| In the pile-anchor support of foundation pits,some accidental factors cause the anchor cables in the foundation pit to be damaged,which leads to the failure of anchor cables and causes the continuity of the foundation pit to collapse.Local anchor cable failure may cause the safety reserve of unfailed anchor cables and supporting piles to be reduced or to be fully used,which may cause damage to the supporting piles and adjacent unfailed anchor cables,or even cause a large-scale collapse of the foundation pit in severe cases.If the supporting system of the foundation pit has sufficient redundancy,when the local anchor cable fails,the restraint system prevents or delays the damage development of the supporting pile and other anchor cables,causing the collapse of the entire supporting system,then the foundation pit will not Continuity collapse occurred.This paper uses Midas GTS software to establish a three-dimensional numerical model based on actual engineering cases.The middle position of the four rows of anchor cables on the north side is simulated by using the rod removal method to simulate 1,2,4,8,and 16 respectively.Roots,32,and 63(whole row)anchor cables fail.Combining the deformation and internal force of the supporting pile and whether the axial force of the anchor cable reaches the deformation control amount of the supporting pile and the safety factor of bending bearing capacity and the pull-out safety factor of the anchor cable,it is judged whether the failure of the anchor cable causes the supporting pile and the adjacent anchor According to the damage of the cable,the rigidity redundancy and strength redundancy of the supporting piles and the strength redundancy of the anchor cable caused by the failure of the anchor cable are judged.On this basis,local reinforcement design schemes for supporting piles and anchor cables are respectively proposed.The main research contents and results are as follows:(1)The ability of foundation pits to resist continuous collapse is related to the stiffness redundancy of supporting piles.The greater the stiffness redundancy,the stronger the ability to resist continuous collapse.When the number of failures of the anchor cables in the middle of the first row and the second row reaches 8,16,32,and 63,both will cause the maximum horizontal displacement of the supporting pile to exceed the deformation control value,the rigidity redundancy of the supporting pile is small,and the ability of the foundation pit to resist continuous collapse is weak.When the third and fourth rows of anchor cables fail with different numbers of anchor cables,the maximum horizontal displacement of the supporting piles meets the deformation control requirements,the rigidity redundancy of the supporting piles is large,and the ability of the foundation pit to resist continuous collapse is strong.(2)The ability of foundation pits to resist continuous collapse is related to the strength redundancy of supporting piles.The greater the strength redundancy,the stronger the ability to resist continuous collapse.When the number of failures of the anchor cables in the middle of the first row and the second row reaches 16,32,and 63,the supporting piles will be damaged,the strength redundancy of the supporting piles is small,and the ability of the foundation pit to resist continuous collapse is weak.When the third and fourth rows of anchor cables fail with different numbers of anchor cables,the supporting piles are not damaged.The strength redundancy of the supporting pile is large,and the ability of the foundation pit to resist continuous collapse is strong.(3)The ability of the foundation pit to resist continuous collapse is related to the strength redundancy of the anchor cable.The greater the strength redundancy,the stronger the ability to resist continuous collapse.When the number of failures of the anchor cables in the middle of the first row and the second row reaches 8,both of them will cause the damage of the adjacent unfailed anchor cables,the strength redundancy of the anchor cables is small,and the ability of the foundation pit to resist continuous collapse is weak.When the third and fourth rows of anchor cables fail with different numbers of anchor cables,the adjacent non-failed anchor cables are not damaged.the strength redundancy of the anchor cables is large,and the ability of the foundation pit to resist continuous collapse is strong.(4)The local reinforcement design of the supporting piles can effectively increase the strength redundancy of the supporting piles and improve the ability of the foundation pit to resist continuous collapse.Two supporting piles with an interval of 24 m are strengthened,it was simulated that the first row of anchor cables did not fail,and the 16 anchor cables in the middle part failed.It is obtained that the maximum bending moment increase multiple of the supporting pile is smaller than that before the design without reinforcement,and the supporting pile is not damaged.the strength redundancy of the supporting pile is large,and the ability of the foundation pit to resist continuous collapse is strong.(5)The local reinforcement design of the anchor cable can effectively increase the stiffness redundancy of the supporting pile and the strength redundancy of the anchor cable,and improve the ability of the foundation pit to resist continuous collapse.The first row of anchor cables with an interval of 13.5m are strengthened,it was simulated that the first row of anchor cables did not fail,and the 8 anchor cables in the middle part failed.It is obtained that the maximum lateral displacement of the supporting pile is less than the deformation control value,and the increase of the axial force of the two anchor cables near the failure position is smaller than that before the strengthening design,which did not cause damage to the adjacent non-failed anchor cables.The rigidity redundancy of the supporting piles and the strength redundancy of the anchor cables are large,and the ability of the foundation pit to resist continuous collapse is strong. |
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