ROMANSTACK Gravity Retaining Wall Installation Specification
SECTION 02832- CONCRETE SEGMENTAL RETAINING WALL
PART 1 GENERAL
1.01	Description
A)	The work covered by this section includes the furnishing of all labor, materials, equipment and incidentals for the design, inspection and construction of a modular concrete retaining wall including drainage system as shown on the Construction Drawings and as described by the Contract Specifications. The work included in this section consists of, but is not limited, to the following:
a)	Design, inspection and certification by a registered professional engineer.
b)	Excavation and foundation soil preparation.
c)	Furnishing and placement of the leveling base.
d)	Furnishing and placement of the drainage system.
e)	Furnishing and placement of geotextiles.
f)	Furnishing and placement of segmental retaining wall facing units.
g)	Furnishing and compaction of drainage and retained soils.
1.02	Related Work
A)	Section 02100 - Site Preparation
B)	Section 02200 - Earthwork
1.03	Reference Standards
A)	Engineering Design
a)	NCMA Design Manual for Segmental Retaining Walls, Second Edition.
b)	NCMA TEK 2-4 - Specifications for Segmental Retaining Wall Units.
c)	NCMA SRWU-2 - Determination of Shear Strength between Segmental Concrete Units.
B)	Segmental Retaining Wall Units
a)	ASTM C 140 - Sampling and Testing Concrete Masonry Units
b)	ASTM C 1262 - Evaluating the Freeze - Thaw Durability of Manufactured Concrete Masonry Units and Related Concrete Units.
c)	ASTM C 33 - Specification for Concrete Aggregates
d)	ASTM C 90 - Standard Specification for Load-Bearing Concrete Masonry Units
e)	ASTM C 150- Specification for Portland Cement
f)	ASTM C 595 - Specification for Blended Hydraulic Cements
C)  Geotextile Filter
a)	ASTM D 4751 - Standard Test Method for Apparent Opening Size
D)	Soils
a)	ASTM D 698 - Moisture Density Relationship for Soils, Standard Method
b)	ASTM D 422 - Gradation of Soils
c)	ASTM D 424 - Atterberg Limits of Soils
d)	ASTM D G51 - Soil pH
E)	Drainage Pipe
a)	ASTM D 3034 - Specification for Polyvinyl Chloride (PVC) Plastic Pipe
b)	ASTM D 1248 - Specification for Corrugated Plastic Pipe
F)	Where specifications and reference documents conflict, the Owner or Owner's representative shall make the final determination of applicable document.
1.04	Approved Products
A)	RomanStack Segmental Retaining Wall System as supplied by Mutual Materials Company.
B)	Colour to be [_______].
1.05	The Contractor
A)	The term Contractor shall refer to the individual or firm who will be installing the retaining wall. 
B)	The Contractor must have the necessary experience for the project and have successfully completed projects of similar scope and size.
1.06	Delivery, Material Handling and Storage
A)	The installing contractor shall check all materials delivered to the site to ensure that the correct materials have been received and are in good condition.
B)	The Contractor shall store and handle all materials in accordance with manufacturer’s recommendations and in a manner to prevent deterioration or damage due to moisture, temperature changes, contaminants, breaking, chipping or other causes.
1.07	Engineering Design and Certification
A)	The term Engineer shall refer to the individuals or firms who have been retained by the Contractor to provide design and inspection services for the retaining wall. The Design Engineer may be a different individual or firm from the Inspecting Engineer as the Manufacturer may provide this service.  The Engineer(s) must be qualified in the area of segmental retaining wall design and construction and must be licensed to practice engineering in the Province or State that the wall is to be constructed.
B)	The Engineer(s) will perform the following tasks:
a)	Produce sealed construction drawings and detailed design calculations, completed in accordance with the design requirements outlined in Part 3 of these specifications.
b)	Review the site soil and geometric conditions to ensure the designed wall is compatible with the site prior to construction.
c)	Inspect the site conditions, materials incorporated into the retaining wall, and the construction practices used during the construction.
d)	Provide the Contractor with a letter after completion, certifying the design meets the requirements of this specification, the design was compatible with the site and the wall was constructed according to design.
