Philippine National Standard - Design of Canal Structures PDF

PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 221:2017 ICS 65.060.35 Design of Canal Structures – Road Crossing, Drop, Siphon and Elevated Flume...

PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 221:2017 ICS 65.060.35 Design of Canal Structures – Road Crossing, Drop, Siphon and Elevated Flume BUREAU OF AGRICULTURE AND FISHERIES STANDARDS BPI Compound Visayas Avenue, Diliman, Quezon City 1101 Philippines Phone (632) 920-6131; (632) 455-2856; (632) 467-9039; Telefax (632) 455-2858 E-mail: [email protected] DEPARTMENT OF Website: www.bafps.da.gov.ph AGRICULTURE PHILIPPINES PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 221:2017 Design of Canal Structures – Road Crossing, Drop, Siphon and Elevated Flume Foreword The formulation of this national standard was initiated by the Agricultural Machinery Testing and Evaluation Center (AMTEC) under the project entitled “Enhancement of Nutrient and Water Use Efficiency Through Standardization of Engineering Support Systems for Precision Farming” funded by the Philippine Council for Agriculture, Aquaculture and Forestry and Natural Resources Research and Development - Department of Science and Technology (PCAARRD - DOST). As provided by the Republic Act 10601 also known as the Agricultural and Fisheries Mechanization Law (AFMech Law of 2013), the Bureau of Agriculture and Fisheries Standards (BAFS) is mandated to develop standard specifications and test procedures for agricultural and fisheries machinery and equipment. Consistent with its standards development process, BAFS has endorsed this standard for the approval of the DA Secretary through the Bureau of Agricultural and Fisheries Engineering (BAFE) and to the Bureau of Philippine Standards (BPS) for appropriate numbering and inclusion to the Philippine National Standard (PNS) repository. This standard has been technically prepared in accordance with BPS Directives Part 3:2003 – Rules fortheStructure and Drafting ofInternational Standards. The word “shall” is used to indicate mandatory requirements to conform to the standard. The word “should” is used to indicate that among several possibilities one is recommended as particularly suitable without mentioning or excluding others. iii PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 221:2017 Design of Canal Structures – Road Crossing, Drop, Siphon and Elevated Flume CONTENTS Page 1 Scope 1 2 References 1 3 Symbols and Nomenclature 1 4 Definitions 2 5 Road Crossing 3 5.1 General Criteria 3 5.2 Data Requirement 3 5.3 Design Procedure 5 5.4 Design Equations 6 6 Drop 9 6.1 General Criteria 9 6.2 Data Requirement 9 6.3 Types of Drop 10 6.3.1 Vertical Drop 10 6.3.2 Rectangular Inclined Drop 13 6.3.3 Baffled Apron Drop 19 7 Inverted Siphon 21 7.1 Components 21 7.2 Data Requirement 23 7.3 Design Considerations 23 7.4 Design Procedure 24 7.5 Design Equations 25 8 Elevated Flume 29 8.1 Data Requirement 29 8.2 Design Criteria 29 8.3 Design Procedure 31 8.4 Design Equations 32 9 Bibliography 34 ii PHILIPPINE NATIONAL STANDARD PNS/BAFS/PAES 221:2017 Design of Canal Structures – Road Crossing, Drop, Siphon and Elevated Flume 1 Scope This standard provides minimum requirements and procedures for hydraulic evaluation andstabledesignofroadcrossing, drop,siphonandelevatedflume. 2 References The following normative documents contain provisions, which, through reference in this text, constitute provisions of this National Standard: PNS/BAFS/PAES 218:2017 Open Channels – Design of Main Canals, Laterals and Farm Ditches 3 Symbols and Nomenclature Parameter Symbol Unit Box Culvert Area Ab m2 Conduit Cross-Sectional Area Ao m2 (based on Orifice Formula) RCP(Reinforced ConcretePipe)Area Ap m2 Canal Area A m2 Canal Bottom Width b m Base Widths b1, b2 m Orifice coefficient C - Canal Bed Elevation Downstream CBD/S m Canal Bed Elevation Upstream CBU/S m Water Depth d m Canal Total Depth D m RCP Actual Diameter Dp m Acceleration due to Gravity g m/s2 Available Head ha m