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HomeMy WebLinkAbout; Beach Avenue Sewer Technical Memorandum; Beech Avenue Sewer Technical Memorandum; 2008-06-01Technical Memorandum City of Carlsbad - Beech Avenue Sewer City of Carlsbad Client Representatives Mark Biskup Terry Smith Boyle Engineering Corporation Project Team Jeff Marchioro, PE Roman Obzejta, PE Dave Arthurs, PE Jacobs Associates Trenchless Design Craig Camp Reviewer 17104.02-0001-001 June 2008 7807 Convoy Court, Suite 200 San Diego, CA 92111 MEETING AGENDA September 25,2008 TO: FROM: ATTENDANCE: Attendees, File (SD- 17104.01 and 17104.02) Jeff Marchioro Mark Biskup Terry Smith Roman Obzejta Amanda Combs Jeff Marchioro City of Carlsbad City of Carlsbad Boyle Engineering Corporation Boyle Engineering Corporation Boyle Engineering Corporation Carlsbad Offices, 1635 Faraday Avenue TIME: 11:30 A.M. Home Plant and Beech Avenue Sewer Pipelines LOCATION: SUBJECT: AGENDA ITEMS: 1. City 60% comments 2. Coordination • Temporary Facilities • Easements and NCTD o Width of permanent easement on private property containing 10-inch VCP sewer o Temporary construction easement dimensions o Home Plant trees and rock wall on NCTD property lines o Beech Avenue manhole - NCTD flagman o Encroachment agreement (new and amendments) • Village Business Association • CEQA • Sewer lateral depth r H:\Carlsbad\17104.0l\Docs\1095-Mtgs\Meetmg Agenda 031808.doc SOVLi Technical Memorandum Beech Avenue Sewer Introduction The City of Carlsbad (City) owns and operates the Beech Avenue sewer line located along Beech Avenue between Ocean Street and Washington Street in Carlsbad, CaUfomia as part of the City's sewer collection system. Figure 1. City staff reported that the sewer line is in poor structural condition. It is located in commercial beach community with the busy time during the summer. Figure 1: Location Map The Preliminary Construction Plans for Beech Avenue Sewer Project, Krieger & Stewart, Inc., June 2007 show replacement of the existing sewer line between the existing manholes in Ocean Street and Washington Street. The previous design called for removal and replacement ofthe existing sewer line; however, a construction method (e.g.; conventional open trench or trenchless construction) was not specified and details corresponding to the selected construction methods were not included. A geotechnical evaluation {Preliminary Geotechnical Report Beech Avenue Sewer Project, Carlsbad, California, Inland Foundation Engineering, Inc., July 9, 2007) was prepared in connection with the previous design. The geotechnical report was revised to include considerations for trenchless construction on February 26, 2008. The City has engaged Boyle Engineering Corporation (Boyle) to provide final design services for the Beech Avenue sewer line replacement. 6/23/2008 XOVLi Technical Memorandum Beech Avenue Sewer Project Background The City desires to improve the existing Beech Avenue 8-inch, 1,000 foot long sewer line is prone to sedimentation and clogging because it contains low spots/sags through a shallow slope. Also, the cast iron and vitrified clay segments is corroded and cracked as shown through CCTV observations. The City prefers trenchless methods because replacement through conventional open trench methods would be challenging because of its depth and proximity to other utilities. Also, traffic control would be difficuh especially for Carlsbad Boulevard, Figure 2. The pipe is relatively deep (range of 13 to 30 foot depth) and the deepest section is generally west of Carlsbad Boulevard near Garfield Street, Figure 3. Figure 2: Project area where the existing sewer line is deepest. Photo taken from intersection of Beech Avenue and Garfield Street looking towards Carlsbad Boulevard 6/23/2008 /3CDVU Technical Memorandum Beech Avenue Sewer Figure 3: Beech Avenue looking towards Carlsbad Boulevard 6/23/2008 Technical Memorandum Beech Avenue Sewer Pipe Hydraulic Capacity Boyle studied the hydraulic capacity of the existing pipe and proposed replacement pipe. Three pipe diameter alternatives were considered - matching the existing 8-inch diameter or upsizing to 10-inch or 12-inch diameter. City staff expressed interest in upsizing the pipe if it makes sense hydraulically. Staff indicated that the peak flow measured in November was 150 gpm. However, the peak flow could be higher during the summer because it's a commercial beach commimity with the busy time during the summer. 