GEOGRAPHY

Geological Earth has confirmed the existence of two forms of dynamic seismic response on a single-sided slope


Earthquake landslides are earthquake-induced secondary disasters, often causing casualties and property losses, and understanding the dynamic response law of slopes is the key to evaluating the seismic stability of slopes, the seismic fortification of engineering rock mass and the prediction of earthquake landslide areas. More post-earthquake investigations and tests have found that there is an obvious seismic amplification phenomenon at the top of the slope, which is an important cause of slope instability. However, there are many factors affecting the dynamic response of slopes, mainly including source characteristics, propagation paths, site characteristics, etc., involving geotechnical dynamics, geophysics and other disciplines, which are quite complex; In addition, there is only one free surface for a single-sided slope (Figure 1), and it is difficult to obtain a universal response law by analytical methods, resulting in slope seismic stability evaluation is still one of the challenging problems in the construction of major projects in the active tectonic area.

Qi Shengwen, a researcher at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, based on similar theories, carried out physical simulation and in situ tests of large slope shakers. The experimental results show that the seismic dynamic response form of the single-sided slope has obvious frequency dependence, and when the loading frequency is less than a certain critical value, the slope acceleration amplification coefficient increases with the increase of the loading frequency, and the slope acceleration amplification coefficient increases with the increase of the slope height. When the loading frequency is greater than this critical value, the slope acceleration amplification coefficient will decrease, and the slope acceleration magnification coefficient will decrease first and then increase with the increase of slope height (Figures 2 and 3). The experimental results further confirm the previous research results[Qi et al. (2003), Qi (2006)]: There are high slope dynamic response and low slope dynamic response forms on single-sided slopes, not just the slope dynamic amplification phenomenon recognized by previous generations.

On this basis, the study uses physical simulation as a constraint, checks the numerical simulation (Figure 2), and conducts a large number of numerical experiments to explore the influence of physical and mechanical parameters (density, elastic modulus, etc.), slope height, slope slope, input seismic frequency and other factors on slope seismic response, and the critical dimensionless slope height H/λ of the unilateral slope dynamic response is found to be about 0.17~0.20: When the dimensionless slope height H/λ ≤0.17-0.2, the slope shoulder acceleration amplification coefficient is increased with H/H/ The increase of λ increases; When H/λ >0.17-0.2, the ramp shoulder acceleration amplification coefficient will decrease with the increase of H/λ, and when H/λ >0.4, the ramp shoulder acceleration amplification coefficient will be less than 1.0, that is, the slope seismic response will have an attenuation effect. At the same time, for a specific slope height, the ramp shoulder acceleration magnification factor increases with the slope (Figure 4). Based on the theory of seismic wave propagation, the study explains the significant differences in particle vibration patterns between the dynamic response of high slope (H/λ>0.2) and the dynamic response of low slope (H/λ≤0.2) on the slope.

This study confirms from the experimental point of view that for a given seismic input, there are two forms of high slope dynamic response and low slope dynamic response of the single-sided slope dynamic response, and the critical dimensionless slope height H/λ is about 0.20; at the same time, when the dimensionless slope height H/λ is about 0.40, the slope dynamic response is no longer dominated by the amplification effect, but dominated by the attenuation effect. This parameter provides a suitable index for quantitative exploration of slope dynamic response problems, and can provide an important reference for slope dynamic stability evaluation.

Fig. 1. Double-sided slope (a) and single-sided slope (b)

Fig. 2. (a) Vibration table test and numerical simulation acceleration time course curve; (b) acceleration local amplification plot; (c) slope PGA amplification coefficient

Figure 3. Distribution of the acceleration amplification coefficient of the slope under different frequencies: (a) the loading frequency is 15Hz; (b) the loading frequency is 30Hz; (c) the loading frequency is 45Hz; and (d) the loading frequency is 60Hz

Fig. 4.Slope shoulder peak acceleration amplification coefficient (slope height H= 60 m) and comparison with previous studies[Ashfordetal1997;B&P(BouckovalasandPapadimitriou2005)andTripeetal2013]

The research was published in Engineering Geology. The research work has been supported by the National Science Foundation of China National Outstanding Youth Science Foundation project and the second comprehensive scientific expedition to the Tibetan Plateau. (Source: Institute of Geology and Geophysics, Chinese Academy of Sciences)

Related paper information:https://doi.org/10.1016/j.enggeo.2022.106762

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