砂土中音波傳遞與量測之研究

Study of the sound wave transmission and measuring in sand layer

古秉弘(Ping-Hung Ku)

指導教授 ： 張惠文

國立中央大學/工學院/土木工程學系/碩士(2006年)

摘要

累積了前人的研究經驗發現，微音錐除了可藉由錐尖阻抗與均方根音壓，探測土層之基本性質外，音波對於砂土層中所發生的微小變動，也具有高敏感度的特性。本試驗利用音波的此項特性，對於砂土層滑動所産生之聲音進行量測。最終目標希望能夠建立一套，利用音波量測技術來監測土壤中變動行為之系統。
本試驗首先量測土壤在貫入過程中所産生的微震音放射，利用貫入試驗所得到的結果，瞭解土層之基本特性。並在室內大型土槽中進行音波的量測，模擬音波在現地砂土層中的傳遞，有助於瞭解音波在現地砂土層中傳播的特性。最後模擬擋土牆後砂土滑動，量測砂土在滑動時，所産生之音波訊號，並探討在不同條件下，砂土發生滑動時之行為與音波訊號之關係。
綜合以上試驗結果顯示，峴港砂之錐尖阻抗、均方根音壓與音射發生率，皆隨著試體相對密度及覆土壓力的增加而增加，而增加相對密度，更可有效提高錐尖阻抗與均方根音壓增加的速率。音波在砂土層中傳遞時，除了愈緊密的砂土層，音波強度衰減愈慢外，均方根音壓還會隨著感測器與音源距離成反比。貫入試驗所得到的音波訊號頻率主要分布在2 ~ 4.5kHz，而砂土滑動試驗所得到頻率分布在5Hz，表示峴港砂在受到微音錐擠壓後，砂土顆粒間因碰撞會産生較高頻之音波訊號，若峴港砂經解壓後發生滑動，砂土顆粒間因碰撞會産生較低頻之音波訊號。

關鍵字

錐尖阻抗 ； 均方根音壓 ； 砂土層滑動 ； 音波傳遞

並列摘要

According to the results of past researches about acoustic cone, it is understood that the acoustic cone can be used to measure cone resistance and root mean square of sound pressure. It is also found that the acoustic cone is sensitive in measuring small sound wave due to a small variation in ground. This research used the measuring technique of sound to record the sound waves in soil during slide. In the future, this technique may be expected to establish a monitoring system for recording small variation of soil behaviors.
This research measured the Acoustic Emission (AE) of soil during the penetration of cone tip in the testing chamber and realized some basic characteristics of soil. In addition, a sound wave propagation test was conducted in the test pit to realize the sound wave transmission in sand layer. Finally, a sand slide model test was performed to simulate the movement of retaining wall and the sound signals were recorded during the slide of sand.
From the results of experiments, it is found that the cone resistance, the root mean square of sound pressure and AE rate increased with the increase of relative density and overburden pressure. Increase the relative density of sand can increase the cone resistance and the root mean square of sound pressure effectively. The amplitude of sound wave will decrease gradually during the transmission in loose sand layer and the root mean square of sound pressure will decrease in inverse proportion with the increase of distance from sound source. From the results of ACPT, the major frequency of sound signals is located at the range of 2~4.5kHz, and for sand slide model test, it located at 5Hz. These experimental results show that the sound signal with high frequency will be generated due to the bump of sand particles during the penetration of cone tip. However, the sound signal with low frequency will be generated during the sand slide under the condition of unloading.

並列關鍵字

root mean square of sound pressure ； sand slide ； cone resistance ； sound wave propagation

參考文獻

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