Study On The Penetration Process And Bearing Characteristics Of Static Pressure Piles In Different Soil Properties

Static pressure piles have no noise and low pollution during construction,are safe and reliable in terms of quality,and can be prefabricated at low cost in terms of economic benefits.With the above advantages,static pressure piles have played a great role in my country’s infrastructure construction.In this paper,the penetration process and bearing characteristics of open-ended static pressure pipe piles in dry sand,saturated sand and saturated silty clay are studied in depth through large-scale indoor model pile tests.The pressure sensor is used to obtain the change of the pile pressure;the fiber grating sensor arranged on the inner and outer tube of the model pile is used to obtain the change of the axial force of the pile body;the water pressure sensor and the earth pressure installed in the hole of the model pile and the outer tube The sensor obtains the soil pressure and pore water pressure change law between the pile-soil contact surface during the pile sinking process;the soil pressure and pore water pressure sensors arranged inside each soil can measure the soil inside the model pile during the pile sinking process.The soil pressure and pore water pressure changes;the soil plug height changes of the model piles in various soils were measured by the cable displacement measurement;the ultimate bearing capacity of the model piles in different soils was obtained by carrying out the static load test.The main research results of this paper are as follows:(1)The pile sinking test of the model pile in dry sand,saturated sand and saturated silty clay shows that at the end of the pile sinking,the pile pressure of the test pile in the three soils is in the order of dry sand and saturated sand,Saturated silty clay.The final pressure of dry sand is 1.76 times that of saturated sand,the final pressure of saturated sand is 3.34 times that of saturated silt clay,and the final pressure of dry sand is 5.88 times that of saturated silt clay.The final pile tip resistance of dry sand is 16.707 KN,the final pile tip resistance of saturated sandy soil is 9.99 KN,and the final pile tip resistance of saturated silty clay is 1.853 KN.In dry sand and saturated sandy soil,at the end of pile sinking,The pile tip resistance accounts for more than 50%of the pile compression force,showing good pile tip bearing characteristics.(2)The Pile sinking tests of model piles in dry sand,saturated sand and saturated silty clay showed that at the end of pile sinking,the total pile side friction resistance accounted for the largest 83.2%in saturated silty clay,followed by dry sand 43.1%,and the total pile side friction in saturated sand accounted for the smallest,which was 39.3%.The frictional resistance per unit side of the inner and outer tubes of the test piles in the three soils showed a trapezoidal descending distribution,and at the same penetration depth in different soils,the unit frictional resistance of the pile side gradually decreased along the top of the pile from the pile end.There is a "weakening effect" in the pile side friction resistance;during the pile sinking process,the unit side friction resistance of the inner tube of the test pile in the three soils is smaller than the unit side friction resistance of the outer tube of the test pile.(3)The Pile sinking tests of model piles in dry sand,saturated sand and saturated silty clay show that the pore water pressure outside the test pile increases with the increase of penetration depth;when the penetration depth reaches the maximum,the test pile The excess pore water pressure in saturated sandy soil is 0.72 kPa,the excess pore water pressure in saturated silty clay is 7.13 kPa,and the excess pore water pressure of test piles in saturated silty clay is about 10 times.The radial earth pressure on the pile side of the test pile basically increases linearly with the increase of the pile sinking depth.At the same penetration depth,the radial earth pressure on the pile side is:dry sand>saturated silty clay>saturated sand.The radial earth pressure of test piles in dry sandy soil is about 3.8-4.4 times that of test piles in saturated sandy soil.The radial earth pressure of test piles in saturated silty clay soil is about 1.2 times that of test piles in saturated sandy soil.(4)Pile sinking tests of model piles in dry sand,saturated sandy soil,and saturated silty clay showed that when the pile sinking was completed,the final soil plug heights of the test piles in the three soils were 39.3 cm,43.2 cm,and 22 cm,respectively.The soil plugging ratios of test piles in dry sand,saturated sandy soil and saturated silty clay are 46.2%,50.8%and 25.9%,respectively.Open static pressure pipe piles are more likely to form closed piles in sandy soil.(5)The static load test of model piles in dry sand,saturated sand and saturated silty clay shows that when the failure load is reached,the Q-s curves of the test piles are all steep-drop failure types;the test piles in dry sand and saturated sand The maximum settlements in and saturated silty clay are 14.61 mm,32.08 mm and 9.105 mm,respectively;the corresponding ultimate bearing capacities are 30 kN,18 kN and 8 kN,respectively.When the test pile is unloaded in dry sand,saturated sand and saturated silty clay,the corresponding final springback displacements are 3.375 mm,2.575 mm and 1.235 mm,respectively.The ultimate bearing capacity of test piles in dry sand,saturated sand and saturated silty clay increased by 3.6%,9.1%and 62.3%respectively compared with the final pressure of pile sinking.Appropriate rest period can improve the bearing capacity of pile foundation.