| (a) In lieu of the requirements of §§12.364
and 12.365 of this title (relating to Disposal of Excess Spoil: Valley
Fills, and to Disposal of Excess Spoil: Head-of-Hollow Fills), the
Commission 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 qualified professional
engineer experienced in the design and construction of earth and rockfill
embankments are utilized and provided the requirements of this section
and §12.363 of this title (relating to Disposal of 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 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) Spoil is to be transported and placed in a specified
and controlled manner which will ensure stability of the fill.
(1) 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.
(2) 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%
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:
Attached Graphic
(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 pass
safely the runoff from a 100-year, 24-hour precipitation event. Diversion
design shall comply with the requirements of §12.341(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
pass safely a 100-year, 24-hour precipitation event. Diversion design
shall comply with the requirements of §12.341(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 (5.0%) 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 5.0% slope toward
the channels specified in subsection (g) of this section, unless steeper
slopes are necessary in conjunction with approved roads.
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| Source Note: The provisions of this §12.366 adopted to be effective April 7, 1997, 22 TexReg 3093; amended to be effective November 4, 1997, 22 TexReg 10640; amended to be effective December 28, 2020, 45 TexReg 9503 |
