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研究生:蔡榮燦
論文名稱:砂土組構及傳波速度
指導教授:李崇正李崇正引用關係
學位類別:碩士
校院名稱:國立中央大學
系所名稱:土木工程研究所
學門:工程學門
學類:土木工程學類
論文種類:學術論文
論文出版年:1999
畢業學年度:87
語文別:中文
論文頁數:100
中文關鍵詞:組構應力路徑波速
外文關鍵詞:fabricstress pathwave velocity
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本研究以壓電晶片製作壓力波元件和剪力波元件(bender element),運用壓電晶片的壓電特性可以傳遞發射波和接收波,當裝置於三軸室上下蓋板內(cap),可求得土體的壓力波速(Vp)和剪力波速(Vs)。
在壓密過程中,不論是渥太華砂、越南石英砂或緊砂、鬆砂,其Vs/Vp值幾乎維持一定,意即孔隙比的改變造成剪力波速和壓力波速增加的影響量,以及有效圍壓造成波速改變的影響量,似乎可以Vs/Vp值正規化。以Vs/Vp為指標以正規化在不同應力狀況下有效圍壓改變和孔隙比改變而使得波速增加的影響,便可單就組構的影響探討反覆加載過程中造成波速變化的現象。
過壓密對於增加渥太華乾砂強度有幫助,中等緊密砂及疏鬆砂效果較緊密砂顯著。過壓密對於增加越南石英乾砂的強度有幫助,不論緊密砂、中等緊密砂還是疏鬆砂,效果都很顯著。
在AC(軸向壓縮)和LE(側向伸張)狀態時,最大主應力方向一直維持在垂直方向,故應力比值愈大,造成組構異向性愈明顯,使得VS/Vp值愈小。在AE(軸向伸張)和LC(側向壓縮)狀態時,最大主應力方向一直維持在水平方向,故隨應力比愈大,造成組構異向性亦愈顯著,使得VS/Vp值愈大。
不論鬆砂、緊砂或渥太華砂、越南石英砂,當Vs/Vp值在壓縮方或伸張方回復至初始應力狀態之值時,應變皆未回復至零應變,故可推論是應力的作用導致組構的改變,而造成應變產生。
以Vs/Vp為指標以觀測乾砂組構變化為一新的概念,在解釋砂土力學行為上與前人研究大部份吻合,故以Vs/Vp為指標的概念在探討組構變化的適用性上尚稱合理。
A set of compression wave transducers and shear wave transducers made from two types of piezoelectric ceramics were designed to be transmitters and receivers. The transmitters were mounted in the cap and the receivers in the base, while a soil sample sit between them. The receivers receive the signal after the transmitters driven by a function generator generate a wave and the waves propagate through the soil sample. Vs and Vp can be calculated for a soil sample during the triaxial test at the different stress paths.
No matter how dense or loose in the remolded dry Ottawa sand and the Vietnam quartz sand, the values of Vs/Vp almost keep constant during isotropic consolidation. This means the changed velocity of wave propagation influenced by change of void ratio may be normalized by the value of Vp. So the velocities of wave propagation can be used to discuss fabric change during the triaxial test at different stress path.
Overconsolidation effect increases the wave velocities of remolded dry Ottawa sand, especially at medium and dense sates. Overconsolidation effect also increases the velocities of remolded dry Vietnam quartz sand, no matter how loose or dense it is.
The direction of the maximum principle stress is vertical during AC and LE. The larger the stress ratio, the more strong fabric anisotropy. The direction of maximum principle stress is horizontal during AE and LC, the larger the stress ratio, the more strong the fabric anisotropy, too.
The new index of Vs/Vp is proposed to describe the change of fabric indirectly for a sand subjected cyclic loading. The index of Vs/Vp may be a good indicator of fabric change.
摘要Ⅰ
英文摘要Ⅱ
目錄Ⅲ
表目錄Ⅵ
圖目錄Ⅶ
符號說明ⅩⅠ
第一章 緒論1
1-1 前言1
1-2 研究動機2
1-3 論文內容2
第二章 文獻回顧3
2-1利用壓電晶片量測剪力波速之發展演進3
2-2影響剪力波和壓力波之因子4
2-2-1圍壓的影響5
2-2-2孔隙比的影響5
2-2-3顆粒形狀的影響5
2-2-4顆粒大小的影響6
2-2-5含水量的影響6
2-2-6應變振幅的影響6
2-3剪力波速的求取6
2-3-1激發波形選取的影響6
2-3-2到達時間之判定7
2-3-3鄰域效應8
2-3-4射頻現象(Overshooting)10
2-4由剪力波彎曲元件求取剪力模數可能造成的誤差10
2-4-1可能的誤差因子10
2-4-2剪力波傳遞的有效長度11
2-4-3剪力波可能的傳遞路徑說明11
2-5 最大剪力模數(Gmax)的研究11
2-5-1 影響Gmax的因素12
2-5-2 過壓密對Gmax的影響12
2-5-3 壓密時間對Gmax的影響13
2-5-4 應力比對Gmax的影響13
2-6 砂土組構14
2-6-1 組構的定義14
2-6-2 組構的異向性15
2-6-3 應力對組構的影響16
2-6-4組構之觀測技術16
2-7 以最大剪力模數探討組構變化之研究17
2-7-1最大剪力模數Gmax正規化概念17
2-7-2 異向性對Gmax的影響17
2-7-3 異向性為體積變化的指標之探討18
2-8以VS/VP探討組構變化之研究18
2-8-1不同應力路徑時之波速18
2-8-2固定有效平均主應力之反覆加載19
第三章 試驗計劃、儀器及試驗方法44
3-1試驗計劃44
3-2試驗土樣說明44
3-2-1渥太華砂44
3-2-2越南石英砂45
3-3試驗儀器設備45
3-3-1波形產生器(Function Generator)45
3-3-2壓電晶片(Piezoelectric Ceramics)45
3-3-3示波器(Oscilloscope)47
3-3-4電壓放大器(Power Supply/Amplifer)47
3-3-5動力三軸試驗設備48
3-4試驗方法49
3-4-1 等向壓密49
3-4-2 不同應力路徑49
3-4-3 下平均主應力固定50
第四章 試驗結果與討論59
4-1 等向壓密59
4-1-1 不同壓密應力下的波速59
4-1-2 過壓密與波速變化60
4-2 不同應力路徑時之波速61
4-2-1 三軸壓縮和伸張試驗61
4-2-2 Vs/Vp值之討論63
4-3 固定有效平均主應力之反覆加載64
4-3-1反覆載重下VS/Vp值與軸向應變之關係65
4-3-2不同應力階段組構的變化65
第五章 結論與建議96
5-1 結論96
5-2 建議97
參考文獻98
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