Crane Barnes EcoTRAN, Installation & Operation Manual

Page: 19 / 35

19
STEP 12: BACKFILLING
When backfilling around the basin, care should be taken to prevent damage to the installed components. It is
imperative that proper backfill materials and methods be used to prevent leaks, cracks and failures. Listed below
are materials approved for backfill per the ASTM D 2321 specification.
Any other material used will void warranty!
Angular Aggregate, Open Grade, Class IA Materials - Class IA materials provide maximum stability and support
for a given density due to angular interlock of particles. With minimum effort these materials can be installed at
relatively high densities over a wide range of moisture contents. In addition, the high permeability of Class IA
materials may aid in the control of water, and these materials are often desirable for embedment in rock cuts where
water is frequently encountered. However, when ground water flow is anticipated, consideration should be given to
the potential for migration of fines from adjacent materials into the open-graded Class IA materials. Examples of
material types:
Angular, crushed stone or rock, crushed gravel, broken coral; contain little or no fines.
Aggregates, Dense Grade, Class IB Materials - Class IB materials are processed by mixing Class IA and sands
to produce a particle size distribution that minimizes migration from adjacent materials that contain fines. They are
more densely graded than Class IA materials and thus require more compactive effort to achieve the minimum
density specified. When properly compacted, Class IB materials offer high stiffness and strength and, depending
on the amount of fines, may be relatively free draining. Examples of material types: Angular, crushed stone (or
other Class 1A materials) and stone/sand mixtures with gradations selected to minimize migration of adjacent soils;
contain little or no fines.
Gravel and Soils, Class II Materials -
Class II materials, when compacted, provide a relatively high level of pipe
support. In most respects, they have all the desirable characteristics of Class IB materials when densely graded.
However, open graded groups may allow migration and the sizes should be checked for compatibility with adjacent
material. Typically, Class II materials consist of rounded particles and are less stable than angular materials unless
they are confined and compacted. Examples of material types: Graded gravels and gravel-sand mixtures with
less than 5 % fines; Sands and gravels, which are borderline between clean and with fines varying from 5 to 12 %.
These materials are usually contained with a fabric or other type of liner to provide proper support.
Backfill materials must be free of lumps, clods, boulders, frozen matter, and debris. The presence of such material
in the backfill material may prevent uniform compaction and result in cracks, fractures, or deflections.
FINAL GRADING
The final grade should slope away from the basin to avoid collecting ground water around the station. Your final
grade should be approximately 2” below the top of the basin flange. Any height taller than this may allow freezing to
develop inside the station if not properly insulated. The top of the basin should never be below grade. This will allow
ground water and sediment to infiltrate into the basin. See illustration below.