Natural Resources Conservation Service and Grade Stabilization Structure | BAE 4012, Study Guides, Projects, Research of Engineering

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Brian Dillard Rachel Oller Ryan Stricklin Mary Womack BAE 4012-Senior Design April 27, 2006 ii Table of Contents Mission Statement ..............................................................................................1 Introduction.........................................................................................................2 Problem Statement .............................................................................................4 Current Design Specifications for Canopy and Sliced Inlets..........................5 Research & Literature Review ...........................................................................6 Patent Search and Pipe Flow Research ........................................................6 Structural Analysis of Corrugated Metal Pipe ..............................................7 NRCS Current Guidelines for Designing Pipes and Spillways in Structures ......................................................................................................12 Statement of Work ............................................................................................13 Initial Investigation ...........................................................................................15 Field Tour of Installation Sites .....................................................................16 Demonstration Flume ...................................................................................17 Physical Modeling.............................................................................................19 Scale Models .................................................................................................19 Construction ..............................................................................................19 Setup...........................................................................................................25 Pressure Tests ...........................................................................................27 Results of Pressure Testing .....................................................................29 Dye Testing ................................................................................................30 Testing of Baffle Arrangement .................................................................31 Strength Test on Full Scale CMP Inlets.......................................................31 Materials and Setup of Test ......................................................................32 Testing........................................................................................................36 Results and Discussion ............................................................................38 Implications.......................................................................................................42 Budget ...............................................................................................................43 Recommendations............................................................................................44 Scale Modeling ..............................................................................................44 v FIGURE 23 - PRESSURE READINGS FOR CANOPY INLET AT 320 CFS (0.64 CFS). .........29 FIGURE 24 – METAL SLATS WELDED TO SUPPORT PLATE FOR INLET ATTACHMENT......33 FIGURE 25 – CLOSE UP OF METAL SLATS WITH DRILLED HOLES ................................34 FIGURE 26 – SET-UP OF HYDRAULIC CYLINDER AND I-BEAM SUPPORTS .....................34 FIGURE 27 – BALL JOINT MECHANISM .....................................................................35 FIGURE 28 – LOAD CELL SETUP .............................................................................35 FIGURE 29 - AREA OF COLLAPSE ...........................................................................38 FIGURE 30 – CANOPY INLET STRENGTH TEST DATA – LOCATION AND AMOUNTS OF LOAD .....................................................................................................................41 FIGURE 31 – SLICED INLET STRENGTH TEST DATA – LOCATION AND AMOUNTS OF LOAD .....................................................................................................................41 vi List of Tables TABLE 1 - HEAD MEASUREMENTS. ..........................................................................29 TABLE 2 - SLICED INLET RESULTS...........................................................................39 TABLE 3 - CANOPY INLET RESULTS.........................................................................39 TABLE 4 – CALCULATION OF PLATE CONTACT AREA ...............................................40 TABLE 5 - BUDGET ................................................................................................44 1 Mission Statement “Vortex Engineers is committed to enhancing and protecting water resources through detailed analysis and innovative design. Our superior solutions of hydraulic and hydrologic concerns aim to maintain the integrity of the natural environment while providing practical and affordable results.” -Vortex Engineers 4 FIGURE 2 – SLICED INLET FIGURE 3 – CANOPY INLET Problem Statement Since the 1980’s, Oklahoma has implemented many canopy and sliced inlet GSSs to control high runoff volumes over rural land. Though proven to be very useful over the years, an increasing number of failures of the inlets have occurred. In a NRCS report, Chris Stoner outlined the first noticed collapse on a sliced inlet. The entrance of a 42” corrugated metal pipe had failed the first time it flowed. The left side had folded inward, creating a 40% blockage of flow. Since that time, other failures have been noticed and reported. These occurrences were typical of 48” diameter or greater pipes with a 16 gauge thickness. In 1995, the NRCS recommended the use of canopy inlets instead of sliced hoods, because the canopy added extra strength to the structure. In 1997, the 5 inlet thickness was increased to 14 gauge for pipes with diameters greater than 42”. However, a failure was reported in November 2000 of 14 gauge pipe. The report by Stoner also details characteristics of the failures, which interestingly enough are all similar. Always occurring on the left side looking downstream, the pipe folded inward, consequently blocking the flow and limiting the capacity for which it was designed. Because the time of failure is difficult to determine, the magnitude of head causing the collapse is also difficult to determine. NRCS is seeking an analysis of canopy and sliced inlets to establish criteria for providing increased strength for corrugated metal canopy inlets, including: • Determining design parameters that govern the need for increased strength; • Identifying pipe sizes, corrugations, and gauges that need increased strength; • Proposing changes to the Oklahoma NRCS Conservation Practice Standards to reflect the analysis. The NRCS also requests alternative methods for strengthening and a cost comparison of options. Current Design Specifications for Canopy and Sliced Inlets The NRCS has published specifications for the dimensions of canopy inlets. These can be found in Appendix B, Chapter 6 of the Engineering Field Handbook. For conduits with slopes less than 15%, the following equation applies: 0.75D. L 0.2D; W == (1) For conduits with slopes greater than 15%: 1.25D L 0.3D; W == (2) 6 where: W = height of the canopy (ft) L = length of the sliced section (ft) D = diameter of the pipe (ft). The auxiliary spillway elevation must be at least 1.8D above the bottom of the pipe. The riser on the drop inlet must be at least 5D if the conduit slope is greater than the friction slope, or at least 2D if the conduit slope is less than or equal to the friction slope. The thickness of the pipe is determined based on the fill height of the grade stabilization structure and the diameter. Research & Literature Review Patent Search and Pipe Flow Research For the patent search Vortex Engineers went to the United States Patent website and searched for patents pertaining to pipe inlet reinforcements. Only one patent was found when running the search. The patent found was for internally reinforcing an extruded plastic pipe. An abstract of the patent is as follows: An internally reinforced extruded plastic pipe is adapted for use as an underground infiltration, collection, or transport conduit for liquids and gases. The pipe is provided with at least one integral reinforcing stem and the critical mode of failure is buckling rather than deflection. The pipe is not dependent upon surrounding backfill for lateral support as with conventional pipe or conventional reinforced pipe. The same amount of plastic is usable per lineal unit as is used in comparable conventional pipe sizes, however, the cross-section is redistributed, which achieves greater loading capacity. This patent is a possible solution to the problem; therefore, consideration will be taken so that patent infringement will not occur. Further information on this patent can be found in Appendix C. 9 FIGURE 5 – CMP LOAD DISTRIBUTIONS The above figure does not necessarily give the characteristics of CMP under hydrostatic conditions, but it does give an idea on how CMP reacts under load stresses. Chris Stoner feels that Vortex could use the data provided from buried conduits in calculating the hydrostatic forces on CMP. With further research and modeling