The Uplift Capacity Of Helical Anchors In Sand

The loads of transmission line are complex which suffering alternating load of tension and compression,horizontal load and bending moment for a long period, geological situation of which is more complex.Screw anchor has the characteristics of light,easier to install,simple manufacture,short time limit,low cost and recycling even in uneven ground and poor soil conditions.Screw anchor is applied to foundations with requirement for pulling more because of less disturbance of disturbed soil and taking full advantage of the strength of undisturbed soil.Screw anchor is widely used in electric power and obtained considerable economic benefits. I would study the uplift capacity of helical anchors in sand in this paper.First of all, this paper analysed the influence of scale effect of circular anchor plate on the uplift capacity in dense sand through model test and finite element method.Experiment of uplift was carried out to anchor plates of 20 mm,50mm,400 mm with embedment ratio of 2,3,4,6.Uplift resistance-displacement curve and ultimate uplift load were obtained.Breakout factor Nγ-embedment ratio H/D curve with different diameters of anchor plate showed that Nγ decrease with the increase of diameter of the anchor plate under the same embedment ratio H/D.The phenomenon is more obvious with the increase of the embedment ratio H/D.The ideal elastic-plastic Mohr-Coulomb model was modified considering the phenomenon of strain softening happened when soil strength varying along with the development of plastic strain and the subroutine of user was writed.The 12 uplift experiments above were simulated based the modified Mohr-Coulomb model which showed that the ultimate uplift loads respectively obtained by numerical calculation and the tests are in good agreement.The modified Mohr-Coulomb model simulated the process of progressive falure well.The cause of scale effect is mainly due to the gradual damage. Secondly, uplift experiment of plate and helical anchors was carried out in sand with the same compactness contraposing the influence of the type and size of helical anchor on uplift capacity.Comparing the uplift capacity of them, determining the critical embedment ratio corresponding to different failure modes according to the variation of the slope of the broken displacement ratio δ/D-embedment ratio H/D curves.Assuming the broken uplft slip surface of plate and helical anchors and analsying the ulift capacity of anchor plate by limit equilibrium method, raising the formula of limit uplift force under the condition of shallow buried and deep buried.Using the theoretical formula to estimate the 41 uplift capacity of anchor plate of experiments and verifing the applicability and accuracy of the theoretical calculation formula in this paper through comparing with the test results.Finally, I make a research of the influence of the interval and number of helical anchor in sand on uplift capacity and limit uplift force by indoor small scale model test not considering the influence of installing.Then I identified the interval for independent damage mode and the critical interval for transition to the column failure mode in dense sand and midium sand.This paper studied the uplift capacity of the screw anchor foundation by model test and numerical simulation, analysed the influence on the uplift capacity and the failure mode of the cause of scale effect,embedment ratio H/D,interval and number of helical anchor,provided theoretical reference for the design of screw anchor foundations of transmission lines.