National Academies Press: OpenBook

Proposed Specifications for LRFD Soil-Nailing Design and Construction (2011)

Chapter: Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls

« Previous: Appendix A - Proposed LRFD Design Specifications for Soil Nail Walls
Page 99
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 99
Page 100
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 100
Page 101
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 101
Page 102
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 102
Page 103
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 103
Page 104
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 104
Page 105
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 105
Page 106
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 106
Page 107
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 107
Page 108
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 108
Page 109
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 109
Page 110
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 110
Page 111
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 111
Page 112
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 112
Page 113
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 113
Page 114
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 114
Page 115
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 115
Page 116
Suggested Citation:"Appendix B - Proposed LRFD Construction Specifications for Soil Nail Walls." National Academies of Sciences, Engineering, and Medicine. 2011. Proposed Specifications for LRFD Soil-Nailing Design and Construction. Washington, DC: The National Academies Press. doi: 10.17226/13327.
×
Page 116

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

B-1 TABLE OF CONTENT S 1.1 DESCRIPTION ................................................................................................................ .............................. B-3 1.2 MATERIALS.................................................................................................................. ................................ B-3 1.2.1 Facing ................................................................................................................... ............................ B-3 1.2.1.1 Cast-in-place Concrete ................................................................................................... B-3 1.2.1.2 Reinforcing Steel ...................................................................................................... ...... B-3 1.2.1.3 Permanent Shotcrete .................................................................................................... ... B-3 1.2.1.4 Architectural Surface Finishes ....................................................................................... B-3 1.2.2 Soil Nails ............................................................................................................... ........................... B-3 1.2.2.1 Solid Soil Nail Bar .................................................................................................... ...... B-3 1.2.2.2 Bar Coupler ............................................................................................................ ......... B-4 1.2.2.3 Fusion-Bonded Epoxy Coating ...................................................................................... B-4 1.2.2.4 Encapsulation .......................................................................................................... ........ B-4 1.2.3 Soil Nail Appurtenances .................................................................................................. ................. B-4 1.2.3.1 Centralizer ............................................................................................................ .......... B-4 1.2.3.2 Grout .................................................................................................................. . ............ B-4 1.2.3.3 Fine Aggregate......................................................................................................... ....... B-4 1.2.3.4 Portland Cement ........................................................................................................ ..... B-4 1.2.3.5 Admixtures ............................................................................................................. ........ B-5 1.2.3.6 Film Protection ........................................................................................................ ....... B-5 1.2.4 Bearing Plates, Nuts, and Head-Stud Shear Connectors .................................................................. B-5 1.2.4.1 Bearing Plates ......................................................................................................... ........ B-5 1.2.4.2 Nuts ................................................................................................................... . ............. B-5 1.2.4.3 Shear Connectors ....................................................................................................... ..... B-5 1.2.5 Welded-Wire Mesh......................................................................................................... .................. B-5 1.2.6 Reinforcing Steel ........................................................................................................ ...................... B-5 1.2.7 Geocomposite Sheet Drain ................................................................................................ ..............B-5 1.2.8 Underdrain and Perforated Pipe ........................................................................................... ............. B-6 1.2.8.1 Pipe ................................................................................................................... . ............. B-6 1.2.8.2 Fittings ............................................................................................................... ............. B-6 1.2.9 Temporary Shotcrete ...................................................................................................... .................. B-6 1.3 CONTRACTOR QUALIFICATIONS .................................................................................................. ......... B-6 1.4 SUBMITTALS ................................................................................................................. .............................. B-6 1.4.1 Personnel ................................................................................................................ .......................... B-6 1.4.2 Surveys .................................................................................................................. ........................... B-7 1.4.3 Construction Plan ........................................................................................................ . .................... B-7 1.5 STORAGE AND HANDLING ....................................................................................................... ............... B-8 1.6 EXCAVATION ................................................................................................................. ............................. B-8 1.7 SOIL NAIL INSTALLATION ..................................................................................................... .................. B-9 1.8 GROUTING................................................................................................................... ................................. B-9 1.9 SOIL NAIL TESTING .......................................................................................................... ......................... B-9 1.9.1 Tests .................................................................................................................... .............................. B-9 1.9.2 Equip ment ................................................................................................................ ......................... B-9 A P P E N D I X B Proposed LRFD Construction Specifications for Soil Nail Walls

1.10 VERIFICATION TESTING.........................................................................................................................B-10 1.10.1 Methods ..........................................................................................................................................B-10 1.10.2 Schedule .........................................................................................................................................B-10 1.11 PROOF TESTING........................................................................................................................................B-11 1.11.1 Methods ..........................................................................................................................................B-11 1.11.2 Schedule .........................................................................................................................................B-12 1.12 ACCEPTANCE CRITERIA OF TEST SOIL NAILS .................................................................................B-13 1.13 REJECTION OF TEST SOIL NAILS ..........................................................................................................B-13 1.13.1 Verification Test Soil Nails ............................................................................................................B-13 1.13.2 Proof Test Soil Nails.......................................................................................................................B-13 1.14 WALL DRAINAGE NETWORK ................................................................................................................B-14 1.14.1 Geocomposite Drain Strips.............................................................................................................B-14 1.14.2 Footing Drains ................................................................................................................................B-14 1.15 SHOTCRETE FACING................................................................................................................................B-14 1.15.1 Final Face Finish ............................................................................................................................B-14 1.15.2 Attachment of Nail Head Bearing Plate and Nut ............................................................................B-15 1.15.3 Shotcrete Facing Tolerances...........................................................................................................B-15 1.16 REINFORCING STEEL...............................................................................................................................B-15 1.17 STRUCTURAL CONCRETE ......................................................................................................................B-15 1.18 ARCHITECTURAL SURFACE FINISHES................................................................................................B-15 1.19 BACKFILLING BEHIND WALL FACING UPPER CANTILEVER ........................................................B-16 1.20 ACCEPTANCE ............................................................................................................................................B-16 2.0 MEASUREMENT AND PAYMENT ..........................................................................................................B-16 2.1 SOIL NAILS.................................................................................................................................................B-16 2.2 STRUCTURE EXCAVATION ....................................................................................................................B-17 2.3 WALL FACE................................................................................................................................................B-17 2.4 PAYMENT ...................................................................................................................................................B-17 2.4.1 Pay Items ........................................................................................................................................B-17 Section xx – Soil Nail Walls 3.0 CORROSION PROTECTION......................................................................................................................B-18 REFERENCES ........................................................................................................................................................B-18 B-2

