本文介紹使用時域反射儀(TDR)於大地工程上的應用，其原理是利用電磁波進入不同介質環境下，造成傳遞時間不同，藉此量得土壤的視介電常數值(εa)，並透過回歸分析建立與體積含水量(θ)之間關係。此外，回歸分析式加入土壤密度的探討，在工程上更具應用價值。 運用時域反射儀在不需置換端頭情況下，能同時量測得土壤的視介電常數以及導電度(EC)。TDR所預估的含水量會受到土壤的細料含量與鹽性影響，進而造成量測值高估。而導電度則為影響TDR量測土壤之視介電常數的主要因素，文中分別從理論與實驗中探討導電性對於土壤影響。 在結果方面，TDR預估含水量值方面有兩點顯示，首先，探討土壤的細料含量以及孔隙水的導電度將會造成TDR偵測到訊息的減弱；第二，具有高含水量與細料含量雙重影響下，將導致量測失其準確性。若能充分了解導電度對預估含水量的影響，有利於對於TDR量測的掌握，並且此將成為具有潛力的量測技術。 在應用方面，利用TDR系統監測並探討地下水位與海水入侵地下水所造成的土層電學性質改變，有助於發展TDR監測廢料處置場地下水及海水入侵等狀況。 Time Domain reflectometry (TDR) evaluates the apparent dielectric constant, εa, of soil by measuring the travel time of an electromagnetic pulse through a sensor. Correlations between the apparent dielectric constant, εa, and the volumetric water content (θ) of soils can be established by regression. A TDR probe is capable of measuring the dielectric constant and electrical conductivity (EC) of soil simultaneously. Overestimate of the water content can occur to soils with high fines content and/or salinity, which exhibit high conductivity level that affects the estimate of moisture by TDR. Further, the electrical conductivity is a main factor affecting the apparent dielectric constant determined by TDR. This influence is investigated theoretically and experimentally. There are two points for attention of measuring content water. First, the reflection of TDR becomes much reduced in soils with high fines content and high pore water conductivity, thus affects the precision in moisture determination. Therefore, a detailed evaluation of the EC on TDR measurements is required, in order to exploit the full potential of the promising TDR technique. By using soils with varying fines contents and pore water with varying concentrations in electrolyte, this study presents information in these regards. In application aspect, utilizing the electrical responses of the TDR to monitor the groundwater level and saline water intrusion will benefit the development of the monitoring system at waste disposal sites.
