EB 20-004 Chapter 9: Section 9.4 Retaining Walls and Reinforced

ENGINEERING

BULLETIN EB 20-004

Title: HDM CHAPTER 9: SECTION 9.4 RETAINING WALLS AND REINFORCED SOIL SLOPES Approved:

/s/ Robert L. Sack 1/10/2020 Robert L. Sack, P.E. Date Deputy Chief Engineer (Research) Expires one year after issue unless replaced sooner

ADMINISTRATIVE INFORMATION: • This Engineering Bulletin (EB) is effective upon signature. • This EB does not supersede any other issuance. • Disposition of issued materials: The information transmitted by this issuance will be incorporated into the Highway Design Manual Chapter 9 Soils, Walls, and Foundations.

PURPOSE: The purpose of this EB is to announce the availability of the revision to the Highway Design Manual Chapter 9: Section 9.4 Retaining Walls and Reinforced Soil Slopes.

TECHNICAL INFORMATION: • A revised Geotechnical Engineering Manual (GEM-16) Mechanically Stabilized Earth System Inspection Manual is being issued concurrently via EB 20-003. • A revised Standard Specification Section 554 Fill Type Retaining Walls is being issued concurrently via EI 20-001. • The revisions to Section 9.4 Retaining Walls and Reinforced Soil Slopes includes the following: 1. Section 9.4.2.1 Externally Stabilized Cut Structures C. – added information regarding Braced Walls. 2. Section 9.4.2.3 Internally Stabilized Fill Structures C. – differentiated between a GRSS Slope and a GRSS Wall. 3. Section 9.4.2.3 C.2. GRSS Slopes – included a warning regarding the susceptibility to erosion. 4. Section 9.4.2.3 C.3. Vegetated Face Vertical GRSS – included additional information regarding geocells. 5. Section 9.4.5 Wall Design & Detailing – added a summary of the major design concerns with a cut type retaining wall in A. Cut Type Retaining Walls. 6. Section 9.4.5 Wall Design & Detailing – identified the specific design requirement manual in A1. Sheeting, Soldier Pile & Lagging Wall, or Anchored Walls. 7. Section 9.4.5 Wall Design & Detailing – identified the specific design requirement manual in A2. Soil Nail Walls. 8. Section 9.4.5 Wall Design & Detailing – added a summary of the major design concerns with a fill type retaining wall in B. Fill Type Retaining Walls. 9. Section 9.4.5 Wall Design & Detailing – identified the specific design requirements in B1. Cast-in-place/Precast Cantilever/Gravity Walls. 10. Section 9.4.5 Wall Design & Detailing – identified the specific design requirements in B2. Proprietary Retaining Wall Systems. 11. Section 9.4.5 Wall Design & Detailing – Expanded on the designer’s responsibilities in B2. Proprietary Retaining Wall Systems. 12. Section 9.4.5 Wall Design & Detailing – Added guidance regarding the assumed fill wall volume to address constructability issues in B2b. Fill Type Retaining Wall Volume. EB 20-004 Page 2 of 2

13. Section 9.4.5 Wall Design & Detailing – Added guidance and figures from the FAQ’s regarding jersey barrier installation in B2c. Fill Type Retaining Walls Supporting a Shoulder and Requiring a Jersey Barrier. 14. Section 9.4.5 Wall Design & Detailing – Added guidance and figures from the FAQ’s regarding subsurface installations conflicting with the fill type retaining wall volume in B2d. Addressing Conflicts with the Fill Type Retaining Wall Volume and Surface/Subsurface Installations. 15. Section 9.4.5 Wall Design & Detailing – Added guidance regarding the choices in the Approved List and highway work permits in B2e. The Exception – Highway Work Permits. 16. Section 9.4.5 Wall Design & Detailing – identified the specific design requirement manual in B4. Geosynthetically Reinforced Soil System (GRSS).

TRANSMITTED MATERIALS: Revision to Section 9.4 Retaining Walls and Reinforced Soil Slopes

BACKGROUND: Retaining walls and reinforced soil slopes are used in areas where free-standing (natural) earth slopes are undesirable, usually because of space restrictions. These walls have, in the past, normally been poured, reinforced concrete (gravity or cantilever), timber, steel, or precast concrete cribbing, stone-filled wire-basket gabions, timber or steel sheeting, or steel soldier pile and lagging walls, all of which provide external support to the retained soil mass. Several innovations in types of retaining walls have become available, including using inherent characteristics of retained or reinforced soil as part of the support system.

CONTACT: Questions or comments regarding this issuance should be directed to Randall J. Romer, P.E., of the Geotechnical Engineering Bureau at (518) 457-4714, or via e-mail at [email protected].

SOILS, WALLS, AND FOUNDATIONS 9-75

9.4 RETAINING WALLS AND REINFORCED SOIL SLOPES

Retaining walls and reinforced soil slopes are used in areas where free-standing (natural) earth slopes are undesirable, usually because of space restrictions. These walls have, in the past, normally been poured reinforced concrete (gravity or cantilever), timber, steel, or precast concrete cribbing, stone-filled wire-basket gabions, timber or steel sheeting, or steel soldier pile and lagging walls, all of which provide external support to the retained soil mass. Several innovations in types of retaining walls have become available, including using inherent characteristics of retained or reinforced soil as part of the support system.

Inadequate drainage of the backfill material can result in unsatisfactory long-term performance of the retaining wall system. A subsurface drainage system is typically installed simultaneously with the erection of the wall to ensure a continuous, uninterrupted system to serve to prevent the accumulation of destabilizing water pressure on the wall. Regional Designers should consult with the Regional Geotechnical Engineer during the retaining wall design phase (see Section 9.4.4 Wall Selection Process).

Good, long term performance of any wall is dependent on the use of well-compacted, good quality backfill. It is not possible to adequately compact backfill in below-freezing temperatures, unless special material that does not require water for compaction (i.e. crushed stone) is used.

9.4.1 Definitions

There are three categories of support systems based on their intended functional life: permanent, temporary, and interim. 1. Permanent: A permanent system provides a structural support function for the life of the facility. 2. Temporary: A temporary system is designed to provide structural support during construction, and is removed when construction is complete. 3. Interim: An interim system is identical to a temporary system in function, except it remains in place (although it no longer provides a structural function) because its removal would be detrimental to the finished work.

The classification of retaining wall systems is based on the basic geotechnical mechanism used to resist lateral loads and the construction method used for the installation of the wall. The following are definitions used to classify retaining wall systems: 1. Externally Stabilized Structures: Externally stabilized structures rely on the integrity of wall elements (with or without braces, struts, walers and/or tiebacks or anchors) to both resist lateral loads and also prevent raveling or erosion of the retained soil. 2. Internally Stabilized Structures: Internally stabilized structures rely on friction developed between closely-spaced reinforcing elements and the backfill to resist lateral soil pressure. A separate, non-structural element (facing, erosion control mat and/or vegetation) is attached to prevent raveling or erosion of the reinforced soil. 3. Fill Type Retaining Walls: Retaining structures constructed from the base of the wall to the top (i.e. “bottom-up” construction). 4. Cut Type Retaining Walls: Retaining structures constructed from the top of the wall to the base (i.e. “top-down” construction). An overview of the classification of retaining wall systems is provided in Table 9-6. The table provides a breakdown of available retaining wall systems, its associated method of construction, means of stability, design requirements and constraints (e.g. typical height range, maximum wall height).

1/10/20 §9.4 9-76 SOILS, WALLS, AND FOUNDATIONS

Table 9-6 Classification of Retaining Wall Systems(14m) Wall Wall Wall Construction Wall Design Constraints Class Type Type1 Group Typical Height Range: Designed & detailed Sheeting Walls Cut Wall Cantilever 6 ft. to 15 ft. in contract. Maximum Wall Height= 15 ft. Soldier Pile & Designed & detailed Typical Height Range: Cut Wall Cantilever Lagging Walls in contract. 6 ft. to 15 ft. Externally Deadman Designed & detailed Stabilized Anchors in contract. Cut Anchored or Detailed in contract. Typical Height Range: 15 ft. to Structures Braced Walls Grouted Designed by 65 ft. (Sheeting or Cut Wall Tiebacks Contractor’s Design Soldier Pile & Consultant. Lagging Walls) Designed & detailed Braced Walls in contract. Precast Designed & detailed Typical Height Range: 6 ft. to Primarily Fill Cantilever in contract. 30 ft. Wall. May be Wall Cantilever Wall installed as a CIP Typical Height Range: 6 ft. to Designed & detailed Cut wall. Cantilevered 30 ft. in contract. Wall Maximum Wall Height = 30 ft. Typical Height Range: 6 ft. to Designed & detailed Gabion 20 ft. in contract. Externally Maximum Wall Height = 20 ft. Stabilized Primarily Fill Fill Wall. May be Gravity Wall Structures installed as a Typical Height Range: 3 ft. to CIP Mass Designed & detailed Cut wall. 10 ft. Gravity in contract. Maximum Wall Height = 23 ft.

Primarily Fill Detailed in contract. Prefabricated Wall. May be Designed by Typical Height Range: 3 ft. to Wall System installed as a Contractor’s Designer 50 ft. (PWS) Cut wall. (Proprietary Wall). Mechanically Detailed in contract. Stabilized Fill Type Designed by Typical Height Range: 10 ft. to Fill Wall Earth Retaining Wall Contractor’s Designer 65 ft. System (Proprietary Wall). Internally (MSES) Stabilized Mechanically Detailed in contract. Fill Stabilized Designed by Typical Height Range: 6 ft. to Fill Wall Structures Wall System Contractor’s Designer 65 ft. (MSWS) (Proprietary Wall). Geosynthetically Designed & detailed Typical Height Range: 6 ft. to Reinforced Soil Fill Wall in contract. 65 ft. System (GRSS) Detailed in contract. Internally Soil Nail Wall Designed by Stabilized Cut Wall Typical Height Range: 10 ft. to System Contractor’s Design Cut 65 ft. Consultant Structures

1 Cut wall construction refers to a wall system in which the wall is constructed from the top of the wall to the base (i.e., “top-down” construction). Fill wall construction refers to a wall system in which the wall is constructed from the base of the wall to the top (i.e., “bottom-up” construction).