Box Culvert Height hb m Inlet TransitionLoss hLi m Outlet TransitionLoss hLo m Total Head Loss hLT m Conduit FrictionLoss hLv m HeadLoss dueto Velocity in the Conduit hvp m Head Loss due to Velocity Upstream hv1 m Head Loss due to Velocity Downstream hv2 m Inlet Coefficient ki Outlet Coefficient ko 1 Conduit Length L m Roughness Coefficient n - Canal Discharge Q m3 Canal HydraulicRadius R m Canal Slope S - Canal Side Slope Ss - Conduit Slope Sf - Canal Top Width T m Top Bank Elevation TB m Velocity V m/s Velocity in the Box Culvert Vb m/s Velocity in the RCP Vp m/s Water Surface Elevation Downstream WSD/S m Water Surface Elevation Upstream WSU/S m 4 Definitions For the purpose of this standard, the following terms shall apply: 4.1 critical depth depth of water flow where the energy content is at minimum hence, no other backwater forces are involved 4.2 drop in-line canal structure designed to convey canal water from a higher level to a lower level, duly dissipating the excess energy resulting from the drop in elevation 4.3 elevated flume waterconveyingconduitortroughwhichissupportedonabutmentsbypiers 4.4 equipment crossing provision for passing of equipment and small machinery 4.5 invert inside bottom or sill of t the conduit 4.6 inverted siphon closed conduit designed to convey canal water in full and under pressure running condition, to convey canal water by gravity under roadways, railways, drainage channels and local depressions 2 4.7 road crossing conveys canal water under roads or railroads 5 Road Crossing A typical plan and half plan view of a road crossing is shown in Figure 1. 5.1 General Criteria 5.1.1 When a road crossing crosses a road or railroad, the intersecting angle must be a right angle as much as possible. 5.1.2 The depth necessary for burying a conduit must be determined, taking into consideration the water level required from hydraulic study, earth cover necessary for the purpose of land use, etc. 5.1.3 The minimum recommended clearance betweenthe road and culvert for railroad and road crossing is 0.90 m while for farmroad and thresher crossing is 0.60 m if needed. 5.2 Data Requirement Profile information of the canal and road crossing such as canal cross-section, velocity of flow, discharge, salient levels on upstream and downstream of the structure shall be provided. Canal Hydraulic Elements: Discharge, Q Velocity, V Area, A Canal Width, b Water Depth, d Total Depth, D Top Width, T Hydraulic Radius, R Canal Slope, S Side Slope (H:V), Ss Roughness Coefficient, n Top Bank Elevation, TB Water Surface Elevation, WS Canal Bed Elevation, CB 3 Figure 1. Plan View of a Road Crossing 4 5.3 Design Procedure 5.3.1 Determine the conduit size – The conduit may be a reinforced concrete pipe (RCP) or box culvert. 5.3.1.1 Determine the area of the conduit assumed full flowing using the orifice formula in section 5.4.1. 5.3.1.2 Select a trial size of the conduit from Table 1. 5.3.1.3 Compute for the area of the selected trial size (Ap or Ab) using the formula in section 5.4.2. 5.3.1.4 If Ao is less than or equal to Ap or Ab, then the computed Ap or Ab is acceptable thus, use the trial size. 5.3.2 Determine the available head – Use the formula in section 5.4.3 5.3.3 Determine the conduit velocity– Use the formula in section 5.4.4. The maximum allowable velocity is shown in Table 2. 5.3.4 Determine the invert elevation– Use the formula in section 5.4.6 and 5.4.5 to account for the head loss due to velocity. 