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the setting out of the final centre was relatively short which again saved time 
and costs. 
2. Underground Work 
In the excavation for T1 power station the Authority applied stereophotogram- 
metry some 1,000 feet underground. At the time of survey the excavation 
comprised the roof section of the machine hall and the transformer hall, the 
latter with approximate dimensions of 120 feet in length, 80 feet in width and 
25 feet in height (Fig. 4.) The objective was to obtain accurate profiles and 
volumes and to produce a plan showing the positions of rock bolts located 
at approximately 5 ft. centres over all exposed rock faces. 
The Authority had decided to use rock bolts as the means of support, a technique 
which creates a strong selfsupporting rock shell around the whole excavation. A 
critical factor in this new method is the spacing of rock bolts depending on 
geological features (joints, fractures, etc.) and general condition of the rock. 
For research statistics it was therefore desirable to have a permanent record 
of the number of positions of rock bolts. 
However, to survey some 3,000 rock bolts by manual methods under the 
conditions prevailing in this underground excavation (ie. dull light, dripping 
water, dust, noise, movement of heavy machinery and constant interruptions 
by blasting and other activities) would have been an onerous task. 
Again phototheodolite survey offered a practical solution. From one base line 
at each end of the excavation photographic coverage was completed when only 
maintenance crews were at work. From these photographs a plan of the 
excavation was produced showing the position of rock bolts. 
  
Fig. 4: Early stage of TI! power station excavatica. 
3. Landslides 
To study landslide movement caused during road construction, a phototheodolite 
survey was made of the affected area. Photographs were again taken after several 
wet periods had passed, to observe whether movement had continued. 
By this method not only checkpoints but the whole surface of the slide could 
be rigorously compared with its previous shape, thus proving the effectiveness 
of soil conservation measures that had been undertaken to prevent future 
blocking of the road. 
4. Sedimentation 
A phototheodolite survey was made of the Guthega Storage basin and another 
regulating pond just prior to commencement of storage. A permanent photo- 
graphic record of the conditions within the flooded valley was thus obtained,