Study On The Application Of Anchor Jacked Pile In The Basement-addition Of Existing Buildings

The background of this paper is the basement expansion project of Yangzhou Branch, Industrialand Commercial Bank of China. The performance of anchor jacked pile used in the basement-additionof existing buildings construction differs from that applied to the general engineering.The differencesare:(1)The anchor jacked pile transfers the pressure through the bolting of the spread footing, and piledriving force can not be greater than the ultimate bearing capacity of spread footing;(2)Under theconstruction of the anchor jacked pile, foundation soil is fine sand, may cause many difficulties toconstruct silent piling and will generate the considerable displacement of soil squeezing to makeadjacent pile highly skew. So the construction of prepared hole have to be used before silentpiling;(3)After the construction of the anchor jacked pile, soil unloading come up to design depth ofthe pit, the ultimate bearing capacity of the pile is reduced as a result of soil unloading. To solve theseproblems, great deals of research works have been done in this paper.1. According to calculation theory of bearing capacity of spread footing, the ultimate bearingcapacity of spread footing is analyzed during construction of anchor jacked pile in this paper. Thefoundation pressure of spread footing is simplified based on the construction of silent piling and thecorresponding bearing capacity of spread footing is analyzed by using ANSYS FEM program. Theresults show that finite element calculation result is close to the utmost load of the construction andthe utmost load calculated by simplified model for the foundation pressure meet the designrequirements.2. The soil compaction displacement problem caused by construction of anchor jacked pile isdiscussed in this paper. The calculation software based on the cavity expansion theory is used inengineering analysis of soil compaction displacement. The soil compaction displacement caused bysingle pile is analyzed using the ABAQUS combined with the displacement penetration method. Andthen, the finite element calculation result of the radial displacement with the change in horizontaldistance is coincident with the theoretical calculation and model test. And the comparative analysis ofthe soil compaction displacement caused by the silent piling of prepared hole is also introduced in thispaper. The element birth-death method of ABAQUS is used in the finite element calculation of thesoil compaction displacement caused by the silent piling of prepared hole. The law showed from thecalculation results is completely consistent with the theoretical formula. the distribution regularities ofthe soil compaction displacement of prepared hole is obtained. 3.Combined with practical work, the size of bearing capacity and the distribution of resistance toside friction of single pile is studied about soil around precast pile under unloading in this paper.Through analyzing the load transfer of pile-soil system and superstructure in the basement-addition,the shaft resistance, tip resistance and ultimate bearing capacity of single pile under soil around singlepile unloading are analyzed by finite element numerical calculation. On this basis, the simplifieddistribution of resistance to side friction of single pile which can be applied to engineering is putforward. And a comparative analysis of ultimate bearing capacity of single pile before soil aroundsingle pile unloading is made by theoretical formulae. The results of this analysis are consistent withthe static load test of pile. Finally, the ultimate bearing capacity of single pile after the reduction isestimated by applying theoretical formulae and distribution of side friction of single pile and it isused in engineering.