techniques, Vortex will determine whether or not this method will represent the forces of water acting on CMP. The following equations illustrate the load distributions that are applied to CMP under soil compression. Vertical unit load on the pipe ,v, (Spangler, 1941): r W v C 2 = (3) 10 where: Wc = distributed load across top portion of pipe r = radius of the pipe. Vertical unit reaction on the bottom of the pipe ,v’, (Spangler, 1941): )sin( ' α v v = (4) where: α = bedding angle with respect to the vertical axis. Passive horizontal pressures on the side of the pipe, h, (Spangler,1941): 2 x eh ∆= (5) where: e = modulus of passive pressure of side fill ∆x = horizontal deflection of the pipe. CMP not buried in compacted soil and subjected to external hydrostatic pressure must be designed for buckling as circular tubes under uniform external pressures (AISI, 1994). If the above method cannot be used, the two formulas below can be used to determine the critical pressure on the surface of the pipe. Critical pressure, Pcr, of a corrugated metal pipe (AISI, 1994): 32 )1( 3 R EI Pcr µ− = (6) where: E = modulus of elasticity (lb/in2) 11 Ipw = pipe wall moment of inertia (in 4) µ = Poisson’s ratio (specific to material) R = mean pipe radius (in). The equation below calculates the estimated collapse pressure, PE, of corrugated metal pipe (AISI, 1994): 3 6 )105.49( R I PE ××= (7) Chapter 52 of the NRCS National Engineering Handbook (NEH) (2005) details basic properties for any type of flexible conduit. It includes corrugated metal pipe and also gives methods to calculate pressures and stresses on a pipe. The maximum allowable pressure should be limited to 20 feet of head for annular pipe and 30 feet of head for helical pipe. The vacuum load per length of pipe, Wv (lb/ft) is determined by the following equation: 12 i vv D PW = (8) where: Pv = internal vacuum pressure (lb/ft 2) Di = inside diameter of the pipe (in). If the pipe is below the water elevation, external hydrostatic pressure, Pg (lb/ft 2) can be found by: wwg hyP ×= (9) where: γw = unit weight of water (lb/ft 3) 14 First a field tour in western Oklahoma of these structures was taken to help the team visualize these structures in the field. Next, at the United States Department of Agriculture, Agriculture Research Service Hydraulics Lab in Stillwater, Oklahoma, a demonstration flume that utilizes scaled Plexiglas replicas of the inlet structures was observed. The demonstration model allowed Vortex Engineers to observe flow characteristics of the pipe with different inlet structures attached (Figure 7). Vortex Engineers performed another demonstration using red transparency film to test if failures will occur under similar conditions, but of a different material (Figure 8). In the model, the same failures occurred with red film as those reported from the field: after a certain head was reached, the left side of the film folded inwards. It is worth noting that though this model was helpful in demonstrating the process of how the pipe entrances failed, the model was not to scale, nor were the materials similar to that of corrugated metal pipe. Therefore, the model did not produce any measurable or useful data, but was useful in illustrating the phenomenon. FIGURE 7 – BLUNT INLET 15 FIGURE 8 – RED TRANSPARENCY FILM To aid in determining where failures are occurring, Vortex has performed preliminary calculations for pressure and head analysis. These calculations will identify pressure distributions which are needed to determine forces throughout a pipe. A scale model will be built of Plexiglas pipe. The scale models will aid in observing what the entrances are experiencing under different flows. Vortex Engineers also hopes to gain actual pressure and velocity measurements from the scale models. Upon completion of these tasks, Vortex can determine whether the current designs are sufficient as specified or if they need to be modified. Initial Investigation To aid Vortex Engineers in trying to solve the source of the collapse of the CMP drop inlet structures, the following procedures were performed. These procedures were successful in providing a better understanding of how the structure functions as well as an initial analysis of the problem. 