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HomeMy WebLinkAbout; Las Encinas Creek Bridge Maintenence/Replace; Las Encinas Creek Bridge Maintenence/Replace; 2008-01-01Job No. CARLSB.001.005 RECOMMENDED OPTIONS FOR THE MAINTENANCE OR REPLACEMENT OF THE LAS ENCINAS CREEK BRIDGE CARLSBAD, CALIFORNIA Prepared for City ofCarlsbad 1635 Faraday Avenue Carlsbad, Ca 92008 January 2008 Prepared by January 2008 RECOMMENDED OPTIONS FOR THE MAINTENANCE OR REPLACEMENT OF THE LAS ENCINAS CREEK BRIDGE 1. SCOPE The scope of this report includes a presentation of two recommended structural options for extending the life of the Las Encinas Creek Bridge for approximately five (5) years and a third option for replacing the bridge with twin concrete box culverts, which would have a life expectancy well beyond twenty (20) years. The following appendices are included as a part ofthe report: Appendix A - Temporary Steel Shoring Option Appendix B - Precast Concrete Box Culverts Option Appendix C - Reinforced Concrete Box Culverts Option Appendix D - Cost Estimates Appendix E - Flow Calculations for Reinforced Concrete Box Culverts Option 2. BACKGROUND The firm of Richard Brady and Associates (RBA) was retained by the City of Carlsbad to provide recommended options to extend the life of the Las Encinas Creek Bridge. The original bridge was built in 1913, widened in 1924, and widened again in 1928. The reinforced concrete bridge consists ofa slab deck supported by twelve (12) cast-in-place concrete T-girders spanning approximately 20 feet between two concrete abutment walls. 3. OBSERVATIONS On October 16, 2007, David Wolfson, PE, and Mary Epperson, PE, of RBA performed field observations of the condition of the existing bridge superstructure. The purpose of the observations was not to perform a condition assessment survey, but to confirm assumptions and verify if the recomrnendations contained herein are feasible due to existing conditions. The condition of the bridge is documented in a report by Nolte and Associates for the City of Carlsbad. The date of this report is unknown, but it was submitted within the last two years. The condition ofthe bridge appears not to have changed significantly since the report was written. 4. RECOMMENDATIONS The following recommendations consist of three options for extending the life ofthe bridge. The first two options will extend the life ofthe bridge by approximately five (5) years. The third option will extend it for approximately twenty (20) years. 1 Temporary Steel Shoring Option This option utilizes temporary shoring in the form of galvanized steel wide flange beams spanning between the existing abutment walls. Please refer to Appendix A which includes plans, sections and details for this scheme. The steel beams will be placed below the bridge deck in a number of locations primarily on the west side of the bridge. In the central portion of the bridge, steel plates are utilized to span between the steel beams. Voids between the plates, beams, and the existing bridge deck soffit will be filled with non-shrink grout to provide continuous bearing support. The connections to the existing abutment walls will be made by installing stainless steel epoxy adhesive anchors and end plates with shear tabs to attach the new steel shoring beams as shown in Appendix A. Access below the bridge will be required. No work will be performed from above. A budget estimate for the temporary steel shoring option