回填土傾角對主動土壓之影響

Abstract

本研究探討隨著回填土傾角i 的改變, 擋土牆所受主動土壓力的變化情 形. 本研究利用國立交通大學模型擋土牆設備進行試驗.回填土所用材料 為呈疏鬆狀態之氣乾渥太華砂(ASTM C-109). 剛性擋土牆以平移型式自靜 止狀態往主動方向移動, 直到回填土達主動破壞才停止. 經分析試驗結果 後, 得到以下幾點結論: 1.隨著牆主動位移量的增加, 作用在牆上的土壓 力逐漸減小, 最後達到一穩定值而不再減小. 實驗所得之水平主動土壓力 係數與Coulomb和 Terzaghi所得之主動土壓力理論符合良好. Rankine 主 動土壓力理論傾向高估主動土壓力, 尤其在回填土傾角為負值時. 2.牆移 動期間, 土壓力分佈大致上仍呈線性分佈. 不論背填土傾角為何, 主動土 壓合力作用點大致保持在距牆底0.29H~0.33H 之位置. 3.隨著回填土傾斜 角增加, 主動土壓力係數增加, 而達主動狀況所需之牆位移量也隨之增 大. 實驗結果發現當i=-20 度和i=+20 度, 達成主動狀況所需之牆位移量 分別為0.001與0.0025. 4.隨著回填土傾斜角增加, 回填土表面所觀察到 之破裂線與牆表面之間的水平距離也隨之增大. 且其值低於Coulomb, Terzaghi 和Rankine的理論值. This paper investigates the development of the earth pressure due to active translational movement of a rigid wall with various backfill inclinations. A unique model retaining wall system was constructed in the National Chiao Tung University for the study. Air-dry Ottawa silica sand (ASTM C-109) is used as backfill for the experiments. Based on the tests results, the following conclusions can be drawn: 1. The experimental horizontal active earth pressure is in good agreement with both Coulomb and Terzaghi's solutions. Rankine's solution tends to overestimate the active thrust, especially for backfills with negative sloping angles. 2. The earth pressure distributions are approximately linear at different stages of wall movement. Irrespective of the sloping angle, the points of application of total thrust remain at about 0.29H~0.33H above the wall base. 3. With the increasing sloping angle(from i=-20 degree to i=+20 degree), the wall movement required to reach the active state increases too. For the sloping angle i=-20 degree, the active wall movement required is about 0.001. However, for i=+20 degree, the active wall movement increased up to about 0.0025. 4. The experimental data show that the location of surface crack on the backfill is farther from the wall with increasing sloping angle. However, the experimental values are shorter than the ones determined with the Coulomb, Rankine and Terzaghi' s theories.