The Parking Forest in GreshamLinear Tree Wells Using Structural Soil

Sustainability for all the places between the buildings

503.334.8634www.greengirlpdx.com

greengirl@greengirlpdx.coma certified women business enterprise

About Me

About You

Why was I invited here today?Tualatin Riverkeepers’ Vision: the Parking

Forest• Increase canopy in parking lots• Manage stormwater• No loss of parking spaces

Two Sites

Watershed base map courtesy of Tualatin River Watershed Council

Redevelopment

Retrofit

Structural Soil (dry)

The Parking ForestA Close Up (12 feet wide)

Pavement outside of

Parking Forest

Re-paved areaTree

Structural SoilAmended native

clayey soilUndisturbed native clayey soil

Crushed aggregate

Wheel stop

THPRD Sunset Swim CenterRedevelopment with Pervious Concrete

THPRD Sunset Swim Center in PlanRedevelopment with Pervious Concrete

PCC Sylvania Lot 10Retrofit with Impervious Asphalt

PCC Sylvania Lot 10in Plan

PCC Sylvania Lot 10Drainage Area

6133 sf

1919 sf

754 sf

615 sf

2815 sf

6103 sf

Parking Lot

Sidewalk

<50% Grass HSG C

Woods, Good HSG C

L Street

?Question

How do structural soils work?

Trees Need to Access Soil to a Depth of 3 Feet Minimum

Photo Source: gratefulmommy.com

Trees Need Adequate Soil Volume to Grow

Graph Source: USDA Forest Service Center for Urban Forest ResearchSlide courtesy of Todd Prager ,Todd Prager & Associates

33326720013367Soil Area Needed Assuming a 3ft min depth (ft2)

Structural Soil Composition

Source: Cornell University – CU Structural Soil - http://www.hort.cornell.edu

Structural stability (similar to porous pavement aggregate):

Tree health:

?Question

• What is different about structural soils than regular construction practices and soils in sidewalk/planter strip applications?

If you have lots of money…

• Structural soils are designed to be on compacted subgrade and compacted to the standard 95% modified proctor density.

• Requires a depth of structural soil = 3 feet, for tree health.

?If you want to save lots of money

on structural soil…

Careful compaction to hit the “Goldilocks” zone:• Not so much that tree roots can’t grow into it• Not so little that vehicular or pedestrian traffic cannot be

supported• = 85% to 90% Modified Proctor Density

Additional Benefit for Tree Health

• Shallow depths of structural soil = little or (more likely) no fertilization

Assembly Procedure

Assembly Procedure

Assembly Procedure

Assembly Procedure

Assembly Procedure

Assembly Procedure

Assembly Procedure

?Are there studies or examples showing the

benefits?

• Been around since the 1990s• Bend, OR

Olympia Results… After 8 Years

Control Trees Planted in Compacted Native Soil

Trees Planted in Structural Soil

4 minute video from Cornell Horticulture(developed CU Structural Soil)

• “Excavation of tree growing in CU-structural soil”

Palo Alto, CA is hooked

Jan 29, 2004 presentation by Dave Dockter, Managing Arborist , Planning Division

From Dave Dockter’s Presentation

From Dave Dockter’s Presentation

?Question

• What are the implementation issues for using structural soils? Design, availability of materials, construction, inspection, etc. How are each of these addressed in a project?

Materials are Commonly Available

• Rock• Clay• Optional amendments (Our mix included mycorrhizae,

biota, biochar, Stabilizer = hydrogel and moisture holding element)

• Hydrogel

Design: You must answer, “Where will the structural soil be used?”

Pedestrian areas only:• Sand Based Structural Soil (SBSS, aka Amsterdam Tree Soil,

Tree Sand)Pedestrian and vehicular areas:• CU Structural Soil (proprietary from NY)• Carolina Stalite Structural Soil• Olympia Soil Mix• Sunmark Environmental Mix (proprietary from Troutdale)

Choosing Adequate Depth for Structural Stability

• Our geotechnical engineer determined an appropriate pavement depth based on:

Geotechnical engineering report excerpt

• For structural soil placed on a wet, uncompacted (clayey) subgrade! (Saved us 1 foot of depth of structural soil. Over the 125 lf of trench, cost savings = $3600.)

