Research On Mechanical Response Of Steel Pipe Mini-piles With Built-in Steel Sections To Support Landslides

As a new type of support structure,steel pipe mini-pile is widely used in landslide（slope）management projects,which has the advantages of simple construction process,short construction period and low cost.Without affecting the construction period,steel pipe mini-pile with built-in steel can improve the anti-slip bearing capacity of mini-pile to a greater extent,but there is not much literature on the study of the force characteristics of this combined structure,and the lack of relevant test and calculation theory restricts the application and development of steel pipe mini-pile with built-in steel.In this paper,the physical model tests on the landslide supported by steel pipe mini-piles without built-in,built-in I-beam and built-in square steel were carried out to study the force characteristics and deformation law of landslide supported by steel pipe mini-piles with different built-in sections;and on the basis of the tests,the numerical analysis models of steel pipe mini-piles without built-in,built-in I-beam,built-in square steel,built-in T-beam,built-in channel steel and built-in round pipe were established by ABAQUS finite element software.Finally,by analyzing the theoretical calculation methods in codes and industry standards,the calculation methods of flexural stiffness and flexural bearing capacity of built-in steel pipe mini-piles are proposed.The main work and results of this paper are as follows:（1）When the built-in steel pipe mini-pile supports the landslide,the sliding body slides along the sliding surface under the load of the slope top;the built-in steel pipe mini-pile has a deformation close to"S"shape at the sliding surface,the whole is bending deformation,above the free section is"C"Bending deformation,embedded section near the sliding surface deformation is larger,with embedded in the slide bed depth increases deformation decreases.Near the sliding surface and before the top of the pile will produce the phenomenon of pile soil dehollowing.（2）The post-slip thrust of the built-in steel pipe mini-pile is triangularly distributed,the maximum slip thrust is near the sliding surface,the post-slip bed resistance is"<"shaped distribution;the pre-pile slip body resistance is"<"shaped distribution,the pre-pile slip bed resistance is inverted triangular distribution,the maximum Slip bed resistance in the vicinity of the sliding surface.（3）Built-in steel pipe mini-pile pile bending moment are S-shaped distribution,embedded section pile face slip side tension,free section pile face slip side compression,positive and negative bending moment dividing point is located below the sliding surface;pile shear force is divided into load section,sliding surface and embedded section,are inverted triangle distribution,the maximum positive shear force is located in the sliding surface.The maximum positive shear force is located at the sliding surface.The bending moment and shear force of the pile are smaller for the built-in steel pipe mini-pile.（4）After the steel pipe mini-pile with built-in section steel,the deformation resistance of the pile is enhanced,the control of landslide deformation is improved,the support effect is better,and the distribution of the landslide thrust after the pile and the sliding bed resistance after the pile is less,but the generation of soil decoupling due to the pile soil pile will affect the resistance before the pile.（5）The flexural stiffness of built-in steel pipe mini-pile can be equated to the superposition of three parts of flexural stiffness of steel pipe,internal grouting body and built-in steel section,and the formula can be expressed asB（28）B_s（10）B_c（10）B_ss;the calculation of flexural bearing capacity can be equated to the sum of flexural bearing capacity of steel pipe concrete and built-in steel section,and the formula can be expressed asM（28）M_sc（10）M_s.In the case of equal cross-sectional area of steel sections,the flexural stiffness and flexural bearing capacity of built-in T-beam and built-in I-beam steel pipe mini-pile are the largest,and the support effect on landslide is the best.The results of the study provide a basis for the test and calculation of the application of built-in steel section steel pipe mini-pile in landslide support,which is of great significance to promote the application and development of built-in steel section steel pipe mini-pile.