Study On Settlement Control Of Prestressed Pipe Pile Composite Foundation Of Expressway In Soft Soil Area

The new Rongwu expressway line will form a highway connecting Tianjin-Hebei in the middle of Hebei Province,and is also an important link in the highway planning network of Xiongan New Area.Because the expressway needs to pass through the soft soil area,and the expressway has higher requirements for settlement,so it needs to strictly control the settlement.Based on the ZT1 section of the new Rongwu expressway line,combined with field test and numerical simulation,this paper studies the settlement control effect of prestressed pipe pile composite foundation of expressway in soft soil area.The main research contents and results are as follows:(1)To interpret the basic composition of prestressed pipe pile composite foundation,the thorough analysis of the embankment filling soil arching effect,geogrid "tension membrane effect",adjust the mattress layer,the effect of pile soil stress ratio of pile-soil composite reinforced area function of prestressed pipe pile composite foundation reinforcement mechanism,subsidence control research to provide theoretical support for the engineering practice.(2)Sensors are embedded in the site to monitor the data of foundation settlement,geogridage tensile strain and pile-soil stress of the prestressed pipe pile composite foundation.Based on the in-depth analysis of the change law of the data in combination with the actual site,it can be seen that: a.The prestressed pipe pile composite foundation can significantly reduce the settlement of the foundation,and reducing the pile spacing can effectively reduce the settlement of the foundation.In the same section,the closer to the center of the subgrade,the greater the settlement of the foundation.b.As the differential settlement of pile and soil increases,the effect of "tension film effect" increases,and the tensile strain of geogrids increases.Because the difference settlement between piles and soil can be increased by reducing the distance from the center of the roadbed and increasing the pile spacing,both methods increase the tensile strain of the geogrid.c.The use of prestressed pipe pile can improve the bearing capacity of the foundation and effectively reduce the settlement of the foundation.Reducing the pile spacing can increase the pile-soil stress ratio,further strengthen the bearing effect of piles,and greatly reduce the settlement of foundation.About 45 days after construction,the "soil arching effect" begins to play a role,and the "soil arching effect" can give full play to the bearing capacity of prestressed pipe piles.(3)Using PLAXIS finite element software to numerically simulate the settlement characteristics of prestressed pipe pile composite foundation,it can be seen that: a.After the foundation is treated by prestressed pipe pile,the maximum settlement of the foundation is reduced by 50.43 mm,and the ratio of settlement reduction is40.08%.The maximum uplift of the foundation decreases by 14.4 mm,and the ratio of the maximum uplift reduction is 51.28%.The maximum horizontal displacement of the foundation is reduced by 44.91 mm,and the ratio of the maximum horizontal displacement reduction is 63.17%.The foundation treated by prestressed pipe pile can significantly reduce the total settlement of foundation,effectively reduce the degree of foundation uplift and greatly reduce the horizontal displacement.b.With the increase of pile length,the settlement decreases.Compared with each other,when the pile length increases by 1.5 m,the average settlement decreases by 11.58%;The settlement decrease with the decrease of pile spacing.Compared with each other,the settlement decrease by 11.88% on average when the pile spacing decrease by 0.5 m.Pile cap can effectively reduce the settlement of foundation,the settlement amount is reduced by 11.07%.With the increase of the internal friction Angle,the settlement decreases.Compared with each other,the settlement decreases by 5.21% when the internal friction Angle increases by 10°.Therefore,with the increase of pile length,the decrease of pile spacing and the setting of pile cap,the foundation settlement energy is significantly reduced,and with the increase of the friction Angle in the filling,the foundation settlement can be significantly reduced.c.Increase of pile stiffness,elastic modulus of cushion and tensile strength of geogrid can all reduce settlement.The average settlement only decreases by about 1%,which is very small,so it is not economical and reasonable to change only these parameters.(4)Settlement control of prestressed pipe pile composite foundation requires comprehensive consideration of economic investment,construction difficulty and other factors,and can be reasonably optimized according to the above parameters,in order to effectively control settlement and reduce economic investment.