主動土壓力模型擋土牆設計與建造

Abstract

本研究探討夯實土壓力作用於垂直擋土牆上主動土壓力之影響。本研究使用重新設計建造之 NCTU KA 模型檔土牆模型設備，探討平移模式牆位移所造成之土壓力變化，根據實驗結果，得到以下結論： 1. 由夯實造成之土壤壓力，隨著牆面外移而迅速消散。達到主動土壓力所需之牆移動量S/H為 0.0010。 2. 主動土壓力分布在從牆頂往下起算牆高三分之一內，側向土壓力略高於 Coulomb 理論解，於牆高中間三分之一的範圍，與 Coulomb 理論解相近，牆底往上起算三分之一牆高內，則略低於 Coulomb 理論解。 3. 水平土壓力係數 Kh 隨著牆位移增加而下降並達到穩定。主動狀態於牆位移約 S/H 為 0.001 時發生。 4. 實驗 Ka,h 之數據，與 Coulomb及Rankine的預測相符。 5. 主動合力位置為距牆底 0.55H 處。 6. 由夯實所得之主動係數Ka,h 值，與 Coulomb 和 Rankine 的預測相符。 7. 主動土壓力所造成的破壞面，於土壤表面出現的分裂位置，則與 Rankine 之預測位置相符。

關鍵字：夯實、土壤壓力、模型測試、擋土牆、砂

This paper presents experimental data of earth pressure acting against a vertical rigid wall, which moved outward a mass of dry sand with a stress-free horizontal surface under translation wall-movement. To investigate the variation of earth pressure induced by compaction and active wall movement, the instrumented KA model retaining wall facility was designed and constructed at National Chiao Tung University. Based on experimental data, the following conclusions can be drawn. 1. The earth pressure induced by compaction vanished rapidly with the active wall movement. An active state of stress is reached at the wall movement of S/H = 0.0010. 2. The distribution of active earth pressure is slightly higher than Coulomb’s solution at the upper one-third of wall height, approximately in agreement with Coulomb’s solution in the middle one-third, and lower than Coulomb’s solution at the lower one-third of wall surface. Stresses that was locked-in the soil element has been released with the lateral extension of the active soil wedge. 3. The horizontal earth presure coefficient Kh decreases with increasing wall movement and finally a constant total thrust is reached. The active condition occurred at the wall movement of approximately S/H= 0.001. 4. The experimental Ka,h values are in good agreement with Coulomb and Rankine’s prediction. 5. The active thrust is located at about 0.55H above the base of the wall. 6. The active coefficient values obtained with compacted dense sand from this study are in fairly good agreement with Coulomb and Rankine’s prediction. 7. The Rankine theory is suitable to predict the location of surface crack for active failure.

Keywords: compaction, earth pressure, model test, retaining wall, sand