Based On The Analysis Of The Bearing Behavior Of Post-grouting Uplift Piles In A Thick Sand Foundation

The theoretical research on side-grouting uplift piles has lagged far behind the development of engineering practice.The study of the bearing capacity and deformation characteristics of uplift piles is based on the theory of the compressive piles.In practical engineering design,the design and calculation method for post-grouting uplift piles given in current national code is based on the design method of compression piles.The shaft resistance of compression piles is multiplied by the uplift coefficient as the bearing capacity of uplift piles.Then grouting effect can be achieved by multiplying the grouting coefficient.However,lack of local engineering data would be difficult to design the uplift pile.Therefore,it is necessary to carry out field test for post-grouting uplift piles and to study bearing capacity characteristics of uplift piles.Based on the field test results of uplift piles for a thick sand layer foundation project in Beijing,this paper studied and analyzed the bearing behavior of side-grouting of full length uplift piles in thick sand layers.The main contents are as follows:(1)Explained the research status of bearing properties of uplift piles in domestic and abroad and related calculation theory of bearing properties of uplift pile.The failure mode of uplift pile,the law of shaft resistance of uplift pile and calculation method of the ultimate bearing capacity of uplift pile in different failure modes were analyzed.(2)Based on the engineering project,the test procedure,test equipment,and test principle of the static load test for post-grouting piles were detailed,and the test results were analyzed in detail.Through the comparison of the test results of post-grouting compression piles and uplift piles,the bearing properties of side-grouting uplift piles were analyzed;and then the test results of side-grouting piles and non-grouted piles were compared,for analysis the influence of post-grouting construction on bearing behavior of uplift piles.(3)The PLAXIS 3D finite element software was used to simulate the loading process of post-grouting and non-grouted piles,and the experimental data was used to verify the rationality of the numerical calculation.On this basis,bearing properties under the ultimate load of the side-grouting uplift piles were discussed.