擋土牆背側存在堅硬岩層對主動土壓力之影響

Abstract

本論文探討擋土牆背側存堅硬岩層對主動土壓力之影響。本研究以渥太華砂作為回填土，回填土高0.5公尺。量測於鬆砂 (Dr = 35%) 狀態下作用於剛性擋土牆的側向土壓力。本研究利用國立交通大學模型擋土牆設備來探討堅硬介面以不同界面傾角□及距擋土牆不同距離b，侵入回填土對擋土牆主動土壓力影響。為了模擬堅硬的岩層介面，本研究使用一片鋼製傾斜介面板，及其支撐系統。本研究共執行三種距牆距離 b = 0、50 mm、100 mm，五種堅硬界面傾角 □ = 0o、50o、60o、70o、80o、90o等多組實驗。依模型擋土牆試驗結果，獲得以下結論： 1、當模擬無岩石介面傾角存在時 (□ = 0)，主動土壓力係數 Ka,h 與 Coulomb 解相符合，而主動合力作用點位置大約作用於擋土牆底0.333H處，與理論值吻合。 2、當模擬岩石介面傾角 □□越大，受界面板的影響越大，所造成主動土壓力合力□Ka,h 越小；在相同角度，岩石介面距擋土牆距離越近 (b越小)，則所受岩石介面的影響越大，主動土壓力合力 Ka,h 也越小。 3、主動土壓力合力 Ka,h 隨介面傾角越大、或距離牆距離越小而逐漸變小，其合力作用點位置則會漸漸高於理論值0.333H。 4、當傾角等於90度時 (擋土牆與介面板相互平行)，主動土壓力係數隨著深度增加而減少，而Coulomb、Rankine理論值的預估則過於保守。 5、當傾斜岩石介面入侵到主動土楔時，造成擋土牆抗滑動之安全係數增加，因此根據Coulomb理論所求解的安全係數會偏向安全。 6、當傾斜岩石介面入侵到主動土楔時，也會造成擋土牆抗傾覆之安全係數增加，因此根據Coulomb理論所求解的安全係數也會偏向安全。

In this paper, the active earth pressure on retaining walls near an inclined rock face into backfill for loose sand is studied. The instrumented model retaining wall facilities at National Chiao Tung University was used to investigate the active earth pressure induced by different interface inclination angles □ and spacing b□ The loose Ottawa silica sand was used as backfill material. To simulate an inclined rock face, a steel interface plate and its supporting system were used. The main parameters considered for this study were the rock face inclination angles □ = 0°, 50°, 60°, 70°, 80°, 90°and the horizontal spacing b = 0, 50 mm, 100 mm. Base on the test results, the following conclusions can be drawn: 1.Without the interface plate (□□= 0o), the active earth pressure coefficient Ka,h is in good agreement with Coulomb’s solution. The point of application h/H of the active soil thrust is located at about 0.333 H above the base of the wall. 2.With the approaching of the interface plate, the soil mass behind the wall decreased, the active earth pressure coefficient Ka,h decreased with increasing stiff interface inclination angle □□or decreasing spacing b. 3.As the interface angle □ increased or spacing b decreased (the rock face approached the wall face), the inclined rock face intruded the active soil wedge, the earth pressure decreased near the base of the wall. This change of earth pressure distribution caused the active thrust to rise to a slightly higher location. 4.For □□= 90° (parallel vertical walls), the lateral pressure coefficient was not a constant with depth as assumed by Coulomb and Rankine. The pressure coefficient decreased with depth. It is obvious that, the evaluation of □h with Coulomb’s and Rankine’s theory would be on the safe side. 5.For all b = 0, b = 0.1H, and b = 0.2H, the horizontal component of active soil thrust Pa,h would decrease with increasing □ angle. The intrusion of the inclined rock face would actually increase the FS against sliding of the wall. The evaluation of FS against sliding with Coulomb’s theory would be on the safe side. 6.For all b = 0, 0.1H, 0.2H, the normalized driving moment would decrease with increasing □□angle. The intrusion of an inclined rock face into the active soil wedge would increase the F.S. against overturning of the retaining wall. The evaluation of F.S. against overturning with Coulomb’s theory would also be safe.