5.3.3 Determine the total head loss– Use the formula in section 5.4.10 which will account for the inlet transition loss, conduit friction loss, and outlet transition loss. The total head loss shall be less than or equal to the available head. Otherwise, a different size of conduit shall be checked for. 5 5.4 Design Equations 5.4.1 Orifice Formula 𝑄 𝐴𝑜 = 𝐶√2𝑔ℎ𝑎 where: Ao is the conduit cross-sectional area (m2) Q is the canal discharge (m3/s) C is the orifice coefficient, 0.60 – 0.75 g istheaccelerationduetogravity,9.805m/s2 ha is the available head (m) 5.4.2 Area of the Conduit For RCP, 𝜋𝐷𝑝2 𝐴𝑝 = 4 For boxculvert, (𝑏1 + 𝑏2) 𝐴𝑏 = ℎ𝑏 2 where: Ap istheRCParea(m2) Ab isthe box culvert (m2) Dp istheRCPactualdiameter,m(Referto Table1) b1, b2 is the base widths (m) hb is the box culvert height (m) Table 1. Nominal and Actual Diameter of RCP Nominal Diameter, cm (in) Actual Diameter, cm 75 (30) 76 60 (24) 61 45 (18) 46 5.4.3 Available Head ℎ𝑎 = 𝑊𝑆𝑈⁄𝑆 − 𝑊𝑆𝐷⁄𝑆 where: WSU/S is the water surface elevation upstream, m WSD/S is the water surface elevation downstream, m 6 5.4.4 Conduit Velocity For RCP, 𝑄 𝑉𝑝 = 𝐴𝑝 For boxculvert, 𝑄 𝑉𝑏 = 𝐴𝑏 where: Vp is the velocity in the RCP (m/s) Vb is the velocity in the box culvert (m/s) Q is the canal discharge (m3/s) Table 2. Maximum Allowable Velocity in Conduits Conduit Velocity, m/s RCP with earth transition 1.00 RCP with concrete transition 1.50 Box Culvert 1.20 5.4.5 Head loss Due to Velocity 𝑉𝑝2 ℎ𝑣𝑝 = 2𝑔 𝑉𝑏 2 ℎ𝑣𝑏 = 2𝑔 where: hvp is the head loss due to velocity in the pipe (m) hvb is the head loss due to velocity in the box culvert (m) g is the acceleration dueto gravity, 9.805 m/s2 5.4.6 Invert Elevation 𝐸𝑙𝐴 = 𝑊𝑆𝑈⁄𝑆 − (𝐷𝑝 + 1.5ℎ𝑣𝑝 ) 𝐸𝑙𝐴 = 𝑊𝑆𝑈⁄𝑆 − (𝐷𝑝 + 1.5ℎ𝑣𝑏 ) 𝐸𝑙𝐵 = 𝐸𝐿𝐴 − 𝑆𝑓 𝐿 where: ElA is the invert elevation at A (m) ELB is the invert elevation at B (m) WSU/S is the upstream water surface level (m) Sf is the conduit slope (Minimum slope = 0.005 for straight line profile) L is the conduit length (m) 7 5.4.7 Inlet transition loss 𝑉12 𝑉𝑝2 ℎ𝐿𝑖 = 𝑘𝑖 ( − ) 2𝑔 2𝑔 𝑉12 𝑉𝑏2 ℎ𝐿𝑖 = 𝑘𝑖 ( − ) 2𝑔 2𝑔 where: ki istheinletcoefficient(Pleasereferto Table3) V1 is the initial velocity (m/s) Vp is the velocity in the pipe (m/s) Vb is the velocity in the box culvert (m/s) g is the acceleration due to gravity, 9.805 m/s2 Table 3. Inlet and Outlet Coefficients of Open Canal Transition to Closed Conduit Type of Transition Inlet Outlet Coefficient Coefficient Streamlined warp to rectangular opening 0.10 0.20 Straight warp to rectangular opening 0.20 0.30 Brokenback to rectangular opening 0.30 0.50 Straight warp with bottom corner fillets to RCP opening 0.30 0.40 Brokenback to RCP opening 0.40 0.70 Earth canal to RCP opening 0.50 1.00 5.4.8 Conduit friction loss 2 2 𝑉𝑝𝑛 𝑉𝑏 𝑛 hLv = [ ] × 𝐿 orℎ𝐿𝑣 = [ ] ×𝐿 𝐴𝑝 2⁄3 𝐴𝑏 2⁄3 (𝑃 ) ( 𝑏) 𝑝 or ℎ𝐿𝑣 = 𝑆𝑓 × 𝐿 where: Vp is the velocity in the pipe (m/s) Ap is the area of the pipe (m) Pp is the perimeter of the pipe (m) L is theconduit length,=(m) Sf is the conduit slope (Minimum conduit slope = 0.005 for straight lineprofile) 8 5.4.9 Outlet transition loss ℎ𝐿𝑜 = 𝑘𝑜 (ℎ𝑣2 − ℎ𝑣𝑝 ) where: ko is the outlet coefficient (Refer to Table 4) hv2 isthe canal headlossdueto velocity downstream, m hvp = hvb is the head loss due to velocity in the pipe or box culvert, m 5.4.10 Total Head Loss ℎ𝐿𝑇 = 1.10 (ℎ𝐿𝑖 + ℎ𝐿𝑣 + ℎ𝐿𝑜 ) where: hLT is the total head loss (m) hLi is the inlet transition loss (m) hLv is the conduit friction loss (m) hLo is the outlettransitionloss(m) 6 Drop 6.1 General Criteria 6.1.1 Dropstructures shall beprovidedforthestabilityofthe canal whenthere is substantial change in canal elevation. 6.1.2 The location and type of drop structures shall be determined through comparative design with regard to the stability and cost. 6.1.3 The lining materials and flow velocities for scouring and erosion shall be considered in type selection. 6.1.4 If the elevation difference is more than 5 m, an inclined drop or chute shall be used. 6.2 Data Requirement 6.2.1 Contour plan of the area. 6.2.2 Profile sheet showing locations and types of all canal structures nearby to study the possibility of combining the drop with any of them. 6.2.3 Canal cross-section, velocity of flow, discharge, salient levels on upstream and downstream of the structure 6.2.4 Details of lining proposed/provided on the upstream and downstream of the structure 9 6.2.5 Proposed height of drop as shown in the profile sheet 6.2.6 Foundation material from the point of view of exit gradient characteristics and for uplift computations 6.2.7 Subsoil water level and its seasonal fluctuations 6.2.8 Detailed functional requirements of drops, when combined with any other type of structure 6.3 Types of Drop Vertical Drop Rectangular Inclined Drop Baffled ApronDrop 6.3.1 Vertical Drop A longitudinal section of a vertical drop and the symbols used in the design procedure are shown in Figure 2. 