12-inch diameter pipe was evaluated because 12-inch corresponds to the smallest micro tunneling machine available. The existing 8-inch sewer pipe shallowly slopes from Ocean Street to Washington Street. The shallow (0.003 per City of Carlsbad, Project 77-27, ref dwg No. 188-9) slope that transitions to a vertical curve containing steeper sections near the railroad tracks. The shallow (0.003) slope segment does not generate sufficient velocity to prevent sediment and oil/grease buildup at low flow conditions as shown through CCTV observations. The length of vertical curve will be reduced to provide a consistent and slightly steeper slope (estimated at 0.0055) that will increase/improve velocity and capacity. The improved slope will not significantly affect replacement costs because the new pipe will be constructed in a new alignment utilizing trenchless methods. The following table summarizes hydraulic data for the existing 8-inch pipe with existing slope (0.003) and proposed the following 8-, 10- and 12-inch pipe alternatives with the improved slope (0.0055). Hydraulic data provided in the table below is derived from Manning Formula based on pipe slope as indicated and friction factor n=0.011. Maximum design capacity of the pipes was established based on 1/2 full pipe (d/D=50%). The minimum flow rate (40 gpm) was based on the maximum flow rate provided by City staff (150 gpm peak flow measured in November) assuming a peaking factor of 4. 6/23/2008 4 GOVLi Technical Memorandum Beech Avenue Sewer Table 1: Pipe Hydraulic Capacity m •m Flow Criteria Flow Rate Depth/ Diameter Ratio (%) Velocity (fps) m (Spm) (mgd) Min Flow 40 0.06 22 1.5 Existing 8-inch, 0.003 slope Max Flow 150 0.22 46 2.1 mi Existing 8-inch, 0.003 slope Capacity 176 0.25 50 2.2 m Alternative 1: 8- Min Flow 40 0.06 19 1.8 m Alternative 1: 8-Max Flow 150 0.22 45 2.9 -inch, improved 0.0055 slope Capacity 238 0.34 50 3.0 Mi Alternative 2: 10- Min Flow 40 0.06 14 1.8 Alternative 2: 10-Max Flow 150 0.22 28 2.6 inch, improved 0.0055 slope Capacity 431 0.62 50 3.5 Alternatives: 12- Min Flow 40 0.06 12 1.7 — Alternatives: 12-Max Flow 150 0.22 22 2.6 inch, improved 0.0055 slope Capacity 700 1.00 50 4.0 The improved 0.0055 slope with either the 8-inch , 10-inch or 12-inch diameter pipe sizes are acceptable using hydraulic criteria. AU considered pipe sizes have reserve capacity and have similar cleansing velocities at the minimum flow rate. The cost differences between the 8-inch, 10-inch and 12-inch alternatives are presented at the end of this Technical Memorandum. Geotechnical Investigation A geotechnical investigation ofthe pipeline alignment titled Preliminary Geotechnical Report Beech Avenue Sewer Project, Carlsbad, California, February 26, 2008 by Inland Foundation Engineering, Inc. Consulting Geotechnical Engineers concluded that there are no unusual geologic hazards (active faults, landslides, or liquefiable soils) and the proposed construction is geotechnically feasible for open-cut and/or trenchless construction techniques. The report also concluded that some existing geotechnical materials are expected to be well cemented; however excavatable with conventional heavy-duty earth moving equipment. Groundwater was encountered only in one of three exploratory borings at a depth of25-ft. The ground type is anticipated to be predominately granular soils consisting of interbeded silty sands and sands. These materials were generally observed to be moderately dense to dense condition. Larger boulders were encountered within one ofthe on the exploratory boring at the depth of 26-ft, the estimated depth ofthe proposed sewer pipe in this location is 17-ft. 6/23/2008 Technical Memorandum Beech Avenue