Crushed Glass-Dredged Material (CG-DM) Blends: Role of Organic Matter Content and DM Variability on Field Compaction

Trial embankments comprised of crushed glass-dredged material (CG-DM) blends and a 100% DM embankment were constructed to provide the necessary data sets to determine if a moisture content (MC) correction was required for the nuclear density (ND) gauge, as DM may contain a high organic matter content (OC). The MCs of thin-walled tube samples of CG-DM blends collected immediately below the ND gauge were compared to the corresponding ND gauge readings. A direct correlation between the MC data pairings from the tube samples and ND gauge readings showed that the ND gauge was greater than 97% accurate for MCs up to 55% and OCs up to 10% for the CG-DM blends evaluated in this study. However, the MC determined by the ND gauge was underpredicted (not overpredicted) by approximately 2.5%, contrary to theoretical expectations. A comparison of the average MC results per embankment indicated that the ND gauge was generally within 1% of the tube sample values, again on the low side. Interestingly, the rutting of the individual embankment lifts, often used as an informal metric for compaction compliance also was found to be contrary to expectations. The (re)constructed CG-DM embankments of this study were again shown to satisfy local Department of Transportation embankment construction criteria in most cases.     

Dynamic Response of Compacted CG, DM, and CG-DM Blends

The cyclic behavior of 9.5 mm (3/8 in.) minus curbside-collected crushed glass (CG) blended with dredged material (DM), classified as an organic silt by the Unified Soil Classification System, was evaluated using a cyclic triaxial testing program. Tests were performed on 100% CG and 100% DM specimens, and 20/80, 40/60, 60/40, and 80/20 CG-DM blends (dry CG content is reported first). The specimens were compacted to a dry unit weight equivalent to 95% of the maximum dry density based on ASTM D1557. For each material, a minimum of three specimens was tested at cyclic stress ratios of 0.20, 0.35, and 0.45. The DM used in this study exhibited significant plasticity, which would be expected to display cyclic softening behavior according to liquefaction susceptibility criteria proposed by Boulanger and Idriss in 2006. However, the high density of the material resulted in transitional behavior between cyclic mobility and cyclic softening. These findings suggest that as long as the CG, DM, and CG-DM blends are compacted, they should not be susceptible to strength loss or large strain under cyclic loading.     

Liquefaction Resistance of Clean and Nonplastic Silty Sands Based on Cone Penetration Resistance

Liquefaction of granular soil deposits is one of the major causes of loss resulting from earthquakes. The accuracy in the assessment of the likelihood of liquefaction at a site affects the safety and economy of the design. In this paper, curves of cyclic resistance ratio (CRR) versus cone penetration test (CPT) stress-normalized cone resistance qc1 are developed from a combination of analysis and laboratory testing. The approach consists of two steps: (1) determination of the CRR as a function of relative density from cyclic triaxial tests performed on samples isotropically consolidated to 100 kPa; and (2) estimation of the stress-normalized cone resistance qc1 for the relative densities at which the soil liquefaction tests were performed. A well-tested penetration resistance analysis based on cavity expansion analysis was used to calculate qc1 for the various soil densities. A set of 64 cyclic triaxial tests were performed on specimens of Ottawa sand with nonplastic silt content in the range of 0–15% by weight, and relative densities from loose to dense for each gradation, to establish the relationship of the CRR to the soil state and fines content. The resulting (CRR)7.5-qc1 relationship for clean sand is consistent with widely accepted empirical relationships. The (CRR)7.5-qc1 relationships for the silty sands depend on the relative effect of silt content on the CRR and qc1. It is shown that the cone resistance increases at a higher rate with increasing silt content than does liquefaction resistance, shifting the (CRR)7.5-qc1 curves to the right. The (CRR)7.5-qc1 curves proposed for both clean and silty sands are consistent with field observations.     

