本文選題：非飽和孔隙介質(zhì) + 自由場地模型�。� 參考：《北京交通大學(xué)》2015年碩士論文

【摘要】：我國位于世界兩大地震活動帶之間,據(jù)史料記載,幾乎各省都曾發(fā)生過破壞性地震。隨著我國經(jīng)濟建設(shè)的迅速發(fā)展,更多大型建設(shè)項目開始不斷出現(xiàn)。為保證這些建設(shè)項目在地震作用下的安全性,必須研究自由場地地震響應(yīng)問題。目前對于自由場地運動的研究大多是將場地簡化為單相或兩相飽和狀態(tài)下進行研究,而實際上我們自然環(huán)境中的介質(zhì)大多數(shù)是處于非飽和狀態(tài)的,即介質(zhì)孔隙中存在氣體。因此對含有三相非飽和孔隙介質(zhì)的自由場地地震地面運動的解析分析顯得尤為重要,目前,對非飽和土自由場地中波動問題的研究還不夠成熟,關(guān)于非飽和彈性孔隙介質(zhì)場地的波動問題的相關(guān)研究亟待展開。 本文首先介紹了線彈性變形條件下的三相非飽和孔隙介質(zhì)波動方程,通過對波動方程中的矢量進行Helmholtz分解,采用Fourier變換求解方程,得到在非飽和孔隙介質(zhì)中存在三種壓縮波和一種剪切波。并分析了不同場地彈性常量下非飽和孔隙介質(zhì)中產(chǎn)生的四種體波的傳播特性受非飽和孔隙介質(zhì)飽和度的影響情況。 在研究非飽和孔隙介質(zhì)波動特征的基礎(chǔ)上,建立非飽和土自由場地模型,分別對平面P波和SV波入射情況下場地中的波場進行分析,根據(jù)場地邊界條件,求解波場中的待定系數(shù),從而得到平面P波和SV波入射情況下非飽和土自由場地地震地面運動的解析解。根據(jù)解析解,計算分析了飽和度、入射角度、入射波頻率、土層剛度、孔隙率等因素對非飽和土自由場地地震地面運動的影響,得到以下結(jié)論：(1)隨入射角度的增加,飽和度的變化對位移放大系數(shù)的影響在最大值附近時相對較大；(2)非飽和狀態(tài)下自由場地共振頻率相同,達到飽和狀態(tài)時發(fā)生變化；(3)隨土層剛度的減小,飽和度的改變對各振幅比和位移放大系數(shù)的影響逐漸增加；(4)隨土層孔隙率的增加,飽和度的改變對位移放大系數(shù)的影響逐漸增加；(5)隨著非飽和土層深度的增加,水平位移放大系數(shù)并不是呈現(xiàn)出單一變化趨勢的；(6)當(dāng)自由場地模型中均勻非飽和土層的厚度趨于無窮時,場地交界面處的位移放大系數(shù)發(fā)生一定的改變。由于在四種不同體波中P1波和S波傳播速度較快且衰減速度較慢,因此本文主要考慮這兩種體波的變化特性。可以看出由于孔隙中氣相的存在,非飽和自由場地中不同體波的傳播特性發(fā)生了顯著的變化。 本文給出了平面P波和SV波入射下非飽和土自由場地地震地面運動的解析解答,得到了非飽和土自由場地地震地面運動的一般規(guī)律和結(jié)論。為復(fù)雜場地地震地面運動提供合理的解釋,為復(fù)雜場地地區(qū)大型結(jié)構(gòu)的抗震設(shè)計提供技術(shù)支持。
[Abstract]:China lies between two major seismicity zones in the world. According to historical records, destructive earthquakes have occurred in almost all provinces. With the rapid development of China's economic construction, more and more large-scale construction projects began to appear. In order to ensure the safety of these construction projects under earthquake action, it is necessary to study the seismic response of free site. At present, most of the research on free site motion is to simplify the site to single-phase or two-phase saturation state, but in fact, most of the media in our natural environment is in unsaturated state, that is, gas exists in the pore of the medium. Therefore, it is very important to analyze the seismic ground motion of the free site with three-phase unsaturated porous media. At present, the research on the wave problem in the unsaturated soil is not mature enough. The research on the fluctuation of unsaturated elastic porous media is urgently needed. In this paper, the wave equation of three-phase unsaturated porous media under the condition of linear elastic deformation is introduced. By Helmholtz decomposition of the vector in the wave equation, Fourier transform is used to solve the equation. Three compression waves and one shear wave are obtained in unsaturated porous media. The propagation characteristics of four kinds of bulk waves produced in unsaturated porous media under different site elastic constants are also analyzed, which are influenced by saturation of unsaturated porous media. On the basis of studying the wave characteristics of unsaturated porous media, the free site model of unsaturated soil is established, and the wave fields in the field under the incident conditions of plane P wave and SV wave are analyzed, respectively, according to the boundary conditions of the site. The undetermined coefficients in the wave field are solved, and the analytical solution of seismic ground motion in the unsaturated soil free site under the incident conditions of plane P wave and SV wave is obtained. Based on the analytical solution, the effects of saturation, incident angle, incident wave frequency, soil stiffness and porosity on seismic ground motion in unsaturated soil free site are calculated and analyzed. The following conclusion is obtained: 1) with the increase of incidence angle, The effect of saturation on the displacement magnification factor is relatively large near the maximum value. (2) the resonance frequency of the free site is the same in the unsaturated state, and the variation of the free site resonance frequency occurs when the saturation state is reached, which changes with the decrease of soil stiffness. The effect of saturation on amplitude ratio and displacement magnification factor increased gradually with the increase of soil porosity, and the effect of saturation on displacement magnification factor gradually increased with the increase of unsaturated soil depth. The horizontal displacement magnification factor does not show a single trend.) when the thickness of the uniform unsaturated soil layer in the free site model tends to be infinite, the displacement magnification factor at the site interface will change to a certain extent. Since P _ 1 and S waves propagate faster and attenuate more slowly in four different body waves, the variation characteristics of these two kinds of bulk waves are mainly considered in this paper. It can be seen that the propagation characteristics of different bulk waves in unsaturated free sites have changed significantly due to the existence of gas phase in pores. In this paper, the analytical solution of seismic ground motion in unsaturated soil free site under the incident of plane P wave and SV wave is given, and the general law and conclusion of earthquake ground motion in unsaturated soil free site are obtained. It provides reasonable explanation for seismic ground motion of complex site and provides technical support for seismic design of large structure in complex site area.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TU435

【引證文獻】

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1 崔春義;孟坤;梁志孟;朱江山;楊剛;;深圳老街地鐵車站自由場地地震動力特性數(shù)值分析[J];沈陽建筑大學(xué)學(xué)報(自然科學(xué)版);2016年06期

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本文編號：2026545