Consider using more than just structural soil

Amended native soil in places where structure isn’t needed (see next slide) gets the trees off to a

good start

Tree planted in amended native soil

What are the implementation issues for using structural soils? Construction observation

• Moisture• Compaction• Depth of lifts• Final depth

?Question

• What are the vendors/sources of structural soils? What different materials and designs are available? How do they range in cost?

Vendors & Costs

• Sunmark Environmental,$105/cy delivered • Olympia DIY, $24/cy (delivered?)

Mixing Structural Soil

Photo Source: www.greelysand.com/cu-soil.html

Olympia Soil Recipe

4 cubic yards Crushed Rock ¾”-1¼” + 1 cubic yard Loam/organic topsoil + 1 pound Soil Binder “Stabilizer” + 46 gallons water__________Makes 4.6 cubic yards Structural Soil

Structural Soil Costs - Olympia

“The price to supply, deliver and install the structural soil material per cubic

yard ranged from $19 to $85 with an average bid of $42, the median price

was $39.50.

The city paid $24 per cubic yard for the structural soil material to the low

bidder.

This compare to a price quote we received for the supply of CU structural

soil at $65 per cubic yard plus delivery. The source was over an hour’s drive

away and delivery charges were $85 per hr with a truck and trailer hauling 22

cubic yard. The expected cost delivered was $72 per cubic yard.”

Excerpted from “Structural Soil Demonstration Project”

http://olympiawa.gov/~/media/Files/CPD/Urban%20Forestry/Forms/StructuralSoil.ash

x

Source: City of Olympia -Structural Soil Demonstration Project

Vendors & Costs

• Olympia DIY soil mix, $42/cy delivered• Sunmark Environmental, $105/cy delivered • CU Structural Soil (coming soon), national average

$58.25/cy (not delivered)

?Question

• How can the stability of the adjacent road subgrade and curb be protected during the installation of structural soils?

Protecting Existing Infrastructure

• Trees don’t seem to really care where the soil is, as long as they can get their roots to them.

Protecting infrastructure

• Gresham staff idea: In retrofits, could set structural soil back from the curb.

?Question

• What different materials and designs are available?

A Second Way of Providing Tree Roots with Adequate Soil Volume Under

Pavement

. Photo courtesy of Jim Labbe

Another Way of Providing Tree Roots with Adequate Soil Volume Under Pavement

A Second Way of Providing Tree Roots with Adequate Soil Volume Under

Pavement

. Photo courtesy of Jim Labbe

A Second Way of Providing Tree Roots with Adequate Soil Volume Under

PavementJim Labbe in Nijmegen Netherlands. Photo courtesy of Jim Labbe

A Third Way of Providing Tree Roots with Adequate Soil Volume Under Pavement

Photo probably ripped off the Silva Cell website by Brian Wegener

?Question

• How much more does it cost to construct a planter strip and sidewalk using structural soils vs. traditional methods? Consider design, excavation, materials, installation, and other issues for a 100’ section of sidewalk (replacing existing curbtight sidewalk with 4’ planter strip and new sidewalk). Are there economies of scale we can expect for larger projects?

SE 182nd Avenue

Retrofit

New Development

Economies of Scale

• Economies of scale are available in:• Engineering design• Geotechnical investigation• Mobilization• Structural soil testing

According to Brian Kalterof Amereq, Inc (Licenses CU Structural Soil)

• Email dated 4/4/14:“As far as installation costs, CU-Soil™ should not cost more to install on a per cubic yard basis than a typical base material since it is installed in 6” lifts and compacted to 95% Proctor Density.”

• …except it’s usually required to be installed to a depth of 3 feet!

?Question

• Are there standard or typical details, cross-sections, and specs available for constructing a planter strip and sidewalk using structural soils that we could review?

?Specs & Designs to review

• I’ve consolidated everything I could find, plus my own details and specs, here: http://www.parkingforest.org/specs.htm

Thank You!

Sustainability for all the places between the buildings

503.334.8634www.greengirlpdx.com

greengirl@greengirlpdx.coma certified women business enterprise