Stability Analysis Method And Engineering Application Of Reinforced Bank By Strength Composite Pile

The stability of pile reinforced bank is an important index to ensure the safe construction and operation of the projects.The strength composite pile made by the internal column of the high strength precast concrete pipe pile embedded in the external column of the cement-soil mixing pile has both the advantages of bearing capacity,the engineering application prospect is broad.But till now,the research on the stability of the dyke supported by the strength composite pile is still in the exploratory stage,and the existing results are difficult to guide the engineering practice.Therefore,the method of field test,numerical simulation and theoretical analysis are combined to carry out a systematic study on the stability analysis method of the embankment supported by the strength composite pile.The results can provide a theoretical basis for the calculation of the stability safety factor of the strength composite pile reinforced bank.The main research contents and results are as follows:(1)Field tests were carried out on the reinforced bank project supported by strength composite piles in Nanjing Qinhuai River Waterway Regulation Project to research the stress variation law and strengthening ability of strength composite piles in 18 months during the construction and operation process.According to the test data law,it was proposed that the composite piles could meet the requirements of bank stability.Hydration of soil-cement piles can reduce the moisture content of soil between piles and protect the inner.The test data show that the internal horizontal displacement of the retaining wall develops rapidly during the two filling periods but slowly during the intermittent and consolidation periods,the top displacement of the retaining wall range in 10 to 20 mm.For the strength composite piles with the diameter ratio of internal and external column 3: 7,the stress concentration effect appeared in the process of backfilling loading,the load of internal core was higher and external core of cement-soil mixing pile the second,the vertical load of soil between piles was limited.After stabilization,the ratio is about 20: 5: 1,and the comprehensive pile-soil stress ratio is about 6: 1 as internal core and external core combined.(2)The Abaqus numerical simulation strength reduction method is used to explore the stability safety factor of the bank under the three conditions of no pile,the original design PHC pipe piles and strength composite piles now,showing the stability maintenance advantages of strength composite piles.The stability safety factor of four PTC-300-55 pipe piles with 8 m length combined with 700 mm external cement-soil column not only meets the safety requirements,but also is 8.32% higher than that of the original plan of five PHC 400(C)pipe piles with 9 m length,and the ability of restrained the deformation of bank towards river is much stronger.When the water level of river keeps stable,the high water level plays a positive role in maintaining the stability of the bank.(3)The most dangerous failure mode of the internal core as the main role of strength composite pile was determined.The concrete plastic damage model was used to determine the failure modes and sequence of the internal column of piles divide with different positions.The maintenance and stability role of the external column was defined.The piles located at the bottom and rear of the sliding arc are unlikely to be crushed or shearing while the possibility of bending is the greatest.The bending deformation of the inner core at the front end of the sliding circular arc is limited,and the pile bottom moves upward obviously.Tensile damage occurs as the cracking moment is not reached,the tensile failure plays the most important role.The failure of tensile-bent piles precedes that of tensile-damaged piles,and then bending-damaged piles.The anti-flexural function of the cement-soil column is close to that of the weakened pile,but it can also contribute strength after destruction because of the coupling with internal column and effectively transfers the horizontal force to the soil around the pile,which shows the characteristics of strengthened soil around the pile.(4)Considering the difference of failure modes and sequence,based on the existing calculation method of rigid piles,a stability analysis method suitable for the reinforced bank of strength composite pile is proposed.Compared with rigid piles,composite piles are more difficult to be crushed.The composite piles within 1/2 of the bank are judged as the most likely to be bent and the external column is seen as the strengthened soil to participate in the calculation.The composite piles outside 1/2 of the bank are most likely to be stretched.In the calculation,three possible failure modes were taken into consideration: the tensile-failure of the internal column,the pull-out of the internal column relative to the external column,and the pull-out of the composite pile as a whole.Through the calculation of the stability safety factor of the two numerical simulation models,it is proved that the stability analysis method of strength composite pile reinforced bank based on failure difference is more acurrate.