B-3 1.1 DESCRIPTION C1.1 This work consists of constructing a permanent soil nail wall as specified herein and as shown on the Plans. The Contractor shall furnish all labor, ma terials, and equipment required to complete the work. The Contractor shall select the excavation, drilling, and grouting meth ods and the diam eter of the drill-holes to me et the performance requirements specifi ed herein or shown on the Plans. The work shall include excavating in staged lifts in accordance with the approved Contractor’s plan; detailing the drilling of the soil nail drill-holes to the diam eter and length required to develop the specified resistance; grouting the soil nails; providing and installing the specified drainage features; providing and installing bearing plates, washers, nuts, and other required misce llaneous mate rials; and constructing the required temporary shotcrete face and constructing the final structural facing. The Owner ma y choose to have the Contractor design and construct the work at the location shown on the drawings. The Contractor shall furnish all labor, plans, drawings, design calculations, and all other ma terial and equipment required to design and construct the soil nail wall(s) in accordance with this Specification. Project-specific needs ma y require a different type of facing including reinforced shotcrete, cast-in-place concrete, and precast concrete panels. 1.2 MATERIALS 1.2.1 Facing Facing mate rial shall conform to the following sections and subsections. 1.2.1.1 Cast-in-place Concrete Cast-in-place (CIP) concrete shall me et the require ments of Section 5 of the AASHTO LRFD Bridge Construction Specifications. 1.2.1.2 Reinforcing Steel Reinforcing steel shall meet the requirements of Section 6 of the AASHTO LRFD Bridge Construction Specifications. 1.2.1.3 Permanent Shotcrete Permanent shotcrete shall me et the requirements of Section 24, “Pneumatically Applied Mortar,” of the AASHTO LRFD Bridge Construction Specifications. 1.2.1.4 Architectural Surface Finishes Architectural surface finishes ma y include textured surfaces or a surface finish with color/stain application. 1.2.2 Soil Nails 1.2.2.1 Solid Soil Nail Bar Solid nail bars shall meet the requirements of AASHTO M 31/ASTM A 615, Grade 420 or 520, or ASTM A 722 for Grade 1035. Soil nail bars shall be continuous without splices or welds, C1.2.2.1 Bars of A 722, Grade 1035, should not be used in conventional soil-nailing applications because the ma terial tends to be mo re brittle and mo re susceptible to stress corrosion Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

new, straight, undamaged, bare or epoxy coated, or encapsulated as shown on the Plans. Bars shall be threaded a mi nimum of 150 mm on the wall anchorage end, to allow proper attachment of the bearing plate and nut. If threads are cut into a soil nail bar, provide the next larger bar nu mb er designation than what is shown on the Plans, at no additional cost. than the more commonly used lower-grade steels. Threading ma y be a continuous spiral, deform ed ribbing provided by the bar deformations (continuous thread bars), or ma y be cut into a reinforcing bar. 1.2.2.2 Bar Coupler Bar couplers shall develop the full no mi nal tensile capacity of the soil nail bars as certified by the manufacturer. 1.2.2.3 Fusion-Bonded Epoxy Coating Fusion-bonded epoxy coating shall meet the require me nts of ASTM A 775 and have a mi nimu m th ickness of 0.4 mm (0.016 in.) as applied electrostatically. Bend test require ments are waived. C1.2.2.3 The coating at the wall anchorage end of epoxy-coated soil nail bars may be om itted over this length provided for threading the nut against the bearing plate. 1.2.2.4 Encapsulation Bar encapsulation shall be a mi ni mu m 1-mm (0.04-in.) thick, corrugated, HDPE tube conforming to AASHTO M 252, or corrugated PVC tube conforming to ASTM D 1784, Class 13464-B. 1.2.3 Soil Nail Appurtenances 1.2.3.1 Centralizer Centralizers shall be ma nufactured from Schedule 40 PVC pipe or tube, steel, or other material not detrimental to the soil nail steel bar. W ood shall not be used. Centralizers shall be securely attached to the soil nail bar and shall be sized to allow: (a) position the soil nail bar within 25 mm (1 in.) of the center of the drill-hole; (b) tr em ie pipe insertion to the bottom of the drill - hole; and (c) grout to freely flow up the drill-hole. 1.2.3.2 Grout Grout shall be a neat ce ment or sand/ce me nt mi xture with a mi ni mu m 3-day co mp ressive strength of 10.5 MPa (1,500 psi) and a mi nimum 28-day co mpressive strength of 21 MPa (3,000 psi), meeting the requirements of AASHTO T 106/ASTM C 109. 1.2.3.3 Fine Aggregate Fine aggregate for grout and/or shotcrete shall meet the require ments of AASHTO M 6/ASTM C 33. 1.2.3.4 Portland Cement Portland cement for grout and/or shotcrete shall me et the require ments of AASHTO M 85/ASTM C 150, Type I, II, III, or V. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-4

