CAPT OF A B757 EXPERIENCED DIFFICULTY IN TAXIING FROM THE RAMP AFTER PUSHBACK USING MAX APPROVED BREAKAWAY PWR DUE TO THE ACFT TIRES SINKING INTO THE TARMAC. THE RPTR BELIEVES THAT THE RAMP SURFACE CONDITION CANNOT APPROPRIATELY SUPPORT THE WT OF HIS ACFT.

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LOCATION: RAMP BTWN CONCOURSES X AND Y AT MIA. DEPARTED GATE Z AT MIA LATE EVENING WEIGHING ABOUT 207000 LBS. PUSHED BACK FROM GATE. USING THE MAX 35% N1 PWR FOR BREAKAWAY THE ACFT WOULD NOT MOVE. IT HAD SUNK INTO THE TARMAC EVEN ON THIS COOL SPRING EVENING. I LEFT 35% PWR FOR 30 SECONDS TO 1 MIN BEFORE THE ACFT FINALLY STARTED TO CREEP OUT OF THE RUTS. I HAVE GONE THROUGH MIA SEVERAL TIMES THE PAST FEW WKS AND HAVE EXPERIENCED SIMILAR PROBS. THE MIA RAMP -- ESPECIALLY BTWN CONCOURSES X AND Y IS SOFT AND FULL OF RUTS AND SUNKEN IN SPOTS. IT IS ALMOST IMPOSSIBLE TO TAXI A MODERATE WT ACFT OUT OF THE TIGHT CORNERS AND STAY WITHIN THE PWR PARAMETERS IN THE OPS MANUAL. MIA SHOULD EITHER FIX THE RAMPS OR AS A STANDARD PROC TUG US FURTHER OUT ONTO THE RAMPS WHERE HIGHER BREAKAWAY PWR SETTINGS CAN SAFELY BE USED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAS NOT BEEN BACK TO THE MIA ARPT SINCE HIS RPT; BUT UNDERSTANDS FROM OTHER COMPANY FLCS THAT THERE HAVE BEEN NO CHANGES TO THE RAMP CONDITION. HE FURTHER ADVISED THAT HE HAD HEARD THAT THERE WAS AN INCIDENT IN WHICH A GND CREW MEMBER WAS KNOCKED DOWN BY JET BLAST WHEN THE DEPARTING ACFT HAD TO GO ABOVE MAX COMPANY RECOMMENDED BREAKAWAY PWR IN LEAVING THE RAMP AREA. HE SAID THAT THERE IS CONSIDERABLE CONSTRUCTION GOING ON NEAR AND AROUND THE AREA AND HEARS THAT THE CONCOURSE AREAS WILL BE RESURFACED. SINCE HE REALIZES THAT IT WILL PROBABLY BE A LONG TIME BEFORE THE CONCOURSE RAMPS ARE RESURFACED; HE HOPES THE COMPANY WILL PROVIDE NOTICE TO CREWS OF HVY ACFT TO BE TUGGED OUT FAR ENOUGH FOR THE USE OF MORE BREAKAWAY PWR. THE RPTR STATED THAT HE HAS 16000 HRS TOTAL TIME: 225 HRS IN THE LAST 90 DAYS AND 900 HRS IN B757 AND B767 TYPE ACFT.