Permeable Aggregate Materials and Filter Fabrics

PER CALTRANS SECTION 68-1.025
By Don Barrett

PERMEABLE AGGREGATE MATERIALS AND FILTER FABRICS
Permeable materials for use in backfilling of trenches, under, around , and over underdrains, shall consist of hard, durable, clean sand, gravel or crushed stone, and shall be free from organic material, clay balls, or other deleterious substances.

The class or kind of Permeable Material to be used will be specified in the special provisions. Class 1 and Class 2 Permeable Material shall conform to the requirements of the special provisions. Class 3 permeable material shall conform the requirements in the special provisions. When permeable material is required and the class or kind is not specified, Class 1 permeable material shall be used.

The alternative gradings within Class 1 permeable material are identified by types. The Contractor will be permitted to furnish and place any one of the types provided for this class.

The percentage composition by weight of permeable material in place shall conform to the following gradings:

GRANITEROCK PRODUCTS MEETING CALTRANS PERMEABLE SPECIFICATIONS

  • Class 1 Type A Permeable is available at the A.R. Wilson Quarry in Aromas.
  • Class 1 Type B Permeable is also available at the A.R. Wilson Quarry in Aromas.
  • Class 2 Permeable is available at Southside Sand in Hollister.

FILTER FABRICS OR ENGINEERING FABRICS PER CALTRANS SPECIFICATIONS
Filter fabric is installed as directed in the engineer’s plans; a typical installation would be as follows.

  • Excavate the trench, taking care to remove excess loose material and avoid sharp objects that might tear or damage the filter fabric.
  • Place the listed type of filter in the excavated trench.
  • Install the required pipe.
  • Backfill with the proper Permeable Material as per project specifications.

FILTER FABRICS OR ENGINEERING FABRICS

The following fabrics are listed per Caltrans Section 88

  1. Pavement Reinforcing Fabric, used as required in Asphaltic Concrete Paving
  2. Filter Fabric, used in trench under drains
  3. Rock Slope Protection Fabric, used in slope stabilization projects (see Technical Note on Rock Slope Protection / Rip Rap)

When required by the Project Engineer, a Certificate of Compliance for each type of fabric being used should be issued by the supplier and furnished to the Engineer.

Please call the Sales Office for pricing and scheduling information office 831.768.2380, Fax 831.768.2401 or e-mailDon Barrett.

Class 1 Percentage Passing

Sieve Sizes Type A Type B
2 100
1 95-100
¾ 100 50-100
½ 95-100
3⁄8 70-100 15-55
No. 4 0-55 0-25
No. 8 0-10 0-5
No. 200 0-3 0-3

Class 2 Percentage Passing

Sieve Sizes Percentage Passing
1 100
¾ 90-100
3⁄8 40-100
No. 4 25-40
No. 8 18-33
No. 30 5-15
No. 50 0-7
No. 200 0-3