Field Evaluation of Crushed Glass–Dredged Material Blends

Based on the laboratory results reported in a companion paper, three crushed glass–dredged material (CG–DM) blends were prepared and evaluated in the field to explore the feasibility of using CG–DM blends in general, embankment and structural fill applications. A trailer-mounted pugmill successfully prepared 20/80, 50/50, and 80/20 CG–DM blends (dry weight percent CG content reported first) within a tolerance of ±5 dry % by weight of the targeted percentages. Blending criteria were routinely met at pugmill throughputs up to 1,500?m3/day. The constructed 20/80 CG–DM embankment was compacted to a minimum of 90% modified Proctor compaction, whereas the 50/50 and 80/20 CG–DM embankments were constructed to a minimum of 95% modified Proctor compaction. Twenty to 80% CG addition to DM resulted in 1.5–5.5?kN/m3 increases in field dry densities above 100% DM, densities not achievable with other DM stabilization techniques such as Portland cement, fly ash, and/or lime (PC/FA/lime) addition. CG substantially improved the workability of DM allowing construction with conventional equipment and three person crew while achieving very consistent and reproducible results during a timeline of frequent and heavy precipitation events. The 20/80, 50/50, and 80/20 CG–DM embankments were characterized by average cone tip resistances on the order of 1.0, 1.5, and 2.0?MPa, respectively. An environmental evaluation of 100% CG, DM and 50/50 CG–DM blend samples coupled with an economic analysis of a scaled-up commercial application illustrated that the CG–DM blending approach is potentially more cost effective than PC/FA/lime stabilization approaches. These features of CG–DM blending make the process attractive for use in urban and industrial settings.     

Random Field Modeling of CPT Data

An extensive set of cone penetration tests (CPT) soundings are analyzed statistically to produce an a priori 1D stochastic soil model for use at other similar sites. The data were collected by the Norwegian Geotechnical Institute at the site of a new airport just north of Oslo, Norway, and consists of 143 CPT soundings over an area of about 18 km2 in a reasonably homogeneous soil mass. The CPT data consist of cone tip resistance, side friction, and pore-water pressure measurements. Only the cone tip resistance is considered in this study, it being considered closest to a “point” property of the soil, and only the vertical variation is characterized. To perform the statistical analysis, the data sets are viewed as independent 1D realizations extracted from a statistically homogeneous 3D random field. Plots of various transformations of the data indicate that the cone tip resistance records are best represented using a fractal stochastic model corresponding to so-called fractional Brownian motion, and its parameters are estimated via maximum likelihood.     

Load Testing and Settlement Prediction of Shallow Foundation

The purpose of this study was to critically examine insitu test methods as a means for predicting settlement of shallow foundations. Accordingly, a 1.8?m (6?ft) diameter concrete footing was statically load tested. Prior to construction, insitu [standard penetration test (SPT), cone penetration test (CPT), dilatometer (DMT), and pressuremeter (PMT)] and laboratory tests were performed to determine engineering properties of the soil. Predictions of the footing settlement were made by traditional as well as finite element methods. The results of the static load test showed settlements were over predicted by all methods. However, the traditional methods provided reasonable settlement estimates using either SPT-N or back computed CPT(N) as input. Finite element analyses using either DMT or CPT derived input parameters provided reasonable settlement estimates. Finite element analyses using SPT or PMT derived input parameters provided poor settlement estimates. The Mohr–Coulomb (elastoplastic) model, accounting for overconsolidation, provided better estimates than the hardening soil (hyperbolic-cap) model for all insitu test derived parameters.     

A Self-Consistent Approach for Necking Correction in Tensile Specimens With Rectangular Cross-Section Using a Novel Mirror Fixture

True stress?Ctrue strain cannot be computed beyond necking, unless the effects of necking on the geometry of the tensile specimen and the stress state are accurately quantified. Necking produces a triaxial stress state that does not reflect the true uniaxial flow stress of the material. Therefore, the true stress must be multiplied by a correction factor to correct for the effect of the triaxial stresses and obtain the true uniaxial flow stress. While necking effects are easily quantified for specimens with circular cross-sections, specimens with rectangular cross-sections can exhibit complex necking geometry. In this paper, the necking behavior of pure Sn and Sn-3.5Ag-0.7Cu solders was studied to: (1) quantify necking geometry in rectangular specimens using a novel mirror fixture and a high speed camera during tests conducted at 10^?3 to 30?s^?1, and (2) develop a self-consistent method of necking correction that incorporates strain rate effects and can be applied to many materials.     