§9.4.1 1/10/20 SOILS, WALLS, AND FOUNDATIONS 9-77

9.4.2 Wall Types

9.4.2.1 Externally Stabilized Cut Structures

The mechanism for stability of an externally stabilized cut structure is obtained by installing a structural wall of sufficient strength to resist the overturning and sliding forces generated by the lateral stresses from the retained soil behind it. Externally stabilized cut structures include sheeting walls, soldier pile and lagging walls, and anchored walls.

A. Sheeting

Sheeting members of a shoring system are structural units which, when connected one to another, will form a continuous wall. The wall continuity is usually obtained by interlocking devices formed as part of the manufactured product. In New York State, the majority of the sheeting used is made of steel, with timber and concrete used less often.

Sheeting is driven to a depth sufficient for the passive pressure exerted on the embedded portion to resist the lateral active earth pressures acting on the cantilevered section. To achieve the required passive earth pressure resistance, embedment depths can often be quite high. Therefore, due to limitations on the availability of certain section moduli and the associated costs, cantilevered sheeting walls are usually restricted to a maximum height of 15 ft. When the height of excavation exceeds 15 ft., or if the embedment depth is limited (e.g., the presence of boulders or bedrock), it becomes necessary to investigate the use of additional support for the wall system. Additional support may be provided by grouted tieback anchors, anchors to a deadman or struts, braces or rakers.

Figure 9.4-1a Sheeting Wall Installation

1/10/20 §9.4.2 9-78 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-1b Sheeting Wall Figure 9.4-1c Sheeting Wall (Permanent Timber Facing) (Permanent Timber Facing)

B. Soldier Pile and Lagging Walls

Soldier piles used as part of a shoring system are vertical structural units, or members, which are spaced at set intervals. Soldier piles in a soldier pile and lagging wall system are typically spaced at 6 ft. to 10 ft. intervals. A lagging material is placed between the soldier piles to complete the shoring system. In New York State, the majority of the soldier piles used are made of steel, with concrete or timber used less often.

A soldier pile and lagging wall derives its resistance from the embedded portion of the wall. The lagging material is usually selected based upon the design life of the wall. A temporary wall will usually incorporate untreated timber lagging, with steel sheeting used less often. A permanent wall will usually incorporate treated timber lagging or concrete lagging with an architectural finish.

Because of the higher available section moduli, greater excavation depths can be supported by soldier piles and lagging as compared to those supported by sheeting. Cantilevered soldier piles are usually practical for excavations up to approximately 15 ft. in height.

Figure 9.4-2a Soldier Pile & Lagging Wall Figure 9.4-2b Soldier Pile & Lagging Wall (Permanent Timber Lagging) (Permanent Precast Concrete Lagging)

§9.4.2.1 1/10/20 SOILS, WALLS, AND FOUNDATIONS 9-79

Figure 9.4-2c Soldier Pile & Lagging Wall (Cast-In-Place Finish)

C. Anchored and Braced Walls

Anchors or braces have been used where it is difficult to attain sufficient embedment to provide cantilever support for a retaining wall. A braced excavation is a retaining structure, usually temporary in nature, which is used to support the sides of deep excavations. Such structures generally consist of vertical steel sheeting braced by a system of wales and struts. They are used primarily for the excavation of trenches in construction situations where adjacent ground must be supported against settlement or slides. Usually in urban areas, the need to prevent settlement of the adjacent ground is a matter of prime importance, as such settlements can have disastrous effects on the structural integrity of adjacent buildings.

In general, the method of construction incorporates the following basic steps: (a) steel sheeting is driven into the ground to a predetermined depth; (b) during excavation the sheeting is braced by horizontal wales supported by a system of struts; the support system for each wale system must be in place and tightened or hydraulically stressed against the sheeting before further excavation can proceed in order to prevent lateral deflection.

Anchor walls derive their support by two means: passive pressure on the front of the embedded portion of the wall and anchor tie rods near the top of the wall system. The wall is anchored to stable earth or bedrock by wire strand or steel bar tendons. Anchors receive their resistance either by being attached to a deadman, or by being grouted in soil or rock. Deadman anchors are attached to an object that is constructed or already exists, located outside the zone of influence. A deadman may be an existing abutment or wall, a length of driven sheeting, a section of cast concrete, or any other member that is buried in the soil. For a deadman to provide maximum resistance, the passive failure wedge for the deadman has to be outside the active failure wedge of the wall to be supported.

A more common type of treatment is similar to deadman anchors, but is more versatile which allows their use under more diverse site and loading conditions. This commonly used category of anchor is called a grouted tieback. These anchors may be used to support temporary, permanent, or interim walls. They are most often used to augment soldier pile and lagging walls and sheeting walls.

1/10/20 §9.4.2.1 9-80 SOILS, WALLS, AND FOUNDATIONS

A tieback consists of a steel tension element called a tendon (may be multistrands or a bar) that transfers tensile forces from the ground to a structural element.

Typical uses for tiebacks include supporting retaining walls (either temporary or permanent), stabilizing abutments, and increasing down force on dams.

Because the tendons extend behind the wall, it is necessary to make sure the Department has the legal right to the property directly above the tiebacks. It may be necessary to obtain temporary or permanent easements or ROW.

To design tiebacks, the Geotechnical Engineering Bureau designer determines the loads on the wall for each maximum depth of excavation. The designer then shows the loading on the tiebacks, tieback spacing, angle of declination, minimum free length, soil parameters, and other design assumptions on the contract plans. It is the Specialty Contractor’s responsibility to design the tendon size, tendon type, and bond length, and use appropriate installation procedures and equipment to properly install the tiebacks.

1/10/20 §9.4.2.1 SOILS, WALLS, AND FOUNDATIONS 9-81

It is also a good idea for the designer to come up with a table or graph that relates excavation height to tieback design load for various spacings. This is not very time consuming to complete during the design stage, when the designer is familiar with the demands of the project, and it may save a lot of time later. Quite often, the Subcontractor adjusts the tieback spacing and recalculates the loads to suit his/her own operations and expertise.

Figure 9.4-3a Sheeting Wall Figure 9.4-3b Anchored Sheeting Wall (Braced Excavation)

Figure 9.4-3c Anchored Soldier Pile & Figure 9.4-3d Anchor (Sheeting Lagging Wall Deadman)

§9.4.2.1 1/10/20 9-82 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-3e Anchor (Concrete Figure 9.4-3f Anchor (Soldier Pile Deadman) Deadman)

9.4.2.2 Externally Stabilized Fill Structures

The mechanism for stability of an externally stabilized fill structure is obtained by gravity providing the righting moment and base friction to resist overturning forces. Externally stabilized fill structures include cast-in-place/precast cantilever/gravity walls, prefabricated wall systems (PWS), and gabions.

Externally stabilized fill structures are best constructed in fill situations. Although they can be constructed in cut situations, doing so requires a strategy for dealing with the cut slope, and may even require temporary walls, all at additional cost in money and construction time.

A. Cast-in-place/ Precast Cantilever/Gravity Walls - General

A cast-in-place/precast gravity wall is an externally stabilized fill structure comprised of a mass of concrete, earth backfill, and a subsurface drainage system to reduce hydrostatic pressure on the wall system. A gravity wall is a massive structure, usually economical only for small heights. Stability of the gravity wall is achieved by the weight of the wall system to resist lateral soil pressure.

Figure 9.4-4a Precast Gravity Wall Figure 9.4-4b Precast Gravity Wall (Foundation Construction) (Stone Facing)

1/10/20 §9.4.2.2 SOILS, WALLS, AND FOUNDATIONS 9-83

A cast-in-place/precast cantilever wall is an externally stabilized fill structure comprised of reinforced concrete, earth backfill, and a subsurface drainage system to reduce hydrostatic pressure on the wall system. A cantilever wall is formed by a thin, reinforced stem cantilevered from a base slab. Stability of the cantilever wall is achieved by the weight of the wall system and the weight of the backfill above the heel projection of the base slab to resist lateral soil pressure.

Figure 9.4-5 Precast Concrete Cantilever Wall

B. Prefabricated Wall Systems (PWS)

A PWS is an externally stabilized fill structure comprised of prefabricated face units & coping units, including leveling pads, unit infill, earth backfill, joint filler material and geotextile, and a subsurface drainage system to reduce hydrostatic pressure on the wall system. PWS are selected by the Contractor and designed by the manufacturer/supplier under the specification for Fill Type Retaining Walls. The prefabricated face units may either be (1) a series of open face units assembled to form bins, which are connected in unbroken sequence or (2) a combination of solid face units with a characteristic alignment and connection method. Stability of the PWS is achieved by the weight of the wall system elements and the weight of the infill to resist lateral soil pressure. As indicated, the bin volume is infilled (if applicable) with backfill material to supplement the face unit geometry, adding to the stability of the system. Supplemental information regarding the proprietary standing of PWS is discussed in Section 9.4.3.

PWS are most applicable when constructed in new fills, such as embankment widenings. Solid face units are typically small in size and weight which results in limited wall heights. However, open face units are larger in size, incorporating infill to add to the weight of the units. This results in an increased height range for these systems. An important consideration in determining the use of these systems is the space required for the size of the units, most notably the base unit. A guide in determining the preliminary base unit length is to use 70% of the proposed PWS wall height (See Section 9.4.5 B2). The installation of the units will sometimes require cutting and benching adjacent fills.

A list of approved PWS systems is maintained on the Departments Approved List.

§9.4.2.2 1/10/20 9-84 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-6a T-Wall: Plain Concrete Figure 9.4-6b T-Wall: Plain Concrete Finish (Wall Construction) Finish (Wall Construction)

Figure 9.4-6c T-Wall: Exposed Aggregate Figure 9.4-6d T-Wall: Exposed Aggregate Finish (Wall Construction) Finish (Wall Construction)

Figure 9.4-6e Stone Strong Wall Figure 9.4-6f Stone Strong Wall (Wall Construction) (Wall Construction)

1/10/20 §9.4.2.2 SOILS, WALLS, AND FOUNDATIONS 9-85

Figure 9.4-6g Stone Strong Wall Figure 9.4-6h Stone Strong Wall (Use of EPS Backfill) (Use of EPS Backfill)

Figure 9.4-6i Evergreen Wall Figure 9.4-6j Evergreen Wall (Constructed Wall) (Plant Growth)

Figure 9.4-6k Unilock Siena Stone 500 Figure 9.4-6l Unilock Siena Stone 500: Back Face

§9.4.2.2 1/10/20 9-86 SOILS, WALLS, AND FOUNDATIONS

C. Gabions

Gabions are an externally stabilized fill structure comprised of twisted or welded wire baskets that are divided by diaphragms into cells, including basket infill consisting of stone fill. Stability of these systems is achieved by the weight of the stone-filled baskets resisting the overturning and sliding forces generated by the lateral stresses from the retained soil.

