Study On The Influence Of Wall-protecting Slurry On Bearing Behavior Of Cast-in-place Pile In Calcareous Cementation Stratum

Calcareous cementation stratum is different from the geotechnical engineering characteristics of conventional cemented soil or structural soil.It is the product of calcium condensation and cementation in the deposition process of cementing materials containing calcium,iron,manganese,silicon and other mineral components and loose pebbles.It is easy to collapse and has strong water sensitivity,and is widely distributed in various regions of southern Xinjiang.The research on the engineering characteristics of calcareous cementation geological construction at home and abroad mostly stays in the finite element numerical simulation analysis.Many engineering projects are often designed and constructed according to similar engineering cases.There are still many gaps and deficiencies in the research of this engineering field.In order to ensure the pore-forming quality of cast-in-place piles in calcareous cementation stratum and provide better bearing capacity,this paper,based on the pile foundation engineering of the substructure of Kashi River Bridge in Yulong,Xinjiang,adopts the slurry wall protection construction scheme,and studies the influence of wall protection slurry on the vertical bearing behavior of cast-in-place piles in calcareous cementation stratum through indoor model test and finite element numerical simulation analysis,so as to provide theoretical basis and design basis for pile foundation construction under this complex geological condition in the future.The specific research contents are as follows:（1）According to the principle of model test similarity theory,the artificial calcareous cementation geological similar material is simulated,and the static load indoor model test of cast-in-place pile in calcareous cementation stratum is carried out.The experimental study shows that compared with the semi-cemented stratum,the pile side resistance in fully cemented calcareous cementation stratum is larger,and the ultimate bearing capacity of cast-in-place pile is higher.（2）In order to ensure the stability of the hole wall,the test uses slurry to protect the wall.The test results show that the No.1 slurry reduces the pile side resistance by about 85%and the vertical bearing capacity by about 3%.No.2 slurry reduced the lateral resistance of pile by about 95%and the vertical bearing capacity by about 8%;Even if the bearing capacity of cast-in-place pile is weakened by the mud between pile and soil,it still meets the requirements of bearing capacity of pile foundation,and No.1 slurry is more suitable for the use of slurry wall protection in calcareous cementation stratum.（3）In calcareous cementation stratum,various indicators of wall-protecting mud have an impact on the bearing properties of cast-in-place piles.With the increase of mud thickness,the pile side friction is reduced,the relative displacement between pile and soil is increased,and the bearing capacity is weakened.In addition,the higher the water loss of slurry,along with a large number of aqueous solution into the soil,the destruction of calcium cementation geological cementation strength,the strength of the soil is reduced,the bearing capacity of the cast-in-place pile is weakened;In order to meet the requirements of bearing capacity,the required specific gravity of slurry used in calcareous cemented geological wall protection is1.1～1.2 g·cm^-3,the water loss rate is not more than 20 m L·30 min^-1,and the thickness of mud skin is not more than 3 mm.（4）Based on ABAQUS finite element analysis software,the vertical bearing capacity of cast-in-place pile in calcareous cementation stratum is numerically simulated and verified with the model test results.The error of ultimate bearing capacity of pile is within 10%,and the distribution of pile side resistance and relative displacement between pile and soil is obtained.The influence of wall protection slurry on the bearing behavior of cast-in-place pile is summarized,which verifies the correctness of geotechnical test parameters and the accuracy of pile foundation model.At the same time,this simulation provides a reference for the numerical simulation analysis of pile foundation dealing with similar complex stratum in the future.