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The concept of effective stress for soil concrete and rock 1

Lade P V de Boer R Ge? otechnique No The concept of e ?ective stress for soil concrete and rock P V L A D E Ã a n d R D E B O E R Many di ?erent expressions have been proposed for the e ?ective stress principle for porous media but none has clearly been acknowledged as being the correct one It should be possible to determine the correct expression because this is a fundamental principle of mechanics Following a review of the candidate expressions proposed for soil concrete and rock a comprehensive expression is derived involving the factors observed in experiments on arti cial rock' In this new expression a distinction is made between the compressibilities of grains and skeleton due to total stresses and pore pressures This general and more comprehensive expression is then tested against the experimental evidence The expression may be specialized for a granular materials with separate grains with contact points and b solid rock with interconnected pores The new expression for the e ?ective stress contains most of the previously proposed expressions as special cases Based on results of compression tests on quartz with hard grains and on gypsum with soft grains it is shown that Terzaghi's e ?ective stress principle works well for most geotechnical applications but signi cant deviations occur at very high stresses KEYWORDS compressibility constitutive relations elasticity laboratory tests pore pressure stress analysis Un grand nombre d'expressions di ?e? rentes du principe de la tension ef cace ont e? te? propose? es pour les mate? riaux poreux mais aucune n'a vraiment e? te? accepte? e comme parfaite Il devrait eÃtre possible de de? terminer la bonne expression vu qu'il s'agit laÁ d'un principe fondamental de me? canique ApreÁs avoir examine? les expressions propose? es pour le sol le be? ton et la roche les auteurs ont de? rive? une expression globale qui met en jeu les facteurs observe? s lors d'essais sur de la roche arti cielle ? Cette nouvelle expression fait la distinction entre les compressibilite? s des grains et du squelette dues aux contraintes totales et aux pressions interstitielles Les re? sultats d'e? tudes expe? rimentales servent ensuite aÁ ve? ri er la validite? de cette expression ge? ne? rale et plus e? tendue L'expression peut eÃtre modi e? e pour les mate? riaux granulaires aÁ grains se? pare? s avec points de contact et la roche en place aÁ interstices interconnecte? s Cette nouvelle expression de la tension ef cace contient comme cas particuliers la plupart des expressions propose? es ante? rieurement AÁ partir des re? sultats d'essais sur du quartz aÁ grains durs et du gypse aÁ grains tendres on montre que le principe de la tension ef cace de Terzaghi s'applique aÁ la plupart des cas ge? otechniques mais qu'il se produit des e? carts importants quand les contraintes sont treÁs e? leve? es INTRODUCTION The formulation of the concept of e ?ective stress for porous media such as soils is most