Research On The Effect Of Cross-sections And Structure Of Anti-slide Piles On Pile-soil Interaction

China's mountains account for the entire country land about two-thirds of the total area,and the unstable landslide disasters continue to occur,causing huge property losses and personal injuries.Anti-slide piles are widely used as one of the main forms of anti-slide structures.At present,the control slopes(landslides)mainly uses anti-slide piles in the form of rectangle and circular cross-sections.Rectangular cross-section piles are common.However,the use of rectangular cross-section anti-slide piles is vulnerable to the construction environment,construction period,and can only be excavated by hand,easily lead to collapse,endanger the safety of the hole-drilling personnel.Relatively speaking,the circular cross-section anti-slide piles can be mechanical hole,speed up the speed of hole formation,high construction efficiency,and being less susceptible to environmental impacts,and reduce construction safety risks,but the bending resistance and reinforcement effect of single pile of the circular cross-section is slightly inferior.So,it have obvious advantages that small-diameter circular cross-section composite structure piles are used in slope reinforcement to replace traditional large rectangular and circular cross-section single pile.But at present,the internal force deformation characteristics and the pile-soil interaction mechanism of rectangular,circular cross-section single pile and small-diameter circular cross-section composite structures are not yet clear.In the structural design process,most of them are based on experience,and the analytical theory is far behind the engineering practice.On the basis of summarizing and analyzing the theories of pile-soil interaction systems,indoor model tests and numerical calculations are used to analyze the load response characteristics,and pile-soil interaction mechanism and anti-slip effect of the rectangular,and circular cross-section single pile and composite structure pile.The effect of design elements on the deformation and reinforcement effect of the composite structure is discussed.The main research work and conclusions are as follows:(1)Based on the mechanical mechanism of the “plug” action of anti-slide piles,the “straight shear box” pile-soil interaction indoor model test instrument is developed.The rectangular and circular cross-sections model piles with the same equal spacing carry out the pile pushing test,and the upper shear box is loaded step by step.Simulating the actual action process of landslide thrust transfer to the pile body and obtaining the internal force and deformation of the model pile and the model pile response data is obtained.The experiment shows that under the conditions of bending stiffness,the rectangular cross-section pile have strong soil arching effect between piles and soil compaction appears in the area of the soil arch.The soil at the dorsal central axis of the circular section pile shows a splitting phenomenon.There is a tendency to flow around,and the soil arching effect weakens.Under the same load conditions,piles head displacement and bending moment of rectangular cross-section piles have little difference from that of corresponding circular section piles,but larger average pressure stress at the dorsal of pile than the circular cross-section.(2)Based on the parameters verification of the finite element model based on the push pile test,a three-dimensional full-scale generalized model is established.The influence law of different section forms on the mechanical response of the pile body and sliding body is discussed.Anti-slip effect is analyzed by the strength reduction method.The calculation shows that with the increase of the depth,the slip volume of the deep soil near the pile is smaller than that of the shallow soil.The scope of stress transfer from soil to piles is increased and the effect is enhanced,and the rectangle is more prominent than the circular cross-section pile.The value of the earth pressure the central axial line of back of the anti-slide pile in the circular cross-section is the largest and the farther away from the central axis,the smaller the earth pressure value.,and the slower-steep-slower attenuation law appears.The earth pressure distribution at the same depth of the rectangular cross-section anti-slide pile is uniform.The Mohr's circle of stress of the circular cross-section pile is larger,and it is prone to shear failure.When the circular pile cross-section area is 1.25 times that of the corresponding rectangular pile or the pile spacing is 89% of the corresponding rectangular pile,the anti-slip effect of both of them is basically the same.(3)For the small-diameter circular cross-section composite structural pile finite element model,the distribution law of the internal force deformation of the composite pile with different structural forms is studied.The single parameter analysis method is used to explore the column spacing,row spacing and elastic modulus of the crown on the stress deformation characteristics and anti-slip effect of the "T"-shaped composite structural pile.The results show that the back stress of the rear row piles of the composite structure is larger than that of the front row piles,but due to the presence of the crown beam,the coordinated deformation of the front and rear row piles and the bending moment and shear force of the pile are not much different.The distribution curves of the bending moment and the shear force of the front and rear rows of the composite structure along the pile are flatter than those of the rectangular cross-section single pile.The maximum bending moment and the maximum shearing force are respectively reduced by 65%~80% and 40%~53% compared with the rectangular cross-section single pile.With the equal cross-section area,the "T"-shaped composite structure pile forms a strong pile-soil interaction core with the best anti-slip effect.pile center column spacing,row spacing and the top beam elasticity modulus has no effect on the distribution of the internal force deformation of the pile,but the numerical value is affected,and the reinforcement effect is only affected by the row spacing and the column spacing of the pile center.Reasonable suggestions are given for optimizing the design of small diameter circular cross-section composite structure piles.In summary,the mechanical response and pile-soil interaction characteristics of anti-slide piles with different cross-sections and structural forms are studied comprehensively,which provides a reference for the engineering design of the single pile with rectangular and circular cross-sections and circular-section composite piles with small cross-sections.