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A-1 APPENDIX A Proposed LRFD Design Specifications for Soil Nail Walls Revisions to SECTION 11 AASHTO LRFD Bridge Design Specifications TABLE OF CONTENTS 11.1 SCOPE ..................................................................................................................... ................. A-2 11.2 DEFINITIONS ............................................................................................................... ........... A-2 11.3 NOTATION .............................................................................................................................. A-2 11.3.1 General ................................................................................................................ ............ A-2 11.5 LIMIT AND RESISTANCE FACTORS .................................................................................. A-5 11.5.2 Service Limit States ................................................................................................... ..... A-5 11.5.4 Resistance Requirement ................................................................................................. . A-5 11.5.6 Resistance Factors ..................................................................................................... ...... A-5 11.12 SOIL NAIL WALLS ................................................................................................................. A-7 11.12.1 General Considerations ................................................................................................. .. A-7 11.12.2 Loading ................................................................................................................ ........... A-8 11.12.3 Movement and Stability at the Service Limit State......................................................... A-8 11.12.3.1 Abutments ............................................................................................................ A-8 11.12.3.2 Displacements ...................................................................................................... A-9 11.12.3.3 Overall Stability ................................................................................................. A-11 11.12.3.4 Seismic Effects on Global Stability .................................................................... A-11 11.12.4 Stability at Strength Limit States: Safety Against Soil Failure ..................................... A-12 11.12.4.1 Sliding .............................................................................................................. .. A-12 11.12.4.2 Basal Heave ........................................................................................................ A-13 11.12.5 Stability at Strength Limit States: Safety Against Structural Failure ............................ A-13 11.12.5.1 General .............................................................................................................. . A-13 11.12.5.2 Nail Pullout Resistance ...................................................................................... A-13 11.12.5.3 Nominal Bond Resistance .................................................................................. A-14 11.12.5.4 Limit State for Soil Nail in Tension ................................................................... A-16 11.12.6 Strength Limit States: Limit States for the Facing of Soil Nail Walls .......................... A-16 11.12.6.1 General .............................................................................................................. . A-16 11.12.6.2 Flexural Limit State ............................................................................................ A-17 11.12.6.3 Punching-Shear Resistance in Facing................................................................. A-20 11.12.6.4 Headed-Stud in Tension ..................................................................................... A-23 11.12.7 Drainage ............................................................................................................... ......... A-24 11.12.8 Corrosion Protection ................................................................................................... .. A-24 REFERENCES ..................................................................................................................... .................... A-25

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A-2 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY C11.1 11.1 SCOPE This section provides requirements for design of abutments and walls. Conventional retaining walls, non- gravity cantilevered walls, anchored walls, mechanically stabilized earth (MSE) walls, prefabricated modular walls, and soil nail walls are considered. 11.2 DEFINITIONS Soil Nail Walls – A soil-retaining system that derives lateral resistance from a regular pattern of soil nails. Soil nails are sub-horizontal closely spaced steel bars (spacing in each direction of approximately 5 FT or with a tributary area of generally no more than 36 sq FT), that are most commonly installed in a predrilled hole and subsequently encased in grout. Other installation methods, including self-drilling nails, exist. Soil nails are most commonly installed as passive elements whereby no post-tensioning is applied. Soil nails are connected with a facing, which is a structurally continuous reinforced shotcrete or concrete layer covering the soil nails. 11.3 NOTATION 11.3.1 General AE = Effective cross-sectional area of threaded anchors (or bolts) (C11.12.6) Cross-sectional area of the connector head (IN2) (11.12.6) AH = ahm = Cross-sectional area (per unit width) of mesh reinforcement in the wall facing, in the horizontal direction, at midspan between soil nails (IN2/FT) (11.12.6) ahn = Cross-sectional area (per unit width) of mesh reinforcement in the wall facing, in the horizontal direction, at soil nail heads (IN2/FT) (11.12.6) AHH = Total cross-sectional area of additional reinforcement (i.e., waler bars) in wall facing, in the horizontal direction and around soil nail heads (IN 2) (C11.12.6) AS = Cross-sectional area of headed-stud shaft (IN2) (11.12.6) Nail bar cross-sectional area (IN2) (11.12.5) At = AVH = Total cross-sectional area of additional reinforcement (rebar) in wall facing, in the vertical direction and around soil nail heads (IN 2) (C11.12.6) avm = Cross-sectional area (per unit width) of mesh reinforcement in the wall facing, in the vertical direction, at soil nail heads (IN2/FT) (11.12.6) avn = Cross-sectional area (per unit width) of mesh reinforcement in the wall facing, in the vertical direction, at soil nail heads (IN2/FT) (11.12.6) C = Coefficient used for the estimation of the soil nail wall displacement (FT) (11.12.3)