Gabions are most applicable when constructed in new fills, such as embankment widenings. Gabions blend very well with natural surroundings and can sustain differential settlements without serious distress. However, this inherent flexibility can be a disadvantage as overlying facilities may distort. An important consideration in determining the use of these systems is the space required for the size of the baskets, most notably the base basket. A guide in determining the preliminary base basket length is to use 70% of the proposed gabion wall height. The installation of the baskets will sometimes require cutting and benching adjacent fills.

Figure 9.4-7a Gabion Wall Figure 9.4-7b Gabion Wall

9.4.2.3 Internally Stabilized Fill Structures

The mechanism for stability of an internally stabilized fill structure is obtained by improving the strength of the backfill soil by placing tensile reinforcing elements (inclusions) in the backfill to create a reinforced mass. The weight of the reinforced soil mass resists the overturning and sliding forces generated by the lateral stresses from the retained soil.

It should be noted that, since internally stabilized fill structures rely on a reinforced mass of soil for stability, these wall systems may not be appropriate where it may be necessary to gain future access to underground utilities by cutting or disturbing the reinforcing elements.

Internally stabilized fill structures include Mechanically Stabilized Earth Systems (MSES), Mechanically Stabilized Wall Systems (MSWS), and Geosynthetically Reinforced Soil Systems (GRSS). MSES and MSWS are selected by the Contractor and designed by the manufacturer/supplier under the specification for Fill Type Retaining Walls.

1/10/20 §9.4.2.2 SOILS, WALLS, AND FOUNDATIONS 9-87

A. Mechanically Stabilized Earth Systems (MSES)

MSES are internally stabilized fill structures comprised of natural select granular backfill (reinforced backfill), precast concrete panels (facing), subsurface drainage system, and high-strength, metallic or polymeric inclusions (reinforcement) to create a reinforced soil mass. The reinforcement is placed in horizontal layers between successive layers of granular soil backfill. Each layer of backfill consists of one or more compacted lifts. A well- draining, non-cohesive backfill is required to ensure adequate performance of the retaining wall system. Each reinforcement is connected to the facing with a mechanical connection. Load is transferred from the backfill soil to the metallic or polymeric inclusion by shear along the interface and/or through the passive resistance on the transverse members of the inclusion. Stability of these systems is achieved by the weight of the reinforced soil mass resisting the overturning and sliding forces generated by the lateral stresses from the retained soil behind the reinforced mass. Supplemental information regarding the proprietary standing of MSES is discussed in Section 9.4.3.

MSES walls are most applicable when constructed in new fills, such as embankment widenings. An important consideration in determining the use of these systems is the space required for embedment of the reinforcing. A guide in determining the preliminary embedment lengths is to use 70% of the proposed MSES wall height (See Section 9.4.5 B2). To install the reinforcing to the required embedment lengths it will sometimes require cutting and benching adjacent fills. In addition, MSES walls should not be used in areas where utilities or highway drainage systems must be constructed within the reinforced zone (as future access for repair would require the reinforcement layers to be cut).

Final selection of this wall type depends on the corrosiveness of the soil mass to be reinforced, and its effect on buried members, such as steel straps.

A list of approved MSES systems is maintained on the Departments Approved List.

Inspection guidance for the construction of MSES walls is summarized in a manual published by the Geotechnical Engineering Bureau(17a).

Figure 9.4-8a MSES Wall Figure 9.4-8b MSES Wall (Reinforcement Layout) (Form Liner Finish)

§9.4.2.3 1/10/20 9-88 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-8c Terraced MSES Wall Figure 9.4-8d MSES Wall (Temporary Stage Line Wall)

Figure 9.4-8e MSES Wall Figure 9.4-8f MSES Wall (Cast-In-Place Facing) (Cast-In-Place Facing)

B. Mechanically Stabilized Wall Systems (MSWS)

MSWS are Prefabricated Wall Systems (PWS) which, when constructed beyond wall heights exceeding the maximum allowable unreinforced height, relies on reinforcing elements within the backfill to provide stability. The reinforcement is connected to the facing either with a mechanical or friction connection, depending on the system. By using internal reinforcing, previously limited wall heights can be increased to meet nearly any highway fill application. Systems like these are similar in function and construction to a permanent GRSS system, however they utilize the PWS face units as a permanent facing. Supplemental information regarding the proprietary standing of MSWS is discussed in Section 9.4.3.

Allowable PWS face units used to construct these systems can be found on the Departments Approved List.

1/10/20 §9.4.2.3 SOILS, WALLS, AND FOUNDATIONS 9-89

Figure 9.4-9a Mechanically Stabilized Wall System (Unilock Siena Stone 500 & Strata grid 200)

Figure 9.4-9b Mechanically Stabilized Wall System (Back Face) (Unilock Siena Stone 500 & Strata grid 200)

§9.4.2.3 1/10/20 9-90 SOILS, WALLS, AND FOUNDATIONS

C. Geosynthetically Reinforced Soil Systems (GRSS)

It is very common to use geosynthetics to reinforce a soil mass, to allow the construction of embankments with very steep and even vertical slopes. These systems are called Geosynthetically Reinforced Soil Systems (GRSS). Simply put, a GRSS is a non-proprietary version of an MSWS. Temporary GRSS systems are very commonly used for staged construction, as they are inexpensive and easy to construct. GRSS slopes or walls can also be constructed with an engineered facing, enabling these systems to serve a permanent support function. To differentiate between a GRSS slope and a GRSS wall, a GRSS slope is defined as a system with a face inclination of less than 70 degrees. All GRSS systems are typically designed in-house by the Geotechnical Engineering Bureau.

Depending on the aesthetic conformity of the available facing systems, a GRSS is a more economical alternative to other fill type retaining walls. These systems can be used to construct permanent and temporary over-steepened slopes and permanent and temporary vertical embankment fills. They are most applicable when constructed in new fills, such as a raise in grade between stages, embankment widenings, or when constructed within the backfill where the proposed abutment is located in front of the existing abutment.

An important consideration in designing these systems is the space required for embedment of the reinforcing. A guide in determining the preliminary embedment lengths is to use 70% of the proposed GRSS wall height. To install the reinforcing to the required embedment lengths will sometimes require cutting and benching adjacent fills. This should also be accounted for when determining available space for GRSS construction. GRSS should not be used in the top 6 ft. of a fill if significant future utility work is expected. Since its development, many applications for GRSS have evolved. These are briefly described below:

C.1 GRSS Stage Walls

One of the major considerations during design of a structure replacement is the work zone traffic control during construction. When detours are not feasible, the new structure is typically constructed in stages using part of the existing structure for stage one traffic. This often requires design and construction of temporary retaining walls such as steel sheeting or soldier pile and lagging walls to support the roadway between stages. The GRSS wall was originally developed as a more economical wall system for this application where new backfills will be placed in front of the existing abutment in stages.

§9.4.2.3 1/10/20 SOILS, WALLS, AND FOUNDATIONS 9-91

Figure 9.4-10a GRSS (Temporary Stage Wall)

The construction procedure for a vertical GRSS wall is simple. A 18 in. by 18 in. L-shaped welded wire mesh is placed on the leveled foundation soil to act as a form for the backfill. (This method to form the face is the default method in the specification. However, the specification allows the Contractor the option of submitting an alternate compaction aid. Regardless of the method used, the face should be constructed with a relatively uniform slope.) Sheets of geosynthetic reinforcing of the required embedment lengths are then placed perpendicular to the face of the wall. A geotextile wrap is laid along the bottom of the welded wire form and up around the face to retain the backfill. The select granular backfill is then placed and compacted. Once the backfill reaches the top of the form, the geotextile wrap is pulled back over the top of the backfill. The next welded wire form is placed and the process is repeated until the final design height is reached.

Figure 9.4-10b GRSS (Temporary Stage Wall Section and Plan)

§9.4.2.3 1/10/20 9-92 SOILS, WALLS, AND FOUNDATIONS

C.2 GRSS Slopes

Another typical application for GRSS is to reinforce over-steepened slopes. In many cases, roadway improvements require widening embankments. These widenings are often restricted by R.O.W. limits, environmental constraints such as wetland areas or at culvert locations. Retaining walls or culvert extensions were typically used to overcome these restrictions.

These widenings can be accommodated more cost effectively and timelier by constructing steeper embankment side slopes with GRSS while maintaining the same toe of slope. The GRSS slopes can be constructed without forms and seeded at slopes of 1V on 1H or flatter. However, tall slopes (typically higher than 10 feet) constructed steeper than 1V on 1.5H can be susceptible to deep rills from storm runoff therefore a permanent surface protection (e.g. multiple horizontal, armored benches, intermittent or continual placement of geocell mats) should be used to prevent long-term maintenance concerns

The requirements for the backfill material for a GRSS slope are less strict as compared to those for a GRSS wall. The requirements for both situations are provided in the specification.

Figure 9.4-11a GRSS Figure 9.4-11b GRSS (Permanent Oversteepened Slope) (Permanent Oversteepened Slope)

Figure 9.4-11c GRSS for Widening/Grade Change

1/10/20 §9.4.2.3 SOILS, WALLS, AND FOUNDATIONS 9-93

C.3 Vegetated Face Vertical GRSS

For realignment or new embankment construction, retaining walls are sometimes required to minimize impact on wetlands or R.O.W. The vegetated-face GRSS wall is an economical alternate, especially in environmentally sensitive areas. The construction of the vegetated-face GRSS is similar to the temporary GRSS for staged construction. However, this “green” wall incorporates stacked layers of geocell mats which allow multiple levels of pockets where grass can be grown. The geocell mats are made of plastic that is resistant to ultra-violet light damage and the vegetative cover provides even further sunlight protection. The vertical depth of each geocell mat and the batter of the slope can be adjusted to ensure a sufficient open pocket width for a thick grass cover (typically a 3 inch width, minimum).

Geocells are listed as an available facing system in the specification. A geocell is a three-dimensional, High Density Polyethylene (HDPE) cellular confinement unit which is infilled. As mentioned above, the outer cell is typically filled with topsoil to provide for plant or turf establishment.

