830 The value of the pullout resistance factor, F*, used in design calculations shall be obtained from AASHTO LRFD Bridge Design Specifications figure 11.10.6.3.2-2. The minimum embedment at the front face of the wall shall be in accordance with the AASHTO LRFD Bridge Design Specifications, section 11.10.2.2. However, the minimum embedment depth to the top of the leveling pad shall never be less than 3 ft unless founded on rock. A 4 ft horizontal bench in front of the wall shall be provided for slopes steeper than 4.0H:1.0V. The embedment and bench material, at th e front face of the wall, shall match the 100 structural backfill material used for the wall and shall be encased in accordance with
203.09 Geotextiles, Type 2B, in accordance with 918.02(a), shall be installed over the
bench material in accordance with 616. 11. The embedment and bench shall be daylighted at the bottom of the slope with uniform riprap placed at a minimum 12 in. depth for erosion control. An MSE wall shall be designed fo r a service life of 75 years.
a.Geotechnical Considerations The theoretical failure plane within the soil mass shall be analyzed so that the soil- 110 stabilizing component extends sufficiently beyond the failure plane to stabilize the material. External loads which affect the internal stability, such as those applied through piling, bridge footings, traffic, crashwall, or slope surcharge, shall be accounted for in the design. The sizes of all structural elements shall be determined such that the design load stresses do not exceed the factored stresses shown in the AASHTO LRFD Bridge Design Specifications. The material used as backfill in the reinforced backfill zone shall be assumed to have a unit weight of at least 120 lb/cu ft unless lightweight fill has been specified. 7KHijDQJOHIRUWKHLQWHUQDOGHVLJQRIWKHUHLQIRUFHGEDFNILOO VKDOOEH7KHijDQJOH 120 of the retained backfill zone shall be 30° for design. For the external design parameters, such as but not limited to, bearing capac ity, sliding, overturn ing, eccentricity, and global stability, the actual soil strength parameters and the expected settlement of the existing soil under the reinforced backfill zone shall be obtained from the geotechnical report. (b) Height of Wall The wall limits shall be defined by the wall envelope shown on the plans. For internal stability design purposes, the design height, H D, of wall shall be as follows:
1.For a wall with a level surcharge, the design height of the wall, HD, shall be measured from the theoretical top of the leveling pad to the top of the coping or to the gutter line of the traffic barrier. The top of the wall shall be the theoretical top of the face panels only where a coping or barrier is not used. 731.03 831 2. For a wall with a sloping surcharge, the design height of the wall, H D, shall be measured from the theoretical top of the leveling pad to a point above the top of the wall as calculated from the formula as follows: 140 HD = H + 0.3H tanȕ 1-0.3 tanȕ where: ȕ VXUFKDUJHVORSHDQJOHDVPHDVXUHGIURPWKHWRSRIWKH coping, and H = height of the wall from the theoretical top of the leveling pad to the top of the coping.
3.For an abutment face, the design height of the wall, H D, shall be measured from the theoretical top of the leveling pad to the top 150 of the roadway surface.
