SHOTCRETE SUPPORT IN ROCK TUNNELS IN SCANDINAVIA

NORWEGIAN AND SWEDISH SHOTCRETE PRACTICE IN TUNNEL SUPPORT FOR ROCK TUNNELS IS REVIEWED. A SUMMARY IS GIVEN OF THE MECHANISM OF SUPPORT THAT SHOTCRETE RENDERS IN THE ROCK EXCAVATION: (1) SHOTCRETE IS FORCED INTO OPEN JOINTS, FISSURES, SEAMS, AND IRREGULARITIES IN THE ROCK SURFACE AND SERVES THE SAME BINDING FUNCTION AS MORTAR IN A STONE WALL, (2) SHOTCRETE HINDERS WATER SEEPAGE FROM JOINTS AND SEAMS IN THE ROCKS AND PREVENTS PIPING OF JOINT FILLING MATERIALS AND AIR AND WATER DETERIORATION OF THE ROCK. (3) SHOTCRETE'S ADHESION TO THE ROCK SURFACE AND ITS OWN SHEAR STRENGTH PROVIDE A CONSIDERABLE RESISTANCE TO THE FALL OF LOOSE ROCK BLOCKS FROM THE ROOF OF A TUNNEL, AND (4) A THICKER SHOTCRETE LAYER PROVIDES STRUCTURAL SUPPORT, EITHER AS A CLOSED RING OR AS AN ARCH TYPE MEMBER. THE TERM SHOTCRETE AS USED IN THIS ARTICLE REFERS TO LARGE AGGREGATE (3/4 IN.) APPLIED BY THE DRY MIX PROCESS. SCANDANAVIAN EXPERIENCE WITH SHOTCRETE IN UNDERGROUND EXCAVATION INVOLVES THREE MAIN TYPES OF GROUND OR ROCK PRESSURES: (1) REAL OR GENUINE ROCK PRESSURE, (2) LOOSENING PRESSURE, AND (3) SWELLING PRESSURE. SHOTCRETE APPLICATIONSS IN LOOSENING GROUND ARE OFTEN DISCONTINUOUS, SPOTWISE APPLICATIONS THAT CAN CONFORM TO IRREGULARITIES IN ROCK CONDITIONS. AS WITH ROCK BOLTS THE GREATEST BENEFIT FROM SHOTCRETE IN LOOSENING GROUND CAN BE ROCK-SHOTCRETE INTERACTION THAT WAS DEALT WITH DURING EXCAVATION. THE PRINCIPAL ROLE OF SHOTCRETE IN PREVENTING LOOSENING IS TO PROVIDE SUFFICIENT SHEAR RESISTANCE ALONG THE FRACTURE AND JOINT SURFACES OF THE TUNNEL PROFILE SO THAT THE NATURAL GROUND ARCH ABOVE THE TUNNEL ROOF CAN BE MAINTAINED NEAR THE PERIPHERY OF THE OPENING. THE OPTIMUM USE OF SHOTCRETE IN STRONGLY SWELLING MATERIAL IS FREQUENTLY THAT OF A VERY TEMPORARY SUPPORT WHOSE SOLE FUNCTION IS TO PROVIDE SHORT TERM PROTECTION AGAINST ROCK FALLS AT THE WORKING FACE. THE SUITABILITY OF SHOTCRETE IN WATER BEARING GROUND WAS GREATLY IMPROVED WITH THE INTRODUCTION OF ACCELERATING AGENTS, BOTH IN POWDER AND LIQUID FORM. GROUTING AND SHOTCRETE WERE USED EXTENSIVELY FOR THE LIMHAMM TUNNEL DRIVEN THROUGH HEAVILY WATER-BEARING LIMESTONE IN SOUTHERN SWEDEN. DRAINAGE OF WATER-BEARING ROCK IS FREQUENTLY PERFOMED BOTH BEFORE AND AFTER SHOTCRETING IN ORDER TO IMPROVE THE ROCK-SHOTCRETE BOND AND THE STABILITY OF THE COMPLETED TUNNEL. A LARGE QUANITY OF EXPERIENCE WITH THE USE OF SHOTCRETE FOR UNDERGROUND SUPPORT WAS ACCUMULATED WITHOUT ANY CONSIDERATION FOR THE TYPE OF PRESSURE OR THE ROCK-SHOTCRETE INTERATION THAT WAS DEALT WITH DURING CONSTRUCTION. THEREFORE, EXPERIENCE IS FREQUENTLY EXPRESSED IN THE FORM OF RULE-OF-THUMB GUIDES FOR THE SELECTION OF A SHOTCRETE DESIGN.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/oclc/10480594
• Supplemental Notes:
  • Vol 40, No 1, PP 74-79, 5 FIG, 2 PHOT
• Authors:
  • Cecil, O S
• Publication Date: 1970-1

Media Info

• Serial:
  • Civil Engineering
  • Publisher: American Society of Civil Engineers
  • ISSN: 0885-7024
  • Serial URL: http://www.pubs.asce.org/ceonline/newce/html

Subject/Index Terms

• TRT Terms: Accelerating agents; Adhesion; Binders; Earth pressure; Erosion; Excavation and tunneling; Foundations; Grouting; Loose soils; Pipe; Rock mechanics; Rocks; Shear strength; Shotcrete; Structural supports; Swelling; Tunneling; Underground structures
• Old TRIS Terms: Piping, erosion; Rock foundations; Supports; Underground
• Subject Areas: Bridges and other structures; Construction; Geotechnology; Highways;

Filing Info

• Accession Number: 00215310
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 26 1970 12:00AM