Figure 9.4-12a Geocell Faced GRSS Figure 9.4-12b Geocell Faced GRSS

C.4 Timber Faced Vertical GRSS

Another option for realignment or new embankment construction is a timber faced GRSS wall. Timbers are listed as an available facing system in the specification. Construction methods are similar to the temporary GRSS for staged construction except that the timbers act as a form and the welded wire mesh forms are not required. Other facings, such as gabions, can be incorporated into GRSS walls.

§9.4.2.3 1/10/20 9-94 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-13a Timber Faced GRSS Wall Figure 9.4-13b Timber Faced GRSS Wall

§9.4.2.3 1/10/20 SOILS, WALLS, AND FOUNDATIONS 9-95

9.4.2.4 Internally Stabilized Cut Structures

The mechanism for stability of an internally stabilized cut structure is obtained by improving the strength of a soil by placing tensile reinforcing elements (inclusions) in the soil to create a reinforced mass. The weight of the reinforced soil mass resists the overturning and sliding forces generated by the lateral stresses from the retained soil.

It should be noted that, since internally stabilized cut structures rely on a reinforced mass of soil for stability, these wall systems may not be appropriate where it may be necessary to gain future access to underground utilities.

Internally stabilized cut structures include the Soil Nail Wall System.

A. Soil Nail Wall

Soil nailing is an operation in which the soil is reinforced by steel to increase its tensile strength, thus forming a gravity retaining mass. This treatment requires highly specialized construction techniques.

Soil nails are steel bars or tendons installed to reinforce or strengthen the existing ground. They are used to support the existing soil for a cut situation. Soil nails are installed into a slope or excavation as construction proceeds from the existing ground surface to the proposed bottom of excavation. The soil nailing process creates a reinforced section that is itself stable and able to retain the ground behind it.

Soil nails are similar in construction but different in function from a grouted tieback. Specifically, soil nails are passive reinforcements which develop their reinforcing action through nail-ground interactions as the ground deforms during and following construction. Soil nailing provides some advantages over grouted tiebacks as they improve construction flexibility where overhead access is limited, reduce right-of-way requirements by being typically shorter than tiebacks and, by eliminating soldier pile/sheeting installation, they reduce construction time and improve construction flexibility in heterogeneous soils with cobbles and boulders. They should not be used where the water table elevation is above the bottom of the excavation for the soil nail wall.

Design and construction guidelines for soil nail walls are summarized in a manual published by the Geotechnical Engineering Bureau(19c).

1/10/20 §9.4.2.4 9-96 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-14a Soil Nail Wall Figure 9.4-14b Soil Nail Wall (Temporary Shotcrete Facing) (Permanent Shotcrete Facing)

Figure 9.4-14c Soil Nail Wall Figure 9.4-14d Soil Nail Wall (Cast-In-Place Facing) (Stone Masonry Facing)

9.4.2.5 Miscellaneous

Fencing to protect pedestrians should be provided where appropriate. This would usually be required when a wall is retaining a cut slope. In urban areas, a 6 ft. chain link fence should be used unless there is community sensitivity and the Department agrees to the use of a suitable alternate material. In rural areas where few pedestrians are anticipated and fencing is not provided at the right of way line, woven wire fencing would be satisfactory. When a wall is retaining a fill and it is located at the outside edge of a shoulder, bridge rail should be used to protect vehicles and, if at the outside edge of a multi-use path, an appropriate railing.

§9.4.2.5 1/10/20 SOILS, WALLS, AND FOUNDATIONS 9-97

9.4.3 Proprietary Retaining Wall Systems

Proprietary retaining wall systems are systems that are protected by specific patents that make them unique from other retaining wall systems. The term “proprietary” is really a misnomer today because many of the vendor-designed retaining wall systems that are used no longer have patents attached to them. In essence, many retaining walls could be designed using component parts from various systems, utilizing proper design procedures. For all but the simplest structures, however, this is impractical, and now, vendor-designed and supported retaining wall systems are considered proprietary retaining wall systems.

The proprietary retaining wall systems now used by the Department fall within three categories; mechanically stabilized earth systems (MSES), mechanically stabilized wall systems (MSWS), and prefabricated wall systems (PWS). These walls are all considered to be “fill walls”. A generic specification entitled Fill Type Retaining Walls combines these proprietary retaining wall systems and allows for a competitive bidding process.

Under the FHWA regulation 23 CFR 635.411 "Material or Product Selection", the FHWA may participate in the costs of a proprietary product under Competitive Bidding, provided under 23 CFR 635.411(a)(1). The regulation requires a proprietary product be obtained through competitive bidding with other suitable proprietary and non-proprietary products from multiple manufacturers. The Departments specification is geared towards a competitive bidding process by placing a wide-range of proprietary systems on an Approved List. All acceptable systems are shown on the Department’s Approved List and the Contractor shall choose an appropriate system based on the maximum wall height shown in the contract documents.

9.4.4 Wall Selection Process

Personnel from the Geotechnical Engineering Bureau, together with the Regional Geotechnical Engineer, are responsible for visiting proposed project sites and then discussing and providing Regional designers and construction personnel with the appropriate selection and design for the various wall system(s) chosen for the project. Selection of a retaining wall category for a particular site is based on the criteria established in FHWA publication “Geotechnical Circular No. 2, Earth Retaining Structures, FHWA-SA-96-038.”(14m) In general, selection is based primarily on whether a wall is going to be placed in a cut or fill section, whether a wall should or must be externally stabilized, internally stabilized, or a gravity type, and whether the wall will be permanent, temporary, or interim. Other factors such as aesthetics, economy, etc., come into play to make the final decision.

All these treatments have particular advantages and disadvantages. The designer should consult the Regional Geotechnical Engineer when wall systems are under consideration.

9.4.5 Wall Design & Detailing

Once a wall type is chosen, proper details shall be provided in the contract documents. The designer should consult the Regional Geotechnical Engineer for the development of a thorough subsurface investigation program to determine the anticipated subsurface conditions. Once all subsurface explorations are complete, a feasibility analysis (i.e. global stability) of the wall system should be analyzed. The Regional Geotechnical Engineer, with assistance from the Geotechnical Engineering Bureau, can perform the geotechnical analysis for any of the following wall types.

1/10/20 §9.4.5 9-98 SOILS, WALLS, AND FOUNDATIONS

Specific design and detailing for each type of retaining wall is as follows:

A. Cut Type Retaining Walls

As identified in 9.4.1 Definitions, cut type classification refers to the construction method used for the installation of the wall. Cut type retaining walls are retaining structures constructed from the top of the wall to the base (i.e. “top-down” construction). Cut type retaining walls are further classified according to the basic mechanism of lateral load support. These classifications include internally stabilized cut structures and externally stabilized cut structures.

The major design concern with a cut type retaining wall is the determination of the required depth of penetration for the structural system to result in a stable wall after material to be excavated is removed. The depth of penetration is based on the evaluation of the forces and lateral pressures that act on the wall, which emerge from the soil attributes and groundwater elevation in the subsurface profile. Another design concern with a cut type retaining wall (internally stabilized) is the nail length and its impact to any project constraints.

The following is an outline of the detailing requirements for cut type retaining walls:

A1. Sheeting, Soldier Pile & Lagging Wall, or Anchored Walls

Sheeting, soldier pile and lagging walls, or anchored walls shall be designed and detailed in the contract documents. These systems may be designed by Regional designers or Consultants and reviewed by the Geotechnical Engineering Bureau. Design requirements for sheeting, soldier pile and lagging walls, or anchored walls are summarized in a manual published by the Geotechnical Engineering Bureau entitled Geotechnical Design Procedure (GDP-11) Geotechnical Design Procedure for Flexible Wall Systems(16a).

Regional Geotechnical Engineers are very familiar with the requirements for a cut type retaining wall design and can work with the Regional designer to obtain the necessary information for the development of the design.

Regional designers will prepare a layout of the proposed wall. The details include a plan view, elevation view and section view including top and toe of cut system, maximum height, minimum embedment below bottom of excavation, minimum section modulus of cut system, existing and final grade profiles in front of (bottom of excavation) and behind the wall, location of wales and/or bracing, minimum section modulus of wales and/or size of bracing, location and size of deadman/raker blocks, grouted tieback loads and grouted tieback free length, right-of-way lines, temporary easements, and potential interferences (utilities). The Regional designer should also include a Table identifying the soil parameters used to design the cut system. An example Table is provided in Chapter 4 of the Bridge Manual(16e).

The items for a sheeting or soldier pile and lagging wall are located in Section 552 Support and Protection Systems of the Standard Specifications.

1/10/20 §9.4.5 SOILS, WALLS, AND FOUNDATIONS 9-99

consist of attaching timber to hide a sheeting system, incorporating a textured precast concrete lagging into the soldier pile and lagging system, or installing a cast-in-place stem in front of an anchored system. The details should include connection of the permanent facing, required reinforcement (if necessary), and all other appropriate items pertinent to the desired permanent facing.

A2. Soil Nail Walls

Soil nail walls are designed by the Contractors Consultant during the construction submittal process. However, it is recommended to perform a feasibility analysis during design to identify potential impacts. Design and construction guidelines of soil nail walls are summarized in a manual published by the Geotechnical Engineering Bureau entitled Geotechnical Engineering Manual (GEM-21) Design and Construction Guidelines for a Soil Nail Wall System(19c).

Regional designers will prepare a general layout of the proposed wall for bidding purposes. The details are to provide sufficient information for a Contractor to bid the wall and for the Contractors Consultant to perform an engineering analysis and final detailing of the wall. Typically, the general layout includes a plan view, elevation view and section view including existing and final grade profiles in front of and behind the wall, right-of-way lines, temporary easements, and potential interferences (utilities).

The items for a soil nail wall are located in Section 211 Internally Stabilized Cut Structures of the Standard Specifications.

Regional Geotechnical Engineers are very familiar with the above process and work very closely with the Regional design and construction personnel to ensure that it is followed closely.

B. Fill Type Retaining Walls

As identified in 9.4.1 Definitions, fill type classification refers to the construction method used for the installation of the wall. Fill type retaining walls are retaining structures constructed from the base of the wall to the top (i.e. “bottom-up” construction). Fill type retaining walls are further classified according to the basic mechanism of lateral load support. These classifications include internally stabilized fill structures and externally stabilized fill structures. These systems are further divided based on patents, or which systems are proprietary retaining wall systems.

