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HomeMy WebLinkAbout19 - Design Report - West Peach Condos - Road, Stormwater _I MAR 2 6 In 1019 ENGINEERING DEPARTP4QT NORTH 3RD AVENUE ROAD AND STORMWATER DESIGN REPORT FOR: WEST PEACH CONDOMINIUM BOZEMAN, MT Prepared By: MADISON ENGINEERING Madison Engineering 895 Technology Drive, Suite 203 Bozeman, MT 59718 (406) 586-0262 MARCH 2O19 NORTH 3" AVENUE ROAD AND STORMWATER DESIGN REPORT FOR: WEST PEACH CONDOMINIUM BOZEMAN, MT CHIRIS G BUDESK T f�o. 10 z5 PE w � . . ::. , g NN Madison Engineering 895 Technology Blvd Ste 203 Bozeman, MT 59718 (406) 586-0262 MARCH 2O19 NORTH 3RD AVENUE IMPROVEMENTS ROAD & STORMWATER DESIGN REPORT A. Introduction This design report will give an overview of the road design and stormwater management plan for the proposed improvements to N. 3rd Avenue from the intersection of West Peach north approximately 180 feet. The Right of Way (ROW) is currently constructed with a 29.5-foot wide asphalt road with no curb and gutter. The existing road centerline is misaligned in the ROW approximately 7 feet east of the ROW centerline. The proposed improvements include removing the existing asphalt road and widening the road to current standards for a local street with the new centerline of the road matching the existing ROW centerline. A 5-foot wide sidewalk is proposed on the west side of the street. Retention/detention of stormwater is not proposed within the ROW. B. Road Design N. 3rd Avenue is considered a local street and is proposed to be constructed 35-feet wide (top back of curb to top back of curb). Two drive approaches will be constructed; one 24-foot wide drive approach to access the proposed West Peach Condominium on the west side of the street and one 17.5-foot wide approach to access an existing property on the east side of the street. For information regarding the pavement design see the Pavement Design Report by C&H Engineering & Surveying dated March 2019 attached with this submittal. Due to the misalignment of the original roadway centerline by approximately 7 feet to the east, the proposed road will need to taper back to meet the existing roadway to the north beyond the extent of this project. A taper length of 36.5 feet was calculated using information given in Tables 6C-3 and 6C-4 of Chapter 6C of the MUTCD 2009 Edition (see Appendix F). However, this was deemed unsatisfactory after initial review by the City of Bozeman. It was required that the Bozeman Design Standards and Specifications Policy (DSSP) be used in calculating taper length. This doubles the length of the taper because the Bozeman DSSP does not differentiate between the different types of tapers and classifies all tapers conservatively as merging tapers. The taper length shown on the updated plans is 73.0 feet. C. Description of existing conditions Currently the subject portion of N. 3rd Avenue ROW is paved and has shallow drainage ditches running north along the east and west sides of the road. The soil in these ditches is compacted more than a typical swale or landscaped area due to the historical use of these areas as street parking. N. 3'Ave. Improvements Road&Stormwater Design Report Page I of 2 .r r ✓s,, Figure 1 Looking north on N. 3rd Ave. Cars parked alongside the road is typical. D. Determining Rational Method C Value In determining a proper Rational Method C coefficient for this "landscaped" area within the existing ROW, an additional resource was used due to the lack of specificity given in Table I-1 of the Bozeman Design Standards and Specifications. The California State Water Resource Control Board Fact Sheet 5.1.3 (see Appendix C) was used as guidance for determining a proper C value that best represents the conditions on site. For smooth, bare packed soil a range of C values from 0.3 to 0.6 were given. An average value of 0.45 was chosen for the existing condition ROW ditches and is referred to as "Pervious, compacted dirt" in the calculations in Appendix A. E. Summary The difference between the proposed and existing