Civil Engineering Reference
In-Depth Information
Arrival in the receiving shaft; 20-40 mm clearance
The boring and tunnel building process ended when the TBM arrived in the
receiving shaft. However, first of all, the transition had to be made from a
loaded situation in the ground to an unloaded atmospheric situation in the
receiving shaft.
Fig. 10.13
Arrival of the TBM in
the receiving shaft
In the southern end wall of the pneumatically submerged caisson that
served as the receiving shaft on the northern riverbank, two round openings
were located which, just like in the starting shaft, served as the wall with the
tunnel openings for the boring machines. In front of this end wall, an imper-
meable block consisting of low strength mortar was located which was
made inside a temporary construction pit. Behind this (seen from the direc-
tion of boring) the caisson with the wall with the tunnel openings, had to be
in the right position before the TBM arrived. Since the accuracy of position-
ing a pneumatic caisson is not very great, a different solution was applied
for the arrival of the TBM than that of the starting shaft. The diameter in the
wall with the tunnel openings was for example considerably larger than the
exterior diameter of the TBM.
This was thus able to pass by with a large clearance. The space behind the
wall with the tunnel openings in the caisson was filled with a layer of stabil-
ized sand, which functioned as a shield cradle. The rest of the space was
filled with sand.
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