Ground Acceleration Response Research Articles

Ground motion amplification pattern with TBM tunnels crossing soil-rock interface: Shaking table test

The current aseismic design has seldom considered the effect caused by underlain tunnels. Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation. This paper aims to investigate the tunnel effect on the surface acceleration response in soil-rock strata by shaking table tests. Three sets of excitations are employed and input along the shaking table in both transverse and longitudinal directions. The soil-rock site is classified as four micro-zones with varying conditions, to mount observation stations of acceleration sensors. Dynamic characteristics of the four zones are identified by the transfer function (TF) method, and the tunnel effect on the ground acceleration response is obtained by comparing the spectral acceleration results between the free-field and ground-tunnel models. The test results indicate that the tunnel effect varies with the site conditions. Distinctively, a significant amplification effect is observed at the A4 zone, located on the soil deposit near the soil-rock interface. Then, it is proved that the scattering waves generated at the interface and the standing waves trapped between the tunnel and upper ground surface account for the amplification, revealed by the discrepancies of the TF results and acceleration details between the free-field and ground-tunnel models.

Study on the Seismic Effect of the Pebble Soil Site in the Zhongwei Basin

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.

Dynamic Response Mechanism of Silt Ground under Vibration Load

The frequent vibration loads during the operation of trains can cause vibration deformation of the tunnel structure and surrounding weak strata, thereby endangering the safe operation of trains. The purpose of this paper is to study the dynamic response of surrounding soil layers caused by train vibrations through the finite difference method with FLAC3D. Based on existing research, we studied the artificially deterministic exciting force function. Then, we simulated the tunnel working conditions of a train with a 3D model, and applied the artificially deterministic exciting force function to the tunnel model. To study the vibration caused by trains in silty soil, we divided the trains into two cases, one-way and two-way. We compared the displacement–time curves of one-way and two-way trains. When the horizontal distance between the monitoring point and the vibration source increases, the peak value of the displacement–time curve decreases. As the speed of the train increases, the peak value of the displacement–time curve increases. The vertical displacement of the ground under the dynamic load of the two-way train is greater than that of the one-way train. In the acceleration–time curve, there is a lag in the ground acceleration response. The faster the speed of the subway train, the greater the peak value of the acceleration–time curve. This study can provide a guide for the evaluation and prevention of ground vibration subsidence and uneven subsidence of strata in the silt area of the Yellow River Region.

Three-dimensional dynamic response analysis of a single-ring structure in a prefabricated subway station

Traditional subway construction technology still mainly involves on-site poured concrete construction, which causes many social and environmental problems and at the same time is not compatible with the modern concept of resilient city construction and sustainable development. A new prefabricated subway station construction technology can effectively solve many of the problems caused by traditional cast-in-situ technology and provide for the sustainable development of subway construction programmes. As an important part of an urban lifeline system, the seismic performance of subway stations has always attracted much attention. This paper focuses on the dynamic response of the single-ring structure of a prefabricated subway station under horizontal earthquake shaking. Using the commercial finite element software ABAQUS, numerical analysis models of two large-scale underground structures have been developed: the single-ring structure of a prefabricated subway station and the traditional cast-in-situ subway station. Under the same earthquake action, there are obvious differences between the prefabricated structure and the traditional cast-in-place structure. Compared to the seismic response of traditional cast-in-situ structures, the ground acceleration response of the prefabricated structure is slightly reduced, the overall deformation is slightly increased, the maximum internal force and stresses are significantly reduced, the internal force transmission path is changed, and the area of influence in the surrounding soil is significantly reduced. Comprehensive comparative analysis shows that the single-ring structure of the prefabricated subway station has good deformation resistance and excellent mechanical properties under horizontal earthquake shaking and the overall seismic performance meets the design requirements. Finally, the seismic response characteristics and energy dissipation advantages of the prefabricated single-ring structure are discussed. The research conclusions will provide useful references for resilient city construction and sustainable urban development.

Repeatability of Centrifuge Tests Containing a Large, Rigid Foundation Subjected to Lateral Spreading

Four centrifuge tests involving liquefaction-induced lateral spreading of loose sand against a large, rigid foundation are summarized with regard to the repeatability of ground motions, porewater pressures, and lateral displacement magnitudes. The base input motions delivered to the models exhibited a large coefficient of variation (COV) of 0.27, chiefly as a result of variations in the shaker hydraulic system, rather than differences in model construction (which exhibited a COV of 0.07 for the relative density of the loose sands). Variations in ground acceleration response, porewater pressure response, and lateral displacement magnitudes were dominated by variations in base motions, with COV values ranging from about 0.01 to 0.47. Nevertheless, more than 90 % of the COV values were less than 0.30, consistent with or less than the COV of the base motions. In addition, the measured COV values are consistent with COV values of other geotechnical measurements reported in the literature. This is especially encouraging because centrifuge tests are relatively complex boundary tests, and many COV values reported in the literature involve element tests. Based on these findings, one must carefully monitor and control base motions (input to the soil container) in order to obtain repeatable results in a centrifuge testing program.