is $290,000. See Appendix D- . . Precast Concrete Box Culverts Option This opfion was developed to correspond to the existing box culverts under the northbound lanes of Carlsbad Blvd. located approximately 200 yards upstream of the Las Encinas Creek Bridge. The execution of this option would entail excavating below the bridge (as necessary) and installing precast concrete box culvert sections below the existing deck. After installation of the precast concrete culvert sections, the voids between the deck soffit and the box culverts would be filled with flowable non-shrink grout. Please refer to Appendix B which illustrates this option. Access below the bridge will be required. No work will be performed from above. A budget estimate for the precast concrete box culverts option is $275,000. See Appendix D. Reinforced Concrete Box Culverts Option This option will replace the existing bridge with cast-in-place double reinforced concrete box culverts similar to the existing box culverts upstream under the northbound lanes of Carlsbad Blvd. The City of Carlsbad originally asked RBA to provide a preliminary size for the new culverts using the flow value from a 100-year flood found in the City of Carlsbad Drainage Master Plan. This value of 1217 cubic feet per second (CFS) is found in the City of Carlsbad Master Plans Appendix A Page 6 of SWMM 5 Model - Basin C. Based on this flow, the size of the culverts required would be unrealistic for this location. RBA recommends sizing the culverts using the flow value for a 25-year flood. This recommendation is based on an excerpt from chapter 820 ofthe CALTRANS Highway Design Manual. It states on page 820-2 that "A more frequent design flood than a 4% probability of exceedance (25-year) should not be used for the hydraulic design of culverts under freeways and highways of major importance." We consider this statement to mean that a 25-year flood should be the maximum flow considered as opposed to that of a 50 or 100 year flood due to site restrictions and economic constraints. Based on the 25-year flood, the recommended size of each cell of the double box culverts is 10 feet wide by 5 feet high. Please refer to Appendix C for conceptual drawings describing this option. Installation of the reinforced concrete box culverts would include diverting the flow of the creek, demolishing the existing bridge, excavating and re-grading as required, and installing the cast in place box culverts. The roadway would be reconstructed above the box culverts. Due to traffic constraints, we recommend leaving in place approximately 16 feet of width on the east side of the bridge during the installation of the box culverts. This area would be used for traffic diverted into a single southbound lane and would be removed after installation of the box culverts and roadway reconstruction is complete. See the Preliminary Traffic Control plan in Appendix C. The reinforced concrete box culverts option-would provide the longest life of the three options proposed. A budget estimate for the reinforced concrete box culverts option is $685,000.00. See Appendix D. 5. CONCLUSION Extending the life of the bridge can be accomplished utilizing several structural schemes. Three options are presented herein with conceptual budget cost estimates. The estimated costs of the first two options are approximately equal. The third option which is a replacement of the bridge with double box culverts will provided the longest life. Environmental impact considerations as well as future demolition requirements should also be considered. Additionally, the differences, if any, in effects on the stream flow should be considered. 