以模型試驗探討錨碇地工織網系統之影響因素

Abstract

錨碇地工織網系統 (Acnchored Geotextile/Geonet System, AGS) 是一種結合地工織物與錨釘之保護邊坡的工法，其除了以錨釘增加潛在滑動面之穩定性外，並以錨碇力使舖設於坡面之織物產生張力，圍束住周圍土壤。此外，地工織物亦提供良好排水與阻止土壤流失之能力。 本研究針對AGS穩定邊坡的能力進行探討，即以不同之錨碇力、地工織物、土壤作為試驗變因，分別製作AGS模型邊坡，再施加滲流促成邊坡破壞並觀察破壞之情形。試驗之過程全程以質點速度儀(Particle Image Velocity, PIV)記錄，再利用所得之影像與數據作向量分析，定義出破壞區間，做為邊坡極限平衡穩定分析之參考。此外，亦藉由水壓計量測坡體內水壓之變化。 由試驗結果顯示，愈接近邊坡下方的錨釘，因受土體自重的影響，其需抵抗滑動之錨定力愈大。另外，地工織物愈緻密，雖強韌性提高，但也會導致滲透性較差，使得當有水流的影響時，造成土壤推擠情形明顯。又天然材料做的織物當受力時會產生局部縮頸現象，造成坡面土壤易產生堆積及阻塞織物之孔隙，使孔隙水壓力累積，進而導致邊坡的不穩定。滲透性越高之土壤，受滲流的影響較大，AGS錨碇阻抗較難發揮。而所有試驗的破壞皆為緩慢滑動而非瞬間潰散，同時，也未觀察到土壤從織物表面流出，此顯示即使AGS逐漸失效，也不致引起織物產生擴孔的現象，故仍能維持邊坡某種程度的穩定。

The anchored geotextile/geonet system (AGS) is a technique for slope protection. In the system, geotextile/geonet is placed on the slope to control soil loss and to provide drainage; while anchors are driven through the fabrics into the soil to stabilize potential failure planes. By combining these two elements, geotextiles and anchors, the AGS can develop a strong armoring network for protecting slopes. This technique has been put into practice through years with good results. The main focus of this research was to investigate the effects of anchoring force distribution, fabric properties, and soil permeability on the AGS. Model slopes were established by using different anchoring forces, various geotextiles, and soils as testing variables. The slopes were triggered to fail by seepage. The image of the movement of soil particles was recorded by a particle image velocimetry (PIV) during the test. Water pressures at several locations in the slopes were monitored as well. These data provided references for slope stability analysis using limit equilibrium concept. The test results showed that the force in the anchor that was located near the bottom of a slope was high due to the effect of soil’s weight. Although a dense fabric has good tensile strength, its drainage function is also poor. As a result, seepage induced more obvious instability in the slope that used the dense fabric. Moreover, a natural geotextile tested was apt to induce necking phenomenon, which caused the soil to clog inside the geotextile. Consequently, the water pressure was built up and slope instability occurred. The slope consisted of more permeable soil was easier to be affected by a seepage flow. In this case, the beneficial from the AGS was less significant. In all the model tests, the slopes failed slowly rather than abruptly and no soil was observed being carried away through the geotextiles. This evidence demonstrated the capability of the AGS in maintaining slope stability, even though some anchors were already failed.