Study On Settlement Law And Calculation Method Of Long Spiral Bottom Pile

The long spiral enlarged bottom pile is different from the traditional straight pile in terms of geometry and load transfer mechanism.The unique structure of the pile body makes the interaction between pile and soil more complicated.At this stage,people do not fully understand the settlement law of this pile type,and there are no detailed theories.These have limited the application of the long spiral bottom pile in engineering.In this paper,field settlement,indoor model testing,numerical simulation,and theoretical analysis are used to explore the settlement law of the long spiral bottomexpanded pile.The single pile settlement of piles provides the basis,and according to the test law,the calculation method of the settlement of the long spiral enlarged bottom pile is derived.The main research results of the paper are as follows:1)In the field test,when the pile length-diameter ratio is constant,the settlement of the long spiral pile with a pile top load of 6000 k N is about 26.5 ～ 37.3mm,while the settlement of the long spiral pile bottom is only 5.6 ～ 19.6mm,and the long spiral pile bottom The pile settlement is about 0.2 ～ 0.5 times of the long spiral pile.From the perspective of settlement,long spiral piles with longer spiral bottoms are safer and more stable.2)In this indoor model test,the settlement performance of the long auger enlarged bottom pile is obviously better than that of the enlarged bottom pile and straight pile.When the load at the top of the pile reaches 15 k N,the settlement of the long spiral bottom-expanded pile is 0.8 times that of the bottom-expanded pile and 0.25 times of the straight pile;when the pile-top load reaches 20 k N,the settlement of the long spiral bottom-expanded pile is bottom expansion 0.2 ～ 0.3 times of piles,0.2 ～ 0.5 times of straight piles.3)The indoor model tests and numerical simulation analysis show that when the length-to-diameter ratio of the long spiral bottom-expanded pile is 16.7,the blade pitch ratio is 2.5,the blade width is 360 mm,and the diameter of the bottom-expanded pile is1.5 ～ 2.0.advantageous.In addition,the smaller the pile-soil modulus ratio,the smaller the pile settlement.4)Based on the Mindlin-Geddes method,and considering the effects of the screw parameters of the pile body and the size of the enlarged head on the extended bottom pile,the calculation method for the settlement of the extended bottom pile is derived.By comparing the experimental measured value with the theoretical calculation value of the long spiral bottom pile in the indoor test,it can be known that the theoretical calculation value needs to be multiplied by a correction coefficient of 0.63 ～ 0.72.