16 Field Tour of Installation Sites On October 4, 2005, Vortex Engineers toured several installed GSS sites in western Oklahoma with Chris Stoner and Baker Eeds, engineers with the NRCS. The first failed inlet in the state occurred in Eeds’ service area and he has been involved with the investigation of the failures since. The first stop on the tour was a GSS owned by Gelene Schreck. The Schreck GSS had a 48” sliced hooded drop inlet with 16 gauge metal thickness (see Figure 9). It was constructed in 1993, failed in 1995, and has since not been repaired. The inlet collapsed on the left side (looking downstream), which is consistent with the other documented failures. Because of the reduced flow of the inlet, a noticeable amount of erosion had occurred in the auxiliary spillway, defeating the purpose of a GSS. FIGURE 9 – SCHRECK’S FAILED DROP INLET STRUCTURE The other three GSSs toured had not failed, though it was beneficial to see the design of the structures and how they operated. All three GSSs had had auxiliary flow in the past but had no visible detrimental effects. One GSS owned by Mr. Alexander had angle iron stiffeners installed on each side directly following construction to prevent any failures from occurring. 19 The sliced and canopy inlets displayed pressures that were slightly higher on the right side of the inlet. The blunt inlet had much more equal pressures than the other two inlets. The pressure measurements using this method are not considered to be hard and accurate data, and will not be treated as such by the design team. However, these data do give Vortex Engineers an idea of what the different inlets are experiencing as far as pressure is concerned. It also allows Vortex to get an idea of what forces could be resulting from these pressures. Physical Modeling To further investigate the pressures and forces seen by the inlets in the field, Vortex conducted two different tests: scale models to measure pressures under normal flow conditions and a full-scale model to test the structural integrity of the sliced CMP inlets. Scale Models The following sections describe the process of construction and testing of the scale models and lastly the results gathered from these tests. Construction The pressures that CMP inlets would experience needed to be determined. Because the flow characteristics for the two inlets would differ, the pressures would also be affected. Therefore, it was important to build and test both a sliced and canopy inlet. Vortex Engineers’ goal was to determine the vacuum and static pressures on a scaled down version of a structure implemented in the field. In doing this, the team could build 20 a model from actual design dimensions. Following testing, forces determined from the model could then be scaled to prototype values. Initially, the team contacted Baker Eeds, who was able to provide several designs that have been implemented in western Oklahoma. After reviewing the designs, the team decided to model a structure that contained a 48” barrel, because it is currently the most common pipe size being implemented in these drop inlet structures. The design of the inlets follows the specifications outlined by the NRCS and were modeled after the Loyd Atkinson GSS no. 1 installation (found in Appendix D), which is on a slope of 11.3%. This meant that all of the design dimensions for the model would be based off structures having a slope less than 15%. To determine the dimensions of the model and the various flow rates that would be tested, Froude scaling was used. The Reynolds number was calculated as 1.35 x 108. The following scale ratios were used from Henderson (1966): DmDpLr /= (12) where: Lr = length ratio (in/in) Dp = diameter of prototype (in) Dm = diameter of the model (in) 2/1 rr Lv = (13) where: vr= velocity ratio between model and prototype 2/5 rr LQ = (14) 21 where: Qr = discharge ratio between model and prototype Using these scaling equations, dimensions for the two models were determined to be a 12:1 ratio. Figure 13 illustrates the dimensions for the two models. FIGURE 13 – DIMENSIONS OF SLICED AND CANOPY MODELS It was not only important to use these formulas to determine the dimensions of the model but to also determine the flow rates as well. Because the model tank at the Hydraulics Lab could produce a maximum flow of 1.0 cfs, the flow rates through the models could not exceed this. After visiting with Baker Eeds, he stated the maximum 24 FIGURE 15 - SLICED INLET MODEL FIGURE 16 - CANOPY INLET DESIGN As seen from figures 15 and 16, the length of the milled areas depended on how far that particular area of the pipe was inserted into the riser. The purpose of these milled areas was to imbed the tubes within the Plexiglas, so the flow around the inlets was not affected due to disturbances on the pipe surface. Tygon tubes were used for measuring pressure and were inserted into the ports and held with super glue within the milled areas. Once the tubes were in place, Bondo® was applied to the milled areas over the Tygon tubing and smoothed to the surface of the pipe. After the Bondo® had hardened, additional tubing was added, by gradually increasing the internal diameter of the tubing and inserting them into the previous tube. Four different sizes of tubing were used to get the inside diameter to 3/16”. This process was done to match the size of the gage fitting that was used to measure the pressures. 