植生困難之坡面的適用工法之評估及試驗研究

Abstract

本研究的主要目的在於透過模糊偏好關係(Fuzzy Preference Relations) 建立一較為客觀之適用性評估指標，從眾多適用於坡面困難工址的植生技術中，遴選出於施工方法、經濟層面、使用限制等，綜合表現較佳的技術—水泥噴凝植生覆蓋技術(Shotcrete Vegetation Mulching Technique , SVMT)。並以此技術為基礎，進行室內之人工降雨試驗，降雨強度約120mm/hr，試驗坡度60度，分6種齡期進行降雨試驗 (分別為1、3、7、14、28、56天)，測試其抵抗降雨沖蝕之能力及表面強度大小，本研究將蒐集包括逕流量、沖蝕量、試體表面強度、表面流速、覆蓋之試驗數據。 試驗結果顯示，水泥噴凝植生覆蓋技術(SVMT)因水泥的固化作用可於施工後三天內快速的提升護坡土壤強度、達到快速抗沖蝕能力。且SVMT試體的表面強度為傳統試體的3~10倍，具有較佳的凝聚性及剪力強度，7天內SVMT試體的抗沖蝕能力明顯優於傳統試體，14天後由於傳統試體土壤結構的改變，沖蝕量陡降，但通氣性、透水性變差，植生效果不彰。然而，各試體之逕流量及流速等結果差異不顯著，顯示工法或齡期非主要影響因子。在覆蓋情形的部分，SVMT於7天後之覆蓋約為傳統的10倍，表示水泥的添加提供了坡面有效的抗沖蝕能力及強度，能有效的留住表土及種子，更能達到植生覆蓋的目的。 (坡面植生困難工址於本研究中係定義為「坡度45度以上之一般邊坡、或噴凝土護坡、混凝土擋牆及岩石坡面等不易植生之坡面」。)

The main purpose of this study is to establish adaptability evaluation indexes by using the method of Fuzzy Preference Relations, FPR, for choosing an optimum method among all the revegetation methods applied on the difficult sites of the slopes. In this study, difficult sites of slope revegetation is defined as「 Slopes steeper than 45 degrees, and with a protective cover of shotcrete, or with rock, or common slopes, or concrete retaining walls…etc., which are difficult to be revegetated」. Accordingly, the method of Shotcrete Vegetation Mulching Technique (SVMT), was then chosen based upon the evaluation indexes of economy, restriction and construction. Using the SVMT method, samples for erosion tests were prepared in the erosion boxes with a length of 125 cm, a width of 100 cm and a height of 11 cm. Using a rainfall simulator developed by Forster et al. (1982) and Fan and Wu (1993), erosion tests were conducted on the samples with the ages of 1, 3, 7, 14, 28 and 56 days, respectively, with a rainfall intensity of 120 mm/hour and a steepness of 60 degrees. During the tests, the data of runoff, erosion, surface strength, surface velocity and vegetation cover were obtained to evaluate the resistance to soil erosion and soil strength. From the obtained results, it was found that the SVMT method was able to strengthen the resistance to erosion and stability of the slope within 3 days after the samples were prepared. Aside from this, the surface strength of soil slopes prepared using the SVMT method were 3 to 10 times higher than those using the conventional method, and approved to be better in both cohesion and shear strength. The results also showed the erosion of the soil samples with the ages less 7 days using the SVMT method were much less than those using the conventional method. However, due to the change of soil structure, the erosion of the samples prepared using the conventional method were slightly less then those using the SVMT method, yet the ventilation and permeability became worse, and consequently the vegetation effects were deteriorated. From the test results, it was found the runoff and velocities of the samples prepared using the two methods were quite similar, indicating revegetation method and the age were not the main factors affecting runoff and velocity. For the vegetation cover of the samples prepared using the two methods with the ages greater than 7 days, and after rainfall erosion tests, the vegetation cover of the SVMT method were approximately 10 times of those of the conventional method, which implied that concrete cement were effective in providing sufficient resistance to erosion and stability to hold the soil and seed. As a result, the SVMT method was approved more capable of revegetation on the difficult sites of the slopes.