conditions composite C values is only 0.03. The resulting difference in runoff volumes between proposed and existing conditions is only 18 cubic feet for the 10-year, 2-hour storm (see Appendix B). Given the approximate nature of the Rational Method and relatively small area of this project a difference in runoff volume of 18 cubic feet between proposed and existing conditions is considered negligible. Therefore, no stormwater improvements are proposed for this project. Appendices A. Composite C Value calculations B. Runoff calculations C. Runoff Coefficient Fact Sheet D. Sheet SDI.0—Drainage Areas exhibit E. Roadway taper calculations N. 3'Ave. Improvements Road&Stormwater Design Report Page 2 of 2 Appendices Appendix A N. 3rd St. Improvements N. 3rd Ave (Existing) Surface Area (ft) C Pervious, compacted dirt 5290 0.45 Paved (road, NO sidewalk) 5581 0.9 Total 10871 0.68 N. 3rd Ave (Proposed) Surface Area (ft) C Landscaped 2973 0.2 Paved (road &sidewalk) 7898 0.9 Total 10871 0.71 N.3rd St. Improvements Appendix B Runoff calculations Design Rainfall Freq. OF coefficient a 0.64 OF coefficient b OF coefficient n 0.65 Pre-development Conditions Area(ft): Exfg ROW 10,871 sq.ft. total area: 0.25 acres composite C: 0.68 Runoff volume calculations: Q=CIA C= 0.68 (pre-development) 1= 0.41 in/hr(10-yr,2-hr storm) A= 0.25 acres Qpost= 0.070 cfs Runoff volume(ft)= 502 ft3 (10 yr,2-hr storm) Post-development Conditions Area(fe): Prop'd ROW 10,871 sq.ft. total area: 0.25 acres composite C: 0.71 Runoff volume calculations: Q=CIA C= 0.71 (post-development) 1= 0.41 in/hr(10-yr,2-hr storm) A= 0.25 acres Qpost= 0.072 cfs Runoff volume(ft)= 519 ft3 (10-yr,2-hr storm) Proposed(ft') Existing(ft')l DDifference b19 buz 13 q Summary Because the difference in runoff volume for the 10-yr,2-hr storm is only 18 cubic feet no stormwater facilities are proposed. Given the approximate nature of the Rational Method,a difference in runoff volume of 18 cubic feet is considered negligible. Fact Sheet-5.1.3 Runoff Coefficient (C) Fact Sheet What is It'? The runoff coefficient (C) is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received. It is a larger value for areas with low infiltration and high runoff (pavement, steep gradient), and lower for permeable, well vegetated areas (forest, flat land). Why is It Important? It is important for flood control channel construction and for possible flood zone hazard delineation. A high runoff coefficient(C) value may indicate flash flooding areas during storms as water moves fast overland on its way to a river channel or a valley floor. It is measured by determining the soil type, gradient, permeability and land use. The values are taken from the table below. The larger values correspond to higher runoff and lower infiltration. Land Use C Land Use I C Lawns: Sandy soil, flat, 2% 0.05 -0.10 Business: Sandy soil,avg., 2-7% 0.10-0.15 Downtown areas 0.70 -0.95 Sandy soil, steep, 7% 0.15 -0.20 Neighborhood areas 0.50-0.70 Heavy soil, flat,2% 0.13 -0.17 Heavy soil,avg.,2-7% 0.18 -0.22 Heavy soil, steep, 7% 0.25 -0.35 Agricultural land: Bare packed soil I *Smooth 0.30-0.60 *Rough 0.20-0.50 Residential. Cultivated rows Single-family areas 0.30-0.50 *Heavy soil,no crop 0.30- 0.60 I Multi units, detached 0.40 - 0.60 *Heavy soil,with crop 0.20-0.50 Munti units, attached 0.60-0.75 *Sandy soil,no crop 0.20-0.40 Suburban 0.25 -0.40 *Sandy soil, with crop 0.10-0.25 Pasture *Heavy soil 0.15-0.45 *Sandy soil 0.05 -0.25 Woodlands 0.05 -0.25 The Clean Water Team Guidance Compendium for Watershed Monitoring and Assessment 1 State Water Resources Control Board 5.1.3 FS-(RC)2011 EXISTING CONDITION PROPOSED CONDITION COVER TYPE AREA (SQ. FT) COVER TYPE AREA (SQ. FT) PERVIOUS, COMPACTED SOIL 5290 LANDSCAPE 2973 PAVED (ROAD & SIDEWALK) 5581 PAVED (ROAD & SIDEWALK) 7898 I i Y.-, _. IY } STORMWATER FLOWS FROM NEW ROAD �>— INTO EXT'G DITCH <>—<>— EXT'G EOP �: =' PROP. ASPHALT ;TAPER EXT'G ROW � I EXT'G ROW Y r �9 T T PROP. TBC EXT'G EOP I b ZEXT'G DITCH I I a a SCALE C- , 0 15 30 a PEACH STREET I inch= 30' PEACH STREET WEST PEACH CONDOMINIUM SDI.