c.Ground Rei nforcement The ground reinforcement length shall be the controlling length resulting from the internal or external design. The minimum ground reinforcement length for an MSE wall shall be the greater of 0.7H D or 8 ft, where H D is the design height of the wall. The ground reinforcement shall be the same length from the bottom to the top of each wall section regardless of the type of ground reinforcement used. Differing ground reinforcement elements shall be mark ed for ease of construction. This element 160 may be used individually or in a prefabricated grouping. The ground reinforcement for the MSE volume shall be sized using the lesser of the factored loads for each sp ecific connection and each specific reinforcing element. The connection’s applied factored load and effective pullout length shall be determined in accordance wi th the AASHTO LRFD Bridge Design Specifications. For mats, grids, or strip steel, the minimum zinc coating thickness shall be 2 oz/sq ft. Such thickness shall be assumed to be 4 mils for purpose of calculation of reduced structural section. 170 The factored applied bearing pressu res under the stabilized mass for each reinforcement unit’s length shall be shown on the working drawings. It shall not exceed the maximum factored soil bearing resistance shown on the plans. Passive pressure in front of the wall mass shall be assumed to be zero for design purposes. (d) Other Criteria 1. Traffic Load Considerations Traffic load shall be considered as live lo ad surcharge. The load factor of traffic 180 load shall be 1.75 in accordance with AASHTO LRFD Bridge Design Specifications table 3.4.1-1. 731.03
2.Traffic Impact Considerations Where traffic barriers are constructed above an MSE wall or reinforced backfill zone, the MSE wall supporting traffic shall include computations showing that the Extreme Event II limit state due to traffic impact has been met. Loadings for MSE wall design for the Extreme Event II limit state shall be in accordance with the following table: 190 Maximum Nominal Tension Rupture and Pullout Impact Loads Layer Tension Impact Load Pullout Impact Load First Top Layer 2,300 lb/ft 1,300 lb/ft Second Top Layer 600 lb/ft 600 lb/ft The Extreme Event II design for the top two layers shall be separately prepared and compared with the routine internal stability design.
3.Tributary Area – Design Basis For internal stability analysis of MSE walls, each layer of reinforcement is assigned a tributary area, A trib in accordance with FH WA publication No. FHWA- NHI-10-025, Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Volume II and as follows: 200 Atrib = (w p) (S vt) where: w p = the wall system concrete panel width of the precast facing element, and Svt = the vertical tributary spacing of the reinforcement based on the location of the reinforcement above and below the level of the reinforcement under consideration. For a wall system with steel reinforcemen t, within each tributary area, the factored reinforcement tensile resistance, T r, and the factored pullout resistance, P rr, shall be no less than the maximum factored tension load, T max. If the calculated minimum number of strips is a decimal number, the minimum number required shall be rounded up to 210 the next whole number.
731.04 Submittals
The Contractor shall submit working drawings in accordance with 105.02. The Contractor shall submit design calculations in accordance with 105.02 and the following additional requirements. In case of discrepancy, the requirements listed below supersede those listed in 105.02. Design calculations shall include each design case of the MSE wall analyzed. Calculations may be in either longhand or computer-731.04 833 printout format and shall follow a systematic and logical methodology. A summary sheet that shows design assumptions and thei r source, controlling parameters and load 220 cases, and other pertinent input and output information shall be included with the calculations package. Wall construction operations shall not begin until the Contractor receives written notice that the working drawings are approved. (a) The working drawings shall include all details, dimensions, quantities, and cross-sections necessary to construct the wall. They shall include, but shall not be limited to, the following:
1.Plan and elevation views along the front face of wall alignment, which shall include the following: 230
a.A final profile along the front face of the wall.
b.A plan layout of the front face of the wall showing all alignment points with stations and offsets.
2.A plan view of the wall that indicates the offsets from the construction centerline to the face of the wall at all changes in horizontal alignment. A plan view and elevation view which detail the placing position and connection of all ground reinforcement units in areas where piling, utility, or other 240 structures are near the wall.
3.An elevation view along the front face of the wall with respect to the wall alignment, which shall include the following:
a.The elevation at the top of the wall at all horizontal and vertical break points at least every 50 ft along the face of the wall.
b.All steps in the leveling pad.
c.The designation as to the type of wall unit. 250
d.The length of ground reinforcement units. e. A wall-elevation envelope that encompasses such envelope shown on the plans.
