蜂巢格網圍束效應之數值分析

Abstract

蜂巢格網於國內外應用的案例雖然不少，但關於其對整體土壤加勁效果的影響仍未盡了解，此皆肇因於蜂巢格網不易於實驗室進行試驗，因此設計分析此類型的加勁結構時，如何適切地選取力學參數常讓人困惑。 本研究使用有限元素軟體PLAXIS分析蜂巢格網的加勁行為。首先，以蜂巢格網加勁砂土試體之三軸壓縮試驗結果為依據，針對土壤參數、加勁材參數與邊界條件設置等進行驗證與比對，藉以驗證數值模式的正確性。而後針對格室尺寸、形狀，以及格室外圍是否有未加勁區等因素進行探討，並求得多格室與單格室之壓縮強度的關係。 在數值驗證上，蜂巢格網材料的接縫強度十分重要。根據分析結果得知：格室直徑對加勁土壤的摩擦角影響不大，但與視凝聚力呈一乘冪關係；直徑越小時，視凝聚力越大。而格室不論原始形狀為何，受三軸壓縮後皆會趨近圓柱形，而格室變形的難易會干擾加勁材張力的發揮，進而對視凝聚力造成影響。若形狀有角隅；如六角柱，則會使得加勁土壤的摩擦角提升。格室外圍有未加勁之砂土時，則可透過公式修正得到有蜂巢格網加勁區的壓縮強度。 最後利用固定格室尺寸並增加格室數量的方式，得到多格結構之壓縮強度與單格壓縮強度之倍數關係，且該關係隨著格室的高徑比而改變。

Geocells have been widely applied to geotechnical engineering, but their reinforcement effects are still not fully understood. Such difficulties are primarily due to geocells not to be easily tested in the laboratory. Thus, selecting appropriate parameters for designing geocell-reinforced structures remains a difficult task. This study analyzed sand reinforced with geocells by the finite element software PLAXIS. In the beginning, verification of the numerical model was based on the triaxial compression test results of geocell-reinforced sand samples, with material parameters, boundary conditions, and strength parameters appropriately selected. After that, the numerical model was used to investigate the effects of size and shape of geocell as well as the effect of soil surrounding the geocells. Furthermore, the relationship of the compressive strength between multiple cells and single cell was found. From the verification of the numerical model, it has been found that the elastic modulus of the seam strengths of cell junction is very important. The analytical results show that the apparent cohesion of reinforced soil is closely related to the diameter of geocell; the cell with smaller diameter induces more apparent cohesion. Nevertheless, the friction angle of reinforced soil seems to be insignificantly affected. In addition, geocell under triaxial compression tends to become cylindrical shape, irrespective of its original shape. The deformation of geocell therefore has effect on the development of the tensile strength of the reinforcement, e.g., hexagonal packs showed the highest friction angle since their shape has many corners. Further, if there is soil surrounding cells, the compression strength of the sample can be obtained through the proposed modification equation. Finally, the relationship between the strengths of multiple cells and single cell was obtained, and it was found to be dependent on the aspect ratio of the geocell.