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研究生：	陳建泰 Chen, Chien-Tai
論文名稱：	連續落水頭雙環入滲試驗之理論推導及應用 Analysis and application of the theory for multi-step falling-head double-ring test
指導教授：	徐國錦 Hsu, Kuo-Chin
學位類別：	碩士 Master
系所名稱：	工學院 - 資源工程學系 Department of Resources Engineering
論文出版年：	2004
畢業學年度：	92
語文別：	英文
論文頁數：	73
中文關鍵詞：	等量潮濕鋒到達時間、連續落水頭雙環入滲試驗
外文關鍵詞：	effective arrival time of the wetting front, multi-step falling-head double-ring test
相關次數：	點閱：99 下載：1
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　　雙環入滲試驗為求取現地土壤水力性質之重要試驗方法，其可區分為定水頭與落水頭二種方式。針對坡地水源有限、土壤表層通透性佳等不利於傳統定水頭雙環入滲試驗之因素，本研究以Philip單次落水頭試驗理論為基礎，推導連續落水頭雙環入滲理論，其理論假設入滲產生之潮濕鋒為階梯函數；但實際上受到土壤擴散效應影響，此假設隨入滲深度之增加與實際情況愈不相等。因此，土壤含水量剖面潮濕鋒到達時間點之決定，乃以Hydrus-2D數值模擬軟體模擬連續落水頭入滲試驗推求之。由清水溪流域草嶺試驗區之現地應用結果顯示，模式計算之水力傳導係數值與現地採樣之室內定水頭試驗水力傳導係數值相近；且模式所得各階段平均水力傳導係數值由上層至下層呈現出遞減之現象，此與現地實際觀測到土壤分佈的情形亦符合一致。與傳統落雙環入滲試驗比較，本研究發展之模式可使用於高傳導係數之場址且可量得不同深度之不擾動土壤水力傳導係數。

　　The double-ring test is one of the most important methods to estimate soil characters in situ. The test can be performed by either constant pressure head or falling pressure head. Constant-head double-ring test is commonly used but not suitable for highly permeable materials due to the fast dissipation of water. To overcome the limitations of the constant-head double-ring test, a novel method named as multi-step falling-head double-ring test was developed. The new method is based on Philip’s single-step falling-head theory. The proposed method is especially useful in measuring the field saturated hydraulic conductivities at different depths and suitable for sites with high permeability or macropores. HYDRUS-2D software is used to simulate multi-step falling-head infiltration tests. The effective arrival time of wetting front is determined based on the numerical results. The mid-time of the variation of potential head is found to be a good approximation to estimate the effective arrival time. By applying the new method to a hill slope site of Tsaoling in the Cingshui-river basin, the result shows that hydraulic conductivities obtained from the new method are very close to the values of core samples obtained by the constant-head test in laboratory. Obtained average hydraulic conductivity decreasing with soil depth is consistent with the soil distribution observed in field. The new method has been shown to be efficient and economic to measure undisturbed hydraulic conductivities at different depths.

Content
Abstract ...................................................................Ⅰ
Acknowledgement ............................................................Ⅲ
Content ....................................................................Ⅳ
List of Tables .............................................................Ⅵ
List of Figures ............................................................Ⅶ
Notation ...................................................................Ⅸ
	
Chapter 1 Introduction ......................................................1
1.1 Research motivation and purposes ........................................1
1.2 Literature review .......................................................2
	
Chapter 2 Theory of models ..................................................7
2.1 Green and Ampt model ....................................................7
2.2 Philip’s single-step falling-head model ................................9
2.3 The multi-step falling-head model ......................................11
	
Chapter 3 Sensitivity analysis and model comparison ........................15
3.1 Sensitivity analysis of hydraulic conductivity .........................16
3.2 Sensitivity analysis of the potential head before wetting front ........17
3.3 Sensitivity analysis of initial water content ..........................18
3.4 Comparison of multi-step falling-head and constant-head model ..........19
	
Chapter 4 Determination of wetting front arrival time ......................21
4.1 Introduction of HYDRUS-2D ..............................................21
4.1.1 The HYDRUS-2D Model ..................................................22
4.1.2 User Interface .......................................................25
4.1.3 Automatic Mesh Generation ............................................25
4.1.4 Post-Processing ......................................................26
4.2 Setting of numerical model .............................................26
4.2.1 Concepts of soil water potential .....................................27
4.2.2 Initial conditions ...................................................28
4.2.3 Boundary conditions ..................................................29
4.3 Results of the numerical model .........................................31
4.4 Determining the effective arrival time of wetting front ................43
	
Chapter 5 Application of the multi-step falling-head model .................49
5.1 Study area .............................................................49
5.2 Results of model application ...........................................51
5.2.1 Double-ring test installation ........................................51
5.2.2 Soil sampling in situ ................................................52
5.2.3 Laboratory results for soil parameters ...............................53
5.2.4 Results of the multi-step falling-head double-ring test ..............56
5.2.5 Arrival time of wetting front for tensiometer readings ...............57
5.3 Discussion .............................................................60
	
Chapter 6 Conclusions and recommendations ..................................62
6.1 Conclusions ............................................................62
6.2 Recommendations ........................................................63
	
References .................................................................64
	
Appendices .................................................................68
Appendix A  Derivation of Equation (2.6) ...................................69
Appendix B  Derivation of Equation (2.18) ..................................71

                                    

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校外：2004-06-29公開

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