Experimental evaluation of strain softening behavior of normally consolidated Chicago clays in plane-strain compression

Recently measured soil deformation within a saturated soft clay mass adjacent to a 12 m deep braced excavation in Chicago revealed two well-defined failure surfaces during construction. Large ground surface settlements accompanied the development of these surfaces.;This thesis presents the results of a laboratory testing program on natural and remolded clays to evaluate the occurrence of non-uniformities of deformation during undrained shear and their relationship to post-peak response. Natural specimens of Chicago glacial clays were obtained from one hundred and twenty-seven mm diameter thin walled tube samples. They were trimmed and K;Several unique features are incorporated in the plane strain device. A total of 15 sensors are employed to operate the system. Four internal load cells measure axial force, its eccentricity and the friction along the side walls. Seven displacement transducers monitor the axial and lateral displacement of the specimen and the horizontal movement of the base plate. Two pressure transducers monitor pore water pressures at the top and bottom of the specimen. Volume change is monitored with a burette system via a base differential pressure transducer. Cell pressure is monitored with a pressure transducer.;Software has been developed to provide automatic control of back pressure saturation, isotropic and K;The distribution of deformation within the specimen during both consolidation and shear are presented. Pre- and post-peak stress-strain and load-deformation responses are also presented to demonstrate the effects of the uniformity of deformation. Data indicate that softening is a result of the nonuniform deformations, which arise from shear band formation, implies that globally-derived stress-strain response is primarily structurally-controlled and not a generalized material response.