Multidirectional Drawing Test And Theoretical Study On Horizontal Uplift Capacity Of Single Screw Anchor

Screw anchor has great development advantages and application prospects in slope control,infrastructure construction,military and civil engineering,communication,power,clean energy,pipeline,industrial buildings and other fields.But because of the existence of spiral blades,the interaction of anchor and soil and failure mode under pulling load is more complex than that of the traditional equal cross section pile.At present,there are few studies on the uplift bearing characteristics of screw anchors at home and abroad.The related experimental and theoretical studies are mostly focused on vertical drawing,which the effect of load direction change on its bearing capacity is neglected.At the same time,in regard to the construction and design specifications of srew anchor,especially the horizontal bearing capacity,it is not clear that how to consider the role of the blade in the uplift process.Most of the time,it is simply the equivalent calculation of geometry or flexural rigidity.This has brought great inconvenience to the design or use of screw anchor in engineering practice,and it also has some hidden dangers.Therefore,it is necessary to carry out the multi-direction drawing bearing test on the single screw anchor and study the theory of the horizontal uplift bearing capacity.This paper developed a set of single screw anchor test model and sand box for multidirectional pull-out test,and the Nandu River sand was used as the foundation.The multidirectional pull-out tests were carried out based on it.The tests were carried out in 25 working conditions,including five buried depths and five drawing directions.According to the test results of load displacement curves were compared and analyzed different buried depth direction and drawing effect on the ultimate pullout capacity.At the same time,the change of soil pressure on every point of the blade during the uplift process was analyzed,based on the soil pressure test data,and the interaction rule between anchor(blade)and soil was further studied.The results show that there is a good linear relationship between the ultimate bearing capacity of single screw anchor with depth ratio and load direction.It increases with depth ratio,and decreases with the angle between the loading direction and the vertical direction.The effect of the latter two on the former can be expressed by the plane equation with better fitting degree.The horizontal and vertical components of the ultimate bearing capacity of the single screw anchor can not reach the limit value at the same time under the oblique load.It can not be calculated by simple decomposition or coupling in these two directions.The whole soil pressure on the blade changes in the process of drawing is that the outer pressure's increment(decrement)is greater than the central region,and the point farther away from the center of rotation is greater than the nearer one too.Its value is not distributing like the special soil pressures of Rankine theory,or linear distribution in pairs.Based on the test data and their analysis results,this paper assumes that the force of each point on the blade is related to its displacement during the horizontal drawing process of the single screw anchor,and the force of the anchor meets the p-y curve.By means of that,the calculation formula of the horizontal ultimate bearing capacity of the single screw anchor in sand is derived.Combined with the formula,p-y curve model in API specification,the Kallehave's improvement model and the Wang's normalization model are used to calculate the test of this paper and Mittal's test.The results show that the horizontal ultimate bearing capacity of single screw anchor can be calculated by the theoretical method of this paper,with the normalized p-y curve model of Wang,and good results can be obtained.