Sewer Proposed Improvements The proposed project includes the following improvements, Figures 4 and 5, assuming that Carlsbad prefers to proceed with the 12-inch diameter alternative because that size corresponds to the smallest microtunneling machine available. One disadvantage ofthe 12-inch diameter alternative is that the new 12-inch pipe will terminate into an 8-inch section near the NCTD Right of Way. • Approximately 1,024 ft of 12-inch sewer pipe constructed through a combination of open trench and trenchless methods. The proposed new pipe alignment is roughly 12 feet north of and parallel to the existing sewer. The project will be completed utilizing a trenchless construction method in four drives (3 long drives at approximately 250 - 280 lineal feet each and 1 short drive at approximately 70 feet long). • Five deep manholes • Modification of one existing manhole at the intersection of Beech Avenue and Ocean Street. • An 8-inch shallow sewer pipe collection system, approximately 350 If long, including three shallow manholes, to intercept five existing sewer laterals. • Re-connection of three existing sewer laterals to the new 12-inch main line. The existing pipe will be filled with concrete slurry and abandoned in place. • Reroute or bypass existing gas main (varies from 1-1/4" to 2" diameter) at excavation sites. • Reroute or bypass existing 8-inch water main through the intersection of Garfield Street. 6/23/2008 6 tBOVLk -50- - t ^ C..55X mnunmmnina can^Ofm-nan 7807 CONVOY COURT, SUITE 200 SAN DIEGO, CA 92111 (858)268-8080 JS - JACKING STATION RS - RECEIVING STATION FIGURE 4 DWC; H.\Cor1sl»tf\17l04.0AC«\f^on»l\Fi9WM t and S.dwg WIE; Jun 21. 2008 11:11am XREFS: 86O-5_2)0_BEE C-m C-B03 D D n D n D I I D D B I I C y I I I I EnoinEEFtina confonnTion 7807 CONVOY COURT. SUITE 200 SAN DIEGO. CA 92111 (858)268-8080 OWC; H\Co'lslwd\l"04.02\C*D\Plansel\Fi9ufM 4 ond S.dwg DATE: Jun 23. 2008 10:54om XREFS: 86O-5_2s0_BEE 40 20 0 40 80 120 FIGURE 5 C-RP C-HA C-BD3 Technical Memorandum Beech Avenue Sewer The open trench construction will be utilized at the ends of the project. The open trenches will serve as receiving locations for the trenchless segments. • West End. The trenchless to open trench transition will be located between Garfield Street and Ocean Street at approximately at Station 11+30 intercept two sewer laterals in the vicinity of Station 11+25, Figures 4 and 6. [j Figure 6: West End of Project East End. The trenchless to open trench transition will be located in the intersection of Beech Avenue and Washington Street, on the northern side of the street knuckle to facilitate flow of the existing one way only traffic traveling west on Beech Avenue from Washington Street Figures 4 and 7. It will include two manholes separated by approximately 20 feet of new sewer pipe to minimize excavation in the NCTD Right-of- Way. The existing manhole located in the NCTD Right-of-Way appears under the structural influence of the railroad tracks. Figure 8. Locating the connection point outside of the NCTD Right-of-way will avoid this manhole near the railroad tracks and also minimize impact to the 12-inch high pressure gas main. The existing sewer to remain (approximately 34 feet) is in excellent condition, with exception of one cracked VCP pipe near the connection to the downstream manhole (2 feet upstream from manhole) per CCTV inspection records. This pipe can be repaired from the existing manhole using a typical repair method such as local lining with polyester felt impregnated with epoxy resin or injection in the pipe's crack epoxy resin or grout to stabilize pipe and prevent infiltration. I 6/23/2008 Technical Memorandum Beech Avenue Sewer Figure 7: East End of Project Figure 8: Existing Manhole in NCTD Right-of-Way 6/23/2008 10 Technical Memorandum Beech Avenue Sewer Construction Methods The following trenchless construction methods were evaluated: • Pilot-tube technology was eliminated from further evaluation because it is unlikely that suitable equipment for this technology will become available for this project. The geotechnical