4.All general notes required for constructing the wall.
b.Panel details shall show all dimensions necessary to construct the element, all reinforcemen t in the element, and the location of ground reinforcement connection devices embedded in the panels.
c.Details for construction of the wall around drainage facilities including outletting of internal drainage from the MSE volume.
d.Details of the architectural treatment. 731.04
e.Details for diverting ground reinforcement around obstructions such as piles, catch basins, or utilities.
f.Details for the connections between the concrete panel and the ground reinforcement. 270 ( g ) 'HWHUPLQDWLRQRIijDQJOHIRUUHLQ IRUFHGPDWHULDOVDQGUHWDLQHG materials.
h.Detailed differential settlement calculations.
i.Detail standard summary sheet of the input values in the following format: MATERIALS
731.05 Materials Materials shall be in acco rdance with the following:
Admixtures for Concrete ............................................. 912.03 Wall Detail Design Value Design Life Reinforcement Type Configuration (strip or grid) Width, in. Ec (Corroded Thickness), in. Reinforcement Strength (F y), ksi Coverage Ratio (R c) Reinforced Fill Type Unit Weight, pcf Friction Angle, degrees Reinforcement Pullout Resistance F* Į Retained Fill Type Unit Weight, pcf Friction Angle, degrees Foundation Soil Type Unit Weight, pcf Friction Angle or cohesionA, degrees or lb/sq ft A Use onl y one value, whichever is a pplicable. 731.05 835 Air Cooled Blast Furnace Slag .................................... 901.09 Alignment Pins ............................................................ 910.07(d) B Borrow ..................................................................... 211.02 Coarse Aggregate, Class A or Higher, 290 Size No. 8, No. 91................................................. 904.03 Coarse Aggregate, Class F or Higher, Size No. 93PG ...................................................... 904.03 Components of MSE Retaining Wa lls ......................... 901.10 Concrete, Class A or Class C....................................... 702 Deformed and Smooth Steel WWR ............................. 910.01(b)5 Fine Aggregate, Size No. 23 ........................................ 904 Fly Ash ........................................................................ 901.02 Geotextile for Use Under Riprap ................................. 918.02 Ground Reinforcement ................................................ 910.07(b) 300 Joint Spacers and Joint Covering ................................. 901.10(b) Portland Ceme nt .......................................................... 901.01(b) Preformed Expansion Joint Filler ................................ 906.03 Rapid Setting Patch Materials ..................................... 901.07 Reinforci ng Bars .......................................................... 910.01 Steel Components of MSE Retaining Walls ................ 910.07 Structure Backfill, Type 3 ........................................... 211.03.1, 904.05 Underdrains ................................................................. 718 Underdrains for MSE Walls ........................................ 718.03 Water ........................................................................... 913.01 310 Concrete for the leveling pad and coping shall be class A. Concrete used in openings to accommodate appurtenances behind , in front of, under, mounted upon, or passing through the wall shall be class C. The Contractor shall supply all materials listed in 901.10, 910.07, and tie strips, bearing pads, and all necessary incidentals through a manufacturer listed on the QPL of Retaining Wall Systems.
a.Backfill 320
1.Reinforced Backfill Zone Structure backfill Type 3 in accordance with 211 shall be used in the MSE wall reinforced backfill zone and the horizontal bench in front of the wall. Structure backfill nominal size aggregates No. 4 and No. 30 shall not be used.
2.Retained Backfill Zone Structure backfill in the retained backfill zone shall be Type 3 or B borrow as shown on the plans. 330
b.Geotextile Requirements in Backfill Zones If the Contractor elects to use a differen t size aggregate in the retained backfill zone from that used in the reinforced back fill zone, geotextiles Type 2B in accordance 731.05 836 with 918.02(a) shall be installed at the interface between the reinforced and retained backfill zones. If the Contractor elects to use the same si ze coarse aggregate in both the reinforced and retained backfill zones, geotextiles Type 2B in accordance with 918.02(a) shall be installed along the interface be tween the retained backfill zone and the adjacent soil. In addition, geotextiles Type 2B in accordance with 918.02(a) shall be installed at all 340 interfaces of coarse aggregate and finer soils when used in the foundation. CONSTRUCTION REQUIREMENTS
731.06 General Requirements The wall manufacturer’s representative shall provide technical instruction,
guidance in pre-construction activities including the pre-construction conference, and on-site technical assistance to the Contractor during construction.
