16 Tex. Admin. Code § 12.534 - Disposal of Underground Development Waste and Excess Spoil: Durable Rock Fills
(a) In lieu of the
requirements of §
12.532 and §
12.533 of this title (relating to
Disposal of Underground Development Waste and Excess Spoil: Valley Fills, and
to Disposal of Underground Development Waste and Excess Spoil: Head-of-Hollow
Fills), the Commission may approve alternate methods for disposal of hard rock
spoil, including fill placement by dumping in a single lift, on a site-specific
basis, provided the services of a qualified professional engineer experienced
in the design and construction of earth and rockfill embankments are utilized,
and provided the requirements of this section and §
12.531 of this title (relating to
Disposal of Underground Development Waste and Excess Spoil: General
Requirements) are met. For this section, hard rock spoil shall be defined as
rockfill consisting of at least 80% by volume of sandstone, limestone, or other
rocks that do not slake in water. Resistance of the hard rock waste or spoil to
slaking shall be determined by using the slake index and slake durability tests
in accordance with guidelines and criteria established by the
Commission.
(b) Waste or spoil is
to be transported and placed in a specified and controlled manner which will
ensure stability of the fill.
(1) The method
of waste spoil placement shall be designed to ensure mass stability and prevent
mass movement in accordance with the additional requirements of this
section.
(2) Loads of noncemented
clay shale and/or clay spoil in the fill shall be mixed with hard rock waste
spoil in a controlled manner to limit, on a unit basis, concentrations of
noncemented clay shale and clay in the fill. Such materials will comprise no
more than 20% of the fill volume as determined by tests performed by a
qualified professional engineer and approved by the
Commission.
(c)
Requirements for design of earth and rockfill embankments shall include the
following:
(1) stability analyses shall be
made by the qualified professional engineer. Parameters used in the stability
analyses shall be based on adequate field reconnaissance, subsurface
investigations including borings, and laboratory tests; and
(2) the embankment which constitutes the
valley fill or head-of-hollow fill shall be designed with the following factors
of safety:
(d) The design of a head-of-hollow 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) 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.
(3) The
internal drain shall be protected by a properly designed filter
system.
(e) 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 safely pass the runoff from a 100-year, 24-hour precipitation
event. Diversion design shall comply with the requirements of §
12.511(6) of
this title (relating to Hydrologic Balance: Diversions).
(f) The top surface of the completed fill
shall be graded such that the final slope after settlement will be no steeper
than 20h:1v (5%) 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.
(g) Surface runoff from the outslope of the
fill shall be diverted off the fill to properly designed channels which will
safely pass a 100-year, 24-hour precipitation event. Diversion design shall
comply with the requirements of §
12.511(6) of
this title (relating to Hydrologic Balance: Diversions).
(h) Terraces shall be constructed on the
outslope if required for control of erosion or for roads included in the
approved postmining land-use plan. Terraces shall meet the following
requirements:
(1) the slope of the outslope
between terrace benches shall not exceed 2h:1v (50%);
(2) to control surface runoff, each terrace
bench shall be graded to a slope of 20h:1v (5%) toward the embankment. Runoff
shall be collected by a ditch along the intersection of each terrace bench and
the outslope; and
(3) terrace
ditches shall have a 5% slope toward the channels specified in subsection (g)
of this section, unless steeper slopes are necessary in conjunction with
approved roads.
Notes
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