1.08	Submittals
A)	The Contractor shall submit the following information for approval thirty (30) days prior to the construction of the segmental retaining wall.
a)	Design Submittal – Provide three (3) sets of stamped construction drawings and detailed design calculations, completed and sealed by the Engineer in accordance with the design requirements outlined in Part 3 of this specification.
b)	Materials Submittal – Manufacturer’s certifications, stating that the SRW units and imported aggregates and soils meet the requirements of this specification and the Engineer’s design.
c)	Installer Qualifications - The Contractor must be able to demonstrate that their field construction supervisor has the necessary experience for the project by providing documentation showing that they have successfully completed projects of similar scope and size.
1.09	Measurement for Payment
A)	Payment for earthworks to prepare the site for the retaining wall construction will be based on the contract unit price per cubic metre (or cubic yard) for site cut and fill earthwork as detailed in the Site Plan. Additional earthwork as directed and approved in writing by the Owner, or Owner’s representative, shall be paid for under a separate pay item.
B)	Payment for the retaining wall system will be based on the contract price per square metre (or square foot) of vertical wall face area as shown on the construction drawings. The vertical wall face area shall be measured from the top of the base or footing to the top of the coping course multiplied by the length of the wall. The contract unit price shall include the cost of all engineering, labour, materials, and equipment used to install the leveling base or spread footing, wall modules, drainage materials, retained soil and site clean up.  Additional items as directed and approved in writing by the Owner, or Owner’s representative, shall be paid for under a separate pay item.
PART 2 MATERIALS
2.01	Definitions
A)	Modular concrete retaining wall units are dry-cast solid concrete units that form the external facia of a modular unit retaining wall system.
B)	Coping units are the last course of concrete units used to finish the top of the wall.
C)	Retained soil is an in-situ soil or a specified soil that is placed behind the wall drainage material.
D)	Foundation soil is the in-situ soil beneath the wall structure.
E)	Drainage aggregate is a free draining soil with natural soil filtering capabilities, or a free draining soil encapsulated in a suitable geotextile, or a combination of free draining soil and perforated pipe all wrapped in a geotextile, placed directly behind the modular concrete units.
F)	Drainage pipe is a perforated polyethylene pipe used to carry water, collected at the base of the retaining wall, to outlets in order to prevent pore water pressures from building up behind the wall facing modules.
G)	Non-woven geotextiles are permeable synthetic fabrics formed from a random arrangement of fibers in a planar structure. They allow the passage of water from one soil medium to another while preventing the migration of fine particles that might clog a drainage medium.
H)	All values stated in metric units shall be considered as accurate. Values in parenthesis stated in imperial units are the nominal equivalents.
2.02	Products
A)	Concrete Segmental Retaining Wall Units
a)	The concrete wall modules shall be 100 x 200/150* x 200 mm (4 x 8 / 6* x 4 inches) with a maximum tolerance of plus or minus 3 mm (1/8 in.) for each dimension.*(units are tapered to allow tight radii).
b)	The retaining wall modules shall be solid units and have a minimum weight of 8.1kg (18 lbs.) per unit.
c)	The concrete wall modules shall have a integral shear key connection that creates a vertical wall alignment.
d)	The concrete wall modules shall have a minimum 28-day compressive strength of 35 MPa (5000 psi) as tested in accordance with ASTM C 140. The concrete shall have a maximum moisture absorption rate of 5 percent to ensure adequate freeze-thaw protection.
B)	Retained Soil
a)	The retained soil shall be on site soils unless specified otherwise in the Construction Specifications or as directed by the Owner or Owner’s Representative. If imported fill is required, it shall be examined and approved by the Engineer.
C)	Foundation Soil
a)	The foundation soil shall be the native undisturbed on site soils. The foundation soil shall be examined and approval by the Engineer prior to the placement of the base material.
D)	Levelling Base Material
a)	The footing material shall be non-frost susceptible, well graded compacted crushed stone (GW-Unified Soil Classification System), or a concrete leveling base, or as shown on the Construction Drawings.
E)	Drainage Soil
a)	The drainage soil shall be a free draining angular granular material of uniform particle size smaller than 25 mm (1 in.) separated from the retained soil by a geotextile filter. The drainage soil shall be installed directly behind the SRW units.
