張力裂縫對邊坡滑動面分佈之影響研究

當岩土邊坡發生不穩定時，常於坡頂產生鉛直張力裂縫，使剪力滑動破壞面轉而沿此張力裂縫向地表發展，而使剪力面縮短，導致邊坡整體安全係數之下降。通常張力裂縫易發生於具有凝聚力的岩土材料，在邊坡滑動變位過程中，當坡體內應力超過岩土材料之抗張強度，則產生張力裂縫，當邊坡出現張力裂縫時，可視為邊坡不穩定的預警。本研究利用SLIDE程式模擬邊坡在不同坡度β、凝聚力C及摩擦角ψ，在臨界破壞時之張力裂縫深度Zc、退縮距b及潛在滑動面特性等關係，並透過SPSS分析β、C及ψ三因子影響之權重。再透過FLAC/Slope分析邊坡張力區分佈與SLIDE分析結果比較，也透過離心機模擬實驗結果之驗證。結果得致主要結論：(1) 張力裂縫發生在距坡趾b’=0.4H~2H之間、Zc介於0.05H~0.6H之間。相同坡度β下，越小則Zc越深、退縮距離b’越遠，邊坡滑動量體越大；相同摩擦角下，β越大則Zc越深、退縮距b’越近坡趾。(2)同張力裂縫深度Zc＝3m下，裂縫位置隨著坡度β越大越靠近坡趾。緩坡β=30 o在距坡趾後方b’/H=1.9處、陡坡β=80 o在b’ / H=0.6處，而β=60 o發生在兩者之間(b’/H=0.88)，都是邊坡穩定FS值最低處。(3) 經SPSS分析知坡度β、凝聚力C及摩擦角三因子影響張力裂縫深度之權重比例約為C:ψ:β＝2.5 :1.1 :1 都成正比關係，C為主控因子；對退縮距之權重約為C:ψ:β=1: -2 :1，ψ為主控因子，唯與退縮距成反比關係。(4) 在緩坡β=30 o，有無張力裂縫之滑出端位置均易發生於「坡底、坡趾」；在陡坡β=80 o易發生在「坡面」(坡趾上方0.04H∼0.2H)；在坡度β=60 o時，無張力裂縫時滑出端易發生在「坡趾、坡面」，而有張力裂縫時發生在「坡面」(坡趾上方0.05H∼0.08H)。(5) 臨近臨界破壞前，有張力裂縫產生時，在上坡面之潛在滑動面較集中、在坡面可能形成潛在滑出端較多。(6) 在有無張力裂縫情況下，相異處：坡度β=30、60度在滑動面上、下端正應力最小抗剪強度最低；但陡坡90度時在滑動面上端之正應力值最小，最先發生破壞處，相同處：無張力裂縫滑動面上端還有抗張強度。(7) 張力裂縫內之積水高度在50%以下，對邊坡穩定FS下降幅度不多；但當積水超過50%時，對陡坡(β=70、80)的FS會急速下降，表示張力裂縫內的積水對陡坡影響較大。(8) SLIDE分析所得之張力裂縫深度與FLAC/Slope分析之張應力區與剪應力區轉換處ㄧ致(Zc=0.17H∼0.57H)；退縮距也位於轉換處向上坡面的位置(b=0.26H∼0.48H)。

關鍵字

邊坡滑動面；張力裂縫深度；退縮距； SLIDE ；滑出端

並列摘要

Happen when the slope is unstable, often produce vertical tension cracks that destroy the surface tension cracks along the surface development, so that the slope safety factor decreased. And the tensile cracks easily occur in a cohesive material, the sliding slope when the internal stress exceeds the tensile strength of the material, the occurrence of cracks in the tension. This study analyzes the use of different slope angles SLIDE β, cohesion C and friction angle ψ, tension crack depth at FS = 1:00, the crack location. Then use SPSS proportion β, C, ψ three-factor analysis and make FLAC / Slope analysis of slope tension zone distribution. Simulation results are also verified through a centrifuge. Conclusions: (1) Happen tension cracks from the slope of the toe position b 'between 0.4H ~ 2H, Zc between 0.05H ~ 0.6H. At the same slope β, β smaller the distance Zc deeper cracks and b 'farther away, the greater the slope of the sliding body block. (2) at the same depth, crack location as close to the slope the greater the slope toe. β = 30 in the toe of the slope behind b '/ H = 1.9, steep β = 80 in b' / H = 0.6, β = 60 in b '/ H = 0.88, slope stability FS values are the lowest. (3) SPSS analysis of β, C and ψ tension crack depth of influence weight ratio of about C : ψ: β = 2.5: 1.1: 1, C is the master factor; flinch from the right to the weight of about C : ψ: β = 1: -2:1, is the master factor. (4) In the gentle slope β = 30, slide the end position of the presence or absence of tension cracks are likely to occur in "its base and toe"; β = 80 in the steep slopes prone on the surface; When the slope β = 60, no tension cracks happen "toe and the surface," and when there is tension cracks happen "surface".(5) Before approaching critical failure, there is tension cracks in the slope of the sliding surface potential more focused, but also in a potential slide slope may end more. (6) Tension fracture height within 50% of water, more than affecting FS decreased; However, when more than 50% water, the steep slope (β = 70,80) of FS will rapidly decrease, which means the maximum tension of water on steep cracks.

並列關鍵字

Slope Slip Surface ； Tension Crack Depth ； Crack Location ； SLIDE ； Slide the End

參考文獻

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3.呂偉哲 (2011)，「由顆粒間微觀鍵結破壞探討邊坡張力裂縫發展及塊體運動行為」，碩士論文，台灣大學土木工程系，台北。

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張力裂縫對邊坡滑動面分佈之影響研究

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