Dana N. Humphrey

Prototype tire-shred embankment construction

The New York State Department of Transportation constructed a pilot project using tire shreds as embankment fill. The prototype section, measuring 200 m in length, used approximately 2500 metric tons of tire shreds as the core of the embankment section. The tire-shred zone had a maximum thickness of 3 m, and the tire shreds were covered with 1.5 and 1.0 m of embankment fill on the top and sides, respectively. The entire section was then surcharged with an additional 1.25 to 2.50 m of fill. After 4 months, the surcharge was removed to subgrade elevation, the granular base was placed, and the section was paved. The project was designed in accordance with the guidelines to limit internal heating of tire-shred fills distributed by the Federal Highway Administration. The tire shreds were produced by a hook and shear shredder, placed in the fill with a front-end loader, and compacted with a smooth-drum roller. Instrumentation of the prototype section was monitored both during and after construction. In all, 10 settlement platforms, 15 temperature sensors, 2 groundwater collection systems, and a groundwater observation well were installed and monitored. Settlements were as expected based on previous projects, and temperature measurements showed that there was no internal heating of the tire shreds. A unique incentive program developed jointly by the state’s Department of Transportation, Department of Economic Development’s Empire State Development Corporation, and Department of Environmental Conservation resulted in 267,000 tires being removed from abandoned stockpiles.

FULL-SCALE FIELD TRIALS OF TIRE SHREDS AS LIGHTWEIGHT RETAINING WALL BACKFILL UNDER AT-REST CONDITIONS

A 4.88-m (16-ft), full-scale retaining wall test facility was constructed to investigate the use of tire shreds as backfill for conventional retaining walls. The facility can test backfill at at-rest and active conditions and is instrumental for measuring horizontal stress and interface shear. Tire shreds from three suppliers were tested. The results for at-rest conditions are presented. The average at-rest horizontal stress for tire shreds was about 45 percent less than expected for conventional granular backfill. Moreover, the at-rest horizontal stress was about the same for tire shreds from the three suppliers. Design parameters were developed by using two procedures. The first used the coefficient of lateral earth pressure and the other was based on equivalent fluid pressure. The horizontal and shear forces acting on the concrete face of the wall were used to determine the angle of wall friction, which ranged from 30° to 32° for tire shreds from the three suppliers.

Evaluating the risk to aquatic ecosystems posed by leachate from tire shred fill in roads using toxicity tests, toxicity identification evaluations, and groundwater modeling

The risk to adjacent aquatic systems posed by leachates from scrap tires used in engineering applications has not been characterized adequately. Toxicity testing, toxicity identification evaluation (TIE), and groundwater modeling were used to determine the circumstances under which tire shreds could be used as roadbed fill with negligible risk to aquatic organisms in adjacent water bodies. Elevated levels of iron, manganese, and several other chemicals were found in tire shred leachates. However, chronic toxicity tests with Ceriodaphnia dubia and fathead minnows (Pimephales promelas) showed no adverse effects caused by leachates collected from tire shreds installed above the water table. Exposure to leachates collected from tire shreds installed below the water table resulted in significant reductions to both survival and reproduction in C. dubia. The TIE results indicated that exposure to soluble metals (likely ferrous iron primarily) and the formation of iron hydroxide precipitates on this invertebrate species likely were the causes of the observed effects. The available chemistry data show that iron concentrations in the affected groundwater decreased substantially within a short distance (0.61 m) downgradient of tire shred fill. Based on geochemical modeling, the use of tire shreds in applications below the water table is appropriate in settings where dissolved oxygen is greater than 2.0 mg/L, pH is greater than 5.8, and a downgradient buffer of approximately 3.0 m exists between the fill and the surface water. For settings with lower dissolved oxygen concentrations or lower pH, results of groundwater modeling indicate that a greater buffer distance (approximately 11 m) is needed to dilute the leachate to nontoxic levels under various soil and groundwater conditions solely through advection and dispersion processes.

EFFECTIVENESS OF DESIGN GUIDELINES FOR USE OF TIRE DERIVED AGGREGATES AS LIGHTWEIGHT EMBANKMENT FILL

The low in-place density of tire derived aggregate (TDA) makes them attractive for use as lightweight fill for embankments constructed on weak ground and backfill for retaining walls. TDA, also known as tire shreds or chips, are scrap tires that have been cut into 50 to 300mm (2 to 12 in.) pieces. There are many examples of projects that have successfully used TDA as lightweight fill. However, as illustrated by three projects built in 1995 that experienced internal heating reactions, car is needed to properly design and construct TDA fills. The underlying cause of these problems was a combination of oxidation of exposed steel belts and freshly cut surfaces on rubber pieces. The lessons learned from these projects resulted in design guidelines to limit internal heating of TDA fills. Nine projects have now been built in accordance with the guidelines. Internal measurements show that TDA temperatures are similar to background soil levels, indicating the effectiveness of the guidelines. Moreover, effective construction specifications have been developed that often result in lower construction costs than competing lightweight fill materials.

Reinforced embankments—A review of case histories

Abstract A review was made of 37 case histories of reinforced embankments, with heights greater than 1 m, constructed on soft ground. Common characteristics of the cases were identified, and the data summarized in tabular form. Foundation materials were generally soft organic soils, and the embankment fill was usually granular. To maintain an acceptable safety factor it was often necessary to combine reinforcement with other special construction measures such as sand drains, stabilizing berms or light weight fill. Relations between the observed height of reinforced embankments at failure and the undrained foundation shear strength, and between the observed bearing capacity factor and normalized embankment width were examined and compared to available bearing capacity theories.

