. Shield and compressed air tunneling . ^ movements are all going on together and the result isrepresented by a curve as shown in Fig. 141. The full line. Fig. Mon+h& 139.—The seasonal fluctuation in elevationof a shield-driven tunnel in mud. Fig. 140.—The tidal fluctu-ations in elevation of a tunnelin mud under a tidal water-way. indicates the actual changes and the dotted line tlie averagemovement. This diagram indicates tlu^ importance of knowingthe separate phases of movements in order to interpret theobservations properly. If for example, the initial elevations aretaken at the ti
. Shield and compressed air tunneling . ^ movements are all going on together and the result isrepresented by a curve as shown in Fig. 141. The full line. Fig. Mon+h& 139.—The seasonal fluctuation in elevationof a shield-driven tunnel in mud. Fig. 140.—The tidal fluctu-ations in elevation of a tunnelin mud under a tidal water-way. indicates the actual changes and the dotted line tlie averagemovement. This diagram indicates tlu^ importance of knowingthe separate phases of movements in order to interpret theobservations properly. If for example, the initial elevations aretaken at the time AA and no further levels are taken until Bis reached, the inference will be that the tunnel has settledfrom A A to B, whereas, looked upon as a long time operation, itreally has settled only from A to B. If levels are run at the time TUNNEL MAINTENANCE 349 CC and tluMi at DD tlio infcronco would be that the tunnel wasrising, although looked upon as a long time operation, it hassettled from C to D. Unless the observations are made at regularintervals for a jioriod of several years, a true picture of what ishappening cannot 1)e obtained.
Size: 3119px × 801px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, bookidshieldcompre, bookyear1922
