imes representing the English, Austrian 

 American systems. Nearby, a series of small relief 

 models (fig. 19) is used to show the sequence of en- 



i hi in a soft-ground railroad tunnel of about 

 1855, using the Austrian system. Temporary timber 

 support of tunnels fell from use gradually after the 

 advent of shield tunneling in conjunction with 

 iron lining. I In- formed .1 perfect support immedi- 

 ate!) behind the shield, as well as the permanent 

 lining of the tunnel. 



BRUNEl/s I H \M1 '& TUNNI I. 



["he interior surfaces of tunnels through ground 

 merely unstable are amenable to support by various 

 systems of timbering and arching. This becomes less 

 true as the fluidity of the ground increases. The 

 soft material which normally comprises the beds of 

 rivers can approach an almost liquid condition 

 resulting in a hydraulic head from the overbearing 

 water sufficient to prevent the driving of even the 

 most carefully worked drift, supported by simple 

 timbering. The basic defect of the timbering v. 

 used in mining and tunneling was that there was 

 inevitably a certain amount of the face or ceiling 

 unsupported just previous to setting a frame, or 

 placing over it the necessary section of lagging. In 

 mine work, runny soil could, and did, break through 

 such gaps, filling the working. For this reason, 

 there were no serious attempts made before 1825 to 

 drive subaqueous tunnels. 



In that year, work was started on a tunnel under the 

 Thames between the Rotherhithe and Wapping 

 sections of London, under guidance of the already 

 famous engineer Marc Isambard Brunei (1769-1849), 

 father of I. K. Brunei. The undertaking is of great 

 interest in that Brunei employed an entirely novel 

 apparatus of his own invention to provide continuous 

 and reliable support of the soft water-bearing clay 

 which formed the riverbed. By means of this 

 "shield," Brunei was able to drive the world's first 

 subaqueous tunnel. 



' In 180" the noted Cornish engineer Trevithick commenced 

 .1 small timbered drift beneath the ["names, 5 feet l>\ 3 feet, .is 

 .in exploratory passage for .1 larger vehicular tunnel. Due to 

 the sin. ill frontal area, he was able to successful!) probe about 



10(1(1 fret, but the river then broke in and halted the work. 

 Mine tunnels had also reached beneath the Irish Sea and various 

 rivers in the coal regions of Newcastle, but these weir so far 

 below the surface as to be in perfectly solid ground and can 

 hardly be considered subaqueous workings. 



PID_XJRANSIT 





Figure 16. Wesi portai upon completion, 1876. 

 {Phut" ■ Historical So 



The shield was of cast iron, rectangular in ele\ ation, 

 and was propelled forward by jackscrews. Shelves at 

 top, bottom, and sides supported the tunnel roof, 

 floor, and walls until the-permanent brick lining was 

 placed. The working face, the critical area, was 

 supported by a large number of small "breasting 

 boards." held against the ground by small individual 

 screws bearing against the shield framework. The 

 shield itself was formed of 12 separate frames, each 

 of which could be advanced independently of the 

 others. The height was 22 feet 3 in< hes: the width 

 37 feet 6 inches. 



The progress was piecemeal. In operation the 

 miners would remove one breasting board at a time. 

 excavate in front of it, and then replace it in the 

 advanced position about 6 inches forward. This 

 was repeated with the next board above or below, and 

 the sequence continued until the ground for the 

 entire height of one of the \2 sections had been 

 removed. The board screws for that section were 

 shifted to bear on the adjacent frames, relieving the 



PAPER 41: TUNNEL ENGINEERING A MUSEUM TRE.VI Ml \ 1 



217 