F)	Drainage Pipe
a)	The drainage pipe shall be perforated corrugated HDPE or PVC pipe, with a minimum diameter of 100 mm (4 inches), protected by a geotextile filter to prevent the migration of soil particles into the pipe, or as specified on the construction drawings.
G)	Geotextile Filter 
a)	The non-woven geotextile shall be installed as specified on the construction drawings. Although selection of the appropriate geotextile specifications is site soil specific, a commonly used geotextile for filtration will have an Apparent Opening Size ranging between 0.149 and 0.210 mm (U.S. Sieve Sizes 100 to 70) and a minimum unit weight of 135 grams per square meter (5.0 oz /square yard). The coefficient of permeability will typically range between 0.1 and 0.3 cm/second.
H)	Concrete Adhesive
a)	The adhesive is used to permanently secure the coping stone to the top course of the wall. The adhesive must provide sufficient strength and remain flexible. 
PART 3 WALL DESIGN
3.01	Design Standard
A)	The Engineer is responsible for providing a design that shall consider the external stability and internal stability, including global stability, total and differential settlement, of the SRW system. The design life of the structure shall be 75 years unless otherwise specified in the construction drawings.
B)	The segmental retaining wall shall be designed in accordance with recommendations of the NCMA Design Manual for Segmental Retaining Walls, Second Edition. The following is a summary of the minimum factors of safety for the various modes of failure evaluated in the proposed design. 
External Stability
	Base Sliding	1.5
	Overturning	1.5
	Bearing Capacity	2.0
	
Internal Stability
	Shear Capacity	1.5
3.02	Soil
A)	Design parameters: The following soil parameters shall be assumed for the design unless otherwise shown on the plans or specified by the Engineer. 
Retained Soil:
	Unit Weight 	= [________] kN/cu.m (lb/cu.ft)
	Friction Angle 	= [________] deg
	Cohesion 		= 0 kPa (lb/sq.ft)
Foundation Soil:
	Unit Weight 	= [________] kN/cu.m (lb/cu.ft)
	Friction Angle 	= [________] deg
	Cohesion 		= 0 kPa (lb/sq.ft)
3.03	Design Geometry
A)	The length, height, and overall elevations of the retaining wall must comply with the requirements of the proposed elevation detail, station information and site grading plan.
B)	The structures' design height, H, shall be measured from the top of the leveling pad to the top of the wall where ground surface intercepts the wall facing.
C)	Slopes above and below all sections of the segmental retaining wall are detailed in the site grading plan
D)	The minimum wall embedment shall be the height of one SRW unit.

3.04	State of Stress
A)	The lateral earth pressure to be resisted by the self weight of the retaining wall shall be calculated using the Coulomb coefficient of earth pressure, Ka, times the vertical stress at the base of the wall.  The coefficient of active earth pressure, Ka, shall be used from the top to the bottom of the wall. The coefficient of active earth pressure, Ka, shall be assumed independent of all external loads except sloping fills. For sloping fills, the coefficient of active earth pressure, Ka, appropriate for the sloping condition, using Coulomb earth pressure shall be used in the analysis.

3.05	Settlement Control
A)	It is the responsibility of the Certifying Engineer or Site Geotechnical Engineer to determine if the foundation soils will require special treatment to control total and differential settlement.
3.06	Global Stability
A)	It is the responsibility of the Certifying Engineer or Site Geotechnical Engineer to determine if further design considerations must be implemented to ensure adequate global/overall slope stability.

PART 4 CONSTRUCTION
4.01	Inspection
A)	The Engineer is responsible for verifying that the contractor meets all the requirements of the specification. This includes the use of approved materials and their proper installation.
B)	The Contractor's field construction supervisor shall have demonstrated experience and be qualified to direct all work related to the retaining wall construction.
4.02	Construction Tolerances
A)	The following tolerances are the maximum allowable deviation from the planned construction,
Vertical Control: +/- 1.25 inches over a 10 ft distance, +/- 3 inches total 
Horizontal Control:  +/- 1.25 inches over a 10 ft distance, +/- 3 inches total
Rotation: +/- 2 degrees from planned wall batter
Bulging:  1.0 inch over a 10 ft distance
4.03	Site Preparation
A)	The foundation soil shall be excavated or filled as required to the grades and dimensions shown on the Construction Drawings or as directed by the Owner or Owner’s Representative.
