蜂巢格網擋土結構數值分析與設計

Abstract

蜂巢格網加勁土壤之優點為增加土壤強度、降低土體變形。經過多年發展，蜂巢格網目前已廣泛應用於抗沖蝕、路基加勁、及擋土結構等。 本研究之主要目的是以數值模式分析蜂巢格網擋土結構物之力學行為。研究方法首先以蜂巢格網擋土結構物理模型試驗結果為依據，先針對物理模型之高度、傾角、型式、及結構物上方之荷重加載區、結構內之加勁區等影響因素，以數值模式分析並與物理模型試驗之結果比較，藉以驗證數值模式之正確性。而後選取一疊塊式擋土結構現地案例進行分析，進一步探討本數值模式應用於現地結構物之適用性。最後針對擋土結構物數種配置進行數值分析，探討各配置之優缺點並提出建議。 在數值模式驗證上，無論與模型試驗或是現地案例比較均獲得不錯的結果。例如，以塑性區定義破壞滑動面，與模型試驗觀察之滑動面相當一致；又利用FLAC內安全係數計算功能可準確預測模型破壞時的載重。而根據數值分析得到以下結：擋土結構的牆面水平位移量與背填土沉陷量，隨著牆面傾角變陡而增加；牆面式蜂巢格網較重力式產生較大之水平位移；而背填土加勁可有效地減少塑性區、水平位移量、與背填土沉陷量。 在配置分析方面，牆面傾角愈大，牆底產生愈大的剪力。以位移曲線及塑性區分布來說，將部分蜂格網層加長作為加勁之用，所得之牆面變形量最低，滑動面最不明顯、效果最好。另外，不同牆體形式或是傾角下，各配置的側向土壓力均接近Rankine主動土壓力分佈，可作為極限分析設計之參考。

Soil reinforced with geocells has the advantage of reducing the settlement and increasing the bearing capacity of the soil. Nowadays, geocells has been extensively employed in erosion control, pavements, as well as retaining walls. The purpose of this study was to establish a numerical model for analyzing the mechanical behavior of geocell-reinforced retaining structures. In the study, the analytical results were compared with the results from model tests for verification the correctness of the numerical model. In addition, comparison with the result of a case study of segmental wall was also made. Finally, various layouts of retaining structures were analyzed, and suggestion was made based on the performance of the structures. The verification of the numerical model shows good results in the aspects of predicting potential slip plane by plastic zones and estimating the load to cause failure. In general, the analysis obtains following results: the wall with steeper inclination has more horizontal displacement of wall face and more settlement at the top of the wall; the facing-type wall displays more horizontal displacement than the gravity-type; the reinforcement in the backfill effectively reduce plastic zones, the horizontal displacement of wall face, and the settlement of backfill. The study on layouts of reinforced wall shows that steeper walls will induce higher shear stress at the bottom of the walls than gentler walls. In general, the wall with certain layer of lengthened geocells, serving as reinforcement, performs best in terms of reducing wall face’s deformation or minimizing potential slip zones. Moreover, Rankine’s active earth pressure may be adopted when conducting limit equilibrium analysis on geocell-reinforced walls.