土層瞬間飽和上揚力效應之初步研究

A Study on Uplifted Effect of Instantaneous Saturated Soil

林芳慈(Lin-Fang-Zte)

Advisor ： 陳彥璋 ； 張守陽

國立臺北科技大學/工程學院/土木與防災研究所/碩士(2007年)

https://doi.org/10.6841/NTUT.2007.00388

Abstracts

暴雨形成之地表水經入滲土壤後，造成表土層內部孔隙水壓增加，當整層土壤瞬間飽和時，其所產生之上揚力效應，可能導致邊坡淺層破壞。本研究探討土層瞬間飽和所造成之上揚力效應，應用理查氏方程式理論基礎，以數值模式及室內實驗模擬圓柱型砂柱實驗之瞬間飽和現象，以驗證土層瞬間飽和之上揚力效應。 數值模式中應用理查氏方程式在不考慮逕流下，假設空氣可從側邊排出，進行單層土體一維數值模擬，模擬濕峰在未飽和土層運移之過程及土層中孔隙水壓變化。本研究以火炎山現場土壤，進行圓型砂柱土層瞬間飽和之室內實驗，藉由不同高度之張力計及測壓管顯現上揚力效應。以向上滲流力及水錘效應力類比解釋上揚力現象，並概估瞬間飽和現象所產生之上揚力，其值低於8N/cm2。並一指數函數求算上揚力上升曲線特性，其反應時間k約為11. 3分鐘。 由數值模擬與室內瞬間飽和實驗結果得知，二者之瞬間飽和現象趨勢接近大致相同。希冀藉本實驗現象之土層瞬間飽和現象，提供未來邊坡淺層破壞及土石流發生機制之應用參考。

Keywords

理查氏方程式 ； 未飽和地下水模式 ； 孔隙水壓 ； 未飽和土層 ； 瞬間飽和。

Parallel abstracts

The infiltration of the surface runoff increases the pore water pressure, which causes the failure of the shallow-layer slopes. The uplift force due to the instantaneous saturated soil may be an extra force cause the slope failure. A series of experiments conducted with soil column will verify the effect of uplift force when the soil is saturated instantaneously. Moreover, a 1-D variably saturated numerical model for groundwater flow based on the Richard’s equation is applied to simulate the saturated process of a soil layer. The numerical results are also to compared with the experimental data. The two practices prove the appearance of uplift force effect.
In this study, the 1-D variably saturated numerical model is performed without runoff and air. In the meantime, the soil of Huo-Yan Mountain filled in the soil column is also to simulate the phenomena of instantaneous saturation. Three tensiometers and piezometric tubes installed at three various depths respectively show the phenomenon of uplift force. By using the theories of Seepage Forces and Water Hammer can analogically explain the appearance of uplift force and estimate the approximate uplift force. The force calculated in this study is lower than 8N/cm2. Finally, an exponential function is applied to set up the response time of the uplift force process. The response time is around 11.3 minutes.
This research concludes that under the circumstance of instantaneous saturation, Both the 1-D variably saturated numerical model for groundwater flow and the experiments with soil column are with same tendency and results. The study of uplift forces caused by instantaneous saturation is hopefully referred to future researches of shallow-layer slopes failure.

Parallel keywords

Richard’s equation ； 1-D variably saturated numerical model ； pore water pressure ； unsaturated soil ； instantaneous saturation

References

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