Current through Register Vol. XLI, No. 37, September 13, 2024
Section 38-4-11 - Structural Considerations11.1. All structures shall be designed to perform as intended for the design life of the dam with proper maintenance or replacement.11.1.a. Structural materials: Materials selected for use in dam construction shall be of adequate quality and durability for the intended purpose of the structure. All structures shall be designed to have sufficient strength plus an adequate safety factor against failure during maximum anticipated loading conditions.11.1.b. Earth materials: Earth materials selected for use in dam construction shall be free from roots, brush, organic materials, construction waste, and other debris. Where rock or rock fill is specified, the rock shall be durable and not subject to slaking or breaking. Size gradations of the earth materials shall be specified to perform as planned. Compaction requirements for earth materials shall be specified in the plan package.11.1.c. The application shall specify the nature of concrete to be used with sufficient detail for on-site quality control. The concrete will be of specific mix, water content, additives, compressive strength, slump, and air entrainment or by reference to specific standards of concrete quality. If published standard specifications are referenced, a copy of the standard or pertinent sections of the standard shall be included in the plan package.11.1.d. The application shall specify methods and limits of placement of concrete including foundation preparation, maximum lift height, maximum time allowed between mixing and placement, methods of working into forms and corners, methods of consolidation and use of vibratory devices, and alliable ambient air temperatures and concrete temperatures.11.1.e. The application shall specify the method of curing the concrete, wetting, types of covering acceptable curing temperature range, any anticipated cold weather curing specifications or methods such as protection from freezing and insulation methods, hot weather placement methods and curing time.11.1.f. The application shall specify the type of finishing to be applied to the concrete and the acceptable temperature range.11.2. Specific structural requirements for embankment dams: 11.2.a. Materials selected for construction of embankment dams shall be free from roots, brush, organic matter, construction waste and other debris. Where rock fill is specified the rock shall be durable and must not slake or breakdown. Unless otherwise approved by the Secretary, the selected materials must be thoroughly tested for density, shear strength, liquid and plastic limits, optimum moisture content. The source of the material and available quantities shall be identified and adequate sampling performed in order to attain consistent quality and soil characteristics.11.2.b. Where coal refuse as defined by 38CSR2 is used for construction of a dam and the dam is used to impound coal slurry waste from a coal preparation plant, such facilities shall comply with 38CSR2-22 of WV Surface Mining Reclamation Rules, Chapter 22 Article 3 of the W. Va. Code and any state or federal laws and regulations.11.2.c. Coarse coal refuse Materials: All coal refuse materials must be analyzed and tested to include soil classification, density, water content, compaction tests, shear strength and permeability. Only such parameters shall be used in the design of the facility. Procedures for spreading and compaction of refuse material during placement shall be specified. Coarse Refuse shall be compacted in layers not exceeding two(2) feet in thickness and shall not have any slope exceeding two horizontal to one vertical, except that the Secretary may approve construction of a refuse pile in compacted layers exceeding two(2) feet in thickness, where engineering data substantiates that both a minimum static factor safety factor of 1.5 and minimum seismic safety factor of 1.2 will be attained. provided, that the operator shall submit plans for the Secretary's approval, and shall also provide documentation showing prior approval by MSHA pursuant to federal regulations at 30 CFR 77.215(h) for the alternate, without which documentation the plans will not be approved.11.2.d. Instrumentation: a description of installation of instrumentation such as piezometers, settlement markers, slope indicators, extensometers and similar monitoring devices shall be included in the plan to monitor present hazardous conditions, construction conditions, and to verify design assumptions. A plan for monitoring devices shall be provided. The monitoring results shall be analyzed by a registered professional engineer.11.2.e. All upstream and downstream stages of construction shall be analyzed for liquefaction potential and provide safeguards against the development of this condition.11.3. Zoned Embankments: 11.3.a. Filter drains: Filter drains shall be used in embankment zones where necessary to intercept seepage, reduce phreatic level, and reduce potential for internal erosion.11.3.b. Gradations: The gradations of the filter material shall be sized to prevent or resist the migration of embankment material into the voids of the filter. The filter shall be permissible relative to the surrounding material.11.3.c. Size: The filter drain shall be capable of passing the maximum anticipated seepage flows without excessive pore pressure. The combination of filter permeability and area shall be considered in sizing the drain.11.3.d. Durability: The material used in the filter shall be hard, durable material that is not subject to slaking, breakdown or chemical reaction.11.3.e. Perforated pipes may be used in the filter drains to increase capacity. Perforation shall be compatible with the filter gradations so that the filter material will not enter the pipe. The pipe shall be capable of supporting the fill load and shall be of a material which will last for the design life of the structure. Corrugated metal pipes shall not be used in critical areas of the embankment or in any areas where the pipe is not reasonably accessible for replacement.11.3.f. Filter cloth if used in a drainage application must be able to retain the protected soil to prevent piping, have sufficient permeability to prevent the build-up of water pressure, not become clogged and have sufficient strength to survive construction procedures.11.3.g. Diaphragm Cut-off Walls: When concrete cut-off walls are used as an impermeable barrier, the concrete wall shall be placed upon an adequate foundation and be constructed of reinforced concrete. Where pipes pass through the concrete wall, adequate support for the pipe shall be provided to prevent differential settlement and pipe shearing.11.4. Embankment Stability. 11.4.a. Slope stability shall be analyzed to show that the embankment design achieves the following factors of safety under the conditions listed:11.4.a.1. A safety factor of 1.5 for embankment loading conditions shall assume a long term steady-state condition with the phreatic surface originating at the elevation of the emergency spillway crest for embankment dams with emergency spillways or at a maximum design pool elevation for embankments without spillways.11.4.a.2. A rapid draw down safety factor of 1.2 and11.4.a.3. An earthquake safety factor under steady-state seepage conditions of 1.2 using seismic loading appropriate to the geological site conditions.11.4.a.4. Embankments constructed as part of an appurtenant structure where failure will lead to a dangerous condition in the dam shall achieve a static safety factor of 1.5.11.4.b. Slope Stability Analyses shall be performed using standard engineering practices. Critical cross-sections of dam indicating embankment limits, foundation zones, soil zones, phreatic line, assumed reservoir elevation, stability arcs or failure planes through the dam and resulting safety factors for each critical arc or failure plane shown. 11.4.b.1. A listing of soil zone unit weights, angles of internal friction, and cohesion values for each soil zone shown on the cross-section shall be provided in the plan package.