Experimental Study On Geometric Parameters And Mechanical Properties Of Grouted Micro-steel-pipe-piles

With the development of highway infrastructure construction in China,especially in some poor and backward areas,great progress has been made under the guidance of the national "precision of poverty alleviation" policy.The construction of medium and small span Bridges should not be ignored.In order to speed up the construction of roads and bridges steadily,A local measure and an economical and applicable basic technology is urgently needed.Grouted micro-steel-pipe-piles are widely used in slope protection,foundation underpinning and foundation pit supporting projects because of their low cost,fast construction,pollution-free and low noise.However,they are seldom used as bridge foundation.In this paper,through geological condition of grouted micro-steel-pipe-piles to propose specific scope and the mechanical test of grouted micro-steel-pipe-piles,some guidance is provided for practical engineering technology.Prepare the grouted micro-steel-pipe-piles,through the static and fixed axial compression tests for 21 grouted micro-steel-pipe-piles and flexural loading test for 15 grouted micro-steel-pipe-piles,the effect of diameter d and wall thickness t of steel pipe,steel pipe,length of pile specimen H,water cement ratio of slurry,diameter r and spacing s of grouting holes on the flexural bearing capacity,deformation and failure properties of grouted micro-steel-pipe-piles are comprehensively analyzed.The results of axial compression tests showed that diameter d and wall thickness t of steel pipe play a dominant role in axial bearing capacity.When pile diameter D is the same,with the increase of diameter and wall thickness of steel pipe,and the failure mode of grouted micro-steel-pipe-piles shifts from brittle failure to ductile fracture.To increase length of grouted micro-steel-pipe-piles specimen or water-cement ratio results in the decrease of axial ultimate bearing capacity,however,when ratio of diameter of steel pipe to diameter of grouted micro-steel-pipe-piles,d/D,increase and fall in the range from 0.59 to0.72,length of grouted micro-steel-pipe-piles specimen,water-cement ratio and layout of hole associated with diameter and spacing do not significantly affect the axial ultimate bearing capacity of grouted micro-steel-pipe-piles.The standard of axial compression failure of grouting micro-steel-pipe-piles is based on the yield of steel pipe.The flexural loading test results showed that for the same diameter of piles body the diameter and wall thickness of steel pipe affected remarkably the ultimate flexural load of grouted micro-steel-pipe-piles.When the diameter of steel pipe increases and falls into0.59<d/D≤0.72,change of grouting water cement ratio from 0.45 to 0.75 and layout of diameters and spacing of grouting holes will not influence significantly the ultimate flexural load of grouted micro-steel-pipe-piles.And the steel pipe at mid-span begins to yield when the applied load is about 0.8 times of the ultimate load,and grouted micro-steel-pipe-piles exhibit well extensible performance.It can be determined that the failure standard for micro-piles is the failure of outside slurry of piles.Herein,the reasonable range of the ratio of the diameter of the steel pipe to the diameter of the pile is0.59≤d/D≤0.72.Further,apply thick-walled cylinder theory of elastic-plastic mechanics to analyze the stress of steel pipe in grouted micro-steel-pipe-piles.The results show that the pressure on the inner and outer surface of steel pipe calculated by Lamé formula under elastic state is close to the measured value,which verifies the effectiveness of test for grouted micro-steel-pipe-pile,and the corresponding calculation formula is put forward.