25 To finalize the models, the inlet entrances were beveled back to sharp edges that would most closely model the flow path. An anti-vortex baffle was applied to the sliced inlet. Figures 17 and 18 show the final setups for each of the models. FIGURE 17 - FINAL SETUP FOR SLICED INLET FIGURE 18 - FINAL SETUP FOR CANOPY INLET Setup The scale models were setup and tested in a demonstration tank located at the USDA ARS Hydraulics lab (Figures 17 and 18). The model setup consisted of the sliced or canopy inlet, 4’’ rubber pipe coupler, hose clamps, roof vent, 7’ of 4’’ PVC, and a 4’’ PVC coupler. Once a hole was cut into the tank, the roof vent was attached to the tank and the PVC pipe was inserted approximately 6 inches into the tank. After the pipe was inserted, it was siliconed and hose clamped to insure that no leaks would occur around the entrance of the pipe. To get a total length of 8 feet of barrel pipe for each of the 26 inlets, an additional 7 feet of PVC pipe had to be added via a coupler. An additional 2 feet of pipe was added to the initial 5 feet that had been inserted into the tank. The rubber coupling was used to transition between the two inlets easily. Hose clamps were used to attach the coupling to the PVC and the model. To change out the model, it took nothing more than to loosen the clamp and remove the model. Figure 19 shows an illustration of how the rubber coupling was used to attach the PVC pipe to the model. FIGURE 19 - ATTACHMENT OF MODEL TO PVC Once the model was inserted into the coupling, a turn buckle was attached to the bottom of the model to the tank. This was done to insure that the model would not rise when water entered the tank and to also insure that the riser bottom was level. As described in the construction section of the scale models, tubes were inserted into ports to measure the vacuum pressures of the inlets. To help keep the tubes organized, numbers were applied to each of the tubes. In addition to numbering the tubes, they were inserted onto nails that were on a numbered board. A complete setup of the scale model testing can be seen in Figure 20. 29 Inlet Type Model Flow (cfs) Model Head (ft) Prototype Flow (cfs) Prototype Head (ft) Sliced 0.3 0.55 150 6.6 Sliced 0.4 0.59 200 7.08 Sliced 0.5 0.77 250 9.24 Sliced 0.6 0.98 300 11.76 Sliced 0.64 1.45 320 17.4 Canopy 0.3 0.54 150 6.48 Canopy 0.4 0.59 200 7.08 Canopy 0.5 0.64 250 7.68 Canopy 0.6 1.00 300 12.00 Canopy 0.64 1.58 320 18.96 TABLE 1 - HEAD MEASUREMENTS. HEAD WAS MEASURED FROM THE INVERT OF THE PIPE TO THE WATER SURFACE. Results of Pressure Testing The highest pressures on both models at the highest flow rates were recorded at ports 9 and 10, on the right side, 2” from the top of the pipe. Lowest pressures were recorded on ports 25-28 which are at the bottom of the pipe. See Figure 14 for a schematic of pipe numbers and Figure 23 for a pressure graph for the canopy inlet at 320 cfs. All other pressure graphs are in Appendix E. 0.00 5.00 10.00 15.00 20.00 25.00 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 Port Number P re ss u re ( in ch es o f w at er ) FIGURE 23 - PRESSURE READINGS FOR CANOPY INLET AT 320 CFS (0.64 CFS). 30 After combining the forces from the internal vacuum pressure and the static water pressure, the highest force seen by the model at one port was 0.7 lbs at port 9 on the canopy inlet at 0.64 cfs, which scales up to 1,211 lbs at 320 cfs on the prototype. Lower flow rates produced lower pressures. When running these tests, it was noticed that the flow was steadier at higher flow rates than at lower flow rates. Vortex Engineers believe that the lower flow rates were unsteady because the pipe would transition from being fully primed to not being fully primed. This created some fluctuation of pressures, similar to a water hammer. It was also noticed that more vortices formed at 150-250 cfs when testing the canopy inlet than were expected. The vortices were most violent at 200 cfs, which could cause pressure fluctuations within the pipe. Since the canopy was developed partially to help prevent vortex formation, it was assumed that it would have less vortex formation. However, it was observed that the canopy inlet had more vortex formation than the sliced inlet that was tested. The sliced inlet was tested with an anti-vortex baffle in place according to current design specifications. Dye Testing To observe flow characteristics around and inside these inlet structures, Vortex Engineers performed a dye test with the assistance of Dr. Glenn Brown. The dye used to perform the tests was red Rhodamine. This test was performed only on the canopy drop inlet. The dye was injected into the water with a syringe. The dye allowed Vortex Engineers to see the