Study On Improvement To Standard Penetration Test Based On Shock Wave Theory

Standard Penetration Test(SPT)is one of in-situ tests which are extensively used in geotechnical engineering area.It has a long history and have advantages such as intuition in measuring variable,easy for workers in operation and for engineers to understand,small in cost,and most importantly,have a huge accumulation of engineering data and corresponding empirical formulas.However,it still have some shortcomings,such as the assessment method of bearing capacity of foundation based on blow counts is lack of theoretical basis;the level of automation of test operating system and the subsequent data processing is also low;the results of test are relatively influenced by types of hammer system,the rod length and the number of joints,and the corresponding amendments are too generalization and simplification.In the previous studies,the studies on the application of shock wave dynamic theory on standard penetration test is much less than the military areas,the low/high strain methods used for pile dynamic testing are more common in geotechnical area.Therefore,the method proposed in this dissertation has a high innovation characteristic SPT area,also has a great significance.In the beginning of dissertation,the literature review had been done focused on the research method and the application of standard penetration test,the assessment of advantages and disadvantages of SPT had been made in this section,and the engineering significance and necessity of quantitative studies are set forth.Then the detailed review and analysis of models was carried out,made on the one-dimensional propagation theory of elastic wave,including the simplified motion equation method,the impact theory proposed by Fairhust,the one-dimensional wave propagation theory proposed by D' Alembert,and the wave equation analysis(WEA)and so on.After making a summary of analysis of previous studies,the suitable model in this dissertation was made for standard penetration test,using Force Square Method,Force Velocity Method,and penetration resistance method based on the propagation theory of elastic stress wave on one-dimensional bar.The preparation of testing equipment was carried out in the view of the impact model of SPT:a special short drill steel pipe was produced,acceleration sensor,strain sensor,the corresponding charge amplifier and dynamic strain amplifier,and data acquisition card were purchased in the light of the basic technical parameters such as the measurement range,the usage frequency,data.sampling frequency etc.The debug and test of the equipment and the data collection&calculation procedure were prepared before field test,where the concepts of Virtual Instruments and the usage of Labview(one of procedure development environments).The field testing were conducted in engineering sites in Jiangxi province and Nanking area,the acceleration and strain data of particle perched at special drill steel pipe were obtained.By signal analysis and data processing which including spectrum analysis,probability analysis,filtering analysis,integral arithmetic,etc,the stress,velocity,displacement,the striking energy,and penetration resistance were procured,the further work were concentrated on the fitting calculation among bearing capacity of foundation,pile tip resistance,pile shaft resistance,internal friction angle,with the above index.In general,the main conclusions are as follows:? the effective time of the signal and the soil depth(the rod length)showed a positive correlation,i.e,it increases with the grow of soil depth;? the signal frequency and had inverse correlation relationship with the soil depth(the rod length);? the velocity of particle and the blow count(N values)of standard penetration test showed inverse correlation relationship with the soil depth(the rod length);? the displacement of particle and the blow count(N values)of standard penetration test were inverse related to the relationship,and showed an inversely correlation relationship with the soil depth(the rod length);? the stress of particle had an inverse relationship with the blow count(N values)of standard penetration test,and was not significantly correlated with the soil depth(the rod length);?the energy obtained by calculation with the force velocity method and the force square method varied very much,and had an anti-correlation relationship with the rod length,besides,the energy changed periodically with time;? the dynamic penetration resistance also changed periodically with time,and was positively correlated relations with the blow count(N values)and the rod length;? the bearing capacity of foundation and other mechanical properties of soil had high identical fit degree with the maximum of velocity and stress and energy,and relatively low fit degree with penetration resistance.Some suggestions were proposed in the final chapter with the view to the characteristics of the field test of this dissertation.The points were mainly focused on the preparation and the selection of the test equipment,the note of field test,the note of signal analysis and data processing and calculation process.It is recommended that the bearing capacity of foundation and other mechanical properties of soil could obtained in the view of the fitting empirical formula with the maximum of velocity and stress and energy.Finally,the dissertation summarized the inadequacies and the content needed to have further research,including the influence from horizontal propagation of elastic stress wave,the further improvement of test equipment,and much more tests to verify the method proposed in this dissertation.