Florida Administrative Code › 62 - DEPARTMENT OF ENVIRONMENTAL PROTECTION › 62 - Departmental › Chapter 62-672 - MINIMUM REQUIREMENTS FOR EARTHEN DAMS USED IN PHOSPHATE MINING AND BENEFICIATION OPERATIONS AND FOR DIKES USED IN PHOSPHOGYPSUM STACK SYSTEM IMPOUNDMENTS › Section 62-672.300 - Construction of New Dams

Current through Reg. 50, No. 138; July 16, 2024
(1) Design.
(a) Site investigation - The general area
				desired for use as a settling area shall be carefully inspected by the design
				engineer prior to selection of the exact location for a dam. Areas of uneven
				natural subsidence, sink-hole, pockets of organic matter, or other unstable
				soils shall be avoided, unless special provisions are made for their
				correction.
(b) Soil testing - A
				program of soil sampling and testing adequate to determine the characteristics
				of the foundation material which will support the proposed dam and of the
				material to be used for construction of the dam shall be performed. Sampling
				shall include borings or in-place samples from the exposed excavation face. All
				borings shall be logged using a recognized engineering soil classification
				system, (such as Unified System) with location and depths of all samples
				recorded on the log. Tests such as the determination of in-place densities,
				shear-strength; and permeabilities of the foundation and embankment soils shall
				be performed. Tests on foundation soils shall be performed on either
				undisturbed samples or on the in-place soil. Tests on embankment soils shall be
				performed on samples remolded to the densities to be used in
				construction.
(c) Cross Section
				design - There shall be a minimum freeboard of five feet (5') below the inside
				crest. The outside crest of the top of the dam shall be higher than the inside
				crest in order to force all crest drainage to the inside of the dam. Both
				inside and outside slopes shall be no steeper than two horizontal to one
				vertical. The design shall provide positive seepage control features, such as:
1. Cut-off trench in natural soil
				foundations.
2. Clay
				core.
3. Blanket drain.
4. Chimney drain and toe drain.
The top of the dam shall include a roadway which will permit
				  wheeled vehicle traffic at all times. The design shall also incorporate an
				  all-weather roadway near the downstream toe which will permit wheeled vehicle
				  traffic around the perimeter of the dam for purposes of inspection of the
				  slope, toe and natural ground beyond the toe, as well as
				  maintenance.
(d)
				Stability analysis - A flow net analysis shall be made to determine the
				location of the phreatic surface, flow lines, and lines of equal head within
				the foundation and fill being designed. This analysis may be based on graphical
				construction, electrical or liquid analogs, soil prototype methods, or other
				accepted methods. The flow net and stability analysis shall use the maximum
				pool elevation with not less than five feet (5') of clear water, this elevation
				being five feet (5') below the inside crest of the dam. Possible fluctuations
				of the tail water level shall be included in the analyses.
(e) Design safety factors - The designing
				engineer shall use the following minimum safety factors: 1.75 for horizontal
				shear at base of fill; 1.5 for horizontal shear within the fill due to seepage
				through the outer face; 1.5 for bearing capacity of foundation soils; 1.5 for
				protection against shear failure of any circular arc in either inside or
				outside slope. It is imperative that water pressure distribution be included in
				the analyses.
(f) If a cast dam is
				to be constructed where adequate site preparation, as defined in subsection
				 62-672.300(2),
				F.A.C., below, has not been accomplished; or where the fill materials do not
				meet the requirements of subsection
				 62-672.300(3),
				F.A.C., below; then the design shall incorporate either of the following
				alternatives:
1. A portion of the material
				which forms the downstream slope shall be removed and the foundation thus
				exposed shall be prepared in the same manner as is prescribed herein for a
				rolled dam. Fill material shall then be placed as a rolled embankment which
				shall be of such design that the safety factor with respect to downstream
				movement of the rolled section shall be no less than 1.2 when assuming that the
				remaining cast material below the phreatic surface has become liquid.
2. Sand tailings shall be placed against the
				downstream slope to the extent that the wedge so formed shall have a safety
				factor with respect to downstream movement of no less than 1.2 when assuming
				that the cast material below the phreatic surface has become
				liquid.
(g) When the
				foundation for a cast dam meets the requirements of subsection
				 62-672.300(2),
				F.A.C., and the materials used for the fill meet the requirements of subsection
				 62-672.300(3),
				F.A.C., then the dam shall be designed in accordance with paragraphs
				 62-672.300(1)(a), (b), (c), (d) and
				(e), F.A.C.; except that the computations of
				all required safety factors shall be based on only seventy-five percent (75%)
				of the indicated strengths of the cast materials which are tested at the same
				density as will exist within the dam.