夯實後之林口紅土長時處於不飽和狀態，易受降雨及日曬等環境因素影響而改變其土壤內部含水量，進而影響其吸力、強度及模數等工程性質。本研究針對不飽和夯實土壤進行一系列室內試驗，包含超音波暨彎曲元件試驗、無圍壓縮暨小應變量測試驗、室內圓錐貫入試驗及不飽和三軸暨彎曲元件多階加載試驗，並且利用數值分析模擬圓錐貫入試驗以做進一步驗證及探討。然後整合所有試驗和數值分析研究結果，探討基質吸力、土壤波速、錐頭阻抗、剪力強度及模數特性之相互關係。
試驗結果顯示，土壤錐頭阻抗及土壤波速均隨著吸力增加而提升，且兩者呈一線性關係。利用數值分析模擬圓錐貫入試驗，其錐頭阻抗與試驗結果亦有相同趨勢，錐頭阻抗可合理反應基質吸力對於土壤強
度之影響。以此為依據，本研究建立以錐頭阻抗推估無圍壓縮強度之關係式，可供工程參考應用。剪力強度試驗結果顯示，絮凝結構土壤會因飽和吸水體積膨脹，導致土壤強度大幅弱化，且絮凝結構含量越
多，弱化情形會越加明顯。此外，在相同吸力下有效圍壓增加，試體破壞時之軸差強度亦會提升，但視凝聚力則不因圍壓改變而有變化。模數特性試驗結果顯示，試體勁度會隨著吸力增加而提升，且在小應
變範圍(0.001%~0.1%)均有明顯之模數劣化。並且最大楊氏模數無論是由波傳理論推估還是透過無圍壓縮試驗求得，其模數亦隨著吸力上升而增加。

Compacted Linkou lateritic soil is often in an unsaturated state. Environmental factors such as sunlight and rainfall will change the water content of the soil, which will affect its matric suction, strength, and modulus. This study conducted a series of tests on unsaturated compacted soils, including the ultrasonic and bender element test, the unconfined compression test with small strain measurement, the laboratory cone penetration test, and the unsaturated triaxial test with bender element. In addition, numerical analysis was conducted to simulate the con penetration test for further verification and discussion. Then, this study integrated laboratory test and numerical analysis results to study the relationship among the matric suction, the wave velocity, the cone resistance, the shear strength, and the modulus of the soil.
Test results show that a positive linear correlation exists between the cone resistance and the soil velocity while the matric suction increased. Numerical analysis results show that the cone resistance evolution has the same trend with the test results. The cone resistance can reasonably reflect the influence of matric suction on soil strength. Based on the above findings, this study established formulas for estimating the unconfined compression strength by the cone resistance that can be adopted for engineering applications. The test results of the shear strength show that the soil with flocculation structure adsorbed more water upon the saturation process; therefore, the soil strength is significantly weakened. Furthermore, as the percentage of flocculation structure increases, the weakening situation will become more severe. Regarding the increase of effective confining pressure under the same matric suction, the deviator stress at failure will also increase, but the apparent cohesion will not change with the change of confining pressure. The test results of the modulus characteristic show that as the matric suction increases, soil modulus will also increase, and there is obvious modulus deterioration in the small strain range (0.001%~0.1%). The maximum Young's modulus, whether estimated by the wave propagation formula or obtained by the unconfined compression test, also increases with the increase of the matric suction.

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