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Preliminary Design Memo - 032116Project # 20164277.001A Page 1 of 9 3/21/2016 Copyright 2016 Kleinfelder MEMORANDUM TO:Douglas McDonald and James R. Laurila, P.E., City of Northampton FROM:Mark Wixted, P.E. and Tulin Fusilier, P.E. DATE :March 21, 2016 SUBJECT: Former Northampton Lumberyard (256 Pleasant St) Drain Relocation CC:File The Valley Community Development Corporation (CDC) is proposing the construction of a new building on the former site of Northampton Lumberyard at 256 Pleasant Street. In order to construct the building a large existing storm drain needs to be relocated. The City of Northampton (City) is managing the design, permitting, and construction of the new 72-inch drain line, with funding provided by CDC. This memorandum summarizes the design criteria and assumptions made during the preliminary design phase, including recommendations for additional field investigations to be made during final design phase. In addition, the Memorandum will describe the several design components and will serve as the basis for final design Summary of Design Criteria Adequacy of Replacement 72-inch RCP Based on the request for proposals (RFP) issued by the City, it is proposed that the replacement to the existing culvert should be a 72-inch RCP. Kleinfelder reviewed the record plan entitled, “Existing Market Street Brook Plan – Profile” provided by Northampton Department of Public Works. The record plan identifies the majority of the existing storm culvert within the Northampton Lumber Yard Site as a 5-ft wide by 6-ft high brick box with brick arch roof and wooden plank floor. The downstream section of the culvert, near Holyoke St. which is identified as a 4.5-ft wide by 5-ft high stone box with brick arch roof and wooden plank floor. Downstream of this section, on the south side of Holyoke St. this transitions to a 60-in diameter concrete pipe. The existing pipe culvert system was included in a Stormwater and Flood Control Study conducted by CDM in May, 2012. According to the report by CDM, the subject existing culvert pipes can provide adequate capacity as part of the greater Northampton stormwater system. Project # 20164277.001A Page 2 of 9 3/21/2016 Copyright 2016 Kleinfelder It is estimated that the existing 5-ft wide by 6-ft high brick arch box pipe within the site has a cross sectional area of approximately 28 square feet. Approximately 270 linear feet of the existing 5-ft x 6-ft culvert is proposed to be replaced with 350 linear feet of 72-in Reinforced Concrete Pipe (RCP) along an alternate alignment. The cross sectional area of the proposed 72-in RCP is approximately 28.27 square feet, which is marginally larger than existing cross sectional pipe capacity. The slope of the existing culvert pipe is approximately 0.0017 vs the 72-in RCP along the proposed alignment is approximately 0.0014, which is a negligible change in slope. Pipe flow losses caused by the existing brick pipe wall material will be significantly improved with the proposed reinforced concrete surface. Based on the improvements to pipe cross sectional flow area, improvements to pipe wall material, insignificant change to pipe slope and with consideration of the smaller 60-in diameter pipe downstream, it appears the proposed 72-in RCP would provide adequate capacity. The replacement of the existing culvert with the new alignment introduces manhole junction angles that will cause some energy loss compared to the existing system. The proposed final design should include special manholes that have swept inverts and pipe deflections to reduce turbulence at the junctions. Abandonment of Existing Brick Arch Based on the depth of the brick arch and the fact that it will be under a building, we believe that filling the culvert with controlled density fill (“flowable fill”) would be the best alternative. We have contacted a local supplier and have included a price in the estimate based on their recommendations. Another consideration is that a building will be placed over the abandoned culvert. It is likely that filling with flowable fill would offer the best way to reduced voids and thereby minimize potential settlement. Precast Structures We have consulted industry manhole sizing guides and determined that round precast manhole structures will not work given the large pipe size and angles. Square structures are the best option either in precast or cast in place. After consulting with a precast manufacturer in the area, we believe 10-ft by 10-ft or larger square manholes can be used. It is anticipated that the structures would be designed with a curved interior or exterior wall to reduce losses at the bends. Special RCP bends will also be considered in the final junction design. Assessment Easements We would recommend temporary and permanent easements of 30-ft wide for the new pipe on the former lumber yard property. Temporary construction easements on the former lumber yard property should include a majority of the site unless there is some reason that is not feasible. Temporary construction easements for the bypass may be Project # 20164277.001A Page 3 of 9 3/21/2016 