unstable conditions of the water inside the riser and as the water exited through the inlet. The team noticed that there was significant turbulence as the water flowed downward into the riser. As it entered the inlet, the water velocity 31 increased tremendously; as a result of the increased velocity, the dye disappeared very quickly from the inside of the inlet structure in a surging fashion. This test was helpful in allowing Vortex Engineers to see the actual flow characteristics in and around the inlet structures and could possible give implications into the cause of the vortices seen inside the inlets. Testing of Baffle Arrangement During the scale model testing, Vortex Engineers took the anti-vortex baffle off of the sliced inlet model and placed it on the canopy inlet model to see if any changes in vortex formation could be observed. There were no significant changes in vortex formation upon adding the anti-vortex baffle to the canopy inlet model. The vortex formations were cut in two, but not eliminated. Vortex Engineers changed the position of the baffle to be perpendicular to the inlet to see if that had any affect on the vortex formations as well as using other flat pieces of Plexiglas to create possible baffle designs that might be implemented. This did not reduce vortex formation either, but simply changed the location of the vortices inside the riser. This tinkering with the anti-vortex baffle did not produce any changes that could lead to a possible redesign; however, this was a very informal investigation because it only involved moving pieces of Plexiglas around by hand and observing any changes in turbulence. Strength Test on Full Scale CMP Inlets The objective of the strength test was to experimentally determine the collapse force of full size sliced and canopy inlets. This was done to provide experimental data that could be related and compared to the data obtained from the pressure tests. To accomplish this task, Vortex Engineers along with the expertise of Wayne Kiner and the BAE lab staff recreated the inlets as closely as possible to those installed in the field. A hydraulic cylinder was used to place a load on one side of the inlet, while a load cell measured the 34 FIGURE 25 – CLOSE UP OF METAL SLATS WITH DRILLED HOLES For each test, 23/64” holes were drilled through the base of an inlet and secured tightly with 5/16” nuts and bolts. This method of securing the inlet accomplished a number of things. To begin, the team members could switch out the inlets quickly and easily themselves by simply bolting and unbolting the pipe. The bolts and welded steel slats also provided ample stability and structural strength for the test. Finally, the amount of materials needed was greatly reduced because the same 1/4” plate could be reused over and over again. This also saved time, since the plate did not need to be set and reset for each run. The load was applied via a 3.5” diameter hydraulic cylinder. To provide pressure for the cylinder, it was connected to a portable pump with an electric power supply. The hydraulic cylinder was attached to a 4 foot I-beam that had been bolted to the floor with 1/2” bolts. A brace that had been fabricated in the lab for this test was attached to the I- beam and used in conjunction with a bolt and eye to support the cylinder. With this brace, the cylinder could be moved up and down to allow for proper placement. A second I-beam was bolted down and set directly behind the first one and a metal bar was wedged between them for extra support and added safety. The setup can be seen in Figure 26. FIGURE 26 – SET-UP OF HYDRAULIC CYLINDER AND I-BEAM SUPPORTS 35 To prevent the cylinder from creeping upward during testing, a long steel plate with a support arm back to another brace was extended over the length of the cylinder. To attach the cylinder to the load cell, a nut was welded to a 1/2” bolt which made the connections rigid. From the load cell, another bolt was welded to a ball joint connection. This ball joint attached to a round metal plate 5.5” in diameter, which was the device that applied the load to the inlet. See Figures 27 and 28 for a close up picture of the ball joint and overall load cell setup. FIGURE 27 – BALL JOINT MECHANISM FIGURE 28 – LOAD CELL SETUP 36 The ball joint mechanism enabled the point of contact of the load to rotate with the pipe as it deflected. This also protected the load cell from undergoing any torque, which can damage the load cell. To prevent slipping when a load was applied, the 5.5” round plate was bolted to the pipe with four 5/16” bolts. In all instances other than the first test run on a sliced inlet, the load was applied at 24” from the bottom of the inlet and 8” from the edge. The load cell used was a Chatillon load cell with a 10,000 lb capacity