The depth of ocean,
h = 3 km = 3000 m
Density of water = 1000 kg m-3 (assumed);
g = 9.8 kg m-2
Pressure (p) = 1000 x 9.8 x 3000 = 2.94 x 107 Pa
This value of pressure is less than the stress of 109 Pa which the structure can with stand. Therefore, the structure may be suitable.