Boston Blue Clay Research Articles

The Importance of a Desiccated Crust on Clay Settlements

Analysis of the settlement at five sites on San Francisco Bay Mud and two sites on Boston Blue Clay has shown that where dessicated crust has developed on the clay, spatial variations in the preconsolidation pressure are the most important cause of differential settlements. A simple probabilistic method is described that can be used to establish confidence limits for settlements at sites with a desiccated crust. Variations in preconsolidation pressure are accounted for by estimating confidence limits for a parameter termed the “radius of preconsolidation.” Application of the methodology to the settlement of fills on San Francisco Bay Mud and Boston Blue Clay has shown that the method produces results in good agreement with field measurements and that it is suitable for use in practice. The method can be used for clay deposits which have an overconsolidated layer and requires no more testing than is performed for conventional settlement analyses. However, unlike conventional settlement analyses, it provides an estimate of the likeli-hood that the settlements will vary from the mean by a given amount due to spatial variations in soil properties.

Double‐Yield‐Surface Model. II: Implementation and Verification

A double‐yield‐surface constitutive model for the stress‐strain‐time behavior of cohesive soils is implemented into a nonlinear finite element program based on Biot's three‐dimensional consolidation theory. The coupled soil deformation‐fluid flow model allows creep effects to be modeled concurrently. The soil's hydraulic conductivity is considered a state variable, which varies with the void ratio so that it decreases as the soil compacts. Parametric, laboratory, and field‐case studies are performed on various cohesive soils such as Weald clay, undisturbed bay mud, and Boston blue clay to validate the model. Numerical simulations include drained, undrained, consolidation, creep, stress‐relaxation, and combined stress‐relaxation and creep tests under triaxial and plane‐strain stress conditions. The constitutive model is shown to predict the stress‐strain‐time behavior of “wet” clays more accurately than did an earlier version based on a single‐yield‐surface criterion.

Automated Triaxial Testing of Soft Clays: An Upgraded Commercial System

Abstract The paper evaluates the ability of a widely used automated commercial testing system to perform Ko consolidated-undrained triaxial compression and extension (CKoUC/E) tests on normally consolidated clay. The commercial system uses control software on a microcomputer to operate three digital pressure-volume controllers that control and measure the pore water pressure and volume, the radial stress, and the axial stress and strain for a specimen within a Bishop and Wesley Hydraulic Triaxial Apparatus. Because the commercial system calculates axial stress and strain by relying on indirect measurements assuming idealized behavior of the axial loading assembly, the system was modified to directly measure axial stress and strain. The system was also enhanced to enable shear in triaxial extension and to improve certain other testing procedures. Comparison of results from CKoUC/E tests obtained by the resulting reference system with prior data on resedimented Boston Blue Clay shows good to excellent agreement in 1-D compressibility and undrained stress-strain-strength characteristics. In contrast, stresses recorded by the commercial system resulted in significant overestimates of preconsolidation pressure, undrained strength, and the effective stress envelope, primarily caused by unquantifiable behavior of the axial loading assembly. Based on these results and other experience, the paper suggests features warranting special attention when selecting a commercially available automated triaxial system in order to upgrade the experimental capabilities of a laboratory.

An Endochronic Constitutive Law for Static Shear Behavior of Overconsolidated Clays

Based on the endochronic theory, constitutive relations for overconsolidated clay subjected to static loading have been obtained. The constitutive relations expressed in a closed form can generally describe both deviatoric shear responses and pore pressure responses including negative responses induced by dilatancy. The model further can account for the effect of effective confining pressure on the responses, strain hardening and softening behaviors, dilatancy behaviors, and the effect of overconsolidated ratio, OCR, on the responses. The model is applied to describe the undrained simple shear test data on Boston Blue clay (Ladd and Foott, 1974) and undrained triaxial compression tests on Shanghai clay as well as South Sea clay carried out by the second author. It is shown in this paper that the model yields a reasonable description for the mechanical behaviors of overconsolidated clays subjected to static loading.