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A-3 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY CF = Factor that considers non-uniform soil pressures behind a soil nail wall facing and is used in the estimation of nominal resistances at the soil nail head (DIM) (11.12.6) CP = Factor that accounts for soil contribution to support and is used in the estimation of nominal resistances at the soil nail head (DIM) (11.12.6) DC = Effective, equivalent diameter of the potential slip conical failure in the facing around soil nail heads (FT) (11.12.6) DDEF = Horizontal distance behind soil nail wall where ground deformation can be significant (FT) (11.12.3) DDH = Average diameter of soil nail drill-hole (IN) (11.12.5) DE = Effective diameter of the core of a threaded anchor (IN) (C11.12.6) DH = Diameter of the head of a soil nail head connector (i.e., headed-stud) (IN) (11.12.6) DS = Diameter of the shaft of a soil nail head connector (i.e., headed-stud) (IN) (11.12.6) fc = Concrete compressive nominal resistance (PSI) (11.12.6) fy = Yield tensile nominal resistance of soil nail bar (KSI) (11.12.5) fy-f = Yield tensile nominal resistance of reinforcement in facing (KSI) (11.12.6) fy-hs = Yield tensile nominal resistance of headed-stud in facing (KSI) (11.12.5) h = Thickness of facing (IN) (11.12.6) H = Wall height (FT) (11.12.3) hC = Effective depth of potential conical slip surface forming in facing around soil nail head (FT) (11.12.6) hf = Thickness of permanent facing (IN) (11.12.6) ht = Thickness of temporary facing (IN) (11.12.6) KA = Active earth pressure coefficient of soils behind soil nail wall (DIM) (C11.12.6) L = Soil nail length (FT) (11.12.6) LBP = Bearing plate side dimension (FT) (11.12.6) LP = Pullout length extending behind slip surface (FT) (11.12.5) LS = Length of headed-stud (FT) (11.12.6) mhm = Horizontal flexural resistance (moment per unit length) mid-span between soil nails (KIP-IN/FT) (11.12.6) mhn = Horizontal flexural resistance (moment per unit length) at soil nail head (KIP-IN/FT) (11.12.6) mvm = Vertical flexural resistance (moment per unit length) mid-span between soil nails (KIP-IN/FT) (11.12.6) mvn = Vertical flexural resistance (moment per unit length) at soil nail head (KIP-IN/FT) (11.12.6) NH = Number of headed-studs in soil nail head connection (DIM) (11.12.6) nt = Number of threads per unit length in threaded anchor (i.e., bolt) (IN) (C11.12.6) qU = Nominal bond resistance of soil nails (KSI) (11.12.5) RFF = Nominal resistance for flexure in facing (KIP) (11.12.6) RFH = Nominal resistance for tension of headed-studs located in facing (KIP) (11.12.6) RFP = Nominal resistance for punching-shear in facing (KIP) (11.12.6) RPO = Nominal pullout resistance of soil nails (KIP) (11.12.5) rPO = Nominal pullout resistance per unit length of soil nails (KIP/FT) (11.12.5) RT = Nominal resistance of a soil nail bar in tension (KIP) (11.12.5) SH = Horizontal spacing of soil nails (FT) (C11.12.6; 11.12.6) SHS = Spacing of headed-studs (FT) (11.12.6) Smax = Maximum spacing of soil nails (FT) (C11.12.6) SV = Vertical spacing of soil nails (FT) (C11.12.6; 11.12.6) tH = Head thickness of headed-studs (FT) (11.12.6)

