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," .~ ~' -- J.',",U SAN JACINTO TUNNEL 21 Lawrence East headings and 5,692 feet between Lawrence and Potrero. Of concrete lining 20,232 feet of arch and 20,233 feet of invert remained to be placed from the east portal and 12,840 feet of arch together with 11,560 feet of invert to be placed from the west portal. Excnvation In Cabazon West and Lawrence East headings, bad rock condi- tions had been encountered in June 1938 necessitating frequent use of crown bars and breastboards in the face. Soft and fractured rock continued into the first week of July, when both headings entered a zone of good rock, making excellent progress until holing through on the 28th of that month. In this period progress in Cabazon West was 529 feet and in Lawrence East 520 feet. In the latter part of May the Lawrence West heading advanced out of badly fractured and into firm, hard granodiorite, better rock conditions continuing until the connection was made with Potrero East on November 19, 1938. Up to the first week in August water flows, occasioually under pressure, were encountered in test holes drilled ahead of the face. During this period some time was lost in making" grout connections to the test holes and injecting cement grout under pressures up to 1,400 pounds per square inch, accomp- lishing virtmilly complete stoppage of the flows. The best month's progress in this heading was 847 feet made in October, with a total advance between July 1st and November 19th of 2,950 feet, at the excellent average rate of 21 feet per working day of three 8-holl!' shifts. In the Potrero East heading, where from its beginning in 1934, '--- so "mu'cll aifficulti \\'US expcrienced' d"ue to oad ground lUld" \Vater, better rock had been entered at the end of March 1938, and this continued through the remaining distance. Occasional zones of badly fractured and soft decomposed granite, necessitating the use of both crown bars and breastboards, were passed through, but only moderate quantities of water were encountered and rapid prog- ress was maintained in" excavation. The best monthly progress ever made in this heading was the 775 feet advanced in October 1938, the last full month of operation. The total progress from July 1st to November 19th was 2,742 feet, at a rate of 19.6 feet per working day, The two headings met exactly on line and only 0.11 of a foot off in grade, the final shot occurring at 10 :04 a.m. November 19, 1938, \ II