731.07 Foundation Preparation 350
Prior to wall construction, the foundation for the structure shall be graded for a width equal to or exceeding the length of the ground reinforcement or as shown on the plans. The foundation, if not in rock, sha ll then be compacted in accordance with 203. After the foundation has been compacted, the resulting grade of the foundation shall be 1 in. per foot sloped from the back of the leveling pad downward toward the back of the reinforced zone. The portion of the foundation beneath the leveling pad shall not be sloped. The foundation shall be pr oofrolled in accordance with 203.26. If unsuitable foundation material is encounter ed, it shall be removed and replaced with B borrow in accordance with 211.02 and compacted in accordance with 211.04. After proofrolling has been completed and all unsuitable foundation material has been removed and replaced, compaction of the portion of the foundation beneath the reinforced backfill zone will be verified by dynamic cone penetrometer, DCP, testing in accordance with ITM 509. One DCP measurement for every 500 sq ft within the reinforced backfill zone and five DCP measurements per end bent will be performed. A DCP measurement is defined as the number of blows per 6 in. increment for a total penetration of 30 in., based on five sets of DCP readings at each location. A 370 minimum of five blows of the DCP for each 6 in. increment is c onsidered acceptable. Unsuitable areas shall be removed, re placed, and compacted in accordance with 203 and 211. DCP verification of compaction beneath the reinforced backfill zone will not be required if the foundation is in an embankment section that is constructed in accordance with 203. 731.06 837 An unreinforced concrete leveling pad sh all be provided at each foundation level as shown on the plans. The leveling pad shall be cured in accordance with 702.22 for a minimum of 12 h before placement of concrete face panels. 380
731.08 Retaining Wall Excavation The Contractor shall notify the Engineer a minimum of 7 calendar days or other time as mutually agreed upon before beginning the excavation so that measurements can be taken of the undisturbed ground.
Prior to starting excavation operations at the wall site, the area shall be cleared and grubbed to the excavation with the lim its shown on the plans and in accordance with 201.03. All timber, stumps, or debris shall be disposed of in accordance with
201.03 Excavation shall include the construction and subsequent removal of all 390
necessary bracing, shoring, sheeting, and cr ibbing. Excavation shall also include all pumping, bailing, and draining. The excavation shall be shored or braced in accordance with Stat e and local safety requirements. Excavation and related work shall be performed such that no portion of the wall is endangered by subsequent operations. Where excavation for the wall requires shoring, sheeting, or bracing, the method shall be shown on the working drawings. Excavation operations shall not begin until the Contractor receives notice that the working drawings are approved. 400 After the excavation for the wall has been performed, the Contractor shall notify the Engineer. The material beneath the leve ling pad shall be compacted in accordance with 203. Concrete for the leveling pad sh all not be placed until the Engineer has approved the depth of the excavation and the foundation material. The leveling pad shall be in accordance with 731.07. When an internal drainage system is shown on the plans, the drain pipe shall be 6 in. underdrain pipe in accordance with 715. 02(d). The remainder of the internal drainage system shall be in accordance with 718, longitudinal underdrains. Video 410 inspection will not be required. 731.09 Wall Erection Concrete face panels shall be handled by means of a lifting device set into the upper edge of each panel. Panels shall be placed in successive horizontal lifts in the sequence shown on the plans as backfill placement proceeds. As backfill material is placed behind the panels, the panels shall be maintained in vertical position by means of temporary wooden wedges placed in the joint at the junction of the two adjacent panels on the external side of the wall. External bracing will be required for the initial lift. 420 731.09 838 Panels shall be stored on blocking to minimize contact with the ground or being covered by standing water. Panels placed in contact with the ground or covered by standing water shall have face discoloration removed by means of a chemical wash. Plumb, vertical tolerances, and horizont al alignment tolerances shall not exceed 3/4 in. as measured with a 10 ft straightedge. The maximum allowable offset in panel joints shall be 3/4 in. For a wall of over 10 ft height, the overall plumb from top to bottom of the wall shall not exceed 0.05 in./ft of wall height. For aesthetic considerations and to make differential settlement unnoticeable, the panels shall