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A-4 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY Tmax = Maximum load in a soil nail (KIP) (11.12.6, 11.12.6) To = Maximum load in the head of a soil nail (KIP) (11.12.6) tP = Thickness of bearing plate (FT) (11.12.6) VF = Punching-shear force acting through facing, around soil nail head (KIP) (11.12.6) α = Angle of batter of soil nail wall (DEG) (11.12.3) = Backslope angle (DEG) (11.12.1) δh = Horizontal displacement at the top of a soil nail wall (FT) (11.12.3) δv = Vertical displacement at the top of a soil nail wall (FT) (11.12.3) φFF = Resistance factor for flexure in facing (DIM) (11.12.6) φFH = Resistance factor for facing headed-stud in tension (DIM) (11.12.6) φFP = Resistance factor for punching-shear in facing (DIM) (11.12.6) φPO = Resistance factor for nail pullout (DIM) (11.12.5) φT = Resistance factor for nail bar in tension (DIM) (11.12.5) γs = Unit weight of soil (KCF) (C11.12.6) ρij = Reinforcement ratio in “i” direction (vertical or horizontal) and location “j” (at nail head “n,” or midspan “m” in-between soil nails) (PERCENT) (C11.12.6) ρmax = Maximum reinforcement ratio in facing (PERCENT) (11.12.6) ρmin = Minimum reinforcement ratio in facing (PERCENT) (11.12.6)

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A-5 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY 11.5 LIMIT AND RESISTANCE FACTORS 11.5.2 Service Limit States C11.5.2 In general, soil nail walls with concrete/shotcrete Deflections of soil nail walls shall be limited to the facing or with precast panels are more rigid than MSE ranges presented in Section 11.12.4. walls with welded wire or geosynthetic facing. 11.5.4 Resistance Requirement C11.5.4 Abutments …… 11.10, 11.11, or 11.12 11.10, 11.11, and 11.12….., and soil nail walls, respectively 11.5.6 Resistance Factors C11.5.6 The limit states shall be as specified in Article 1.3.2. Wall-specific provisions are contained in this article. Walls shall be proportioned so that the factored resistance is not less than the effects of the factored loads specified in Section 3.

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A-6 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY Table 11.5.6-1 Resistance Factors Limit Resistance Resistance Condition Value State Factor φτ Sliding All 0.90 Soil Failure φb Basal Heave 0.70 ALL φs 0.75 (1) Slope does not support a structure Overall φs 0.65 (2) (3) NA Slope supports a structure Stability φs 0.90 (4) Seismic Mild steel bars – Grades 60 and φT 0.56 75 (ASTM A 615) Static High-resistance – Grade 150 φT 0.50 (ASTM A 722) Nail in Tension Mild steel bars – Grades 60 and φT 0.74 75 (ASTM A 615) Seismic High-resistance – Grade 150 φT 0.67 (ASTM A 722) Temporary and final facing φFF Facing Flexure 0.67 reinforced shotcrete or concrete Structural Temporary and final facing φFP Facing Punching-Shear 0.67 reinforced shotcrete or concrete φFH A307 Steel Bolt (ASTM A 307) 0.50 Facing Headed-Stud Tensile φFH A325 Steel Bolt (ASTM A 325) 0.59 φPO 0.47 (5) Sand φPO 0.51 (5) Clay Pullout Soil/Rock Type φPO 0.45 (5) Weathered Rock φPO 0.49 (5) All Notes: (1) Also when geotechnical parameters are well-defined. (2) Also when geotechnical parameters are based on limited information. For temporary SNWs, use φs = 0.75. (3) Per current practice but subject to modifications. A value φs = 1.00 may be acceptable, as long as (4) permanent deformations are calculated (see Anderson et al., 2008) and are found not to be excessive. Currently, there is no differentiation for temporary structures under seismic loading; therefore, use φs = 1.00. (5) From reliability-based calibration. Values shown correspond to a load factor γ = 1.00.

