夯實土壤異向性行為室內試驗探討

Abstract

為提升碾壓土壤品質檢測的效率，近年來有各種應用物理量量測之非核子式檢測技術發展。柳儒錚(2010)將剪力波應用於碾壓土壤檢測，發現採用表面波震測量測所得之現地剪力波速與飽和度之關係與實驗室標定之結果存有差異，不同的夯實能量與碾壓方法皆可能是造成誤差之原因，另外，碾壓土壤之異向性亦可能為誤差原因之一。碾壓土壤之異向性程度與可能造成的波速影響程度皆不清楚，因此，本研究將透過室內試驗的方式對夯實土壤之異向性行為進行探討。本研究建立壓縮波速與剪力波速室內量測系統，以Bender-extender element進行夯實土壤之波速量測，藉由不同量測角度之波速來探討夯實土壤之彈性波速行為與異向性程度。由試驗結果顯示，在夯實曲線乾側，當含水量(或飽和度)逐漸降低時，垂直於橫向等向面的剪力波速會有升高、降低再提升之情形；在夯實曲線溼側，各量測方向之壓縮波速與剪力波速則會明顯下降，顯示波速受含水量(或飽和度)之影響甚大。以波速求得異向性因子來探討夯實湖山砂土之異向性程度，可觀察到當含水量接近或大於最佳含水量時，隨含水量之上升，夯實土壤試體之異向性越加明顯。

In order to increase the efficiency of quality control and assurance, several non-nuclear testing technologies have been under development in recent years. Liu (2010) applied shear wave velocity measurement for such a purpose. However, his results show that there is a significant difference between the shear wave velocities obtained in-situ by the multichannel analysis of surface wave and that obtained from bender element system in the laboratory. Compaction energy and compaction techniques may play roles in the difference. The anisotropy of the compacted soil is probably another one. However, the degree of anisotropy in compacted soil and the effect of anisotropy on wave velocities are not known. Thus, the aim of this study is to investigate the anisotropic behavior of compacted soil by laboratory experiments. A bender-extender element system was established to measure both the compression and shear wave velocity in compacted soils. Several details on assembling of the testing system were discussed and optimized. A multi-angle measurement device was designed to measure the elastic wave velocity in different angle relative to the symmetric axis of the compacted soil sample. According to the experimental results, on the wet side, the shear wave velocity parallel to the symmetric axis keeps decreasing while water content increase. On the contrary, the shear wave velocity on the dry side fluctuates as water content decreases. Furthermore, observation from the anisotropy factors reveals that the anisotropy becomes more obvious (greater or smaller than one) when water content is close to or greater than the optimum water content. Further studies worth to be conducted were suggested.