16 Tex. Admin. Code § 12.366 - Disposal of Excess Spoil: Durable Rock Fills
(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:
(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.
Notes
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