地工格網應用於無鋪面道路之加勁效果，已有許多學者利用物理試驗及現地實驗等不同方式進行加州貫入比(CBR)之評估，但其產製方式與幾何性質對於加勁效果的相關研究，仍屬少數。 本研究分別以物理實驗與數值模型進行分析與探討，在物理實驗部分以CBR試驗進行分析，並以高嶺土作為軟弱路基黏土層的材料，基底層材料為單一尺寸的人造三角柱研磨石，由不同變數包含基底層厚度、地工格網開口幾何形狀、產製方式(市售PET材料與3D列印材料)等條件下探討加勁機制與效益。研究結果顯示，地工格網於軟弱黏土之加勁效果顯而易見，並以三角形孔徑地工格網加勁效果較佳。 在數值模型部分，本研究依據物理實驗模型，運用有限差分分析軟體(FLAC3D)以連體力學建立路基層架構，由離散元素分析軟體(PFC3D)以顆粒力學建立基底層與地工格網架構，並將FLAC3D與PFC3D藉由等效力系統轉換概念進行耦合運算，以探討無鋪面道路加載過程，路基層、基底層及地工格網加勁機制與微觀行為，並由實驗結果進行參數校正與模型驗證。研究結果顯示，地工格網提供張力作用，減少路基層與基底層界面之垂直應力；此外，由基底材顆粒位移、接觸力發展、路基層剪應力及累積剪應變等分析結果顯示，地工格網之加勁機制使基底層發揮顆粒互鎖機制，並與其產生圍束效應，使應力分布較寬廣，進而導致路基層頂部的接觸壓力相對較低，此一現象及加勁機制為相關課題首次以數值耦合分析證實。 綜合以上所述，運用3D列印之地工格網，具有與市售加勁格網之類似效果，因此可在後續研究中客製化不同類型地工格網，並藉由連續體耦合非連續體數值模型，調整路基層、基底層與地工格網相關參數，可進一步先行模擬各參數於設計路基剖面所產生之等值加勁效果，提供給工程設計使用。 ;The reinforcing effect of geogrid has been studied through physical tests, numerical modeling, and in-situ testing for the past decades. The effect is usually expressed in terms of California Bearing Ratio (CBR) or the equivalent shear strength. The reinforcing mechanisms of geogrid applied in soft subgrade have been studied by many researchers while producing customized geogrid using 3D printing technology and evaluating the reinforcing effect is uncommon yet necessary to study different configurations of geogrids. This study aims at evaluating the geogrid reinforcing effects among geogrids with various configurations using CBR tests. Afterward, the reinforcing mechanisms are evaluated through a novel numerical coupling analysis. Stress and deformation variations of the discrete base aggregate material and the subgrade represented by continuum medium during CBR simulation were investigated. In physical tests, Kaolin powders were mixed with the specified water content as the soft subgrade material, while the aggregate base material was represented by artificial triangular-prism-type grindstone. Various design parameters such as base thickness, geogrid aperture shape, manufacturing method (commercial and 3D printed products) were considered to evaluate the effect of reinforcement. Results have shown that the geogrid improves the overall performance of the simulated soil layers, and triangular aperture geogrid performs better than square ones. After the numerical models were verified using the physical test results, the aggregate layer simulated by discrete elements and the subgrade layer simulated by finite-difference models were coupled to investigate the reinforcing mechanisms of the unpaved roadway foundations. It was observed that due to the high stiffness of the geogrid, the vertical stress transferred to the subgrade layer was significantly reduced. Based on the displacement vectors, contact forces between aggregate particles, and subgrade shear strains, it could be seen that the geogrid provides an effective approach to limit the displacement of the aggregate particles close to the interface of two layers. The above response results in the effective interlocking between aggregate particles and the confinement of the aggregate layers. Based on the above discussions and findings, the 3D-printed geogrid can perform equally as the commercial products. Hence the effect of different geogrid configurations could be customized during the research phase. Employing the numerical coupling analysis in this study is suitable for both aggregate and subgrade layers and interpreting the reinforcing mechanisms is straightforward. Therefore, the design of geogrid-reinforced roadways could be analyzed first using the proposed numerical approach and an optimized design cross-section could be provided to practitioners for further applications.
