加勁砂樁穩固邊坡受滲流作用之模型試驗

Abstract

加勁砂樁（Geosynthetic Encased Column, GEC）目前主要應用於基礎結構下方，由於其加勁材料的約束作用，使其能增強柱體的剪切強度和承載能力。然而，加勁砂樁具有機械和排水功能，使其適用於滲流區域。除此之外，它們的彈性使其能夠容忍大變形，增強了邊坡的穩定性。因此，本研究旨在探討在滲流條件下利用加勁砂樁穩定邊坡的能力。 本研究通過一系列模型試驗(reduced model tests)研究了受滲流影響的加勁砂樁穩定邊坡的性能，以評估其作為防止邊坡滑動的有效性，為此，在模型試驗中，總共進行了五次模型試驗，以研究未經加固邊坡和加勁砂樁穩定的邊坡在滲流作用下的行為。研究評估自然邊坡以及加勁砂樁穩定邊坡在加勁砂樁不同填充砂的情況以及樁底部位在兩種不同地質環境（砂岩和頁岩）中對水壓分布、邊坡變形、剪切應變發展與加勁砂樁機制的影響。試驗結果將其破壞模式分作三類敘述：（1）天然邊坡的快速滑動；（2）加勁砂樁穩定邊坡提供土壤剪力強度增強；（3）加勁砂樁穩定邊坡中水位的延遲發展。試驗結果顯示，增加填充土壤的勁度及樁底部位在砂岩中(有排水功能)的加勁砂樁能夠提高牆體穩定性，並減少邊坡變形。基於這些結果，本研究討論了加勁砂樁作為替代的邊坡穩定結構，加勁砂樁穩定邊坡的性能是由土壤剪切強度（機械功能）和垂直排水特性（水力功能）的綜合效應所改善。

The proposition of employing Geosynthetic Encased Columns (GECs) for slope stabilization under seepage conditions holds significant promise. GECs offer both mechanical and hydraulic functions, making them suitable for areas with rising groundwater levels. Their flexibility allows them to tolerate large deformations, enhancing slope stability. The study aims to examine GECs' potential effectiveness in seepage environments. This approach could provide an alternative flexible measure for slope stabilization. A series of reduced model tests were conducted to evaluate the performance of GEC stabilized slopes affected by seepage and to assess their effectiveness in preventing slope failure. To this end, model tests were performed to examine the behavior of unreinforced and GEC stabilized slopes subject to seepage, with five model tests conducted. In the conducted model tests, a simulated slope with a height of 5 m was employed to represent a prototype scenario under seepage conditions, where the groundwater level reached a maximum of 4 m. The study of GEC stabilized slopes evaluated the influence of different infilled materials in GECs and the installation of GEC toes in two distinct geological contexts: sandstone and shale. Digital image analysis (DIA) techniques were employed to determine the slope surface profile and analyze shear strain propagation at various groundwater levels. The phreatic surface level was also monitored and studied. The results of the tests categorized the failure modes into three groups: (1) rapid failure of natural slope; (2) enhanced shear strength provided by GEC stabilized slope; and (3) postponed development of the phreatic surface level in GEC stabilized slope. The tests revealed that increasing the stiffness of the infilled soil and GECs with drainage function (bedrock of sandstone) demonstrated improved efficiency in enhancing wall stability and reducing slope deformation. Based on these findings, the research discusses GEC stabilized slopes as alternative slope stabilization structures, specifically in large slope deformation. The improved performance of GEC stabilized slopes is attributed to the combined effects of soil shear strength (mechanical function) and vertical drainage property (hydraulic function).