Research On Vertical Bearing Properties Of X-section Pile Foundation In Calcareous Sand

The South China Sea,which is one of the three marginal seas in China with nearly3.5 million square kilometers,possesses numerous islands covered with calcareous sand.The calcareous sand is formed by the marine biological skeletons,such as the corals,shells and ancient limestone,after the destruction,transportation and accumulation in the sea.Due to the tiny pores produced in the process of formulation,the calcareous sand is characterized with irregular shape,much porous,fragile particles and potential cementation.Inspection of physical characteristics of the calcareous,which are different from mechanical properties of the sand coming from land,makes it a major technological challenge in the marine civil engineering.The X-sectional Cast-in-place Concrete pile?referred to as XCC?which is developed by professor Hanlong Liu is a new type pile featured with environmental protection,high efficient and saving materials.Principles of contour extension of the contour area are adopted to change the direction of arc arch to make it beneficial to the bearing capacities.The bearing capacities of a single XCC has been investigated by researchers.In order to apply the new type pile in the more engineering application,model tests and numerical analyses are carried out in this thesis to investigate the vertical bearing capacities of X pile raft foundation.Major findings can be concluded as follows:?1?Tests of basic physical and mechanical properties have been conducted to obtain basic physical parameters of the calcareous sand including the specific gravity G_s?28?2.7 9,the maximum and minimum dry density ?_dmax=1.38g/cm³ and ?_dmin=1.08g/cm³,and the internal friction angle ?=41.35°.?2?Tests of single pile and pile group including the XCC pile and circular pile embedded in the calcareous sand have been carried out,adopting the pile foundation test system which owes the independent intellectual property right.?3?The Q-S curve,ultimate bearing capacity,axial force distribution curve,frictional resistance distribution,ratio of end-friction and ratio of side-friction for circular and XCC piles are plotted through the model test,respectively.Inspection of the results finds that the single pile embedded in the calcareous sand shows damage of mutant type;the XCC pile is more applicable than the circular pile with the same sectional area,with bearing capacities improved by 11%.A comparison study is conducted between the case of XCC embedded in the quartz sand and that in the calcareous sand,with the following conclusion:the bearing capacity of XCC in the calcareous sand is much lower than that imbedded in the quartz sand.?4?Pile groups with 4 piles and 9 piles under vertical loads are carried out respectively to obtain the Q-S curve,ultimate bearing capacity,axial force distribution curve,frictional resistance distribution,ratio of end-friction and ratio of side-friction for circular and XCC piles.Based on the test results,effects of pile groups are analyzed and findings can be concluded as:for the case of pile groups with 9 piles,load sharing ratio of the pile located at corner of the pile group is decreased with the gradual increase of the applied loads;load sharing ratio of the side pile to the central pile is gradually increased;the sequence of the main bearing pile for the vertical loads is corner pile,side pile and central pile.