invesfigation found well-cemented soils conditions (N-value »50) at the proposed pipe elevation. Currently, pilot-mbe methods are generally better suited to soft soils (N-values 50 or less) for the equipment available in this region. It is unlikely that equipment powerfiil enough for N-values greater than 50 would become available at the time of construction. However, pilot tube technology should not be completely ruled out because the technology is rapidly developing. The availability of pilot tube equipment suitable for this project will be monitored during the design phase. • Pipe bursting method was eliminated due to presence of concrete encasement of existing sewer. Also, bursting would not improve the existing sag issues or cleaning velocity. • Microtunneling and auger boring methods are suitable for this project, and both methods will be specified in contract documents. As discussed in the Pipe Hydraulic Capacity section above, 12-inch diameter pipe was also evaluated because 12-inch diameter corresponds to the smallest microtuimeling machine available. o Cost. Compared to auger boring, microtunneling is generally more expensive because of relatively high cost of rental and operation of equipment. o Access Pits. • The main advantage of microtunneling equipment is that it requires a smaller footprint, resulting in less disruption to the surrounding area and minimized loss of vegetation, compared to auger boring. Microtunneling access pits for launching and retrieving equipment are smaller compared to auger boring access pits. Microtunneling pits must be water tight for a slurry system. A vertical auger drilled pit (Anderson Drilling type) can be used for smaller microtunneling machines with 12-14 foot inside diameter jacking pits and 12 foot inside diameter receiving pits. The open trench portion at each end would also use pre-drilled speed shore system. • Auger boring proposed access pits would be pre-drilled utiHzing a speed shoring rail system because of restricted access, proximity to other facilities, stiff soil conditions (N-value 90-110), and limited probability of ground water. The shoring method requires close contact with the ground at all times. Systems similar to trench boxes are not acceptable. Shored trenches should be the same system - a pre-drilled speed shore rail system. Water tight construction is not required because auger boring uses limited slurry or 6/23/2008 11 raovLk Technical Memorandum Beech Avenue Sewer lubricant. Auger boring would require, depending on the pipe segment length, up to 40 foot long jacking pits. The receiving pit would be much smaller, approximately 6-8 ft in diameter. The receiving pit can be shored trenches used to tie-in to the existing structures. o Pipe Material. Microtunneling method is a one pass method with the carrier pipe installed directly in the ground. Possible pipe materials for carrier pipe are: Vitrified Clay Pipe (VCP), Reinforced Polymer Mortar Pipe (Hobas), and Polymer Concrete Pipe (Meyer). Auger boring would require a two pass method with a separate steel casing and a carrier pipe installed inside the steel casing. Casing pipe inside diameter shall be a minimum of 8-inches larger than the outside diameter of carrier pipe. Possible pipe materials for carrier pipe are: Vitrified Clay Pipe (VCP), Reinforced Polymer Mortar Pipe (Hobas), Polymer Concrete Pipe (Meyer), and PVC pipe. o Accuracv/Tolerances. • Microtunneling method provides ability for accurate control, usually ±1 inch, of line and ±2 inches of grade, which is important for gravity sewers. • Auger boring method provides limited tracking and steering capability. Usually accuracy is in the range of 1% of bore length at short distances (less than 200 ft). To maintain the required grade ofthe carrier pipe, a larger casing pipe (30-inch) will be specified; the grade of carrier pipe inside will be adjusted with casing spacers. Also a larger, man-entry sized casing will allow for line and grade verification and some steering corrections during construction. Considerations for Final Design Existing