CU-Structural Tree Soil -Specifications

In this section you will find detailed descriptions, technical details, images etc. relating to all our products. Please contact us with any queries you might have.

The Unique Benefits of using CU-Soil:

Tree Growth & Survival, CU-Soil installed in an appropriately sized rootzone space, gives the tree a significantly improved chance of long term survival and of being a benefit to its surroundings and the local environment.

Reduced Tree Root damage to pavements. CU-Soil has been shown to promote the downward growth of tree roots – reducing cracked & damaged pavements surfaces and thereby, the consequential liability claims.

CU-Soil is SUDS compliant and the installation of a large CU-Soil rootzone space can, along with providing a healthy space for tree growth, it can act as an attenuation space that can help to meet the SUDS obligations for the development.

Simplified Groundworks – CU-Soil is quick and easy to install. Installation is similar installation as any soil or rootzone material – just install the CU-Soil in 150mm “lifis” and compact each layer.

Environmentally friendly – No underground plastic structures to be installed.
CU-Soil is reusable and can be excavated and re-used – without destroying the usefulness of the material.

A quick and easy way to install a stable, load bearing base material that is suitable for construction of access roads, car parks and footpaths and is suitable for all types of surfacing options, block paving, asphalt, and geo-grids with stone fill.

Tree Anchoring systems – CU-Soil forms the ideal consolidated rootzone material which makes it ideal for use with the most commonly specified rootball fixing systems.

Underground Services – pipes and ducts – CU-Soil is safe to use and is the ideal material for use as a back-fill material when service ducts are installed adjacent to the tree pit.

CU-Soil allows for total flexibility and facilitates the installation of a healthy rootzone growing medium in even the most restricted and irregular shaped urban spaces.
Ecobound Ecogrid Tree Pit Surfacing: CU-Soil provides the ideal load bearing and stable foundation for the installation of Rein bound stone surfacing, such as the Ecobound Ecogrid surfacing system, it has structurally stability equal to standard ‘Type 1’ aggregates used for sub-base construction.


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CU-Soil – Satisfies the Engineer’s Structural Requirements

CU Structural Soil satisfies the Engineering structural need for the planting area by supporting the paved surfaces. Cu-Soil– which is composed of 20-36mm (3/4” – 1½”) crushed angular stone that is coated with a loamy soil so that when the material is compacted the stones still touch one another which gives the material it’s strength.

This maintains stone-to-stone contact even though the soil component is suspended within the void space between the stones. This void space allows for a much higher degree of air and water flow throughout the soil.

Satisfying the Horticultural – Root systems requirements

The void space mentioned above allows for a much higher degree of air and water flow throughout the soil providing a much higher level of nutrients and moisture to the roots. This also allows the roots to grow in a downward and horizontal direction, whereas in a traditional tree planting the roots follow the path of least resistance, which unfortunately, is always vertical, causing very destructive upheaval of the paved surface.

  • It will also promote biodiversity, and provides a long term habitat for plants and animals and insects, such as butterflies.
  • Green roofs help combat the effect of pollution.
  • A Green Roof can help to reduce flood risk by absorbing rainfall, and reducing run-off,an important issue in an urban landscape.
  • In an urban setting, a Green Roof, can reduce the ‘urban heat island effect’.
  • A Green Roof serves to eliminate fine dust and pollutants, produces oxygen, and improves the visual and climatic quality of the environment.


1. Install CU-Structural Soil® in 150mm (6”) lifts and compact each lift.

2. Compact all materials to at least 95% Proctor Density from a standard compaction curve AASHTO T 99 (ASTM D 698). No compaction shall occur when moisture content exceeds maximum as listed herein. Delay compaction if moisture content exceeds maximum allowable and protect CU-Structural Soil® during delays in compaction with plastic or plywood as directed by the engineer.
3. Bring CU-Structural Soil® to finished grades as shown on the drawings. Immediately protect the CU-Structural Soil® from contamination by toxic materials, trash, debris, water containing cement, clay, silt or materials that will alter the particle size distribution of the mix with
PRIOR TO THE INSTALLATION OF CU-Structural Soil® – Site Preparation

  • Install subsurface drain lines as shown on the plan drawings prior to installation of CU-Structural Soil® material.
  • Excavate and compact the proposed subgrade to depths, slopes and widths as shown on the drawings. Maintain all required angles of repose of the adjacent materials as shown on the drawings. Do not over excavate compacted subgrades of adjacent pavement or structures.
  • Confirm that the subgrade is at the proper elevation and compacted as required. Subgrade elevations shall slope parallel to the finished grade and/or toward the subsurface drain lines as shown on the drawings.
  • Clear the excavation of all construction debris, trash, rubble and any foreign material. In the event that fuels, oils, concrete washout silts or other material harmful to plants have been spilled into the subgrade material, excavate the soil sufficiently to remove the harmful material. Fill any over excavation with approved fill and compact to the required subgrade compaction.
  • Do not proceed with the installation of CU-Structural Soil® until all utility work in the area has been installed. All subsurface drainage systems shall be operational prior to installation of CU-Structural Soil®.
  • Protect adjacent walls, walks and utilities from damage. Use ½” plywood and/or plastic sheeting as directed to cover existing concrete, metal and masonry work and other items as directed during the progress of the work. Clean up all trash and any soil or dirt spilled on any paved surface at the end of each working day.

