Inspection Research Of The Adjustment Coefficients Of Site Effect Stipulated By The Chinese Fifth-generation Seismic Zonation Map

Site effects are one of the important factors that must be considered in seismicresistant design,seismic zonation map,earthquake prediction models,and other fields.The rationality and applicability of design seismic parameters in evaluation of seismic safety reports for engineering sites will have an important impact on the safety and economy of engineering construction.Therefore,in order to better consider the engineering impact of site effects,this paper collected soil dynamic parameter data and engineering site borehole profile data from the Capital Metropolitan(CM),Xinjiang(XJ),Guangdong-Guangxi(GG),Sichuan-Yunnan(SY)regions in China.The statistically significant values of soil dynamic parameters with regional applicability were established,and 1-D equivalent linear seismic site response analysis models were developed.The peak acceleration amplification factor and response spectrum characteristic period of the same site class in each region were calculated,and the regional differences and regularities of site characteristic parameters and site seismic response were analyzed under the same site class.Furthermore,the regional applicability of the adjustment coefficients of site effect by the Chinese fifthgeneration seismic zonation map was tested.The main contents of the work and research results obtained are as follows:1.This article collects and organizes the soil dynamic parameter data for engineering sites in CM,GG,and SY regions.Eight common types of soil,including silty clay,clay,clayey gravel,silt,peaty soil,fine sand,medium sand and clayey sand with gravel,were grouped and statistically analyzed according to burial depth,providing the statistical values for each type of soil within different burial depth ranges.The Davidenkov model and Chen-Guoxing model were used to fit the variation curves of dynamic shear modulus and damping ratio of soils with shear strain,respectively.The dynamic parameters curves of silty clay and clay at different burial depths were compared among the three regions,confirming the presence of regional differences in soil dynamic parameters.2.This article calculates the peak ground acceleration amplification factor(Ka)and response spectrum characteristic period(Tg)of engineering sites for Class Ⅱ,Ⅲ,and Ⅳ sites.The study reveals the variations of these two factors with changes in class site and the increased PGAs of input ground motions.This article compares and analyzes the calculated results of Ka and Tg with the mandatory values given by the seismic zonation map and the recommended values given by some previous studies.It is found that the mandatory coefficient for peak ground acceleration specified in the fifth-generation zoning map underestimates the actual amplification effect of Class Ⅱsites to some extent,while it has a high guarantee rate for Class Ⅲ and Ⅳ sites in the Tianjin region.It is also found that the mandatory Tg value for Class Ⅱ sites in the fifth-generation zoning map is reasonable,but for the CM region,this article suggests adding 0.05s to the existing value.The mandatory Tg value for Class Ⅳ sites in the fifth-generation zoning map is also reasonable,but due to the thickness of covering soil layer,it shows that the value of Tg for Class Ⅲ site needs a further validation calling for more borehole data collected.Through comparing the characteristic parameters Vse,H,and VS30 distribution of Class Ⅱ sites in four regions,as well as the correlation between these parameters,this article analyzes and finds significant regional differences in site conditions among sites of the same category in different areas.3.Through comparing the site characteristic parameters Vse,H,and VS30 and their correlations of Class II sites in four different regions,this article analyzes and finds significant regional differences in site conditions among the same class sites in different areas.Based on soil-layer seismic response analysis calculations,the study compared and analyzed median spectral shape of amplification spectra,peak value Amax of amplification spectrum,fitting lines between Amax and site characteristic parameters Im and Vse,median curves of PGA amplification factor Ka and Kx+S in different seismic intensity ranges,Tg values at different input PGA levels for the four regions,discovering certain regional differences in site amplification effects.