Cyclic Behavior of Clays in Undrained Simple Shear

Undrained cyclic shearing of normally consolidated (NC) clays develops positive excess pore pressures and causes a reduction in effective stresses. As a result, initially cycled NC clay subjected to subsequent undrained monotonic shearing behaves as an overconsolidated clay. This observation is extended herein to form the basis of the apparent overconsolidation (AOCR) hypothesis and to develop a framework for predicting the undrained cyclic behavior of slightly overconsolidated clays from the NC behavior. In addition, the AOCR framework allows predictions of clay response due to cyclic shear with variable intensities. Comparisons of predictions with results of cyclic direct simple shear tests on Boston blue clay show generally favorable agreement.

Application of a bounding surface model to Boston blue clay

A formulation for an elastic-plastic Bounding Surface model for soils is presented. The model is calibrated and the predicted and measured response compared for laboratory stress paths and a boundary value problem. The predictions are reasonable, providing confidence in the model formulation, numeric implementation and numeric solution techniques. Possible improvements to the model are discussed.

Capped plasticity model applied to Boston blue clay: McCarron, W O; Chen, W F Can Geotech JV24, N4, Nov 1987, P630–644

Capped plasticity model applied to Boston blue clay: McCarron, W O; Chen, W F Can Geotech JV24, N4, Nov 1987, P630–644

A capped plasticity model applied to Boston blue clay

The performance of a capped plasticity model is evaluated with respect to Boston blue clay. Computed and measured responses are compared for laboratory stress paths and boundary value problems involving construction of highway embankments. It is shown that simplifying assumptions in the model development may lead to difficulties in calibrating the model for general stress paths. The chief model limitations are the use of a circular deviatoric plane and the assumption of symmetry about the hydrostatic axis. However, given the simplicity of the model, it performs well if the limitations are recognized. Key words: cap model, soil plasticity, finite element, embankment analysis.

Disturbances Due to “Ideal” Tube Sampling

The “ideal sampling approach” (ISA) for elucidating, formulating, and predicting minimum disturbance effects in deep tube samples of saturated clays is proposed. The ISA relies on approximate solutions based on the strain path method to incorporate tube penetration disturbances. Laboratory test results on normally consolidated Boston blue clay indicate that the ISA provides more realistic predictions than the existing perfect sampling approach and that tube penetration disturbances are significant in “undisturbed” tube samples of soft clays obtained by means of existing thin‐walled sampling techniques.

Application of a bounding surface model to Boston blue clay

A formulation for an elastic-plastic Bounding Surface model for soils is presented. The model is calibrated and the predicted and measured response compared for laboratory stress paths and a boundary value problem. The predictions are reasonable, providing confidence in the model formulation, numeric implementation and numeric solution techniques. Possible improvements to the model are discussed.

Consolidation After Undrained Piezocone Penetration. II: Interpretation

A rational interpretation method for estimating the in situ consolidation and permeability characteristics of clays from pore pressure dissipation measurements after piezocone penetration is presented. The method is based on linear consolidation analyses and initial pore pressure distributions calculated by the strain path method for undrained penetration in Boston blue clay (BBC). Extensive dissipation measurements in BBC are consistent with predictions for two cone angles and various locations of the porous element. Backfigured values of the coefficients of consolidation and permeability are in reasonable agreement with laboratory and field performance data.

True triaxial tests on Boston blue clay : Wood, D M Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V1, P825–830. Publ Rotterdam: A. A. Balkema, 1981

True triaxial tests on Boston blue clay : Wood, D M Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V1, P825–830. Publ Rotterdam: A. A. Balkema, 1981

Foundation Response Caused by Disturbance of Clay

The history of several selected settlement points at the Prudential Center in Boston, Mass., has been reviewed, and the response of the mat foundation caused by the disturbance of the clay in the installation of piles has been observed. The soil beneath the complex consists primarily of sands and gravel underlain by about 100 ft (30.5 m) of Boston Blue Clay over till and bedrock. Some of the structures are founded on predrilled pipe piles through the clay and evidence suggests that the method of installing these piles, predrilling for two-thirds of the depth of the clay, did not completely prevent volume displacements, disturbance, and settlements in the surrounding area. The data presented also show actual settlements, apparent extent of the disturbed zone, and anticipated future settlements at the selected points.