B-5 1.2.3.5 Admixtures Admixtures shall me et the require me nts of AASHTO M 194/ASTM C 494. Ad mi xtures shall be compatible with the grout and mi xed in accordance with the manufacturer’s recommendations. C1.2.3.5 Admixtures that control bleed, im prove flowability, reduce water content, and retard set ma y be used in the gr out subject to review and acceptance by the Engineer. Accelerators are not permitted. Expansive ad mi xtures may only be used in grout used for filling sealed encapsulations. 1.2.3.6 Film Protection Polyethylene film for mois ture loss control shall meet the require ments of AASHTO M 171. 1.2.4 Bearing Plates, Nuts, and Head-Stud Shear Connectors 1.2.4.1 Bearing Plates Bearing plates shall meet the requirements of AASHTO M 183/ASTM A 36. C1.2.4.1 For no mi nal resistance of bearing plates refer to Article 5.10.9.7.2 of the AASHTO LRFD Bridge Design Specifications. 1.2.4.2 Nuts Nuts shall meet the require me nts of AASHTO M 291, Grade B, hexagonal, and fitted with beveled washer or spherical seat to provide uniform bearing. 1.2.4.3 Shear Connectors Shear connectors of the soil nail head ma y consist of headed- studs, threaded bolts, etc. C1.2.4.3 See Article 11.3.3.1 of the AASHTO LRFD Bridge Construction Specifications. 1.2.5 Welded-Wire Mesh Welded wire me sh shall me et the requirements of AASH TO M 55/ASTM A 185 or A 497. 1.2.6 Reinforcing Steel Reinforcing steel shall meet the require me nts of AASHTO M 31/ASTM A 615, Grade 420, deformed. 1.2.7 Geocomposite Sheet Drain Geoco mposite sheet drain shall be ma nufactured with a drainage core (e.g., geonet) and a drainage geotextile attached to or encapsulating the core. Drainage core shall be manufactured fro m long-chain synthetic polymers co mp osed of at least 85 percent by mass of polypropylenes, polyester, polyamine, polyvinyl chloride, polyoleofin, or polystyrene and have a mi ni mu m compressive strength of 275 kPa (40 psi) when tested in accordance with ASTM D 1621 Procedure A. The drainage core with the geotextile fully encapsulating the core shall have a mi ni mu m flow rate of 1 liter per second per me ter of width tested in accordance with ASTM D 4716. The test conditions shall be under an applied load of 69 kPa (10 psi) at a gradient of 1.0 after a 100-hour seating period. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

1.2.8 Underdrain and Perforated Pipe 1.2.8.1 Pipe Underdrain and perforated pipe shall m eet the requir em ents of ASTM 1785 Schedule 40 PVC solid and perforated wall; cell classification 12454-B or 12354-C, wall thickness SDR 35, with solvent weld or elasto meric joints. 1.2.8.2 Fittings Fittings for underdrain and perforated pipe shall meet the require ments of ASTM D 3034, Cell classification 12454-B or C, wall thickness SDR 35, with solvent or elastomeric joints. 1.2.9 Temporary Shotcrete All ma terials, me thods, and control procedures for te mp orary shotcrete shall be sub mit ted to the Owner’s Engineer for review and approval. 1.3 CONTRACTOR QUALIFICATIONS The soil-nailing contractor shall meet the following qualification require me nts: 1. Completed at least three permanent soil nail wall projects during the past three years totaling at least 1,000 m 2 (10,000 ft 2 ) of soil nail wall face area and at least 500 permanent soil nails. 2. Provide a Registered Professional Engineer with experience in the construction of permanent soil nai l walls on at least three co mp leted projects over the past three years. 3. Provide on-site supervisors and drill operators with experience installing permanent soil nail walls on at least three projects over the past three years. 4. Sub mi t a brief description of at least three projects, including the owning agency’s name, address, and current phone nu mb er; location of project; project contract value; and scheduled completion date and completion date fo r the project. 1.4 SUBMITTALS 1.4.1 Personnel At least 60 calendar days before starting soil nail work, subm it names of the Engineer, on-site supervisors, and drill operators assigned to the project, and a summary of each individual’s experience. Only those individuals designated as me eting the qualification requirements shall be used for the project. The Contractor cannot substitute any of these individuals without written approval of the Owner or the Owner’s Engineer. The Owner’s Engineer shall approve or reject the Contractor Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-6

