Research On Calibration Theory And Application Of CPTU Technology Based On In-situ Standard Test Site

In recent years,with the rapid development of geotechnical testing technology and instruments,the in-situ testing technology represented by multi-functional and highprecision Piezocone Penetration Test(CPTU)has been widely used in engineering.Therefore,the construction of standard test sites for in-situ test technology calibration has begun in developed countries in Europe and the United States,while the construction of standard test sites in China has just started.This makes it difficult to analyze and evaluate the field application effect of in-situ testing equipment qualitatively and quantitatively,and also seriously hinders the development of engineering application of in-situ testing technology.Therefore,the construction of China’s in-situ test standard test field and the establishment of systematic CPTU test technology calibration method have important theoretical significance and engineering application value.The main research contents of this paper are as follows:(1)This paper introduces the research status and engineering application of the construction of American in-situ test standard test site,designs a construction plan of in-situ test standard test site,and analyzes and demonstrates the feasibility of the construction of in-situ test standard test site by analyzing the horizontal correlation and normal distribution characteristics of CPTU test curve in the small-scale simulation test site in Southeast University.(2)Based on the traditional statistical method of soil parameters,a drawing method of standard profile of in-situ test standard site is proposed,including the specific design methods of soil layer stratification interval,standard reference line,fluctuation standard residual interval and dip standard line.Through the CPTU test curve in the small-scale simulation test site,the standard profile of the small-scale simulation test site is drawn,and based on this standard profile,the accuracy of each CPTU test curve is analyzed qualitatively and quantitatively.(3)The indoor sensor calibration test of CPTU test equipment and the field calibration test based on the standard test site were carried out.The sensor accuracy and field test accuracy of CPTU test probe to be tested and evaluated after maintenance are analyzed and evaluated qualitatively and quantitatively,and a calibration correction function based on standard test site is proposed to significantly improved the accuracy of CPTU test equipment in field test.(4)Based on an underground engineering construction project in Jiangsu Province,the comparative analysis test of CPTU test probe to be tested and evaluated was carried out on site.Through the comparison and analysis between the original test curve obtained by the CPTU test probe to be tested and evaluated and the modified test curve corrected by the calibration correction function,and the reference test curve obtained by the CPTU test probe with high accuracy in normal service,the accuracy of the calibration method based on the in-situ test standard test field is verified in engineering practice.