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Vegetated Slope

BY:  LANCE CARTER, P.E. - TECHNICAL DIRECTOR, STRATA SYSTEMS, INC. USA

INTRODUCTION

There are many questions that must be answered when considering a vegetated reinforced soil slope for a site development project.  Many of these questions are quite straight forward.

• Is the technology proven?  Yes- Vegetated reinforced soil slopes are an accepted and proven technology.

• Is the solution economical?  Yes – Vegetated reinforced soil slopes are economical solutions to grade separation needs as compared to convention concrete or hardscape structures.

• Is the system constructible?  Yes – Vegetated reinforced soil slopes are constructible, even to slope angles of 1H:2V (70-degrees from horizontal).

However, it is becoming more common during site development projects that an answer is provided to a very basic question.  
What is the impact on the environment?

The answer is not easy.  Site development has a direct impact on the local environment, as well as potentially influencing the global environment.  One way to address the issue has been an increased focus on the types of materials and systems incorporated in the project.  This has led to the creation of the Leadership in Energy and Environmental Design (LEED) Green Building Rating System™.  The system was developed to provide independent, third-party verification that a building project is environmentally responsible, profitable and a healthy place to live and work. 
The StrataSlope system can be an integral part of site development and the LEED system.

 

LEED – WHAT IS IT?

“The LEED for New Construction Rating Systems is designed to build and distinguish high-performance commercial and institutional projects, including office buildings, high-rise residential buildings, government buildings, recreational facilities, manufacturing plants and laboratories”, as stated by the U.S. Green Building Council.

The LEED rating system is effectively a point system.  Projects are qualified based on the number of points they achieve under the system.  A project garners points within six major categories or credit areas (points possible): Sustainable Sites (14), Water Efficiency (5), Energy & Atmosphere (17), Materials & Resources (13), Indoor Environmental Quality (15), and Innovation & Design Process (5).   There are a total of 69 possible points from which a project can be qualified as ‘Certified: 26-32 points’, ‘Silver: 33-38 points’, ‘Gold: 39-51 points’, and ‘Platinum: 52-60 points’.  Local municipalities or developers are establishing minimum LEED point requirements for their sites.

 

HOW DOES THE VEGETATED STRATASLOPE SOLUTION PROVIDE POINTS UNDER LEED?

SUSTAINABLE SITES

Twenty percent (14 of 69) of the points possible under LEED are achieved through Sustainable Sites (SS) credits. The StrataSlope System with vegetated facing consists of the design and construction of a Stratagrid geogrid reinforced soil slope using two possible slope face systems; 1.) A wrap-faced construction using Microgrid and welded-wire forms to construct a slope face steeper than 45-degrees (1H:1V) from horizontal (See Detail 1), or 2.) A conventional slope face constructed to a steepness less than 45-degrees (1H:1V) from horizontal incorporating an erosion blanket on the finished slope face (See Detail 2).  The StrataSlope System can assist in obtaining points within several credit areas.

SS Credit 1 (1 point): Site Selection – Utilize the StrataSlope System to avoid development of inappropriate sites and reduce the environmental impact from the location of a building on a site.  The StrataSlope system facilitates this by minimizing the required footprint to locate a building and/or parking structures on a given site.  Unreinforced soil slopes are generally constructed to relatively flat slopes (i.e. 3H1V (18° from horizontal) to 2H1V (26°)).  The StrataSlope System readily facilitates the design and construction of 1H1V (45°) to 1H2V (63° from horizontal) slopes.

SS Credit 4.1 (1 point): Alternative Transportation: Public Transportation Access – Reduce pollution and land development impact from automobile use by locating a project within ½ mile of an existing or planned commuter rail or subway station, or within ¼ mile of one or more stops for two or more public bus lines usable by the occupants of the proposed building.  This is often accomplished by placing the proposed building near mass transit, which in turn is found most often in high developed areas where large or easily developed sites are difficult to find.  The StrataSlope System provides an opportunity to reduce the area necessary for development, or it can facilitate the development of a more challenging site.  This would include a site where significant numbers of grade change structures are required, and the benefit of a low cost and flexibility solution like the StrataSlope System can be recognized.

SS Credit 5.1 (1 point): Protect or Restore Habitat – Conserve existing natural areas and restore damaged areas to provide habitat and promote biodiversity.  This is accomplished by considering two options.  Option 1 – Limit all site disturbances to 40 feet beyond the building perimeter; 10 feet beyond surface walkways and utilities less than 12 inches in diameter; 15 feet beyond primary roadway curbs and main utility trenches; and 25 feet beyond constructed areas with permeable surfaces.  Option 2 – Restore or protect a minimum of 50% of the site area with native or adapted vegetation on previously developed or graded sites.  The StrataSlope system is ideal for this credit. First, the system directly influences the ability to satisfy Option 1 by allowing steeper grade separation structured to be constructed reducing the required footprint of the proposed site.  Secondly, the system directly applies to Option 2 in that the StrataSlope System utilizes a vegetated slope face that can be used to restore native vegetation or support adapted vegetation.