B-7 qualifications and staff within 15 working days after receipt of the sub mission. Work shall not be started nor ma terials ordered until the Contractor’s qualifications have been approved by the Owner’s Engineer. The Owner’s Engineer ma y suspend the work if the Contractor substitutes unqualified personnel for approved personnel during construction. If work is suspended due to the substitution of unqualified personnel, the Contractor shall be fully liable for all additional costs resulting fro m the suspension of work, and no adjust ment in contract ti me resulting fro m the suspe nsion of the work shall be allowed. 1.4.2 Surveys The Contractor shall be responsible for providing the necessary survey and alignment control during the excavation for each lift, locating drill-holes and verifying limits of the soil nail wall installation. 1.4.3 Construction Plan At least 30 days before starting soil nail work, the Contractor shall sub mit a Construction Plan to the Owner’s Engineer that includes the following. 1. Project start date and proposed detailed wall construction sequence. 2. Drilling and grouting met hods and equi pm ent, including the drill-hole diam eter proposed to achieve the specified nominal pullout resistance values shown on the Plans and any variation of these along the wall align me nt. 3. Nail grout mi x design, including compressive strength test results (per AASHTO T 106/ASTM C 109) supplied by a qualified independent testing lab verifying the specified mi ni mu m 3-day and 28-day grout compressive strengths. 4. Nail grout placement procedures and equipment. 5. Temporary shotcrete materials and methods. 6. Soil nail testing methods and equip me nt setup. 7. Identification num ber and certified calibration records for each test jack, pressure gauge, dial gauge and load cell to be used. Jack and pressure gauge shall be calibrated as a unit. Calibration records shall include the date tested, the device identification nu mber, and the calibration test results and shall be certified for an accuracy of at least 2 percent of the applied certification loads by a qualified independent testing laboratory within 90 days prior to submittal. 8. Manufacturer Certificates of Compliance for the soil nail ultimate strength, nail bar steel, Portland cement, centralizers, bearing plates, epoxy coating, and encapsulation 9. The Owner’s Engineer shall approve or reject the Contractor’s Construction Plan within 30 working days after the sub mi ssion. Approval of the Construction Plan does not relieve the Contractor of his responsibility for the successful completion of the work. C1.4.3 In a performance type contract, the Contractor must select one of the specialty contractors listed in the docu me nts and shall identify the specialty contractor on his proposal at the bid opening. No substitution will be permitted without written approval of the Owner’s Engineer. S ubstitution after the bid opening will not be grounds for changes in bid prices. Under a performance type contract, the design of soil nail walls shall be based on geotechnical data and project require ments provided by the Owner including but not li mi ted to soil/rock nom inal shear strength parameters, slope and external surcharge loads, seismic design coefficient, type of wall facing, architectural treat me nt, corrosion protection require ments, ease me nts, and rights-of-way. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

At least 45 days before the planned start of the wall excavation, the Contractor shall submit complete design calculations and working drawings to the Owner’s Engineer fo r review and approval. Include all details, dimensions, quantities, ground profiles and cross-sections necessary to construct the wall. The Contractor shall verify the li mi ts of the wall and ground survey data before preparing the dr awings. The working drawings shall be prepared to the (Agency) standards. The Owner’s Engineer will approve or reject the Contractor’s submittals within 30 calendar days after the receipt of the complete submission. The Contractor shall not begin construction or incorporate ma terials into the work until the submittal requirements are satisfied and found acceptable to the Owner’s Engineer. 1.5 STORAGE AND HANDLING Soil nail bars shall be stored and handled in a ma nner to avoid damage or corrosion. Soil nail bars exhibiting abrasions, cuts, welds, weld splatter, corrosion, or pitting shall be replaced. Bars exhibiting da mage to encapsulation or epoxy coating shall be repaired or replaced at no additional cost. Repaired epoxy coating areas shall have a mi nimu m 0.3-mm (0.012-in.) thick coating. 1.6 EX CAVATION The height of exposed unsupported final excavation face cut shall not exceed the vertical nail spacing plus the required reinforcing lap or the short-term stand-up height of the ground, whichever is less. Excavation to the final wall excavation line and shotcrete application shall be completed in the same work shift, unless otherwise approved by the Owner’s Engineer. Excavation of the next-lower lift shall not proceed until soil nail installation, reinforced shotcrete placement, attach me nt of bearing plates and nuts, and nail testing have been co mp leted and accepted in the current lift. Nail grout and shotcrete shall have cured for at least 72 hours or attained at least their specified 3-day co mp ressive strength before excavating the next underlying lift. C1.6 For construction on side hills, a mini mu m 5-m (15-ft) wide working bench is required for adequate drill rig access. Shotcrete application may be delayed up to 24 hours if the contractor can demonstrate that the delay will not adversely affect the excavation face stability. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-8

