Experimental Study On Treatment Of Secondary Diseases Of Loess Foundation With Cement Graded Crushed Stone Rammed Pile

With the gradual shift of the focus of China ’ s infrastructure construction to the west,the loess accumulation area in the west has attracted more and more attention.In today ’s sustained and efficient development of social economy,loess area construction process is facing many problems,mainly in the loess collapsibility caused by insufficient foundation bearing capacity,excessive settlement,and even part of the original treatment foundation by groundwater uplift wet,secondary diseases and so on.The starting point of this study is a treatment method for secondary diseases caused by immersion saturation in the lower layer of loess foundation in a narrow space similar to the height limit and width limit under the background of the existing traffic engineering operation of a project in Lanzhou,that is,cement graded gravel compaction pile composite foundation.It belongs to a new type of semirigid pile composite foundation with high bond strength.In this paper,a series of research work is carried out through the combination of theoretical research,model test under different working conditions of interior design and numerical simulation,which provides certain reference for better promotion and application in practical engineering in the future.The remolded loess in Yuzhong area of Lanzhou is selected as the model fill in the indoor model test.The specific design of the model test is as follows : the method of pumping and water injection is used to make the fully compacted lower soil saturated;The pile hole is reserved by circular plastic pipe,the mixture is poured into the hole layer by layer,and the pile is rammed and rammed.After the completion of the filling of the model box,the loading tests were carried out on the nonimmersed foundation,the saturated foundation of the lower part of the soil with different degrees of immersion,the singlepile composite foundation of the cement graded gravel compaction pile,and the grouppile composite foundation.By testing the foundation settlement,the stress and deformation at different depths of the pile and soil before and after the treatment,the bearing performance before and after the treatment and the bearing characteristics of the singlepile and grouppile composite foundation of the cement graded gravel compaction pile were compared and analyzed.The research research contents of this paper are as follows :1)The dimensional analysis method is used to derive the geometric and physical parameters in the model test.On this basis,the test scheme is designed and the test process is planned.2)Loading tests were carried out on the original treated foundation and the subimmersed saturated foundation.The test results show that when the local subsoil is soaked to 20 cm,the soil sample saturation strength decreases sharply,and the foundation deformation is large,resulting in secondary diseases.At this time,the disease foundation needs to be reinforced.3)Cement graded gravel compaction pile is used to reinforce the diseased foundation,and then the single pile and group pile composite foundation are graded loaded to analyze the settlement characteristics.It is concluded that the bearing capacity of the treated foundation is improved,and the problem of insufficient bearing capacity caused by secondary diseases is solved.By analyzing the stress distribution of pile and soil at different depths of single pile and group pile composite foundation,it is concluded that cement graded gravel compaction pile has obvious group pile effect.4)With the help of Midas GTS NX finite element software,the models of different pile lengths,pile diameters and cushion thickness are established.Under various working conditions of changing pile parameters,the variation law of composite foundation bearing characteristics under single variable is compared,which provides certain reference for the optimization design of practical engineering application in the future.