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Primary Method of Construction — Blind Drilling _Prior to the beginning of the blind drilling process, a pressurized
<br />pre -grout operation utilizing up to ten small diameter (6.25 ") holes, approximately 600 -800 feet deep around the
<br />perimeter each shaft will be considered and undertaken, as needed, to limit groundwater flows between the shaft
<br />and the formations. Individual grout holes will be drilled, and a cement grout pumped under pressure into each
<br />borehole before completing the next hole, to seal any wet zones encountered. Each borehole will be filled with
<br />grout and allowed to set -up, effectively sealing the borehole and any fractures or voids in the grouted formation(s).
<br />Any surface casing extending above ground surface will be cut -off flush with, or below, natural ground level.
<br />If needed, and once the pre -grout operation is completed, approximately 10 -foot diameter shaft collars will be
<br />excavated for each shaft to competent rock, at a depth of approximately 40 feet. Material from the collar
<br />excavation will be placed within and on either end of the cuttings pit. Surface casing approximately 8 feet in
<br />diameter (inside) and large enough to accept the shaft casing and drilling tools will be installed in each shaft collar.
<br />This surface casing will be either steel casing grouted in -place or cast -in -place concrete. Maximum 18 -inch
<br />diameter auger holes will be drilled into competent rock and reinforced concrete piers will be poured to anchor the
<br />shaft pads and any other significant structures. It is anticipated that up to 40 anchor piers may be required. Two
<br />concrete pads, either "T" shaped or rectangular, will be poured to accommodate the drilling and casing equipment;
<br />emergency escape hoist, and shaft heater, for the ventilation intake shaft; and fan, fan shroud, mechanical building,
<br />and silencer, for the ventilation exhaust shaft. Average thickness for the reinforced concrete pads will be 2 feet,
<br />and the pads will be a maximum of 4,050 square feet. Specialized blind drilling equipment consisting of A -leg
<br />derricks, drive motors, and drill -string handling components will be installed on the shaft pads and used to drill the
<br />pilot holes and, complete shaft drilling.
<br />Nominal 17.5 -inch pilot holes will be drilled for each shaft to an approximate depth of 1,360 feet and surveyed to
<br />determine vertical shaft deviation and location underground for mine entry tie -ins. The pilot holes will then be
<br />reamed to a nominal diameter of 7.5 -8.0 feet to accommodate the final steel liner. The reaming technique utilizes
<br />an inverted disc cutter equipped hemispherical raise -bore head, to cut the rock. During the drilling of the pilot
<br />holes and the 7.5 -8.0 -foot diameter excavation, all cuttings will be removed from the excavation using an airlift
<br />J system, with water (reverse circulation) being used as the circulation media. Supplemental water, for drilling and
<br />to adjust the density of the drilling medium, may be supplied, as needed, by hauling water from a nearby location
<br />where TCC's holds valid existing water rights. The cuttings will be placed in 115 x 425 x 10 foot, four cell, lined
<br />temporary cuttings pit excavated within the shaft pad adjacent to the shaft excavation. The cuttings pit will be lined
<br />with a nominal 30 -mil PVC flexible membrane liner having a permeability of 10 -12 cm/sec.
<br />The cutting head will be rotated from the surface by the drill pipe, which also serves as a conduit to transfer
<br />cuttings from the shaft bottom to the surface collection pit. The drill pipe also serves to suspend the drilling
<br />assembly in the hole and is tensioned to adjust the cutting weight on the head and to keep the drill pipe straight.
<br />The cutting head moves the water from near the center of the head and discharges it at the periphery of the head.
<br />This water then flows down around the cutters and washes the cuttings towards the pick -up pipe in the center of the
<br />head. The drill pipe's upward flow is activated by compressed air injected down the center of the drill pipe. Rock
<br />cuttings are moved by the circulation of the water down the hole, across the shaft bottom and up the drill pipe to the
<br />surface collection pit. Within the collection pit, the rock cuttings are separated or settled out and the water is
<br />allowed to drain back or is pumped back into the hole for re -use. The cuttings volume will be approximately
<br />12,500 cy.
<br />Once the cutter head reaches the coal seam, the cutter head will be disassembled and removed from the A -leg
<br />derrick. Using the same A -leg derrick, the excavated shaft will then be lined to a nominal 6 -foot inside diameter
<br />using a hydrostatic steel liner. The steel liner sections will be pre- fabricated off -site, hauled to the site and field
<br />welded in 30 -50 foot joints. The liner will be floated into place. This is accomplished by securing a steel bulkhead
<br />to the bottom joint and leaving the excavated hole full of water while the liner is being lowered into place. By
<br />calculating the buoyancy of the liner, and adding water to the capped liner column, as needed, the liner is easily and
<br />safely lowered into position. Once the liner is in place, a nominal 9 -inch thick grout seal will be pumped between
<br />the strata and liner. The grouted steel liner will serve to isolate the Twentymile Sandstone from the Wadge
<br />Overburden. As previously noted, TCC plans to pressure grout the Twentymile Sandstone to minimize seepage to.
<br />TR09 -66 2.05 — 45.6k 04/07/09
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