SS Credit 5.2 (1 point): Maximize Open Space – Provide a high ratio of open space to the development footprint to promote biodiversity.  Three options are considered under this credit.  Option 1 – reduce the development footprint and/or provided vegetated open space to exceed the local zoning’s requirement for the site by 25%.

Option 2 – Where no local zoning requirements exist, provide vegetated open space equal to the building footprint. Option 3 – Where zoning ordinance exists, but there is no requirement for open space, provide vegetated space equal to 20% of the project’s area.   As with other credit areas, the StrataSlope System facilitates the selection of sites having a smaller footprint as well as providing opportunity to increase the percentage of open and/or vegetated area on the site.

SS Credit 7.1 (1 point): Heat Island Effect – Non-Roof – Reduce heat islands to minimize impact on microclimate and human and wildlife habitat.  Option 1 requires that 50% of the site hardscapes are shaded within 5 years, use paving materials with a high solar reflectance index, or incorporate grid pavement systems. Option 2 requires 50% of parking spaces to be under cover.  The StrataSlope System may assist in gaining a point under this credit by providing additional areas that can be planted with vegetation that will shade hardscapes within 5 years, or provide the ability to place parking under cover by reducing the area required to develop the site by steepening side slopes supporting the structure.

WATER EFFICIENCY

Five of the total 69 points possible may be achieved through water efficiency.  The StrataSlope System can be an integral part of this design aspect.

WE Credit 1.1 (1 point): Water Efficient Landscaping: Reduce by 50% - Limit or eliminate the use of potable water for landscape irrigation.  One approach to reducing landscape irrigation is through the use of captured rainwater.  A StrataSlope System can increase the available vegetated area and reduce surface water runoff.  The system can readily be designed as part of underground surface water collection systems.  This is possible because the StrataSlope system can be designed to support these structures, or increase the available area for grid pavement systems by using steeper side slope gradients.

WE Credit 1.2 (1 point) Water Efficient Landscaping: No Potable Water Use or No Irrigation – Eliminate the use of potable water for landscape irrigation.  This is accomplished by installing landscaping that does not require permanent irrigation.  The StrataSlope System can be used as an integral part of developing the sustainable site byl allowing the planting of vegetation species that do not require irrigation.  The installation of vegetation is an important aspect of a site development, and the StrataSlope System can be a part of the solution.

MATERIALS & RESOURCES

Thirteen of the total 69 points are possible through the reuse of materials and resources. The StrataSlope system can be a component of many strategies used under this credit area.

MR Credit 5.1 and 5.2: Regional Materials: Extracted, Process & Manufactured Regionally – Increase demand for materials and products that are extracted within the region.  Credit 5.1 requires a minimum 10% of the materials and Credit 5.2 requires a minimum 20% of the materials to be extracted, processed or manufactured regionally (within 500 miles).  The StrataSlope System is very flexible with respect to the type of backfill material used in constructing reinforced soil structures. In many cases, the StrataSlope System can be constructed with the on-site soils allowing 100% re-use of excavated materials.  In other instances, the StrataSlope can be constructed from soil acquired from a nearby (within 500 miles) borrow source or quarry.  The reuse or utilization of nearby fill soils can be a major cost aspect of the project, and the StrataSlope system provides an opportunity to account for these materials.

INNOVATION & DESIGN PROCESS

ID Credit 1 – 1.4 (1 to 4 points): Innovation in Design – Provide the design team and project the opportunity to be awarded points for exceptional performance above the requirements set by the LEED for New Construction Green Building Rating System.  As part of the overall project, the StrataSlope System can be an integral design aspect that incorporates innovative technologies, such as vegetation or use of available resources, while exceeding the requirements of LEED.  Additionally, the design and construction of the StrataSlope System and geogrid reinforced soil structures in general are very flexible in their adaptability to a site.  The System provides opportunity to consider innovative design practices, new construction techniques, new materials and resources, and consideration of sites that may not be developed using traditional technology as a result of structural performance or costs.

The StrataSlope System provides an effective means for meeting the requirements under LEED rating system and provides the design team with an effective, technically based and low cost solution to their site development and grade separation needs.

Contact Strata Systems, Inc. at 800-680-7750 for additional information.