Transportation Research Record: Journal of the Transportation Research Board

Results are presented of large-scale laboratory pullout tests on ribbed steel strip reinforcement embedded in six types of aggregates with uniformity coefficients (ratio of the particle size at 60% finer to that at 10% finer) ranging from 1.4 to 14. These aggregates satisfied the AASHTO standard gradation requirements for select backfill. Each backfill material was placed in two lifts and compacted until the required degree of compaction was achieved. The normal stress was applied with a pressurized air bag placed on top of the compacted backfill. A double-acting hydraulic jack was used to apply the pullout load, which was measured with a load cell. Displacement transducers were installed to measure the rear and front strip displacements. The test results demonstrated that the uniform aggregates generally behaved the same way as did the well-graded aggregates in terms of pullout resistance. The effect of uniformity was more obvious in the tests under a lower normal stress than those under a higher normal stress. Moreover, the pullout resistance factors, F*, from this study lie to the right of the default F*-values for ribbed strip reinforcement suggested by AASHTO. The comparison also shows that the pullout resistance factor for ribbed steel strips decreased with depth in the same way as that suggested by AASHTO. However, the F*-values recommended by AASHTO are conservative as compared with the test results when gravel backfill is used. The formula suggested by AASHTO can be used to conservatively estimate the F*-value with the uniformity coefficient ranging from 1.4 to 14.

Permanent earth-retaining structures (ERSs), including retaining walls, have been systematically managed, inventoried, and assessed by several government organizations, including the City of Cincinnati, Ohio; the Oregon and Pennsylvania Departments of Transportation; and the Central Federal Lands Highway Division of FHWA (for the National Park Service). For a comprehensive ERS asset management program, a careful evaluation of the structural health, criticality, and risk of ERSs is essential for proper management (preservation, rehabilitation, or replacement) of these aging assets. However, many transportation agencies struggle with the evaluation and incorporation of risk in their ERS management programs. This study addressed the development of a framework that would evaluate risk and would define its relationship to ERS condition (likelihood of failure) and ERS criticality (consequence of failure). A methodology for relating risk to routine inspection cycles for ERSs and remedial actions for those in distress is proposed.

This paper analyzes the results of 15 instrumented prestressed concrete test piles that were driven in four sites in Louisiana as part of a pile setup study. Static and dynamic load tests were conducted at specific time intervals to quantify the amount of setup after the end of driving. Laboratory and in situ soil investigations, such as the Piezocone penetration test (PCPT), were conducted at each test pile location to evaluate the subsurface soil condition. Vibrating wire strain gauges were installed in pairs in all instrumented test piles to measure the load transfer and increase in side resistance of individual soil layers over time. The load test results showed that setup followed a linear logarithmic trend. The unit side resistance, instead of the total pile resistance, was used to measure the logarithmic setup parameter A for individual soil layers along the pile lengths. Observations from the test results showed that the average A values for clayey and sandy soil layers for the four tested sites were 0.31 and 0.15, respectively. Analyses of the setup of individual soil layers showed that the parameter A decreases with increased corrected cone tip resistance measured by PCPT. A simple linear regression model is proposed to predict the side resistance setup for individual soil layers by correlating the setup parameter A with the corrected cone tip resistance.

This case study summarizes the design, construction, load testing, and integrity testing of nonredundant drilled shafts for a bridge project in northwest Florida. The subsurface profile consisted mainly of calcareous sandy and silty clay (marl and marlstone) interfingered with limestone and cemented sand layers. The results of unconfined compression tests revealed significant variability in strength, with strata within the depth of interest holding strength properties that fall within the generally accepted range of cohesive intermediate geomaterial. This paper discusses local geology, geotechnical investigation, design, construction, load testing, and site-specific correlations. Important aspects of the project, including the use of the shaft inspection device to examine the cleanliness of the bottom of the shafts, Osterberg cell load testing, and the site-specific correlations developed from the results, as well as integrity testing with cross-hole sonic logging and a thermal integrity profiler, are presented. The inability of the standard penetration test (SPT) to delineate boundaries adequately between strong and (relatively) weaker layers is presented, as well as nonlinear site-specific relationships between anticipated skin friction resistance and SPT blow count. The nonlinear SPT-based relationships attempt to address the strain incompatibility between strong and weak seams that may exist within a given stratum. Proposed correlations for skin friction and end bearing that are based on laboratory strength testing are presented in terms of revised unconfined compressive strength to address variability in strength characteristics across the site.

Uneven settlement and variation in track stiffness are inherent issues of culvert–embankment transition zones. Therefore, the construction of a shield tunnel (a temporary support structure for tunnel construction) in the vicinity of a transition zone may aggravate track geometry deterioration, increase maintenance demand, and cause poor ride quality. This study investigated the influence of shield tunnel construction on the distribution of soil dynamic stress. A construction project of shield tunnels for a metro line beneath an existing railroad was employed as a case study. A plane strain model that was realized by the finite element analysis method was employed to investigate the distribution discipline of the soil dynamic stress in transition zones, which was induced by the passing train and the shield tunnel beneath the railway. The results indicate that the existence of a shield tunnel structure will increase the soil dynamic stress in the transition zone. Because of the tunnel structure, the soil dynamic stress is 38% greater than the soil dynamic stress in the case without a tunnel at a depth of 16 m. Consequently, a recommended treatment is introduced according to the properties of the surrounding soil. Numerical simulation revealed that this treatment is appropriate for reducing the soil dynamic stress in a transition zone.

