Minimizing Roadway Embankment Damage from Flooding (2016) / Chapter Skim
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From page 41... ...
39 CHAPTER FIVE GEOTECHNICAL AND GEOLOGICAL FACTORS INTRODUCTION The modes of failure identified in chapter two deal with the interaction between the water and the soil. The water represents the "load" and the soil the "resistance." The water effect is characterized by the water velocity v (m/s)
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40 Erosion Function and Soil Classification The most effective way to obtain the erosion function is to measure it on a site-specific basis by testing samples or by in situ testing. If this preferred approach is not possible, the erosion function can be estimated on the basis of the Unified Soil Classification System by using the erosion category chart shown in Figure 67 (Briaud 2013)
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41 • Rotating Cylinder Test (RCT) • Erosion Function Apparatus (EFA)
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42 FIGURE 71 Hole erosion test. FIGURE 72 Hole erosion test (continued)
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43 Based on many tests performed over the past 25 years, Briaud proposed an erosion classification and related the soil classification to the erosion classification (Figure 67)
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44 ing geology brings a big-picture understanding of the surroundings of an embankment and river setting. Within the engineering geology framework, it is necessary to understand the geomorphology of rivers and the impact it has on nearby embankments.
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45 chapter two. Design considerations for failure modes resulting from overtopping and wave action were considered in previous chapters -- within the limits of existing knowledge and practice.
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46 between coarse particles. In this case, the fines can move easily between the coarse particles and erode away to an exit face.
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47 drainage elements can be introduced into the embankment (USACE 2000)
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48 Rapid drawdown is associated with a prolonged flood stage that saturates -- by seepage -- a major part of the upstream portion of the embankment. The floodwaters then recede faster than the embankment soil can drain, thus resulting in potential instability.
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49 FIGURE 91 Erosion function and soil classification (Briaud 2013)
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50 Tree roots can be considered as reinforcement for the slope of a levee if the tree is on the levee and is alive and healthy. However, if the tree on a levee is uprooted and topples over during a flood, it will create a major hole in the levee.
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51 downstream (landward) slope.
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52 Case Example 2: SH-24 North of Washington, Oklahoma/McClain County Christopher (2007) carried out FWD at this site after the flood.
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