B)	The foundation soil shall be proof rolled and examined by the Engineer to ensure that it meets the minimum strength requirements according to the design assumptions. If unacceptable foundation soil is encountered, the contractor shall excavate the affected areas and replace with suitable quality material under the direction of the Engineer.
C)	In cut situations, the native soil shall be excavated to the lines and grades shown on the Construction Drawings and removed from the site or stockpiled for reuse as retained soil.
4.04	Installing Drainage System
A)	The approved non-woven geotextile shall be set against the back of the first retaining wall unit, over the prepared foundation, and extend towards the back of the excavation, up the excavation face and back over the top of the drainage material to the retaining wall, or as shown in the Construction Drawings.
B)	The drainage pipe shall be placed behind the leveling base, or lower course of facing units as shown in the Construction Drawings or as directed by the Engineer. The pipe shall be laid at a minimum gradient of 2% to ensure adequate drainage to free outlets.
C)	T - Sections and outlet pipes shall be installed on the drainage pipe at 15 m (50 ft.) centers or as shown on the Construction Drawings.
D)	The remaining length of geotextile shall be pulled taut and pinned over the face of the retained soil. Geotextile overlaps shall be a minimum of 300 mm (1 ft.) and shall be shingled down the face of the excavation in order to prevent the infiltration of retained soil into the drainage layer.
4.05	Levelling Base or Spread Footing Placement
A)	The leveling base material shall be crushed stone compacted to 98% Standard Proctor Density, or vibrated concrete along the grades and dimensions shown on the Construction Drawings or as directed by the Engineer. The minimum thickness of the leveling base shall be 100 mm (4 inches)
4.06	Installation of Modular Concrete Retaining Wall Units
A)	The bottom row of retaining wall modules shall be placed on the prepared leveling base as shown on the Construction Drawings. Care shall be taken to ensure that the wall modules are aligned properly, leveled from side to side and front to back and are in complete contact with the base material.
B)	The wall modules above the bottom course shall be placed such that the tongue and grove arrangement provides the design batter (i.e. setback) of the wall face. Successive courses shall be placed to create a running bond pattern with the edge of all units being approximately aligned with the middle of the unit in the course below it.
C)	The wall modules shall be swept clean before placing additional levels to ensure that no dirt, concrete or other foreign materials become lodged between successive lifts of the wall modules.
D)	A maximum of 2 courses of wall units can be placed above the level of the drainage material at any time.
E) The contractor shall check the level of wall modules with each lift to ensure that no gaps are formed between successive lifts.
F)  Care shall be taken to ensure that the wall are not broken or damaged during handling and placement.
4.07	Drainage Soil
A)	The drainage soil will be placed behind the retaining wall modules with a minimum width of 300mm (1 ft.) and separated from other soils using the approved non-woven geotextile.
B)	Drainage soil shall be placed behind the wall facing in maximum lifts of 6 inches and compacted to a minimum density of 95% Standard Proctor.
C)	No heavy compaction equipment shall be allowed within 1 metre (3 ft.) of the back of the wall facia.
4.08	Retained Soil
A)	Retained soils shall be placed and compacted behind the drainage material in maximum lift thickness of 150 mm (6 inches). The retained soils shall be undisturbed native material or engineered fill compacted to a minimum density of 95% Standard Proctor.
B)	No heavy compaction equipment shall be allowed within 1 m (3 ft.) of the back of the wall modules.
4.09	Finishing Wall
A)	Items 4.05 to 4.08 shall be repeated until the grades indicated on the Construction Drawings are achieved.
B)	Coping units shall be secured to the top of the wall with two 10mm (3/8 inch) beads of the approved flexible concrete adhesive positioned 50mm (2 inches) in front and behind the tongue of the last course of retaining wall units.
C)	Finish grading above the wall to direct surface run off water away from the segmental retaining wall. Use a soil with a low permeability to restrict the rate of water infiltration into the retaining wall structure.