受限背填土對主動土壓力之影響

Abstract

摘要 本研究探討受限背填土對主動土壓力之影響。本研究利用國立交通大學模型擋土牆設備來探討受限背填土作用在擋土牆上的主動土壓力。本研究以氣乾渥太華砂作為回填土，相對密度Dr = 36%，回填土高0.5公尺。為了模擬束制背填土的岩層介面，本研究設計並建造一片鋼製傾斜界面板及其支撐系統。本研究兩個重要參數為界面板與擋土牆底之水平間距b及界面板傾角□。試驗結果顯示，以空中霣降法填入土槽之背填土密度均勻，且背填土之相對密度不受界面板位置與傾角影響。當界面板遠離擋土牆(b/H = 4.0)，量測到的水平主動土壓力與Coulomb解符合良好。當b/H = 1.0，量測到的主動土壓力接近於Coulomb解，於此狀況界面板對主動土壓力沒有明顯的影響。當界面板逐漸接近擋土牆時(b/H減小)，界面板逐漸侵入主動土楔，造成主動土楔無法完全發展，且牆後填土量逐漸減少，隨著逐漸減小的水平距離b，和逐漸增大的界面板傾斜角度□，主動土壓力逐漸下降。於□□= 90°(牆面垂直)且b/H < 1.0狀況，量測到的主動土壓力小於Coulomb解，靠近牆面之垂直界面板對於主動土壓力的影響相當明顯。於b/H = 0.3、0.5、0.7及1.0，主動土壓力合力作用點的位置大約都在距牆底H/3處。當傾斜岩石介面逐漸接近擋土牆，依據Coulomb理論所求之擋土牆抗滑動之安全係數及抗傾覆之安全係數增大。

Abstract This thesis investigates the effects of constrained backfill on active earth pressure. The instrumented model retaining wall facilities at National Chiao Tung University was used to study the active earth pressure on retaining wall with constrained backfill. Loose Ottawa sand with the relative density Dr = 36% was used as backfill material. The height of backfill H was 0.5 m. To simulate an inclined rock face, a steel interface plate and its supporting system were designed and constructed. Two main parameters considered were rock face inclination angle □□and the horizontal spacing b between the rock face and the wall base. The backfill in the soil bin was prepared by air-pluviated method. Test results show the distribution relative density in the soil bin is uniform and independent of the interface plate inclination and location. With a faraway interface plate (b/H = 4.0), the measured active pressure distribution was in good agreement with Coulomb’s solution. When the vertical boundary was relatively far from the wall face, the measured stress was not strongly affected by the existence of the vertical plate. With the approaching of the interface plate (b/H ratio decreasing), the plate intruded the active soil wedge, so that the active soil wedge behind the wall can not develop fully. The active earth pressure coefficient Ka,h decreased with decreasing wall-plate spacing b. Coefficient Ka,h decreased with decreasing plate inclination angle □. For □ = 90° (vertical plate) and b/H < 1.0, the measured active pressure was less than Coulomb’s solution. Coulomb’s solution is the upper bound for all experimental Ka,h values based on different b/H ratios and □ angles. The constrained backfill would result in a greater factor of safety against sliding for the retaining wall. Under the aspect ratio b/H = 0.3, 0.5, 0.7, and 1.0, the point of application of the active soil thrust was located at about H/3 above the wall base. The evaluation of the factors of safety against sliding and overturning with Coulomb’s solution would be on safe side.