Bearing Behavior And Numerical Simulation Analysis Of Squeezed Branch Pile In Ollapsible Loess Area

As a new type of pile,the squeezed branch pile is in the stage of continuous exploration and development,and its engineering application has shown its excellent bearing capacity and great development potential.In view of the fact that the foundation treatment effect in the collapsible loess area is difficult to be ensured,the squeezed branch piles are widely used in many non-collapsed loess areas,but the application status is less in the collapsible loess area.On the basis of scientific research,through the combination of theoretical analysis and numerical simulation,the applicability of the pile structure in collapsible loess area is discussed in detail,and its bearing performance in collapsible loess area,The load transfer characteristics,the stress distribution in the pile-soil system and the settlement deformation are studied in detail.Finally,the following conclusions are drawn and some suggestions are put forward:(1)Through detailed analysis of the working mechanism of the squeezed piles,it is concluded that the process of extrusion and expansion of the extrusion equipment includes the extrusion of the extrusion equipment and the consolidation of the soil around the pile;The failure form of the pile can be divided into two types: the shear strength of the support caused by insufficient strength of the support plate and the shear strength damage of the soil caused by the strength of the soil around the support plate being too small.(2)By analyzing the settlement deformation of the squeezed branch pile,it is concluded that the settlement of the pile structure includes the compression of the main pile,the compression displacement of the support disc and the settlement of the soil under the pile end;The compression amount of the pile can be divided into the compression amount of the main pile part above the top plate,the compression amount of the main pile part between the bearing plates and the compression amount of the main pile part below the last disk;based on the principle of “force water equivalent”,the expansion The settlement of the piles of piles is theoretically analyzed and the calculation formula of the settlements is obtained.The settlement of the ordinary equal section piles and the squeezed branch piles under the same working conditions is calculated by the formula,and the squeezed expansion trays are obtained under the same conditions.The final settlement of the pile is reduced by about 50% compared with the ordinary cross-section pile.By numerical simulation of the two pile types,it is found that the two results are basically consistent,which verifies the correctness of the theoretical analysis method proposed by this paper and the numerical simulation method.Feasibility;the main factors affecting the bearing capacity of the squeezed branch pile are the nature of the surrounding soil layer,the construction process,the shape of the support disc and the spacing of the support discs.(3)By establishing the finite element model of the squeezed branch pile and the ordinary bored straight pile,the P-S curves of the two types of single pile are obtained,There is an obvious sags segments on the P-S curve of the ordinary bored straight pile.It shows that its failure is sudden and unpredictable.However,the P-S curve of the squeezed branch pile is always smooth,indicating that its failure is more gentle and there is a certain buffer phase.The bearing disk mainly plays the roles of transferring load,distributing load and bearing load.There has certain order and time when each bearing disk plays its role,and its force mechanism is very scientific.(4)By establishing the finite element model of the squeezed branch pile and the ordinary equal section pile,the single pile PS curve is extracted,and the rationality of the calculation method and simulation method of the above bearing capacity and settlement is verified.It can be reflected that there are obvious turning points and sudden drop sections on the single-pile PS curve of ordinary equal-section piles,indicating that the damage is sudden and unpredictable,and the single-pile PS curve of the squeezed branch piles is relatively flat.It shows that the damage process is more moderate,and there is a certain buffering stage in the actual project.By extracting the partial curve of the axial force of the pile structure with depth,the axial force is suddenly reduced at the lower end of the bearing plate,and the reduced part is the bearing plate.The load bearing;the bearing plate mainly plays the role of transmitting load,distributing load,dispersing load and bearing load.Each bearing plate has a certain order and time when it plays its role,and its force mechanism is very scientific.(5)By analyzing the displacement field and stress field of the squeezed branch pile,it is found that under the working load,a "stretching crack zone" will be formed between the bearing plate and the upper soil.At this time,the bearing plate and the soil body The actual mutual contact will not occur,so the side friction resistance of the bearing plate setting section will be greatly reduced,but the bearing plate will produce the end bearing force slightly behind the side frictional resistance;the connection of each bearing plate to the main pile Stress concentration occurs at the position,the top corner of the bearing plate and the end of the pile.This is also an important reason for the punching damage of the bearing plate.When setting the bearing plate,the proper disk spacing is very important.If the spacing between the discs is too close,the soil between the disc spacing may be sheared and even collapsed into the gap of the air bearing surface of the lower bearing disc,thus affecting the frictional resistance between the piles and the soil.The resulting "stress bubble" will also affect the stress distribution of the lower plate,causing stress superposition and additional stress.Therefore,in actual engineering design,the distance between the bearing plates should be greater than the critical spacing value,and the bearing force should be as far as possible.Disk set in soil Stable soil,the soil bearing capacity into full play the same time,each load-bearing plate can work independently,carrying the greatest degree role to play too.