【摘要】：近年來全球范圍內(nèi)長(zhǎng)持時(shí)強(qiáng)震頻發(fā),長(zhǎng)持時(shí)強(qiáng)震液化后產(chǎn)生過大沉降變形異常嚴(yán)重,是導(dǎo)致強(qiáng)震區(qū)地下基礎(chǔ)設(shè)施及生命線系統(tǒng)失效破壞的主要原因之一。本文針對(duì)長(zhǎng)持時(shí)強(qiáng)震作用下場(chǎng)地液化后沉降機(jī)制問題,開展單元體固結(jié)試驗(yàn)、動(dòng)三軸振動(dòng)試驗(yàn)(包括液化工況和非液化工況)研究,了解砂土受振動(dòng)荷載后的變形特性,并進(jìn)一步提出了基于固結(jié)和循環(huán)應(yīng)力歷史的再固結(jié)排水模型和沉降簡(jiǎn)化計(jì)算方法。同時(shí),開展了兩個(gè)離心機(jī)模型試驗(yàn)(正弦波模型和地震波模型)模擬長(zhǎng)持時(shí)強(qiáng)震后的液化沉降,對(duì)上述模型和計(jì)算方法加以驗(yàn)證。本文還針對(duì)液化場(chǎng)地的邊值問題提出相應(yīng)的累積剪應(yīng)變比的計(jì)算方法,并做了現(xiàn)場(chǎng)實(shí)例沉降計(jì)算。具體內(nèi)容包括： (1)動(dòng)三軸振動(dòng)(包括液化工況和非液化工況)研究中采用累積剪應(yīng)變比作為砂土結(jié)構(gòu)性損傷的表征指標(biāo),確定了單元體試樣中臨界累積剪應(yīng)變作為液化判別的標(biāo)準(zhǔn)； (2)飽和砂土在振動(dòng)非液化工況下排水體變僅由再固結(jié)機(jī)制控制,其再固結(jié)過程的規(guī)律與固結(jié)試驗(yàn)中的回彈段的規(guī)律相似,其再固結(jié)指數(shù)在e-logp曲線中的斜率隨著有效應(yīng)力的增大而增大,且再固結(jié)指數(shù)與相同條件下的回彈指數(shù)相當(dāng)； (3)飽和砂土液化后體變由再沉積和再固結(jié)兩種機(jī)制組成：其中再沉積部分與所受振動(dòng)歷史密切相關(guān),土骨架累積剪應(yīng)變比越大、再沉積體變?cè)酱�；而再固結(jié)部分受先期固結(jié)歷史影響顯著,再固結(jié)曲線會(huì)沿原有正常固結(jié)曲線趨勢(shì)發(fā)展,其穩(wěn)定段再固結(jié)指數(shù)與相同條件下的壓縮指數(shù)稍大,前者大約為后者的1.3-1.5倍之間,于是,壓縮指數(shù)可以用于再固結(jié)指數(shù)的估算； (4)提出了考慮先期固結(jié)和振動(dòng)歷史的砂土再固結(jié)模型和簡(jiǎn)化算法,將再沉積和再固結(jié)兩者統(tǒng)一表達(dá)成再固結(jié)體變,該簡(jiǎn)化后體變的規(guī)律可用累積剪應(yīng)變比(γacm/γacm0)與假設(shè)起始應(yīng)力比(σ1a：/σ1v0)的相關(guān)關(guān)系加以描述,并建議了再固結(jié)指數(shù)和假設(shè)初始應(yīng)力的確定方法； (5)開展了系列水平場(chǎng)地地震液化離心機(jī)模型試驗(yàn),監(jiān)測(cè)模型固結(jié)和振動(dòng)液化過程急排水過程的沉降,從模型尺度進(jìn)一步揭示砂土在長(zhǎng)持時(shí)強(qiáng)震作用下的液化工況下的體變規(guī)律,并初步驗(yàn)證了本文模型與簡(jiǎn)化算法在計(jì)算非液化工況和液化工況下沉降的有效性。 (6)根據(jù)模型場(chǎng)地累積剪應(yīng)變數(shù)據(jù)給出了模型或現(xiàn)場(chǎng)等邊值問題下的臨界累積剪應(yīng)變判別液化標(biāo)準(zhǔn),提出了依據(jù)現(xiàn)場(chǎng)地表加速度記錄計(jì)算地表下各土層的累積剪應(yīng)變的方法,并針對(duì)東日本地震中Urayasu地區(qū)某液化場(chǎng)地的液化進(jìn)行沉降計(jì)算。
[Abstract]:In recent years, the long-lasting strong earthquakes occur frequently in the world, and the excessive settlement and deformation caused by the liquefaction of long-lasting strong earthquakes are very serious, which is one of the main reasons leading to the failure of underground infrastructure and lifeline system in strong earthquake areas. Aiming at the settlement mechanism of site liquefaction under the action of long-lasting strong earthquake, the consolidation test and dynamic triaxial vibration test (including liquefaction condition and non-liquefaction condition) are carried out to understand the deformation characteristics of sand under vibration load. Furthermore, a reconsolidation drainage model based on consolidation and cyclic stress history and a simplified settlement calculation method are proposed. At the same time, two centrifuge model tests (sinusoidal wave model and seismic wave model) were carried out to simulate the liquefaction settlement after long duration strong earthquake. In this paper, the corresponding calculation method of cumulative shear strain ratio is proposed for the boundary value problem of liquefaction site, and the settlement calculation of site example is