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A-7 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY 11.12 SOIL NAIL WALLS 11.12.1 General Considerations C11.12.1 Soil nail walls most commonly consist of: (a) a soil Soil nail walls are top-down construction structures nail (i.e., steel bar) that is placed in a pre-drilled hole, that are particularly well suited for ground conditions that require vertical or near-vertical cuts. Favorable then grouted along its entire length in the hole; (b) ground conditions make soil nailing technically feasible connectors in the soil nail head; and (c) a structurally and cost effective, compared with other techniques, continuous reinforced concrete or shotcrete cover when: (facing) connecting all nail heads. Figure 11.2.1-1a • the soil in which the excavation is advanced is shows a cross-section of a typical soil nail wall and main components. able to stand unsupported in vertical or nearly vertical, 3- to 6-FT high cuts for one to two days; Horizontal nail spacing, SH, is typically the same as • all soil nails are above the groundwater table; and vertical nail spacing, SV, and can be between 4 and 6.5 • the long-term integrity of the soil nails can be FT, and most commonly 5 FT. Soil nail spacing may be maintained through corrosion protection. modified to accommodate the presence of existing underground structures or utilities behind the wall. Subsurface conditions that are generally well suited for soil nails applications include stiff to hard fine- Soil nail spacing in horizontal and vertical direction grained soils, dense to very dense granular soils with must be such that each nail has an influence area SH × some cohesion (apparent cohesion due to cementation), Sv 40 FT2. weathered rock without weakness planes, and other competent soils with a wide gradation (i.e., glacial tills). Examples of unfavorable soil types and ground conditions include dry, loose, poorly graded cohesionless soil, soils with high groundwater, soils with cobbles and boulders, soft to very soft fine-grained soils, organic soil, highly corrosive soil (e.g., cinder, slag), weathered rock with weakness planes, karstic ground, loess, and soils that generally have a liquidity index 0.2. Corrosion protection is provided by grouting, epoxy coating, galvanized coating, or encapsulation [not shown in Figure 11.12.1-1(a)]. See Section 11.12.8 “Corrosion Protection” for references to consider corrosion protection in the design.

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A-9 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY 11.12.3.2 Displacements C11.12.3.2 The considerations of Article 11.6.2.2 shall be In addition to the considerations of article 11.6.2.2, considered. the effects of the movement of a soil nail wall on adjacent structures shall be considered in the design. A soil nail wall shall be designed so as the Empirical data indicate that for soil nail walls with: movements of the wall remain within tolerable ranges. (a) nail-length ratios, L/H, between 0.7 and 1.0; (b) negligible surcharge loads; and (c) adequate safety margins achieved for overall stability, the maximum long-term horizontal and vertical displacements at the top of the wall, δh and δv, respectively, can be estimated as follows (Byrne et al., 1998): = ×H (C11.12.3-1) h h H ≈ (C11.12.3-2) v h where: (δh/H) = ratio presented in Table 11.12.3.2-1 (DIM) H = wall height (FT) Ground deformation considered to be of significance can occur within a horizontal distance, DDEF, which can be estimated as follows: D DEF = C (1 − tan ) (C11.12.3-3) H where: α = batter angle of wall (DEG) C = coefficient presented in Table 11.12.3.2-1 (DIM) For soil nail walls resisting relatively large loads (e.g., walls being part of bridges abutments), more advanced methods (e.g., finite element method) may be required to produce a more precise estimation of the wall deformation.