The major design concern with a fill type retaining wall is the determination of the required foundation elevation for the structural system to result in a stable wall after material to be

1/10/20 §9.4.5 9-100 SOILS, WALLS, AND FOUNDATIONS

retained is placed. The foundation elevation is dictated by geotechnical bearing and stability requirements based on the evaluation of forces and lateral pressures that act on the wall, which emerge from the soil attributes and groundwater elevation in the subsurface profile, the proposed grade retained by the wall, and the location of the wall (e.g. if the wall is located within an existing slope and/or if there will be a sloping ground line in front of the wall). Another design concern with a fill type retaining wall is the foundation width and its impact to any project constraints.

The following is an outline of the detailing requirements for fill type retaining walls:

B1. Cast-in-place/ Precast Cantilever/ Gravity Walls

Figures 9.4-15a through 15h (at the end of this subsection) are intended to divide CIP/ precast cantilever/ gravity walls into two categories: • Standard design structures which can be detailed completely from these sheets and; • Special design structures, which require site-specific designs.

The purpose of establishing two separate categories of structures is to identify the more expensive and the more structurally critical structures for careful review. Special design structures are those which must be designed independently (not by these Figures) and then reviewed by both the Geotechnical Engineering Bureau and the Office of Structures. Design methodology follows a gravity retaining wall method. Design requirements for cast-in-place/ precast cantilever/ gravity walls are outlined in Chapter 11 of AASHTO(17d). Standard structures are defined as those which may be designed and detailed entirely from Figures 9.4-15a through 15h and do not require review beyond the Region level.

Figure 9.4-15a gives details for cantilever walls. Figures 9.4-15b through 15h gives details for both gravity and cantilever walls. These standard designs were developed with three (3) specific goals in mind. First, the standards are developed in order to provide the Regions with the capability to generate contract plans from the standards without the need to refer to any outside organization. Second, criteria are to be provided for making quick preliminary cost estimates, and for converting the theoretical individual designs into practical overall wall details. These details are to emphasize simplicity and standardization. Third, costs are minimized by the use of low pressure wall designs, made possible by a limited amount of soil preparation beneath the footing.

To achieve the capability of performing complete designs at the Regional office, it is necessary to involve the skills of the Regional Geotechnical Engineer, as well as those of the structure designer. Standard designs shall not be used unless both the designer and the geotechnical engineer agree that they are applicable to the individual case. The tabulated designs include soil pressures as low as 1 tsf and sliding friction coefficients down to 0.35. These values enable the use of a spread footing design for almost any site. The function of the geotechnical engineer is to determine the design parameters for the soil at all footing locations along with recommended bottom of footing elevations. In the event that undercutting of unstable material beneath the proposed spread footing is required to provide a stable foundation, this undercut shall be limited to 6 ft. maximum for cantilever walls (Figure 9.4-15b) and 4 ft. maximum for gravity walls (Figure 9.4-15g). Greater depths of soil removal require careful analysis and review by the Office of Structures and the Geotechnical Engineering Bureau to determine the feasibility of using standard design as compared to special pile-supported (or other) designs.

1/10/20 §9.4.5 SOILS, WALLS, AND FOUNDATIONS 9-101

Standard designs are restricted to the use of spread footings. They are available up to a maximum stem design height of 24 ft. Separate tables for level surcharge and sloping surcharge are provided to enable the designer to compensate for varying earth pressures due to backfill conditions. Whenever soil conditions dictate the use of a pile foundation, the design stem height exceeds 24 ft., or a railroad live load surcharge may be applied to the retaining wall, a special design is required.

Standard cantilever wall designs may be used at any wall location. Walls required for the retention of highway fills (not connected with a major structure) may be either of cantilever or gravity design. When highway fills are high enough to require the use of retaining walls which exceed 12 ft. in height, other wall types should be considered.

B1a. Cantilever Walls

B1ai. BASIS OF DESIGN These walls have been designed by means of computer program No. B5000 as maintained by the Structures Design Systems Unit of the Structures Subdivision. Some of the assumptions and input data for these designs are listed below:

1. Unit weight of earth: 120 pcf 2. Unit weight of concrete: 150 pcf 3. Active earth pressure of soil behind wall = 30 psf for level surcharge only. 4. Calculated by program for a 1 on 2 sloping surcharge = 46 psf maximum. 5. Earth fill behind wall was assumed with the top of finished ground 9 in. below the wall coping. 6. A 1 ft. depth of surcharge was applied above the toe of the footing. No passive earth pressure was applied. 7. A 2 ft. depth of surcharge, simulating the effect of live load, was applied above the heel when level surcharge was used. No provision for Railroad live load surcharge was included. 8. No loads, vertical or horizontal, other than that caused by the earth backfill and surcharge were imposed on the wall. 9. The designs were developed with the absence of hydrostatic pressure behind the wall. The material placed behind the retaining wall is a select, free-draining granular material and the walls are to be detailed with weep holes as identified in the notes. 10. The placement of backfill was assumed to extend full depth behind the wall. No sheeting or intervening rock which would limit the effect of the backfill upon the wall was considered to exist. 11. All the cantilever walls are supported by 2 ft. thick footings except for certain walls with a stem design height of 20 ft. or greater which have a sloping surcharge imposed on them. All walls have stems which measure 18 in. at the coping. The exposed face of wall is vertical and the face against which earth is placed is battered at 24 vertical on 1 horizontal starting at the coping and extending to the footing. 12. Reinforcement is designed based on a 3 in. concrete cover over footing steel and a 2 in. cover over the stem steel. 13. Allowable concrete stress: 1200 psi. 14. Allowable reinforcing bars stress: 24000 psi. 15. Ratio of elastic moduli (n): 10. 16. Allowable shear in concrete: 90 psi.

1/10/20 §9.4.5 9-102 SOILS, WALLS, AND FOUNDATIONS

17. Allowable bond stress for reinforcement: 300 psi 18. Factor of safety, sliding: 1.5. 19. Factor of safety, overturning: 2.0.

The following input values were varied over a range to produce the family of designs from which the tables were extracted: 1. Stem height: 6 ft. to 24 ft. 2. Soil pressure: 2 ksf to 10 ksf 3. Sliding friction coefficient: 0.35, 0.50, 0.65.

B1aii. METHOD OF DESIGN The program checks the wall for both permanent loadings and temporary loadings during construction except that wind forces during the construction are not analyzed. Since no restrictions were placed on either toe projection or heel projection, the design is accomplished by incrementing both toe and heel until a width of footing is attained which will meet the design criteria. In cases where the projection of the footing must be limited, a special design or review should be requested from the Office of Structures if the toe or heel projection given by Table 9-7 exceeds the allowable. The program calculates the required areas of steel for stem steel and footing steel and the required perimeter for bond. The reinforcement shown in the table was chosen in accordance with a collated summary of these values. Calculated values of soil pressure and safety factors are also listed in the output. These values were the basis for the selection of the individual designs to be included in the table. Separate designs for footings with shear keys were automatically computed but were discarded as being less desirable than other designs which were offered. Table 9-7 is the result of editing over 1,500 designs to provide a complete coverage of soil conditions. The 7 ksf thru 10 ksf pressure designs were eliminated because the extra soil capacity was not required for reasonable economical design.

The 0.35 sliding friction coefficient will satisfactorily represent designs in the 0.30 to 0.44 range, the 0.50 sliding friction coefficient designs are accurate within the 0.45 to 0.59 range, and the 0.65 sliding friction coefficient designs pertain to the 0.60 to 0.70 range. It remains then for the Regional Geotechnical Engineer to classify soils as either being in the “LOW” sliding resistance range, the “NORMAL” sliding resistance range, or in the “HIGH” sliding resistance range in accordance with these ranges of values.

The concrete unit quantity column was added by means of an independent computation. The sole purpose of this value is to provide a means for making comparative estimates when preparing preliminary plans.

B1aiii. DESIGN AND DETAILING SEQUENCE 1. Locate retaining wall in plan by offsets from adjacent center line of improvement or base line. 2. Plot boring holes in plan. 3. Regional Geotechnical Engineer shall be consulted to ascertain from the borings the required depth of excavation, bearing value of the soil, and sliding friction coefficient of the soil. 4. The bottom of footing elevations should be tentatively set at various points along the wall. A 4 ft. minimum earth cover below final grade should be maintained and an effort made to place the proposed footing subgrade in a consistent band of subsoil.

1/10/20 §9.4.5 SOILS, WALLS, AND FOUNDATIONS 9-103

5. Wall should be subdivided into separate footing segments (pours) between footing expansion joints and into the individual wall panels between stem contraction joints. Stem panel lengths should not exceed 30 ft. Footing segments should not exceed 90 ft. 6. At appropriate intervals along the wall (not exceeding 100 ft. even stations), the height of wall required to retain the earth fill should be calculated from profile and topographic data. 7. From the raw data now available, the bottom of footing elevations shall be finally set and the top of wall profile established forming a smooth, aesthetic profile rather than a series of straight line connections to computed theoretical points. Footing segments (pours) on rock or hardpan should be stepped as necessary in 2 ft. minimum step increments. Footing segments in earth cut or on fill should not be stepped, but the footing segment lengths should be limited such that the height of fill over the toe of the footing does not vary by more than 8 ft. The coping shall protrude above the earth fill a minimum of 9 in. 8. Compute the height of wall at the joints between each stem panel. If the wall height within the panel varies by 6 ft. or less, select the height of the higher third point as the design height for the panel. For panels of more than 6 ft. variation in height, the greatest height must be used for one design height and a second design height may be selected from the height of the lower third point if the panel is long enough to warrant more accurate design. 9. Enter the Table of Proportions with the appropriate stem height, allowable soil pressure and sliding friction coefficient, and list the design values for all design sections. 10. If either toe or heel projection is limited by clearance requirements, the footing dimensions which have been listed should be checked for interference. A special design will be prepared by the Office of Structures in cases of unavoidable interference. 11. Design values of toe and heel projections should be plotted about the respective points along the layout control line at which the design sections were taken. 12. Actual footing dimensions, extrapolated from the required theoretical dimensions, are next determined for each footing segment. Variations in either toe or heel projections of less than 18 in. may be neglected in order to maintain a constant toe or heel dimension. In such cases, the designer should use the larger design projection. 13. Once the concrete dimensions are fixed, the footing reinforcement must be decided upon. If the footing segment is of constant cross-section, the maximum required heel and toe reinforcement must be carried throughout the length of the footing segment. If the footing is trapezoidal in shape, heel and toe reinforcement should be varied in accordance with the respective design section values. 14. Relatively level panels, which have been designed on the basis of a higher third point design height, shall carry the design dowel reinforcement for the entire length of the stem panel. Those steeply sloped panels, which are designed on the basis of the greatest height in the panel, should use two dowel sizes in the panel. More than two dowel sizes will not be economical except in walls with the most extreme (1 vertical on 2 horizontal) slopes. The variation in the dowel size may be extracted from the table in accordance with the stem height. 15. Main stem reinforcement shall be detailed as follows: Use #7 bars at 18 in. centers for all stem heights above 20 ft. Use #5 bars at 18 in. centers for all portions of wall where the stem height is 20 ft. or less.

