現地夯實土壤之電阻率

Abstract

近年來各種土壤性質的檢測方式不斷進步，在夯實土壤的含水比和乾密度檢測，從以往費時耗力的取樣烘乾和現地砂錐法試驗，進步到目前利用核子密度儀等設備來快速檢測出結果。此外，在電學方面的進步，也從以往單純的利用地電阻量測取得地層的相關資訊，到目前可以利用同軸電纜的時域反射法(TDR)來檢測不同的土壤性質。本研究試圖利用土壤電阻率對照現地土壤夯實的狀況與所具有之物理性質，來瞭解夯實土壤的工程特性與地電阻之間的關聯性。 由於土方夯實工程所採用的施工檢測往往具有時效性，檢測結果愈快得知，則施工單位可以進行下一層土方之夯實。然而，一般檢測之夯實土壤含水比與乾密度，僅代表土壤之夯實度，卻無法完全充分反映與土壤結構相關之其他工程性質，諸如剪力強度、壓縮性、導水度。因此，若能夠透過地電阻的量測來幫助施工單位確定除了最重要的工程性質符合需求，遠較單純的量測含水比與乾密度還要有價值。若能建立有意義的關聯性，相信可以在面對複雜的土壤組成、或不同的含水量及土壤的孔隙情形時，利用地電阻的調查資料，對量化土壤的工程性質。對現地施工檢驗與工程效果評估提供一更快速有效的方法，除可節省檢測時間和經費之外，更可大幅縮短整體施工時程。 本研究藉由在寶山第二水庫工地之輾壓試驗場進行現地電阻量測之外，並配合實驗室內之夯實土壤利用電阻量測儀和TDR設備行電阻量測。之後將電阻量測結果與夯實土壤之工程性質，做一系列的分析，以瞭解夯實土壤性質對電阻率的影響。在這些工程性質中，本研究選擇夯實土壤之飽和度、孔隙率、以及導水度做為主要的分析對象。 本研究的結果顯示以下結論：現地量測出之夯實土壤電阻隨著飽和度的增加，有明顯的降低情形；但隨著孔隙比的增加，現地夯實土壤之電阻率有漸增的情況。針對不同於夯實方向的電阻率來比較，可發現在同一種夯實厚度與夯實次數下，平行於夯實方向的電阻率明顯大於其他方向的電阻率。此外，在導水度與地電阻的關聯性分析顯示，由於控制現地與試驗室內導水度的量測是在土壤試體接近飽和的狀況下進行，且孔隙率並非決定土壤導水度之唯一因素，因此，透過地電阻之量測並無法準確地推估夯實土壤之導水度。

The quality control of construction of earth structures such as earth dams and clay liners requires a huge number of field tests to determine the water content and the dry density of compacted soil. In the past, standard procedures such as the sand cone method had been used to measure field density, while on the other hand, soil samples had to be oven dried to determine the field water content. However, recent development in the non-destructive testing technology has enable the engineers to shorten the testing periods with devices such as the nuclear density gauge. In addition, the methods based on measurement of soil resistivity and other electrical properties have evolved as promising tools for probing a much wider range of engineering properties of soils. In most cases, the modification or enhancement of these engineering properties instead of increasing the dry density is the major purpose of compaction. In this study, the electrical resistivity of soils of the test pads built for the Second Bao Shan Dam was measured in the field. In addition, the same soils were taken back to the laboratory and compacted for determination of electrical resistivity. The resistivity of the laboratory compacted samples was also measured with TDR for comparison. The results of resistivity measurements were used to correlate with the physical and engineering properties of compacted soils such as degree of saturation, void ratio, and hydraulic conductivity. The conclusions of this study will be reported as follows: While testing electric resistivity of compacted soils in the field, the higher degree of saturation, the lower resistivity; resistivity increases as the voild ratio increases; in accordance with those different compacted direction of resistivity, under the same compacted thickness and frequency, resistivity of parallel compacted direction will clearly greater than other directions. Moreover, the results were used to correlate with the hydraulic conductivity and resistuvuty show the measured controlling of hydraulic conductivity on the field and laboratory is proceed under near-saturated soil sample condition , and void is not only factor to decide the hydraulic conductivity, so, the measurement by way of electrical resistivity is not correctly to calculate the hydraulic conductivity of campacted soils