Research And Development Of New Anti-floating Anchor Structure And Bearing Mechanism

Anchor has been widely used in geotechnical engineering because of its simple construction,short construction period,low cost and effective reinforcement of building structures and rock and soil.Especially in anti-floating engineering,anti-floating anchor is one of the preferred engineering measures.However,the load concentration anchor has some disadvantages,such as local stress concentration,low ultimate bearing capacity and shallow critical anchor age depth,which greatly reduce the role of the anchor.At present,the single-hole composite anchor proposed for the disadvantages of the load-concentrated anchor has good engineering value,but the research mostly focuses on the single-hole composite anchor with a single force form,and there is little research on the tension-compression dispersed composite anchor,and there is little research on the influence of the length of the tension-compression section on the anchoring performance of the tension-compression dispersed composite anchor.In view of the disadvantages of the load-concentrated anchor,the load-dispersed composite anchor is proposed,which can make the load evenly distributed to the anchorage section of each unit of the anchor,so that the anchorage performance of the anchor is greatly improved.However,when the cohesive strength between the rock mass and the grouting body changes along the anchorage depth,the ultimate bearing capacity of the anchorage section of each unit of the anchor rod is different.Studies have shown that it will have an adverse effect on the anchorage performance of the anchor rod,but there are few solutions to the problem.Under this new working condition,it is necessary to propose a new anchor structure that distributes the load of the anchor head according to the ultimate bearing capacity of each unit anchorage section of the anchor,so as to avoid the failure of the load higher than the ultimate bearing capacity of the unit anchorage section in advance,or the insufficient load distribution of the unit anchorage section leads to the low call rate of rock and soil strength.In view of the actual problems in the above two projects,the tension-compression dispersed composite anchor and the load-distribution composite anchor structure are proposed respectively,and multiple sets of traditional tension anchors and load-dispersed composite anchors are set as control groups.The combination of in-situ full-scale test and later ABAQUS simulation evaluates the anchoring performance of the two anchors,and draws the following conclusions :(1)Test conclusion of tension-compression dispersed composite anchor1)The shear stress of the first interface of the tension-compression dispersed composite anchor is obviously lower than that of the first interface of the tension anchor,and the bearing plate welded on the anchor body can effectively hinder the relative displacement between the anchor body and the grouting bod y,and the stability of the anchor is further improved.With the increase of the length of the bearing section(the ratio of the length of the bearing section to the length of the bearing section decreases),the ultimate bearing capacity of the tension-compression dispersed composite anchor is further improved,which is 1.17 times,1.22 times and1.44 times of the ultimate bearing capacity of the tensile anchor with the same anchorage length,respectively.The steep drop of the load-displacement curve gradually disappears and the fitting degree is higher.On the premise of improving the ultimate bearing capacity,the tension-compression dispersed composite anchor can still achieve higher anchor head displacement.Compared with the tension anchor,its structure has better ductility.2)Although the ultimate bearing capacity of tension anchor can be further improved with the increase of anchorage length,the axial force distribution law and distribution range of tension anchor with different anchorage length are close under the same level load.Therefore,the axial force variation law of tension anchor can be reasonably predicted by the variation law of axial force of tension anchor with anchor head load along anchorage depth.The mutation point of the axial force in the anchorage depth is used as the optimal anchorage length of the composite anchor,which helps to better call the strength of the rock and soil in the anchorage section of each unit of the composite anchor.3)Compared with the tension anchor,the tension-compression dispersed composite anchor can better call the rock and soil strength of the lower anchorage section of the anchor,so that the critical anchorage depth of the anchor moves down.The tension-compression dispersed composite anchor makes the distribution of anchor head load more uniform in the anchorage section,the peak stress of the anchor decreases,and the side friction resistance is more exerted.As an engineering anti-floating anchor,it has certain engineering application prospects.(2)Load distribution composite bolt test conclusion1)According to the ultimate bearing capacity of the anchoring section of each unit,the load distribution type composite anchor reasonably distributes the anchor head load,and its ultimate bearing capacity is more than 1.13,1.52,1.17 times of the ultimate bearing capacity of the load dispersion type composite anchor with the same anchoring length,the tensile anchor with the same anchoring length,and the tensile anchor with the anchoring length of 4m.Under the premise of considering the ultimate tensile value of the anchor body,it can be equivalent to replace the tensile anchor with an anchorage length of 5m,which greatly reduces the effective anchorage length of the anchor and further reduces the project cost.Under the premise of high bearing capacity,it can produce large displacement of anchor head and better ductility of anchor structure under each load.2)Compared with the load dispersion composite anchor,on the basis of the reasonable distribution of the anchor head load,the load distribution composite anchor can make the strength of the rock and soil with high ultimate bearing capacity of the unit anchorage section more effectively called.The force of avoiding the anchorage section with low ultimate bearing capacity is too high,the damage occurs in advance at the weak point,and the interaction between the anchorage sections of each unit of the anchor is reduced.The load distribution composite anchor effectively reduces the adverse effect of the different u ltimate bearing capacity of each element of the anchor on the anchorage performance of the anchor,and has better adaptability in the anchorage engineering of rock and soil with different ultimate bearing capacity of each element.3)According to the change of the side friction resistance of the upper and lower unit anchoring section of the Unsoaked and soaked anchor with the load distribution,it can be seen that the surface of the middle weathered mudstone on the anchoring section of the lower unit of the anchor is affected by the wetting.The bond strength between the middle weathered mudstone and the grouting body decreased by 0.92 MPa,and the attenuation was 66%.The attenuation of the bond strength between the weathered mudstone and the grouting body i n the lower anchoring section of the anchor leads to the difference of the ultimate bearing capacity of the upper and lower unit anchoring section of the anchor,which has an adverse effect on the anchoring performance of the anchor.It should be fully con sidered in the design and construction of the anchor.