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16. In using the concrete volume figures for steeply sloping walls, a sufficiently accurate preliminary estimate may be arrived at by assigning a corresponding length of wall to each different volume figure. 17. The designer should develop scoring details and patterns appropriate to enhance the aesthetic quality of the retaining walls especially if wall heights exceed 8 ft. of exposed stem and the walls can be readily viewed by the public. The aesthetic attributes of the final product need to be clearly stated in the Contract Plans, through the use of a vivid description or a detailed series of sketches, or both. All descriptions should make use of industry-standard terminology.

B1b. Gravity Walls

Gravity walls are designed by manual calculations. They are intended to provide a low cost alternative to the cantilever designs where design heights do not exceed 12 ft. Provided the appearance of the gravity wall is suitable to the overall site plan, a gravity design may be used to retain highway fills more economically than the corresponding cantilever wall.

B1c. Cantilever and Gravity Wall Figures and Table of Proportions

B1ci. GENERAL NOTES: 1. Walls which cannot be designed within the range of designs listed must be referred to the Office of Structures for review. The applicability of the wall designs to a given situation shall be determined within the Region by the concurrence of both the structures designer and the geotechnical engineer. In cases where doubt exists as to the relative economy of alternate designs, approval to vary from the standard wall design shall be requested from the Deputy Chief Engineer (Structures). 2. Two weep holes shall be provide in every panel, located at the quarter points. 3. The invert of the weep hole at the front of the wall shall be located 6 in. above the finished grade or 6 in. above low water for stream bridges, whichever is higher. 4. Waterstops: In accordance with BD-MS3 R1, use Type “E” or Type “D” Waterstops behind joints thru the stem, if staining would be objectionable. 5. Construction Joints: Detail in accordance with BD-AB6 R1.

1/10/20 §9.4.5 SOILS, WALLS, AND FOUNDATIONS 9-105

Figure 9.4-15a Section Through Wall

Cantilever Wall Notes: See B1ai. BASIS OF DESIGN

§9.4.5 1/10/20 9-106 SOILS, WALLS, AND FOUNDATIONS

Notes: 1. When required, footing excavation shall be undercut and backfilled with Select Structure Fill. 2. For excavation, drainage and backfill details, see BD-EE1 R1 & 3 R1

Figure 9.4-15b Section Foundation & Backfill Preparation

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Figure 9.4-15c Illustrative Example (Slightly Sloping Wall – Elevation View)

Figure 9.4-15d Illustrative Example (Slightly Sloping Wall - Plan View)

§9.4.5 1/10/20 9-108 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-15e Illustrative Example (Steeply Sloping Wall – Elevation View)

Figure 9.4-15f Illustrative Example (Steeply Sloping Wall – Plan View)

1/10/20 §9.4.5 SOILS, WALLS, AND FOUNDATIONS 9-109

Figure 9.4-15g Section Gravity Wall

Gravity Wall Notes:

1. The gravity wall section may be used as an alternate to the cantilever section where it will not be compatible with adjacent work and the wall height (dimension “H”) is a minimum of 4 ft. and a maximum of 12 ft. 2. Required Soil Capacity: Allowable Pressure: 3 ksf. Friction Coefficient: 0.35. 3. Steel fabric reinforcement shall be placed as shown behind the full area of the vertical form. 4. Maximum Panel Length Between Construction Joints: 20 ft. 5. Maximum Length Between Expansion Joints: 100 ft. 6. All joints shall be formed with an adequate shear key.

§9.4.5 1/10/20 9-110 SOILS, WALLS, AND FOUNDATIONS

Figure 9.4-15h Layout Control

Layout Control Notes:

Walls situated adjacent to a curved centerline of improvement should be detailed as a series of straight segmental walls. Where it is necessary that the wall layout control line be curved itself, one of the following layout methods shall be used: 1. Curved walls (Radius greater than 450 ft.): Layout on chords, unless horizontal clearance is critical. Locate footing as shown above by perpendicular offsets to a chord between the third points of the footing pour between expansion joints. Lay out stem panels on chords between the contraction joints. 2. Curved walls (Radius 450 ft. or less): Lay out both footing and stem on curve. If the distance between footing expansion joints is reduced so that it does not exceed one-fifth of the radius, lay out on chords may be used on radii shorter than 450 ft.

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Table 9-7 Table of Proportions Design Parameters Reinforcement Stem Req’d Design Conc. Ftg. Toe “T” Bars “H” Bars “D” Bars “S” Bars Heigh Min. Coeff. of Unit Width Proj. Size Spac Size Spac Size Spac Size Spac t Soil Friction Quant. (ft) (ft) (in) (in) (in) (in) (ft) Press. (yd3 per (tsf) ft of wall) 6’-0” 1 0.50 0.66 4’-1” 0’-8” #5 18” #5 18” #5 18” #5 18” 6’-0” 1 0.35 0.74 5’-1” 0’-10” #5 18” #5 18” #5 18” #5 18” 7’-0” 1 0.50 0.75 4’-5” 1’-4” #5 18” #5 18” #5 18” #5 18” 7’-0” 1 0.35 0.83 5’-6” 0’-10” #5 18” #5 18” #5 18” #5 18” 8’-0” 1 ½ 0.50 0.83 4’-6” 0’-8” #5 18” #5 18” #5 18” #5 18” 8’-0” 1 0.50 0.88 5’-2” 1’-8” #5 18” #5 18” #5 18” #5 18” 8’-0” 1 0.35 0.96 6’-4” 1’-0” #5 18” #5 18” #5 18” #5 18” 9’-0” 1 ½ 0.50 0.95 5’-2” 0’-10” #5 18” #5 18” #5 18” #5 18” 9’-0” 1 0.50 0.99 5’-10” 2’-0” #5 18” #5 18” #5 18” #5 18” 9’-0” 1 0.35 1.09 7’-1” 1’-2” #5 18” #5 18” #5 18” #5 18” 10’-0” 1 ½ 0.50 1.05 5’-8” 1’-6” #5 18” #5 18” #5 18” #5 18” 10’-0” 1 0.50 1.12 6’-7” 2’-4” #5 18” #5 18” #5 18” #5 18” 10’-0” 1 0.35 1.22 7’-11” 1’-6” #5 18” #5 18” #5 18” #5 18” 11’-0” 1 ½ 0.50 1.18 6’-5” 1’-6” #5 18” #5 18” #5 18” #5 18” 11’-0” 1 0.50 1.24 7’-3” 2’-8” #5 18” #5 18” #5 18” #5 18” 11’-0” 1 0.35 1.36 8’-11” 2’-0” #5 18” #6 18” #5 18” #5 18” 12’-0” 1 ½ 0.50 1.30 7’-0” 1’-8” #5 18” #6 18” #5 9” #5 18” 12’-0” 1 0.50 1.37 8’-0” 3’-0” #6 18” #5 18” #5 9” #5 18” 12’-0” 1 ½ 0.35 1.43 8’-9” 1’-6” #5 18” #5 9” #5 9” #5 18” 12’-0” 1 0.35 1.49 9’-7” 2’-2” #5 18” #6 18” #5 9” #5 18” 13’-0” 1 ½ 0.50 1.40 7’-5” 2’-2” #5 18” #6 18” #5 9” #5 18” 13’-0” 1 0.50 1.49 8’-8” 3’-4” #6 18” #5 18” #5 9” #5 18” 13’-0” 1 ½ 0.35 1.56 9’-6” 1’-8” #5 18” #6 9” #5 9” #5 18” 13’-0” 1 0.35 1.63 10’-6” 2’-10” #5 18” #5 9” #5 9” #5 18” 14’-0” 1 ½ 0.50 1.52 7’-11” 2’-4” #6 18” #5 9” #5 9” #5 18” 14’-0” 1 0.50 1.63 9’-5” 3’-8” #5 9” #6 18” #5 9” #5 18” 14’-0” 1 ½ 0.35 1.69 10’-4” 1’-10” #5 18” #6 9” #5 9” #5 18” 14’-0” 1 0.35 1.75 11’-1” 3’-0” #6 18” #5 9” #5 9” #5 18” 15’-0” 2 0.50 1.59 7’-11” 1’-8” #5 18” #6 9” #6 9” #5 18” 15’-0” 1 ½ 0.50 1.66 8’-9” 2’-8” #6 18” #5 9” #6 9” #5 18” 15’-0” 1 0.50 1.75 10’-1” 4’-0” #6 9” #6 18” #6 9” #5 18” 15’-0” 1 ½ 0.35 1.88 11’-1” 2’-0” #5 18” #7 9” #6 9” #5 18” 15’-0” 1 0.35 1.90 12’-1” 3’-4” #5 9” #6 9” #6 9” #5 18” 16’-0” 2 0.50 1.72 8’-7” 1’-10” #5 18” #7 9” #6 9” #5 18” 16’-0” 1 ½ 0.50 1.80 9’-8” 3’-0” #5 9” #6 9” #6 9” #5 18” 16’-0” 1 0.50 1.89 10’-10” 4’-4” #6 9” #5 9” #6 9” #5 18” 16’-0” 1 ½ 0.35 1.97 11’-11” 2’-2” #5 18” #7 9” #6 9” #5 18” 16’-0” 1 0.35 2.06 13’-2” 3’-8” #5 9” #6 9” #6 9” #5 18”