in both tension and compression. A Chatillon handheld display monitor was linked up to the load cell so that forces could be read and recorded. Testing To run the tests, the electric pump was first turned on, and a lever was used to displace the cylinder. As pressure was applied to the CMP inlet, it began to deflect. At the point where permanent deformation was noticed, the test ceased. Because the round 5.5” plate was bolted to the inlets, the cylinder rod had to be retracted back to a point where the load cell monitor read close to zero. Therefore, in pulling the cylinder back, some of the deformation in the metal was corrected, though the permanent deformation can still be seen. First tests on the sliced inlets were run, followed by the three canopy inlets. The data on the first sliced inlet may have been somewhat compromised because Vortex needed to use it as means to perfect the procedure and several trials were run before a failure was achieved. For most of the sliced inlets, Vortex Engineers tested both the right and the left side. The team wanted to investigate whether a failure on the left affected the strength on the 39 Sliced Inlet : Results of Strength Test for Full Scale Inlets Force Applied Pressure (Force/Area) Failure Occurred (measured from bottom) Notes Inlet 1 Left: 2500 lb Right: 2000 lb Left: 2834 psi Right: 2268 psi Left: 13.5” Tested left side first; ran 4 or 5 tests before achieved a failure Inlet 2 Left: 2200 lb Left: 2494 psi Left: 17.0 “ Only tested left side. Inlet 3 Left: 2350 lb Right: 2650 lb Left: 2664 psi Right: 3005 psi Left: 16.5” Tested right side first. Average Left: 2350 lb Left: 2664 psi Left: 15.5” TABLE 2 - SLICED INLET RESULTS Canopy Inlet : Results of Strength Test for Full Scale Inlets Force Applied Pressure (Force/Area) Failure Occurred (measured from bottom) Notes Inlet 1 Left: 2950 lb Left: 3345 psi Left: 13.5” Inlet 2 Left: 3200 lb Left: 3628 psi Left: 13.5 “ Canopy slightly bent Inlet 3 Left: 2640 lb Left: 2993 psi Left: 12.5” Canopy bent and left sides bent Average Left: 2930 lb Left: 3322 psi Left: 13.2” TABLE 3 - CANOPY INLET RESULTS The load applied for these tests was a point load. Though Vortex Engineers understands this load is different than that which an inlet would experience in the field, it was important to determine how much force would cause these inlets to collapse. Due to the difficulty presented by the corrugations, the best way to apply loads without causing slippage was bolting a flat plate to the pipe. The points of contact between the plate and the pipe are the points where the load was actually applied. 40 To determine this area of contact, blue paint was sprayed on a piece of spare corrugated pipe and the plate was laid on top of the paint then rocked back and forth. When removed from the paint, the paint left a mark on the plate where there had been contact. This area, along with the area of four 5/16” bolts was calculated and summed to give the total area. See the calculations in Table 4. From this area, pressures could be calculated from pressure equals force divided by area. Area of four 5/16” bolts 0.307 square inches Area of plate in contact with pipe (2.3”x0.25”) 0.575 square inches Total Area 0.882 square inches TABLE 4 – CALCULATION OF PLATE CONTACT AREA To make CMP, sheets of metal are corrugated and then interlocked together, making a seam that is four layers thick of metal and approximately 1” wide, and located every 21” along the pipe. This seam is therefore four times stronger than any where else on the pipe. For the sake of consistency during testing, the load was applied in the same location of the inlet, regardless of where the seam fell in relation to the load. After all tests had been completed, failure locations were measured from the bottom of the pipe and up from the closest seam. The location of failure was also measured from the closest seam. It was found that the load applied closest to the midline of the seams was the lowest force that caused a collapse in both the sliced and canopy inlets. The following figures, Figures 30 and 31 summarize the collapse force and its location on the inlets in relation to the nearest seam for the canopy and sliced inlets respectively. 