邊坡重力變形運動特性受地下水位變化及坡趾河道下切與加積影響之數值模擬

Abstract

深層重力邊坡變形(Deep-seated gravitational slope deformation)為一種特殊的邊坡運動現象，變形受到坡體自重影響，具有發生時間長、速率慢，規模大等特性，若轉為遽變式運動可能造成嚴重災害。然而，此類邊坡變形速率不一致，現有大地材料組成律難以有效描述其運動特性，造成邊坡穩定分析評估困難，邊坡保護與防治對策欠缺量化依據。 臺20線鄰近嘉寶隧道西洞口路段邊坡具深層重力變形特性，造成公路沿線擋土結構物與隧道經常需修補養護，依據1990年代展開的監測記錄與現地調查資料，足以界定嘉寶邊坡的滑動範圍與滑動深度，並可解釋邊坡變形受到通過坡趾河道下切與加積影響，然而，對於滑動面的生成，不同滑動面的運動速度變化，仍無法具體描述。 本研究提出一新的力學模型，導入了潛變應力閥值的概念，修正既有的黏彈塑組成律，描述邊坡運動特性的變化。本研究運用有限差分法軟體結合自行定義的新力學模型，依據嘉寶邊坡監測記錄解析其變形特性後，估計黏彈塑模式參數以及潛變應力閥值後，可以有效描述嘉寶邊坡重力變形特性。 模擬結果顯示：河道下切和加積由於時間尺度長，影響了不同深度剪切帶的發育，而地下水位的升降則是可能造成剪切帶向冠部發育，河道的加積造成坡趾達到潛變門檻的岩體增加，整體潛變速率與地表沉陷量皆上升。 關鍵字:重力變形邊坡、依時變形、黏彈塑組成律、河道下切、河道加積

Deep-seated gravitational slope deformation (DSGSD) is a special type of slope movement phenomenon influenced by the self-weight of the slope. It is characterized by long occurrence time, slow velocity, and large scale. If it undergoes sudden changes, it can lead to severe disasters. However, the deformation rate of such slopes is inconsistent, and the existing composition laws of earth materials are insufficient to effectively describe their movement characteristics, making it difficult to analyze and assess slope stability. As a result, there is a lack of quantifiable basis for slope protection and mitigation strategies. The slopes near the western entrance of the Jiabao Tunnel in the vicinity of National Highway 20 exhibit characteristics of deep-seated gravitational deformation, causing frequent repairs and maintenance of the retaining structures along the highway and the tunnel. Based on monitoring records and field investigation data from the 1990s, it is possible to define the sliding range and depth of the Jiabao slope and explain that slope deformation is influenced by the incision and sedimentation of the river at the toe of the slope. However, the generation of sliding surfaces and variations in their movement velocities are still not adequately described. This study proposes a new mechanical model that incorporates the concept of creep stress threshold and modifies the existing visco-elasto-plastic constitutive law to describe the variations in slope movement characteristics. By using finite difference software combined with the newly defined mechanical model and analyzing the deformation characteristics of the Jiabao slope based on monitoring records, the parameters of the visco-elasto-plastic model and creep stress threshold are estimated, effectively describing the gravitational deformation characteristics of the Jiabao slope. The simulation results show that: The incision and aggradation of the river over a long time scale have influenced the development of different depth shear zones. The fluctuation of the groundwater level can potentially lead to the development of shear zones towards the crown. River aggradation increases the amount of rock masses reaching the threshold, resulting in an overall increase in strain rate and surface settlement Key word: DSGSD, Time dependent deformation, Viscoelastic-plastic constitutive law River incision, River aggradation