Copyright 2016 Kleinfelder required on private properties to the east of the railroad. We would assume a 10-ft to 20- ft easement would be adequate. By-pass Pumping Locations Based on the plan entitled, “Existing Market Street Brook, Plan – Profile, dated June 1981,” we have identified the nearest bypass pumping locations as A and B in the figure below. We assume Location A and the path from Location A to B may by on private property. The distance of this bypass would be approximately 500-ft. Location A and B have not been inspected An alternative to this would be to install a doghouse manhole on the site and pump to Location B, using a shorter bypass and avoiding work on private property has some advantages. We do not believe the difference in the distance between the two options would warrant the cost and risk associated with installing a doghouse manhole just for the bypass. From, “Existing Market Street Brook, Plan – Profile, dated June 1981” Pipe and Structure Costs and Lead Times We have consulted with Scituate Ray Precast regarding stocking and productions of 72- inch pipe. They can produce 80-feet of 72-inch pipe per week. So we would estimate a lead time of at least 6 weeks for the project. Geotechnical Criteria Our understanding of the geotechnical conditions at the site is based on review of the mapped regional geology, and our review of information presented in the following reports: Project # 20164277.001A Page 4 of 9 3/21/2016 Copyright 2016 Kleinfelder x “Limited Subsurface Investigation Report, Northampton Lumber Company, 256 Pleasant Street, Northampton, Massachusetts” prepared by Environmental Compliance Services (ECS), dated July 31, 3013; x “Preliminary Geotechnical Engineering Recommendations, Northampton Lumber Site, Northampton, Massachusetts” prepared by O’Reilly, Talbot, & Okun Associates, Inc. (OTO), dated January 6, 2015. Regional Geology Based on the “Surficial Geologic Map of the Easthampton Quadrangle, Massachusetts” (Stone & DiGiacomo-Cohen, 2010), the site is underlain by stream-terrace deposits of sand, silt, and gravel. In general, these deposits are reportedly less than 10-feet thick, and in the Connecticut River Valley are often underlain by lake-bottom silt and clay deposits. The GIS data compiled by the Massachusetts Geological Survey and viewed in Google Earth indicates that the bedrock at the site is part of the New Haven Arkose of Upper Triassic age. This formation consists of red, pink, and gray conglomerate arkose interbedded with brick-red shaley siltstone and fine-grained arkose sandstone. Based on the proposed depth of the infrastructure, this formation will not have any anticipated geotechnical impacts on construction. Geotechnical Investigations by Others OTO performed a subsurface exploration program at the site in December, 2014, as part of their preliminary geotechnical evaluation for the proposed redevelopment of the former Northampton Lumber Yard. The exploration consisted of ten soil borings (NL-1 through NL-10) and two in-situ hydraulic conductivity tests. The soil borings were advanced to depths ranging from 5 to 102 feet below ground surface. The boring locations are shown on Sheet C-1, Proposed Drainage Plan. Based on the information presented in the OTO geotechnical report and the borings logs, the soils at the site generally consist of loose to medium dense sandy fill with some debris and pockets of organic material. Where fully penetrated, the thickness of the fill ranged from approximately 15 to 21 feet. The fill is underlain by a deposit of soft to very soft varved silt and clay. The deepest boring terminated within the varved silt and clay at a depth of 102 feet. ECS performed subsurface investigations to evaluate environmental conditions at the Northampton Lumber property in July 2013. Their explorations consisted of 8 soil probes to 15 feet depth, and 5 probes to 5 feet. The soil descriptions reported in their boring logs are generally similar to those encountered by OTO, except that soil probes do not provide soil density information. Project # 20164277.001A Page 5 of 9 3/21/2016 Copyright 2016 Kleinfelder Groundwater Conditions ECS reported that groundwater levels during drilling ranged from about 11 to 15 feet below ground surface. Four monitoring wells were installed as part of their subsurface exploration program. The groundwater levels in the wells were measured on July 19, 2013, and ranged from 9.7 to 11.72 feet below ground surface. OTO reportedly encountered groundwater during drilling at depths ranging from 10 to 20 feet below ground surface, and in one of the borings (NL-2), groundwater reportedly rose from 20 ft depth to 8.5 ft depth over the course of one hour. No monitoring wells were installed as part of their subsurface exploration program. For the purposes of this preliminary study we assume that groundwater levels at the site are at 8.5 ft depth. However, more recent readings should be obtained from the existing monitoring wells on the site. Pipe Positioning Considerations Kleinfelder has set the alignment for the proposed drain based on the following considerations: x The pipe alignment has been placed