made. The main contents are as follows: (1) in the study of dynamic triaxial vibration (including liquefaction and non-liquefaction), the cumulative shear strain ratio is used as the index to characterize the structural damage of sand. The critical cumulative shear strain in the unit sample is determined as the criterion of liquefaction. (2) the deformation of saturated sand is controlled only by the mechanism of reconsolidation under the condition of vibration and non-liquefaction. The law of the reconsolidation process is similar to that of the springback section in the consolidation test. The slope of the reconsolidation index in the e-logp curve increases with the increase of the effective stress, and the re-consolidation index is similar to the springback index under the same conditions. (3) the liquefaction of saturated sand consists of two mechanisms: redeposition and reconsolidation. The redepositional part is closely related to the vibration history, and the larger the cumulative shear strain ratio of soil skeleton is, the larger the redepositional body is; However, the reconsolidation part is significantly affected by the preconsolidation history, and the reconsolidation curve will develop along the trend of the original normal consolidation curve. The reconsolidation index of the stable section is slightly larger than that of the compression index under the same conditions, and the former is about 1.3-1.5 times of the latter, so, Compression exponent can be used to estimate the reconsolidation index. (4) A sand soil reconsolidation model and a simplified algorithm considering the pre-consolidation and vibration history are proposed. The simplified law of body deformation can be described by the correlation between the cumulative shear strain ratio (緯 acm/ 緯 acm0) and the assumed initial stress ratio (蟽 1a:/ 蟽 1v0), and the method of determining the reconsolidation index and the hypothetical initial stress is suggested. (5) A series of horizontal site seismic liquefaction centrifuge model tests were carried out to monitor the settlement of the model during consolidation and vibration liquefaction. Based on the model scale, the body deformation law of sand under the condition of liquefaction under the action of long-lasting strong earthquake is further revealed. The validity of the proposed model and the simplified algorithm in the calculation of settlement under non-liquefaction and liquefaction conditions are preliminarily verified. (6) based on the cumulative shear strain data of the model site, the impending problem of model or field isobaric value is given. Boundary cumulative shear strain criterion for liquefaction, A method for calculating the accumulated shear strain of each soil layer under the ground surface based on the field acceleration records is proposed and the settlement of a liquefaction site in Urayasu area during the East Japan earthquake is calculated.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TU441

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