TXWY EXCURSION.

Narrative

WE LANDED RWY 15L AT PM10 LCL. WE EXITED THE RWY AT TXWY C-3 (R TURNOFF) AT TAXI SPD. I THEN TOOK A R TURN ON C TXWY. WE THEN ATTEMPTED A L TURN ON B-5 TO ENTER THE RAMP. TOWARD THE END OF THE TURN; THE L MAIN WENT APPROX 1 INCH INTO THE SOFT SOIL OFF THE TXWY. THE ACFT WAS IMMEDIATELY STOPPED AND THE ENGS SHUT DOWN. TWR WAS NOTIFIED AND RAMP WAS CALLED FOR A VISUAL INSPECTION OF THE SIT. I DECIDED TO DEPLANE THE PAX AND ACR OPS SENT TRANSPORTATION FOR OUR 50 PAX. WE THEN TRANSFERRED FUEL FROM THE L SIDE TO THE R SIDE TO TAKE WT OFF THE L MAIN GEAR. THEN; WITH THE HELP OF GND PERSONNEL FROM OPS; WE STARTED THE ENGS AND TAXIED THE L MAIN BACK ONTO THE TXWY. FOLLOWING A MAINT INSPECTION; WE THEN PROCEEDED TO THE GATE. AS FOR CORRECTIVE ACTIONS; FIRST OF ALL; MY CHOICE OF ENTRY INTO THE RAMP WAS NOT A GOOD ONE CONSIDERING THE NARROW TXWYS AND TXWY LIGHTING PLACEMENT. I WOULD SUGGEST LIGHTS BE MOVED TO EDGE OF TXWY AND WIDER TURNING AREA FOR TXWYS WITH TURNS OF MORE THAN 90 DEGS. CONTRIBUTING FACTORS TO THE INCIDENT WERE THE BLUE TAXI LIGHTS ARE 10 FT DISPLACED FROM THE PAVED SURFACE ON BOTH SIDES OF THE TXWYS. I WAS AWARE OF THIS AS A NOTAM; HOWEVER; IT WAS STILL DECEIVING. ALSO; MY L TAXI LIGHT WAS INOP AND I MADE A TURN TO THE L OF 135 DEGS. IT WAS NOT EVIDENT THAT YOU COULD ENTER THE RAMP AT C-3 DUE TO OVERNIGHT ACFT PARKED E OF THE TERMINAL BUILDING. GND CTL GAVE NO INSTRUCTION. SUPPLEMENTAL INFO FROM ACN 294778: CORRECTIVE ACTIONS: 1) LOCATE A TAXI RTE FROM THE RWY TO THE GATE WITHOUT MAKING TURNS GREATER THAN 90 DEGS. 2) LOCATE THE BLUE TXWY LIGHTS ON THE EDGE OF THE TXWY . 3) FOR TURNS OF 90 DEGS AND GREATER; WIDEN THE TXWYS -- ESPECIALLY ON THE INSIDE OF THE TURNS. CONTRIBUTING FACTORS: 1) THE LOCATION OF THE BLUE TXWY LIGHTS (10 FT OFF THE EDGE OF THE TXWY). 2) THE WINTER GRASS BEING THE SAME COLOR AS THE TXWY (NOT BEING ABLE TO SEE THE REAL EDGE. 3) L NOSE TAXI LIGHT INOP. 4) RAMP APPARENTLY BEING INACCESSIBLE AT C-3 DUE TO AN ACR Y ON THE RAMP. 5) GND CTL GAVE NO INSTRUCTION.