Phillip S. K. Ooi

RESILIENT MODULUS MODELS FOR COMPACTED COHESIVE SOILS

Three-parameter models have been used to represent the effects of confining and shear stresses on the value of resilient modulus. A new generation of such models allows better characterization of the variation of resilient modulus at low deviator stress. These models can be extended to incorporate the effects of soil type, soil structure, and the soil physical state (combination of molding water content and dry unit weight) by relating the three parameters to explanatory variables consisting of common soil parameters. A simple methodology was applied to the results of 78 resilient modulus tests on low- and high-plasticity silts from the island of Oahu, Hawaii, to optimize the choice of explanatory variables. Then, the nonlinear ordinary least-squares method was used to estimate the model parameters. The results indicate that the new generation models not only provide a better fit than the older models, but they also provide a reasonable fit to the data that can capture the effects of stress state, soil type, soil structure, and the soil physical state quite effectively.

Shear Strength Characteristics of Recycled Glass

A comparison of the California bearing ratio (CBR) for recycled glass (RG) with other recycled materials and a basaltic virgin aggregate, all having similar gradations, revealed that the CBR of RG is superior to that of recycled asphalt pavement but less than that of recycled concrete and virgin aggregate. Direct shear tests were then run on the as-received gradation to derive strength parameters for RG prepared at very high and very low relative densities. For “dense” RG, the peak failure envelope was nonlinear with secant friction angles varying from 50° to 61°. For “loose” RG, the peak and critical state failure envelopes were linear with friction angles of 41° and 38°, respectively. Boltons postulate that the peak friction angle is approximately equal to the critical friction angle plus 0.8 times the maximum angle of dilation works well for the RG tested in direct shear. A friction angle of 38° at critical state is significant, implying that RG has the potential to be used in even more foundation and ground improvement applications that are so often associated with transportation infrastructure construction. With increased use of recycled materials, civil engineers can help comply with the demand for sustainable development, a major theme in society today.

Numerical Study of an Integral Abutment Bridge Supported on Drilled Shafts

The majority of integral abutment bridges (IABs) in the United States are supported on steel H-piles to provide the flexibility necessary to minimize the attraction of large lateral loads to the foundation and abutment. In Hawaii, steel H-piles have to be imported, corrosion tends to be severe in the middle of the Pacific Ocean, and the low buckling capacity of steel H-piles in scour-susceptible soils has led to a preference for the use of concrete deep foundations. A drilled shaft-supported IAB was instrumented to study its behavior during and after construction over a 45-month period. This same IAB was studied using the finite-element method (FEM) in both two- (2D) and three dimensional (3D). The 3D FEM yields larger overall pile curvature and moments than 2D because in 3D, the high plasticity soil is able to displace in between the drilled shafts thereby “dragging” the shafts to a more highly curved profile while soil flow is restricted by plane strain beam elements in 2D. Measured drilled shaft axial ...

Performance of a single-propped wall during excavation and during freezing of the retained soil

Abstract A single-propped soldier-pile-tremie-concrete wall was constructed as part of the excavation support system for a tunnel jacking project. This wall supported a 14.3-m-high cut with a significant unbraced height (13.4 m) above the excavation subgrade. A limited area of the excavation subgrade next to the wall was jet grouted to provide stability against base heave. The jet grout also served as a “brace” for the wall below subgrade. The wall and prop were designed to support lateral loads during excavation as well as during ground freezing behind the wall. A ground freezing operation was implemented and carefully controlled to prevent wall yielding. Its success was facilitated by monitoring of wall movements, by drilling relief holes adjacent to the wall to reduce lateral heave pressures due to the soil freezing operation, and by limiting the exposure time of the wall to frost expansion. Measured wall behavior during excavation and during ground freezing is compared to those from finite element analysis for this very unique case history.

Field Behavior of an Integral Abutment Bridge Supported on Drilled Shafts

The abutments of integral bridges are traditionally supported on a single row of steel-H-piles that are flexible and that are able to accommodate lateral deflections well. In Hawaii, steel-H-piles have to be imported, corrosion tends to be severe in the middle of the Pacific Ocean, and the low buckling capacity of steel-H-piles in scour-susceptible soils has led to a preference for the use of drilled shaft foundations. A drilled shaft-supported integral abutment bridge was monitored from foundation installation to in-service behavior. Strain gauge data indicate that drilled shaft foundations worked well for this integral bridge. After 45 months, the drilled shafts appear to remain uncracked. However, inclinometer readings provide a conflicting viewpoint. Full passive earth pressures never developed behind the abutments as a result of temperature loading because thermal movements were small and the long term movements were dominated by concrete creep and shrinkage of the superstructure that pulled the abutments towards the stream. In the stream, hydrodynamic loading during the wet season had a greater effect on the abutment movements than seasonal temperature cycling. After becoming integral, the upright members of the longitudinal bridge frame were not vertical because the excavation and backfilling process caused deep seated movements of the underlying clay resulting in the drilled shafts bellying out towards the stream. This indicates the importance and need for staged construction analysis in design of integral bridges in highly plastic clays. Also, the drilled shaft axial loads from strain gauges are larger than expected.