CPT-Based Probabilistic and Deterministic Assessment of In Situ Seismic Soil Liquefaction Potential

This paper presents a complete methodology for both probabilistic and deterministic assessment of seismic soil liquefaction triggering potential based on the cone penetration test (CPT). A comprehensive worldwide set of CPT-based liquefaction field case histories were compiled and back analyzed, and the data then used to develop probabilistic triggering correlations. Issues investigated in this study include improved normalization of CPT resistance measurements for the influence of effective overburden stress, and adjustment to CPT tip resistance for the potential influence of “thin” liquefiable layers. The effects of soil type and soil character (i.e., “fines” adjustment) for the new correlations are based on a combination of CPT tip and sleeve resistance. To quantify probability for performance-based engineering applications, Bayesian “regression” methods were used, and the uncertainties of all variables comprising both the seismic demand and the liquefaction resistance were estimated and included in the analysis. The resulting correlations were developed using a Bayesian framework and are presented in both probabilistic and deterministic formats. The results are compared to previous probabilistic and deterministic correlations.     

Characterization of Liquefaction Susceptibility of Sands by Means of Extreme Void Ratios and/or Void Ratio Range

The liquefaction susceptibility of various graded fine to medium saturated sands are evaluated by stress controlled cyclic triaxial laboratory tests. Cyclic triaxial tests are performed on reconstituted specimens having global relative density of 60%. In all cyclic triaxial tests, loading pattern is selected as a sinusoidal wave form with 1.0 Hz frequency and effective consolidation pressure is chosen as 100 kPa. Liquefaction resistance is defined as the required cyclic stress ratio causing initial liquefaction in 10 cycles during the cyclic triaxial test. The results are used to draw conclusions on the effect of the extreme void ratios and void ratio range on the liquefaction resistance of various graded sands.     

Case History Evaluation of Laterally Loaded Piles

This paper examines seven case histories of load tests on piles or drilled shafts under lateral load. Since the current design software to estimate lateral load resistance of deep foundations requires p-y curves. The first approach used was correlative whereby soil parameters determined from in situ tests [standard penetration test (SPT) and cone penetration test (CPT)] were used as input values for standard p-y curves. In the second approach p-y curves were calculated directly from the stress deformation data measured in dilatometer (DMT) and cone pressuremeter tests. The correlative evaluation revealed that, on the average, predictions based upon the SPT were conservative for all loading levels, and using parameters from the CPT best predicted field behavior. Typically, predictions were conservative, except at the maximum load. Since traditionally SPT and CPT correlation-based p-y curves are for “sands” or “clays,” this study suggests that silts, silty sands, and clayey sands should use cohesive p-y curves. For the directly calculated curves, DMT derived p-y curves predict well at low lateral loads, but at higher load levels the predictions become unconservative. p-y curves derived from pressuremeter tests predicted well for both “sands” and “clays” where pore pressures are not anticipated.     

Effects of Cross Anisotropy on Three-Dimensional Behavior of Sand. II: Volume Change Behavior and Failure

The volume change behavior of cross-anisotropic sand is studied using results of a series of cubical triaxial tests. The relationships between the volumetric response, failure, and shear localization are addressed. Rates of dilation under various three-dimensional stress conditions are evaluated in conjunction with the peak shear resistance and initiation of shear banding in specimens of dense Santa Monica beach sand. The location of the line in principal stress space along which the tendency to deform changes from compressive to dilative (the characteristic line) is determined using two different methods. The uniqueness of this characteristic line for cross-anisotropic materials is analyzed.     

Shear Strength Behavior of Fiber-Reinforced Sand Considering Triaxial Tests under Distinct Stress Paths

The results of drained triaxial tests on fiber reinforced and nonreinforced sand (Osorio sand) specimens are presented in this work, considering effective stresses varying from 20 to 680?kPa and a variety of stress paths. The tests on nonreinforced samples yielded effective strength envelopes that were approximately linear and defined by a friction angle of 32.5° for the Osorio sand, with a cohesion intercept of zero. The failure envelope for sand when reinforced with fibers was distinctly nonlinear, with a well-defined kink point, so that it could be approximated by a bilinear envelope. The failure envelope of the fiber-reinforced sand was found to be independent of the stress path followed by the triaxial tests. The strength parameters for the lower-pressure part of the failure envelope, where failure is governed by both fiber stretching and slippage, were, respectively, a cohesion intercept of about 15?kPa and friction angle of 48.6?deg. The higher-pressure part of the failure envelope, governed by tensile yielding or stretching of the fibers, had a cohesion intercept of 124?kPa, and friction angle of 34.6?deg. No fiber breakage was measured and only fiber extension was observed. It is, therefore, believed that the fibers did not break because they are highly extensible, with a fiber strain at failure of 80%, and the necessary strain to cause fiber breakage was not reached under triaxial conditions at these stress and strain levels.     