B-9 1.7 SOIL NAIL INSTALLATION The soil nail length and drill-hole dia me ter necessary to develop the load capacity and to satisfy the acceptance criteria for the design load required shall be provided, but they shall be not less than the lengths or diameters shown in the Plans. Drill-holes for the soil nails shall be drilled at the locations, elevations, orientations, and lengths shown on the Plans. The drilling equipment and me thods shall be selected to be suitable for the ground conditions and in accordance with the accepted installation me thods subm itted by the Contractor. The use of drilling mu d or other fluids to re mo ve cuttings will not be allowed. If caving ground is encountered, cased drilling me thods shall be used to support the sides of the drill-holes. Soil nail bars shall be provided as shown in the Plans. Centralizers shall be provided and sized to position the soil nail bars to within 25 mm (1 in.) of the center of the drill-hole. Centralizers shall be positioned as shown on the Plans so that their maximu m center-to-center spacing does not exceed 2.5 m (8.2 ft) and shall be located to within 0.5 m (1.5 ft) fro m the top and botto m of the drill-hole. C1.7 The use of self-drilling soil nail bars (also known as hollow, self-grouting or pressure-grouted nail bars) are not allowed for permanent construction, unless approved by the Owner. 1.8 GROUTING The drill-hole shall be grouted after installation of the soil nail bar and within 2 hours of completion of drilling. The grout sh all be injected at the lowest point of each drill-hole through a grout tube, casing, hollow-ste m auger, or drill rods. The outlet end of the conduit shall deliver grout below the surface of the grout as the conduit is withdrawn to prevent the creation of voids. The drill-hole shall be filled in one continuous operation. Cold joints in the grout column shall not be allowed except at the top of the test bond length of proof tested production nails. Grout shall be tested in accordance with AASHTO T 106/ASTM C 109 at a frequency of one test per mi x design and a minimu m of one test for every 40 m 3 (52 cy) of grout placed. Grout cube test results shall be provided to the Owner’s Engineer within 24 hours of testing. 1.9 SOIL NAIL TESTING 1.9.1 Tests The Contractor shall perform both verification and proof testing of designated test soil nails. Verification tests on sacrificial test nails shall be conducted at locations shown on the Plans. P roof tests on production nails shall be conducted at locations selected by the Owner’s Engineer. Testing of any nail shall not be performed until the nail grout and shotcrete facing have cured for at least 72 hours or attained at least their specified 3-day co mp ressive strength. 1.9.2 Equipment Testing equipment shall include 2 dial gauges, dial gauge support, jack and pressure gauge, electronic load cell, and a Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

reaction frame. The pressure gauge shall be graduated in 500 kPa (75 psi) increments or less. Nail head mo ve me nt shall be me asured with a mi ni mu m of 2 dial gauges capable of m easuring to 0.025 mm (0.001 in.). 1.10 VERIFICATION TESTING Verification testing shall be conducted prior to installation of production soil nails on sacrificial soil nails to confirm the appropriateness of the Contractor’s drilling and installation me thods, and verify the required nail pullout resistance. 1.10.1 Methods The verification tests must be conducted on nails of the sa me design and constructed with the same construction met hods to be used on production nails for meaningful results. Verification test nails shall have both bonded and unbonded lengths. The nail bar shall not be grouted along the unbonded length. The unbonded length of the test nails shall be at least 1 m (3 ft). The bonded length of the soil nail during verification tests, L B VT , shall be the smaller value of the following range: C1.10.1 At least two verification tests should be conducted in each soil strata in which it is anticipated that nail bond zone will be grouted. Where possible, verification tests should be conducted to failure to establish a maxi mu m resistance with respect to pullout. = max VT B VT B L L ft ) (10 m 3 of greater The maxi mu m length, L B VT ma x , is defined as: PO PO VT T Y t RT ma x VT B r f A C L φ φ × ××× = − where: C RT = reduction coefficient; A t = cross-sectional area of soil nail bar; f Y = nominal yield resistance of soil nail bar; r PO = nominal pullout resistance (per unit length) of soil nail, as specified herein or in Plans; φ T-VT = resistance factor for soil nail in tension in verification tests; and φ PO = resistance factor for soil nail pullout. The ma ximum bonded length shall be preferably based on production nail maxi mu m bar grade. Larger bar sizes shall be provided at no additional cost, if required, to meet the 3-m (10- ft) mi ni mu m te st bonded length require ment . The Design Load during the verification test, DL , shall be calculated based on as-built bonded lengths, as follows: DL = L B VT × r PO ×φ PO The maxi mu m length for verification tests, L B VT ma x , is selected so that the nail load does not exceed 90 percent of factored no minal tensile resistance of the soil nail bar durin g the verification test. Use C RT = 0.9 for 420 and 520 MPa (Grade 60 and 75) bars. If 1,035 MPa (Grade 150) soil nail bars are allowed in the job, use C RT = 0.8. In verifications tests, select φ T-VT = 0.4 or, preferably, 0.33. Select φ PO based on Table 11.5.6-1, “Res istance Factors,” of AAHTO LRFD Bridge Design Specifications. For preliminary values, use φ PO = 0.5. The selection of φ T-V T during verification tests should be consistent with the ma ximu m test load that has been selected for the verification test. The ma ximu m load depends on the selected φ PO and mu st be selected such that the test bars are not overstressed during the test. 1.10.2 Schedule Verification tests shall be conducted by increm entally loading the verification test nails to failure or a ma ximu m test load of C1.10.2 Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-10

