Figure 612 shows a flowchart of design procedures for groundsill The following

Figure 612 shows a flowchart of design procedures for

This preview shows page 88 - 92 out of 138 pages.

Figure 6.12 shows a flowchart of design procedures for groundsill. The following parameters such as roughness of the riverbed, velocity of river flow and slope/gradient of the river are important factors to consider in the design. START River and geological surveys Preliminary planning: - Location, cross and longitudinal sectional details - Alignment of groundsills - Height of groundsills Selection of type: - Consider flow velocity and slope gradient Design: -Design load computation -Stability Analysis of groudsills (overturning, tensile stress, sliding, bearing capacity of foundation) -Structural design computation Design of apron and side wall END Figure 6.12 Design Procedure for Groundsill The position of groundsill should be linear and at right angle to the direction of the water flow as shown in Figure 6.13.
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Guidebook for Road Construction and Maintenance Management 6 - 9 Figure 6.13 Arrangement of groundsills relative to the direction of flow A detailed drawing of groundsill is shown below: Figure 6.14 Details of Groundsill The depth of embedment is the most important factor for the stability of groundsill (refer to the table below). A B C D H=height of groundsill body (m) B=Thickness of crest opening (m) H 1 =Height of fall (m) h 1 =Overflow depth (m) b=Embedment depth of main body (m) B Design flood level Height of groundsill H H 1 h 1 b 1:0.2 1:m Flow direction
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6 - 10 Guidebook for Road Construction and Maintenance Management Table 6.2 Required Depth and Width of Groundsill Part of Groundsill Symbol (See Fig.) Condition of Foundation Sand and gravel Soft rock Hard rock Depth of Embedment (Main Body) B 1.5 to 2.0 m 1.5 to 2.0 m 1.5 to 2.0 m Width of Wing (Top) b 1 2.0 m or more 1.5 m or more 1.0 m or more Embedded Width of Wing (Top) b 2 2.0 m or more 1.5 to 2.0 m 1.0 m or more Width of Wing (Bottom) b 3 2.0 m or more 1.0 m or more 0.5 m or more Depth of embedment of Wing b 4 1.0 m or more 0.5 m or more 0.5 m or more Inclination Degree of Wing Edge m Depends on Excavation Line 1.0 : 2.0 (H : V) 1.0 : 2.0 (H : V) Note: Refer to Figure 6.16 Figure 6.15 Typical Section of Groundsill 6.1.2.3 Rechanneling Rechanneling is considered as a countermeasure against riverbank and riverbed erosions. The concept of this countermeasure is shown in Figure 6.16
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Guidebook for Road Construction and Maintenance Management 6 - 11 Figure 6.16 Rechanneling Concept for Riverbank and Riverbed Protections Construction of spur dike is also an effective countermeasure against riverbank and riverbed erosions. Spur dike change the river flow direction to protect river bank and also controls sedimentation of the riverbed. There are three types of spur dikes namely; 1) perpendicular; 2) upward and 3) downward- as shown in Figure 6.17. For riverbanks, upward spur dike is recommendable. For reference, shown in Figure 6.18 is a typical cross-section of spur dike.
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