Influence of Structure on the Aseismic Stability and Dynamic Responses of Liquefiable Soil

Abstract

In previous major earthquakes, the damage and collapse of structures located in liquefied field which caused by site failure a common occurrence, and the problem of evaluation and disscusion on site liquefaction and the seismic stability is still a key topic in geotechnical earthquake engineering. To study the influence of the presence of structure on the seismic stability of liquefiable sites, a series of shaking table tests on liquefiable free field and non-free field with the same soil sample was carried out. It can be summarized from experimental results as following. The natural frequency of non-free field is larger and the damping ratio is smaller than that of free field. For the weak seismic loading condition, the dynamic response of sites show similar rules and trend. For the strong ground motion condition, soils in both experiments all liquefied obviously and the depth of liquefaction soil in the free field is significantly greater than that in the non-free field, besides, porewater pressure in the non-free field accumulated relately slow and the dissapited quikly from analysis of porewater pressure ratios(PPRs) in both experiments. The amplitudes of lateral displacements and acceleration of soil in the non-free field is obviously smaller than that in the free field caused by the effect of presence of the structure. In a word, the presence of structures will lead to the increase of site stiffness, site more difficult to liquefy, and the seismic stability of the non-free site is higher than that of the free site due to soil-structure interaction.

Influence of the soil liquefaction on dynamic characteristics of a base-isolated structure investigated by the experimental method

“…Meanwhile, the greater the burial depth of the pore pressure meter, the less time it takes for the PWPR growing to its peak value. The above result conforms to the general changing rule for the dynamic PWPR of a lique able soil foundation, and is basically in accord with the results found in the model test conducted by Dou et al (2021). This shows that the lique able soil foundation in this test completely meets the design purpose of the liqu able model soil foundation, which is also an important premise for the following analysis.…”

“…Based on the analysis of above-mentioned test results, soil liquefaction should be one of the main factors that induce a signi cant increase in the bending-moment amplitude at the top end of the pile under a base-isolated structure. Existing studies (Dou et al, 2021) and this test all found that the lateral displacement of the soil layer at the top end of the pile increased signi cantly during the foundation liquefaction, as shown in Fig. 10, which further increased the bending moment response of the pile.…”

“…In accordance with the experience of previous similar model tests (Zhuang et al, 2014;Dou et al, 2021), in shaking-table model tests involving lique able soil, the input seismic records should be either the original time-holding records or slightly time-compressed records. In this test, to model the long-period properties of the input ground motion, the original El Centro wave was selected as the input ground motion, which peak acceleration was adjusted to the preset value according to loading conditions shown in Table 2.…”

“…In the shaking-table model test of the soil-structure dynamic interaction, it is almost impossible to design the entire model test under a completely consistent similarity ratio system, owing to the de ciency of the 1-g shaking-table test method. According to previous test experiences (Stehmeyer and Rizos, 2008;Zhuang et al, 2019;Wu et al, 2020;Dou et al, 2021), the model structure and model soil foundation need to be designed separately by considering the soil-structure coupling interaction as far as possible. In this study, the length, elastic modulus, and acceleration were selected as the basic physical quantities of the model structure, and the shear-wave velocity, density, and acceleration were selected as the basic physical quantities of the model soil foundation.…”

“…The model-to-prototype similarity ratios of the soil-pile-isolated structure interaction system are shown in Table 1. To ensure the occurrence of liquefaction, previous studies have proven that the duration of the input ground motion should not be shortened severely (Chen et al, 2020;Dou et al, 2021), and the similarity ratio of the time should be considered separately, which is 1.0 in this test.…”