Study On Mechanical Properties Of Rigid Composite Pipe Pile Supporting Structure

Stiffened composite pipe pile is a new type of pile composed of flexible piles(such as cement soil mixing piles)and rigid piles(such as reinforced concrete precast piles).Because its pile body has high strength and good coordination with the soil around the pile,it is mainly used in the foundation engineering that bears the vertical load at present,while it is rarely used in the actual engineering as a support structure that bears the horizontal load.In order to fully understand the supporting effect and mechanical characteristics of the stiffened composite pipe pile retaining structure,this paper uses the method of combining indoor model test and numerical simulation to study the stress of the stiffened composite pipe pile retaining structure in the process of foundation pit excavation and the influence of different parameters on its supporting effect,aiming to lay a theoretical foundation for its practical application as a supporting structure.The main research work and conclusions are as follows :(1)Indoor model test of rigid composite pipe pile supporting structure.The ordinary pipe pile supporting structure and the rigid composite pipe pile supporting structure were designed and manufactured according to the similarity ratio.The foundation pit excavation test was carried out under four excavation depths(150mm,300 mm,450mm,600mm).The horizontal displacement of the model pile,the surface settlement after the pile and the bending moment of the pile body were recorded during the excavation process,and their changes were analyzed.The test results show that the supporting effect of the rigid composite pipe pile supporting structure is greatly improved compared with the supporting effect of the ordinary pipe pile supporting structure.The horizontal displacement of the pile,the settlement of the soil behind the pile and the bending moment of the pile are shown.Among them,the horizontal displacement of the pile is reduced by 27 %-48 %.The settlement of the soil after the pile decreases by 26 %-50 %;the bending moment of the pile is also reduced to a certain extent.(2)Numerical Simulation Study on Model Test of Stiffened Composite Pipe Pile Support Structure.In PLAXIS 3D,a finite element model was established based on model tests,and the numerical simulation results were compared with the pile horizontal displacement,soil settlement behind the pile,and pile bending moment curves of the indoor model tests.The relevant curves of the indoor model tests and numerical simulation were consistent.The simulation results showed that the support effect of the rigid composite pipe pile support structure was better than that of the ordinary pipe pile support structure.(3)Parameter analysis process of rigid composite pipe pile supporting structure.Using PLAXIS 3D finite element software to carry out parameter analysis,the influence of cement soil strength,thickness and formation parameters on the mechanical properties of the rigid composite pipe pile support structure is studied.The results show that the presence or absence of cement soil has a great influence on the horizontal displacement of the support structure,the bending moment of the pile body and the settlement of the soil behind the pile,but the decrease is small.It can be considered that changing the cement soil strength of the rigid composite pipe pile has limited improvement on its support effect.The thickness of cement soil has obvious effect on improving the supporting effect of rigid composite pipe pile,and this method is also very suitable in practical application.Under different stratum conditions,the supporting effect of the rigid composite pipe pile supporting structure is different.In the hard soil areas such as Nanchang and Beijing,the supporting effect is better.In soft soil areas,such as coastal areas,it is necessary to increase the embedded depth to make the support effect meet the requirements.