A field investigation was conducted with two testing devices, the miniaturized pressuremeter test (MPMT) and a lightweight deflectometer (LWD), to evaluate the elastic characteristics of granular pavement layers. The stress–strain data from the MPMT tests were used to determine the stiffness of pavement materials under the influence of static loading conditions in initial elastic modulus (E_i) and reload elastic modulus (E_r). The time–deflection data from the LWD tests were used to determine the stiffness parameters of pavement materials under the influence of dynamic loading conditions in dynamic deformation modulus (E_d) and LWD plate deflection. The results of the MPMT tests were compared with the results of the LWD tests in two phases. First, a direct approach was conducted with statistical analysis. MPMT elastic moduli were compared with LWD dynamic moduli. The results indicate that E_i and E_r could be used to estimate E_d. The initial-modulus model had the best prediction for granular pavement dynamic moduli, followed by the reload moduli model. Second, an inverse approach was achieved by implementing finite element analysis. Three MPMT modulus models were utilized as inputs in the two-dimensional finite element simulation to predict pavement layer deflections. The predicted deflections were compared with deflections measured from LWD tests. The results revealed that a strain-level model in numerical simulation of base course moduli provided satisfactory values of predicted deflection and that the reload modulus model yielded the best prediction deflections for subgrade soils.

Proper quality control and quality improvement strategies during compaction can improve the quality of the subgrade and minimize premature failures of asphalt pavements. This paper discusses the use of the Intelligent Compaction Analyzer (ICA), which was developed at the University of Oklahoma, in quality control and quality improvement during compaction of stabilized subgrade. Six case studies were conducted to demonstrate the ability of the ICA in monitoring subgrade density and subgrade modulus (known as ICA modulus) in real time. The ICA modulus correlated reasonably with the subgrade modulus backcalculated from the falling weight deflectometer data (R² = .63), fairly with the dynamic cone penetrometer test results (R² = .50), and excellently with the in situ subgrade resilient modulus (R² = .72 to .97). The subgrade modulus in undercompacted areas could be increased by more than 50% by applying additional roller passes.

The beneficial use of municipal solid waste incineration (MSWI) fly ash promotes sustainability in highway construction. This study investigated the geotechnical and chemical leaching characteristics of fresh and aged MSWI fly ash samples for use of the material in highway construction applications. The results show that the geotechnical properties of MSWI fly ash resemble those of silty sands with poor drainage capacity. Compared with fresh ash (<10 days since placement), aged ash (3 to 6 months) has a higher California bearing ratio, higher unconfined compressive strength, and greater freeze–thaw durability. The concentrations of cadmium, chromium, selenium, silver, and sulfate from water leach tests are below the limits stipulated in Wisconsin NR 538. The concentrations of heavy metals in leachate from Synthetic Precipitation Leaching Procedure tests are below the U.S. Environmental Protection Agency’s standard maximum contaminant level, with the exception of arsenic. Cumulative mass release from column leach tests indicates that fresh ash will release more heavy metals than aged ash during long-term leaching processes. According to the geotechnical and environmental test results in this investigation, aged MSWI fly ash is identified as a viable material for potential use in roadway construction.

The ability to predict the timing of thaw is important to the design and the maintenance of roads. Such knowledge allows highway agencies to reduce the damage caused by enacting seasonal load restrictions during thawing. Because measurement by observation or testing requires time and resources, one desirable solution is a predictive model. Simple models, such as the Cornell Pavement Frost Model (CPFM), require only daily temperature weather inputs. Possible improvements to the CPFM were tried with a primary goal of improving thaw timing while keeping the model simple and applicable across New York State and beyond. The proposed modifications included changing the thaw reference temperature, providing better tracking of thermal properties throughout seasonal changes, and driving thaw from underneath with a constant underground temperature. During the investigation, further changes were tested involving ways to treat latent heat during thaw, including decoupling. Changes were tested against frost tube data from Ithaca, New York. The model was evaluated and adjusted at other sites in Maine and New Hampshire. The additional inputs required by the resulting modified model were depth and value of constant temperature, moisture content, and estimated shade. The modified model greatly improved the depth and timing of the model for most sites. The final model used the original formulation with minor modifications for freezing and a latent heat formulation for thawing. With more than one freezing–thawing front, the formulas were decoupled. Further investigation should be done to improve frost depth and timing, and in particular, to find out why rapid thawing from underneath does not occur at some sites.

Seasonal variation in the subgrade resilient modulus is likely caused by external factors, such as precipitation and freeze–thaw cycles. One of the strategies for minimizing the impact of this variation on the subgrade modulus is to use insulation layers to prevent frost penetration. This study investigated the effects of the use of insulation layers on pavement performance in the fully instrumented Integrated Road Research Facility in Edmonton, Alberta, Canada. Three insulated sections of the test road were comprised of bottom ash (BA) (100 cm) and polystyrene boards of two thicknesses (5 and 10 cm), and the adjacent conventional section was considered the control section (CS). The resilient modulus and the effective modulus of pavement were backcalculated with the data obtained from falling weight deflectometer testing conducted at the test road during a 1-year monitoring period, from July 2014 to July 2015. Temperature and moisture probes, installed across the depth of the sections, were used to determine the frozen, thawed, or recovering condition of the pavement. The study results revealed that polystyrene boards protected subgrade soil from freezing and thawing effects. The minimum ratio of the backcalculated subgrade modulus of each test to the resilient modulus of the test performed in September was 0.94 in the BA section, and the ratio of the CS could decrease to 0.88 in the recovering period. Comparison of the load-bearing capacity of insulated sections and the CS indicated that, unlike BA, polystyrene boards significantly decreased the load-bearing capacity of the pavement.