Abstract
Dynamic response characteristics and antiseismic performance of the structures which were constructed on the super-deep overburden layer are affected obviously by the seismic motion characteristics of the super-deep overburden layer foundation. In this paper, the seismic motion characteristics of horizontally stratified super-deep overburdenIn this paper, the seismic motion characteristics of horizontally stratified super-deep overburden based on the research results of on-site in situ tests and indoor material property tests, the horizontal shear layer method that can consider the nonlinear characteristics of dynamic soil deformation and the characteristics of seismic wave propagation in the soil is used to study the characteristics of ground motions of super-deep and thick overburden level of an earth-rock dam in China. The influence law of input ground motion characteristics and input ground motion position on seismic response analysis results of overburden ground is studied. Taking the uniform overburden layer model as an example, the coupling influence analysis of soil layer thickness and shear velocity on ground motion response are carried out, and the coupling influence law is proposed. The study shows that the seismic motion propagating characteristics of the earthquake in super-deep overburden layer is involved, inputting location of the seismic motion affects the results of ground seismic response greatly; super-deep overburden layer thickness and the soil shear wave velocity on influence law of ground motion characteristics have coupling. When the shear wave velocity of the soil layer is constant, the surface acceleration response has an inflection point with the change of the soil layer thickness; when the thickness of overburden is constant, the surface acceleration response also has an inflection point with the change of shear wave velocity of the soil layer; these inflexion values are influenced by both soil thickness and shear wave velocity.
Highlights
It is advisable to cutoff the foundation of the overburden layer and take only a cover layer of a certain thickness is used as the calculated near-field foundation. e seismic motion of this truncated boundary is different from the seismic motion of the bedrock surface under the soil layer. e ground seismic response analysis of the deep overburden layer should be conducted to study the influence law of overburden layer on the characteristics of the seismic motion inputted from bedrock. e seismic motion characteristics of calculation model boundary should be determined to provide seismic motion characteristic parameters for the dynamic analysis of the structure and foundation system on the deep overburden layer [2]
Influencing of the ground mean shear wave velocity on the distribution of acceleration magnified factors in the ground is shown in Figure when the thickness of ground soil layer is a certain value, and influencing of the ground soil layer thickness on the distribution of acceleration magnified factors in the ground is shown in Figure when the mean shear wave velocity of the ground is a certain value
The acceleration magnified factor on ground surface increases at first and decreases with the increasing of soil layer shear wave velocity when the soil layer thickness is a fixed value, and the inflection wave velocity value in which acceleration magnified factor on ground surface changed from increasing to decreasing increases with the increasing of soil layer thickness; all these can be represented as yellow labels in Table 2; the acceleration
Summary
With the extensive and in-depth development of the global water conservancy and hydropower industry, the problem of strong earthquakes and deep overburden foundations has become a double challenge for hydropower project construction, and it is difficult to evade, becoming a controlling factor for the successful construction of many projects [1].e main structure of the CCS (Coca Codo Sinclair) hydro project in Ecuador has been built on a super-deep overburden over 200 m thickness. ere are several active volcanoes around the project site, and the intensity of the maximum credible earthquake is IX degree. e asphalt concrete core dam of Xiabandi hydro-junction (in Xinjiang province of China) was constructed on the deep overburden layer which has a maximum depth of 150 m, and the basic earthquake intensity of the dam site is VIII degree. e Yele earth-rock fill dam had been constructed in the Sichuan province of China, and the maximum depth of the dam foundation overburden layer is over 400 m. e seismic fortification intensity of the dam is IX degree, and the maximum horizontal acceleration of the bedrock was determined as 441.5 gals according to the results of region earthquake hazard analysis.e ground motion characteristics of the site with deep overburden in the river valley have an essential influence on the dynamic response characteristics of the upper earth-rock dam, gate dam, and diversion structure [1], because theShock and Vibration characteristics of earthquake inputting from the bedrock down overburden layer are changed greatly by the deep overburden layer. e analyzed object is the structural system that contains the structure and its near-field foundation in the dynamic analysis of hydraulic structure on deep overburden layer normally, and the size of the structure near-field foundation is limited. E ground seismic response analysis of the deep overburden layer should be conducted to study the influence law of overburden layer on the characteristics of the seismic motion inputted from bedrock. E seismic motion characteristics of calculation model boundary should be determined to provide seismic motion characteristic parameters for the dynamic analysis of the structure and foundation system on the deep overburden layer [2]. E results show that the impulse ground motion has a certain influence on the acceleration response of the high earth-rock dam on the deep overburden. It makes the dam body deform greatly in a very short time, which is not conducive to the dam safety. Zhu et al [8] and Wang et al [9] believe that the dynamic response of the dam on the deep overburden is a single relationship with the thickness of the overburden and the input of ground motion, and there is no superposition effect
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