® N.3rd Avenue N. 3RD .AVENUE IMPROVEMENTS MADISON ENGINEERING Drainage Areas 895 TECHNOLOGY BLVD SUITE 203 PROJECT ht 17-147 STORM WATER DRAINAGE EXHIBIT BOZEMAN,MT 59718 DATE: 03/26/19 (406)586-0262 DRAWN BY: MS DRAINAGE AREAS REVIEWED BY: CGS BOZEIOItp,N,MT PROJECT ENGINEER:CGB tet'V DESIGNED BY: COB ROojwtj TAp-er CcA',,(A,fa I I19yi s � 1v, ��d Avuvl(�[� ( fur 5 C� l r v+�i f S i fi l�tGt/f'! A L . _ y ) F ���c�T P w5 160 „Jk.e�Q= lN= w.c1-f� � �•�ls� .z U T rfi:v� Tu w� �uVIP- �- 7 / ci,�rrt'il�f Gob t7 s S-e4— cc�- 5 P �S ✓�of a��vrt/ �T.— a- plei rQ,dl vtp 7ps i �LFMAR 2 6 201 1 ENGIi�!EERING DEPARTMEN PAVEMENT DESIGN REPORT NORTH 3" AVENUE Prepared for: IRONWOOD DEVELOPMENT, INC. E-mail: j@ironwoodd.com Prepared by: Engineering and Surveying Inc. 1091 Stoneridge Drive • Bozeman, MT 59718 Phone(406] 587-1115 • Fax(406) 587-9768 www.chengineers.com • info@)chengineers.com !3�'r �i' `ct off:• Project Number: 180792 ,tip` s G r r L March 2019 i PAVEMENT DESIGN REPORT—NORTH 3 RD AVENUE WIDENING A total of two test holes were excavated along the north side of North 3 d Avenue using a tracked excavator on March 8, 2019. The subsurface soils consisted of approximately 29 to 30 inches of undocumented fill (mix of clay, gravel, sand, concrete, metal and woody debris) underlain by a layer of sandy lean clay (CL). Poorly graded gravel with sand and cobbles (GP) followed the sandy lean clay to the end of each exploratory excavation. Groundwater was not encountered within the depth of exploration. Penetration tests were performed with a static cone penetrometer on the sandy lean clay to estimate its California Bearing Ratio (CBR). The estimated CBR is obtained by the equation Q� = 3.3(CBR), or CBR= Qc/3.3, with Qc being the cone index. With the average measured value of the cone index being 15,we calculate the estimated as CBR= 15/3.3 = 4.54. A conservative value for the CBR of 2 was used for this report to provide for possible inconsistencies in the road subgrade, and the approximate testing methods used. The Standard Test Method for CBR (California Bearing Ratio) of Soils in-situ, based on ASTM Designation D 4429-4, requires complex and specialized equipment,the expense of which, in our opinion, is not warranted for this small street widening project. STREET DESIGN Criteria for design: Bozeman Municipal Code, Section 38.24.060 and City of Bozeman Design Standards and Specifications Policy, Addendum No. 4, Section IV.G: pavement thickness design will be based on the current AASHTO Guide for Design of Pavement Structures, or the current Asphalt Institute Manual Series No.I (MS-I). The design shall be based on a minimum 20-year performance period traffic volume, with the minimum design lane based on a minimum of 50,000 ESAL. According to the penetration tests performed by C&H Engineering Inc. on the sandy lean clay, the CBR assigned to the road subgrade is 2.0. CBR can be related to the subgrade Resilient Modulus MR by the following: (Sec. 3.5.4, Highway Engineering Handbook, McGraw Hill, 1996) Subgrade Resilient Modulus MR(psi): MR= 1,500 CBR (Shell Oil Co.) This value used by Asphalt Institute. MR= 5,409 CBR0-"i (United States Army Waterway Experiment Station) MR=2,550 CBRo.64 (Transport&Research Laboratory, England) With CBR=2.0 MR= 1,500 CBR= 1,500 (2.0) =3,000 psi MR= 5,409 CBR0-"' =5,409 (2.0)"" = 8,854.2 psi MR=2,550 CBR0-64=2,550 (2.0)0-64 =3,973.74 psi Use most conservative value =3,000 psi USING THE AASHTO METHOD OF FLEXIBLE PAVEMENT DESIGN The AASHTO method utilizes a value known as the Structural Number (SN) which relates the below variables to the wear surface, base, and sub-base depths. Structural Number Equation (EQ 1): tog APSI log W18 = ZRSo +9.36[log(SN + 1)) — 0.20 + 2.7 1094 + 2.32 log MR — 8.07 0.40+ (SN + 1)5.19 Variables: 1. ESAL (Wig) = 50,000 2. Level of Reliability (ZR) = -1.282 for Local Streets based on 90% reliability from Part 1, Table 4.1, and Part II, Table 2.2, AASHTO Guide. Level of reliability is based on the cumulative percent of probability of reliability with a standard normal distribution. 