傳統土壤力學的研究領域，通常專注在飽和土壤的行為上。飽和土壤力學2個主要缺點分別為：（1）缺乏對於不飽和土壤行為機制的了解；（2）氣候變動因素影響地下水文狀態邊界模式的評估。然而許多工程實務問題是屬於不飽和土壤的問題，本研究的目的即在應用不飽和土壤力學理論與試驗，針對不飽和紅土吸力行為及其在路基土壤與邊坡工程的應用進行深入探討，以提供日後不飽和土壤力學研究及工程維護管理工作時的參考。
本研究先從基質吸力的觀點探討紅土的基質吸力行為，並根據紅土吸力特性探討其回彈模數的行為。考慮滲流與植生之不飽和土壤邊坡穩定分析則為在邊坡工程之應用。基質吸力研究成果顯示，夯實土壤在乾濕測的微觀組構與夯實能量為影響夯實土壤基質吸力的關鍵因素。OMC（Optimum Moisture Content）狀態之夯實土壤有較佳之工程性質，此現象也可從其吸力特性得到印證。
路基土壤的應力狀態、含水量及基質吸力等因素將會影響其回彈模數與塑性應變。當土壤含水量達到較濕潤的近飽和狀態時，將會產生極大之回彈模數損失，營運階段必須注意路基土壤的排水情況，以避免雨水入滲造成基質吸力降低，進一步引發路基土壤的破壞。本研究已成功應用張力計進行現地邊坡基質吸力的量測，量測結果顯示接近地表之土壤在乾季時屬於水分蒸散之行為，在足夠的雨量下則呈現入滲之行為。
根據現地邊坡監測成果，在平時由於邊坡土體中存在之基質吸力，造成土壤剪力強度提高而使邊坡處於穩定狀態，但當暴雨來臨時，降雨入滲在邊坡表面形成之浸潤帶，將會使得邊坡因基質吸力的下降，而導致邊坡於浸潤帶內發生淺層近似平面的破壞面。本研究亦成功組合有限元素滲流分析軟體Seep/w與邊坡穩定分析軟體Slope/w，進行考慮基質吸力與不飽和滲流之邊坡穩定分析，分析結果可合理模擬不飽和土壤淺層滑動之行為。

Classical soil mechanics has focused on the behavior of saturated soils. The shortcomings associated with classical soil mechanics are the lack of consideration of the behavior of unsaturated soils and a comprehensive model for the moisture flux boundary condition imposed by climate conditions. However, many geotechnical problems involve unsaturated soils above the groundwater table. The objective of this research is to apply the principle of the unsaturated soil mechanics to study behavior of matric suction of unsaturated lateratic soils and its engineering application.
The main goal of this research is to investigate the behavior of matric suction of unsaturated soils and the influence of matric suction on the resilient modulus. The applications on the slope engineering include the monitoring of matric suction and slope stability analysis integrating unsaturated seepage and vegetation in it. Both the micro structure of compacted soils and the compaction energy were found to be the key parameter to control the matric suction of compacted soils. Compared to the dry side or the wet side of the compacted soils, the soils compacted as OMC(Optimum Moisture Content) condition exhibit the most favorable engineering property. This phenomenon can also be verified by the matric suction characteristics.
The experimental results demonstrated that the stress state, moisture, and the soil suction influence the resilient modulus and plastic strain. Furthermore, the high subgrade moisture or low matric suction would result in large decrease in subgrade resilient modulus, and should be carefully taken care of in the drainage system of the subgrade during the service period. If not, failure of the subgrade soils may occur due to the loss of matric suction during infiltration. The tensiometer has been tested in the field to monitor the matric suction in the slope successfully. The measured results showed that the slope is dominated by the evaporation behavior during the dry season and exhibits infiltration behavior under the storm condition.
The characteristics of unsaturated soil slope can be summarized as follows:（1）matric suction increases the shear strength of unsaturated soils and thus increase the factory of safety of the slope stability in the dry season; （2） rain infiltration results in the forming of a wetting band and reduction of matric suction, consequently, decreases the apparent cohesion of the unsaturated soil. Then, a shallow-type of failure would take place within the wetting zone. Considering the unsaturated seepage and matric suction, this study integrated the finite element seepage program-seep/w and slope stability software-slope/w to carry out the slope stability analyses. The analytical results show representative and comprehensive simulation of the behavior of the unsaturated soil slope subjected to rainfall infiltration as summarized above.

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