順向坡體淺層變形機制分析

順向坡現地調查經常可見岩坡面淺層撓曲變形或滑動面出現。然順向坡岩坡之力學分析，一般考慮外在因素（如極端降雨事件、地震）及自身因素（如弱面，地下水，邊界條件變化如坡角被挖除等），惟此分析模式均無法解釋順向坡面淺層撓曲變形及滑動之行為。本文嘗試以粘彈力學觀點探討此一現象。岩坡坡體材料於長期自重作用下出現潛變，促使順向坡表層發展出多階段拱曲的變形。在束制壓力低下，這些岩坡表層拱曲的變形，形成之驅動力相對較低，滑動剪出面發展較淺，進而發展成淺層滑動破壞的狀況。本研究利用分離元素法進行數值模擬，探討坡體岩層彈性模數、弱面勁度、高度風化層厚度、坡長、弱面間距等參數對板岩順向坡體淺層變形的影響，並找出造成坡體表層變形的機制。經研究結果顯示：順向坡體淺層的變形，主要有兩種變形機制，以深層的剪應變集中延伸造成表層拱曲變形，與坡面表層拱曲變動二種型態；影響順向坡體淺層變形數量的主要因子為：岩層彈性模數、弱面間距、坡長三項參數。在岩層彈性模數中，變形的數量會隨著彈性模數的降低而增加，且在較高的彈性模數岩層中，主要產生表層變形的機制是以深層的剪應變集中延伸造成表層拱曲變形為主。當弱面間距小於2m時，坡面拱曲變形的數量，會隨著弱面間距的增大而增加；間距大於2m後，弱面間距數量會隨著間距的增加而下降，弱面間距越密（間距0.5m、1m），主應力較不會出現集中狀況，剪應力則會沿著弱面間的交界面作用，剪應變集中區域仍會從深處向坡面延伸，但變化值較小；弱面間距較疏（間距5m），主應力作用以深層為主，在坡面表層處，主應力幾乎沒有作用。剪應變變化，則是集中在坡頂與坡腳兩處，不論弱面間距的密或疏，在坡體變形的機制上，仍是以深層的剪應變集中延伸造成表層拱曲變形，與坡面表層拱曲變動二種型態。當坡長越長，坡面上產生拱曲形變的數量就越多，在坡長小於100m，坡面上除坡腳的挫曲變形外，並無其他變形產生，坡長大於150m後，在變形區的坡體主應力與剪應力分佈的趨勢會相同，皆是由深處朝坡面延伸，在剪應變的分佈上變化更為明顯。綜整順向坡體之主要兩種變形: 深層剪應變集中延伸造成表層拱曲變形與坡面表層拱曲變形。本文應用動力學概念，分別定義前二者為主要頻率波形及次要頻率波形。分析的案例中顯示變形波主頻率的出現之趨勢，此一現象應與隨著往坡腳位置，重力作用增加相關；在次頻率方面，在邊坡坡長50%後形成較有規律，在50%坡長之前則較無規律存在。

關鍵字

坡體淺層變形；數值模擬；潛變地形

並列摘要

The local bulking and shallow slip surface were founded frequently on the surface of dip slope. The mechanism and behavior could not be modelling in normally mechanical analysis although which based on external factors (such as extreme rainfall events and earthquake) and internal factors (such as joints, ground water, and the change of boundry condition slope etc.). The visco-elasticity mechanism was adopted in this study to explore the problem. Under the influence of the self-weight of the rock slope in a long time period, the slope body creeps will promote the development of multi-stage bulking deformation along the surface of the forward slope. Due to the relatively small driving force of sliding, the surface arch developed in the shear plane easily, and then the development of shallow sliding failure. In this study, the separation element method is used for numerical simulation to discuss the influence of parameters such as the elastic modulus of the slope rock layer, the stiffness of the weak surface, the thickness of the highly weathered layer, the slope length, and the distance between the weak surfaces on the shallow deformation of the slate forward slope body, and Find out the mechanism that causes deformation of the slope surface. The research results show that: There are two main deformation mechanisms for the deformation of the shallow layer of the forward slope body. The concentrated extension of the shear strain in the deep layer causes the surface arch deformation and two types of changes in the surface arch of the slope; it affects the forward slope. The main factors of the amount of deformation of the shallow layer are: the elastic modulus of the rock layer, the distance between the weak surfaces and the slope length. In the elastic modulus of the rock layer, the amount of deformation will increase with the decrease of the elastic modulus, and in the higher elastic modulus rock layer, the main mechanism of surface deformation is the concentrated extension of the deep layer shear strain to cause surface arch Deformation-based. When the distance between the weak surfaces is less than 2m, the amount of slope deformation of the slope will increase with the increase of the distance between the weak surfaces; after the distance is greater than 2m, the number of weak surfaces will decrease with the increase of the distance. Dense (0.5m, 1m spacing), the main stress is less concentrated, the shear stress will act along the interface between the weak surfaces, the shear strain concentration area will still extend from the depth to the slope, but the change value is relatively Small; the spacing of the weak surface is relatively sparse (spacing 5m), the main stress is mainly in the deep layer, and at the surface of the slope, the main stress has little effect. The change of shear strain is concentrated at the top and bottom of the slope. Regardless of the dense or sparse spacing of the weak surface, the deformation mechanism of the slope body is still due to the concentrated extension of the deep shear strain to cause the surface arch deformation and the slope There are two types of surface arch changes. When the slope length is longer, the amount of arch deformation on the slope surface is greater. On the slope length less than 100m, there is no other deformation except the buckling deformation of the slope foot. After the slope length is greater than 150m, the The trend of the principal stress and shear stress distribution in the deformation zone will be the same, both of which extend from the depth towards the slope surface, and the change in the distribution of shear strain is more obvious. There are two main types of deformations of the slope : the shear strain concentration of deep-slope causes surface camber deformation and slope surface camber deformation. This article use the concept of dynamics to define both of the primary frequency waveform and the secondary frequency waveform. The case of analysis shows a trend of deformation: one of the frequency waves should be related to the increase of gravity as the position of the slope toe; the other of secondary frequency, the formation of the slope is more regular after the slope is 50% long. Before 50% slope length, it is more irregular.

並列關鍵字

Surface deformation ； UDEC ； Creep deformation

參考文獻

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