3. Standard Deviation (So) =0.49 for flexible pavements. See Part I, Sec. 4.3, AASHTO Guide. The standard deviation is the statistical error in the estimates for future values within the formula. Typical values range from 0.40-0.50 for flexible pavements, with a value of 0.49 used to ensure a conservative solution. 4. Serviceability Loss (APSI) =2.2 for Local Streets. The designed allowable deterioration of the roadway is represented by the serviceability loss. A new road is usually assigned a serviceability index of 4.2 and the final index is based on the type of roadway. Local streets are normally allowed to deteriorate to 2.0. The resulting difference in the initial to final indexes is the total serviceability loss. 5. Soil Resistance Modulus (MR) = 3,000 psi Solution: using (EQ 1), the SN for Local Streets=2.98 Pavement Design Equation (EQ2): SN = a1D1 + a2D2M2 d a3D3M3� 1. Layer Coefficients: al = 0.44 (Hot-mix asphalt concrete) a2 = 0.14 (Base Course- 1 '/2" minus crushed gravel) a3 = 0.11 (Sub-base Course - 6" minus crushed stone) 2. Drainage Coefficients: m2= 1.00 (good drainage 5-25%) m3 = 1.00 (good drainage>25%) %of time base & sub-base will approach saturation 3. Layer Depth Assumptions: Di =3" for Local Streets D2= 6" for Local Streets Solution: using the values given for Di and D2, and solving (EQ2), D3 =7.49" for Local Streets Based on our analysis, we recommend the following minimum pavement cross section: Asphalt Section=3 Inches Base Course=6 Inches Sub-Base Course= 9 Inches However,please note that undocumented fill was encountered in both exploratory excavations and will need to be removed from beneath the area where the street will be widened, likely resulting in a much thicker Sub-Base Course than the minimum recommended. The Sub-Base Course shall be thickened as necessary and shall not be less than the minimum recommended above. Also, a woven geotextile (such as a Mirafi 50OX) shall be installed across the native subgrade prior to the placement and compaction of the Sub-Base Course. N. 3" Avenue Improvements for West Peach Condominium _ Response to Review Comments from Griffin Nielsen dated March =2;9J 11 H\U/ l MAR 2 6 2019 Pavement Design Report: ENGINEERING DLPAPTrfEj 1. The pavement design report does not meet the requirements City of Bozeman Design Standard and Specifications (DSSP) section IV.G. The provided report does not demonstrate that City's performance period traffic loading and minimum loading were considered with the recommended section. In addition the assumed soil conditions must be verified prior to approved of the pavement design. Response: See Pavement Design Report by C&H Engineering & Surveying dated March 2019. 2. The pavement design report does not identify a specification for the recommend woven geotextile, however Detail 2 on Sheet C3.0 reference the design report for clarification. DSSP I.F.1. The specified geotextile must be identified. Response: The C&H Pavement Design Report recommends a woven geotextile such as Mirafi 50OX which is now called out on Detail 2/C2.0. Plans: 3. Flowable backfill is required in lieu of native backfill within the Peach Street right-of-way, per the City of Bozeman Modifications to the Montana Public Works Standard Specification Detail No02221. Detail 5 on Sheet C6.0 should be updated to include this requirement and the reference to Thomas Drive removed. Response: Detail 5 has been updated per these comments. 4. Sheet C3.0: The taper length of the transition from the proposed to exist North 3rd Ave street section should be calculated based on DSSP Section IV.7. Response: Per conversation with Griffin Nielsen on March 14, 2019 the use of the MUTCD to calculate taper length is not allowed at this time. The City of Bozeman Engineering Department will address the issue of the difference in taper length calculations between Bozeman DSSP and the MUTCD at their meeting at the end of March 2019. If they decide at the meeting that the use of MUTCD to calculate taper length is permissible, then the plans will be allowed to change back to the half length (36.5-foot taper) but for now it must be shown at full length (73-foot taper). The plans have been updated with this change. 