6.3.1.1 Range of Drop and Discharge - may be conveniently used for drops up to 1 m but can be designed for drops up to 2.5 meter and final selection shall be on cost considerations by comparing with other alternatives. The discharge can be safely designed up to 8 m3. 6.3.1.2 Energy Dissipation - turbulent diffusion. A basin serves as a water cushion protects the floor against impact of falling water. 6.3.1.3 Design Procedure 6.3.1.3.1 Determine the critical depth – Use the formula in section 6.3.1.4.1 to compute for the headloss due to upstream canal velocity, height of drop and critical depth. 6.3.1.3.2 Compute for the basin length – Use the formula in section 6.3.1.4.3 while the formula for critical velocity is shown in section 6.3.1.4.2. 6.3.1.3.3 Determine the basin elevation – Use the formula in section 6.3.1.4.4. 6.3.1.3.4 Check for the discharge– Use the formula in section 6.3.1.4.5. If the determined value for the discharge is significantly different from the canal discharge, adjust the width. 10 Figure 2. Longitudinal Section of a Vertical Drop 11 6.3.1.4 Design Equations 6.3.1.4.1 Critical Depth 𝑉𝑎2 ℎ𝑣𝑎 = 2𝑔 𝐻𝐸 = 𝑑𝑎 + ℎ𝑣𝑎 2 𝑑𝑐 = 𝐻𝐸 3 where: hva istheheadloss dueto upstreamcanalvelocity(m) Va is the upstrem velocity (m/s) g is the gravitational acceleration (m/s 2) HE is the height of drop (m) da isthe water depthupstream (m) dc is the critical depth (m) 6.3.1.4.2 Critical Velocity 𝑄 𝑉𝑐 = 𝑏𝑑 𝑐 where: Vc is the critical velocity (m) Q isthecanaldischarge(m 3/s) b is the canal width (m) dc is the critical depth (m) 6.3.1.4.3 Basin Length 𝑦 = 𝐶𝐵𝑈⁄𝑆 − 𝐶𝐵𝐷⁄𝑆 + 𝑑𝑐 2𝑦 𝑡=√ 9.8 𝑥 = 𝑉𝑐× 𝑡 𝐿 = 2𝑥 + 0.30 where: CBU/S istheelevationofthecanalbedupstream(m) CBD/S is the elevation of the canal bed downstream (m) dc is the critical depth (m) L is the basin length 12 6.3.1.4.4 Basin Elevation 𝐿 𝐸𝑙𝐵 = 𝐶𝐵𝐷/𝑆 − 6 where: ELB is the basin elevation (m) CBD/S isthe elevationofthe canal bed downstream (m) L is the basin length 6.3.1.4.5 Discharge 𝑄 = 1.705𝑏𝐻𝐸 3⁄2 where: b is thecanal width(m) HE is the height of drop (m) 6.3.2 Rectangular Inclined Drop Alongitudinal sectionofarectangular inclineddropandthesymblos usedin the design procedure are shown in Figure 3. 6.3.2.1 Range of Drop and Discharge - convenient for all discharges and for drops up to 5 m 6.3.2.2 Energy Dissipation - affected by formation of hydraulic jump in the stilling pool at the end of rectangular inclined through and is more effective when tail water has no wide fluctuations 6.3.2.3 Components 6.3.2.3.1 Upstream Transition - produce gradual change of water prism and velocity from canal to the structure 6.3.2.3.2 Inlet – controls the upstream water level and prevents erosion of the canal bed on the upstream 6.3.2.3.3 Inclined Channel chute - accelerates the water to flow at supercritical velocity so that hydraulic jump is formed in the stilling pool & excess energy is dissipated 6.3.2.3.4 Stilling Pool – provided at the lower end of the inclined channel to create hydraulic conditions conductive to formation of a hydraulic jump under full and partial flows nd accomplish dissipation of excess energy 6.3.2.3.5 Outlet – controls the water level in the stilling pool 6.3.2.3.6 Downstream transition - provides smooth change of velocity from the outlet to canal section to reduce turbulence and erosion. 13 Figure 3. Longitudinal Section of a Rectangular Inclined Drop 14 6.3.2.4 Design Procedure 6.3.2.4.1 Determine the basin width – Use the formula in section 6.3.2.5.1 and subsequently compute for the critical depth. 6.3.2.4.2 Determine d1 (refer to Figure 3) 6.3.2.4.2.1 Assume a pool elevation and compute for the upstream energy elevation using the formula in section 6.3.2.5.3. 6.4.2.4.2.2 Compute for the upstream velocity head (section 6.3.2.5.2) 6.4.2.4.2.3 Assume a value for d1 (