利用砂箱試驗與遲滯模式探討土壤保水曲線與沈陷特性關係之研究

Investigation of Relation between Soil Water Characteristic Curve and Consolidation by Sand Box Test and Hysteresis Modeling

柯凱元(Kai-Yuan Ke)

指導教授 ： 譚義績

國立臺灣大學/生物資源暨農學院/生物環境系統工程學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.02394

摘要

由於天然（季節變化、降雨入滲、地震）或是人為活動（灌溉、抽水、蓋建築物），皆會導致土壤體積變化，亦可說是孔隙率改變，因此研究之主題常分為兩類，第一類為由於天然或人為活動造成土壤中應力變化時，可造成土壤多少之壓密或是沈陷量，而此類研究在計算未飽和土壤之壓密或是沈陷量時，常是在保水曲線之性質為固定之情形下，去討論或計算水份變化與土壤體積變化之關係；而另外一類討論的是當土壤體積或是孔隙率變化時，可知土壤之水力性質(如飽和水力傳導係數、保水曲線)亦會受到一定程度之影響，進而去求得孔隙率變化與土壤之水力性質間的關係，卻無探討當水力性質受到孔隙率變化影響後，如何真正影響到土壤中之水份運移行為。
因此本研究的目的在於藉由砂箱實驗及數值模式以深入瞭解（土壤孔隙率變化－保水曲線遲滯現象－水份運移行為）三者之交互影響，因為本研究認為未飽和土壤中之體積或是孔隙率變化，最直接受到影響的必然是其保水曲線之行為，且更進一步會影響土壤內水份運移機制。
本研究進行保水曲線砂箱試驗，以夯實石英砂之方式瞭解孔隙率影響保水曲線變化，並得到保水曲線參數與孔隙率間之線性關係。另進行循環水位升降試驗，以控制邊界上水位之變化模擬自然界中地下水位之升降。如此一來，藉由水箱中水位之循環升降，可觀察砂箱內土壤於乾溼過程中，水份含量、土壤水份張力，及土壤體積三者之間之相互關係，同時發現土壤在排水的過程中，會有先沈陷後膨脹之趨勢。
本研究亦以遲滯模式探討土壤水份入滲曲線受到孔隙率變化之影響，而於定流量入滲數值模擬中發現，孔隙率因夯實而越低時，上邊界附近對應之含水比越高，溼鋒深度則越淺。而排水過程中，最大含水比之深度亦會隨著孔隙率之減少而變淺。此外，對於單一級配之石英砂而言，不論在溼潤或排水過程中，溼鋒發生的深度永遠是高孔隙率之土壤較深。
另外驗証循環水位升降砂箱試驗之土壤水份變化，試驗及模式驗証結果顯示，循環水位升降試驗將造成土壤之保水曲線性質及孔隙率之明顯改變，表示在水位升降之同時，含水比及水份張力之變化並非是單純由遲滯現象造成，而需同時考量孔隙率對保水曲線之影響。

關鍵字

壓密 ； 砂箱實驗 ； 遲滯現象 ； 孔隙率

並列摘要

The soil volumn (or the porosity) would change with respect to natural event such as seasonal variation, precipitation, earthquake, or human activities, such as irrigation, pumping, and structure building. Two kinds of previous studies on this field:(1) the consolidation or compaction due to stress changed in the soil by natural enents or human activities, while the the water retention curve(WRC) is considered to have fixed parameters; (2) the relation between the change of porosity and hydraulic parameters of soil, because the hydraulic properties, such as the saturated hydraulic conductivity or parameters of water retention curve, of the soil must be somewhat changed due to the change in soil volume or porosity. But this kind of research barely discussed the soil water movement with respect to the change of hydraulic parameters.
The purpose of this study is to find out the interactive mechanism between change of porosity, hysteresis and soil water movement. This research considers that the change of volumn or porosity in the unsaturated soil will directly influence the behavior of the water retention curve, and thus the mechanism of soil water movement.
This study finds out the linear relation between the WRC parameters and the porosity of quartz sand with a WRC sand box test. Besides, a recycling water level sand box test is also conducted to study the interactive relation of water content, soil water tension and soil volumn by controlling the boundary condition to similuate the groundwater change. In the mean time, a consolidation process followed by a swelling process is found during drainage.
In the infiltration simulation, while the porosity becomes smaller due to compaction, higher water content appears near the top boundary, and the wetting front depth decreases with the porosity. When top boundary flux is set to zero, the depth of the highest water content decreases with porosity. Besides, no matter the top boundary is zero flux or non-zero flux, the deepest wetting front always occurs in the soil with the highest porosity.
In addition, the result of the recycling water level sand box test is verified with a hysteresis model. The results show that the repeated water level change will lead to the change of property of water retention curve and soil consolidation, indicating that the change of water content and soil water tension is caused by hysteresis, as well as change of porosity.

並列關鍵字

consolidation ； sand box test ； hysteresis ； porosity

參考文獻

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