6. DISCLAIMER AND OUALIFICATION The conclusions and recommendations of this report are based on limited field observations, calculations, and research. The report does not provide any warranty, either expressed or implied, for any aspect of the recommended repair options. The preliminary design sketches herein, provided in appendices A, B and C, are conceptual only and are not to be considered fmal drawings for construction purposes. Respectfully submitted. Reviewed by: David L Wolfson R.L. Biggers PE 66290. SE1825 APPENDIX A TEMPORARY STEEL SHOREVG OPTION A EDGE OF EXISTING BRIDGE DECK- V -NEW STEEL BEAM TYP. EXISTING CONCRETE DIAPHRAGM, TYP. EXISTING CONCRETE ABUTMENT WALL, TYP. -,<-69'-7 1/2 ± NOTE: ALL STEEL ELEMENTS SHALL BE GALVANIZED. LAS ENCINAS CREEK BRIDGE CITY OF CARLSBAD California BRIDGE PLAN FOR TEMPORARY STEEL SHORING OPTION DATE: November 9, 2007 DRAWN BY: ME CHECKED BY: DW, RLB CAD FILE: CARLSB-001-004 Al SCALE: 1/8" = I'-O" JOB NUMBER: CARLSB.001.004.00 REVISION: REFERENCE; SKETCH: A1 •EXISTING RAILING, TYP EXISTING CONCRETE BRIDGE DECK: EXISTING CONCRETE DIAPHRAGM BEYOND, TYP. NEW STEEL WIDE FLANGE BEAM, TYP. EXISTING CONCRETE T-GIRDER, TYP. SECTION THROUGH BRIDGE LOOKING NORTH SCALE: 3/16" = I'-O" NEW NON-SHRINK GROUT NOTE: ALL STEEL ELEMENTS SHALL BE GALVANIZED. CONNECTION DETAIL SCALE: NONE NEW STEEL WIDE FLANGE BEAM NEW STEEL CONNECTION PLATE NEW A325 BOLT IN LONG SLOTTED HOLE, TYP: NEW STEEL PLATE NEW EPOXY ADHESIVE THREADED STAINLESS STEEL ROD, TYP. EXISTING CONCRETE ABUTMENT WALL CONNECTION DETAIL SCALE: NONE EXISTING CONCRETE BRIDGE DECK NEW STEEL PLATE EXISTING CONCRETE ABUTMENT WALL 'i^,/ff^u- i^i/k -.y^'.,: fKi? 49/^: G^G-J LAS ENCINAS CREEK BRIDGE CITY OF CARLSBAD California ^SECTION AND DETAILS FOR TEMPORARY STEEL SHORING OPTION DATE: November 9, 2007 DRAWN BY: ME CHECKED BY: DW, RLB' CAD FILE: CARLSB-001-004 A2 SCALE: AS NOTED JOB NUMBER: CARLSB.OOI.004.00 REVISION: REFERENCE: SKETCH: A2 APPENDIX B PRECAST CONCRETE BOX CULVERTS OPTION B FILL VOIDS SOLID WITH NON-SHRINK FLOWABLE GROUT CONC. CUT OFF WALL LCRUSHED ROCK LEVELING BED W/ PERIMETER RIP RAP LAS ENCINAS CREEK BRIDGE CITY OF CARLSBAD California ELEVATION OF BRIDGE WITH PRECAST CONCRETE BOX CULVERTS DATE: November 9, 2007 SCALE: NONE REFERENCE: DRAWN BY: JN JOB NUMBER: CARLSB.OOI.004.00 REFERENCE: CHECKED BY: DW, RLB REVISION: SKETCH: B1 CAD FILE: CARLSB-001-004 Bl SKETCH: B1 LAYING LENGTH SECTIONS TO ACCOMMODATE BRIDGE SOFFIT INTERLOCKING TOP SECTION PRECAST CONCRETE BOX CULVERTS SHALL CONFORM TO ASTM 01433. * ELEVATION VARIES TO ACCOMMODATE VARYING BRIDGE SOFFIT HEIGHTS LAS ENCINAS CREEK BRIDGE CITY OF CARLSBAD California PRECAST CONCRETE BOX CULVERT ELEMENTS DATE: November 9, 2007 SCALE: NONE REFERENCE: DRAWN BY: DW JOB NUMBER: CARLSB.001.004.00 REFERENCE: CHECKED BY: DW, RLB REVISION: SKETCH: B2 CAD FILE: CARLSB-001-004 B2 SKETCH: B2 APPENDIX C REINFORCED CONCRETE BOX CULVERTS OPTION LAS ENCINAS CREEK BRIDGE CITY OF CARLSBAD Califomia LOCATION PLAN OF REINFORCED CONCRETE BOX CULVERTS OPTION cc C ..yi^i^^/*- *f<f. -(^is: /^jiffj ^oit sjrf. (»is: fjs/'v DATE: DECEMBER 15, 2007 SCALE: 1/16" = I'-O" REFERENCE: cc C ..yi^i^^/*- *f<f. -(^is: /^jiffj ^oit sjrf. (»is: fjs/'v DRAWN BY: DW JOB NUMBER: CARLSB.OOI .005.00 