B-11 200 percent of the DL in accordance with the following loading schedule. The Contractor shall record soil nail mo vements at each load increment. Verification Test Loading Schedule Load Hold Time 0.05 DL max. (= align me nt load, AL) 1 minute 0.25 DL 10 minutes 0.50 DL 10 minutes 0.75 DL 10 minutes 1.00 DL 10 minutes 1.25 DL 10 minutes 1.50 DL (Creep Test) 60 minutes 1.75 DL 10 minutes 2.00 DL 10 minutes 0.05 DL max. (AL) 1 minute (record permanent set) Load levels beyond 200 percent of DL are optional. Dial gauges shall be set to “zero” after the alignment load has been applied. Following application of the maximu m load (3.0 × DL ), the load shall be reduced to the alignment load (0.05 × DL ma ximum) and the permanent set shall be recorded. Each load increment shall be held for at least 10 minutes. The verification test nail shall be monitored for creep at the 1.50 × DL load increment. Nail movements shall be m easured and recorded during the creep portion of the test in incre men ts of 1, 2, 3, 5, 6, 10, 20, 30, 50, and 60 mi nute(s). The load shall be ma intained during the creep test to within 2 percent of the intended load by use of a load cell. In soils that are susceptible to creep, extended creep tests beyond the tests required by these specifications should be conducted based on PTI (2005) me thods. The align me nt load, AL, should be the mi ni mu m load required to align the testing apparatus and should not exceed 5 percent of the DL. In projects, for which there is no local experience in soil nailing or the degree of uncertainty in the pre-selected no mi nal pullout resistance (per unit length) values is significant, the Owner or the Owner’s Engineer ma y require the Contractor to perform verification tests up to a maxi mu m test load of 300 percent of the DL in the tests. For these situations, the loading shall be performed according to the schedule below: Additional Verification Test Loading Schedule Load Hold Time From AL to 2.00 DL (or Failure) as shown previously 2.50 DL (optional) 10 minutes 3.0 DL (optional) 10 minutes 0.05 DL max. (AL) 1 minute (record permanent set) 1.11 PROOF TESTING Successful proof testing shall be demonstrated on at least 5 percent of production soil nails in each nail row or a mini mu m of one per row. The Owner’s Engineer shall determine the locations and num ber of proof tests prior to nail installation in each row. C1.11 1.11.1 Methods Production proof test nails shall have both bonded and temporary unbonded lengths. The unbonded length of the test nail shall be at least 1 m (3 ft). The bonded length of the soil nail during proof production tests, L B PT , shall be at least 3 m (10 ft) but not longer than a ma xi mu m length, L B PT ma x . Therefore, the following requirements shall be met: = max PT B PT B L L ft ) (10 m 3 of greater C1.11.1 The unbonded length is temporary because this length is grouted after the proof test is completed. The ma xi mu m length for proof tests, L B PT ma x , is selected so that the nail load does not exceed 90 percent of factored nominal tensile resistance of the soil nail bar during the proof test. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

The maxi mu m length L B PT ma x is defined as: PO PO PT T Y t RT max PT B r f A C L φ φ × ××× = − where: C RT = reduction coefficient; A t = cross-sectional area of soil nail bar; f Y = nominal yield resistance of soil nail bar; r PO = nominal pullout resistance (per unit length) of soil nail, as specified herein or in Plans; φ T-PT = resistance factor for soil nail in tension in proof tests; and φ PO = resistance factor for soil nail pullout. The Design Load during the verification test, DL , shall be calculated based on as-built bonded lengths, as follows: DL = L B PT × r PO ×φ PO Use C RT = 0.9 for 420 and 520 MPa (Grade 60 and 75) bars. If 1,035 MPa (Grade 150) soil nail bars are allowed in the job, use C RT = 0.8. In proof tests, select φ T-PT = 0.67. Select φ PO based on Table 11.5.6-1, “Resistance Factors,” of AAHTO LRFD Bridge Design Specifications. For preliminary values, use φ PO = 0.5. The selection of φ T-PT during proof tests should be consistent with the maxim um test load that has been selected for these tests. The ma xi mu m load depends on the selected φ PO a nd mu st be selected such that the test bars are not overstressed during the test. This is usually 1.5 DTL. Avoiding bar overstressing during the test allows using the test bars as production bars after the test. Production proof test nails shorter than 4 m (12 ft) may be constructed with less than the mi ni mu m 3-m (10-ft) bond length. 1.11.2 Schedule Proof tests shall be conducted by incre mentally loading the proof test nail to 150 percent of DL in accordance with the following loading schedule. Soil nail mo vements shall be recorded at each load increment. Proof Test Loading Schedule Load Hold Time 0.05 DL max. ( AL ) Until Move me nt Stabilizes 0.25 DL Until Move me nt Stabilizes 0.50 DL Until Move me nt Stabilizes 0.75 DL Until Move me nt Stabilizes 1.00 DL Until Move me nt Stabilizes 1.25 DL Until Move me nt Stabilizes 1.50 DL (Max. Test Load) Creep Test (see below) Dial gauges shall be set to “zero” after the alignment load has been applied. The creep period shall start as soon as the ma ximu m test load (1.50 × DL ) is applied and the nail mo vement shall be measured and recorded at 1, 2, 3, 5, 6, and 10 mi nute(s). Where the nail mo ve ment between 1 mi nute and 10 mi nutes exceeds 1 mm (0.04 in.), the ma ximu m test load shall be ma intained for an additional 50 mi nutes and nail move me nts shall be recorded at 20, 30, 50, and 60 mi nutes. All load increments shall be ma intained to within 5 percent of the intended load. C1.11.2 The alignment load, AL , should be the mi ni mu m load required to align the testing apparatus and should not exceed 5 percent of the DL. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-12