Undrained Anisotropic Monotonic Behavior of Sand from In Situ Tests

A procedure for estimating the undrained stress-strain behavior of sand from drained self-boring pressuremeter and seismic piezocone penetration tests is proposed in this paper. The procedure offers an inexpensive alternative to laboratory testing and avoids the uncertainty of the empirical methods based on index measurements such as the Standard Penetration Test blow count and the tip resistance in a Piezocone Penetration Test (CPTU). To check its validity, the proposed procedure was used to infer the undrained triaxial stress-strain curves and the results were compared with laboratory triaxial tests on undisturbed samples. The undrained limit equilibrium stability of a dike was also assessed using the inferred stress-strain behavior to illustrate the usefulness of the procedure. The result of the stability analysis was found to be in qualitative agreement with the observed performance of the dike during a recent field experiment attempting to trigger static liquefaction.     

Modeling Cross Anisotropy in Granular Materials

A constitutive model has been developed to capture the behavior of cross-anisotropic frictional materials. The elastoplastic, single hardening model for isotropic materials serves as the basic framework. Based on the experimental results of cross-anisotropic sands in isotropic compression tests, the principal stress coordinate system is rotated such that the model operates isotropically within the rotated framework. Experimental plastic work contours on the octahedral plane are plotted for a series of true triaxial tests on dense Santa Monica Beach sand to study the effects of cross anisotropy on the evolution of yield surfaces. The amount of rotation of the yield and plastic potential surfaces decreases to zero (isotropic state) with loading. The model is constructed for cases where the principal stress and material symmetry axes are collinear and no significant rotation of principal stresses occur. The model incorporates fourteen parameters that can be determined from simple experiments, such as isotropic compression, drained triaxial compression, and triaxial extension tests. A series of true triaxial and isotropic compression tests on dense Santa Monica Beach sand are used as a basis for verification of the capabilities of the proposed model.     

Saturation and Preloading Effects on the Cyclic Behavior of Sand

In order to study pore water pressure response and liquefaction characteristics of sand, which has previously experienced liquefaction, two series of cyclic triaxial tests were run on medium dense sand specimens. In the first test series the influence of the soil saturation under undrained cyclic loading has been studied. It summarizes results of cyclic triaxial tests performed on Hostun-RF sand at various values of the Skempton’s pore-pressure coefficient. Analysis of experimental results gives valuable insights on the effect of soil saturation on sand response to undrained cyclic paths. In the second series of tests, the preloading influence on the resistance to the sands liquefaction has been realized on samples at various histories of loading. It was found that a large preloading induces a reduction of the resistance of sands to liquefaction.     

SPT and CPT Testing for Evaluating Lateral Loading of Deep Foundations

Current design software (FloridaPier, Com624P) requires p-y curves to estimate the foundation lateral load resistance. Input parameters used to develop these curves can be obtained from in situ [standard penetration test (SPT) and cone penetration test (CPT)] correlations. This paper presents an evaluation of predictions using input soil parameters from SPT and CPT correlations versus field measured values. A lateral load test database consisting of 24 SPT and 6 CPT data sets was developed. The comparisons showed that four different SPT correlations for ? coupled with three different k-values all produce similar R-values. (R-value = measured∕predicted × 100%). Therefore, little difference exists between the SPT correlation combinations, albeit the estimated k value has a greater effect on predicted deformation. Similar combinations of CPT correlations also show little effect among the commonly used correlations. SPT predictions are quite conservative at low load levels (R-values ≈ 53%) and remain conservative (R-values ≈ 87%) at high load levels. Also, the scatter (standard deviation) is high (≈40%). CPT evaluations gave unconservative predictions (R-values ≈ 105 to 154%). In addition, the scatter (standard deviation) is high (≈34 to 74%).     

