Undrained behaviour of soft clays in triaxial tests

74~

equation relating void r~tio to effective stress. It is co~cluded that axial deformations depend on in~tis_l void r~Btio and a parmneter defining the shape of the consolidation curve, and, since preconsolidation pressure depends only on the shape parameter, that ~reconsolidation pressure is not sufficient to estimate a foundation's allowable stress.

833089

DIRECTIONAL ~{F~:RING CFI/. Rodriguez del Camlno, J I; Dunstan, T Proc 10th Internatlon~l Conference on Soil Mechanics and Foundation Engineering, StockhoLm, 15-19 June ]981, VI, P765-7V0. Publ Rotterdam: :.. A. Balkema, 198] Describes apparatus capable of spplyirg normal and shear stresses unlfor~ly to four faces of a cubic sample under plane strain testing conditions by means of fl~xlble boundaries. It allows freedom of sample deformation up to 16 per cent of the major principal strain and has a working range limited to 150kN per cu m. Loose, dry samples of sand, prepared by pouring through air to produce a void ratio of aplroxlmately 0.72, were tested. Strain measurements were made from photogral~hs taken after each losdlng increment. Results indicate that stress-straln-strength behavlour is not influenced by the direction of the major ~rlnclpal stress, confirming that edge effects and non-uniformity of strain within the sample are negligible.

833o9o

BIAXIAL APPARATUS FOR TESTING SS{FA]9 BANDS IN SOILS Vardoulakls, I; Goldscheider, M Proc 10th Interrmtional Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15-19 June 1981, V1, P819-824. Publ Rotterdam: A. A. Bslkema, 1981 Describes a new bisxial apparatus which allows for spontaneous shear band formation within a h o m ~ e n e o u s l y defcanned sample. The device allows simple and accurate measurement of: (I) the shear band inclination angle, (2) the Mmhr-Coulomb friction angle at peak and in the critical state, and (3) the Coulomb friction angle and the ec~resporztlng dilatancy a r ~ e for all states between peak and the critical state.

833092

Surface properties 833o93

TRUE TRIAXIAL TESTS ON BOSTON BLUE CLAY Wood, D M Proc lOth Interrmtlonal Conference on Soil Mechanics and Foundation Engineering, ~tockholm, 15-19 June 1981, Vl, I~325-830. Publ Rotterdam: A. A. Ba]~kema, 1981

LUBRICANT ih~9 ANTILUBRIC:-?~ ~ ~:FECT 0~- "<
UNDRAINED BEHAVIOUR OF SOFT CL&YS IN TRIAXIAL TESTS Sanchez, J M; Sagaseta, C Proc 10th Internstiorml Conference on Soll Mechanics and Foundation Engineering, StockhoLm, 15-19 June 1981, V!, FI71-TV4. Publ Rotterdam: A. A. Balkema, 1981 Undrained triaxial compression tests, using lubricated end platens, were carried out on remoulded samples of soft clay consolidated with different stress histories. The results show that the effective stress paths follow a bi-linear shape with a break point, corresponding to some abrupt change in the cluny structure. Pore pressure coefficients are related to the previous stress history, and undrained shear strength results show reasonable agreemerit with the failure condition proposed by Ballester and Sagaseta.

833o91

True tri'aa:i~l te~ts on Boston blue cl'y ~'ere performed as p ~ t of 'n Investlg.:tion of ::.:i1 capacity of offshore piles. ~ e r'pid Inst liation of a pile w~s modc]l~] ~s the undrained expansion of ~ cylindric~:l c vlty. The ':ssOc~ated strain path co~n be followed coruo!etely in constant volume pl~ne str
833o94

FRICTION BETk~I,N : ~ :9!T I, "URF CP Yoshin~, Y; K i s h i d ~ T Proc 10th Interr~tlo~l Conference on "oil ~!echanlcs ~nd Foundation Engineering, Stockholm~ 15-19 June 199!, V1, P831-834. Publ Rotterdam: / . . B~lkem~:, ]98~ Presents results of l~,bor~tory te~ts on friction between dry sand und ~ metul surf~ce under constant normal stress conditions over "~ wide range of surface roughness and s~nd density. A ring torsion apparatus was used to achieve uniform stress distribution over the cont:~ct surf~ce and within the s-~nd specimen. _The deformation in sand r~ar the met~=l surf~ce was observed by means of Z ray r:~diogr~phy. ~ e effects of surface roughness on the ultim: te coefficient of friction, and the rel,~tionship between mobilized friction, shear strain ~nd slip were e×amined. It was concluded th:~t: (I) the frlctior~:l resistance between s~nd and the met~l surface w~s Irlmsrily governed by the roughness of the methyl surface irrespective of the kind of methyl and density of the s~nd, (2) the friction angle of a very smooth metal w3s less th~n one half of the particle-to-partlcle friction angle, (3) the friction ar~le for m very rough surface could be expressed as a function of the ultlm~te angle of internal friction .~nd the p~.rticle-to-particle friction, and (4) no sllp occurred ~:t the contact surfece when the she:~r stress r:=tio was less than 70 to 80 per cent of the coefficient of friction.