| The topic of deep foundation pit support has become a new hot spot and difficulty in civil engineering building as society has progressed and urbanization has accelerated.The supporting structure of a deep foundation pit near a underpass tunnel,underpass station,or other under surface structures is constrained by nearby under surface buildings and soil,which affects the supporting method and deformation strength of the supporting structure,out coming in a dissimilar dispensation of earth burden than in normal circumstances,and the supporting structure design is more complicated.Founded on prior research,this study addresses the joint action of double layer piles of the underpass tunnel,foundation pit,and foundation pit support structure,and creates a three-dimensional finite element calculation model by using the largescale general calculation program ABAQUS to simulate the formation procedure in Xi’an.The ideal design approach and deformation properties of a double layer pile support strategy for a deep foundation hole in finite width soil are studied,with the following conclusions:1、In a deep foundation pit project near a underpass tunnel,the double layer piles can effectively respond to the complicated nearby atmosphere,reduce soil displacement round the foundation pit,and provide good foundation pit excavation support.(a double layer pile support strategy)pile length 33 meters,pile thickness 1.2 meters,pile stiffness,pile spacing 2D,pile layer spacing 4D.2、The main deformation aspects of a dual layer pile support layout disagree with those of a single layer heap:a single layer pile’s deformation curve is a gradual curve with a large upper part and a small lower part,whereas a double layer pile’s deformation curve is a bow or double reverse bending point curve with small upper and lower bases and a large middle part.The conclusive displacement of the pile body in a double layer pile support strategy is reasonably minor than that of a single layer pile support structure.The existence of the crown beam can1、drastically alter the deformation condition of the double layer pile,outcoming in a significant deduction in pile top displacement.The beginning and back piles will have a bow or double reverse bending point displacement curve with a big in the middle and tiny on both edge,causing the soil round the foundation pit to be more restricted.2、Modifications in the stress or deformation condition of the double layer pile support strategy can be effected by modifications in pile length,thickness,stiffness,pile spacing,and pile layer spacing:(1)The conclusive horizontal displacement of the pile is lowered by round 2cm when the pile length is increased from 27m to 35m,with a deduction range of 29 percent.The pile length can change the deformation form of the double layer pile support structure,effectively reduce the pile top displacement and conclusive displacement,and effectively increase the rooted effect of the pile.It can effectively reduce the horizontal displacement of double layer piles and is beneficial to the strength of the double layer pile support structure.(2)The conclusive horizontal displacement of the pile body is lowered by round 3cm when the pile thickness is extended from 0.6m to 1.4m,with a deduction range of 38 percent.The lateral bending stiffness of double layer piles is increased by increasing pile thickness,which immediately enhances the limiting effect of double layer piles on the soil round the foundation pit.This technology efficiently reduces horizontal soil displacement round the foundation pit while also increasing the strength of the double layer pile support structure.(3)The conclusive horizontal displacement of the pile is reduced by round 2.2cm when the section stiffness is increased from 0.5ei to 1.5E,a deduction of 27%.The friction of the pile to the nearby soil is improved when pile stiffness is increased,and the horizontal displacement of the pile is reduced as a outcome,which aids in the strength of the double layer pile support strategy.(4)The conclusive horizontal displacement of the rear pile grow by 1.99cm when the pile spacing increases from 2D to 6D,whereas the conclusive horizontal displacement of the beginning pile increases by 3.30cm,according to study.The rise rates are 52 percent and 75 percent,respectively,with beginning layer piles experiencing a substantially bigger increase in horizontal displacement than rear layer piles.With increased pile spacing,the number of double layer piles within the same distance will be lowered,reducing their lateral bending capacity in an unnoticed manner,which is detrimental to the foundation pit’s support condition.(5)The conclusive horizontal displacement of the beginning and rear piles is reduced by 3.32cm and 2.65cm,respectively,when the pile layer spacing is increased from 2D to 6D,with a deduction range of 50.69 percent and 38.97 percent.By increasing the pile layer spacing of double layer piles,the soil dispensation proportion into piles can be adjusted,thus reducing pile horizontal displacement.The horizontal displacement of the pile will continue to reduce when the pile layer spacing is increased.3、Varied reinforcement methods for dissimilar bending moment dispensation features of double layer piles can be used to reduce project costs:sectional reinforcement can be used when pile lengths and single pile bending moment dispensation are dissimilar.Asymmetric reinforcement can be used when the beginning and back layers of piles have varying thicknesss and bending moments.When the pile layer spacing and the increase in bending moment of a single pile are dissimilar,segmented reinforcing and asymmetric reinforcement can be used together.4、As the base tunnel distance grow from 10 to 30 meters,the horizontal displacement of the underpass tunnel drops from 5.66 to 2.10 meters,a deduction of 62.9 percent;the vertical displacement reduces from 3.79 to 0.73 meters,a deduction of 80.7 percent.With a vast deduction range,the horizontal and vertical displacements showed a declining tendency.The impact of foundation pit excavation on the underpass tunnel is increasingly noticeable the closer the distance into the foundation pit and the tunnel is.The existence of the underpass tunnel will change the mechanical deformation achievement of the double layer pile when the distance into the foundation pit and the tunnel is small,and the surface arrangement into the foundation pit and the tunnel will be reduced,but the surface arrangement far from the end of the foundation pit will continue to increase,and the underpass tunnel will have a certain shielding effect on the foundation pit;when the distance into the foundation pit and the tunnel is large,the surface arrangement into the foundation pit and the tunnel will be reduced。5、The horizontal displacement of the underpass tunnel increases from 0.76 cm to 11.6 cm,a difference of 1426.3 percent,as the excavation depth of the foundation pit increases from 15 to 25 meters;the vertical displacement increases from 2.56 cm to 10.45 cm,a difference of 308.2 percent.The displacement in both the horizontal and vertical axes was increasing,and the grow range was unusually broad.The deeper the foundation pit excavation,the greater the strength of the foundation pit excavation on the underpass tube.The presence of an underpass tunnel has a significant impact on the excavation of the foundation pit directly adjacent to it.The presence of an underpass tunnel can change the soil arrangement mode into the foundation pit and underpass tunnel,as well as the deformation aspect of a double layer pile support strategy.The strength of the underpass tunnel on foundation pit excavation will gradually deteriorate as the depth of the foundation pit excavation increases,as will the horizontal displacement of the double layer pile support structure and the surface arrangement around the foundation pit. |
