Current through Register Vol. 50, No. 9, September 20, 2024
A. In lieu of the requirements of
§5367 and 5369, the office may approve
alternate methods for disposal of hard rock spoil, including fill placement of
dumping in a single lift, on a site specific basis, provided the services of a
registered professional engineer experienced in the design and construction of
earth and rockfill embankments are utilized and provided the requirements of
this Section and
§5365 are met. For this Section, hard
rock spoil shall be defined as rockfill consisting of at least 80 percent by
volume of durable, non-acid- and non-toxic-forming rock (e.g., sandstone or
limestone) that does not slake in water and will not degrade to soil material.
Resistance of the hard rock spoil to slaking shall be determined by using the
slake index and slake durability tests in accordance with guidelines and
criteria established by the office.
1. Spoil
is to be transported and placed in a specified and controlled manner which will
ensure stability of the fill.
a. The method
of spoil placement shall be designed to ensure mass stability and prevent mass
movement in accordance with the additional requirements of this
Section.
b. Loads of noncemented
clay shale and/or clay spoil in the fill shall be mixed with hard rock spoil in
a controlled manner to limit on a unit basis concentrations of noncemented clay
shale and clay in the fill. Such materials shall comprise no more than 20
percent of the fill volume as determined by tests performed by a registered
engineer and approved by the office.
2.
a.
Stability analyses shall be made by the registered professional engineer.
Parameters used in the stability analyses shall be based on adequate field
reconnaissance, subsurface investigations, including borings, and laboratory
tests.
b. The embankment which
constitutes the valley fill or head-of-hollow fill shall be designed with the
following factors of safety.
|
Case
|
Design Condition
|
Minimum Factor of Safety
|
|
I
|
End of Construction
|
1.5
|
|
II
|
Earthquake
|
1.1
|
3. The design of a head-of-hollow fill shall
include an internal drainage system which will insure continued free drainage
of anticipated seepage from precipitation and from springs or wet weather
seeps.
a. 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.
b. All granular material used for the
drainage system shall be free of clay and consist of durable particles such as
natural sands and gravels, sandstone, limestone, or other durable rock which
will not slake in water.
c. The
internal drain shall be protected by a properly designed filter
system.
4. Surface water
runoff from the areas adjacent to and above the fill shall not be allowed to
flow onto the fill and shall be diverted into stabilized channels which are
designed to pass safely the runoff from a 100-year, 6-hour precipitation event.
Diversion design shall comply with the requirements of §5323
5. The top surface of the completed fill
shall be graded such that the final slope after settlement will be no steeper
than 1v:20h (5 percent) toward properly designed drainage channels in natural
ground along the periphery of the fill. Surface runoff from the top surface of
the fill shall not be allowed to flow over the outslope of the fill.
6. Surface runoff from the outslope of the
fill shall be diverted off the fill to properly designed channels which will
pass safely a 100-year, 6-hour precipitation event. Diversion design shall
comply with the requirements of §5323
7. Terraces shall be constructed on the
outslope if required for control of erosion or for roads included in the
approved post-mining land use plan. Terraces shall meet the following
requirements.
a. The slope of the outslope
between terrace benches shall not exceed 1v:2h (50 percent).
b. To control surface runoff, each terrace
bench shall be graded to a slope of 1v:20h (5 percent) toward the embankment.
Runoff shall be collected by a ditch along the intersection of each terrace
bench and the outslope.
c. Terrace
ditches shall have a five percent slope toward the channel specified in
§5371. A 6, unless
steeper slopes are necessary in conjunction with approved roads.
AUTHORITY NOTE:
Promulgated in accordance with
R.S.
30:901-932.
