BUTTERFIELD, R. & ANDRAWES, K. Z. (1972). Ge’otechnique, 22, No. 4, 597-617. An investigation of a plane strain continuous penetration problem R. BUTTERFIELD and K. Z. ANDRAWES* The Paper presents the results of a series of experi- ments in which both rough and smooth faced, long, symmetrical 60” wedges were driven vertically, at a constant rate, into uniform beds of sand prepared at different porosities. The apparatus, instrumenta- tion and sample preparation are described and the measured values of penetration resistance, normal and tangential forces and stresses on the wedge face and the friction angles developed are presented and discussed in detail. Continuous penetration problems of this kind are unique in that the displacement field grows at a constant rate whilst maintaining complete geometri- cal similarity unless instability arises due to strain softening of the deforming material. The test re- sults show that instability does not occur in loose sand but develops as the sand bed porosity is de- creased, demonstrating quite conclusively the inade- quacy of analyses which take no account of the kine- matic aspect of the system being investigated. Cette communication donne les rCsultats d’une s&ie d’experiences dans lesquelles de longs coins sym& triques ayant un angle de 60”, rugueux ou lisses, ont CtC enfoncCs verticalement, % vitesse constante dans des lits uniformes de sable prCparCs de man&e & avoir diverses porosit6s. L’appareil, l’instrumenta- tion, et la preparation des Cchantillons sont dhcrits, et on prbsente et discute en detail les valeurs mesurkes de la rCsistance & la p&&ration, des forces et contraintes normales et tangentielles sur la face du coin ainsi que les angles de frottement qui se sont d&elopp&. Les problbmes de p&&ration continue de ce type sont uniques en ce que le champ de diplacement croit & vitesse constante en maintenant une similitude geometrique compl&e, & moins qu’apparaisse une instabilite provoquee par une chute de rCsistance due ?I la deformation du mattriau. Les rbultats des essais montrent que l’instabilitk n’appardt pas dans le sable I&he, mais se d&eloppe pe par reduction de la posositb du lit de sable, ce qui demontre d’une man&e manifeste les insuffisances des analyses qui ne tiennent pas compte de l’aspect cinetique du systeme &udi& The plane strain, continuously penetrating wedge problem has been studied statically and kinematically for classical rigid-plastic weightless, cohesive materials by Hill et al. (1947) and for weightless frictional materials by Shield (1953), Cheatham (1958) and Pariseau and Fairhurst (1967) although only Shield considered the kinematic aspect of the latter problem. By incorporating a flow rule based on the use of the Mohr-Coulomb yield criterion as a plastic potential he predicted unrealistically high dilatancy rates and only more recently have any analyses become available in which fully consistent stress fields, velocity fields and specified dilatancy rates are combined (Butterfield and Harkness, 1971). A preliminary analysis of the wedge penetration problem using the theory mentioned and incorporating material weight, an uplifted-ground surface, specified wedge-soil friction angles and dilatancy rates has now been published (Butterfield and Andrawes, 1972a), although this analysis takes no account of either the non-stationary, expanding deformation field which develops or the essential strain depend- ence of the Coulomb friction angle of granular materials. The experimental results presented show that the work softening (brittle) behaviour of dense granular materials is of paramount importance in continuous deformation problems. Al- though the oscillating penetration resistance which this kind of instability produces is a relevant and common experience in connexion with penetrometers and in soil cutting processes the wedge-soil interaction problem has not previously been explored in any depth. Such a system * Department of Civil Engineering, University of Southampton.