Model Test Study On The Permeable Rigid Pile Composite Foundation

Soft soil is widely distributed in coastal areas of China.Because of its high natural water content,low shear strength and high compressibility,it is necessary to reinforce the soft soil foundation in the construction of soft soil projects.Permeable rigid pile,which combines the advantages of drainage consolidation method and composite foundation method,can accelerate the consolidation of the foundation soil,improve the bearing capacity of the foundation soil,reduce post-construction settlement,and reduce compaction effect.It is a new foundation treatment method with good development prospects.At present,there are few studies on the composite foundation of permeable rigid piles,and no systematic research results have been formed to guide the design and site construction.Therefore,it is necessary to study the consolidation and bearing characteristics of permeable rigid pile composite foundation.In view of the consolidation and bearing characteristics of composite foundation with permeable rigid piles,the consolidation mechanism of permeable rigid piles under load,the dissipation law of pore water pressure,the influencing factors of consolidation settlement,the stress ratio of pile to soil and the load-sharing ratio,the development of axial force and side friction of pile body are studied by means of model test and numerical analysis.The main contents and achievements are as follows:(1)Permeable concrete model piles and specimens with designed porosity of 20%,25%,30% and 35% were prepared,and the relevant performance parameters were measured.Consolidation model tests of composite foundation with pervious rigid piles under graded loads were carried out to study the reinforcement and bearing mechanism during consolidation process.(2)Through the consolidation model test of permeable rigid pile composite foundation under graded load,it can be concluded that compared with impervious pile composite foundation,permeable rigid pile composite foundation can improve the consolidation rate of foundation soil and shorten the consolidation time.With the increase of load,the accelerated consolidation effect is more prominent.Compared with impervious piles,the consolidation time of rigid permeable piles with designed porosity of 30% can be shortened by about 30.3%.The closer the radial direction to the pile,the faster the dissipation of pore pressure,the better the accelerated consolidation effect.At the moment of loading,the rise of excess pore pressure of composite foundation with permeable piles is smaller than that of impervious piles.The greater the difference between horizontal and vertical directions is,the smaller the difference between vertical and downward directions is.(3)Through the analysis of pile-soil stress ratio and pile load-sharing ratio,pile shaft force and lateral friction resistance,light dynamic penetration number before and after soil test,it can be concluded that with the increase of load and consolidation of soil around piles,the pile-soil stress ratio and pile load-sharing ratio of permeable rigid piles increase first,then decrease,then gently.Potential.The distribution of the axial force of the pile body is large and small,the increase range of the axial force of the lower part of the pile body becomes smaller,the negative friction resistance of the upper part of the pile body appears,the lateral friction resistance of the lower part of the pile body plays a role first,and the upper part plays a role later.It shows that the permeable rigid pile can improve the strength and bearing capacity of the soil around the pile and play the role of the soil around the pile bearing load.Compared with impervious piles,rigid pervious piles can improve the lateral friction,with an average increase of about 11%.Compared with impervious piles and before the test,the number of light dynamic penetration tests of composite foundation with permeable rigid piles has increased significantly,with an average of 4.8 times as much as that before the test and 2.6 times as much as that of impervious piles.(4)Through silting test,it can be concluded that the silting effect of sand,silt and clay on permeable concrete increases in turn under the condition of the same design porosity.Under the same soil,with the increase of porosity,silting of permeable concrete decreases,and the permeability attenuation rate of permeable concrete is similar to that of pore plugging.(5)By establishing an axisymmetric model,the numerical simulation and comparative analysis of the model test are carried out.The results show that the numerical simulation results are consistent with the model test.According to the results of numerical simulation,compared with natural foundation and impervious pile composite foundation,pervious pile composite foundation can shorten the consolidation time by 17.9% and 22.0%.Compared with natural foundation,the final settlement of pervious rigid pile composite foundation after consolidation is reduced by about 7.0%,which is basically the same as that of impervious pile composite foundation.At the moment of loading,the increment of excess pore pressure of permeable pile composite foundation is smaller than that of impermeable pile composite foundation and natural foundation.The frictional resistance of composite foundation with permeable rigid piles is larger than that of impervious piles,with an average increase of about 5.6%.