B-13 1.12 ACCEPTANCE CRITERIA OF TEST SOIL NAILS A test nail shall be considered acceptable when all of the following criteria are met: 1. For verification tests, the total creep mo vement is less than 2 mm (0.08 in.) between the 6- and 60-minute readings, and the creep rate is linear or decreasing throughout the creep test load hold period. 2. For proof tests, the total creep mo vement is less than 1 mm (0.04 in.) during the 10-minute readings or the total creep mo ve me nt is less than 2 mm (0.08 in.) during the 60-minute readings, and the creep rate is linear or decreasing throughout the creep test load hold period. 3. For verification and proof tests, the total measured mo ve ment at the ma ximu m test load exceeds 80 percen t of the theoretical elastic elongation of the unbonde d length of the test nail. 4. A pullout lim it state does not occur at 2.0 × DL under verification testing and 1.5 × DL test load under proof testing. Pullout li mit state is defined at a load level at which the test load cannot be further increased while there is continued pullout movement of the test nail. The load at the pullout limit state shall be recorded as part of the test data. 5. Maintaining stability of the temporary unbonded test length for subsequent grouting is the Contractor’s responsibility. If the unbonded test length of productio n proof test nails cannot be satisfactorily grouted after testing; the proof test nail shall beco me sacrificial and shall be replaced with an additional production nail installed at no additional cost to the Owner. 1.13 REJECTION OF TEST SOIL NAILS 1.13.1 Verification Test Soil Nails The Owner’s Engineer will evaluate the results of eac h verification test. Installation me thods that do not satisfy the nail testing requirements shall be rejected. The Contractor shall propose alternative meth ods for review by the Owner’s Engineer and shall install replacement verification test nails. Replacement test nails shall be installed and tested at no additional cost. 1.13.2 Proof Test Soil Nails For proof test nails, the Owner’s Engineer ma y require the Contractor to replace so me or all of the installed production nails between a failed proof test soil nail and the adjacent passing proof test nail. Alternatively, the Owner’s Engineer ma y require Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

the installation and testing of additional proof test nails to verify that adjacent previously installed production nails have sufficient nominal pullout resistance. Installation and tes ting of additional proof test nails or installation of additional or mo dified nails as a result of proof test nail failure(s) shall be at no additional cost. 1.14 WALL DRAINAGE NETWORK All ele ments of the soil nail wall drainage network shall be installed and secured as shown on the Plans. The drainage network shall consist of geoco mp osite drain strips, PVC connection pipes, soil nail wall footing drains, and weepholes, as shown on the Plans. Exclusive of the wall footing drains, all elements of the drainage network shall be installed prior to shotcreting. 1.14.1 Geoco mposite Drain Strips Geoco mposite drain strips shall be centered between the colu mns of soil nails, as shown on the Plans. Drain strips shall be at least 300 mm (12 in.) wide and placed with the geotextile side against the ground. Strips shall be secured to the excavation face. C onta mination of the geotextile with shotcrete shall be prevented. Drain strips shall be vertically continuous. Splices shall be made with a 300 mm (12 in.) mi ni mu m overlap such that the flow of water is not impeded. Drain plate and connector pipe shall be installed at the base of each strip. Damage to the geoco mposite drain strip shall be repaired so that water flow is not interrupted. 1.14.2 Footing Drains Footing drains shall be installed at the bottom of the wall, as shown on the Plans. The drainage geotextile shall envelope the footing drain aggregate and pipe and shall conform to the dimensions of the trench. The drainage geotextile shall overlap on top of the drainage aggregate as shown on the Plans. Damaged or defective drainage geotextile shall be repaired or replaced. 1.15 SHOTCRETE FACING Shotcrete facing and permanent shotcrete facing shall be provided as required. Where shotcrete is used to complete the top ungrouted zone of the soil nail drill-hole near the face, the nozzle shall be positioned into the mo uth of the drill-hole to completely fill the void. 1.15.1 Final Face Finish Shotcrete finish shall be either an undisturbed gun finish as applied from the nozzle or a rod, broo m, wood float, rubber float, steel trowel, or rough screeded finish as shown on the Plans. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-14

B-15 1.15.2 Attach ment of Nail Head Bearing Plate and Nut A bearing plate , washers, and nut shall be attached to each nail head as shown on the Plans. While the shotcrete construction facing is still plastic and before its initial set, the plate shall be uniformly seated on the shotcrete by hand-wrench tightening the nut. Where uniform contact between the plate and the shotcrete cannot be provided, the plate shall be set in a bed of grout. After grout has set for 24 hours, hand-wrench tighten the nut. The bearing plates with headed studs shall be located within the tolerances shown on the Plans. 1.15.3 Shotcrete Facing Tolerances Construction tolerances for the shotcrete facing fro m plan location and plan dimensions shall be as follows: Horizontal location of welded wire mesh; reinforcing bars, and headed studs: 10 mm (0.4 in.) Location of headed-studs on bearing plate: 6 mm (1/4 in.) Spacing between reinforcing bars: 25 mm (1 in. ) Reinforcing lap: 25mm (1 in.) Complete thickness of shotcrete: • If troweled or screeded: 15 mm (0.6 in. ) • If left as shot: 30 mm (1.2 in. ) Planeness of finish face surface-gap under 3-m (10-ft) straightedge: • If troweled or screeded: 15 mm (0.6 in. ) • If left as shot: 30 mm (1.2 in. ) Nail head bearing plate deviation fro m parallel to wall face: 10 degrees 1.16 REINFORCING STEEL The Contractor shall su bm it all order lists and reinforcement bending diagra ms to the Owner’s Engineer and shall fabricate reinforcing steel; ship and protect material; and place, fasten, and splice reinforcing steel as required by the Plans. 1.17 STRUCTURAL CONCRETE The Contractor shall design the concrete mi x; store, handle, batch, and mi x ma terial and deliver concrete; provide quality control; and construct concrete facing. 1.18 ARCHITECTURAL SURFACE FINISHES Textured form liners shall be furnished, form liners installed, and a surface finish (color/stain application) applied that will duplicate the architectural surface finish shown on the Plans . Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

