering Project

Foundation stabilization and the construction of super-long pile in loess area are two difficulties in civil engineering for a long time. Based on the foundation stabilization and super-long pile of the construction of a high-rise buildings engineering project, several significant questions about the construction of the super-long drilling piles in dynamic compacted collapsible loess foundation was studied through the combination of site test, numerical analysis and theoretical summarization. The following conclusions were drawn.(1)By analyzing the detailed geological survey data and summarizing the improvement method of loess foundation in similar engineering project, dynamic compaction was proposed to deal with the collapsibility of the foundation soil.Furthermore, reinforcement effect was analyzed based on the test results of load test,dynamic penetration test and laboratory soil tests. Also, correction factor in Menard Formula was obtained according to the variation of the soil strength indexes, which ranges from 0.34 to 0.35.Recommendation values of the dynamic compaction center distance, quantity of dynamic compaction point effective reinforced depth of the construction of dynamic compaction under dynamic compaction energy of 2000kN·m and 3000kN·m. Research result shows that, in loess tableland area, collapsibility of the loess that within the effective reinforced depth can be eliminated when the dynamic compaction energy is higher than 2000kN·m. Moreover, when the characteristic value of foundation capacity reaches 250 kPa, compressibility of the foundation soil changesfrom medium-high into medium low. In conclusion, dynamic compaction is a appropriate reinforcement method in loess area.(2)According to pile hole quality test and pile quality test, construction quality of the super-long pile was detected. By analyzing the test data, conclusion can be drawn that the construction quality of the pile foundation was good enough to guarantee the function of the pile foundation. Furthermore, characteristic of the bearing capacity and the basic law between load and deformation of the super-long drilling piles was clarified though load tests. Test results show that the load-deformation curve of the super-long drilling piles in loess foundation represent a gradual shape, indicating that its bearing potential is huge. Thus, it can be concluded that the bearing capacity of the super-long drilling piles meet the design demand while reserving pretty much potential.(3)Based on numerical 3D-modeling, basic law between the load and deformation of the super-long drilling piles was analyzed under multiple construction conditions.Influence of the length of pile, diameter of pile and the elastic modular ratio of soil and pile on the bearing capacity and load-deformation curve of the pile was studied. Test results and numerical analysis results were consistent with each other according to comparative study. Moreover, an experimental optimization design for the super-long drilling piles in the engineering project was carried out. The appropriate range and optimal value of the draw ration of single pile was given as 33 to 92 and 38 respectively.(4)The recomended values of construction parameters and design parameters obtained in this study can provide fundamental data for the writing of local or industrial standard.