Richard J. Finno

DIGITAL IMAGE CORRELATION TO EVALUATE SHEAR BANDING IN DILATIVE SANDS

In this paper, experimental results are presented of plane strain compression experiments on dense sands, in which the technique of Digital Image Correlation (DIC) was used to quantify localized displacements. The technique is described in detail. Results of accuracy tests of the DIC technique indicated that localized displacements were measured to an accuracy of 0.008 mm. Typical DIC analyses produced approximately 250 displacement points within a shear band, which served as input for regression-based strain computation, yielding highly accurate volumetric strain data for determining evolutions to critical state. Displacement data was also used to examine volume changes outside the shear band. The DIC technique also enabled measurement of shear band inclination and thickness throughout the deformation process.

Influence of depositional processes on the geotechnical parameters of Chicago glacial clays

Abstract The effects of depositional environment on properties, stress history, and undrained and drained shear-strength parameters are evaluated for Chicago glacial clay. Recent geology and basic depositional environments are described. Both laboratory and in-situ shear-strength evaluations have been conducted at several sites in the study area. Results of the investigations indicate that, while depositional environment has a large impact on the engineering properties of these clays, identification of the depositional environment is in itself insufficient to strength parameters. Post-depositional events are shown to alter the stress history imparted during deposition and thus impact shear-strength parameters.

Stress-Strain Responses of Block Samples of Compressible Chicago Glacial Clays

This paper presents the results and analysis of a laboratory investigation of the behavior of lightly overconsolidated compressible Chicago glacial clays over a wide strain range. Each specimen was trimmed from high quality block samples taken from an excavation in Evanston, Illinois. Specimens were instrumented with three sets of bender elements and local LVDTs. After K0 consolidation to the in situ vertical effective stress of the block, drained stress probe tests were conducted. Results of bender elements tests obtained prior to stress probing show that compressible Chicago glacial clay initially is cross anisotropic. Propagation velocities measured by bender elements in axial direction after K0 reconsolidation and drained creep agrees well with the in situ shear wave velocity measured by seismic cone penetration tests. Results of drained stress probe tests are analyzed in terms of shear, volumetric and coupled stiffness, stiffness degradation, and direction of loading. The significant variability of s...

Analysis of braced excavations with coupled finite element formulations

Abstract Parametric studies of braced excavation behavior based on a coupled finite element formulation are presented to evaluate the current state-of-the-art. Effects of constitutive model, boundary conditions, and details of the construction process including sheet-pile installation and amount of overexcavation are considered in the analyses. Capabilities of current methods to replicate various aspects of observed performance are presented. The relative effect of each of the modeling aspects are illustrated by comparing results of both boundary displacement and stress-controlled simulations of construction with observed performance of a 40 ft deep cut through saturated clay.

Effects of swelling during saturation in triaxial tests in clays

Effects of swelling during saturation in triaxial tests on compressible Chicago glacial clays are assessed from results of triaxial compression tests on block samples cut from excavations, thin-wall Shelby tube samples, and reconstituted specimens. The results are presented in terms of the stress-strain response during saturation, k 0 reconsolidation and shearing. Bender element tests were also performed to investigate the effects of swelling on the shear wave velocities during k 0 reconsolidation. Results showed that the swelling during saturation lowered the shear wave velocity, thereby inferring a change in the original structure of natural clay. Responses at strains less than 0.01 % were most affected by the saturation-induced swelling. To minimize these changes, it is recommended that the measured residual stress is applied prior to saturating the soil. Based on these results, the saturation stage should be considered as much a part of a triaxial test as consolidation and shearing.

Anisotropy Evolution and Irrecoverable Deformation in Triaxial Stress Probes

This paper presents the results and analysis of experimental investigations of compressible Chicago clays with regard to the evolution of stiffness anisotropy. The experimental program was conducted on high-quality block samples obtained from the excavation for the Block 37 project in Chicago. The specimens were consolidated to in situ stresses via a recompression technique and then were subjected to directional stress probes. On-specimen LVDTs and an internal load cell with high accuracy were used for stress-strain response of the specimen. The stiffness and stiffness anisotropy ratio at very small strains were obtained synchronously from bender element tests during the consolidation and stress probes. The structural change as anisotropy evolves within a specimen is discussed. The results of the experimental program showed that compressible Chicago clay is an initially cross-anisotropic material under the in situ stresses. This anisotropy changes at the onset of irrecoverable deformation at stresses defined by previously established Y2 yield surfaces. DOI: 10.1061/(ASCE)GT.1943-5606.0000575.

Observed Performance of the One Museum Park West Excavation

AbstractGround movements observed during foundation installation and basement construction of a residential 53-story RC tower are presented. The One Museum Park West building is located in Chicago, Illinois, and was developed using a combination of bottom-up methods, used for the construction of a central concrete core of the building, and top-down methods to build five levels of basements. The excavation extended 13–15 m below grade and was made through soft to medium-stiff clays. The building was supported by drilled shafts and a perimeter wall formed by secant piles that transitioned to tangent piles below the bottom of the cut. The system was laterally braced with RC floor slabs structurally connected to the secant pile walls and the RC core. Field performance data were collected by means of settlement points and inclinometers located close to the walls on two sides of the excavation. The construction sequence and attendant ground movements during each main activity are summarized. As much as 160 mm o...

Effect of Gas on the Mechanical Behavior of Medium-Dense Sands

AbstractThis paper presents the results of monotonic and cyclic triaxial tests performed on gassy, medium-dense sand specimens. These sands are representative of conditions in a loose-sand deposit that was densified using multiple blasting passes at a site in South Carolina. The equipment and laboratory testing procedures used to reproduce the postblast densification conditions observed at a field test are described in detail. Results of undrained and drained compression tests showed that the gassy-specimen responses were bounded by the fully saturated drained and undrained responses. The undrained test results showed that the presence of gas, even in small amounts, made the soil more compressible and restricted the buildup of excess pore-water pressures as compared with those pressures observed in fully saturated specimens. Additionally, the shear strengths of gassy, medium-dense sand specimens were similar to those observed in saturated, loose sands sheared under drained conditions. For a given cyclic s...

Automated Monitoring of Supported Excavations

This paper describes remote and automatic monitoring systems for measuring vertical and horizontal displacements and tilt of structural elements. An automated total station and system of tiltmeters were employed at the excavation for the Ford Engineering Design Center. The 9.1-m-deep excavation was made through fill and soft clays and undercut the shallow foundations for a building 6 m from the edge of the excavation. The excavation support system consisted of a sheet pile wall supported by two levels of cross-lot and diagonal internal bracing. The two automated systems, the structural support system and construction details are described. Selected ground and structural responses collected by the automated systems are compared to those collected with conventional methods. The accuracies of the measured automated responses are discussed. The tilt meter data are shown to supplement the inclinometer data so that structural responses of an adjacent structure to the excavation can be evaluated.

EFFECT OF CONSOLIDATION ON STRAIN LOCALIZATION OF SOFT CLAYS

Abstract A finite element formulation developed by Belytschko and his coworkers [1] is used to examine localized deformation as it exists for laboratory specimens of compressible Chicago clays. The element is based on an assumed strain formulation wherein localized and non-localized zones are embedded into an element when material based bifurcation is detected. A plane strain compression test of a natural clay specimen in which deformations localized into a single shear band during undrained shear is simulated using this element. Localization is initiated by imposing a non-uniform applied displacement consistent with that measured experimentally. Results indicate that to insure localization to a single band, considerations must be made for non-uniformities developed during the consolidation phase.