SPECIAL APPLICATION OF CAST-IN-PLACE WALLS FOR TUNNELS IN SOFT CLAY IN OSLO

WESTERN SUBURBAN LINES AND ONE FOR THE RAILWAY LINK FROM EAST TO WEST THROUGH THE CENTER OF OSLO ARE TO BE CONSTRUCTED TOGETHER OVER A LENGTH OF APPROXIMATELY 250 METERS THROUGH A DEEP CLAY FILLED CANYON. THE CLAY IS SOFT TO MEDIUM IN STIFFNESS AND THE MAXIMUM DEPTH TO THE BEDROCK IS APPROXIMATELY 40 METERS. THE RAILWAY TUNNEL WILL BE THE DEEPER OF THE TWO, WITH AN EXCAVATED DEPTH OF APPROXIMATELY 16 METERS. THIS IS TWICE AS DEEP AS IT IS POSSIBLE TO CARRY OUT AN OPEN STRUTTED EXCAVATION, WITH RESPECT TO THE DANGER OF BOTTOM HEAVE FAILURE AT THIS SITE. IN ADDITION, THE CONSTRUCTION WILL PASS WITHIN A FEW METERS OF THE NATIONAL THEATER BUILDING. THIS OLD HISTORIC BUILDING IS FOUNDED ON FLOATING PILES AND HAS SUCH SERIOUS SETTLEMENT DAMAGE THAT IT WILL NOT WITHSTAND ANY FURTHER UNEVEN SETTLEMENTS. THIS ARTICLE DESCRIBES THE SITE CONDITIONS AND DISCUSSES THE ALTERNATIVE SOLUTIONS WHICH HAVE BEEN CONSIDERED. THE CHOSEN METHOD IS BASED ON THE USE OF CAST-IN-PLACE WALLS WHICH ARE EXTENDED WELL BELOW THE EXCAVATION LEVEL, BUT WHICH DO NOT EXTEND TO ROCK AT THE DEEPEST SECTION. A SPECIAL FACTOR IN THIS PROJECT IS THAT THE LONGITUDINAL WALLS ARE STRUTTED BY DIGGING TRANSVERSE TRENCHES AND CASTING CROSS WALLS BENEATH THE EXCAVATION LEVEL. THE LONGITUDINAL AND TRANSVERSE WALLS THEN FORM A STIFF SYSTEM OF RIBS BELOW THE LEVEL OF THE EXCAVATION SO THAT THE SHEAR STRENGTH BETWEEN THE CLAY AND THE CONCRETE WALLS PREVENT BOTTOM HEAVE. LATERAL MOVEMENTS OF THE WALLS AND SETTLEMENTS WILL BE SMALL DUE TO THE STRUTS, AS TRANSVERSE WALLS ARE PLACED BEFORE THE MAIN EXCAVATION IS STARTED. CASINGS WILL BE PLACED IN THE LONGITUDINAL WALLS FOR THE RAMMING OF STEEL PILES TO ROCK, AND THE PILING WILL BE DONE BEFORE THE MAIN EXCAVATOR COMMENCES. A TRIAL EXCAVATION TO A DEPTH OF 28 METERS WAS UNDERTAKEN IN 1970. TO DETERMINE THE SHEARING STRENGTH BETWEEN CLAY AND CAST-IN-PLACE CONCRETE, PULLING OUT TESTS ON PILES WERE CARRIED OUT. PILES CAST IN WATER, CLAY, OR MIKROSIL SLURRY GAVE RESULTS SIMILAR TO THOSE OBTAINED FROM VANE BORINGS; FOR CONCRETE CAST IN BENTONITE SLURRY, HOWEVER, THE SHEAR STRENGTH WAS 25% LOWER. /TRRL/

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 485-98

Subject/Index Terms

Filing Info

  • Accession Number: 00236980
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Report/Paper Numbers: Conf Paper
  • Files: TRIS
  • Created Date: Feb 11 1973 12:00AM