Physical Model Test Of Micro-pile And Theoretical Research On Design Calculation

Micropiles have the advantages of smaller pile diameter,flexible pile placement and strong adaptability,and are increasingly used in landslide control.However,the application of micropiles is relatively short,and the lack of a set of systematic and mature computational theory has limited the application of micropiles to a certain extent.Therefore,this paper is based on the major topic of "Key Technology of Micro Group Pile Design Based on Evolutionary Process",and uses the combination of physical model test and theoretical analysis and calculation to study the stress-strain law of the pile body under the action of landslide thrust,so as to improve the theory of internal force calculation of micro pile.The physical model tests of independent and linked three-row miniature group piles are conducted separately.In addition,the pile body will be rotated and deformed,and the rotation angles are 2.8°,1.6° and 1.0° for independent pile and 1.5°,1.3° and 1.3° for linked pile,indicating that the pile top link can limit the bending deformation of pile body.The post-slip thrust of freestanding micropile piles is triangularly distributed,while the linked type is similar to a trapezoidal distribution,gradually increasing with depth and reaching a maximum at the slip surface.The pile front resistance reaches its maximum value below the slip surface and then shrinks rapidly to zero.The three rows of piles are subject to the same force law,but the share of the landslide thrust decreases in turn.The pile top link can transfer the landslide thrust,so that the three rows of piles can jointly resist the slip and the pile top can bear more soil stress.In addition,the pile top connecting beam can improve the structural integrity of the miniature group pile and give better play to the anti-slip performance of the miniature group pile,so that the ratio of landslide thrust sharing is improved from 1.35:1.01:0.64 to 1.25:0.95:0.80,and the three rows of piles are more uniformly stressed,but it cannot effectively improve the ultimate bearing capacity of the miniature group pile.The bending moment of miniature pile is distributed in "s" shape,the loaded section of the pile is subjected to positive bending moment,the embedded end is subjected to negative bending moment,the maximum positive and negative bending moment near the slip surface,bending damage occurs,the critical values of bending moment at the slip surface of independent three-row pile are 5.4 k N*m,4.2 k N*m,2.5 k N*m,the critical values of critical moment of linked three-row pile are 4.4 k N*m,3.0 k N*m,2.7 k N*m.The pile top link beam can change the internal force distribution of the pile,which makes the pile top bear larger load and negative bending moment.With the increase of depth,the influence of the connecting beam gradually decreases,and the force at the embedded end of the pile is basically the same in the two groups of model tests.Based on the test results and combined with the Winkel elastic foundation beam theory,a set of calculation methods on the internal force and deformation law of miniature piles is proposed to calculate the pile displacement,angle,shear force and bending moment of independent and linked miniature group piles under the action of landslide thrust respectively.By comparing with the experimental results,we found that the calculation results can fit well with the experimental results of the linked model box,but there are some differences with the independent type,which can provide some theoretical support for the construction in general.However,more model tests and further improvement of the calculation theory are needed to confirm each other and arrive at a more suitable calculation theory.