微音錐應用於土壤音射特性之研究; Study of Acoustic Cone Penetration Test on Acoustic Emission Characteristics of Soil.

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Title:	微音錐應用於土壤音射特性之研究;Study of Acoustic Cone Penetration Test on Acoustic Emission Characteristics of Soil.
Authors:	王志偉;Chih-Wei Wang
Contributors:	土木工程研究所
Keywords:	錐尖阻抗;音射;均方根音壓;音射發生率;頻譜分析;RMS of sound pressure;AE rate;frequency spectrum;acoustic emission;cone resistance
Date:	2002-07-05
Issue Date:	2009-09-18 17:11:34 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	圓錐貫入試驗在工程上的應用主要有土壤分類、推求土壤工程性質與相關參數及評估土層支承力與液化等，其中以土壤分類與土層研判為最常應用的項目。在土層中進行圓錐貫入試驗主要係量測錐尖阻抗、袖管摩擦及孔隙水壓等數據，然而錐尖阻抗因所在位置上下約5?10倍錐徑內的土壤變化而有所反應，此一反應將造成土層界面判斷的不準確，同時也可能對土壤工程性質的評估結果造成影響。本研究主要係利用音射的量測技術，在錐尖內部加裝一微音器，探討錐體穩態貫入土層時，伴隨貫入行為所產生的音射，此訊號可以利用資料擷取系統加以記錄，並透過音射數、均方根計算及快速傅立葉轉換得到音波訊號的音射發生率、均方根音壓與頻譜，而這些音波分析的結果與土壤種類有關。本研究應用音射於圓錐貫入試驗中，利用圓形土槽與霣降儀等設備，探討各種砂土在不同的邊界效應、相對密度以及覆土應力之條件下，進行一系列的貫入試驗。綜合上述試驗結果顯示，中等緊密之砂土在BC3的邊界條件下，錐尖阻抗值會隨著深度的增加而持續上升。然對不同的相對密度與覆土應力之試驗結果而言，福隆砂與峴港砂之錐尖阻抗、均方根音壓與音射發生率有隨相對密度或覆土應力之增加而提高之趨勢。至於西螺砂，在本研究所施加之覆土應力作用下，音射能量之均方根音壓並不受相對密度之影響。此外，在頻譜分析方面，福隆砂、峴港砂與西螺砂於不同的實驗條件下，音射能量分布曲線之趨勢皆很相似，且主要頻率均分布於2?4kHz之間。在室內大型土槽互層土壤貫入試驗之研究方面，實驗結果顯示利用均方根音壓與音射發生率並配合頻譜分析能掌握砂土和黏性土壤互層之分布情形及層面位置。故利用音波訊號以判定土層界面應屬一良好的方法。 Cone Penetration Tests (CPT) are usually applied to the investigations, of soil classification, calculation of soil parameters, estimation of bearing capacity of soil and liquefaction. Soil classification and layer verification are the major applications in CPT for measuring cone resistance, sleeve friction and pore water pressure etc. Cone resistance usually varied in the area of 5~10 times of tip diameters of the cone. The reasons above-mentioned will influence the judgement of soil layer and soil properties. This research used the measuring techniques of sound with a small microphone set in the cone tip to measure the Acoustic Emission (AE) of soils during the penetration of cone tip. The data was recorded by data acquisition system and the acoustic emission rate, RMS of sound pressure and frequency spectrum were ananlyzed. Two circular chambers and a movable sand pluviator were used to carry out a series of laboratory cone penetration tests under the different conditions of boundaries of chamber, relative densities of sand and overburden pressures of speciments. From the experimental results, it is understood that the cone resistance in sand with medium density will increase continuously with depth under the boundary condition of BC3. It is also show that the cone resistance, RMS of sound pressure and AE rate of Fulong and Danang Sand would be increased with the increase of relative density and overburden pressure. However the RMS of sound pressure of Shiluo Sand is not affected by relative density under the overburden pressures applied in this research. The analysis of frequency spectrum of Fulong Sand, Danang Sand and Shiluo Sand showed that the major frequency distribution of these tests are located at the range of 2kHz~4kHz. According to the experimental results of composed soil layer which is embedded in the big test pit in ECCE (Experimental Center of Civil Engineering) showed that the results of RMS of sound pressure, AE rate and frequency spectrum can estimate the interface of soil layer accurately. Therefore, it is recognized that the technique of AE for determining the soil interface location is an effecient method.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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