Research On The Influence Of Water Level Rise And Fall On The Bearing Behavior Of Rigid Pile Composite Foundation In The Yellow River Flooding Area

The silt in the flooded area of the Yellow River has the characteristics of high powder content,poor gradation,and high particle roundness.In actual engineering,it is difficult to form a densely structured soil according to the current standard compaction method,and the capillary body of the soil after compaction Welldeveloped pores are conducive to water migration.The rigid pile composite ground gene has the advantages of large processing depth,high bearing capacity,short construction period and low engineering cost.It has a wide range of applications in housing and infrastructure construction(such as roads and railway subgrades)in the Yellow River flooding area.The existing rigid pile composite foundation is analyzed based on saturated soil theory,and the influence of water level changes and saturation changes on the bearing properties of existing composite foundations is not considered.In actual engineering,most of the soil is in an unsaturated state.In addition,the unreasonable exploitation of the groundwater level will lead to a decrease in the groundwater level,while factors such as increased seasonal rainfall,reduced groundwater level extraction,and the replenishment of rivers and lakes to the groundwater level will cause the groundwater level to rise.Since the engineering properties of silt in the yellow flooded area are greatly affected by water content,the use of traditional saturated soil mechanics to analyze the load-bearing deformation of the soil will inevitably produce large errors.Therefore,it is necessary to introduce unsaturated soil theory to improve the rigidity of the yellow flooded area.The bearing behavior of pile composite foundation is studied.Groundwater level changes cause changes in soil moisture content and internal pore structure,which in turn causes the weakening of soil compression modulus and strength parameters of the pile-soil interface.The soil between the piles will settle under the upper load,and the relative displacement of the pile-soil will increase.,The negative friction resistance of the pile body increases,the axial force of each node of the pile body increases,and the safety margin of the pile body strength decreases,which induces engineering problems.However,the current design and safety assessment of rigid-pile composite foundations in this area have not considered the special properties of the silt and the influence of the cyclic rise and fall of groundwater level on the longterm bearing properties of rigid-pile composite foundations in the Yellow River flooding area,so there are huge safety hazards.This study takes rigid pile composite foundations in the yellow flooding area as the research object.Through a combination of laboratory experiments and theoretical analysis,considering the influence of matrix suction on the compressive modulus of silt and the shear strength of the pile-silt interface in the yellow flooding area,it is proposed Settlement calculation method of composite foundation based on pile-soil deformation coordination.The specific research results are as follows:(1)Under normal load conditions,as the groundwater level rises,the soil at the end of the pile and the soil between the piles turn from an unsaturated state to a saturated state,and the compressive modulus and shear strength parameters of the soil around the pile are weakened.The surrounding soil undergoes overall settlement under the combined action of groundwater rise and upper load.As the cushion adjusts the pile and the load distribution of the soil between the piles,the amount of penetration on the pile top increases,the load borne by the pile increases,the load borne by the soil between the piles decreases,and the overall settlement of the composite foundation increases.With the increase in the number of cycles of water level rise and fall,the composite foundation continues to undergo settlement,and the settlement is irreversible plastic settlement.(2)In the cyclical rise and fall of the water level except the first rise and fall of the water level,the effective stress of the soil changes periodically due to the rise and fall of the water level,which in turn causes the piles and the soil between the piles to undergo periodic changes.The rise in water level causes the effective stress of the soil to decrease,the soil rebounds slightly,the penetration amount on the pile top decreases,the load borne by the soil between the piles increases slightly,the load borne by the piles decreases slightly,and the pile-soil stress ratio decreases.Axial force is reduced.The drop in the water level causes the effective stress of the soil to increase.The soil between the piles and the water level drop together to produce settlement.The load borne by the soil between the piles decreases,the load borne by the piles increases,the pile-soil stress ratio increases,and the relative displacement of the pile-soil Increase the axial force of the pile shaft.(3)Establish a calculation method for the settlement of rigid pile composite foundation based on load transfer method,introduce a side resistance softening model that is more in line with actual working conditions to calculate the pile side friction resistance,and consider the impact of the matrix suction on the soil compression modulus and the pile-soil interface shear The influence of the strength parameters expands the scope of application of the method,and the accuracy of the method is verified by the results of indoor model tests.