Experimental Study On The Influence Of Forming A Disk On The Pull-out Performance For The Rotary Excavation Cast-in-place Pile

Compared with other pile types,the rotary excavation and expansion cast-in-place pile has excellent bearing performance,mainly because the pile body is provided with one or more bearing disks.At present,the construction technology of extruding and expanding piles into disks is mainly divided into two methods: "extrusion and expansion into disks" and "cutting into disks",and the research on these two methods of disk formation is mostly limited to the direction of compression resistance,and the research methods are not very mature,the uplift bearing performance,bearing mechanism and changes of soil properties around the piles of the two types of piles need to be further studied.In this paper,two types of compression and expansion pile uplift model tests were designed,and the bearing performance,bearing mechanism,soil pressure changes around the piles,and changes in soil properties around the piles were compared and studied.The main research contents were And the conclusions are as follows:(1)The pull-up test was carried out in clay and sand foundations.The test proved that the load-displacement curve of the squeezed and expanded pile is a slowly-deformed type.carrying capacity.The bearing characteristics of the extruded and expanded piles are also different between the two methods.The ultimate bearing capacity is increased by more than 10%,and the uplift displacement is reduced by more than 19%.Through analysis,it can be seen that the total bearing capacity is increased by increasing the proportion of disk resistance by extruding and expanding the pile.(2)The earth pressure data around the pile is obtained by burying the earth pressure box.The analysis shows that the earth pressure around the equal-diameter pile has almost no change,and due to the existence of the bearing plate,the earth pressure around the squeezed and expanded pile increases with the increase of the load,but The soil pressure value of extruded and expanded piles is always smaller than that of cut piles.In addition,through the geotechnical test of soil samples around the extruded coil pile,the variation law of dry density and strength parameters in the horizontal and vertical directions caused by the compaction of the extruded coil pile to the surrounding soil of the pile is revealed.The connotation of forming a coil pile to improve the bearing capacity.(3)Use PIV technology to analyze the influence range of the up-pulling process of extruding and expanding piles with different disk forming methods on the soil surrounding the pile,and transform the vector diagram into the contour map of the lateral and vertical displacements of the soil surrounding the pile.The influence of the disk pile on the soil is larger,and the extreme value of the soil displacement around the pile is also larger,which verifies the conclusion that the bearing capacity of the disk pile cut into the above test is smaller.And it can be intuitively seen that the bearing plate has obvious time effect,which is also consistent with the previous test results.(4)The influence of different disk shapes on the pull-out performance of the squeeze-expanded piles was studied.The test proved that the disk shape had no effect on the bearing mechanism of the squeeze-expanded piles with the two disk-forming methods,but had a greater impact on the bearing capacity.In the PIV test,the relationship between the lateral influence range of the pile surrounding soil and the bearing capacity of different disk shapes is consistent with the relationship between the bearing capacity,which can prove that the 35° disk is the optimal disk shape in this test.