Research On Bearing Characteristics And Bearing Capacity Calculation Method Of Inclined Pulled Helical Pile In Sand

Helical piles have been and will continue to be widely used in electric power,communication,construction,marine engineering,slope support and other engineering fields because of their easy construction,economic efficiency and other characteristics.As an important index for the design of helical anchor pile foundation,the mechanism of pullout resistance and the method of calculating the bearing capacity have been the hot spots and difficulties of research.The current research is mostly focused on the vertical and horizontal pullout resistance of helical piles,but there is less research on inclined pullout,and the law of the influence of load angle on its bearing characteristics is not fully understood.For multianchor helical piles with independent bearing of each anchor piece,relevant theoretical and experimental studies on oblique pullout resistance are more rare and difficult to guide engineering practice.In addition,the current scholars do not have a unified understanding of the uplift bearing mechanism in the vertical and horizontal directions of the helical pile,and there are many mechanical models of the sliding surface,and the calculation results of different methods vary greatly,which is essentially caused by the inadequate disclosure of the bearing mechanism.Therefore,it is important to study the bearing characteristics of tilt-drawing helical piles in order to deepen the mechanism of pullout resistance,improve the theory of ultimate bearing capacity calculation and guide engineering practice.In this paper,based on the visualization model test device,digital photogrammetry was used to conduct pullout tests on double-anchored helical pile under 25 test conditions including 5 burial depth ratios and 5 load inclination angles.Based on the load displacement curves and the soil displacement and deformation fields around the pile(anchor)under different working conditions,the effects of the burial depth and load inclination on the bearing characteristics of the helical pile are analyzed.The test shows that: when the load inclination angle is the same,the ultimate bearing capacity increases continuously with the increase of burial depth,but the growth rate is different due to the difference of load inclination angle,the burial depth ratio of the first layer anchor piece reaches 5,when the load inclination angle is greater than 45°,with the increase of burial depth,the growth rate of ultimate bearing capacity gradually decreases and tends to a critical value,but when the inclination angle is less than 45°,the growth rate increases continuously.It can be foreseen that there exists a burial depth such that the ultimate pullout load capacity at smaller inclinations is equal to the load capacity at larger inclinations.Under this test condition,when the burial depth ratio is the same,the ultimate bearing capacity increases first and then decreases with the increase of the load inclination,and the load inclination corresponding to its maximum value decreases with the increase of the burial depth and tends to 67.5°.Under certain conditions,the existence of vertical load component can significantly improve the horizontal bearing capacity of helical piles.The finite element analysis software Optum G2 was used to simulate the oblique drawing of the single anchor helical pile to further clarify the influence of the burial depth and the load inclination angle on the bearing characteristics of the helical pile.In addition,the vertical and horizontal drawing of double anchor helical pile under different layer spacings is simulated to study the effect of layer spacing on the earth pressure coefficient of the anchor sheet surface.The results show that increasing the load inclination angle or increasing the burial depth will weaken the rotation effect of the helical pile and strengthen the vertical movement mode;The spacing of the anchor sheets has a weak effect on the earth pressure coefficient of the interlayer anchor sheet detachment zone,while for the interlayer compression zone,under the action of vertical pulling load,the bearing capacity of the anchor sheet will be affected when the layer spacing is small,and under the action of horizontal load,The earth pressure coefficient of the compression zone on the drawing side is affected by the layer spacing,while the other side is less affected.Based on the numerical simulation results the influence factor of layer spacing is fitted and calculated in this paper.In addition,this paper studies and establishes the mechanical analysis model of single anchor screw pile inclined pulling,finds the soil pressure on the anchor piece by introducing the "approximate calculation method of soil pressure considering the effect of displacement",calculates the horizontal resistance force on the pile by using the Wang Guocui normalized model,considering other forces,carry out the mechanical limit equilibrium analysis,and deduce the theoretical solution of the ultimate bearing capacity of the single anchor screw pile oblique pull;On this basis,combining the influence coefficients of anchor piece spacing on the soil pressure on the interlayer anchor pieces in the numerical simulation results,the force pattern of double-anchored helical pile is analyzed,and the mechanical equilibrium analysis is carried out to derive the theoretical solution of the ultimate pullout resistance of doubleanchored helical pile.The calculation results show that the theoretical calculation method established in this paper shows good applicability to the existing test cases.