Predicted and measured behaviour of an embankment on Boston blue clay : DAVIS, EH UNIV. SYDNEY, AUST POULOS, HG UNIV. SYDNEY, AUST 19F, 1T, 10R. AUST. GEOMECH. J. N1, 1975, P1–9

Predicted and measured behaviour of an embankment on Boston blue clay : DAVIS, EH UNIV. SYDNEY, AUST POULOS, HG UNIV. SYDNEY, AUST 19F, 1T, 10R. AUST. GEOMECH. J. N1, 1975, P1–9

Performance of two mat foundations on Boston blue clay : Desimone, SV Gould, JP In Performance of earth and earth supported structures, Vol. 2. Proc. Speciality Conference, Purdue Univ. 1972. 9F, 2T, 11R ASCE, New York, 1972, P953–980

Performance of two mat foundations on Boston blue clay : Desimone, SV Gould, JP In Performance of earth and earth supported structures, Vol. 2. Proc. Speciality Conference, Purdue Univ. 1972. 9F, 2T, 11R ASCE, New York, 1972, P953–980

Pore Size Distribution Studies

Pore-size distribution data for pores of diameters down to 0.016 μm were obtained by mercury porosimetry for a number of laboratory-prepared specimens. Statically-compacted specimens of a kaolinite, an illite, and Boston Blue Clay were evaluated, and changes in the pore-size distribution of the kaolinite were followed as a function of increasing amount of static compaction. In this clay several distinct classes of pore sizes were recognized. Initial compaction reduced the gross pore sizes without influencing the finer classes. After the elimination of the gross pores, further compaction was at the expense of an intermediate class of pores above about 0.14 μm in diameter, pores finer than this being unaffected. Specimens of the kaolinite prepared from a slurry or by sedimentation showed substantially different pore-size distributions from the compacted clay. Drying shrinkage tended to eliminate the larger pores while leaving the smaller ones unaffected. Pore-size distribution appears to be a sensitive parameter with which to follow the effects of microstructural changes which may influence the engineering behavior of the material.

Hydraulic Flow Through Saturated Clays

AbstractThe factors. (1) possible violations of Darcy’s law. (2) electrokinetic coupling. (3) high viscosity. (4) tortuous flow paths, an. (5) unequal pore sizes have been suggested as possible explanations for the differences between hydraulic flow rates in liquid-saturated clays and sands. The effects of these factors on hydraulic flow rates through saturated clays were investigated.Hydraulic flow rates, electrical conductivities, and streaming potentials were measured on natural, sodium, and calcium samples of kaolinite, illite and Boston blue clay. Data were taken after increments of one-dimensional consolidation and rebound over the pressure range from one-sixteenth to 256 atm.The influences of electrokinetic coupling on the hydraulic flow rates were calculated from irreversible thermodynamic relationships together with the hydraulic and electrical data. The other factors were studied by examining the extent to which each factor explains the discrepancies between measured flow rates and those predicted from Darcy’s law and the Kozeny-Carman equation.The results show that. (1) the possible violations of Darcy’s law and electrokinetic coupling are insignificant. (2) high viscosity and/or tortuous flow paths fail completely to account for the discrepancies between measured and predicted flow rates in clays, an. (3) unequal pore sizes can explain all the discrepancies.

Conditioning of agricultural soils with fatty acid still pitch

SummaryStill pitch remaining after the commercial distillation of soy and cottonseed oil fatty acids may be an effective agent for improving the tilth of certain agricultural soils. It greatly increases the water‐holding capacity. Up to 98% of Boston blue clay was converted to water‐stable aggregates by 4% of pitch. One per cent of pitch (.02/1b.) gave 10.8% aggregation while 0.1% of Krilium ($1.47/1b.) gave 8.5%.The cost of soil conditioning with pitch is estimated to be only 15% of the cost in using synthetic polyelectrolytes. Possible methods of application and the use of pitch as a vehicle for trace elements are discussed. Toxicity to plants and effective life in the soil are not known. Field evaluation is urged.