Research And Analysis On The Factors Affecting The Bearing Capacity Of The Enlarged Head Anti Floating Anchor

With the increasing demand for the development of underground engineering in China,the anti floating problem of underground engineering is becoming more and more difficult,and the common anti floating anchor can no longer meet the needs of development.Therefore,in recent years,a variety of new anti floating anchors have emerged in China,and the expanded head anti floating anchor is one of them.Compared with the ordinary anti floating anchor,the expanded anti floating anchor has the characteristics of high uplift resistance and good anti floating effect.Although the anti floating bolt with enlarged head has been widely used in the anti floating of underground engineering,the stress process of the anti floating bolt with enlarged head is more complex than that of the ordinary bolt,so it is still necessary to study the anti floating bolt with enlarged head.On the basis of a large number of researchers’ indoor scale experiments on the tensile failure of the anti floating anchor rod with enlarged head and the results of in-situ inspection tests of an office building project in Nanjing,this paper uses the numerical analysis software ABAQUS to study the relationship between the failure mode of the anti floating anchor rod with enlarged head in clay and the burial depth,and the influence of the physical factors of the soil layer,the size factors of the anchor rod and the anchor group effect between the anchor rods on the bearing capacity of the anti floating anchor rod with enlarged head,It is also proposed that the effect of anchor groups can be effectively reduced by adopting the method of staggered arrangement of the anti floating anchor rods with enlarged ends.The main conclusions of this paper are as follows:(1)Through the method of numerical analysis software simulating the whole process of the tensile failure of the anti floating anchor bolt with enlarged head in the soil layer,it is concluded that the failure mode of the anti floating anchor bolt with enlarged head is related to the burial depth of the anchor bolt,corresponding to different burial depths.The anti floating anchor bolt with enlarged head has three failure modes,namely shallow burial failure,transitional failure and deep burial failure.The transitional failure mode has both shallow burial failure and deep burial failure characteristics;When the burial depth is large enough,the elliptical transverse width formed by the maximum principal stress nephogram of the front section of the enlarged head gradually tends to a fixed value.(2)The buried depth,the length of the enlarged head and the diameter of the enlarged head are in direct proportion to the bearing capacity of the anti floating anchor bolt with the enlarged head,and the increase of the diameter of the enlarged head is the most effective for improving the bearing capacity of the anti floating anchor bolt with the enlarged head,while the diameter of the ordinary anchoring section is in inverse proportion to the bearing capacity of the anti floating anchor bolt with the enlarged head;The increase of soil density,elastic modulus,cohesion and internal friction angle can improve the bearing capacity of the anti floating anchor rod with enlarged head,and the internal friction angle has the greatest influence on the bearing capacity of the anti floating anchor rod with enlarged head.(3)Under the same burial depth,the relationship curve between the horizontal spacing of the anti floating anchor with enlarged head and the group anchor effect coefficient is nonlinear,and the group anchor effect coefficient will increase with the increase of the horizontal spacing of the anchor,and the ultimate bearing capacity of the anti floating anchor with enlarged head will increase with the increase of the horizontal spacing of the anchor;Under different buried depths,the larger the buried depth of the expanded head anti floating anchor,the smaller the horizontal spacing required to reduce the anchor group effect;At the same horizontal spacing,the group anchor effect coefficient when three anchor bolts and the soil layer act together is lower than the group anchor effect coefficient when two anchor bolts and the soil layer act together,and the corresponding group anchor effect coefficient when three anchor bolts and the soil layer act together is roughly equal to the square of the group anchor effect coefficient when two anchor bolts and the soil layer act together.(4)Compared with two expansion head anti floating anchors with the same burial depth acting together with the soil layer,two expansion head anti floating anchors with different burial depth,that is,when the anchor bolts are staggered up and down,smaller horizontal spacing is required to eliminate the anchor group effect,so in the same area,more anchor rods can be arranged in the way of staggered up and down to obtain greater bearing capacity.