5. Sheet C3.0: The east boulevard of North 3rd Ave must be sloped at 2.0% towards to the curb and gutter. The boulevard may be considered half the 11.5 width. Response: Detail 2/C3.0 has been changed per this comment. 6. Sheet C3.0: identify the right-of-way/property line for the lot(s) to the northeast the improved section of North 3rd Ave. Response: The right of way and adjacent property lines in the northeast of the improvement section are now shown on Sheet C3.0. 7. Sheet C3.0: The improved section of North 3rd Avenue, including sidewalk, must extend to the northern boundary of the northern alley. Response: Sheet C3.0 has been changed per this comment. 8. Sheet C3.0 and C6.0 Detail 3: A City standard drive approach must be installed at the existing eastern residential drive access. Use the City standard detail No. 02529-11. Response: Per conversation with Griffin Nielsen on March 14, 2019 the main issue here is the lack of sidewalk shown on the drawings. A 5-foot wide sidewalk is now shown on the plan Sheet C3.0 and Detail 3/C6.0. However, due to the existing low elevation of the eastern adjacent lots, the typical approach grades are not used and the customized, shallower approach grades previously submitted are still used. These shallower approach grades will create a softer approach to the existing residence and will lessen the extent of necessary re- grading onto the individual's property. 9. Sheet C3.0 and C6.0 Detail 1: A City standard drive approach must be installed for the proposed commercial drive access. Use the City standard detail No. 02529-12. Response: The site plan for West Peach Condominium utilized this drop-down approach because of grading concerns on site. Given the designed foundation elevations of the proposed structures and their adjacency to the access road through the site, a typical commercial drive access approach would create an abrupt grade break as the road slopes back down into the site after making the connection to N. 3'd Ave. The modified approach allows for a much smoother entrance to the site. Additionally, The West Peach Condominium site plan has been reviewed multiple times and is approved at the time of this writing. These infrastructure plans are showing the drop-down style approach that was previously approved with West Peach Condos and it remains the same in this re-submittal. 10. Sheet C4.0: The blowoff should be located in the boulevard outside of the traveled way. Response: The blowoff is now shown located in the boulevard. 11. Sheet C3.0 and Sheet C4.0: The proposed valve access road alignment STA 0+19 is shown at two different locations between Sheet C3.0 and C4.0. The plans must be updated. Response: The valve location has been updated and is the same between Sheets C3.0 and C4.0. 12. Sheet E-3: The detail does not meet City standards, please use the City of Bozeman Typical Lighting Control Center Metered Pedestal Standard Detail—Figure 8 found within the Design Standard and Specifications Policy Manual. Response: This detail sheet (E-3) has been removed entirely. Now the lighting plan set only includes three sheets instead of four. The single lighting service assembly is called out in plan view on Sheet E-1 "Per City of Bozeman Standard Drawing Figure 8". Condition of Approval: 13. The street cuts should be laid out to minimize the number of joints within the traveled way (perpendicular to the vehicle wheel path). The street cuts in Peach Street for the water main connection and abandonment of the water service must be coordinated with the City Engineering Department (Griffin Nielsen and Kellen Gamradt). Response: Per discussion with Griffin Nielsen on March 14, 2019 street cuts will be coordinated during the pre-construction meeting. No changes to street cuts have been made on the plans for this re-submittal.