Preliminary Design Report Clay County, Florida Carpet n Drapes Culvert Repair and Rehabilitation July 21, 2006

Transcription

1 Clay County, Florida Carpet n Drapes Culvert Repair and Rehabilitation July 21, Background and Repair and Rehabilitation Recommendation Clay County has contracted Camp Dresser & McKee Inc. (CDM) to perform design and permitting of the repair and rehabilitation associated with the failing underground culvert near Carpet n Drapes on Blanding Blvd., east of Blanding Blvd., north of Spencer Rd. (Figure 1) The twin 72-inch corrugated metal culverts are to be rehabilitated, as the parking lot above the pipe and adjacent to the building has collapsed several times. Evaluation of hydraulics, constructability, design life, and cost has yielded the recommendation that the County rehabilitate the existing twin corrugated metal pipes with a high density resin lining commonly known as Cured in Place Pipe (CIPP). Other options for replacement and alternate routes were more costly than the available budget. 2.0 Stormwater Evaluation 2.1 Problem Identification Several sinkholes developed in the parking lot of Carpet n Drapes during 2005 (Figure 2). Internal inspection of the pipes found that the northern culvert was failing in multiple locations, typically at or below the normal flowline elevation. The worst failure area in the pipe consists of a Figure 2: Sinkhole in Parking Lot of Carpet N Drapes A 1

2 Blanding Blvd. Headwall Failure Area Carpet n' Drapes All-Tune Sp en ce r Rd. Figure 1 Clay County: Carpet 'n Drapes Culvert Design Location Map Model Conduit A Feet 200 µ ORANGE PARK, FL

3 portion of pipe that has failed and the bottom of the pipe is now protruding upward into the area of flow (Figure 3). Exposed soil at such failure locations is at risk of being dislodged due to event flow in the pipe. Large events or multiple small events can result in large underground voids, which can collapse, forming surface sinkholes as shown in Figure 2. As part of the site investigation, a geophysical study of the parking lot was conducted using ground penetrating radar. The intent of this study was to determine if any voids in the soil had fingered out laterally to the flowline of the pipes. No anomalies in soil density were identified lateral to the pipes. Figure 3: Failure within Pipe with Bottom Protruding Into Center of Pipe 2.2 Existing Conditions Model The Stormwater Management Model (SWMM) developed by CDM in 2001 for the Loch Rane and Bel-Med Stormwater Management Plan was used as the basis for the hydraulic evaluation of the recommended alternative. The mean-annual, 10-year, 25- year, and 100-year/24-hour design storms were used to determine the hydraulic equivalent for each of the alternatives evaluated (hydraulically equivalent to the existing system). The portion of the model relevant to this study is shown in Figure Equivalent Conduit Evaluation For the twin 72-inch culverts, 4 equivalent pipe types were evaluated for replacement: 1. Twin 72-inch aluminized steel 2. Twin 62-inch reinforced concrete pipe A 2

4 Blanding Blvd. LR Acres "/ LR064S LR065S LR070 "/ LR Acres "/ LR Acres LR Acres LR Acres Kingsley Blvd. LR064S LR Acres LR065S LR070 LR Acres PROJECT AREA µ 0 Feet ,000 1,500 2,000 Figure 4 Clay County: Carpet 'n Drapes Culvert Design Model Schematic A Hydrologic Units Model Junctions TYPE Extran Linking "/ Extran Storage Model Conduits ORANGE PARK, FL

