Study On The Application Of CPT In Tianjin Soft Soil Area

As an important in-situ soil testing method, CPT (cone penetration test) has been accepted by more and more geotechnical engineers. China has a history of more than 50 years in applying CPT. Compared with the traditonal drilling method, CPT is charaterized by continuous and visible data, reliability and good repetitiveness.This paper first analyzes and introduces the development, status quo and theoretic basis of CPT. Based on the survey data completed in Tianjin, this paper discusses and studies in depth the application of CPT in the following aspects:1. Analyze the characteristics of CPT curves of the subsoils with different origin periods in Tianjin soft soil area.2. Verify the conversion formulas of the specific penetration resistance and cone tip resistance.3. Verify the naming of subsoils by CPT parameters.4. Correlation analysis of CPT parameters and physical and mechanical indexes of subsoils, empirical formulas eduction between CPT parameters and subsoil specific weight, modulus of compressibility, blow numbers of standard penetration test and shear wave velocity.5. Discuss how to use CPT parameters to estimate the ultimate bearing capacity of a single pile and empirical formulas eduction through the comparison of CPT parameters and the results of pile static loading tests.The method employed in this paper includes (1) collection of the data and information of survey, design, construction and testing of the geotechnical engineering projects in Tianjin urban area and TEDA. (2) comprehensive analysis and study; one-variate and multivariate correlation analysis of the collectd data by computer programme; empirical formulas eduction; verification of the empirical formulas, make comparison and analysis of the estimated values and the actual values, perfect the empirical formulas.Based on the above mentioned analysis and study, the paper summarizes the characteristics of CPT curves of the subsoils with different origin periods in Tianjin soft soil area, which can provide regional experiences for CPT soil classification and layer division and suggests a conversion formula for the specific penetration resistance and cone tip resistance; establishes the correlative formulas between the cone tip resistance qc and subsoil specific weightγ, modulus of compressibility Es, blow numbers N63.5 of standard penetration test and shear wave velocity Vs; establishes the empirical formulas for estimation by CPT parameters of the ultimate bearing capacity of cast-in-situ bored pile and vibro-sinking pile. These formulas have been verified in actual engineering projects and have proved rational and applicable.