Some bases are very difficult to destroy: a tight photon cannon package, dozens of sunkens and spore colonies and bunkers full of elite marines. Either wait for a nuclear to go off or try some other difficult advanced technology tactics?
Solution: Bunker Penetration. This strategy requires a couple of Space Construction Vehicles, marines and if you have the right technology, siege tanks with siege technology. Bunker penetration involves forcing your way into an opponents base by destroying the front line. Sounds easy, but the front line can be easily defended by enemy units and wipe your attack out. That's where the bunker come in, construct bunkers a little far from the enemy base's edge where he cannot see. Use 2 scvs to construct bunkers or even a turret. The load it up with marines and continue pushing the bunkers forward until the enemy base is conquered.

• Siege mode your tanks beside bunkers and use comsat on the enemy base to allow your tanks to hit preemptively.
• Use your scvs to repair your tanks and bunkers.
• Never unsiege all tanks at once when pushing through. Just unsiege half and move them forward then siege mode to keep firepower running while pushing through the enemy base.
• Construct bunkers strategically allowing them to protect each other. As a rule of thumb, bunkers should be far from each other in a distance of two siege tanks in length.
• U-238 upgrades are a must for this strategy to work. Marines should receive the best to be effective.