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Table 9-7 (cont.) Table of Proportions Design Parameters Reinforcement Stem Req’d Design Conc. Ftg. Toe “T” Bars “H” Bars “D” Bars “S” Bars Heigh Min. Coeff. of Unit Width Proj. Size Spac Size Spac Size Spac Size Spac t Soil Friction Quant. (ft) (ft) (in) (in) (in) (in) (ft) Press. (yd3 per (tsf) ft of wall) 17’-0” 2 0.50 1.85 9’-2” 2’-0” #6 18” #7 9” #7 9” #5 18” 17’-0” 1 ½ 0.50 1.91 10’-1” 3’-2” #5 9” #6 9” #7 9” #5 18” 17’-0” 1 0.50 2.04 11’-10” 4’-10” #7 9” #5 9” #7 9” #5 18” 17’-0” 1 ½ 0.35 2.11 12’-8” 2’-4” #6 18” #8 9” #7 9” #5 18” 17’-0” 1 0.35 2.20 13’-11” 4’-6” #6 9” #6 9” #7 9” #5 18” 18’-0” 2 0.50 1.97 9’-9” 2’-6” #5 9” #7 9” #7 9” #5 18” 18’-0” 1 ½ 0.50 2.06 11’-0” 3’-6” #6 9” #7 9” #7 9” #5 18” 18’-0” 1 0.50 2.18 12’-7” 5’-2” #7 9” #6 9” #7 9” #5 18” 18’-0” 1 ½ 0.35 2.25 13’-6” 2’-6” #6 18” #8 9” #7 9” #5 18” 19’-0” 2 ½ 0.50 2.04 9’-7” 1’-10” #6 18” #9 9” #8 9” #5 18” 19’-0” 2 0.50 2.09 10’-3” 2’-8” #5 9” #8 9” #8 9” #5 18” 19’-0” 1 ½ 0.50 2.21 11’-10” 3’-10” #6 9” #7 9” #8 9” #5 18” 19’-0” 1 0.50 2.32 13’-3” 5’-6” #8 9” #6 9” #8 9” #5 18” 19’-0” 1 ½ 0.35 2.39 14’-3” 3’-0” #5 9” #9 9” #8 9” #5 18” 20’-0” 2 ½ 0.50 2.19 10’-4” 2’-0” #6 18” #9 9” #8 9” #5 18” 20’-0” 2 0.50 2.26 11’-4” 3’-0” #6 9” #8 9” #8 9” #5 18” 20’-0” 1 ½ 0.50 2.33 12’-4” 4’-0” #7 9” #8 9” #8 9” #5 18” 20’-0” 1 0.50 2.46 14’-0” 5’-10” #8 9” #7 9” #8 9” #5 18” 20’-0” 1 ½ 0.35 2.53 15’-0” 3’-2” #6 9” #9 9” #8 9” #5 18” 21’-0” 2 ½ 0.50 2.32 11’-0” 2’-2” #5 9” #10 9” #9 9” #7 18” 21’-0” 2 0.50 2.38 11’-10” 3’-2” #6 9” #9 9” #9 9” #7 18” 21’-0” 1 ½ 0.50 2.48 13’-2” 4’-4” #7 9” #8 9” #9 9” #7 18” 21’-0” 1 ½ 0.35 2.67 15’-8” 3’-4” #6 9” #10 9” #9 9” #7 18” 22’-0” 2 ½ 0.50 2.47 11’-9” 2’-4” #5 9” #9 6” #8 6” #7 18” 22’-0” 2 0.50 2.52 12’-5” 4’-0” #8 9” #7 6” #8 6” #7 18” 22’-0” 1 ½ 0.50 2.64 14’-1” 5’-10” #9 9” #6 6” #8 6” #7 18” 22’-0” 1 ½ 0.35 2.81 16’-5” 4’-0” #7 9” #8 6” #8 6” #7 18” 23’-0” 3 0.50 2.53 11’-5” 2’-0” #5 9” #9 6” #8 6” #7 18” 23’-0” 2 ½ 0.50 2.60 12’-4” 2’-10” #6 9” #9 6” #8 6” #7 18” 23’-0” 2 0.50 2.64 12’-10” 4’-2” #8 9” #8 6” #8 6” #7 18” 23’-0” 1 ½ 0.50 2.78 14’-9” 6’-2” #8 6” #7 6” #8 6” #7 18” 23’-0” 1 ½ 0.35 2.95 17’-0” 4’-2” #7 9” #9 6” #8 6” #7 18” 24’-0” 3 0.50 2.65 11’-10” 2’-4” #6 9” #10 6” #9 6” #7 18” 24’-0” 2 ½ 0.50 2.74 13’-0” 3’-6” #7 9” #9 6” #9 6” #7 18” 24’-0” 2 0.50 2.80 13’-9” 4’-6” #9 9” #8 6” #9 6” #7 18” 24’-0” 1 ½ 0.50 2.90 15’-2” 6’-4” #8 6” #7 6” #9 6” #7 18” 24’-0” 2 0.35 3.02 16’-9” 3’-2” #6 9” #10 6” #9 6” #7 18” 24’-0” 1 ½ 0.35 3.13 18’-3” 4’-6” #8 9” #9 6” #9 6” #7 18”

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B2. Proprietary Retaining Wall Systems

The proprietary retaining wall systems now used by the Department fall within three categories; mechanically stabilized earth systems (MSES), mechanically stabilized wall systems (MSWS), and prefabricated wall systems (PWS). This is discussed in 9.4.3. Acceptable systems are shown on the Department’s Approved List and the Contractor shall choose an appropriate system based on the maximum wall height shown in the contract documents.

Proprietary retaining walls are designed by the Contractors Consultant or the manufacturer/supplier during the construction submittal process. Design requirements for proprietary retaining walls are outlined in Chapter 11 of AASHTO(17d). Although the site- specific design is submitted during construction, a feasibility analysis is required during design to identify potential impacts. A feasibility analysis for these fill type retaining walls includes analysis of the subsurface conditions to determine the potential for excessive settlement and/or bearing capacity failure of the foundation soil. The GEB will perform the geotechnical analyses needed for use of a fill type retaining wall.

Regional Designers will prepare a general layout of the proposed wall for bidding purposes. The details are to provide sufficient information for a Contractor to bid the wall and for the Contractors Consultant to perform an engineering analysis and final detailing of the wall. Typically, the general layout includes a: • plan view, • elevation view, and • section view (show a “box” for the wall system to fit into, H high and the depth based on Table 9-7a). The views should include existing and final grade profiles in front of and behind the wall, right-of-way lines, temporary easements, and potential interferences (utilities).

The Designer needs to identify any potential conflicts within the section view (i.e. the ”box”) such as drainage runs, catch basins, underdrain, utilities, etc. so that the Fill Type Retaining Wall designer/supplier may address these conflicts in the Shop Drawing submittal and are not left as construction obstacles and addressed in the field.

Although the Regional Designer cannot assume a specific wall system, the Approved List will identify the (1) maximum unreinforced height, (2) if reinforcement applications are available, and (3) if abutment support applications are acceptable. Based on this information, the Designer can identify which various prefabricated wall systems (PWS), mechanically stabilized wall systems (MSWS), and mechanically stabilized earth systems (MSES) will be applicable considering the projects constraints. Based on this information, the Regional Designer and Regional Geotechnical Engineer will review the available wall systems and identify any concerns associated with each type. Special Notes shall be developed to address these potential design concerns and included in the contract documents. The details and notes are to provide sufficient information for a Contractor to bid the wall and for the Contractors Consultant to perform an engineering analysis and final detailing of the chosen wall system. Design parameters for the wall backfill shall be obtained from the Design Parameters given on the Approved List unless otherwise stated in the contract documents. The Contractor will select a wall system from the Approved List during the construction phase.

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Regional Designers and the Regional Geotechnical Engineer will also investigate the constructability of the Fill Type Retaining Wall. Straight or Inline walls are the preferred arrangement. Walls with flares or abrupt corners introduce acute angles and, with some systems, are difficult to construct. Designers should avoid acute angles or tight radii. If required, constructability of each type of Fill Type Retaining Wall should be investigated with respect to the desired alignment.

Once the details of a wall have been completed, the aesthetics or visual impact of the system can be addressed. The designer should consult the Regional Landscape Architect to address the need for an aesthetic treatment. The specification for the fill type retaining wall contains standard default treatments. If aesthetics are not a concern, the standard default treatments in the specification shall apply. However, if aesthetics are a concern, the Regional Designer will add, in addition to the fill type retaining wall item, an item for the aesthetic treatment for the face units. The Designer needs to vividly describe the desired aesthetic treatment using industry-standard descriptions for color and texture, and provide special notes, and special details. The Regional Landscape Architect and the Landscape Architecture Bureau are available to help develop these descriptions. See Section 9.4.6 Aesthetic Treatments.

Designers need to become familiar with the available categories (textured surface, exposed aggregate finish, architectural pattern) for presentation to communities. They need to keep in mind that the Contractor will ultimately choose the specific wall system. Therefore, while negotiating a “look”, the Designer should avoid promises regarding the specific type of wall and concentrate on the finish or treatment and the possible variations (joints, unit size, etc.) between wall types.

B2a. Fill Type Retaining Wall Item Number Designation

The items for a fill type retaining wall are located in Section 554 Fill Type Retaining Walls of the Standard Specifications. Standard Sheets are available for Section 554 Fill Type Retaining Walls.

As stated previously, the generic specification entitled Fill Type Retaining Walls combines the three categories of approved proprietary retaining wall systems and allows for a competitive bidding process via the Approved List. In the preparation of the general layout of the wall, the Regional designer will designate the fill type retaining wall item number based on the maximum wall height. • If aesthetics are not a concern and the default treatments are acceptable, this is the only item number necessary. • If aesthetics are a concern, the Regional designer will add, in addition to the fill type retaining wall item, an item for the aesthetic treatment for the face units. The aesthetic treatment is paid for separately and additional details should be provided. See Section 9.4.6 Aesthetic Treatments.

B2b. Fill Type Retaining Wall Volume

Although the Regional Designer cannot assume a specific wall system, in order to prepare the general layout for bidding purposes and to investigate constructability aspects of its installation, the Fill Type Retaining Wall volume will be specified based on

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the walls height. A guide in determining the preliminary wall base width is to typically use 70% of the proposed wall height. Table 9-7a provides additional explanation.

Table 9-7a Estimating Fill Type Retaining Wall Base Width

WALL SIZE RATIO(1): WALL BASE WIDTH(2) / WALL HEIGHT

Back Slope Up Level Back Slope Bridge Foundation Support To 1V on 2H(3) 1.0 0.7 0.8 See BD-EE13E

(1) Each column assumes a 250 psf traffic surcharge behind the wall regardless of backslope. (2) Wall Base Width = face to heel length of gravity wall base or wall face + soil reinforcement. (3) For back slopes steeper than 1V on 2H, the wall volume may be increased up to a ratio value of 1.0.

