Theoretical Analysis And Experimental Verification Of Slope Reinforcement By Small Diameter Steel Pipe Row Piles

Small diameter steel pipe row-pile is a new type of environmental slope retaining structure which has advantages of fast retaining effect, strong horizontal bearing capacity, quick and safe construction and good economical benefits. Due to lacking researches of anti-sliding mechanism, pile-soil acting mechanism and calculation method etc, it is severely restricted to be a permanent retaining structure. Making use of theoretical analysis, calculation proof and numeral analysis etc, the anti-sliding mechanism, practical design and calculation method and factors relevant to bearing capacity are studied in this article, the results are as follows:1. The mechanism of small diameter steel pipe row piles register as:firstly, the steel row-pile skeleton system has excellent properties of shearing resistance, tensile resistance and compressive resistance etc, which could withstand a comparatively large thrust and restrict rock and soil mass among piles into a triaxial state of stress which comparatively increases the soil strength sharply; secondly, the concrete coupling beams with strong stiffness have good coordination and transfer effect of internal forces, the combination of "strong beams and weak piles" and the soil body in front of the row-piles have a comparatively strong resistance effect; finally, high pressure grouting solidify the piles and soil, which makes them stronger.2. According to forcing characteristics of small diameter steel pipe row-pile, plane rigid frame model considering pile-soil three-dimensional effect is put forward. Based on Winkler beam on elastic foundation theory, deformation computation formula of pile internal force is derived; reasonable pile spacing is obtained from "anti-shearing soil body" sneak out calculation; the anchorage depth calculation method is derived from row-pile anti-plucking and anti-bending factors; on the basis of those formula, fifteen-step design method of small diameter steel pipe row-pile is raised.3. when the ratio between pile spacing and pile diameter L/d is5-15, the row-pile anti-sliding capacity is declining, when L/d=15, soil among row-pile is sneaking out. Through row-pile internal force and deformation comparative analysis of different row spacing combined with mass engineering projects experiences:for non-soft plastic to fluid plastic cohesive soil, composite soil, the value of L/d is suggested5~12, that is pile spacing is1-2m, pile-soil could bring comparatively good anti-sliding capacity.4. When the thrust behind row-piles is comparatively small, the variance of pile internal force and deformation is very small along the increase of pile spacing, but along the increase of load, the internal force and deformation represents from increase to decrease along the increase of pile spacing, when pile spacing is1~2m, that is b/d is6-12, compared with other row spacing, pile-soil composite body display a larger anti-sliding. So, considering the group pile effect ignoring row spacing, the value b/d is suggested8-12, that is1~2m.5. The row-pile horizontal displacement is influenced comparatively small by anchorage depth, yet, the row-pile internal force of anchorage section is influenced comparatively large by anchorage depth, the internal force decreases along the increases of anchorage depth. When h/l varies from1/4-1/3, the internal force of row-pile is much reasonable, it is suggested that anchorage depth should be controlled into1/4-1-3.6. The anti-sliding capacity is largely influence by cohesion c, internal friction angle φ, modulus of compression E, along with the increase of c, φ, E, the resisting force in front of row-pile is increasing, the soil anchoring effect is more obvious, correspondingly, the row-pile resisting force is increasing, among c, φ, E, E is the most obvious effective factor.