Experimental Study On The Compressive Bearing Capacity Of Vertical And Inclined Combined Reinforced High-pressure Jet Grouting Pile Foundatio

Recently,with the continuous expansion of the construction scale of power engineering,higher requirements have been put forward for the design and construction of high-voltage tower foundation.The conventional transmission tower foundation is mainly pile foundation,but the traditional pile foundation has many unfavorable factors,such as inconvenient construction,difficult construction and high cost.In order to facilitate the construction of the tower foundation,in view of the above practical problems,this paper proposes a new type of tower foundation-straight and oblique combined reinforced high-pressure jet grouting pile foundation.The inclined pile in the vertical and inclined composite pile group foundation can increase the overall stability and bearing capacity of the foundation.Compared with the pile group foundation with straight piles,its mechanical characteristics are more reasonable.In this paper,the cement-soil high-pressure jet grouting pile is taken as the research object.The mechanical properties and bearing deformation mechanism of single inclined pile and vertical-inclined composite pile group under vertical load under different working conditions are discussed by means of indoor model test and numerical simulation.The variation law of pile top settlement,pile axial force,pile side friction resistance,pile bending moment and pile top load sharing ratio with pile top mechanical load under different working conditions is analyzed.Due to the particularity of high pressure jet grouting pile technology,jet grouting pile technology has strong regionality,and the influence of geological conditions must be considered in practical engineering.In this paper,red clay is used as foundation soil.Firstly,the indoor mix ratio test of high pressure jet grouting pile consolidation body is carried out,and the unconfined compressive strength and elastic modulus of cement soil consolidation body under different mix ratios are measured.Then,the influence of pile inclination angle and length-diameter ratio on horizontal displacement,vertical settlement and internal force of pile top is studied by single pile model test.It is found that the difference of pile top settlement under different working conditions is small when the top of jet grouting pile is subjected to small mechanical load.As the vertical mechanical load increases to a stable state,the vertical bearing capacity of the 10° and 20° oblique jet grouting piles is about 1.12 and 1.2 times that of the straight piles.When the length-diameter ratio and the inclination angle of the pile are large,the negative bending moment of the pile at a certain depth will appear;with the increase of the effective penetration depth of the pile,the average side friction resistance of the pile shows a trend of decreasing first,then stabilizing and finally increasing.Subsequently,the pile group model test of the vertical-inclined composite reinforced high-pressure jet grouting pile foundation with the angle pile inclination angle of 20° and the length-diameter ratio of 16.5 was carried out.The internal force of the center pile and the angle pile under different vertical loads and the load sharing ratio of the pile cap are analyzed.Compared with the single pile under the same test conditions,it is found that the axial force of the angle pile and the center pile is the maximum near the pile top and the minimum near the pile end.With the increase of the mechanical load on the pile top,the load sharing ratio of the pile cap gradually decreases,and finally stabilizes at about 37 %.Finally,the finite element software PLAXIS is used to analyze the vertical loading state of the straight-inclined composite reinforced high-pressure jet grouting pile foundation.The top settlement of the pile foundation and the internal force of the pile body with different inclination angles and aspect ratios are studied.It is found that under different test conditions,the bending moment of the pile body is basically the same under the same inclination angle,and the maximum bending moment decreases with the increase of the aspect ratio.The maximum bending moment of the pile is near the top of the pile.When the mechanical load of 40 k N is applied to the pile top,the axial force of the central pile is 1.13 times that of the corner pile.When the length-diameter ratio is the same,with the increase of the inclination angle of the pile body,the load sharing of the pile cap gradually decreases,and the load borne by the pile top is about 30 % ～ 40 % of the total load.