Md. Code Regs. 26.20.26.04

Current through Register Vol. 51, No. 21, October 18, 2024

Section 26.20.26.04 - Durable Rock Fills

A. The Bureau may approve alternative methods of disposal of hard rock spoil, including fill placement by dumping in a single lift, on a site specific basis, provided the services of a registered professional engineer experienced in the design and construction of earth and rockfill embankments are used and provided the requirements of this regulation and the general requirements for disposal of excess spoil are met.

B. "Hard rock spoil" means rock fill consisting of at least 80 percent 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 Bureau.

C. Special Placement.

(1) Spoil is to be transported and placed in a specified and controlled manner which will ensure stability of the fill.

(2) The method of spoil placement shall be designed to ensure mass stability and prevent mass movement.

(3) Loads of noncemented clay shale, clay spoil, or both, 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. These materials shall comprise not more than 20 percent of the fill volume as determined by tests performed by a registered professional engineer and approved by the Bureau.

D. Stability Analyses.

(1) Stability analyses shall be made by a registered professional engineer.

(2) Parameters used in the stability analyses shall be based on adequate field reconnaissance, subsurface investigations, including borings, and laboratory tests.

(3) The embankment which constitutes the valley fill or head-of-hollow fill shall be designed with the following factors of safety:

Case	Design Condition	Minimum factor of safety
I	End of construction	1.5
II	Earthquake	1.3

E. Internal Drainage System.

(1) 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.

(2) Anticipated discharge from springs and seeps and due to precipitation shall be based on records, field investigations, or both, to determine seasonal variation. The design of the internal drainage system shall be based on the maximum anticipated discharge.

(3) 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.

(4) The internal drain shall be protected by a properly designed filter system.

F. Surface water runoff from the areas adjacent to and above the fill may 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.

G. The top surface of the completed fill shall be graded so that the final slope after settlement will be no steeper than 20:1 toward properly designed drainage channels in natural ground and the periphery of the fill. Surface runoff from the top surface of fill may not be allowed to flow over the outslope of the fill.

H. 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.

I. 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 may not exceed 2:1.

(2) To control surface runoff, each terrace bench shall be graded to a slope of 20:1 toward the embankment. Runoff shall be collected by a ditch along the intersection of each terrace bench and the outslope.

(3) Terrace ditches shall have a 5 percent slope toward the channels specified in Regulation .04H of this chapter unless steeper slopes are necessary in conjunction with approved roads.

Md. Code Regs. 26.20.26.04

Regulations .04 were previously codified as COMAR 08.13.09.32 a A_D, respectively. Recodification occurred in April, 1993. For a history of these regulations before April, 1993, see "Administrative History of COMAR 08.13.09 before April, 1993" which follows COMAR 26.20.01.