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A-11 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY 11.12.3.3 Overall Stability C11.12.3.3 The provisions of Article 11.6.2.3 shall apply. Overall stability of soil nail walls is commonly evaluated using two-dimensional limit-equilibrium- The evaluation of overall stability of soil nail based methods, in which the contribution of nails is walls shall be performed using acceptable methods accounted for in equilibrium equations. that consider all reinforcement elements of a soil nail and loads. Stability analyses of soil nail walls are commonly performed using computer programs specifically Global stability analyses may be necessary for developed for the design of soil nail walls. Other intermediate excavation conditions. computer programs developed for general slope stability analysis can also be used, if various The potential slip surfaces to be considered in reinforcement bars developing pullout resistance can overall stability may or may not intersect soil nails be considered by the software. (Figure 11.12.3.3-1). For the case of slip surfaces intersecting soil nails, the nominal resistance of soil nails shall be adequately considered in analy ses. For soil nail walls with complex geometry (e.g., multiple-tiered walls) involving composed failure surfaces, the provisions of Article 11.10.4.3 shall apply. (b) (a) SOIL RESISTANCE SOIL NAIL RESISTANCE RESISTANCE FAILURE FAILURE SURFACE SURFACE Figure 11.12.3.3-1 Limit States in Soil Nail Walls—Overall Stabilit y: (a) Slip Surface not Intersecting Nails; (b) Slip Surface Intersecting Nails In general, the vertical seismic coefficient is 11.12.3.4 Seismic Effects on Global Stability disregarded in global stability analysis. The pseudo-static method shall be routinely used For flexible structures such as soil nail walls, it is for the seismic stability analysis of soil nail walls. reasonable to use horizontal seismic coefficients that are The provisions of Article 11.6.5 shall apply to a function of the expected seismically induced wall consider the effect of seismic loads on the global displacement. The following expressions can be used to stability of soil nail walls. estimate the horizontal seismic coefficient as a function of the tolerable seismically induced wall lateral movement, d, in inches before any wall/sliding block takes place (Kavazanjian et al., 1997; Elias et al., 2001): 0.25 Am k h = 0.74 A m (C11.12.3.4-1) d where: kh = horizontal seismic coefficient (DIM)

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A-15 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY Table 11.12.5.3-1 Presumptive Nominal Bond Resistance for Soil Nails in Soil and Rock Nominal Bond Soil Nail Installion Soil/Rock Type Nominal Resistance, Material Method qu (psi) Marl/limestone 45 - 58 Phyllite 15 - 45 Chalk 75 - 90 Dolomite (soft) 60 - 90 Dolomite (fissured) 90 - 145 Rock Rotary Drilling Sandstone (weathered) 30 - 45 Shale (weathered) 15 - 22 Schist (weathered) 15 - 25 Basalt 75 - 90 Slate/hard shale 45 - 60 Sand/gravel 15 - 26 Silty sand 15 - 22 Rotary Drilling Silt 9 - 11 Piedmont residual 6 - 17 Fine Colluvium 11 - 22 Sand/gravel low overburden 28 - 35 Cohesionless Soils Driven Casing high overburden 40 - 62 Dense Moraine 55 - 70 Colluvium 15 - 26 Silty sand fill 3 -6 Auger Silty fine sand 8 - 13 Silty clayey sand 9 - 20 Rotary Drilling Silty clay 5 - 7 Driven Casing Clayey silt 13 - 20 Loess 4 - 11 Fine-Grained Soils Soft clay 3 -4 Auger Stiff clay 6 -9 Stiff clayey silt 6 - 15 Calcareous sandy clay 13 - 20 Modified after Elias and Juran (1991).