The Contractor shall sub mi t detailed drawings of the form liner for approval by the Ow ner’s Engineer at least 7 days before form liner work begins. Before production work begins, a 1-m (3-ft) high by 0.5-m (1.5-ft) wide by 3-m (10-ft) long test panel shall be constructed on site using the same forming me thods, procedures, form liner, texture configuration, expansion joint, concrete mi xture and color/stain application proposed for the production work. 1.19 BACKFILLING BEHIND WALL FACING UPPER CANTILEVER If backfilling is required behind an extension of the wall facing at the top of a soil nail wall, comp action of the soil backfill within 1 m (3 ft) shall be lim ited to light mechanical tampers. Backfill shall be relatively free-draining granular soil m eeting the requirement of Article 7.3.5 (of the AASHTO LRFD Bridge Construction Specifications). 1.20 ACCEPTANCE Material for soil nail retaining walls will be accepted based on the ma nufacturer production certification or from production records. C onstruction of soil nail retaining walls will be accepted based on visual inspection and the examination of relevant production testing records by the Owner’s Engineer. 2.0 MEASUREMENT AND PAYMENT 2.1 SOIL NAILS Production soil nails shall be me asured by the linear me ter (or foot). The length to be paid will be the length measured along the soil nail bar centerline from the back face of shotcrete to the bottom tip end of the nail bar as shown on the Plans. No separate measurement will be ma de for proof test nails, which shall be considered incidental to production nail installation. Verification test nails shall be measured by each test meeting the acceptance criteria of Article 1.10. Failed verification test nails or additional verification test nails installed to verify alternative nail installation me thods proposed by the Contractor will not be measured. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-16

B-17 2.2 STRUCTURE EX CAVATION Structure excavation for the soil nail wall shall be m easured as the theoretical plan volu me in cubic mete rs (cubic feet) within the structure excavation limits shown on the Plans. This will be the excavation volume within the zone me asured fro m top to bottom of shotcrete wall facing and extending out 2 m (6 ft ) horizontally in front of the plan wall final excavation line. Additional excavation beyond the Plan wall final excavation line resulting from irregularities in the cut face, excavation overbreak or inadvertent excavation will not be measured. No me asure ment will be made for using temporary stabilizing berms. General roadway excavation, including hauling, will not be a separate wall pay ite m but will be measured and paid as part of the general roadway excavation. 2.3 WALL FACE The wall face of soil nail walls shall be me asured by the square meter (square foot) of wall face. M easurement will be ma de on the vertical plane of front face accepted in the final work. No me asure me nt or payment will be ma de for additional shotcrete or CIP concrete needed to fill voids created by irregularities in the cut face, excavation overbreak or inadvertent excavation beyond the Plan final wall face excavation line, or failure to construct the facing to the specified line and grade and tolerances. The final pay quantity shall include all structural shotcrete, admixtures, reinforcement, welded wire mesh, wire holding devices, wall drainage mate rials, bearing plates and nuts, test panels and all sa mp ling, testing and reporting required by the Plans and this Specification. The final pay quantity shall be the design quantity increased or decreased by any changes authorized by the Owner’s Engineer. 2.4 PAYMENT The accepted quantities, measured as provided in Articles 2.1, 2.2 and 2.3, will be paid for at the contract unit price per unit of me asure ment for the pay ite ms listed below that are shown on the bid schedule. Pay ment will be full co mp ensation for the work prescribed in this section. Payment will be made under: C2.4 Under a performance type contract, pay me nt ma y be made on a lump-sum basis to include all ma terials, labor and design costs. 2.4.1 Pay Items Pay Ite m Pay Unit Permanent Soil Nails. No. _ Bar (Grade _) Linear meter (or linear foot) Verification Test Nails Each Structure Excavation-Soil Nail Wall Cubic meter (or cubic foot) Soil Nail Wall Square meter (or square foot) Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY

3 CORROSION PROTECTION Soil nails and soil nail head components shall be protecte d against corrosion consistent with the ground and groundwater conditions at the site. The level and extent of corrosion protection shall be a function of the ground environment and the potential consequences of a soil nail failure. C3 Corrosion protection shall be applied in accordance with the provisions of AASHTO LRFD Bridge Construction Specifications, Section 6, “Ground Anchors.” A full discussion on corrosion of meta llic co mp onents and a me thodology that assists in selecting the appropriate level of corrosion protection of soil nail walls is presented in Lazarte et al. (2003). REFERENCES Lazarte, C.A., V. Elias, R.D. Espinoza, and P.J. Sabatini (2003). “Soil Nail Walls,” Geothechnical Engineering Circular No. 7, FHWAO-IF-03-017, Federal Highway Administration, Washington, D.C., 305p. PTI (2005). “Recommendations for Prestressed Rock and Soil Anchors,” 4th ed. Post-Tensioning Institute, Phoenix, Arizona. Section xx – Soil Nail Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY B-18

Next: Appendix C - Soil Nail Test Pullout Resistance Database »
Proposed Specifications for LRFD Soil-Nailing Design and Construction Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB's National Cooperative Highway Research Program (NCHRP) Report 701: Proposed Specifications for LRFD Soil-Nailing Design and Construction contains proposed specifications for the design and construction of soil-nailed retaining structures.

The American Association of State Highway and Transportation Officials (AASHTO) Standard Bridge Specifications, the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications, and the AASHTO LRFD Bridge Construction Specifications do not include guidance for soil-nailed structures.

In the absence of AASHTO LRFD specifications, some state departments of transportation will not use soil-nailed retaining structures. Given the potential advantages of soil-nailed structures, there was a need to develop proposed standard design and construction specifications for soil-nailed structures for incorporation into the AASHTO LRFD Bridge Design and Construction Specifications.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!