REFERENCE: cc C ..yi^i^^/*- *f<f. -(^is: /^jiffj ^oit sjrf. (»is: fjs/'v CHECKED BY: DW, RLB REVISION: SKETCH: 01 cc C ..yi^i^^/*- *f<f. -(^is: /^jiffj ^oit sjrf. (»is: fjs/'v CAD FILE: CARLSB-001-005 Cl SKETCH: 01 EXISTING GUARDRAIL TO BE REMOVED RECONSTRUCT ROADWAY PAVEMENT FILTER FABRIC-J CONC. CUT-OFF WALL — IG'-O" CRUSHED ROCK LEVELING BED W/ PERIMETER RIP RAP lO'-O" LAS ENCINAS CREEK BRIDGE CITY OF CARLSBAD California ELEVATION OF REINFORCED CONCRETE BOX CULVERTS OPTION (/ DATE: DECEMBER 15, 2007 SCALE: NONE REFERENCE: (/ DRAWN BY: JN JOB NUMBER: CARLSB.OOI .005.00 REFERENCE: (/ CHECKED BY: DW, RLB REVISION: SKETCH: 02 (/ CAD FILE: CARLSB-001-005 C2 SKETCH: 02 LAS ENCINAS CREEK BRIDGE CITY OF CARLSBAD Califomia TfltAFF/C CONTROL PLAN FOR REINFORCED CONCRETE BOX CULVERTS OPTION • y^tlC/ir ,fj.t. -(96: t:ji:V , J^ai- SJrf. (96: l9Ji-l} DATE: DECEMBER 15, 2007 SCALE: NTS REFERENCE: • y^tlC/ir ,fj.t. -(96: t:ji:V , J^ai- SJrf. (96: l9Ji-l} DRAWN BY: DW JOB NUMBER: CARLSB.OOI.005.00 REFERENCE: • y^tlC/ir ,fj.t. -(96: t:ji:V , J^ai- SJrf. (96: l9Ji-l} CHECKED BY: DW, RLB REVISION: SKETCH: 03 • y^tlC/ir ,fj.t. -(96: t:ji:V , J^ai- SJrf. 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Tht» plan moy M u«*<l for nJtlfM c«ll c^<¥«rt» raraiTirsiifflpifarTirsisgiiE CO j Sooclno ••=-bor.i?-^M-^ 'd",tK)r». -for •ortd cov«ri ixi to ond Inckx^rw 10 . _. ^9sn , 1 '<'Ti-'i;jFl "cToTir M- i*>«>»-/c^ I < Tsui « I ctiTtrjfe ROOF SECTION SPANS A- THRU 8 NVEWT SMLAB Coftat Jt (Opttorx*) 14 ii.Rce ^ ^ "o"C-_Jlior.- -' ^-M . , -— .- • «, tor . ^ - 1 •< • « Uo< •4 . m uo«.^— FLAT INVERT ALTERNATIVE EXTERIOR WALL SECTION SPANS 4- THRU 8' TTPICAL SPfTinN - SPANS 4' THRU B- •4 -IT' bart, or "4 • B, for cov«r ov«r IO' Con«t Jt ..-"ij... 7 !_/ lOptlanai ^ ' " r\ .-1- -«5-i- . I I AJt«rT>otlv« Con»t Jt "g" or "b" bar* W SM Hat* fi - . - r 1 •- OS-"/" I CO H > Z ROOF SECTION SPANS 10' THRU 14- .'^^^ TYPICAL SECTION - SPANS 10' THRU 14' EXTERIOR WAI I, ^pCTfffN SPANS 10- THRU STATE Cf CM.rof—A DCPMIIEHT OF TUMSPORTATCN CAST-IN-PLACE REINFORCED CONCRETE DOUBLE BOX CULVERT , NO SCALE D81 APPENDIX D COST ESTIMATES D COST ESTIMATE - TEMPOFiARY STEEL SHORING DATE PREPARED 12/7/2007 SHEET ^ OF _ 1 2 ACTIVITY AND LOCATION City of Carlsbad CONSTRUCTION CONTRACT NO. IDENTIFICATION NUMBER ACTIVITY AND LOCATION City of Carlsbad ESTIMATED BY . ,. , " JN CATEGORY CODE NUMBER PROJECT TITLE Temporary Support for Las Encinas Creels Bridge ESTIMATED BY . ,. , " JN CATEGORY CODE NUMBER PROJECT TITLE Temporary Support for Las Encinas Creels Bridge STATUS OF DESIGN C PED .0 35% n 100% O FINAL ^ Olher (Specify) Concept JOB ORDER NUMBER ITEM DESCRIPTION QUANTITY MATERIAL COST LABOR COST ENGINEERING ESTIMATE ITEM DESCRIPTION NUMBER UNIT UNIT COST TOTAL UNIT COST TOTAL UNIT COST TOTAL SUMMARY DIVISION 01 GENERAL REQUIREMENTS (10%) 15,619.00 2,548.00 18,167.00 05 METALS 156,191.00 25,482.00 181,673.00 SUBTOTAL 199,840.00 CONTRACTOR OH & P (20%) 39,968.00 DESIGN CONTINGENCY (10%) 23,980.80 6 MO.S ESCALATION (6%) 15,827.00 BOND (1.5%) 4,194.00 PROJECT TOTAL 283,809.80 COST ESTIMATE - TEIVIPORARY STEEL SHORING DATE PREPARED 12/7/2007 SHEET ^ av 2 ACTIVITY AND LOCATION City of Carlsbad CONSTRUCTION CONTRACT NO, IDENTIFICATION NUMBER ACTIVITY AND LOCATION City of Carlsbad ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Temporary Support for Las Encinas Creek Bridge ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Temporary Support for Las Encinas