Study Of Standard Penetration Test In Typical Loess-Paleosol Strata In Shanxi Province

In recent years,under the background of the continuous promotion of the "the Belt and Road" and the gradual implementation of the "transportation power construction project",the engineering survey activities in the Loess Plateau of China are increasing day by day.Standard penetration test plays an important role in engineering investigation.It is often used to obtain soil physical and mechanical parameters,determine the bearing capacity of shallow foundation and predict foundation settlement.Loess paleosol strata are widely distributed in the Loess Plateau.When researchers conducted standard penetration test research in this area,they mostly treated the paleosol interlayer as the loess strata,and did not clearly point out whether there are differences in the application of standard penetration test in loess paleosol.In engineering practice,the same empirical formula of standard penetration test is usually used to determine the mechanical properties of strata in loess areas,but there are obvious differences in the physical and chemical properties(material composition and structure)of loess and paleosol in different areas.Whether this difference will affect the use of empirical formula of standard penetration test in loess strata and paleosol strata in different areas is still not clearly defined.In this paper,a representative loess paleosol stratum is selected from sandy loess,silty loess and clayey loess zones,and field standard penetration test(270 tests in total)is carried out,supplemented by wave velocity test,static cone penetration test,water content test,dry density test,particle analysis test and boundary water content test.Through the comparative analysis of test results,the applicability and difference of standard penetration test in loess paleosol stratum are clarified,and the empirical formula between standard penetration blow count,shear wave velocity and cone resistance in loess paleosol stratum is improved.The main conclusions are as follows:(1)In the three study areas of sandy loess,silty loess and clayey loess,there is an obvious linear correlation between the SPT N values of loess and paleosol strata and the formation dry density,plasticity index,water content and average particle size,indicating that the SPT is applicable to the loess paleosol strata of the above three zones.(2)The correlation between SPT N values and some physical parameters of loess stratum and paleosol stratum in the three study areas is different.This difference is caused by the different physical and chemical properties between loess and paleosol.Therefore,loess stratum and paleosol stratum should be treated differently when carrying out standard penetration test.(3)In the three study areas of sandy loess,silty loess and clayey loess,the correlation between SPT N values of loess stratum and paleosol stratum and stratum dry density has little difference,and there are regional differences in the correlation with stratum plasticity index,water content and average particle size.This is due to the different physical and mechanical properties between loess paleosol strata in the three study areas.It shows that the regionality should be considered when applying standard penetration test in loess paleosol strata.(4)According to the good correlation between SPT N values and shear wave velocity and cone tip resistance in sandy loess,silty loess and clayey loess zones,the empirical formula of SPT in the three study areas is improved.It is found that SPT N values and shear wave velocity are power functions,and SPT N values and cone tip resistance are proportional functions.