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A-16 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY 11.12.5.4 Limit State for Soil Nail in Tension C11.12.5.4 The limit state for a soil nail in tension shall be The contribution of the grout to the nominal resistance in tension shall be disregarded. verified as follows: φT RT ≥ Tmax (11.12.5.4-1) where: φT = resistance factor for soil nail in tension (DIM) RT = nominal tensile resistance of a soil nail (KIP) Tmax is estimated from global stability analyses Tmax = maximum load in soil nail (KIP) performed with computer programs. The nominal tensile resistance of a soil nail shall be computed as: RT = At f y (11.12.5.4-2) where: = cross-sectional area of a soil nail bar (IN2) At fy = nominal yield resistance of soil nail bar (KSI) 11.12.6 Strength Limit States: Limit States for the Facing of Soil Nail Walls 11.12.6.1 General C11.12.6.1 The limit states of the facing of a soil nail wall that The limit states for flexure and punching-shear in shall be considered include: (a) flexure; (b) punching- the facing shall be considered separately for the shear; and (c) headed-stud in tension. These limit states temporary and the permanent facing. The limit state for are shown schematically in Figure 11.12.6.1-1(a) and tension in the headed-stud shall be considered only in (c). permanent facings.

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A-18 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY where: φFF = resistance factor for flexure in the facing (DIM) RFF = nominal tensile resistance for flexure in the facing (KIP) To = maximum tensile load at soil nail head (at The nail head tensile force may be estimated based on the equations below (Clouterre, 1991) that were facing) (KIP) developed for working conditions: RFF can be estimated using the following expression: T = Tmax [0.6 + 0.057 (S max − 3)] ≤ Tmax (C11.12.6.2-1) [ksi ] [ kip ] o = 3.8 × C ×f × R F y FF where: (a vn + a vm ) S in 2 /ft H h[ft] × Tmax = maximum nail load (KIP) S V Smax = maximum soil nail spacing (i.e., greater of SV greater of and SH) (FT) (a hn + a hn ) S in 2 /ft V h[ft] × S The maximum nail load under working conditions H typically varies from To = 0.60 KA γ H SV SH to 0.70 KA γs H SV SH (Byrne et al., 1998), where KA is the active (11.12.6.2-2) earth pressure coefficient, γs is the unit weight of the where: soil behind the wall, H is the wall height, and SV and SH are the nail vertical and horizontal spacing, CF = f actor that considers non-uniform soil respectively. pressures behind a soil nail wall facing and is used in the estimation of nominal resistances at The nominal resistance for flexure in the facing the soil nail head (DIM) depends on the soil pressures mobilized behind the h = thickness of facing (IN) that can take the values facing, horizontal and vertical soil nail spacing, soil ht or hf. conditions, and facing stiffness. To account for non- uniform soil pressure distributions and other conditions, avn = Cross-sectional area (per unit width) of mesh CF is used (Byrne et al., 1998). reinforcement in the wall facing, in the vertical direction, at soil nail heads (IN2/FT) Table C11.12.6.2-1 presents values of CF for typical avm = Cross-sectional area (per unit width) of mesh facing thickness. For all permanent facings and “thick” reinforcement in the wall facing, in the vertical (i.e., ht 8 IN) temporary facings, the soil pressure is direction, at soil nail heads (IN2/FT) assumed to be relatively uniform. ahn = Cross-sectional area (per unit width) of mesh Reinforcement can be welded wire mesh (WWM) reinforcement in the wall facing, in the horizontal direction, at soil nail heads (IN2/FT) or concrete reinforcement bars. ahm = Cross-sectional area (per unit width) of mesh If (vertical) bars are used behind the nail heads, the reinforcement in the wall facing, in the total reinforcement area per unit length in the vertical horizontal direction, at midspan between soil direction can be calculated as: nails (IN2/FT) AVH (C11.12.6.2-1) fy-f = Yield tensile nominal resistance of avn = avm + reinforcement in facing (KSI) SH where: The cross-sectional areas of reinforcement per unit width in the vertical or horizontal direction and around AVH = Total cross-sectional area of additional and in-between nails are shown schematically in Figure reinforcement (rebar) in wall facing, in the

