Research On Bearing Capacity Of Composite Foundation With High Pressure Jet Grouting Pile

The high-pressure jet grouting pile composite foundation is increasingly used in engineering practice due to its extensive engineering applicability,simple construction equipment and good treatment effects.The bearing capacity of high-pressure jet grouting pile composite foundation is the most direct and effective parameter to judge the foundation reinforcement effect.Whether it meets the design requirements is directly related to the safety and normal use of the building(structure).During the construction of the project,the construction method,construction parameters,test methods and so on will affect the bearing capacity of the composite foundation of high-pressure jet grouting piles.On the basis of summarizing the development and application of high pressure jet grouting pile composite foundation at home and abroad,this paper first elaborates on the mechanical characteristics of high pressure jet,the pile forming mechanism of high pressure jet grouting pile,the reinforcement mechanism and the construction method.Then the calculation of the bearing capacity of composite foundation and its force characteristics under vertical load are analyzed.Finally,based on the expansion project of a railway hub,based on the test results of the engineering construction site,combined with the theoretical calculation and numerical simulation results,the bearing capacity of the high-pressure jet grouting pile composite foundation is analyzed and the following conclusions are drawn:(1)Through low-strain detection and core drilling inspection,it is found that the integrity and pile strength of the high-pressure jet-jet piles completed on site meet the design requirements.However,the unconfined compressive strength of the core sample taken during the core inspection is down from the top of the pile to the bottom of the pile.The core sample near the top of the pile has better hardness,integrity and consolidation than near the bottom of the pile.(2)The load-settlement curves obtained from the static load test on site are slowly deformed,and the proportional and ultimate loads are not obvious.Under the vertical load,the compaction,local shear failure and complete failure characteristics of the foundation are not obvious,which indicates that the bearing capacity of the composite foundation has not reached the limit state during the test.(3)The bearing capacity of the high-pressure jet grouting pile single pile composite foundation obtained by static load test on site is 150kPa,and the theoretical calculation value is 248.7kPa.The theoretical calculation value is greater than the field test value,and the theoretical calculation value is the result when the parameters ? and ?p both take the minimum value.If ? and ?p take a larger value within the range of values,the calculated value will be larger than the measured value.(4)The numerical value of the bearing capacity of the high-pressure jet grouting pile composite foundation calculated by numerical simulation is slightly smaller than the static static load test result,but the difference is small.Therefore,when the field test conditions are not available,the numerical value of the composite foundation bearing capacity characteristic value can be used as a reference for design and construction.(5)The numerical simulation results show that under the vertical load,the negative frictional resistance exists in the range of 15-20cm below the pile top,and the axial force of the pile reaches the maximum at about 45cm from the top of the pile.During the loading process,about 80%of the load is carried by the pile,and the rest of the load is carried by the soil between the piles and the soil at the bottom of the pile.