Utilities The utilities along Beech Avenue and crossing streets should not be affected by trenchless construction methods because the depth ofthe replacement sewer is much deeper than the utilities except for the following utilities at the trenchless access pits. • Gas Main. The gas main will be relocated at three locations, Figure 4. • 8-inch Watermain. The 8-inch water main at the access pit in the intersection of Garfield Street and Beech Avenue will be removed and reconstructed. The existing sewer will be kept in service during construction except for making connections to the existing system. Sewage will be diverted to the line within Ocean Street, at the manhole at the intersection of Beech Avenue and Ocean Street during construction of the connections. 6/23/2008 12 f30VLE Technical Memorandum Beech Avenue Sewer Most ofthe existing sewer laterals will be intercepted in a shallow sewer pipe collection system except that the sewer lateral near Station 17+33 will be connected directly to the new manhole per Standard Drawing S-2 and the two laterals in the vicinity of Station 11+25 that will be reconnected ^ to the new pipe per Standard Drawing S-8. It is not recommended to reconnect sewer laterals directly to the main pipe where depth exceeds 20 ft due to high cost of excavation and shoring. ^ Traffic m The Contract Documents will require that the Contractor prepare traffic control plans. Traffic «i through Carlsbad Boulevard will not be affected because the new sewer pipeline will be constructed ^ under the intersection with Beech Avenue utilizing trenchless methods. Traffic along Beech Avenue will be affected; however, continuous, access to the properties along Beech Avenue will be mm maintained at all the times because only small areas will be required for access pit and trenchless ^ surface equipment. Construction of local sewer collection system intercepting sewer laterals, and connections to the existing sewers will require traffic control to maintain flow of traffic. m Staging Area, Permits, and Easements ^ Construction ofthe new pipeline will utilize a staging area for the temporary storage of all ^ equipment, materials, and the contractor offices will be located near the Home Plant Sewer Lift Station, approximately one-quarter mile north from the project site. The Contractor might also — arrange other locations such a vacant lot located on the south-east comer of Beech Avenue and ^ Ocean Street. Selection of staging area is regulated through a special use permit process. ^ All constmction will be located within public right-of-way. However sewer pipe repair at the east end of the project will require access to the manhole located within NCTD right-of-way. A Right- of-Entry from NCTD will be required. The City will lead NCTD coordination efforts and Boyle will support the City with preparation of necessary drawings, calculations, and graphs. Sewer IVIanhoies ^ New deep sewer manholes (over 15-feet deep) will be 5-ft diameter, PVC-lined manholes constructed per Standard Drawing S-IA. The existing manhole on the west end will be re- — channeled to meet new sewer flow pattern and coated with epoxy coating to prevent corrosion. New sewer manholes for local sewer system serving laterals will be 5-ft diameter constructed per ^ Standard Drawing S-1. street Improvements Existing street improvements will be removed as necessary to construct trenchless access pits and for open-cut installations. The Contractor will be required to reconstruct "in kind" or repair ^ improvements damaged or removed. After completion of construction the AC pavement along Beech Avenue will be slurry sealed. 