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A-19 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY 11.12.7.2-2. vertical direction and around soil nail heads (IN2) The nomenclature for the reinforcement areas per unit width is presented in Table 11.12.3.2-2: Similar concepts can be applied if additional horizontal rebar (i.e., waler bars) is used in this direction. The total reinforcement area per unit length in the horizontal direction can then be calculated as: (C11.12.6.2-2) AHH ahn = ahm + SV AHH = Total cross-sectional area of additional reinforcement (i.e., waler bars) in wall facing, in the horizontal direction and around soil nail heads (IN 2) Table 11.12.6.2-1 Factor CF Nominal Facing Thickness, ht or hf Type of Wall Factor CF (IN) 4 2.0 Temporary 6 1.5 8 1.0 Permanent All 1.0 Table 11.12.6.2-2 Nomenclature for Facing Reinforcement Area per Unit Width Cross-Sectional Area of Direction Location Reinforcement per Unit Width AVH avn = aVM + Nail head (1) SH Vertical Mid-span a vm AHH ahn = ahm + Nail head (2) SV Horizontal Mid-span ahm Notes: (1) At the nail head, the total cross-sectional area (per unit length) of reinforcement is the sum of the welded-wire mesh area, avm, and the area of additional vertical bars, AVH, divided by the horizontal spacing, Sh. (2) At the nail head, the total area is the sum of the area of the welded- wire mesh, ahm, and the area of additional horizontal bars (i.e., waler bars, AHH) divided by Sv.

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A-21 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY φ FP RFP ≥ To bearing plate or headed studs and may punch through (11.12.6.3-1) the facing thickness at an inclination of about 45 where: degrees and form two punching limit states (Figure 11.12.6.3-1). φFP = resistance factor for punching-shear in the facing (DIM) The size of the conical slip surface depends on the facing thickness and the type of the nail-facing RFP = nominal resistance for punching-shear in facing connection (i.e., bearing-plate or headed-studs). (KIP) The factored soil nail tensile force from punching- shear failure shall be calculated as: RFP = CPVF (11.12.6.3-2) where: VF = nominal punching-shear resistance acting through the facing section (KIP) Generally, the contribution from the soil support is CP = correction factor that accounts for the ignored and CP = 1.0. If the soil reaction is considered, contribution of the support resistance of the soil CP can assume values up to 1.15. (DIM) These equations shall be separately used for The nominal punching-shear resistance shall be temporary and permanent facing. The maximum and calculated as: average diameters of the slip surface (DC and D’C on VF = 0.58 f c' Dc'hC Figure 11.12.6.3-1), as well as the effective depth of the (11.12.6.3-3) slip surface (hC) shall be selected separately for temporary and permanent facings. where: For temporary facing, only the dimensions of the D’C = effective diameter of conical failure surface at bearing plate and facing thickness shall be considered. the center of section (i.e., an average cylindrical For permanent facings, the dimensions of headed-studs failure surface is considered) (FT) and bearing plate, and the facing thickness shall be considered. hC = effective depth of conical surface (FT), as discussed below.

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A-23 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY The effective diameter of the slip surfaces must be considered as follows: Temporary facing D’ C = LBP + ht hC = ht where: LBP = bearing plate length (FT) ht = temporary facing thickness (FT) Permanent facing D’ C = minimum of (SHS + hC, or 2hC) hC = LS – th + tP where: SHS = headed-stud spacing (FT) LS = headed-stud length (FT) tH = headed-stud head thickness (FT) tP = bearing plate thickness (FT) 11.12.6.4 Headed-Stud in Tension C11.12.6.4 For the limit state of facing headed-stud in tension, To provide sufficient anchorage, the length of the it shall be verified that: headed-studs shall extend beyond the mid-section of the facing, while maintaining 2 IN minimum cover. φFH RFH ≥ To (11.12.6.4-1) When threaded bolts are used in lieu of headed- where: stud connectors, the effective cross-sectional area of the bolts must be employed in the equations above. The φFH effective cross-sectional area, AE, of threaded anchors is = resistance factor for headed-stud in tension computed as follows: (DIM) RFH = nominal tensile resistance of headed-stud 2 0.9743 (KIP) AE = DE − (C11.12.6.4-1) 4 nt RFH is computed as: where: RFH = N H AS f y-hs (11.12.6.4-2) DE = effective diameter of the bolt core nt = number of threads per unit length where: NH = number of headed-studs in the connection (usually 4) (DIM) AS = cross-sectional area of the headed-stud shaft (IN2) fy-hs = yield tensile nominal resistance of headed- stud in facing (KSI)

