ENFORCE37590 - Laserfiche WebLink

Home Browse Search

Koehler Tunnel Bulkhead Certification Report Page 4 Bulkhead pours. The concrete pump was set up downstream of the bulkhead form and outside of the portal to accommodate concrete trucks; and, concrete was pumped approximately 300' to fill the bulkhead form. The concrete was hauled to mine site from the portable batch plant with a travel time of less than 1 hour. Delay set was added at the batch plant and again after trucks amved at the portal. 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 5070 psi and the average 28 day strength obtained from the break tests was 6727 psi, well in excess of the required 3000 psi. A1128 day samples exceeded the 3000 psi compressive strength required by design, therefore no additional testing was planned or done. The test reports are attached. Low aressure eroutinE 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 September 16, 17, 18, 19, 22, and 23. Each hole was pressured to 200+ psi and grout pumped until very little grout take occurred. The pressure applied to the formed bulkhead appears to have been adequate to fill the contact fractures except for one void projecting above the top of the bulkhead. This void was pumped full of grout. The valve was closed on September 19th to stop the water and allow pressure to start building on the bulkhead to determine if additional grouting might be required. The valve was reopened and additional grouting was placed on September 22 and 23`d and the valve closed again. Initial indications were that no additional pressure grouting was required. Only minor seepage has been observed from fractures downstream of the bulkhead.