Study On The Application Of High Strain Measuring Force On The Hammer

In this paper,the hammer force measurement technology used in high strain testing of foundation piles is studied.The research progress of high strain,the basic theory of high strain and the basic theory of high strain hammer force measurement,the comparative study of traditional high strain pile force measurement and hammer force measurement technology,the advantages and disadvantages of high strain hammer force measurement and the influence of high strain testing precision are discussed.Through the comparative test of on-site testing,this paper analyzes the problems existing in the practical application of force measurement technology on hammer,and optimizes the selection of different combinations of hammer and hammer pad in the field testing on the assumption of idealization in the theoretical model of hammer and hammer pad,so as to improve the force measurement on high strain testing hammer.Detection accuracy.The contents and conclusions of his paper as follows:(1)This paper summarizes the current research status of high strain testing technology in China,Combining with the characteristics of high strain technology,the existing problems and the limitations of high strain testing technology,and referring to the research results of other authors,the high strain theory and the theory of measuring force on hammer are discussed in detail,and the high strain theory is combined to analyze the high strain hammer force measurement The advantages and disadvantages of this new technology relative to the traditional high strain pile body force measurement.(2)Two projects with different site conditions and geological conditions were compared by using high strain hammer and high strain pile body force measurement technology.The ultimate bearing capacity of the pile was obtained by single pile static load test method after the comparison test,and the high strain measured force and velocity time history curve,soil resistance distribution and high stress were obtained.The results of simulation and static load are compared and analyzed in order to study the accuracy and practicability of the technology.(3)The relationship between the elastic modulus of pile material and the level of static and dynamic load is studied.It is concluded that the elastic modulus of pile body used in dynamic measurement is lower than that measured in static load test when the strain(or load)level is low,and that the elastic modulus of pile body used in dynamic measurement calculation is higher than that measured in static load test when the strain(or load)level is high.(4)By using different bammer weight,different thickness of backing plate and different impact height in the comparative test of measuring force on high strain hammer,it is found that low impact with heavy hammer and thin backing plate should be used in the test of measuring force on high strain hammer,which can make the impact load of heavy hammer closer to the response load at the top of pile and reduce the eccentricity of pile head.At the same time,it is easier to excite the frictional resistance and end resistance when the impact pulse width of the heavy hammer is larger,so that the measured limit resistance is closer to the static load test.The weight of the heavy hammer and the thickness of the backing plate material are the key factors which affect the consistency of the stress of the hammer and the first soil element of the pile under the impact of the heavy hammer.(5)The practical results of the application of high strain hammer are verified by engineering examples.The high strain hammer has the advantages of high speed,low cost and adaptability to complex sites.The results of the test are basically in agreement with those of static load test.It is not significantly different from the high strain pile tester produced by PDI Company of America,which is the best one in this field.This new method of installing accelerometers on heavy hammers to measure the force is feasible and can be applied to the quality survey of a large number of Engineering piles.