土石流為山區最具破壞性的重力驅動型質量運動之一，其特徵包括高速運動、高衝擊力，以及水體、泥砂與夾帶物質之間的複雜交互作用。在自然環境中，土石流常夾帶木質殘體（woody debris），其可顯著影響流動動力特性，包括流速、流深、流動距離及堆積型態。然而，目前多數研究主要聚焦於泥砂主導之流動，對於木質殘體在土石流流變性與流動性中的作用仍缺乏系統性探討。
準確掌握流變特性對於預測土石流行為、提升災害評估及防治策略至關重要。傳統流變儀雖可對均質或細顆粒懸浮體提供可靠量測，然而對於含有粗顆粒或木質殘體之土石流材料，其應用受到顆粒尺寸限制、沉降效應及邊界交互作用之影響而顯著受限。因此，有必要發展替代方法，以評估此類複雜且非均質混合物之流變特性。
本研究旨在透過間接實驗方法探討含木質殘體之土石流材料的流變特性。試驗材料由黏土、粉土、水及木質殘體所組成，並透過改變細顆粒體積濃度、木質殘體比例及其尺寸，系統性配置高濃度混合物。研究結合傳統流變量測與流動試驗（包括L-box試驗與傾斜水槽試驗），以分析流動變形、流動性及運移距離等特性。
首先，利用兩種傳統流變儀（Brookfield DV-III與ICAR）探討細顆粒濃度、木質殘體比例及尺寸對流變特性的影響。結果顯示，降伏應力與黏滯係數隨細顆粒濃度與木質殘體比例增加而上升，並隨木質殘體尺寸減小而增加。敏感度分析指出，細顆粒濃度對流變參數之影響最為顯著，且材料組成變化對黏滯係數之影響大於對降伏應力之影響。
其次，從流變觀點分析L-box試驗，量測兩項關鍵坍流參數：流動高度與最終擴展距離。結果顯示，無因次流動高度與擴展比隨細顆粒濃度與木質殘體比例增加而降低，並隨木質殘體尺寸減小而降低。透過建立經驗關係式，將坍流參數與材料組成加以連結。敏感度分析顯示，細顆粒濃度為主要控制因子，且擴展量對材料變化之敏感度高於坍落高度。
第三，進行傾斜水槽試驗以模擬自然重力驅動流動行為，並量測進入速度、運移距離、堆積寬度及堆積厚度等關鍵參數。結果顯示，當細顆粒濃度與木質殘體比例降低，且木質殘體尺寸增加時，進入速度與運移距離隨之增加，並導致堆積厚度增加而寬度減小。其中，運移距離對堆積幾何變化最為敏感。研究進一步建立材料組成與運移參數之經驗關係。
最後，流變參數與坍流參數及運移參數之間呈現良好相關性，顯示流動試驗結果可有效預測流變特性。綜合實驗與理論分析結果，L-box試驗與傾斜水槽試驗可作為一種簡單、低成本且具相當可靠性的間接方法，用以評估含木質殘體之複雜土石流材料的流變特性。

Debris flows are among the most destructive types of gravity-driven mass flows in mountainous regions, characterized by rapid movement, high impact forces, and complex interactions among water, sediments, and entrained materials. In natural environments, debris flows often incorporate woody debris, which can significantly influence flow dynamics by altering flow speed, flow depth, runout distance, and deposition patterns. Despite its importance, the role of woody debris in debris-flow rheology and mobility remains insufficiently understood, as most previous studies have primarily focused on sediment-dominated flows.
Accurate characterization of rheological properties is essential for predicting debris-flow behavior and improving hazard assessment and mitigation strategies. Conventional rheometers can provide reliable measurements for homogeneous or fine-sediment suspensions; however, their application to debris-flow materials containing coarse particles or woody debris is limited due to particle-size constraints, sedimentation effects, and boundary interactions. This limitation highlights the need for alternative approaches to evaluate the rheology of complex and heterogeneous mixtures.
This study aims to investigate the rheological properties of complex debris flow materials containing woody debris by employing indirect experimental approaches using indirect experimental methods. Highly concentrated mixtures composed of clay, silt, water, and woody debris were systematically prepared by varying fine-sediment fraction, woody-debris proportion, and woody-debris size. A combination of traditional rheometric measurements and flow-based tests, including L-box tests and inclined-channel tests, was employed to characterize flow deformation, mobility, and runout behavior.
First, the effects of fine-sediment fraction, woody-debris proportion, and woody-debris size on the rheological properties of woody-debris suspensions are investigated using two conventional rheometers (Brookfield DV-III and ICAR). The results show that both yield stress and viscosity increase with increasing fine-sediment fraction and woody-debris proportion, and with decreasing woody-debris size. Sensitivity analysis indicates that the fine-sediment fraction has a more pronounced influence on rheological parameters than woody-debris proportion and size. Furthermore, variations in material composition have a greater impact on viscosity than on yield stress.
Second, the L-box test is interpreted from a rheological perspective, and two key slump-flow parameters, flow height and final flow distance, are quantified. These parameters serve as qualitative indicators of rheological behavior. The results show that the dimensionless flow height and final flow distance decrease with increasing fine-sediment fraction and woody-debris proportion, and with decreasing woody-debris size. Empirical relationships are established to link slump-flow parameters with material composition. Sensitivity analysis reveals that fine-sediment fraction exerts the strongest control on these parameters, while the spread is more sensitive than the slump to variations in sediment conditions.
Third, inclined-channel tests are conducted to simulate the flow behavior of sediment suspensions under conditions representative of natural gravity-driven flows. Key runout parameters, including entry speed, runout distance, deposit width, and deposit thickness, are measured. The results indicate that entry speed increases with decreasing fine-sediment fraction and woody-debris proportion, and with increasing woody-debris size, leading to longer runout distances and thicker deposits, while deposit width decreases. Among these parameters, runout distance exhibits the highest sensitivity to variations in deposit geometry. Empirical relationships are developed to quantify the influence of material composition on runout behavior.
Finally, strong correlations are identified between rheological parameters and both slump-flow and runout parameters. The empirical relationships demonstrate that flow test results can effectively predict rheological properties. Given the strong agreement between theoretical predictions and experimental observations, flow tests such as the L-box test and inclined-channel test provide a simple, cost-effective, and reasonably reliable approach for indirectly estimating the rheological properties of complex woody-debris suspensions.

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