outside a line which extends horizontally from 5.5 ft off center line of the adjacent track, then on a 2 horizontal to 1 vertical (2H:1V) slope, known as the “Zone of Influence”. Excavations within this Zone may require sheeting supporting rail road loads. Setting the pipe alignment outside this Zone allows present and future excavations to be conducted with easily available support of excavation methods such as trench boxes, or open excavation methods. x The pipe alignment has been placed outside a line which extends on a downward 1H:1V “Zone of Influence” of a future footing of the proposed building, again to allow for present and future excavations to be conducted with easily available support of excavation methods. x The pipe alignment has been placed as far from the railroad as possible, but appears to be within 60-ft of the centerline of the nearest track. This may require permitting and the need for rail road operations safety flaggers. Sheet C-2 shows the proposed pipe profile and sections views, including the Zone of Influence from the rail road and future footings. In the event that the alignment is shifted eastward and would require excavation within this zone, the shoring system must be designed to withstand railroad loads during construction. Railroad loads should be determined using the most current edition of the Manual for Railway Engineering by the American Railway Engineering and Maintenance-of-Way Association (AREMA). Project # 20164277.001A Page 6 of 9 3/21/2016 Copyright 2016 Kleinfelder Recommendations for Temporary Support of Excavation General Excavations for the proposed infrastructure are expected to extend to about 16 feet below existing grade. Based on the reported water levels we anticipate that the excavation may extend below groundwater levels. Given the variability in the reported water levels, additional investigations are recommended to further evaluate the groundwater conditions at the site. If significant dewatering of the excavation will be required, we recommend supporting the excavation with interlocked steel sheeting, driven into the varved clay layer to provide a groundwater cutoff. If the excavation will not extend far below groundwater, other shoring systems such as open excavation, trench boxes, soldier piles and timber lagging, or a combination of such systems may be used. Because the groundwater is assume to be 8.5-ft below grade we have assume steel sheeting will be used for the entire length of the pipe installation. The shoring system should be designed to support lateral earth pressures, construction surcharge loads, and unbalanced hydrostatic pressures. Temporary excavation support systems should be designed and installed in accordance with the requirements of the OSHA Standards and Interpretations: "Part 1926 Subpart P - Excavation, Trenching, and Shoring", and all other applicable laws, regulations, rules, and codes. Excavations near Existing Utilities Buried natural gas lines and an existing telecom ductbank run parallel to the proposed drain along Holyoke Street, each approximately 12 feet from the centerline. Several utilities also cross above the proposed drain line in various locations. In these areas, the shoring system should be designed and constructed in a manner that prevents ground loss on the outside of the excavation, thereby minimizing the potential for movement that may damage sensitive utilities. The location, depth, and diameter of all the existing utilities have not been confirmed, and should be verified prior to construction. We have received a plan from Columbia Gas indicating a four and an eight inch gas line on the north side of Holyoke St. Water Control Considerations Dewatering of excavations and groundwater management during construction may be required due to groundwater, infiltrating surface water, or pockets of “trapped” water. Construction dewatering may require a combination of wells, well points, and/or open pumping with collector sumps and trenches. The dewatering system should be designed by an experienced specialty contractor and should be designed and operated to prevent pumping of soil, disturbance of subgrades, and adverse effects to existing site features. Project # 20164277.001A Page 7 of 9 3/21/2016 Copyright 2016 Kleinfelder Construction Monitoring We recommend installing utility monitoring points (UMPs) along the existing natural gas main and telecom ductbank to check for movements of these utilities during construction along Holyoke Street. If excavations fall within the railroad “zone-of-influence” as defined above, the parallel rail tracks should be monitored for movement using optical survey techniques. Track monitoring stations should be spaced at 15.5-ft intervals, with 4 additional stations beyond the limits of the work in either direction. Track and utility monitoring should be performed during shoring installation, excavation and backfilling activities, and during removal of excavation support systems. Post-Construction Considerations In general, recommendations provided above are applicable for future excavations to expose and repair the drain line. Additional considerations are