2001-03-15_REVISION - M1977378 (3)

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Terry Tunnel Near Surface Bulkhead Construction Certification Report Page 4 Approximately 12 cubic yards was dry batched from the Sandco plant in Durango and the remainder was batched from the portable Sandco batch plant that was set up in Silverton. This is the same plant and concrete supplier used for the American Tunnel bulkhead pour. The concrete pump was set up on surface and concrete was pumped approximately 350' to fill the bulkhead form. The bulkhead was poured on September 28, 2000 with the first truck arriving around 10:00 a.m.. The bulkhead form was determined to be full at approximately 7:00 p.m.. A set of concrete test cylinders was taken for approximately every 8 cu. yds. placed in the bulkhead form. The test cylinders were cured on -site. Break tests were performed at 7 days and 28 days to verify that the 3000 psi design strength was met or exceeded. The average 7 day strength obtained from the break tests was 3534 psi with no single test below the required strength of 3000 psi. The average 28 day strength obtained from the break tests was 5860 psi, well in excess of the required 3000 psi. All tests, 7 day and 28 day, exceeded the 3000 psi compressive strength required by design, therefore no additional testing was planned or done. The test reports are attached. Low pressure grouting of the concrete -rock contact After construction of the air -side bulkhead form and placement of rebar, the form was marked for drillhole collars by nailing faucet washers to the form at the selected locations. One ring consisting of nine holes was drilled to intersect the rock contact along the perimeter at approximately the mid -point or center of the bulkhead. The target points were selected and then appropriate corresponding collar points were selected such that the hole could physically be drilled without hitting the rebar mat. Angles and distances were measured so the selected lines could be reproduced after the bulkhead form was stripped. The bulkhead was drilled and the contact was low pressure grouted on October 4, 2000. Each hole was pressured to 200+ psi with very little grout take. The pressure applied to the formed bulkhead appears to have been adequate to fill the contact fractures. The bulkhead rock - concrete contact has been grouted to specifications and all indications are that low pressure grouting was successful and complete. The construction drain pipe was permanently grouted closed and capped on October 5, 2000. A grout pig was pumped ahead of the grout to separate the water and grout. The catch bars placed in the up- stream end of the pipe provided a stop for the grout pig allowing complete and total filling of the pipe. The valve was closed under pressure to prevent bleed -off. The drain pipe has been permanently sealed.