Creek Bridge STATUS OF DESIGN OPED 0 35% 0 100% O FINAL E other fSpec/M ConcepJ JOB ORDER NUMBER ITEM DESCRIPTION QUANTITY MATERIAL COST LABOR COST ENGINEERING ESTIMATE ITEM DESCRIPTION NUMBER UNIT UNIT COST TOTAL UNIT COST TOTAL UNIT COST TOTAL DIVISION 5 - METALS 05120 STRUCTURAL STEEL Traffic Deviation 1.00 LOT 13,320.00 13,320 2,922.00 2,922 16,242.00 16,242 Steel Beams 14.00 TON 2,691.00 37,674 471.50 6,601 3,162.50 44,275 Steel Plate 12.00 TON 2,691.00 32,292 471.50 5,658 3,162.50 37,950 Steel Angle 1.00 TON 2,691.00 2,691 471.50 472 3,162.50 3,163 Connections 14.00 BM 437.00 6,118 218.50. 3,059 655.50 9,177 Galvanizing Steel 27.00 TON 1,345.00 36,315 47.00 1,269 1,392.00 37,584 • Grout 120.00 SF 20.00 2,400 14.00 1,680 34.00 4,080 Abutment Shotcrete 1.00 LS 12,086.00 12,086 1,820.00 1,820 '13,906.00 13,906 Clean up 1.00 LS 13,295.00 13,295 2,001.00 2,001 15,296.00 15,296 - TOTAL 156,191 25,482 181,673 COST ESTIMATE - PRECAST CONCRETE BOX CULVERTS DATE PREPARED 12/7/2007 SHEET ^ OF 2 ACTIVITY AND LOCATION City of Carlsbad CONSTRUCTION CONTRACT NO. IDENTIFICATION NUMBER ACTIVITY AND LOCATION City of Carlsbad ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Temporary Support for Las Encinas Creek Bridge ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Temporary Support for Las Encinas Creek Bridge STATUS OF DESIGN l~i PED O 35% n 100% in FINAL E Oiher (Spedfyl Ccncept JOB ORDER NUMBER ITEM DESCRIPTION QUANTITY MATERIAL COST LABOR COST ENGINEERING ESTIMATE ITEM DESCRIPTION NUMBER UNIT UNIT COST TOTAL UNIT COST TOTAL UNIT COST TOTAL SUMMARY DIVISION . 01 GENERAL REQUIREMENTS (10%) 14,210.00 3,135.00 17,345.00 03 PRECAST BOX CULVERTS 142,103.00 31,350.00 173,453.00 SUBTOTAL 190,798.00 CONTRACTOR OH & P (20%) 38,160.00 DESIGN CONTINGENCY (10%) 22,896.00 6 MO.S ESCALATION (6%) 15,111.00 BOND (1.5%) 4,004.00 PROJECT TOTAL 270,969.00 COST ESTIMATE - PRECAST CONCRETE BOX CULVERTS DATE PREPARED 12/7/2007 SHEET 2 2 ACTIVITY AND LOCATION City of Carlsbad CONSTRUCTION CONTRACT NO. IDENTIFICATION NUMBER ACTIVITY AND LOCATION City of Carlsbad ESTIMATED BY JN CATEGORY CODE NUMBER PROJECT TITLE Temporary Support for Las Encinas Creek Bridge ESTIMATED BY JN CATEGORY CODE NUMBER PROJECT TITLE Temporary Support for Las Encinas Creek Bridge STATUS OF DESIGN OPED 0 35% O 100% O FINAL 171 other (Specify) Concept JOB ORDER NUMBER ITEM DESCRIPTION QUANTITY MATERIAL COST LABOR COST ENGINEERING ESTIMATE ITEM DESCRIPTION NUMBER UNIT UNIT COST TOTAL UNIT COST TOTAL UNIT COST TOTAL DIVISION 03 - CONCRETE PRECAST CONCRETE Traffic Deviation 1.00 LOT '13,320.00 13,320 2,922.00 2,922 16,242.00 16,242 Concrete Removal 17.77 CY 59.46 1,057 172.50 3.065 231.96 4,122 Excavation to Fit 150.00 CY 5.75 863 80.00 12,000 85.75 12,863 Crushed Rock and Rip Rap Fill 18.00 CY 3.00 54 15.00 270 18.00 324 (2) Concrete Box Culverts 1.00 LS 79,000.00 79,000 0.00 0 79,000.00 79,000 Formwork 68.00 LF 8.00 544 12.00 816 20.00 1,360 Grout Fill 166.00 CY 150.00 24,900 42.00 6,972 192.00 31,872 Seals Between Joints 258.00 LF 27.00 6,966 2.50 645 29.50 7,611 Shotcrete Abutments 1.00 LS 3,600.00 • 3,600 2,220.00 2,220 5,820.00 5,820 Clean up 1.00 LS 11,800.00 11,800 2,440.00 2,440 14,240.00 14,240 TOTAL 142,103 31,350 173,453 COST ESTIMATE - REINFORCED CONCRETE BOX CULVERTS DATE PREPARED 12/12/2007 SHEET ^ OF 2 ACTIVITY AND LOCATION City ofCarlsbad CONSTRUCTION CONTRACT NO. IDENTIFICATION NUMBER ACTIVITY AND LOCATION City ofCarlsbad ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Replacement of Las Encinas Creek Bridge ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Replacement of Las Encinas Creek Bridge STATUS OF DESIGN PED 35% 100% FINAL Olher (•Spec;/y; JOB ORDER NUMBER ITEM DESCRIPTION QUANTITY MATERIAL COST LABOR COST ENGINEERING ESTIMATE ITEM DESCRIPTION NUMBER UNIT UNIT COST TOTAL UNIT COST TOTAL UNIT COST TOTAL SUMMARY DIVISION * 01 GENERAL REQUIREMENTS (10%) 23,696.00 .21,834.00 45,530.00 03 CAST IN PLACE CULVERTS 236,959.00 218,338.00 455,297.00 SUBTOTALS 500,827.00 CONTRACTOR OH & P (15%) 75,124.00 DESIGN CONTINGENCY (10%) 57,595.00 6 MO. ESCALATION (6%) 38,013.00 BOND (1.5%) 10,073.00 PROJECT TOTAL 681,632.00 COST ESTIMATE - REINFORCED CONCRETE BOX CULVERTS DATE PREPARED 12/12/2007 SHEET 2 ""^ 2 ACTIVITY AND LOCATION City of Carlsbad CONSTRUCTION CONTRACT NO. IDENTIFICATION NUMBER ACTIVITY AND LOCATION City of Carlsbad ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Replacement of Las Encinas Creek Bridge ESTIMATED BY JN CATEGORY CODE NUMBER PROJECTTITLE Replacement of Las Encinas Creek Bridge STATUS OF DESIGN IZI PED IZI 35% O 10'"'" IZI FINAL IZI Olher (Specify) JOB ORDER NUMBER ITEM DESCRIPTION QUANTITY MATERIAL COST LABOR COST ENGINEERING ESTIMATE ITEM DESCRIPTION NUMBER UNIT UNIT COST TOTAL UNIT COST TOTAL UNIT COST TOTAL DIVISION 3-CONCRETE 03300 CAST IN PLACE Construction & Demolition of New Lane 710.00 SY 62.54 44,402 13.72 9,741 76.26 54,143 Traffic Diversion 1.00 LOT 13,320.59 13,321 2,922.36 2,922 16,242.95 16,243 Demolition of Existing Bridge. 327.00 CY 62.04 20,287 126.00 41,202 188.04 61,489 Stream Diversion 1.00 LOT 10,143.54 10,144 20,601.00 20,601 30,744.54 30,745 Excavation, Leveling & Fill. 350.00 CY 0.00 0 69.24 24,234 69.24 24,234 Sand Shoring 888.00 SQFT 9.29 8,248 4.96 4,401 14.24 12,649 C.I.P. Reinforced Concrete Double Box Culverts 171.00 CY 595.82 101,884 487.49 83,360 1,083.30 185,244 Pavement restoration 171.00 SY 40.54 6,932 9.52 1,627 50.05 8,559 Stripping of Lanes, Traffic Signs & Poles 20,000.00 SQFT 0.51 10,200 0.52 10,400 1.03 20,600 Clean up 1.00 LOT 21,541.70 21,542 19,848.87 19,849 41,390.56 41,391 TOTAL 236,959 218,338 455,297 APPENDIX E FLOW CALCULATIONS FOR REINFORCED CONCRETE BOX CUVERTS OPTION HIGHWAY DESIGN MANUAL 820-1 September I, 2006 CHAPTER 820 CROSS DRAINAGE Topic 821 - General Index 82L1 - Introduction Cross drainage involves the conveyance of surface water and stream flow across or from the highway right of way. This is accomplished by providing either a culvert or a bridge to convey the flow from one side of the roadway to the other side or past some other type of flow obstruction. In addition to the hydraulic function, a culvert must carry construction and highway traffic and earth loads._ Culvert design, therefore, involves both hydraulic and structural design. This section of the manual is basically concemed with the hydraulic design of culverts. Both the hydraulic and structural designs must be consistent with good engineering practice and economics. An itemized listing of good drainage design objectives and economic factors to be considered are listed in Index 801.4. Information on strength requirements, height of fill tables, and other physical characteristics of altemate culvert shapes and materials may be found in Chapter 850, Physical Standards. More complete infonnation on hydraulic principles and engineering techniques of culvert design may be found in the FHWA