台灣西南部麓山帶軟岩區地層以新第三紀碎屑狀沉積岩為主，該區出露之岩盤有砂岩、泥岩及其互層，其中以古亭坑層泥岩分布最廣，其成岩時間較短，此泥岩特性為遇水極易軟化崩解，乾燥時堅硬如岩石，隨含水量增加，其行為又漸趨於粘性土壤。
本研究係針對古亭坑層泥岩進行一系列相關試驗以了解不同含水量下泥岩的基本性質與靜、動態力學行為。其中自由回脹試驗結果為回脹應變量18.1%；回脹壓力為0.45MPa。在單軸壓縮試驗部分，發現泥岩試體隨含水量的增加，泥岩的單軸壓縮強度逐漸降低；而破壞應變卻逐漸增加，並且乾燥泥岩試體(w=0%)的單軸壓縮強度為高含水量泥岩試體(w=9%~10%)的11倍。另一方面，泥岩試體的含水量增加則泥岩體積應變最大值越早出現。而透過巴西試驗可知，乾燥泥岩試體的張力強度為高含水量泥岩試體張力強度的18倍。至於在三軸壓縮試驗當中，當泥岩試體所受圍壓增加，其尖峰強度及殘餘強度也同時提高。而在相同圍壓條件下，較高含水量的泥岩試體，其尖峰強度、殘餘強度及正割模數較低。且泥岩在圍壓小於40MPa時，正割模數與圍壓呈線性關係增加，但在圍壓大於40MPa後，受到材料應變硬化的影響，正割模數與圍壓則呈現非線性之關係。此外，泥岩的脆延性轉換壓力隨含水量增加而有逐漸下降的趨勢。以Mohr－Coulomb、Hoek－Brown、Adachi和Johnston破壞準則分析三軸壓縮試驗結果發現，Adachi和Johnston破壞準則模擬泥岩的破壞行為適用性最佳，並且模擬殘餘強度曲線也有相當不錯的結果。而在動態岩石三軸試驗結果部分，泥岩試體的剪力模數隨著反覆振動次數增加而增加，阻尼比則降低，當試體即將發生破壞時，剪力模數會急速下降，而阻尼比則急速上升。

The geological deposits are mainly consisted of Neogene debris sedimentary rock in the foothills of southwestern Taiwan. The rock masses consist of sandstone, mudstone and alternating sandstone-mudstone formations. The Gutingkeng mudstone is distributed most widely in this area. Due to the short diagenetic time, this mudstone easily slakes with water. It behaves as a hard rock in the dry state but acts as a cohesive soil under high water content.
In this study, a series of tests was conducted to understand the basic property and static and dynamic mechanical behavior of the Gutingkeng mudstone under different water contents. Swelling test results show that the swelling strain is 18.1 %; swelling pressure is 0.45 MPa. In uniaxial compression test, the uniaxial compressive strength gradually decreased and the failure strain has gradually increased with the increase of the water content in the mudstone. The test results show that the uniaxial compressive strength of the dry mudstone sample in w = 0% is 12 times of the one with high water content (w = 9% ~ 10%). On the other hand, the maximum values of volume strain of specimens occur faster with the increase of the water content. The results of Brazil tests indicate that the tensile strength of dry mudstone is 18 times as the ones with high water content. In addition, the triaxial test results indicate that the peak and residual strengths of mudstone increase with increase of the confining pressure, and the higher water content sample has the lower secant modulus. Moreover, when the confining pressure is less than 40 MPa, the secant modulus of the mudstone and confining pressure is linear. But not in the cases when the confining pressure is greater than 40 MPa. Besides, the Brittle-Ductile transition pressure increases gradually with the increasing water content of the specimen. Finally, using Mohr－Coulomb, Hoek－Brown, Adachi and Johnston criterion to analyze triaxial test results, we found that the Adachi and Johnston criterion fits the best among the selected failure criterion to simulate the mudstone failure behavior. The cyclic triaxial test results indicate that as the numbers of cyclic loading increase, the shear modulus increases, but the damping ratio decreases. Furthermore, when the mudstone specimen approach failure, the shear modulus rapidly declines, while the damping ratio rises rapidly.

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