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A-24 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY In addition, the limit state for compression of the concrete behind the head of the headed-stud shall be established by assuring that the following geometric constraints are met (ACI, 1998): AH ≥ 2.5 AS (11.12.6.4-3) tH ≥ 0.5 (DH – DS) (11.12.6.4-4) where (see Figure 11.12.6.4-1): AH = cross-sectional area of the stud head tH = head thickness DH = diameter of the stud head DS = diameter of the headed-stud shaft DH tH LS DS Figure 11.12.6.4-1 Geometry of a Headed-Stud 11.12.7 Drainage C11.12.7 Drainage Surface water runoff and groundwater shall be Permanent surface and groundwater controls may controlled both during and after construction of the soil consist of a combination of the following features: nail wall. If appropriate performance cannot be permanent surface water controls, geocomposite drain achieved, the effect of the groundwater table shall be strips, shallow drains (weep-holes), toe drain, and drain considered in the analysis. pipes. Geocomposite drain strips are routinely placed in vertical strips against the excavation face along the entire depth of the wall. The lower end of the strips typically discharges into a pipe drain that runs along the base of the wall or through weep holes at the bottom of the wall. 11.12.8 Corrosion Protection C11.12.8 For all permanent soil nail walls and, in some cases, A full discussion on corrosion of metallic for temporary walls, the soil corrosion potential shall be components and a methodology that assists in selecting evaluated and considered part of the design. See the appropriate level of corrosion protection of soil nail Appendix B, Proposed LRFD Construction walls is presented in Lazarte et al. (2003). Specifications for Soil Nail Walls.

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A-25 Section 11 - Abutments, Piers and Walls PROPOSED SPECIFICATIONS PROPOSED COMMENTARY REFERENCES American Concrete Institute (ACI) (1998) “Code Requirements for Nuclear Safety-Related Concrete Structures (ACI 349-97) and commentary,” ACI 349R-97, ACI Committee 349, American Concrete Institute, Farmington Hills, MI, p. 129. Byrne, R.J., Cotton, D., Porterfield, J., Wolschlag, C., and Ueblacker, G. (1998). “Manual for Design and Construction Monitoring of Soil Nail Walls,” FHWA-SA-96-69R, Federal Highway Administration, Washington, D.C. Clouterre (1991). “Recommendations Clouterre 1991” (Trans.: Soil Nailing Recommendations 1991), English Translation, Presses de l’Ecole Nationale des Ponts et Chaussées, Paris, France. Elias, V., Christopher, B.R., and Berg, R. (2001). “Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines,” Federal Highway Administration, FHWA-NHI-00-043, Washington, D.C., 394 pp. Elias, V., and Juran, I. (1991). “Soil Nailing for Stabilization of Highway Slopes and Excavations,” FHWA-RD-89- 198, Federal Highway Administration, Washington, D.C. Kavazanjian, E., Jr., Matasovi , N., Hadj-Hamou, T., and Sabatini, P.J. (1997). “Design Guidance: Geotechnical Earthquake Engineering for Highways, Volume I, Design Principles,” Geotechnical Engineering Circular No. 3, FHWA-SA-97-076, Federal Highway Administration, Washington, D.C. Lazarte, C.A., V. Elias, R.D. Espinoza, and P.J. Sabatini (2003). “Soil Nail Walls,” Geotechnical Engineering Circular No. 7, FHWA0-IF-03-017, Federal Highway Administration, Washington, D.C., 305p.