Hydraulic Design Series No. 5, "Hydraulic Design of Highway Culverts". Key aspects of culvert design and a good overview of the subject are more fully discussed in the AASHTO Highway Drainage Guidelines. Stmctures measuring more than 20 feet along the roadway centerline are conventionally classified as bridges, assigned a bridge number, and maintained and inspected by the Division of Structures. However, some stmctures classified as bridges are designed hydraulically and stmcturally as culverts. Some examples are certain multi-barreled box culverts and arch culverts. Culverts, as distin- guished from bridges, are usually covered with embankment and have structural material around the entire perimeter, although some are supported on spread footings with the streambed serving as the bottom ofthe culvert. Bridges are not designed to take advantage of submergence to increase hydraulic capacity even though some are designed to be inundated under flood conditions. For economic and hydraulic efficiency, culverts should be designed to operate with the inlets submerged during flood flows, if conditions permit. At many locations, either a bridge or a culvert will fulfill both the stmctural and hydraulic requirements of the stream crossing. Stmcture choice at these locations should be based on constmction and maintenance costs, risk of failure, risk of property damage, traffic safety, and environmental and aesthetic considerations. Culverts are usually considered minor stmctures, but they are of great importance to adequate drainage and the integrity of the highway facility. Although the cost of individual culverts is relatively small, the cumulative cost of culvert constmction constitutes a substantial share of the total cost of highway constmction. Similarly, the cost of maintaining highway drainage features is substantial, and culvert maintenance is a large share of these costs. Improved service to the public and a reduction in the total cost of highway constmction and mamtenance can be achieved by judicious choice of design criteria and careful attention to the hydraulic design of each culvert. 82L2 Hydrologic Considerations Before the hydraulic design of a culvert or bridge can begin, the design discharge, the quantity (Q) of water in cubic feet per second, that the facility may reasonably be expected to convey must be estknated. The most important step is to establish the appropriate design storm or flood frequency for the specific site and prevailing conditions. Refer to Chapter 810, Hydrology and specifically Topics 818 and 819 for useful information on hydrological analysis methods and considerations. When empirical methods are used to estimate the peak rate of mnoff, design Q, for important culverts, it is recommended that at least two methods be tried. By comparing results a more reliable discharge estimate for the drainage basin may be obtained. This is more important for large 820-2 September 1. 2006 HIGHWAY DESIGN M.A.NliAL basins having areas in excess of 320 acres than for small basins. 