Elastic Anisotropic Viscoplastic Modeling of the Strain-Rate-Dependent Stress–Strain Behavior of K0-Consolidated Natural Marine Clays in Triaxial Shear Tests

This paper presents a new three-dimensional (3D) anisotropic elastic viscoplastic (EVP) model for the time-dependent stress–strain behavior of K0-consolidated marine clays. A nonlinear creep function with a limit for the creep volumetric strain under an isotropic or odometer K0-consolidated stressing condition and a nonsymmetrical elliptical loading locus are incorporated in the 3D anisotropic EVP model. An α-line defines the inclination of the nonsymmetrical elliptical loading locus in the p′-q plane and is commonly used for natural soils. All model parameters are determined from the results of one set of consolidated undrained compression tests and an isotropic consolidation/creep test. With the parameters determined, the 3D anisotropic EVP model is used to simulate the behavior of K0-consolidation tests and the strain-rate-dependent stress–strain behaviors of the K0-consolidated triaxial compression and extension tests on natural Hong Kong marine deposit clay specimens. These triaxial K0-consolidated specimens were sheared at step-changed axial strain rates from +2?to?+0.2, +20, ?2 (unloading) and +2%/h (reloading) for compression tests; or from ?2?to??0.2, ?20, +2 (unloading), and ?2%/h (reloading) for extension tests, all in an undrained condition. The simulation results of all these tests are compared with the test results. The validation and limitations of the model are then evaluated and discussed.     

Behavior of Concrete in Water Subjected to Dynamic Triaxial Compression

To understand the behavior of concrete material in ambient water, a series of triaxial compressive tests of concrete cylindrical specimens (? 100×200?mm) was conducted on a large scale triaxial machine. The acting pattern of water, confining pressure, loading strain rate, and moisture content were chosen as test parameters. The water acting patterns on concrete were directly divided into mechanical loading and real water loading according to whether the specimens were directly exposed to water or not. The confining pressure ranged from 0–8 MPa and the strain rate included 10?5/s, 10?3/s, and 10?2/s. By testing dry and saturated specimens, the effect of moisture on concrete strength was also examined. The test results indicated that the compressive strengths of both dry and saturated concrete increase obviously with the confining pressure under mechanical confining pressure. However, the effect on the strengthened dry concrete specimens is more significant. The strength of dry concrete under real water loading decreased remarkably, even less than its uniaxial strength, whereas the compressive strength of the saturated concrete specimen under real water loading is close to its uniaxial compressive strength. The strength of concrete increases with strain rate, and this phenomenon becomes more apparent under water loading.     

Examination of the Response of Regularly Packed Specimens of Spherical Particles Using Physical Tests and Discrete Element Simulations

Significant insight into the response of granular materials can be gained by coupling accurately controlled physical tests with complementary discrete element simulations. This paper discusses a series of triaxial and plane strain laboratory compression tests on steel spheres with face-centered-cubic and rhombic packings, as well as discrete element simulations of these tests. The tests were performed on specimens of uniform-sized steel balls and on specimens of steel balls with specified distributions of ball diameters. The packing configurations are ideal and differ considerably from real sand specimens, however, studies of such idealized granular materials can yield considerable insight into the response of granular materials and the capability of discrete element simulations to capture the response. The differences in response for the two packing configurations considered illustrate the importance of fabric. The numerical simulations captured the observed laboratory response well if the particle configurations, particle sizes, and boundary conditions were accurately represented. However, the postpeak response is more difficult to capture, and it is shown to be sensitive to the coefficient of friction assumed along the specimen boundaries. The simulations of the tests on the nonuniform-sized specimens demonstrated a clear correlation between strength and coordination number.     

Shear Banding in True Triaxial Tests and Its Effect on Failure in Sand

The occurrence of failure, mechanisms that create failure, and soil behavior in the vicinity of failure have been investigated. One mechanism is smooth peak failure, in which the soil continues to behave as a continuum with uniform strains, and smooth peak failure is followed by strain softening. Another mechanism is shear banding, whose occurrence in the plastic hardening regime limits the strength of the soil. True triaxial tests have been performed on tall prismatic specimens of Santa Monica Beach sand at three relative densities in a modified version of a cubical triaxial apparatus to study the effect of shear banding on failure in the full range of the intermediate principal stress. The experiments show that the strength increases as b [=(σ2 ? σ3)/(σ1 ? σ3)] increases from 0 to about 0.18, remains almost constant until b reaches 0.85, and then decreases slightly at b = 1.0. Shear banding initiates in the hardening regime for b-values of 0.18–0.85. Thus, peak failure is caused by shear banding in this middle range of b-values, and a smooth, continuous 3D failure surface is therefore not generally obtained for soils.