本研究採用改良式直剪儀，進行砂土材料之剪動實驗，在氣乾狀態進行不同正向應力之剪動，以及部分飽和狀態下進行不同正向應力之剪動，量測破壞時之音波與振波訊號。利用頻譜比對法，比對後得到峴港砂音波之顯著頻率為10~16Hz，而西螺砂之顯著頻率為8~14Hz與22~26Hz。亦經比對得知兩種砂之加速度顯著頻率是在14~16Hz，兩者所分析出的顯著頻率皆屬低頻範圍。而後為了將機械儀器或環境等造成之頻率濾除，也避免將試驗之重要數據濾除，因此實驗後之音波數據，保留30Hz以下之數值外，其他數值則予以濾除，並利用濾波後之音波與加速度訊號，分析砂土受剪時之力學特性。 峴港砂之破壞屬於顆粒間之摩擦破壞，而西螺砂則屬於顆粒破裂或顆粒間之摩擦破壞，故破壞產生之聲音比西螺砂來得小。飽和度並不會影響顯著頻率，但會影響音壓、加速度及破壞剪應力之大小，飽和度增加使得砂土顆粒與顆粒之間越濕潤，讓砂土之抗剪強度降低。 根據氣乾峴港砂及西螺砂受剪時之降伏剪應力與正向應力關係圖，得知降伏值分別約為破壞剪應力之76%與73%。同理可知部分飽和峴港砂與西螺砂，其降伏值分別約為破壞剪應力之82%與78%。經由上述之結果，得知可利用儀器測得之加速度訊號與其對應之剪應力來瞭解降伏之徵兆，藉此來輔助判斷其是否有破壞之可能，並可做為往後預警之參考依據。 This research performed a series of direct shear tests of sand material under various conditions of normal stress and degree of saturation to study the properties of shear strength, sound waves and vibration waves. A spectrum comparison method of waves is used in this paper to distinguish and to filter the sound waves and vibration waves generated in the process of shearing. According to the results of experiments, the apparent frequency of Danang sand is 10-16Hz and the values of Shiluo sand is 8-14Hz and 22-26Hz. As to the spectrum of acceleration of vibration waves, similar apparent frequency was found in the area of 14-16Hz. This showed that there exists a close relationship between sound waves and vibration waves, and both of their apparent frequencies were found in the low area of frequency. In order to filter the noise caused by the machine and the surrounding environment and to avoid the important data to be filtered, so the sound waves and the acceleration of vibration waves larger than 30Hz were filtered to examine the shear strength properties of sand in this study. The failure of Danang sand is caused by the failure of friction, but the failure of Shiluo sand is due to the fraction of sand particles and the failure of friction between particles. Therefore, the sound of Danang sand is smaller than Shiluo sand. The degree of saturation would not affect the apparent frequency, but it would influence the values of sound pressure, acceleration of vibration and shear stresses at failure. According to the relationships between shear stress and normal stress at yielding or failure, it is recognized that the yielding stresses of both air dried Danang sand and air dried Shiluo sand is about 73% to 76% of failure shear stresses. Furthermore, the values of partially saturated sands located between 78% and 82% with the same method. By combining the sound and acceleration signals, the yielding and failure of sand can be distinguished. The kind of judgment can be used to offer an early warning to prevent slope slide disaster.
