碾壓土壤剪力波速之行為探討

Abstract

土壤夯實品質對於土壤填方之土壩、土堤及擋土結構等工程之施工品質影響甚鉅，因此土壤夯實之檢測技術顯得重要不得輕忽，為發展新興之結合剪力波速與時域反射法(Time Domain Reflecmetry, TDR)之碾壓土壤檢測技術，首要釐清碾壓土壤剪力波速之行為以評估其可行性。 本研究以彎曲元件(Bender Element)法進行土壤之剪力波速量測，試驗內容主要分成夯實土壤組構影響以及含水量與乾密度之影響兩部份，在夯實土壤組構影響上，透過在乾濕側夯實，控制相同乾密度、相同土壤以及相同量測含水量下，進行剪力波速量測，以探討乾濕側夯實造成之土壤組構對於剪力波速之影響；而在含水量與乾密度之影響試驗上，透過不同夯實含水量下夯實試體之量測含水量調整，探討在不同乾密度以及含水量下剪力波速之行為。試驗結果顯示，同一種土壤中土壤組構達到足夠差異時確實會影響剪力波速的行為；此外，含水量及乾密度對剪力波速影響之試驗結果顯示，在飽和度40%~90%之間剪力波速與飽和度呈線性之關係，因所探討之土壤為碾壓土壤，故此飽和度範圍內之線性關係足以適用，最後以所得之結果驗證Fratta et al.(2005)之半理論模型也適用於本研究所使用之寶二土與湖山土，但由於該模型過於複雜，且剪力波速與量測含水量關係顯示剪力波速對應到之乾密度並無唯一解，因此現地應用上還需再調整含水量以求解，並不利於現地應用。 故本研究以另一角度出發，從剪力波速對新鮮碾壓土壤飽和度之關係中發現一個一對一之函數(V_s=a_s+b_s×S^m, 3.7式)，並於現地應用架構上提出一初步應用之建議，利用該式於室內標定之結果，於現地透過表面波震測法結合TDR含水量量測，以達到無需取土便可快速進行土壤碾壓品管檢核之目標。

Quality control of compacted soils is important in earth dam, levee, retaining wall backfill...etc. To develope a new measurement technique incorporating both electromagnetic wave based on Time domain reflecmetry(TDR) and Shear wave velocity, it is necessary to first figure out the behavior of Shear wave velocity in compacted soils. In order to measure shear wave velocity of compacted soils, bender element(BE) method is performed in laboratory, and the purpose of experiment were divided into two parts: investigating the influence soil fabric on shear wave velocity of compacted soil, and to figure out the relationship between soil phase parameters and shear wave velocity. Experimental results show that soil fabric of fine soils does affect the behavior of shear wave velocity in compacted soils under the same dry density and water content, and the shear wave velocity of the compacted soil has a linear relationship with the degree of saturation if it is between 40%~90%, the semi-theoretical model( Fratta et al. 2005) was successfully applied to analyze the data. However, it requires varying the water content to be able to measure water content and dry density in the field. Alternatively, an empirical formula ( V_s=a_s+b_s×S^m) was found to well describe the shear wave velocity in terms of degree of saturation of freshly-compacted soil. Through this function, a method combined with surface wave testing and TDR technology was proposed. Preliminary laboratory results show that the proposed method can achieve 3% accuracy in dry density and 1% accuracy in water content.