Research On The Influence Of Excavation Of Foundation Pit On Bearing Behavior Of Pipe Pile In The Pit

Many studies have shown that concrete pipe piles are different from Concrete pouring pile.Because concrete pipe piles have a strong squeezing effect,their bearing capacity mainly depends on the friction of the pile-soil interface,so the rebound of the soil caused by the excavation of the foundation pit And the influence of the change of soil stress on its bearing capacity is very important.For such a research purpose,this paper firstly focuses on the effects of compaction,water content,overburden pressure on the soil surface and stress history on the shear stress of the interface between the concrete and the soil by making a set of indoor shearing devices.Then a model test was designed to load and unload the surface of the soil to simulate the excavation process of an overlying soil,so as to explore the influence of the bearing behavior of the pile foundation in the pit after excavation.Finally,numerical simulation is conducted through ABAQUS software,and the test data is compared and analyzed.The specific research contents are as follows:Through the self-made concrete and soil interface shear test device,by changing the moisture content and compaction degree of clay soil,The effects of moisture content and compaction of clay on shear stress at the interface between concrete and soil under different vertical stress conditions were studied.The results show that the increase of vertical pressure and compaction degree can enhance the ultimate shear stress of the pile-soil interface;the soil moisture content equal to or slightly larger than the optimal moisture content is also conducive to the improvement of the interface ultimate shear stress;the surface of the soil body The effect of the pre-compressive stress on the ultimate shear stress gradually weakens with the increase of vertical pressure.Through the indoor model test,the axial force and lateral friction resistance curves of the concrete model pile under the unloading of the soil surface and the settlement curve of the model pile under vertical load before and after unloading are studied.The results show that during t he excavation of the foundation pit,the pile body is always under tension,and the tension gradually increases,and the neutral point gradually moves down.After the excavation is completed,the bearing capacity of the concrete pile is reduced by 12.33%,and the maximum settlement is increased by 6.67%,which obviously increases the risk of accidents.Through the numerical software,the finite element model of the model test is established,and the numerical calculation results are compared with the model test results.Consistently,the reliability of the built model was verified,and the effect of pile length and overburden pressure on the axial force of the pile body during unloading was further studied.