41 FIGURE 30 – CANOPY INLET STRENGTH TEST DATA – LOCATION AND AMOUNTS OF LOAD FIGURE 31 – SLICED INLET STRENGTH TEST DATA – LOCATION AND AMOUNTS OF LOAD Though more testing needs to be performed to confirm this finding, it is possible that the placement of the seam will affect the inlets ability to withstand loads. It was also concluded that the variation in failure location son the sliced inlet was due to the seam. The canopy, on the other hand, has an upper support from the canopy, resulting in a more uniform failure location for the canopy inlet tests. Since the drop inlet structures in the field were failing on the left side of the pipe when looking downstream, the team decided initially to test the left side of the structure. After just testing the left side of the first sliced inlet, the team was interested to see if the overall strength of the pipe was weakened once one side of the pipe had failed. So the 44 Cost for Scale Modeling Cost Description Equipment Usage $123 BAE Lab Materials $310.75 5” Plexi-Glass Tubing Materials $66.00 PVC/Adhesive/Fittings Materials $98.00 Small Plastic Tubing for Manometer Additional Supplies $319.05 Misc. Building Supplies Total for Scale Modeling $916.80 Cost for Full-Scale Strength Test Cost Description Equipment Usage $240.00 BAE Lab-Cutting Pipe/Building Crush Test Setup $96.00 BAE Lab-Hydraulic Cylinder/Stabilizer Materials $50.00 ¼” Steel Plate Materials $500.00 48” Corrugated Metal Pipe Total for Full-Scale Strength Test $886.00 Grand Total for Project $1802.80 TABLE 5 - BUDGET Recommendations After completing the scale modeling and the full-scale strength testing, Vortex Engineers came up with recommendations to help the NRCS combat the problem. These recommendations are listed below. Scale Modeling In the testing of the scale models, it was noticed that the flow patterns of the inlets were very unstable at medium flow conditions, between 200 and 250 cfs. To help combat this problem, the head on the pipe should be raised or lowered. Three solutions to change the head on the pipe are: 1. Increase tailwater. This will cause an increase of the head on the pipe. 2. Decrease pipe size and increase dam height. This will decrease the flow rate through the pipe and create more head. 3. Increase pipe size and keep same dam height. This will move the water through the pipe faster so that the flow rate will never reach the 200-250 cfs range. 45 Vortex Engineers recognizes though, that these are engineering solutions but might not be very practical for the landowner. Another observation made during the scale model testing was that the levelness of the riser made a difference in the flow pattern and formation of vortices. Keeping the riser as level as possible during installation will help reduce disturbances in the flow pattern and decreases the amount of vortices formed. Full-Scale Strength Testing Some recommendations derived from the full-scale strength testing are: 1. Current Solution – Angle Iron. Vortex Engineers believes that the current solution of reinforcing the pipe with angle iron is sufficient to prevent collapse. 2. One-Piece Angle Iron, two arcs on each side. One way to make installation of angle iron easier would be to use one bent piece of angle iron, as opposed to three separate pieces, as is currently the standard. 3. Seam placement. It was found that a seam where the pipe is fused resists more force than normal corrugations. If the inlet could be cut so that a seam is located on the left side of the pipe near the area of concern, the inlet could withstand more force. The final recommendation would be to complete further testing and analysis of the design and specifications for the inlets. This might include a complete redesign of the drop inlet structure. 46 References American Iron and Steel Institute 1994. Handbook of Steel Drainage & Highway Construction Products. Washington D.C.: AISI. Blaisdale, F. Hydraulics of closed conduit spillways: Part I. Technical Paper No. 12, Series B. St. Anthony Falls Hydraulic Laborotory. United Stated Department of Agriculture. 1952. Haan, T., B. Barfield, J. Hayes, Design Hydrology and Sedimentology for Small Catchments. Academic Press, San Diego, CA. 1994. Henderson, F.M. Open Channel Flow. Macmillan, New York, NY. 1966. Kitoh, Osami. 1991. “Experimental study of turbulent swirling flow in a straight pipe”. Journal of Fluid Mechanics. (225):445-479. Spangler, M.G. December 24,1941. The Structural Design of Pipe Culverts. Bulletin 153. Ames, Iowa: Iowa State College of Agriculture and Mechanic Arts. Steichen, J. 1993. Design Criteria for Canopy and Hood Inlet Spillways. Columbia, Missouri: University of Missouri. Stoner, C. December 15, 2000. Memo: Research Needs –Canopy Inlet Drop Structures to Johnny Green, State Conservation Engineer, NRCS. USDA – NRCS. USDA-NRCS. 1984. National Engineering Field Handbook, Ch. 6: Structures. USDA Natural Resources Conservation Service. USDA-NRCS. 1968. National Engineering Handbook, Section 11: Drop Spillways. USDA Natural Resources Conservation Service. USDA-NRCS. 2005. National Engineering Handbook, Ch. 52: Structural Design of Flexible Conduits. USDA Natural Resources Conservation Service. USDA-NRCS. 1956. Technical Release 3: Hood Inlets for Culvert Spillways. USDA Natural Resources Conservation Service. USDA-NRCS. www.nrcs.usda.gov, accessed September 2005.