Examination of Proof Test Extrapolation for Drilled Shafts

The difference between a load test and a proof test is that in a load test, the foundation is loaded to failure, whereas in a proof test, it is usually tested to the design load times the desired margin of safety, and failure may not necessarily be reached. Paikowsky and Tolosko (1999) presented and examined methodologies for obtaining the ultimate capacity from proof test data for driven piles. Load test data on drilled shafts supporting the H-3 freeway viaduct on the island of Oahu in Hawaii are used to test six extrapolation techniques by incrementally truncating the load versus settlement data and then comparing the predicted with measured capacities. With some limitations, several of these methods can be used to provide very reliable estimates of capacity of drilled shafts from proof tests, verifying the recommendations of Paikowsky and Tolosko. The more reliable methods and their limitations are identified and ways of maximizing the accuracy are suggested. With increased confidence in the use of extrapolation techniques, substantial savings can be realized in the construction industry and the engineering community. Also, in deriving the top-down load-settlement curves for the shafts tested with the Osterberg load cell, a simple method is proposed to account for the elastic compression of the shaft.

USE OF STIFFNESS FOR EVALUATING COMPACTNESS OF COHESIVE PAVEMENT GEOMATERIALS

There has been a recent push toward adoption of in-place soil stiffness as a means of assessing compactness of pavement geomaterials. From a series of low strain GeoGauge stiffness measurements made under controlled laboratory conditions on compacted silts, the variation of stiffness with water content, dry unit weight, degree of saturation, volume change upon wetting, shear strength, and soil plasticity is discussed. In general, the GeoGauge stiffness is not directly related to dry unit weight, and it peaks dry of optimum and decreases upon wetting. Soil specimens with a large stiffness also tend to be stronger, but they also tend to swell more upon wetting, implying that the shrink–swell potential is not optimized if stiffness is. These results help advance the understanding of the role of stiffness in assessing compactness of cohesive geomaterials.

Interpretation of Shakedown Limit from Multistage Permanent Deformation Tests

A multistage permanent deformation (PD) test of geomaterials is more economical than the single-stage variety. Only one sample must be tested for the former, whereas several tests on multiple samples are required for the latter. Yet no standards exist for this test in the United States, nor is there a generally accepted procedure for determining the deviator stress to separate acceptable from unacceptable behavior in a multistage PD test. On the basis of both single- and multistage PD tests on a virgin aggregate and two recycled materials and their blends, this paper proposes a procedure to identify the material shakedown limit in a multistage PD test. Resilient modulus increases under low deviator stresses and decreases when deviator stresses are high or near failure. When applied to the materials tested, the multistage PD test predicted correctly the behavior of single-stage test samples 78% of the time. To validate the procedure, additional verification and a standard test load sequence are needed. The sequence proposed in NCHRP Report 598 presents a good starting point. The deviator stress intervals should be small enough to allow all three behavioral ranges to be captured and the load frequency low enough for the sample to drain and recover from viscous effects. One more recommendation is to use a confining stress representative of the field pavement section to be studied.

Forensic Investigation of Distressed Pavement Supported on a Base Course Containing Recycled Concrete Aggregate

The pressure for pavement and geotechnical engineers to incorporate sustainability into engineering projects has led to a rise in the use of recycled concrete aggregate (RCA) as fill and in pavement sublayers. Although the use of RCA has many economical, environmental, and engineering advantages, an oversight in quality control can lead to the use of contaminated RCA in the unbound layers. This can lead to premature deterioration that is costly to repair but, more important, can slow down the market acceptance of RCA. The authors forensically investigated an asphalt concrete pavement supported on a base course containing RCA and that had experienced a significant number of eruptions. Significant amounts of a white substance were found within the base course below each eruption. Sampling and testing showed the primary constituent of the substance to be bayerite, an unstable form of gibbsite, which could form when aluminum metal corroded in an alkaline environment. The adjacent ground topography would have encouraged drainage through the pavement site and thereby rendered the base course moisture susceptible to high alkalinity, because RCA in an aqueous solution has a high pH. Exposing aluminum metal to alkali in the laboratory to duplicate the field reaction confirmed the formation of bayerite. Moreover, exposing aluminum powder to an alkaline environment in a Geonor H-200 apparatus attained a maximum swell pressure of 430 kPa. When the pavement was numerically subjected to this swell pressure, the calculated deflections were found to be consistent with the observed pavement deflections and thus corroborated the hypothesized cause of distress. Suggestions are offered to avoid this type of distress.

Mini-Pier Testing To Estimate Performance of Full-Scale Geosynthetic Reinforced Soil Bridge Abutments

The geosynthetic reinforced soil (GRS) performance test (PT), also called a mini-pier experiment, was developed by the Federal Highway Administration (FHWA) to evaluate the material strength properties of GRS composites built with a unique combination of reinforcement, compacted fill, and facing elements. The PT consists of constructing a 1.4-m square column of alternating layers of compacted granular fill and geosynthetic reinforcement with a facing element that is frictionally connected up to a height of 2 m, then axially loading the GRS mass while measuring deformation to monitor performance. The results can be directly used in the design of GRS abutments and integrated bridge systems. Considering that the geometry of the PT is square in plan, the equivalency of the results to a bridge application, which more resembles a plane strain condition, is evaluated and presented in this paper. The analysis indicates that the PT closely approximates the bearing resistance, or capacity, of a typical GRS abutment, and is a conservative estimate when predicting stiffness. These results indicate that the PT can be used as a design tool for GRS abutments at both the strength and service limit states.