6/23/2008 13 mOVLi Technical Memorandum Beech Avenue Sewer Home Plant Lift Station Sewer Project Coordination It may be possible to combine Home Plant Lift Station Influent Sewer and Beech Avenue Sewer projects into tiie same construction contract (i.e. the same bid package). The projects are located in close proximity, less then quarter mile apart and they may utilize the same methods. The benefit of constructing both projects through one contract is reduced mobilization costs and schedule. The contractor can also use the same staging area. The bigger project (containing both Home Plant and Beech Avenue) may attract more bidders. Project Schedule It is our understanding, that the City would like complete construction prior to the beginning ofthe 2009 summer busy season (i.e.; complete construction before April/May of 2009). A fast-track construction project would require at least two months for construction, not including about four weeks for equipment and materials procurement. Therefore the Contractor should receive Notice to Proceed no later tiian January I, 2009. Allowing two months for advertisement and award, the project should be advertised by the first part of October 2008. This aggressive schedule will require close coordination with NCTD to avoid delays and secure necessary permits in timely fashion. To expedite constmction, the contract documents may require that contractor include submittals for pipe and boring equipment in his bid package. Opinion of Probable Construction Cost A preliminary opinion of probable construction cost for Beech Avenue Sewer Project is provided below. The cost estimate was provided for both constmction methods (auger boring and microtunneling) and 8-inch, 10-inch and 12-inch pipe altematives. The constmction costs do not include construction management, inspection, testing, offsite environmental mitigation, right-of-way acquisition, permits, or City administration. They represent Boyle's judgment as a design professional and are supphed for the general guidance of the City. Other factors such as the cost of labor and materials, competitive biding or market conditions, over which Boyle has no control, may affect actual costs to the City. 6/23/2008 14 &OVLi Technical Memorandum Beech Avenue Sewer Table 2. Preliminary Opinion of Probable Construction Cost Auger Boring Method, 8-inch Sewer Main Item Cost Item Quantity Unit Unit Price Cost 1 Mobilization 1 LS $45,000 $45,000 2 Auger Boring; 30 Steel Casing w/ 8" PVC Pipe 877 LF $400 $350,800 3 Access Pits 3 EA $80,000 $240,000 4 5' Dia PVC Lined Sewer Manholes 5 EA $15,000 $75,000 5 8" VCP Sewer - Open Trench (Deep) 146 FT $500 $73,000 6 8" PVC Sewer -Open Trench 350 FT $100 $35,000 7 Sewer Laterals 8 EA $2,000 $16,000 4 5' Dia Sewer Manholes 3 EA $4,500 $13,500 6 Connections to Exist System 1 LS $15,000 $15,000 7 Pipe Spot Repair 1 LS $3,000 $3,000 8 Traffic Control 1 LS $10,000 $10,000 9 Slurry seal 5000 SY $5 $25,000 Subtotal $901,300 Contingency 20% $180,260 Total $1,080,000 Table 3. Preliminary Opinion of Probable Construction Cost Auger Boring Method, 10-inch Sewer Main Item Cost Item Quantity Unit Unit Price Cost 1 Mobilization 1 LS $45,000 $45,000 2 Auger Boring; 30 Steel Casing w/10" PVC Pipe 877 LF $410 $359,570 3 Access Pits 3 EA $80,000 $240,000 4 5' Dia PVC Lined Sewer Manholes 5 EA $15,000 $75,000 5 10" VCP Sewer - Open Trench (Deep) 146 FT $520 $75,920 6 8" PVC Sewer -Open Trench 350 FT $100 $35,000 7 Sewer Laterals 8 EA $2,000 $16,000 4 5' Dia Sewer Manholes 3 EA $4,500 $13,500 6 Connections to Exist System 1 LS $15,000 $15,000 7 Pipe Spot Repair 1 LS $3,000 $3,000 8 Traffic Control 1 LS $10,000 $10,000 9 Slurry seal 5000 SY $5 $25,000 Subtotal $912,990 Contingency 20% $182,598 Total $1,100,000 6/23/2008 15 Technical Memorandum Beech Avenue Sewer Table 4. Preliminary Opinion of Probable Construction Cost Microtunneling Method, 12-inch Sewer Main Item Cost Item Quantity Unit Unit Price Cost 1 Mobilization 1 LS $100,000 $100,000 2 Microtunneling; 12" VCP Pipe 877 LF $640 $561,280 3 Access Pits 3 EA $50,000 $150,000 4 5' Dia PVC Lined Sewer Manholes 5 EA $15,000 $75,000 5 12" VCP Sewer - Open Trench (Deep) 146 FT $560 $81,760 6 8" PVC Sewer 350 FT $100 $35,000 7 Sewer Laterals 8 EA $2,000 $16,000 4 5' Dia Sewer Manholes 3 EA $4,500 $13,500 6 Connections to Exist System 1 LS $15,000 $15,000 7 Pipe Spot Repair 1 LS $3,000 $3,000 8 Traffic Control 1 LS $10,000 $10,000 9 Slurry seal 5000 SY $5 $25,000 Subtotal $1,085,540 Contingency 20% $217,108 Total $1,300,000 6/23/2008 16