B2c. Fill Type Retaining Walls Supporting a Shoulder and Requiring a Concrete Barrier

Although some Designer-Suppliers have their own designs that incorporate cast-in-place concrete within the top unit to enhance its capability to withstand impact loads, the design details and items for a concrete barrier on top of a Fill Type Retaining Wall are addressed separately.

The Regional Designer should identify the wall volume and, if the wall is located directly below a shoulder and a concrete barrier is required, the detail should identify a concrete barrier – moment slab directly on top of the wall (with appropriate details & pay items – see Figures 9.4-16a, b, and c). This way, all walls are appropriate for the application at hand when the corresponding AASHTO wall design guidance is followed.

A note may be added to the moment slab detail stating that systems which have the ability to address impact within their wall design may incorporate a concrete barrier connection as part of the wall. Any guiderail system incorporated into the wall design must meet NYSDOT requirements, including NCHRP 350. Item and payment would be taken out of the original moment slab design identified in the contract. Incorporating a concrete barrier or guiderail connection within the wall design may lead to a significantly larger sized wall. Isolating the concrete barrier from the wall, or providing a 3 foot minimum separation between guiderail and the top of wall (where allowed by guiderail deflection), will help minimize the wall size necessary for a barrier impact.

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Figure 9.4-16a

Figure 9.4-16b

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Figure 9.4-16c

B2d. Addressing Conflicts with the Fill Type Retaining Wall Volume and Surface/Subsurface Installations

For Fill Type Retaining Walls located below and/or offset from the shoulder area, there may be potential conflicts between the material within the wall volume and the pavement section (e.g. edgedrains, guiderail installations, or other necessary appurtenances).

Roadside design dictates the deflection distance of the proposed guiderail/barrier installation. For walls located directly below the shoulder, see the previous section B2b. addressing a moment slab/concrete barrier installation. If the roadside design proposes to utilize guiderail, the deflection distance must be accounted for within the offset location to the wall. Considering this distance and the common practice of minimizing wall heights, a typical roadway section view of a wall supporting (and adjacent to) a shoulder incorporates the shoulder, guiderail, shoulder break, and a 1V on 2H sideslope down to the top of wall.

To provide an example, the deflection distance for box beam guiderail (HDM Ch. 10 (p. 10-33) – weak post, 3’ spacing) is 4’-0”, which would be an initial controlling offset for a wall (if guide rail is used). Assuming a 1V on 2H sideslope, the resulting subsurface clearance for guide rail installation would be 2’-0”. However, a typical guide rail post is embedded 2’-9”, indicating a potential conflict with the wall volume. Investigating other aspects of the roadway section, the governing factor appears to be the edgedrain installation. The typical embedment for an edgedrain trench (CPDM Ch. 9 (p. 9-7)) is 1’- 0” below bottom of subbase elevation. Noting that a typical pavement section is approx. 2’-0” thick, the additional 1’-0” would allow a subsurface clearance of 3’-0” (enough to allow the 2’-9” guide rail embedment). Considering this and the need for a 2’-0” offset from the shoulder break point to provide appropriate support, the closest recommended offset distance (preferred offset) to the wall face is 8’-0” (see Figure 9.4-16d). If walls are required to be installed within the offset range of 4’-0” to 8’-0” (restricted setback),

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the Regional Designer should consider adjusting the conflicting factors (such as the location of the edgedrain trench). If other factors cannot be modified (e.g. guiderail installation), the Special Notes should alert the Contractor and Designer-Supplier of the conditions, and direct him to ensure that his design can accommodate the conflict or employ appropriate protective measures (see Figure 9.4-16e).

For MSWS, MSES, and GRSS, and other flexible facing walls, soil embedded guiderail posts offset at least 8’-0” from the wall face may use standard length posts, and posts set at less than 8’-0” from the wall face shall use extra long posts. Guiderail deflection distance shall be considered when choosing the minimum offset distance. No guiderail, regardless of post spacing or size, shall be placed with a post offset of less than 5’-0” from the wall face of MSWS, MSES, and GRSS walls.

Figure 9.4-16d

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Figure 9.4-16e

B2e. The Exception – Highway Work Permits

The exception to the generic presentation of a Fill Type Retaining Wall for open competition among the Approved List systems is within the Departments oversight of Highway Work Permits.

The Operations Division Office of Traffic Safety and Mobility has been assigned continuing responsibility for all powers and duties related to Highway Work Permits (private work within State right-of-way). Inspection during the performance of the work is normally the responsibility of the Resident Engineers in the Operations Division’s Office of Transportation Maintenance.

Highway Work Permit projects are not part of the State or Local Programs, where the design-bid-build process is instituted to ensure taxpayers money is being appropriately spent on properly designed and constructed projects, with safeguards against collusion. A Permitee is still required to submit the proprietary retaining wall system design, including settlement, stability and globality stability analyses, to the Department to ensure it meets our Standards. However, the conspiracy concern regarding a competitively bid product is not an issue as the Permitee is the venture paying for the roadway improvements. In fact, in lieu of the Contractor choosing the type of fill wall system to be installed, the Permitee may identify a particular wall system as long as it appears on our Approved List and the design addresses any concerns identified by the Department.

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B3. Gabions

As stated earlier, gabions blend very well with natural surroundings and can sustain differential settlements without serious distress. However, this inherent flexibility can be a disadvantage as overlying facilities may distort. Designers should be cognizant of this attribute in regards to the proposed placement of gabions and what they are supporting.

Gabion walls shall be designed and detailed in the contract documents. These systems may be designed by Regional designers or Consultants and reviewed by the Geotechnical Engineering Bureau. Design methodology follows a gravity retaining wall method. Design requirements for gabions are outlined in Chapter 11 of AASHTO(17d). Additional information the design of a gabion can be found in manufacturer’s literature such as Maccaferri’s Design Guide.

The items for a gabion wall are located in Section 620 Bank and Channel Protection of the Standard Specifications.

Regional Geotechnical Engineers are very familiar with the requirements for gabions and can work with the Regional designer to obtain the necessary information for the development of the design.

Regional designers will prepare a layout of the proposed wall. The details include a plan view, elevation view and section view including existing and final grade profiles in front of and behind the wall, maximum design height, installation details, right-of-way lines, temporary easements, and potential interferences (utilities).

B4. Geosynthetically Reinforced Soil Systems (GRSS)

GRSS systems shall be designed and detailed in the contract documents. These systems are typically designed in-house by the Geotechnical Engineering Bureau. Design requirements for GRSS are outlined in Chapter 11 of AASHTO(17d). Additional information on the design of a GRSS can be found in the FHWA manual on Reinforced Soil Structures: Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines(17b). Regional Geotechnical Engineers are very familiar with the requirements for a GRSS design and can work with the Regional designer to obtain the necessary information for the development of the design.

The Geotechnical Engineering Bureau will prepare a layout of the proposed wall. The details include a plan view, elevation view and section view including existing and final grade profiles in front of and behind the wall, minimum embedment, design strength, and vertical spacing of geosynthetic reinforcement, maximum design height, installation details, right-of-way lines, temporary easements, and potential interferences (utilities).

The items for GRSS are located in Section 554 Fill Type Retaining Walls of the Standard Specifications. Standard Sheets are available for Section 554 Geosynthetically Reinforced Soil Systems. Design parameters for GRSS walls are assumed as follows: Unit Weight of Reinforced Soil (γ) = 125 pcf Friction Angle of Reinforced Soil (φ) = 34°

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Once the details of a wall have been completed, the aesthetics or visual impact of the system can be addressed. The designer should consult the Regional Landscape Architect to address the need for an aesthetic treatment. For these systems, a permanent facing may consist of attaching geocells, timbers or gabions. The appropriate facing details are provided with the Geotechnical Engineering Bureau’s layout of the proposed wall.

9.4.6 Aesthetic Treatments

Proprietary fill type retaining walls may incorporate various aesthetic treatments to enhance features of the wall or blend the wall into the surrounding environment. Aesthetic treatments are treatments applied to the face of a wall system either during or after the manufacture of the units to modify the appearance of the units and of the wall as a whole. Aesthetic treatments can include modifications to color, texture, architectural pattern, the addition of exposed surface aggregate (real or artificial), the addition of simulated joints or cracks, or any other treatment or material that modifies the appearance, provided that the structural integrity, function, or life span of the wall is not negatively impacted.

The specification identifies some categories for organizational and bidding purposes. Since the Approved List allows the Contractor to choose the type of wall, the categories only provide a general idea of the type of aesthetic treatment for either a face panel/unit as described below:

A. Textured Surface: Texturing precast concrete panels/units can be achieved through formliners to develop the desired texture of grooves, ribs, ropes, or flutes. Solid dry cast units may be manufactured in rib configurations and split to reveal the texture of the aggregate with the ribbed appearance.

Figure 9.4-17a Textured Surface Figure 9.4-17b Textured Surface (Cast-In-Place MSES) (PWS)

B. Exposed Aggregate Finish: Precast concrete panels/units can achieve an exposed aggregate finish through formliners and releasing agents developing the appearance of sandblast, aggregate, or round stone. Solid dry cast units are manufactured and split to reveal the texture of the aggregate.

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Figure 9.4-17c Exposed Aggregate Figure 9.4-17d Exposed Aggregate (Open Modular Units) (Solid Blocks)

C. Architectural Pattern: Precast concrete panels/units can achieve an architectural pattern through formliners to develop the pattern of stacked stone, or block. Solid dry cast units are themselves stacked blocks.

Figure 9.4-17e Architectural Pattern Figure 9.4-17f Architectural Pattern (Open Modular Units) (Solid Blocks)

Although the above categories provide a general idea of the type of aesthetic treatment, the specific requirements should be vividly described in the contract documents using special notes and sketches, as needed. The requirements for color, texture and pattern should use industry- standard descriptions and terminology.

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9.4.7 Sole Source

There are a limited number of instances where sole sourcing retaining walls (identifying a particular wall type) is appropriate. In these situations, the Regions must create a special specification and justify and document their reasons for using a sole source system because they are eliminating competition. A sole source special specification is said to be proprietary if it mentions, either directly, or by reference, that as a requirement for acceptance a product be that of a certain named manufacturer. The justifiable reasons for a sole source proprietary special specification are identified in Chapter 21, section 21.3.5 Proprietary Specifications. Once the justification is complete, Regional designers can then contact the retaining wall company directly and have a design prepared for inclusion in the contract plans.

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