needed for repair excavations which fall within the “zone- of-influence” of the proposed building. If the building is supported on shallow foundations (such as footings bearing on compacted site soils or on soils improved by rammed- aggregate-piers), support of excavation systems should be designed to resist the surcharge pressures imparted by the footings, and should be installed in a manner that prevents ground loss beneath the footing. If the building is supported on deep foundations, such as piles which transfer the load beneath the drain invert, lateral surcharge pressures would be minimized. Shoring systems installed near the building should be drilled or hydraulically pushed in place. Impact or vibratory installation methods should not be used. We recommend that the building is monitored for movement during any future repair work which may impact the building. Assumptions Existing Drain Line Based on information from the City, it is assumed that a majority of the existing drain line is a 5-ft by 6-ft stone and brick arch culvert with a wood plank floor and was built in 1846. The culvert transitions to a 4-ft to 4.5-ft wide by 5-ft high brick box with brick arch roof and wooden plank floor near where the culvert crosses Holyoke St. Existing Railroad Track Elevation and Location For the purpose of the design recommendations, Kleinfelder used Google Earth to estimate the elevation of the railroad tracks as 133-ft and approximately 13-ft above the Project # 20164277.001A Page 8 of 9 3/21/2016 Copyright 2016 Kleinfelder grade of the proposed parking lot and driveway. This estimated elevation of the rail road tracks will be used for preliminary design unless the City has more accurate information. Existing Geotechnical Conditions Our understanding of the geotechnical conditions at the site is based on review of the mapped regional geology, and our review existing reports by others, as specified above. Recommendations for Additional Field Investigations The following information should be verified by field investigation, survey or other means for the final design: Additional Explorations Of the ten geotechnical borings conducted by OTO, boring NL-10 was advanced in closest proximity to the proposed drain line, located at the centerline at approximately Sta. 1+00 (see Sheet C-1). This boring terminated within the fill at a depth of 9 feet. The next closest borings are borings NL-3, NL-4, and NL-7, each located about 25 to 40 feet from the drain centerline at approximately Sta. -0+20, 1+10, and 2+90, respectively. Each of these borings terminated within the varved clay layer. We recommend additional borings be conducted along the proposed drain alignment in order to assess the thickness and composition of the fill layer, and to obtain further information on groundwater levels. We recommend three (3) to four (4) borings be drilled, and water levels in the existing monitoring wells be obtained. Depending on the findings, one (1) of the test borings may be completed as a monitoring well. Bypass Location The bypass locations should be investigated in the field to verify that they are functional and adequate for the pumping operation. They should be added to the plan either in an approximate location or picked up by the survey. Survey We would recommend obtaining the horizontal and vertical location of the railroad tracks in order to design the support of excavation and to complete any permitting that may be required with the railroad. Utility Test Pits We would recommend obtaining test pits to determine the location and sizes of the existing utilities adjacent to the proposed drain line on Holyoke St. CCTV of Existing Culvert We would recommend completing a CCTV investigation of the two sections of the existing culvert and structures where connections will be made to the proposed drain structures. Project # 20164277.001A Page 9 of 9 3/21/2016 Copyright 2016 Kleinfelder Overall Bidding, Award and Construction Schedule We assume the durations for the overall project will be as follows. This includes project advertisement through end of construction. 1. Advertisement and Bid Period (4 weeks) 2. Bid Review and Contract Award (4 weeks) 3. Pre-Construction Administration Period (2-3 weeks) 4. Materials Lead Time (2-3 weeks) 5. Construction Duration (6-12 weeks) Construction Logistics, Sequence and Simplified Schedule We assume the sequence and durations will be as follows, for a total duration of 6 to 12 weeks, depending on concurrent activities, the use of multiple crews and weather. 1. Mobilization, survey control, Install erosion and sedimentation controls (5 days) 2. Begin excavation and pipe installation within the site, near the existing brick culvert and build from north to south toward Holyoke St. (10 days) 3. Install piping in Holyoke St. up to the existing brick culvert. (10 days) 4. Set-up pumping by-pass (10 days) 5. Install two structures to join new piping to existing arch pipe (10 days) 6. Transfer flow to new piping and cease by-pass (2 days) 7. Pump flowable fill into abandoned brick arch culvert (3 days) 8. Finish any pavement patching, remove erosion controls and demobilize (3 days)