Section 816.75. Disposal of excess spoil; zoned concept

The disposal of spoil under the zoned concept shall meet the requirements of 4VAC25-130-816.71 and the additional requirements of this section.

(a) The fill and appurtenant structures shall be designed using current, prudent engineering practices, and certified by a qualified registered professional engineer experienced in the design of earth and rockfill embankments.

(b) The fill shall be designed to attain a long-term minimum safety factor of 1.5 under static loading conditions and 1.1 under earthquake loading conditions.

(c) All vegetative and organic materials and topsoil in the structural and nonstructural zones shall be removed from the disposal area prior to placement of excess spoil. Topsoil shall be removed, segregated and stored or redistributed in accordance with 4VAC25-130-816.22. If approved by the division, organic material may be used as mulch or may be included in the topsoil to control erosion, promote growth of vegetation, or increase the moisture retention of the soil.

(d) Excess spoil shall be transported and placed in a specified controlled manner as follows:

(1) Structural zone. In the structural zone, spoil shall be placed in horizontal lifts and compacted to densities and strengths required to ensure mass stability and prevent mass movement. The lift thickness and gradational requirements of the spoil shall be consistent with the design parameters. The extent of this zone shall be based on accepted engineering analyses.

(2) Nonstructural zone. In the nonstructural zone, the spoil shall be placed in a controlled manner to avoid contamination of the internal drainage system and to ensure mass stability and prevent mass movement, to provide for the safety of persons on or near the fill, and to provide mass stability and prevent mass movement during construction. The extent of this zone shall be determined by accepted engineering analyses.

The temporary outside slope of the nonstructural zone shall not exceed the angle of repose and the height of the nonstructural zone shall be limited to a height determined not to pose an actual or probable hazard to property, public health and safety, or the environment in the event of failure during construction.

(3) The structural zone and the nonstructural zone shall be constructed as concurrently as practicable and the distance between the structural zone and the nonstructural zone shall be minimized to assure proper stability and control of the temporary fill slope.

(e) In addition to the inspection requirements of 4VAC25-130-816.71(h), regular inspections by the engineer or specialist shall be conducted during placement and compaction of fill materials in both the structural and non-structural zones.

(f) The design of the fill shall include an internal drainage system which will ensure continued free drainage of anticipated seepage from precipitation and from springs or wet weather seeps.

(1) Anticipated discharge from springs and seeps and due to precipitation shall be based on records and/or field investigations to determine seasonal variation. The design of the internal drainage system shall be based on the maximum anticipated discharge.

(2) Underdrains constructed of granular material shall consist of durable, nonacid-, nontoxic-forming material such as natural sand and gravel, sandstone, or other durable rock that does not slake in water or degrade to soil material, and which is free of coal, clay, shale, or other nondurable material.

(3) A filter system shall be included to insure proper functioning of the underdrain system. This filter shall be designed and constructed using current geotechnical engineering methods.

(4) In constructing the underdrains, no more than 10 percent of the rock shall be less than 12 inches in size and no single rock may be larger than 25 percent of the width of the drain.

(5) The drain size shall be designed to safely route the anticipated seepage flows. Minimum drain sizes shall be six feet wide and two feet high.

(6) Prior to placing the underdrain materials, all vegetation and topsoil shall be removed.

(7) The internal drainage system shall be designed to assure that the phreatic surface within the structural zone is controlled.

(8) The internal drainage system shall be designed to prevent channeling of surface runoff through the underdrains.

(g) Surface water runoff from the area above the fill shall be diverted away from the fill and into stabilized diversion channels designed to pass safely the runoff from a 100-year, 6-hour precipitation event or larger event specified by the division. Runoff from the fill surface shall be diverted to stabilized channels which will safely pass the runoff from a 100-year, 6-hour precipitation event. Diversion design shall comply with the requirements of 4VAC25-130-816.43. Temporary diversions may be approved by the division for use during fill construction, provided that erosion is minimized and no threat to the public or the environment results.

(h) The top surface of the fill and any terrace constructed shall be graded such that the final slope after settlement shall be toward properly designed drainage channels. The maximum slope of the top of the fill shall be 20h:1v (5 percent). The vertical distance between terraces shall not exceed 50 feet.

(i) Drainage shall not be directed over the outslope of the fill unless it is in a channel properly designed to minimize infiltration into the fill and to safely pass the runoff from a 100-year, 6-hour precipitation event or larger event specified by the division.

(j) The outslope of the completed fill shall not exceed an overall slope of 1v:2h. The division may require a flatter slope.

Historical Notes

Derived from VR480-03-19 § 816.75, eff. December 15, 1981; amended, eff. June 28, 1982; October 28, 1982; December 14, 1982; October 11, 1983; December 27, 1983; May 8, 1984; June 22, 1984; August 2, 1984; October 16, 1985; January 7, 1987; July 22, 1987; November 25, 1987; October 12, 1988; December 26, 1990; July 1, 1991; July 17, 1991; November 20, 1991; July 7, 1992; May 5, 1993; October 19, 1994.

Statutory Authority

§§ 45.1-161.3 and 45.1-230 of the Code of Virginia.