5 x 6.5 preformed concrete box culvert inch CIPP rehabilitated pipe: in-place high density resin lining of existing pipe approximately 1-ft thick CIPP. Manning s roughness values (n) for the existing pipes and the four alternatives are shown in Table 1. For each alternative, pipe sizes were adjusted such that no stage increase occurs upstream or downstream of the replacement pipe for the 25- and 100- year storms. The aluminized steel option was not evaluated for hydraulic equivalency, as it would perform identically to the existing corrugated steel pipes. Table 1: Manning s n Values Conduit n Existing Aluminized Steel Reinforced concrete (round) Reinforced concrete (box) CIPP (resin-lined) For the CIPP option, peak stages and flows are shown to increase for all design storms by replacing the 72-inch CMP with a 70-inch CIPP alone. This is due to the low friction and n value for the resin lining combined with the relatively small reduction in area associated with the lining. As part of the recommended design, a trash rack is recommended at the inlet to the pipes. The rack will provide a public safety function and has been designed to also compensate for the increased flow capacity of the CIPP rehabilitated pipes. This hydraulic equivalency is to be the basis of the SJRWMD permit exemption. 3.0 Construction 3.1 Project Considerations for Culvert Rehabilitation Several constraints and project considerations exist regarding the constructability of any of the replacement options specified above: 1. The pipe run contains two bends of approximately 40 degrees each. The resin lining system is only able to be applied through one bend at a time. Therefore, excavation at the location of the easternmost bend will be required; one length of the CIPP run will be applied west, and one east. A concrete junction box is recommended at this location with manhole access to both pipes. 2. The excavation of the area in (1) may be an open cut or potentially a sheetpiled excavation, according to the contractor s discretion. Due to the proximity of the building and previous earth movements near it, a preconstruction survey is required as previously agreed with the County. In addition, temporary shoring of the southeastern corner of the building with mini-piles is required to ensure no property loss is incurred due to the construction of the junction box. A 3

6 3. Contingencies for construction in the wet will be required, as the system will need to have the ability to convey baseflow and event flow during construction for any replacement option. 3.2 Rehabilitation Options An alternative to rehabilitate the pipe with a CIPP was evaluated and found to be the preferred alternative for this project. A 1.06-inch thick application of resin lining would be required to be adhered to the existing pipe to obtain a structurally sound pipe with a safety factor of 2.0 and a design life of 50 years. One advantage of this technology as typically employed is that above ground structures and infrastructure are minimally disturbed. The technology has been used since the 1970 s and has a proven track record: CIPP is the most widely used pipe rehabilitation method worldwide and accounts for more than all other methods of rehabilitation combined (Figure 5). Figure 5: CIPP Diagram and Example Rehabilitation Project A 4

7 3.2.1 Snap Lining Rehabilitation Another pipe rehabilitation method that was evaluated and found not to be the preferred option is a snap lining system. This system involves lining the existing pipe with a segmental high density polyethylene (HDPE) pipe which contains a system which snaps the segments together automatically when pressed in place. This type of system for this project has two disadvantages which were found to preclude this option. First, three excavations would be required: one at each bend in the pipe and one at the sidewalk/apron adjacent to Blanding Blvd. One of these excavations would be much closer to the Carpet n Drapes building than the excavation proposed in the CIPP alternative. The excavation near Blanding Blvd. would require a retail traffic detour/contingency plan for the three affected retail establishments. Second, the snap lining system results in a system with up to 32 individual pipe joints. Each joint is a point of potential future failure if not installed, or snapped, correctly. In contrast, the CIPP solution has no joints and only one excavation near the rear of the retail establishments, which should not impact traffic significantly. 3.3 Headwall and Lined Ditch The channel near the headwall has multiple failure areas and areas where flow is below or behind the ditch pavement (Figure 6). There does not appear to be steel rebar in the concrete. There are three additional large failures upstream of the headwall, and many signs of more failure areas to come. Due to the steep sideslopes (1.5:1 H:V) and the high rate of flow (385 cfs for the mean annual storm), re-armoring the channel with a more durable material is required. Articulated concrete block is recommended to provide the needed channel protection (Figure 7). It is able to be installed on the steep slopes and will allow vegetation to become established through interstitial spaces between concrete blocks. Figure 6: Failure Area at Headwall A 5

