Project Cyclops, A Design... - Department of Earth and Planetary ...

TABLE L-3
r=l r=2
AC = $566
X n X s X (f-fla)
n fla fib f2a f2b fla flb f2a f2b
100 1 1.05 .987 1.12 1.10 1.22 1.07 1.26
200 1 1.04 .989 1.09 1.07 1.18 1.06 1.27
500 1 2.03 .993 1.06 1.05 1.12 1.04 1.18
1000 1 1.02 .995 1.05 1.03 1.09 1.03 1.14
2000 1 1.01 .997 1.03 1.02 1.06 1.02 1.10
If the side tunnels are 8 ft in diameter and the main
tunnels are 10 ft in diameter, the value r = 2 is about
right. However, the main tunnels do not have to be
larger for their entire lengths and, depending on their
number, may not need any larger sections. With the 8-ft
tunnel cross section shown in Figure L-3, about 8 sq ft
or more of area is available for the IF cables. This will
accommodate 1700 cables 7/8 in. in diameter or about
500 cables 1-5/8 in. in diameter. The number of array
elements that can be used without requiring larger main
tunnels is given in the Table L-4.
IF CABLE
TABLE
L4
TUNNEL
PATTERN
DIAMETER la 1b 2a 2b
7/8 in. 3432 6840 3430 10,360
1-5/8 in. 1018 2050 1016 3,084
Clearly, if we use the b patterns, or 7/8-in. cable, or
both, very large arrays can be built without oversize
main tunnels. In this case r = 1 and the cost difference
between patterns is only a few percent-much less than
our uncertainty in the basic price. Further, any difference
is partially offset by the saving in IF cable lengths
when the b patterns are used.
At the present state of refinement we can therefore
estimate the tunnel cost as
C = $600 X n X s (LI5)
where the $600 is about 6% greater than the estimated
cost of $566[m for 8 ft tunneling.
However, in deciding among the various tunnel patterns,
we must take account of the variations given in
Table L-3. For convenience we compute the incremental
cost over that represented by pattern la
= $566 ns (f- l) (LISa)
Using r = 1 and s = 300 m we obtain the incremental
cost figures given in Table L-5
TABLE L-5
Excess Tunnel Cost Over That of Pattern I a
ACI b A-.-C2a A---C2b
($ million) ($ million) ($ million)
100 0.85 -0.22 2.04
200 1.39 -0.37 3.06
500 2.21 -0.59 5.09
1000 3.40 -0.85 8.15
2000 4.75 -1.02 11.21
GROUND
LEVEL
t5 V2 fI