STAND-UP TIME OF TUNNELS IN SQUEEZING GROUND. PART II. A GENERAL CONSTITUTIVE RELATIONSHIP FOR SOFT SOILS
The effect of tunnel size, advance rate, and depth of cover on the stand-up time of tunnels in squeezing ground was investigated through a series of 12 physical model tests. The stand-up time, defined as the time elapsed before instability develops, was found to be characterized by increasing deformations and deformation rates rather than a catastrophic collapse of the tunnel. Test results showed a 25% increase in stand-up time was realized by halving the size of the opening (from 5.0 m dia. to 2.4 m dia. when scaled to prototype dimensions) or by decreasing the advance rate by a factor of four (from 1.3 m/hr to 0.3 m/hr for the 5.0 m dia. tunnel). Depth of cover was described in terms of the ratio of confining pressure to material strength. Decreasing the depth (or increasing material strength) by 10% also increased stand-up time by 25%. In order to establish a predictive capability, a constitutive theory describing the time dependent behavior of soft clays has been developed. By generalizing existing empirical rules developed for fixed boundary conditions and then unifying these empirical rules with a tensor framework, a multi-axial constitutive equation describing the stress-strain-time behavior of normally loaded soft clays was formulated.
University of California, BerkeleyInstitute of Transportation Studies Library
Berkeley, CA United States 94720
Department of TransportationOffice of University Research, 1200 New Jersey Avenue, SE
Washington, DC United States 20590
- Kavazanjian, E
- Mitchell, J K
- Publication Date: 1977-6-30
- Pagination: 36 p.
- TRT Terms: Clay; Clay soils; Construction projects; Deformation; Deformation curve; Dynamics; Forecasting; Pressure; Properties of materials; Soft clays; Soil mechanics; Soils; Stability (Mechanics); Strength of materials; Tensor analysis; Time dependence; Tunneling; Tunnels
- Uncontrolled Terms: Confinement; Soil dynamics; Soil properties
- Old TRIS Terms: Cover; Tunnel excavation
- Subject Areas: Bridges and other structures; Construction; Geotechnology; Highways; Materials;
- Accession Number: 00167309
- Record Type: Publication
- Source Agency: National Technical Information Service
- Report/Paper Numbers: DOT/TST-77/60 Final Rpt.
- Contract Numbers: DOT-OS-50108
- Files: NTIS, TRIS, USDOT
- Created Date: Nov 23 1978 12:00AM