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Analysis of tunnel front stability, using the yield calculation approach
339 A N A L Y S I S OF T U N N E L FRONT STABILITY, U S I N G THE Y I E L D C A L C U L A T I O N A P P R O A C H
CERMES - Ecole Nationale des Ponts et Chauss~es - Noisy le Grand - France SIMECSOL - Le Plessis Robinson - France
E. LECA M. PANET
In Revue Frangaise de G4otechnique,
Nr 43, Second quarter 1988, 5-19. SUMMARY
Front stability must be examined prior to tunnel construction in order to ensure good safety conditions while boring it. When the tunnel is at shallow depth and is driven using a boring machine with full face support, three loading effects need to be considered : influence of the soil weight, soil surface loads, retaining pressure at the front. The yield calculation approach is used in this paper to estimate stability conditions for the tunnel front. Two material types are considered : in the case of a purely cohesive material (TRESCA yield criterion) combining lower bound and upper bound analyses leads to bracketting stability conditions for the front with respect to two loading parameters only. In the more difficult case of a MOHR-COULOMB criterion however, it is necessary to account for three loading parameters ; for this latter material type the lower bound approach only is considered in the present study.
M O D E L L I N G OF THE B E H A V I O U R OF A W H I T E H I G H POROUS C H A L K A N D V A L I D A T I O N
J.F. SHAO - J.P. HENRY
Laboratoire de M4canique de Lille EUDIL - Villeneuve d'Ascq - France
In Revue FranGaise de G~otechnique,
Nr. 43, second quarter 1988, 35-46.
SUMMARY Hydrostatic compression and conventional triaxial compression tests were performed on a white, highly porous chalk for confining pressure up to 50 MPa. The obtained results have allowed fondamental aspects of the chalk behaviour to be revealed. A LADE elastoplastic model with two yield surfaces was used for modelling : some important modifications were proposed for taking into account special aspects of the chalk behaviour. Proportional loading tests and lateral extension tests were performed to study the chalk's behaviour in homogeneous problems. The modified LADE elastoplastic model was used to simulate these tests. In global way, model's predictions were found to be in satisfactory agreement with the experimental results. Finally, hollow cylinder tests were realized to examine chalk's behaviour in typical boundary conditions problems. The modified elastoplastic model has then been introduced into a finite elements program which was used to simulate the hollow cylinder tests. Comparisons between experimental and predicted results were also given and seem to be satisfactory.
CERMES - Ecole Nationale des Ponts et Chauss~es - Noisy le Grand - France SIMECSOL - Le Plessis Robinson - France
E. LECA M. PANET
In Revue Frangaise de G4otechnique,
Nr 43, Second quarter 1988, 5-19. SUMMARY
Front stability must be examined prior to tunnel construction in order to ensure good safety conditions while boring it. When the tunnel is at shallow depth and is driven using a boring machine with full face support, three loading effects need to be considered : influence of the soil weight, soil surface loads, retaining pressure at the front. The yield calculation approach is used in this paper to estimate stability conditions for the tunnel front. Two material types are considered : in the case of a purely cohesive material (TRESCA yield criterion) combining lower bound and upper bound analyses leads to bracketting stability conditions for the front with respect to two loading parameters only. In the more difficult case of a MOHR-COULOMB criterion however, it is necessary to account for three loading parameters ; for this latter material type the lower bound approach only is considered in the present study.
M O D E L L I N G OF THE B E H A V I O U R OF A W H I T E H I G H POROUS C H A L K A N D V A L I D A T I O N
J.F. SHAO - J.P. HENRY
Laboratoire de M4canique de Lille EUDIL - Villeneuve d'Ascq - France
In Revue FranGaise de G~otechnique,
Nr. 43, second quarter 1988, 35-46.
SUMMARY Hydrostatic compression and conventional triaxial compression tests were performed on a white, highly porous chalk for confining pressure up to 50 MPa. The obtained results have allowed fondamental aspects of the chalk behaviour to be revealed. A LADE elastoplastic model with two yield surfaces was used for modelling : some important modifications were proposed for taking into account special aspects of the chalk behaviour. Proportional loading tests and lateral extension tests were performed to study the chalk's behaviour in homogeneous problems. The modified LADE elastoplastic model was used to simulate these tests. In global way, model's predictions were found to be in satisfactory agreement with the experimental results. Finally, hollow cylinder tests were realized to examine chalk's behaviour in typical boundary conditions problems. The modified elastoplastic model has then been introduced into a finite elements program which was used to simulate the hollow cylinder tests. Comparisons between experimental and predicted results were also given and seem to be satisfactory.