台灣地處亞熱帶地區，頻繁的季節性變化可能是影響鋪面成效的關 鍵，但因國內缺乏長期鋪面成效觀測數據，故援用美國長期鋪面成效觀測 計劃LTPP (Long Term Pavement Performance) 資料庫軟體(DataPave 3.0)中 現地觀測資料，擷取現地數據，探討季節性環境變化如降雨、凍融、地下 水位昇降等對路基土壤行為特性的影響，結果發現路基土壤含水量會受到 季節性降雨影響而產生變動。以凝聚性土壤而言，變動多於最佳含水量 (Optimum Moisture Content, OMC)濕側，變動範圍小於3 %之內，此因乃土 壤自身組構能力與環境達到一平衡狀態，此稱平衡含水量(Equilibrium moisture content, EMC)。回彈模數會因為降雨引致含水量的增加而折減， 變化趨勢及反應時間上與降雨歷時曲線較相似。 路基土壤地層位置因常位於地下水位面以上，而呈現不飽和狀態。土 壤在不飽和狀態時，土壤吸力是一項重要的參數，因土壤有效應力會受到 土壤吸力(Soil Suction)作用而改變，利用實驗室夯實試體，控制不同單位 重及含水量變化，進而模擬現地路基土壤自建造時OMC 狀態至鋪面開通 服務後，在現地環境所受之應力狀態及EMC 對回彈模數的影響，並利用 濾紙法(Filter Paper Method)量測不飽和土壤之吸力強度，結果發現土壤吸 力會隨含水量增加及相對夯實度的降低而折減。 實驗結果藉由建立回彈模數-土壤吸力模式能有效預測路基土壤回彈 模數受季節性變因之變動，取代繁鎖且昂貴的回彈模數試驗，幫助對現地 回彈模數的預測及監控，而影響路基土壤回彈模數的因子，依權重大小依 序為土壤單位重、土壤吸力、應力狀態，故建構時夯實度的控制，可能是 將來鋪面成效的一項重要因素。 Moisture content of pavement materials plays a significant role in the performance of pavements. Variation in moisture content in the subgrade can induce volume change of swelling soil and result in detrimental deformation to the pavement structure. An increase in moisture content of the subgrade and unbound subbase/base often results in decreases in the bearing capacity of these materials, weakens the pavement’s response to loads, and reduces pavement service life. Soil suction will affect the mechanical properties of unsaturated soils much, such as effective stress, resilient modulus, and strength. This study attempted to collect information from LTPP database and study the climatic model of subgrade soil under seasonal environmental variation. Resilient modulus tests were conducted for 2 cohesive subgrade soils at a range of water contents that is likely to occur in the field. Also, soil suction was determined by filter paper method at various water contents to correlate with the resilient modulus test results. Experimental results indicate that: (1) field water content of cohesive soils are found to remain in the wet side of OMC, while that of granular soils varies in both the wet and dry side of OMC; (2) the resilient modulus of cohesive soils reduces sharply with increasing water content and decreasing degree of compaction; (3) the relative compaction of subgrade during construction is of great importance and may affect the performance of pavements; (4) the matric suction was found to be a good indicator of the stiffness of the subgrade and is used to establish a model for predicting the resilient modulus of subgrade with varying water contents; (5) the dry unit weight of soil also plays an important role in the resilient modulus-matric suction model.
