Study On Standard Penetration Test Based On Stress Wave Test

Standard penetration test(SPT)is a widely used in-situ test method in the world.The method is simple in equipment,easy to operate,low cost,widely used in different soil properties,can take soil samples,and have accumulated abundant engineering data in different regions.But there are also some problems,such as lack of theoretical basis,the judgment of physical and mechanical indexes of soil is usually based on the empirical formula established by the blow counts(N-value);the N-value is affected by many factors such as hammer system and rod length;the equipment of standard penetration test is different in different countries;the soil types in different areas are quite different.At present,it is generally accepted that the variation of hammer energy transmitted due to different types of hammer systems is the main factor leading to the variation of the N-value of standard penetration test,and stress wave test is used to analyze and measure the energy of different hammer systems.At present,there are few quantitative researches on the standard penetration test in China.Therefore,we consider using the international research results for reference to carry out the stress wave test and quantitative research on SPT in China.The main research contents and conclusions are as follows:1.The factors influencing the N-value of the standard penetration test are systematically analyzed,and the quantitative research results of the standard penetration test are summarized.Comparing the differences between SPT at home and abroad,it shows the necessity and significance of quantitative research on SPT in China.2.According to the equipment and parameter requirements of the stress wave test,the corresponding sensor,acceleration sensor are selected,and the test equipment is determined for stress wave test in combination with the field performance test.The test scheme is designed,the installation position and fixing mode of the sensor are determined,and the drill pipe for installing the sensor is drilled.3.The stress wave test of SPT was carried out on a test site in Jiangsu Province.The corresponding time history curves and data of strain,acceleration,force,velocity,energy and penetration were obtained through the stress wave test,and the propagation law of stress wave and energy in drill pipe was analyzed.Compared with the force square(F~2)method,the force velocity(FV)method can get all the energy transferred to the drill pipe more accurately.According to the energy transfer efficiency of the drop hammer system obtained from the test,combined with the research on various influencing factors of the standard penetration test at home and abroad,and comparing the correction coefficients obtained from the common correction methods,a new correction formula for N-value is established.4.Based on a large number of data of standard penetration test,laboratory soil test and in-situ test in Nantong area,the correlation between N-value and soil parameters as well as other in-situ test indexes(specific penetration resistance of CPT and foundation bearing capacity)is analyzed.The applicability of four different correction methods of N-value is compared,including the proposed method in this paper,no correction,rod length correction according to Chinese standard,correction methods according to European and American standard.The results show that the proposed method is effective,and the relevant empirical formula is given,which can provide reference for the analysis of soil properties and practical engineering design in Nantong and similar areas.