多點分佈式TDR含水量感測器改良

Abstract

地層下非飽和土層其含水特性與邊坡穩定性有密切的關係，常因降雨雨水入滲土層造成地層下非飽和區的含水量快速增加而產生地滑問題。因此對非飽和土層進行含水特性監測有其必要性。前期研究嘗試以TDR考慮可以監測含水量與電阻率剖面的多點TDR貫入式感測器，並結合ERT的2D甚至3D電阻率分佈的探測能力，達到大範圍的含水特性監測。但前期的感測器尺寸較小且弱面較多因此在貫入土層時發生挫曲的情形，而導致感測器只有貫入至地層下30公分。為改良上述的缺失，本研究改良現有貫入式TDR感測器安裝於現地，進行淺層 (地下3米)含水量剖面監測，並建立現地導電度與含水量相關率定關係。本研究另探討可以進一步增加監測空間解析度的新型感測器評估不同的螺旋式感測器設計，利用纏繞的方式維持足夠的感應長度但縮小TDR感測器整體長度提高空間解析度，研究結果顯示雙螺旋的效果較佳，具有良好的量測靈敏度，但空間影響範圍顯著小於現有的平型式TDR貫入式感測器。

Soil water content is a critical parameter in unsaturated slopes, in which saturation due to rainfall water infiltration often causes shallow landslides. Monitoring of water content profile is important but difficult. A previous study tried to develop a multi-point TDR penetrometer to be used with 2D electrical resistivity tomography for large range of monitoring. However, the design was not robust enough and the probe buckled at the connection section. This study was aimed to improve the design of multi-point TDR penetrometer and conduct a pilot field testing to monitor water content profile within top 3 m. To explore alternative probe design for better spatial resolution, this study also investigated the feasibility of different types of spiral waveguides. The spiral waveguide can drastically shorten the penetrometer probe while maintain sufficiently long sensing length. The results show that double spiral waveguide performs well with sufficient measurement sensitivity, but the spatial influence range is significantly less than current parallel type of TDR penetrometer probe.