Study On Bearing Performance Of The Post-grouting Piles With Different Hole-forming Methods In Non Collaosible Loess Area

Post-grouting technology,which can improve the bearing performance of the pile foundation and increase the bearing capacity effectively,has been widely used in engineering construction.The post-grouting piles with a variety of hole-forming methods are used during construction,and different methods cause different effect of the grouting,so that the bearing performance of the post-grouting piles are different,at present,there are relatively few researches on how the hole forming methods will influence the bearing performance of the post-grouting piles.Studying this effect can help us to understand the mechanism of post grouting better,provide reasonable pile parameters,basis for reasonable selection of hole-forming methods and determination of bearing capacity.The project of department of transporation of Shanxi,?study on bearing capacity of friction pile under different pore-forming in loess area?(15-21K),and Wuqi to Dingbian Highway engineering is supported.Based on the static load test and theoretical analysis,the bearing performance of the post-grouting piles with different hole-forming methods were deeply and systematically studied,and some major results have achieved:1.Based on the laminar flow theory of circular tubes,the columnar seepage diffusion model of slurry was established,which considers the number of grouted pores and the effect of soil filtration,how the influential factors of the slurry seepage diffusion were analyzed,the accept called ?effective diffusion distance? of slurry was proposed.Based on the cylindrical cavity expansion theory and unified strength theory,slurry column pressure mechanism and the soil strength parameters on the column hole reaming after the influence of the radius were studied,Which give an access to estimating the effective diffusion distance of the slurry and the diameter of the pile tip.2.Based on the laminar flow theory of circular tubes and elasticity equations,the slurry return model that considers the late time variation of slurry was established,through the analysis of the relationship between thickness of mud cake,the length of pile,the pressure of slurry,the property of soil and the height slurry can return,the formula for calculating the return height under the slurry pressure in different soils was obtained,and verified by engineering examples,the model has good applicability and accuracy,provides a method to determine serum on return height.3.Through the static loading failure test,some data of post tip grouting piles with different hole-forming methods were obtained,including grouting volume,slurry pressure,ultimate bearing capacity,side friction and pile tip resistance.This paper compared the bearing performances of post-grouting bored piles in three different hole-forming methods,then accepted what led to the different ultimate bearing capacity;the reason why residual stress of post-grouting pile could produce and its' influence on the post-grouting bearing capacity were analyzed,then get the meachanism that pile tip grouting improve the bearing capacity of different hole methods bored pile,the results of the analysis can provide a reference for choosing a reasonable post-grouting hole-forming method.4.Based on the cylindrical cavity contraction and unified strength theory,this paper studied the influence of soil strength parameters,ranging from drilling to concrete pouring,on the radial pressure and side friction,with the effect of concrete pouring on the radial pressure has been considered,the pile side friction with the changing rule of the soil strength parameters were obtained;according to the effect of dissection around the pile that different hole-forming methods formend,a model for calculating the shear displacement was established,which contains the effect of dissection around the pile,then analyzed the influencing factors of the soil settlement around piles with the changing rule of mud thickness,concrete thickness,and shear modulus were obtained.Combines with the data of the test pile,the ?depth effect?,?softening effect?,?strengthening effect? of side friction were analyzed,the interaction relationship of this three were determined;the analysis of characteristics of side frictional resistance can provide reasonable value and reference for the calculation of the side friction.5.Combining the grouting volume,the slurry return model and the bearing characteristics of post tip grouting piles with different hole-forming methods,together with the existing calculation method for the bearing capacity,an new method for calculating ultimate bearing capacity of post tip grouting piles(friction piles),which considers the effect of hole-forming was built.The analysis results show that the new built method is in good agreement with the measured values,improved the limit bearing capacity of post-grouting piles calculation accuracy and it could be a reference for actual engineering construction.