CU-Soil Installation – Underground Structure Drainage Layer Specification

CU-Structural Soil Installation – as the tree rooting substrate and drainage back-fill over an underground (basement) structure.

Cu-Soil with its unique open structure of macro-pores which facilitates both tree root growth and also allow for rapid drainage of excess moisture, is proving to be the material of choice as the back-fill material for a number of basement construction projects on confined city sites.

Sample Specification / Recommendation for Drainage layer installation over a concrete structure.

On to the top of the finished concrete structure onto which the finished waterproofing membrane has been installed. (Installed by others) – Installation of drainage layer is as follows:

1. ND WSB-80 Root Barrier – required only if the waterproofing membrane is not root resistant. Material is supplied in rolls.

2. ND TSF-100 Slip and Protection Sheet – this is 1mm thick modified HDPE sheet which is installed directly on top of the waterproofing membrane. The function of this sheet is to protect the waterproofing membrane against mechanical damage especially during installation and to prevent the ND Drainage System from adhering to the waterproofing membrane. Material is delivered in rolls and is loose laid directly on top of the root resistant waterproofing membrane, if fitted, otherwise directly onto the waterproofing membrane.

3. ND 620 Drainage System – this is a special drainage system with a high compressive strength (> 900kPa) which is fitted with a special mono-filament woven geotextile. The geotextile has very good puncture resistance and little elongation. The function of the product is for both drainage and protection of the underlying waterproof membrane. The material has a pressure dividing slip film glued to the back of the dimples. This assures a smooth movement of the drainage system over the ND TSF-100 Slip and Protection Sheet. The ND 620 Drainage Composite is delivered in rolls and has a geotextile overlap on both edges and is therefore easy to install.

The above sample specification is for materials as supplied by Nophadrain, there are a number of similar products, of similar specification and quality from other suppliers that could also be used for this application.

For queries and for further technical information please contact our Product Support Department, contact details as below.

A. Delivered CU-Structural Soil® shall be at or near optimum compaction moisture content as determined by AASHTO T 99 (ASTM D 698) and should not be placed in frozen, wet or muddy sites.

B. Protect CU-Structural Soil® from exposure to excess water and from erosion at all times. Do not store CU-Soil™ unprotected. Do not allow excess water to enter site prior to compaction. If water is introduced into the CU-Soil™ after grading, allow water to drain to optimum compaction moisture content.

CU-Soil™ should not be stockpiled long-term. Any CU-Soil™ not installed immediately should be protected by a tarp or other waterproof covering.

CU-Structural Tree Soil has an interesting application where it can be installed as a dual function option, to provide a healthy, load-bearing rooting medium for urban tree planting, as well as a rainwater attenuation system to help comply with SuDS obligations for an urban development project.

CU-Structural Tree Soil has been developed and extensively tested by Cornell University over the past twenty years, to develop a structural tree rooting medium that can be compacted to meet both Engineer’s load bearing standards for the construction of the sub-base for paved surfaces, access roads, car parks etc, and to also meet the qualities that will allow tree roots to grow freely beneath paved area, thereby providing an environment for the healthy growth of the tree as well as greatly reducing the likelihood of heaving or cracking caused by the tree roots.

Rain water attenuation with a Porous Surface
Rain water attenuation – SuDS

CU-Soils water reservoir capabilities

CU-Soil also allows for the opportunity to develop a storm water reservoir, with up to 40% macro-pore spaces within the material, the attenuation area can be sized to accommodate the rainfall run-off of even a 50 year rain fall event. When used in conjunction with a porous surface material CU-Soil is particularly effective for reducing the burden on current urban storm water facilities. CU-Soil can be an important element in helping to meet SuDS requirements in an urban development.

Depth of Reservoir Needed to Mitigate Rain Event

Benefits of CU-Structural Tree Soil

  • Satisfies the Engineer’s Structural Requirements
  • An engineered structural base for paved surfaces
  • Supports paved surfaces
  • High degree of air and water flow
  • Satisfies the Horticultural – Root systems requirements
  • Higher level of nutrients and moisture to the roots
  • Promotes downward growth & development of roots
  • Meets SuDS requirements
  • Can be utilised as a storm water reservoir


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