be erected such that the horizontal site line is discontinuous at every other panel. This shall be accomplished by starti ng erection with the lower panel level of each wall by alternating full-height and half -height panels. Panels above the lowest level shall be of a uniform size, except as required to top out the wall, to be in accordance with the plan elevations. The Contractor shall perform the necessary work to verify that the foundation is at the correct elevation, that the wall is constructed to the correct alignment, and that the work is in accordance w ith the specified tolerances. The checking of alignments 440 and tolerances shall include verifying that the plumb of the face panels is in accordance with 731.10 over the entire height of the wall. Alignment shall be checked at each layer of panels after the backfill behind the panels has been compacted, and the results shall be recorded. The connections of the ground reinforcement to the panels shall be in two elevations for full height panels. The connections shall not be more than 30 in. vertically apart. To prevent out-of-plane rotation, full height face panels shall be connected to the ground reinforcement on at least three different points in two different planes. However, a preapproved system utilizing a horizontal stabilizing leg to prevent 450 rotation shall require only ground reinforcement attachments in one plane. Partial size panels shall have three different connection points, but only one plane shall be attached to the ground reinforcement. Panels located at the top of the wall shall not be attached to the coping or traffic barrier. Ground reinforcement shall be placed no rmal to the face of the wall, unless otherwise shown on the plans or as dir ected. Prior to placement of the ground reinforcement, backfill shall be co mpacted in accordance with 731.11.
731.10 Joint Spacers and Joint Covering for Wall Panels 460
Horizontal and vertical joint spacers shall be provided between adjacent face panels to prevent concrete-to-concrete contact and chipping if differential settlement occurs. Panels without an uninterrupted vertical joint shall have a minimum joint thickness of 3/4 in. Joint covering shall be provided and attached to the rear face of the panels. Geotextiles used to cover the joint behind the MSE wall facing panels shall be in accordance with 918.02(a), Type 2B. 731.10 839 731.11 Backfill Placement Backfill placement shall follow erection of each course of panels and ground reinforcement. All sheeting and bracing shall be removed as the backfilling progresses. 470 Backfill shall be placed to avoid damage or disturbance to the wall materials or misalignment of the concrete face panels. All material for backfill shall be subject to approval and shall be free from lumps, wood, or other undesirable material. Wall materials that become damaged or disturbed during backfill placement shall be removed and replaced or corrected as directed. All misalignment or distortion of the concrete face panels due to placement of ba ckfill outside the limits described herein shall be corrected as directed. B borrow shall be compacted in accordan ce with 203.23 or 203.24. For structure backfill Type 3, compaction shall consist of five passes with a vibratory roller and one 480 pass with the same roller in static mode. Compaction equipment shall be in accordance with 409.03(d). All displacemen t or rutting of the aggregate shall be repaired prior to placing subsequent material. The maximum loose lift thickness shall not exceed 9 in. Howeve r, lifts within 3 ft of the wall shall not exceed 5 in. in loose thickness. This lift thickness shall be decreased, if necessary, to ob tain the specified density. Compaction within 3 ft of the back f ace of the concrete face panels shall be achieved by means of a minimum of five passes with a lightweight mechanical tamper, 490 roller, or an alternative vibratory system. At the end of each day's operation, the last level of backfill shall be sloped away from the wall units. Surface runoff from adjacent areas shall not enter the wall construction site. Subsurface drainage for the pavement s ection shall be underdrains for MSE walls and shall be as shown on the plans. Cutting or altering of ground reinforcement in the field shall not be performed 500 unless one of the alternatives in Article 11.10.10.4 of the AASHTO LRFD Bridge Design Specifications is followed and a compensating adjustment is made in the wall design. All adjustments shall be shown on revised working drawings, signed by, and shall bear the seal of a professional engineer, and submitted to the Engineer for approval. Cutting shall be considered only if adequate additional ground reinforcement is provided to produce the required strength shown in the approved calculations. If the ground reinforcement is shortened in the field, the cut ends shall be covered with a galvanized paint or coal tar to prevent corrosion of the metal.
