回填土密度對主動土壓力的影響

Abstract

本論文探討回填土密度對作用於擋土牆主動土壓力之影響。本研究利用國立交通大學模型擋土牆設備探討平移模式牆位移所造成土壓力之變化。試驗採用35%、63%與85%相對密度之渥太華砂為回填材料。根據實驗結果，獲得以下各項結論。 1. 以空中霣降法所製作之土體，其靜止土壓力係數Ko隨著密度增加而減少。若與Jaky建議的公式相較，除了鬆砂之外，Jaky建議的公式均高估Ko值。 2. 以夯實法所製作之土體，其靜止土壓力係數Ko隨著密度增加而增加，實驗結果與Sherif 等 (1982) 建議的公式頗為吻合。 3. 主動土壓力係數Ka,h隨著內摩擦角φ的增加而減少，此趨勢與Coulomb理論之計算結果一致。 4. Coulomb理論能合理的估計鬆砂之Ka,h值。但隨著土壤內摩擦角的增高，Coulomb計算值與實驗值的差距逐漸加大。以夯實法製作之緊砂試體，實驗所得到之Ka,h值約比Coulomb計算值低35%。 5. 以空中霣降法製作之土體，實驗所得緊砂之Ka,h值約比Coulomb值低50%。Coulomb理論並不適用於推估空中霣降法所製作之中等緊密砂與緊砂之Ka,h值。 6. 達到主動狀態所需之牆位移 (S/H)a 隨著φ角的增加而減少。緊砂試體之(S/H)a約為0.0005~0.001，中等緊密砂之(S/H)a約為0.0005~0.0015，鬆砂之(S/H)a約為0.0015~0.0025。

This paper presents experimental data of earth pressure acting against a vertical rigid wall, which moved away from a mass of dry sand. Ottawa sand is prepared at relative densities of 35%, 63%, and 85%, with the compaction method and air-pluviation method. The instrumented retaining-wall 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. 1. For soil placed with the air-pluviation method, the coefficient of earth pressures at-rest Ko decreases with increasing soil density. As comparing with the well-known Jaky solution, Ko values have been overestimated by the Jaky formula except the loose sand. 2. The Ko coefficient of compacted backfill increases with increasing soil density. The test data are in good agreements with the equation recommended by Sherif et al. (1982). 3. The active coefficient Ka,h decreases with increasing angle. This trend coincides with the result calculated with Coulomb theory. 4. The Coulomb theory can provide a reasonable estimation of Ka,h for loose sand. However, the discrepancy between the Coulomb and experimental values become greater with increasing φ angle. For compacted backfill, the experimental Ka,h values for dense sand are approximately 35% less than Coulomb’s solution. 5. For air-pluviated backfill, the experimental Ka,h coefficient for dense sand about 50% less than Coulomb’s solution. The Coulomb theory may not be a suitable method to estimate the Ka,h value of the medium dense and dense backfill, prepared with air-pluviation method. 6. The wall movement needed to reach active condition (S/H)a decreases with increasing φ angle. For dense sand, the required (S/H)a is about 0.0005~0.001. For medium dense sand, the (S/H)a needed is about 0.0005~0.0015. For loose sand, the (S/H)a required is about 0.0015~0.0025.