82L3 Selection of Design Flood As discussed in Index 818.2, there are two recognized ahematives to selecting the design flood frequency (probability of exceedance) in the hydraulic design of bridges and culverts. They are: • By policy - using a preselected recurrence interval. • By analysis - using the recurtence interval that is most cost effective and best satisfies the specific site conditions and associated risks. Although either of these altematives may be used exclusive of the other, in actual practice both altematives are often considered and used jointly to select the flood frequency for hydraulic design. For culverts and small bridges, apply the following general mles for first consideration in the process for ultimate selection of the design flood. (1) Bridges. The basic mle for the hydraulic design of bridges is that they should pass a 2% probability flood (50-year). Freeboard, vertical clearance between the lowest stmctural member and the water surface elevation of the design flood, sufficient to pass the 1% probability flood should be provided. Two feet of freeboard is often assumed for preliminary bridge designs. The effects of bedload and debris should be considered in the design of the bridge waterway. (2) Culverts. There are ' two primary design frequencies that should be considered: • A 10% probability flood (10-year) without causing the headwater elevation to rise above the inlet top of the culvert and, • A 1% probability flood (100-year) with-out headwaters rising above an elevation that would cause objectionable backwater depths or outlet velocities. The designer must use discretion in applying the above criteria. Design floods selected on this basis may not be the most appropriate for specific project site locations or conditions. The cost of providing facilities to pass peak discharges suggested by these criteria need to be balanced against potential damage to the highway and adjacent properties upstream and downstream of the site. The selection of a design flood with a lesser or greater peak discharge may be warranted and justified by economic analysis. A more frequent design flood than a 4% probability of exceedance (25-vear) should not be used for the hydraulic design of culverts under freeways and other highways of major importance. Alternatively, where predictive data is limited, or where the risks associated with drainage facility failure are high, the greatest flood of record or other suitably large event should be evaluated by the designer. When channels or drainage facilities under the jurisdiction of local flood control agencies or Corps of Engineers are involved, the design flood must be detennined through negotiations with the agencies involved. 82L4 Headwater and Tailwater (1) Headwater. The term, headwater, refers to the depth of the upstream water surface measured from the invert of the culvert entrance. Any culvert which constricts the natural stream flow will cause a rise in the upstream water surface. It is not always economical or practical to utilize all the available head. This apphes particularly to simations where debris must pass through the culvert, where a headwater pool cannot be tolerated, or where the natural gradient is steep and high outlet velocities are objectionable. The available head may be hmited by the fill height, damage to the highway facility, or the effects of ponding on upstream property. The extent of ponding should be brought to the attention of all interested funcfions, including Project Development, Maintenance, and Right of Way. Full use of available head may develop some vortex related problems and also develop objectionable velocities resulting in abrasion of the culvert itself or in downstream erosion. In most cases, provided the culvert is not flowing under pressure, an increase in the culvert size does not appreciably change the outlet velocities.