Study on the Ground Response Analysis for Stiff Soil

In order to test the applicable of the seismic response analysis procedures SHAKE2000 and LSSRLI-1 for class ІІ site, 17 stations and 35 underground strong motion records of KiK-net are selected from Class ІІ site. 210 working conditions are used to verify the applicability of the two soil seismic response analysis programs at Class ІІ site. These two programs are used to calculate the selected working conditions, giving the peak acceleration of the ground, the shear strain and the ground acceleration response spectra. By analyzing the results of the two programs and the measured results to assess the degree of difference between the two methods and which program is closer to the real situation. Studies have shown that in class ІІ site, in most cases, the results of SHAKE2000 and LSSRLI-1 differ little. While comparing with the actual records, SHAKE2000 is closer to the strong motion records.

Large-Scale Two-Dimensional Nonlinear Analysis on Seismic Effect of Fuzhou Basin

So far, nonlinear analyses on seismic effect of large-scale basin model have rarely been reported. Based on the explicit finite element method and 32 CPU parallel computing cluster platform of ABAQUS, a two-dimensional（2D） large-scale refined model for Fuzhou Basin is established using a nonlinear analytical method in the time domain. Both the peak ground acceleration (PGA) and acceleration response spectra of ground surface are emphatically analyzed. Meanwhile, the results by one-dimensional equivalent linearization method in frequency domain are added for the sake of contrast. The study results show that the PGA of ground surface will be obviously amplified when compared with the peak acceleration of bedrock ground motion; and the ground acceleration response spectra of Fuzhou Basin may appear a double-peak or multi-peak phenomenon. Moreover, the 2D large-scale model can reflect amplification effect of Fuzhou Basin soil to bedrock ground motion in particular periods; In addition, the acceleration responses of ground surface right above the bedrock valleys and crests appear larger than the other positions adjacent to them, these phenomenon are generally manifested as focusing effect and amplification effect, which are thought to be produced by the recently deposited soils in the basins as well as the special soil layer such as lens. In general, the PGA of ground surface obtained by 2D model present to be greater than that obtained by the one-dimensional model.

Study on the Influence of Seismic Wave Inputting Interface on the Earthquake Response of Deep Soft Sites

Earthquake effects of two typical deep soft sites selected from Tianjin(site 1)and Shanghai(site 2) are studied when the vertical inputting earthquake waves are located in different depth of sites. As far as the shear wave velocity of soil layers is concerned, seven kinds of soil layers in site 1 and eight soil layers in site 2 are selected as the vertical imputing interfaces of earthquake waves. Two acceleration waves recorded during Taft earthquake and Northbridge earthquake are selected, and the peak values of two waves are adjusted to be 0.35m/s2、0 70m /s2 and 0 98m /s2, respectively. The earthquake response of sites is calculated by SHAKE91 program. The results are compared to those of site when the input interfaces of earthquake waves are located in bedrock with shear wave velocity larger than 500m/s. The conclusion is as following: With the depth of input position (or shear wave velocity) increasing, the value of the ground acceleration response spectrum gradually closes to the actual data.; For the general building the soil layer with shear wave velocity for 400m/s or so can be chosen as the input interface, and the building with long natural vibration period should be treated seriously, and the soil layer whose shear wave velocity is above 500m/s can be chosen as the input interface.

Seismic motion attenuation relations in Sichuan and adjacent areas

The Sichuan and adjacent areas is divided into southwest China region (SWCR) and Sichuan Basin region (SCBR) according to tectonic backgrounds and seismic damage distribution features. 96 modern destructive earthquakes in SWCR and 40 in SCBR are gathered respectively. All their magnitude parameters are checked. Based on the statistic relations between epicentral intensity and magnitude as well as relation between sensible radius and magnitude, the near and far field seismic intensity attenuation features are represented and controlled. And then the seismic intensity attenuation relations along major axis, minor axis and mean axis are established separately. The systematic deviations of surface wave magnitude between China seismograph network and U.S. seismograph network are considered in this paper. By making use of the new attenuation relations of bedrock horizontal ground acceleration response spectrum in west U.S., the attenuation relations of bedrock horizontal ground acceleration response spectrum in SWCR and SCBR are digital transformed based on the attenuation model considering acceleration saturation of distance and magnitude in near field.