CE415L Applied Fluid Mechanics Laboratory

Transcription

1 Applied Fluid Mechanics Laboratory Learning Objective Following completion of this experiment and the analysis of the data, you should be able to 1. generalize results of introducing changes to a natural stream 2. distinguish between qualitative and quantitative forms of observation and analysis 3. use photographs to document observations and to support the verbal description and analysis Introduction Many civil engineering projects involve placing structures in or near natural waterways, such as streams and rivers. These structures may be bridges or culverts that allow a road, railroad, path or pipeline to pass over them. A structure, such as a pipeline, might also be placed below the stream bed to convey the material to be transported across the stream. Modifications to the stream elements, such as armoring the stream bank or bed might also be constructed with the intention of controlling erosion at those locations. A more drastic change would be to reroute the stream to make way for a building project. Regardless of the type of construction or its intended purpose, the stream dynamics will always affect and be affected by changes imposed on the stream. Purpose The primary purpose of this experiment is to initiate a variety of modifications to a model stream and to observe, record and describe how the stream responds to those changes. Modeling real-life systems is an inherently complex undertaking. Though such modeling can provide useful data and insight into actual processes, it is also difficult to ensure that results obtained in the model are truly representative of the real world. In this experiment, we are mainly interested in observing basic erosion-deposition processes common to many civil engineering projects. Another purpose of this experiment is to help you to distinguish between qualitative quantitative observation and analysis. Working definitions we could use for conducting and report this experiment include qualitative noting the physical appearance of and changes to the stream bed material distribution and water flow rates and patterns quantitative -- measuring the physical dimensions of and measurable changes to the stream bed materials and water flow patterns Equipment The following equipment will be provided: Stream table with moveable bed material (plastic sand-size particles) Timer Camera Various structure models and components Procedure For all of the following parts, assume that the normal stream flow is generally north to south Dept of Civil Engineering, SIUE 1 of 7 Revised 8/22/2013

2 Part 1 - Establishing the Existing Stream (Baseline) The water supply to the stream table should be connected. With no structures in the streamway, slowly turn on the water and adjust the flow rate using the knob (at the bottom of the flow meter unit) so that a natural-looking, relatively stable, channel forms over several minutes. You should note that the foam subbase underlying the stream bed material has two shallow channels formed into it to encourage the stream to form into two relatively narrow portions of the table. Be sure to keep this in mind and locate the constructed modifications so that the stream is not forced to go too far outside the pre-formed channel areas. Part 2 Constructing Projects in the Existing Stream A. Bridge Foundations 1. Construct the model bridge across a developed channel. Install approach slopes. 2. Restore the channel and bank surfaces to the original condition after the bridge is constructed. 3. Photograph the as-built conditions. 4. Resume stream flow. Observe: a. Erosion (scour) at foundation elements and in adjacent areas of the channel and bank b. Deposition at foundation elements and in adjacent areas of the channel and bank 5. Stop stream flow after 2 minutes. Photograph the new conditions. 6. Photograph or sketch (in plan view) the stream channel shape after the stream flows. 7. For the analysis, describe a. how the bridge foundation affected the stream channel, b. how the approach slope backfill affected the stream channel c. how changes to the stream channel could affect the bridge or approach slopes. B. Culverts 1. Construct the model single culvert in a well-developed channel. The inside bottom (invert) of the culvert should be level with the top of the sediment on the stream bed. 2. Backfill up to the sides of the culvert. Otherwise restore the channel and bank surfaces to their original condition after the culvert is constructed. 3. Photograph the as-built conditions. 4. Resume stream flow. Observe: a. Erosion (scour) at culvert and in adjacent areas of the channel and bank b. Deposition at culvert and in adjacent areas of the channel and bank 5. Stop stream flow after 2 minutes. Photograph the new conditions. 6. Photograph or sketch (in plan view) the stream channel shape in the area of the culvert (within a length up to 2 times the channel width both upstream and downstream of the culvert) before and after constructing the culvert Dept of Civil Engineering, SIUE 2 of 7 8/22/2013

3 7. For the analysis, describe d. how the culvert affected the stream channel e. how observed changes to the stream channel could affect the culvert performance, both structurally and hydraulically. 8. Repeat the steps above using a double culvert with both culverts having the same invert elevation. Part 3 Stream Modifications A. Stream Relocation 1. In a reach of the stream that appears to be relatively stable, relocate the main channel to either straighten it or induce a curve around some hypothetical structure or building project area. Do not merely insert a structure into the stream, but instead reconstruct the stream channel shape to force the stream to follow a new intended path. Using flags, mark the boundaries (property line) of the project area. 2. Restore the channel surface where the relocation begins and ends to the original condition. 3. Photograph the as-built conditions. 4. Resume stream flow. 5. Stop stream flow after 2 minutes. Observe any significant changes to either the newly constructed reach or adjacent portions of the existing stream. Photograph the new conditions. 6. For the analysis, describe a. how the relocation affected the stream channel, b. how changes to the relocated stream channel are tending to affect the relocation project c. observable or potential problems for adjacent properties resulting from the project. B. Bank Stabilization 1. Select a straight section of the stream channel that seems to have a well-defined, yet eroding bank shape. 2. Photograph the existing conditions. 3. Add protection to the face of the bank with the goal of protecting a structure located near the top edge of the bank. 4. Resume stream flow. Observe: a. Erosion (scour) in adjacent areas of the channel and bank b. Deposition in adjacent areas of the channel and bank 5. Stop stream flow after 2 minutes. Photograph the new conditions. 6. Photograph or sketch (in plan view) the stream channel shape in the area of the protected bank (within a length up to 2 times the channel width both upstream and downstream of the construction) before and after constructing the bank stabilization Dept of Civil Engineering, SIUE 3 of 7 8/22/2013

