Evaluation and Experiments on revegetation methods applicable to difficult slope sites.
Date Issued
2010
Date
2010
Author(s)
Liao, Wen-Wen
Abstract
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.
Subjects
hydraulic mulching
Shotcrete Vegetation Mulching Technique(SVMT)
revegetation
difficult sites of slope revegetation
Fuzzy Preference Relations
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