PROGRESSIVE RELAXATION OF ROCK MASSES DURING EXCAVATION OF UNDERGROUND CAVITY

PAST ROCK MECHANICS CONCERNED WITH THE EXCAVATION OF UNDERGROUND CAVITIES HAVE BEEN BASED ON THE UNREALISTIC ASSUMPTION OF "PRE-EXISTING EXCAVATING CAVITY" AND "POST- APPLYING GROUND PRESSURE" AROUND THIS CAVITY AFTER EXCAVATION. THE AUTHORS POINT OUT THAT THIS CLASSICAL BASIC ASSUMPTION DOES NOT AGREE WITH THE REAL EXCAVATING PROCESS AND PROPOSE TO CHANGE THE BASIC ASSUMPTION TO A MORE REALISTIC ONE OF "PRE-EXISTING GROUND PRESSURE" AT SEVERAL EXCAVATING STAGES AND "POST-RELAXATION OF THIS GROUND PRESSURE" BY EXCAVATION. THE FINITE ELEMENT METHOD WAS USED TO IMPROVE THIS BASIC ASSUMPTION. THE PROPOSED NUMERICAL METHOD TAKES INTO ACCOUNT THE SUCCESSIVE EXCAVATING STAGES, EXISTING GROUND PRESSURE, PROGRESSIVE RELAXATION OF ROCK MASSES AROUND THE EXCAVATION, NON LINEAR STRESS-STRAIN RELATION, CREEP CHARACTERISTICS, AND CHANGE OF COHESION AND MODULUS OF DEFORMABILITY DEPENDING ON THE BOUNDARY CONDITION. ACCORDING TO THIS ANALYSIS, THE SIDE RELAXED ZONE CAN BE EVALUATED, A FACTOR WHICH IS IMPORTANT IN ESTIMATING THE STABILITY OF THE EXCAVATED ZONE BUT WHICH WAS DIFFICULT TO ESTIMATE BY THE TRADITIONAL TERZAGHI'S CRITERION. MENTION IS MADE OF THE RELATION BETWEEN THE ZONE DIRECTLY DAMAGED BY BLASTING AND THE RELAXED ZONE DAMAGED BY RELEASE OF THE EXISTING GROUND PRESSURE, AND THE UPHEAVAL AND SETTLEMENT AROUND THE ROCK MASS OR INCREMENTAL STRESS IN THE LINING DURING THE EXCAVATION OF A LARGE UNDERGROUND POWER STATION. /RRL/

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 343-9

Subject/Index Terms

Filing Info

  • Accession Number: 00235253
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: TRIS
  • Created Date: Apr 23 1972 12:00AM