8 Figure 7: Articulated Block Installed on Steep Slopes 4.0 Cost Analysis A preliminary conceptual cost estimate was prepared for each alternative evaluated for the culvert replacement using vendor estimated pricing, average 2004 City of Jacksonville bid prices and 2005 Florida Dept. of Transportation (FDOT) Statewide Average Construction Cost Index (Table 2). 5.0 Recommendation The recommendation for CIPP solution is based on three factors: 1. Constructability 2. Durability a. The CIPP solution is the least invasive option available to the County. There is only one excavation of the parking lot which will not affect access to Blanding Blvd. Pipe replacement methods would require a longer construction window, site-wide excavation and sheetpiling, more time of exposure to risk (e.g., a large flood event), no joints in the pipe run, and maintenance of traffic plans. a. Durability and performance of CIPP is superior to other rehabilitation methods available. b. Calculation of design life for the CIPP rehabilitation option is 50 years. A 6

9 Table 2 Clay County Carpet 'n Drapes Culvert Replacement Preliminary Cost Estimates Cast in place pipe Twin 72" aluminized steel pipe replacement Units Quantity Unit Price Estimated Cost Units Quantity Unit Price Estimated Cost Mobilization EA 1 $ 5,000 $ 5,000 Mobilization EA $ 5,000 Pipe Lining EA 640 $ 906 $ 580,000 Excavation CY $ 12,960 Excavation (regular) CY 261 $ 6 $ 1,566 Sheet piling SF $ 556,800 Junction Box EA 1 $ 102,315 $ 102,315 Bldg. shoring EA $ 60,000 Mitered End EA 1 $ 20,843 $ 20,843 Pipe cost LF $ 99,097 Articulated Block SY 2,034 $ 63 $ 128,142 Junction Box EA $ 102,315 Fence LF 420 $ 16 $ 6,720 Pipe installation EA $ 276,480 Silt Fence LF 820 $ 3.71 $ 3,042 Headwall EA $ 20,843 Building Shoring EA 1 $ 45,000 $ 45,000 Site demo SY $ 14,560 As-builts EA 1 $ 5,000 $ 5,000 Paving SY $ 8,320 As-builts EA $ 5,000 Contingency 30% $ 269,000 Contingency 30% $ 348,000 Total 1 $ 1,167,000 Total $ 1,509,000 Equivalent 6.0' X 6.5' RC precast box culvert Twin 62" RCP Class II pipe replacement Units Quantity Unit Price Estimated Cost Units Quantity Unit Price Estimated Cost Mobilization EA 1 $ 5,000 $ 5,000 Mobilization EA $ 5,000 Excavation CY 2160 $ 6 $ 12,960 Excavation CY $ 12,960 Sheet piling SF 40,000 $ 14 $ 556,800 Sheet piling SF $ 556,800 Bldg. shoring EA 3 $ 20,000 $ 60,000 Bldg. shoring EA $ 60,000 Pipe cost LF 320 $ 960 $ 307,200 Pipe cost LF $ 131,241 Junction Box EA 1 $ 102, $ 102,315 Junction Box EA $ 102,315 Pipe installation EA 1 $ 276,480 $ 276,480 Pipe installation EA $ 276,480 Headwall EA 1 $ 20,843 $ 20,843 Headwall EA $ 20,843 Site demo SY 520 $ 28 $ 14,560 Site demo SY $ 14,560 Paving SY 520 $ 16 $ 8,320 Paving SY $ 8,320 As-builts EA 1 $ 5,000 $ 5,000 As-builts EA $ 5, Rounded to nearest 1,000 Contingency 30% $ 411,000 Contingency % $ 358,000 Total $ 1,780,000 Total $ 1,552,000 Z:\6222_Clay_County\49775_Carpet-n-Drapes\PDR-2\CIPPCostTable xls 7/27/2006

10 3. Cost References a. The cost differential between a pipe replacement solution and a pipe rehabilitation solution is approximately $700,000 and would be greater than the available budget. This excludes all replacement options from recommendation. Chow, V.T., (1959), Open-Channel Hydraulics; McGraw-Hill, New York, NY. Metcalf and Eddy, (1972), Municipal Stormwater Management; McGraw-Hill, New York, NY. A 7