回填土密度對被動土壓力之影響

Abstract

本論文探討回填土密度對作用於垂直擋土牆被動土壓力之影響。模型試驗採用 31%，60%，與84%相對密度之渥太華砂為回填材料。本研究利用國立交通大學模型檔土牆設備研討由於平移模式牆位移所造成土壓力之變化。根據實驗結果，得到以下各項結論。當被動牆位移量達到0.14H（H=牆高）時，被動土壓力就達到一定值，無論其初始狀態為疏鬆或緊密。這是因土體內之破壞面上已大量剪力變形，達成一「臨界狀態」（Critical State）。兩種類型之土壓力可視為被動狀態。一者以「尖峰」被動土壓合力定義，另一者以大量牆位移引致「臨界狀態」被動土壓合力定義。實驗結果顯示，傳統庫侖與德在基理論明顯高估了被動土壓力。然而，若將由直接剪力實驗中所得到之臨界狀況下之內摩擦角鷯r與牆摩擦角踄r 帶入Coulomb公式中，理論值與實驗值吻合良好。大地工程師於設計檔土牆時，必須將臨界狀態之觀念加入被動土壓力之計算。

This paper presents experimental data of earth pressure acting against a veritical wall, which moved toward a mass of dry sand with different densities. Backfills with relative density of 31%, 60%, and 84% are tested. The instrumented retaining-wall facility at National Chiao Tung University was used to investigate the variation of earth pressure induced by the translational wall movement. Based on this study, the following conclusions can be drawn. As the passive wall movement S/H exceeds 0.14, the passive soil thrust reaches a constant value regardless of the initial density of the backfill. This is because at this state the soil along the failure surface has deformed significantly and reached the "critical state". Two types of earth pressure can be defined as passive. One group is defined by the peak passive thrust, and the other group is defined by the critical passive thrust. Experimental results indicate that both Coulomb and Terzaghi theories overestimated the passive soil thrust. However, if the □ and □ angles obtained from direct shear tests at its critical state are used in the Coulomb and Terzaghi solution. The theoretical solutions are found to be in very good agreement with the experimental data. It is important that the concept of critical state should be included by geotechnical engineers during the design of retaining structures.