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Grating must be placed on competent bedrock, unless otherwise noted in the Special Conditions. The shaft <br />opening to be grated shall be excavated to bedrock, cleaned of Bose rock and trimmed to provide a uniform <br />contact with the framework. The angle iron framework shall be securely anchored as described above. Rock <br />bolts or anchor bars shall be welded to the framework The grating shall be welded to the framework: welds <br />will be on every other bearing bar. All edges of grate sections will be welded to each other. All voids below <br />the edges of the grating larger than one inch (11") must be filled with concrete mix or pieces of welded grating <br />or angle iron to fill the void. The concreted area must be a minimum of twelve (12") inches in width. Where <br />gaps between the grating and bedrock exceed six inches (6"), a grouted durable rock wall with a minimum <br />width of eighteen inches (18") must be constructed. <br />Spread Footings shall be used on sites where the surficial material is incompetent as determined by the <br />PROJECT MANAGER. The framework will extend a minimum of three feet (3') beyond the opening on all <br />sides and be anchored to spread footings. Footings will be constructed around the entire perimeter of the <br />grating per Standard Drawing Number 4. <br />In circumstances where vein material is to be spanned and the vein material appears weak, the angle iron <br />framework over the vein must be replaced with an appropriately sized beam to span the anticipated weak <br />zone. <br />If a hinging and locking mechanism is required, the hatch will be welded into the center of the grate in <br />accordance with Standard Drawing Number 6. Following installation of the grating, the CONTRACTOR shall <br />install the brass cap in a three-inch (3') I.D. (inside diameter), four4nch (4") long galvanized pipe that is <br />welded to the grate frame. The brass cap shall be grouted flush to '1Z below the top of the pipe using a <br />nom-shrink grout or adhesive. The brass cap will be supplied by the OWNER. <br />8.32. Grating Placed Inside Shaft Opening <br />Fabrication <br />The grating and an angle iron grate frame (L 2"x 2" x 114") will be cut and welded on-site to fit the irregularities <br />of the opening. The frame will be anchored to the shaft walls using imbedded anchor bolts protruding through <br />holes drilled in the frame, or mbar anchor rods welded to the bottom of the iron grate frame. All field welds <br />shall be in accordance with the requirements of the American Welding Society AWS D1.1. If there is an <br />access requirement, the grating shall be designed with a hinging and locking mechanism in accordance with <br />Standard Drawing Number 6. <br />Installation <br />In competent rock, the shaft opening to be grated shall be cleaned of loose rock and trimmed to provide a <br />uniform contact with the framework. The grate shall be positioned over or slightly inside the shaft walls at a <br />stable location as directed by the PROJECT MANAGER. All loose or weathered rock and other materials <br />must be scaled from the shaft walls and the opening trimmed to provide the most competent, clean, and <br />uniform contact with the grating frame as passible. <br />The angle-iron frame shall be cut, formed, and fitted continuously around the perimeter of the opening. <br />Spacing between the shaft perimeter and the angle-iron frame shall not exceed Y. Rock bolts or 3/4" <br />diameter anchor bars shall be installed on twelve inch (12") centers around the entire perimeter of the shaft <br />opening. The rock bolts or anchor bars shall be anchored an eightminch (8*) minimum embedded depth into <br />horizontally drilled fides in competent rock. Hiles receiving bars may be drilled at a slight downwards angle <br />not more than 20 degrees from horizontal, so that the bars when inserted angle upwards from the shaft walls- <br />In no rase will bars be installed so that they angle downwards towards the grate. Rock bolts shall be installed <br />in horizontal holes. Anchoring shall be by bolt expansion, Moly Parabond epoxy capsules (or equivalent epoxy <br />capsules), or by swaging anchor bars into the drilled holes such that an interference fit is obtained. ff rock is <br />soft or excessively fractured, 3/4-inch anchor bars must be used, and a minimum anchoring depth of eighteen <br />inches (18") is required with epoxy capsule anchoring. <br />The grate frame shall be positioned onto anchor bars from above with a minanum two inch (2") weld length <br />Colorado Division of Minerals and Geology GENERAL BID SPECIFICATIONS <br />2004 Page 40 <br />