4 project. Include important dimensions, such as distance from the bank edge to the structure you are trying to protect, channel width, erosion, etc. 7. For the analysis, describe a. how the bank protection affected the stream channel b. how changes to the stream channel affected the protected bank. 8. Repeat the steps above for a structure located at the top of the bank on the outside of a curved stretch of the stream. Part 4 Stream Flow Changes A. Stream Flow Rate Increase a. Remove all structures from the stream and re-establish a stable stream profile at a low flow rate. Use the flow meter indication times ten as the flow rate quantity in units of cubic feet per second. b. Choose and mark reference points at three selected locations along the stream length. c. Photograph and sketch the streambed and bank details at each reference location. d. Note significant channel and bank changes resulting from the increased flow rate. e. Adjust the stream flow rate to be twice the original flow rate. Run the stream at this flow rate for 2 minutes. f. Photograph and sketch the streambed and bank details at each reference location. B. Stream Flow Rate Decrease a. Adjust the stream flow rate to be equal to the original low flow rate. Run the stream at this flow rate for 2 minutes. b. Photograph and sketch the streambed and bank details at each reference location. c. Note significant channel and bank changes resulting from the decreased flow rate. Analysis and Report Analysis for this report should focus on carefully observing and concisely commenting on the qualitative behavior of the stream channel following the introduction of changes to the stream. You should note that this differs from your other civil engineering lab courses where specific physical measurements were dictated by the lab procedure and the results were expressed numerically following prescribed computations. The Summary of Results table shall include a description, written in two or three complete sentences (including references to figures), that summarizes the most significant observations for each structural change made to the stream. Please note that the figures (photographs and sketches) comprise your data for which your work is evaluated. This evaluation then is strongly based on the following items: clearly annotated with captions and callouts (see Exhibit A, attached) to aid the reader in identifying the features mentioned in the commentary; original and modified stream flow path(s) are clearly marked; figures are in the order that you refer to them in the Summary of Results. only include figures that you reference in the Summary of Results Dept of Civil Engineering, SIUE 4 of 7 8/22/2013

5 Photography suggestions Photographs are a very important tool commonly used to document engineering explorations, observations and conditions. Photographs not only help you tell the story to others but can also help remind you about important features and even help you see something you may not have noticed when you were originally on site. The photographs that you take in the course of this experiment they will be the primary data used to illustrate the observations for your experiment. Here are some tips to help get good quality photographic documentation. 1. Take lots of photographs. You can choose which ones to keep and use later. 2. Take photographs standing back at a distance to establish the project surroundings. These photo graphs help to establish a sense of scale and how the project fits into its surroundings. Shoot from a high (aerial) point of view if feasible and from the point of view of an observer on the ground. 3. Come closer to the subject of the photograph, such as to frame the entire bridge or culvert. This helps the viewer to narrow the frame of reference and concentrate on the main subject. This is where many details may be highlighted if clearly visible at this scale. 4. Zoom in or use macro-focus to take a close-up view of some detail. When you get to within a few inches of the subject you should consider turning the flash to OFF to avoid hot-spots and unequal coverage of the flash. Also be sure to avoid moving the camera because at close distance and low light camera movement becomes very apparent. 5. Take lots of photographs Dept of Civil Engineering, SIUE 5 of 7 8/22/2013

6 Exhibit A Examples of photographs with annotations to include in the report. Be sure to include the legend on the first page of the photo attachments. The general stream direction is assumed to be north to south. Figure A-1 - Looking upstream at the proposed bridge site from the downstream (south) side. The red line traces the approximate stream profile at the bridge location. Original stream path Modified stream path Channel profile (light from laser level) LEGEND Dept of Civil Engineering, SIUE 6 of 7 8/22/2013

7 The piers supporting the east end of the bridge are located at about the location of the main channel the stream had created prior to construction. Figure A-2 - Looking upstream at the bridge nearing completion of construction. Water was not flowing in the stream during construction. Scour downstream of the bridge and a deflected channel caused erosion of the east embankment. Upstream of the bridge, scour of the stream channel pattern widened somewhat to the east and west. Figure A-3 Aerial view of the bridge and stream following five minutes of flow occurring after the end of construction. The stream runs left (north) to right (south). The bridge piers and new abutment slopes have caused the stream channel to split around the piers and flow at greater velocity at and to a distance of eight to ten stream-widths downstream of the bridge location Dept of Civil Engineering, SIUE 7 of 7 8/22/2013