Study On Mechanism And Effect Of Intensive Micropile Group Reinforced Embankment Landslide Based On Pile-soil Interaction

With many researches focused on the failure mechanism of landslide, it is realized that efficient countermeasures should be economic with light and small sized structure, of which the Intensive Micropiles Group (IMG) is the most representative one.In this paper, theoretical, experimental and numerical studies were carried out to study the internal forces computational theory of the IMG, the effect of side friction of micropile and the horizontal bearing capacity of micropiles group, other aspects like the assessment of the reinforcement effect were also comprehensively discussed. The main results obtained are summarized as follows:(1) Based on the elastic foundation beam theory, the micropile’s deflection differential equations considering the side friction of micropile was established. The general solution of homogeneous differential equation, initial parameter solution, together with the particular solution under uniform and concentrated loading condition was obtained respectively, the internal force calculation theory of IMG considering the side friction of micropile was also proposed.(2) Comparing the change of soil pressure (△P) within a certain range of the micropile with the soil pressure decrement (P0) around the pile due to the side friction effect, the concepts of the high, medium, low impact region and the non-influence region were proposed, and the corresponding radius were also introduced. The coupled anti-slide effect can be fully utilized when the space of piles is between the high and the medium impact radius.(3) The strong anti-slide capacity of the grouted soil between piles was verified based on the in-situ horizontal bearing capacity test of IMG. For a silty clay slope, the micropiles group can provide 69.2% of the resistance against the landslide thrust, which is over two times of that undertaken by soil between piles(30.8%), and the specific ratio is nearly 7:3.(4) Results from the finite element calculation and normalized analysis showed that: horizontal bearing capacity of intensive micropile group could be enhanced and decrease the top displacement of the pile.by measurements including optimize the pile length, pile diameter, pile rows and spacing. When conducting IMG engineering design, it is recommended to set micropile anchored length over the free section length of 2/3 to 1, the number of pile rows is 3 to 4, the best row spacing is 5 times of pile diameter.(5) Numerical model of the reinforcement slope under asymmetric traffic dynamic load was established to study the transient dynamic response of embankment and micropile, the influence of the load magnitude was analyzed thoroughly.(6) The long-term in-situ testing was carried out to monitor the bending stress of the pile, soil pressure and deep displacement of slope, based on which, the motility pattern of landslide, the stress state of supporting and retaining structures was analyzed respectively. Finally, the reinforcement effect was evaluated according to the long-term loss law of cable prestress and time displacement curves of measuring points of different depth.