. Shield and compressed air tunneling . on of the tunnel is large enough a special engineers lockshould be provided. 90. Position of Lock.—Whatever lock is used, its position inthe l)ulkhead wall should be laid out with reference to the carry-ing forward of the working lines through it without having tomake a special offset in the line to get through the lock. It willbe found better not to place the axis of the lock directly coincidentwath the working line but a little to the one side, thus givingmore room to pass the transit when set up in the lock. 91. Transferring Line through Lock.—The met
. Shield and compressed air tunneling . on of the tunnel is large enough a special engineers lockshould be provided. 90. Position of Lock.—Whatever lock is used, its position inthe l)ulkhead wall should be laid out with reference to the carry-ing forward of the working lines through it without having tomake a special offset in the line to get through the lock. It willbe found better not to place the axis of the lock directly coincidentwath the working line but a little to the one side, thus givingmore room to pass the transit when set up in the lock. 91. Transferring Line through Lock.—The method of settingan instrument in the lock is shown in Fig. 159. The hne point may 398 SHIELD TUNNELING be marked by a brass plug set in a (irill hole in the l)ottom of thelock. A plumb-bob is hung above, and just avoiding, the plugand readings taken on a small scale temporarily set for thepurpose at each run of the line. This gives no permanent record,however, and it is better to set in the crown or floor of the lock ^~To /iormaf/T/r. Pre//m/narySef-i/p ofObjen/af/o/?Tan^it ot^&r /nuer-f P/uq. Typica/^etao of O^Kseri/aPon ^^rae^t^aT^ fa so ^^h^oc^ /ni/ep^^~^%f^enf-cA
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Keywords: ., bookcentury1900, bookdecade1920, bookidshieldcompre, bookyear1922