731.12 Method of Measurement 510
The measurement of concrete face panels and wall erection will be based on the square foot of area contained within the neat line limits of the wall envelope shown on the plans and not that of the wall system supplier. 731.12 Concrete leveling pad will be measured by the linear foot. Common excavation will be measured by the cubic yard in accordance with 203.27(a) to the neat lines shown on the plans. Structure backfill and B borrow will be measured in accordance with 211.09. Unsuitable foundation materials, if found, will be measured in accordance with 211.09. Geotextile used in conjunction with MSE wall construction will not be measured for payment. Underdrains for MSE walls and components of the 520 internal drainage system will be measured in accordance with 718.09. If unsuitable foundation material is encountered in the portion of the foundation beneath the leveling pad in a section constructed on original ground or in a cut section, the removal, replacement, and compaction of the new material will be measured in accordance with 203 and 211. Precast or cast-in-place concrete coping will not be measured.
731.13 Basis of Payment The accepted quantities of concrete face panels will be paid for at the contract unit 530
price per square foot. Wall erection will be paid for at the contract unit price per square foot. Concrete leveling pad, complete and in place, will be paid for at the contract unit price per linear foot for leveling pad. Common excavation will be paid for in accordance with 203.28. Structure backfill and B borrow will be paid for in accordance with 211.10, except that structure backfill used in the retained backfill zone will be paid for as B borrow. Unsuitable foundation materials, if found, will be paid for in accordance with 211.10. Underdrains for MSE walls and components of an internal drainage system will be paid for in accordance with 718.10. Payment will be made under: 540 Pay Item Pay Unit Symbol Face Panels, Concrete ................................................................ SFT Leveling Pad, Concrete ............................................................. LFT Wall Erection ............................................................................. SFT The cost of designing the wall system, services including the testing laboratory, certified testing personnel, and the testing and inspection of the concrete panels shall be included in the cost of face panels, concrete. 550 The cost of all wall materials including concrete face panels, ground reinforcement, tie strips, fasteners, joint materials, joint covering, precast or cast-in-place concrete coping, repair or replacemen t of face panels damaged or removed due to backfill placement, and incidentals shall be included in the cost of face panels, concrete. 731.13 841 The cost of all labor and materials required to prepare the wall foundation, place the ground reinforcement, and erect the concre te face panels shall be included in the cost of wall erection. 560 If unsuitable foundation material is encountered in the portion of the foundation beneath the reinforced backfill zone in a section constructed on original ground or in a cut section, the cost of removal, replacement, and compaction of new material will be paid for in accordance with 203 and 211. If unsuitable foundation material is encountered in the portion of the foundation beneath the reinforced backfill zone that is constructed on an embankment section that is constructed under the same contract, the cost of removal, replacement, and compaction of new material will not be considered for payment. 570 The cost for geotextile used in MSE wall construction shall be included in the cost of the pay items in this section. The cost of refilling and refinishing of the core holes from verification coring shall be included in the cost of face panels, concrete. The cost of performing the laboratory tests by a qualified geotechnical consultant for structure backfill or ACBF slag shall be included in the cost of the pay items in this section. 580 The cost of cutting, altering, or recoating the ground reinforcement at the site shall be included in the cost of wall erection.
Source: Indiana Standard Specifications, 2024 Edition. Pages 73–85 of 1,248.