Research On Dynamic Response Performance Of Pile Based On High Strain Dynamic Test

Pile is the most important foundation form of housing construction,municipal road and bridge engineering.High strain dynamic test(HSDT)is the most practical and reliable method for testing the bearing capacity of pile and evaluating the quality integrity of pile.With the use of more and more large-diameter cast-in-place piles,the requirement of high bearing capacity on the weight of pile hammer for HSDT is higher and higher,and the hammer weight is larger and larger,which brings great hidden danger to the safety of HSDT,especially the heavy hammer high impact not only makes the transmission efficiency of dynamic effect low,but also makes the site very dangerous.There is a lack of theoretical research on the dynamic response process of high strain pile hammer,which leads to the lack of theoretical guidance for the selection of dynamic parameters and the selection of pile hammer detection methods in the detection process,which seriously affects the detection accuracy and engineering quality and safety.In order to give full play to the dynamic response efficiency of pile hammer and pile-soil,and ensure the safety and reliability of large-diameter cast-in-place pile,this thesis collects and collates a large number of high strain test data results in Guangdong area,conducts in-depth theoretical and Experimental Research on the dynamic response mechanism of high strain test,and clarifies the parameter selection and quality evaluation method of high strain in the detection of large-diameter cast-in-place pile,It improves the efficiency of dynamic response system of HSDT and provides reference for the revision of corresponding specifications.The work and research contents of this paper are as follows:(1)In order to improve the dynamic response effect of HSDT,improve the accuracy and efficiency of HSDT,and reduce the risk of engineering accidents.In this thesis,the dynamic response system of HSDT is studied theoretically,and the excitation mode of soil resistance around the pile is discussed.The relationship between the hammer energy,the energy received by the pile,the dynamic response system and the excitation mode of soil resistance is explored.It is considered that there is a close relationship between the energy consumed by the excitation of soil resistance and the effectiveness of the dynamic response system The purpose of this thesis is to find out the key factors that affect the efficiency of HSDT and dynamic response system through the combination of the formula and experimental research,and to evaluate the efficiency of each hammering.Finally,through the correlation study with the engineering example,the calculation results are in good correspondence with the actual engineering phenomenon,which proves that the research on the dynamic response of HSDT using the formula is reliable,and provides a new direction for the application research of HSDT.(2)By collecting and referring to a large number of high strain field test data of practical engineering,combining the theoretical research and Application Research of high strain dynamic response system,through the comparative analysis of the energy transfer efficiency and the measured bearing capacity of the dynamic response system when each hammering energy is close to the engineering example,and summarizing its principle,it is considered that the pile hammer action time has a great influence on the hammering energy transfer efficiency Finally,the reliability and rationality of the principle of "heavy hammer with low impact" are verified from the perspective of improving the efficacy of dynamic response system and the safety of detection process.(3)Based on the dynamic response theory of HSDT,the calculation results of hammering energy transfer efficiency are combined with the measured bearing capacity to analyze the typical phenomena in practical engineering.Finally,the effects of hammer weight,drop distance,high-energy hitting times,pile end bearing layer stiffness and pile length on the dynamic response system and the accuracy of HSDT bearing capacity are clarified It provides a direction for the optimization of test parameters of HSDT.(4)The selection of hammering combination has a great impact on the efficiency of HSDT dynamic response system,and also affects the safety and accuracy of HSDT process.In order to solve the problem that the selection of hammering combination in HSDT is too empirical,the measured data of high-energy hammering are statistically sorted and compared,and then the comparison results are analyzed theoretically According to the principle of "hammering with low impact",the parameter window of hammering weight and drop distance for HSDT of large diameter cast-in-place end-bearing pile is defined.It is suggested that the selection of hammering weight should not be less than 2.7% of the characteristic value and the drop distance should be about 1.2m in Guangdong.The field test is carried out again,and the results are in good correspondence with the field test results,which proves that the conclusion is reliable,improves the effectiveness of the dynamic response system,and solves the influence of unreasonable hammer combination selection on the accuracy of the test results and the safety of the test project.(5)In order to solve the problems of poor waveform quality and eccentric impact in HSDT of large diameter cast-in-place pile,the applicability of force measurement on hammer in HSDT was studied.In this thesis,a large number of original data of pile body force measurement and pile on hammer force measurement are collected,and the probability of obtaining effective waveform is compared.Combined with the dynamic response process of pile hammer,the causes of low quality waveform in the two detection methods are analyzed.The results are in good agreement with the field test results.The conclusion shows that the hammer force method is easier to obtain high-quality waveforms,which has a wide application prospect for engineering practice.The large-scale application of this method will improve the detection efficiency and detection ability of HSDT.(6)The integrity detection method of high strain pile is studied.High strain pile integrity testing and other integrity testing(acoustic transmission method,core drilling method)are carried out on the same pile.According to the test results,it is considered that the high strain method can accurately evaluate the integrity of foundation piles.