This paper presents a numerical analysis of two types of representative site profiles in the Yinchuan Plain under earthquake loading. The analyzed soil profiles, based on borehole investigations performed over the years, are used to explore the seismic response of the sites in this area. In total, eleven stratified soil models are used in this study, which can be grouped into two categories: a single interbedded soil model and multiple interbedded soil model. A one-dimensional equivalent linearization method is applied to evaluate the seismic response of different soil models under four exceeding probabilities in terms of peak ground acceleration (PGA), peak ground velocity (PGV), peak ground displacement (PGD), and spectral acceleration (Sa). The results show that the significant amplification effect of PGA occurs in rare and extremely rare earthquakes, with an amplification ratio of 1.4∼1.7 when the single silty clay layer is located at the model ground. In this scenario, the spectral acceleration is amplified at a period of approximately 1.0 s. For the multilayered soil cases, the amplification effect tends to decrease, whereas the characteristic periods increase with increasing numbers of soil layers and the ground acceleration is deamplified under a high motion intensity when the number of soil layers is ≥ 5. This study, to a certain degree, has reference value for seismic microzonation in this area.
Based on a large amount of drilling and geophysical exploration work in the Zhongwei Basin, and combined with the collected borehole data of a seismic safety assessment, this paper summarizes and builds 16 typical pebble soil layer calculation models. The effects of the thickness of the pebble layer, the thickness of the overlying silty clay, the top interface of the pebble layer on the peak acceleration and the response spectrum of the site seismic response were analyzed using the equivalent linearization method of the one-dimensional soil layer seismic response. The analysis results showed that the variation in pebble layer thickness had no obvious effect on the peak acceleration of the ground surface under different inputs; the influence of the pebble layer thickness on the ground acceleration response spectrum was primarily concentrated in the middle/high-frequency band of 0.2–0.6 s. Within this range, the acceleration response spectrum of the site with a 30 m pebble layer thickness was small, and the response spectrum curve showed a “trough” shape with a certain “weak isolation” effect. Under the same pebble layer thickness, the upper ground surface peak acceleration with a silty clay layer thickness increased with the increase in the central basin pebble soil field, where a short cycle of the seismic wave amplification effect was more obvious. The response spectrum peak period points were within 0.1–0.2 s and were influenced by the action of rare earthquakes. Moreover, the response spectrum curve showed a more obvious phenomenon of “twin peaks”, and the second peak point appeared in the period of 0.5–0.7 s. With the increase in the input intensity, the PGA amplification ratio of the pebble-top interface was significantly smaller than that of the site surface; under different intensities of input, the acceleration response spectrum of the pebble-top interface showed a “trough” phenomenon that was lower than the bedrock input at approximately 0.1 s. Under the action of rare ground motion, the acceleration response spectrum curve of the pebble-top interface showed a “double peak” phenomenon, and within 0.24–0.4 s, the spectrum value was lower than the bedrock input, showing an obvious shock absorption and isolation effect. Under the action of an earthquake, the energy of the pebble-top interface was concentrated in the low-frequency range of 1.1–2.2 Hz, and the amplification effect was obvious. In the range of 8–10 Hz, the amplitude was lower than the bedrock input, and the seismic isolation effect was obvious.
The calibration of response spectra is an important issue that needs further research in engineering earthquake resistance. This paper proposes an improved calibration method for site-related response spectra. The seismic acceleration response spectra are statistically analyzed in the random period bands in the form of regression analysis, and the fitting indices in each frequency band under 11 different functions are given. Accordingly, the best fitting function for each period band is determined. Combined with a genetic algorithm, the control parameters of the seismic acceleration response spectrum are calibrated according to the determined new design spectral shape. After comparing the calibration results with the proposed piecewise results, a new calibration model of the three-section curve expression is proposed by improving the piecewise standard until the calibration results are identical to the proposed period point. The accuracy of the proposed calibration method is validated against the other four available methods using Qian’a earthquake records and actual engineering examples. The research results show that the site-related response spectrum calibration method given in this paper objectively reflects the spectrum characteristics of the site-related response spectrum. The proposed method may have a certain reference value for the calibration of the site-related response spectrum.
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