非飽和土壤多點式基質吸力分佈量測

Abstract

現有量測現地非飽和土壤基質吸力(負的孔隙水壓)方法可分為直接法與間接法，直接法最常用的是張力計，可直接量測土壤基質吸力；間接法包含熱導感測器。雖然量測範圍較大可達1500kPa以及可進行長時間監測，但其精度較低、材質易老化、易受溫度影響以及使用前必須在實驗室將溫度對基質吸力之關係進行標定。雖然有高吸力的張力計最高可量測1500kPa，但因水的氣穴效應在高吸力情況下量測時間較短，設計上無法使張力計在同一鑽孔內做不同深度的量測以及。本研究目的為利用張力計能快速達到吸力平衡、成本較低以及操作方便等優點，結合BAT sampler之設計概念，研發一個能直接貫入土層並且能在同一鑽孔內進行土壤基質吸力分佈量測之多點式張力計。本研究配合自製應力控制壓力板試驗儀(一維壓縮)對不同深度土壤薄管試體並進行試驗，將室內之應力控制土壤水分特性曲線以及現地使用多點式張力計量測之結果進行比較對照。

The measurement of maritc suction (negative pore water pressure) in unsaturated soil can generally be divided into direct and indirect methods. The most popular diect method is tensiometer. The indirect method can include the thermal conductivity sensor. Athough capable of measure matric suction up to 1500kPa for extended amount of time, it lacks sensitivity and tends to deteriate, affected by temperature and requires a laboratory calibration prior to field application. It is possible to use tensiometer for measuring matric suction as high as 1500kPa. Due to cavitation, the measurement time is short under high suction. Also, in most cases, it is not possible to insert multiple sensors in the same borehole location. The aim of this research is to develop a penetrometion type tensiometer that can measure matric suction at multiple depths in the same borehole. Using the concept of BAT sampler, the penetrometer/tensiometer has the advantage of low cost, easy to operate and reach equilibrium with the surrounding soil quickly. Concurrent with the development of the penetrometer/tensiometer, the author fabricated a stress constrolled pressure plate device to obtain the 1D stress dependent soil water characteristic curve (SDSWCC) for tube soil samples taken from the field. The SDSWCC obtained from field measurements using the new penetrometer/tensiometer and laboratory tests were then compared.