音波式圓錐貫入試驗於土層界面判定之應用

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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/505

Title:	音波式圓錐貫入試驗於土層界面判定之應用
Authors:	黃建民;Jing-Ming Huang
Contributors:	土木工程研究所
Keywords:	微震音放射;方均根音壓;圓錐貫入阻抗;acoustic emission;RMS sound pressure;cone resistance
Date:	2000-07-13
Issue Date:	2009-09-18 17:06:43 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	傳統圓錐貫入試驗所量測之圓錐貫入阻抗變化可能受到土壤層次間土壤類型、強度以及壓縮性等因素影響，造成土壤層面判斷不準確，因此本研究在貫入圓錐錐頭部份裝置微型麥克風，量測土壤在貫入過程所產生的微震音放射，希望藉由音波反應的高敏感特性來改進量測的準確度。本研究規劃砂土－粘土互層、單層均勻砂土、粘土等微音錐貫入試驗，同時量測圓錐貫入阻抗與聲波訊號，分別就圓錐貫入阻抗於互層貫入之反應及方均根音壓、頻譜分析於土層界面判定等項目進行探討。均勻砂土貫入試驗中，隨砂土之相對密度Dr愈大所量測到之方均根音壓也愈大，福隆砂之方均根音壓約介於50∼100μV間，套用Tringale(1983)所提出之方均根音壓與土壤粒徑關係圖，符合細砂之等級，並可利用公式進行平均粒徑估算。綜合比較砂土、粘土之音波反應特性，砂土之音壓振幅較大且其頻率分布範圍較廣。互層土壤貫入試驗結果顯示，在圓錐貫入通過土層界面時，圓錐貫入阻抗有一過渡影響範圍，此一影響範圍隨砂土層之相對密度增加而增加。若利用圓錐貫入阻抗反應來判定土層界面，當圓錐貫入阻抗於兩土層呈現相近之數值時可能造成誤判，此一情況可藉由微音錐貫入試驗獲得改善。以方均音壓反應來判定土層界面位置，實驗結果顯示，由砂土層貫入至粘土層方均根音壓達尖峰值或穩定後，方均根音壓開始衰減所對應的深度位置即為兩土層界面位置。以頻譜分析來判斷土層界面位置雖不若方均根音壓明顯但仍可作為輔助之用。 It makes the soil layer decision not very precise, because the cone resistance measured by traditional CPT maybe affected by the effect of soil interface, shear strength and compressibility. For this reason, this research installed a mini microphone into the cone tip to measure acoustic signal during cone penetration into soil so that to improve the accuracy of locating soil interface by using acoustic signal. This research included three kinds of acoustic cone penetration tests： pure sand, pure clay and sand-clay layered specimens. Also, we measure cone resistance and acoustic signal to study the response of cone resistance, RMS sound pressure, and frequency spectrum in locating the soil interface. In the test of pure sand specimens, the RMS sound pressure increase with the relative density of the sand. The RMS sound pressure of Fu-Long sand is between 50~100μV. In the figure of the relationship between RMS sound pressure and soil gain size offer by Tringale (1983), it matches the fine sand grade so that we can use the formula to predict the average gain size of sand. This research compares the response of acoustic signal of sand and clay, reveal that not only the amplitude of the acoustic signal of sand is greater than clay but also the consist of frequency is more complex than clay. In the test of sand-clay layered specimens shows that it has transition coverage in cone resistance when cone is advanced through soil interface. The transition coverage increases with the increase of the relative density of sand layer. If we use cone resistance to determine soil interface, it could make a mistake when cone resistance between sand and clay layers are similar. But it can be improved by acoustic cone penetration test. In the research of locating soil interface by the RMS sound pressure shows that as penetrating from sand layer to clay layer, the RMS sound pressure is limited or stable, the location of soil interface is the depth where the RMS sound pressure begin decay. Although using frequency analysis to determine the soil interface is not as clear as using the RMS sound pressure, but it still can be used for assistance.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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