【摘要】：小應(yīng)變剪切模量Gmax是場地地震響應(yīng)分析中的重要參數(shù)。在以往的場地地震響應(yīng)有效應(yīng)力分析法中,通常假定循環(huán)振動作用過程中土體的Gmax等同于相同有效應(yīng)力靜力狀態(tài)下的Gmax,采用Hardin公式計(jì)算Gmax。而Hardin公式是根據(jù)土體靜力狀態(tài)下的試驗(yàn)所得到的,只考慮了有效應(yīng)力和孔隙比等參數(shù)對Gmax的影響,未考慮循環(huán)振動歷史這一重要因素。但已有的研究表明,在地震動中大應(yīng)變幅振動將導(dǎo)致Gmax附加衰減,即地震過程中Gmax要比相應(yīng)有效應(yīng)力下Hardin公式計(jì)算得到的Gmax還要低,這部分由于地震振動導(dǎo)致的Gmax與靜力狀態(tài)下Gmax的區(qū)別,被稱為附加衰減。目前,尚未有人探討這種由于地震振動作用而產(chǎn)生的Gmax附加衰減給場地地震響應(yīng)帶來的影響。 本文在回顧前人對各類土體Gmax受大振幅振動影響研究的基礎(chǔ)上,得到了對應(yīng)于強(qiáng)結(jié)構(gòu)性土和弱結(jié)構(gòu)性土的兩種不同Gmax附加衰減模式。將附加衰減模量值GmaxⅡ與相同有效應(yīng)力下靜力狀態(tài)的小應(yīng)變剪切模量值GmaxⅠ之比作為參量進(jìn)行分析發(fā)現(xiàn),弱結(jié)構(gòu)性土和強(qiáng)結(jié)構(gòu)性土的模量比GmaxⅡ/GmaxⅠ與有效應(yīng)力比σm'/σm0'。的關(guān)系可分別用兩段式和三段式來表示,文中擬合得到了不同衰減模式對應(yīng)的數(shù)學(xué)表達(dá)式。 通過編制可考慮Gmax附加衰減影響的一維場地地震響應(yīng)分析程序,對典型場地地震響應(yīng)進(jìn)行了分析對比。結(jié)果發(fā)現(xiàn)：Gmax附加衰減對場地加速度和剪應(yīng)力響應(yīng)均有較大影響,并將加速場地液化、擴(kuò)大場地最終液化范圍。地表加速度譜分析表明,考慮Gmax附加衰減后土體更加軟化,對地震波短周期部分有減震作用,對長周期部分有加震作用。此外,文中還考察了場地條件和輸入波卓越周期的影響,發(fā)現(xiàn)Gmax附加衰減對場地地震響應(yīng)的影響程度隨地下水位下降而增強(qiáng),隨場地土層厚度的增加無明顯變化；強(qiáng)結(jié)構(gòu)性土場地受到的影響比弱結(jié)構(gòu)性土場地更大；不同卓越周期輸入下均表現(xiàn)出由于Gmax附加衰減加快場地液化的現(xiàn)象。 為進(jìn)一步考察Gmax附加衰減對場地地震響應(yīng)的影響,采用該程序模擬分析了飽和砂土場地的離心機(jī)振動臺模型試驗(yàn)。為獲得離心機(jī)振動臺試驗(yàn)所采用福建砂的孔壓模型參數(shù),進(jìn)行了排水條件下等剪應(yīng)變幅扭剪試驗(yàn)和壓縮回彈試驗(yàn),得到應(yīng)變型孔壓模型中計(jì)算體應(yīng)變增量Δεvd和土體回彈模量Er的試驗(yàn)參數(shù)。通過對不同幅值地震加速度輸入下模型場地動力響應(yīng)的數(shù)值模擬,并和試驗(yàn)結(jié)果比較,兩者所得加速度響應(yīng)吻合得很好,孔壓響應(yīng)存在數(shù)值模擬中孔壓增長慢于試驗(yàn)實(shí)測結(jié)果的現(xiàn)象,認(rèn)為可能是由于離心機(jī)振動臺試驗(yàn)?zāi)Ｐ瓦吔绾痛_定孔壓參數(shù)的試驗(yàn)中空心圓柱試樣邊界不同造成的；兩者所得土層液化深度及各層達(dá)到液化的時(shí)間均較為相符�？紤]Gmax附加衰減對模型場地的影響,得出：當(dāng)輸入峰值加速度較小時(shí),Gmax附加衰減對場地地震響應(yīng)有顯著影響；當(dāng)場地輸入峰值加速度較大時(shí),由于場地迅速發(fā)生液化,Gmax附加衰減對場地地震響應(yīng)影響減弱甚至無影響。
[Abstract]:Small strain shear modulus Gmax is an important parameter in site seismic response analysis. In the past effective stress analysis of site seismic response, it was assumed that Gmax of soil was equivalent to Gmax of the same effective stress static state in the process of cyclic vibration. Hardin formula was used to calculate Gmax. Hardin formula was based on the static state of soil. However, previous studies have shown that large strain amplitude vibration during earthquake will lead to additional attenuation of Gmax, that is, Gmax is calculated by Hardin formula under the corresponding effective stress than under the corresponding effective stress. The difference between Gmax caused by seismic vibration and Gmax under static state is called additional attenuation.
On the basis of reviewing the previous studies on the influence of large amplitude vibration on Gmax of various soils, two different additional attenuation modes of Gmax corresponding to strong structural soils and weak structural soils are obtained. The ratio of the additional attenuation modulus Gmax II to the small strain shear modulus Gmax I under the same effective stress is taken as a parameter. It is found that the relationship between modulus ratio Gmax II/Gmax I and effective stress ratio_m'/_m 0'. of weak and strong structural soils can be expressed by two-stage and three-stage formulas respectively. The corresponding mathematical expressions of different attenuation modes are obtained by fitting.
The seismic response of a typical site is analyzed and compared by compiling a one-dimensional seismic response analysis program which can consider the effect of additional attenuation of Gmax. The results show that the additional attenuation of Gmax has great influence on the site acceleration and shear stress response, and will accelerate the site liquefaction and expand the final liquefaction range of the site. It is shown that the soil softens more after considering the additional attenuation of Gmax, which can reduce the short-period part of seismic wave and increase the long-period part. In addition, the influence of site conditions and the predominant period of input wave is also investigated. It is found that the influence of additional attenuation of Gmax on the seismic response of the site increases with the decrease of groundwater level and with the site. The increase of soil thickness has no obvious change; the influence of strong structural soil is greater than that of weak structural soil; the liquefaction of site is accelerated by Gmax additional attenuation under different predominant period input.
In order to further investigate the effect of Gmax additional attenuation on the seismic response of the site, the centrifuge shaking table model test on saturated sand site is simulated and analyzed by using the program. The test parameters for calculating the increment of volume strain______________ The phenomena of the measured results may be due to the difference of the boundary between the centrifuge shaking table test model and the hollow cylindrical specimen in the test to determine the pore pressure parameters. When the peak acceleration is small, the additional attenuation of Gmax has a significant effect on the seismic response of the site; when the input peak acceleration is large, the impact of the additional attenuation of Gmax on the seismic response of the site is weakened or even no effect due to the rapid liquefaction of the site.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2013
【分類號】：TU435

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