Determining When to Place and Remove Spring Load Restrictions on Low-Volume Roads: Three Low-Cost Techniques

Damage to low-volume roads in seasonal frost areas can be kept to a minimum by implementing seasonal load restrictions (SLRs). However, not all agencies responsible for road management implement such restrictions, and among those that do, there is no standard technique. Some use qualitative methods, such as observation or dates. Others use quantitative methods, such as measuring or estimating stiffness or subsurface temperature. Loss and recovery of summertime pavement strengths can be directly measured with a falling-weight deflectometer (FWD). Alternatively, mathematical models of varying levels of complexity, using meteorological data, are in existence or are undergoing development for SLR placement. However, initial investment for an FWD can be prohibitive for agencies such as the U.S. Department of Agriculture Forest Service (FS), for which road management is not a primary mission. Similarly, such agencies have limited personnel to conduct detailed calculations required of complex mathematical models. Consequently, easy-to-use, low-cost alternatives are needed. In cooperation with other partnering agencies, FS has recently been evaluating several techniques for determining when to place and remove SLRs. Three methods that appear promising include (a) subsurface instrumentation for temperature and moisture, (b) portable or lightweight FWDs, and (c) the thaw index. Technology-and-development efforts in each of these areas are outlined here; field test programs, observations, and analysis procedures are discussed; and recommendations for implementing each method are provided.

Permeability of Base Material for Maine Roads

Cutting the cost of road maintenance and reducing life-cycle costs are the main reasons the FHWA has increased its emphasis on drainage in the pavement structural section. Good drainage requires that the base and subbase drain freely and relatively quickly. Poor drainage is thought to cause the Maine Department of Transportation (MaineDOT) to spend millions of extra dollars each year maintaining its state highways. Improved specifications and design policies for subbase material were developed by investigating the gradation and permeability of the subbase currently used by MaineDOT. Eight field projects were selected to investigate the permeability and gradation of subbase material for Maine roads. Results indicate that typical MaineDOT subbase gradations have excess fines and sand-size fraction compared with FHWA recommendations. The standard subbase currently used by MaineDOT has an average coefficient of permeability of 5.9 10 4 cm/s (1.7 ft/day) whereas the FHWA recommends a minimum coefficient of per...

Water-Quality Effects of Tire Shreds Placed Above the Water Table: Five-Year Field Study

A field trial was constructed beneath a secondary state highway in North Yarmouth, Maine, to investigate the water-quality effects of tire shred fills placed above the groundwater table. Samples were collected in three 3-m2 geomembrane-lined basins located beneath the shoulder of the road. Two of the basins are overlaid by 0.61 m of tire shreds with a 75-mm maximum size topped by 0.72 to 1.37 m of granular soil. The third basin serves as a control and is overlaid by only 0.72 m of granular soil. Quarterly samples for inorganic constituents were taken from January 1994 through June 1999. In addition, samples were taken for volatile and semivolatile organic compounds on three dates. Filtered and unfiltered samples were analyzed for the following substances, which have a primary drinking water standard: barium, cadmium, chromium, lead, and selenium. There was no evidence that the presence of tire shreds altered the concentrations of these substances from their naturally occurring background levels. In addition, there was no evidence that tire shreds increased the levels of aluminum, zinc, chloride, and sulfate, which have secondary (aesthetic) drinking water standards. In a few samples, iron levels exceed their secondary standard. Manganese levels consistently exceeded their secondary standard; however, this is an aesthetic-based standard. Three sets of samples were tested for organics. Negligible levels of organics were found.

VARIABILITY AND SCALE-DEPENDENCY OF RECYCLED RUBBER TIRE MATERIALS

This paper presents a variability study of several engineering properties of recycled rubber tire pieces based on a comprehensive literature survey of experimental test programs. The unit weight, cohesion, internal friction angle, Youngs modulus of elasticity and Poissons ratio were evaluated and compared to engineering property variability of natural soils. In addition, a series of regression and residual analysis were performed to investigate the presence and significance of scale-dependency on the engineering properties of rubber tire pieces. The results of the variability analysis show that unit weight and Poissons ration have the lowest values of coefficient of variation whereas the shear strength parameters ad he elastic modulus have the highest. From the regression analysis, cohesion and Youngs modulus showed the greatest sensitivity to changes in maximum tire particle size. However, these results are based on statistics that have limitations when used for interpretive purposes. A non-statistical investigation based on geotechnical theory was used to further evaluate the scale-dependency of the shear strength parameters. Using Mohr-Coulomb failure theory and assuming that the cohesion component of strength is justifiable neglected, the analysis showed a scale-independent relationship which is consistent with the statistical findings for internal friction angle.

A study of temperature and traffic load related response in different layers in an instrumented flexible pavement

The first fully instrumented flexible pavement test section in Maine was constructed in Fall, 2005. Temperature data were collected for a period of 5 months and stress–strain data were collected by running a truck at different speeds. The temperature data were analysed to develop models to predict these temperatures on the basis of ambient temperature and solar radiation. The haversine equation was found to be suitable for modelling the strain response in HMA layers, whereas slight variations were used for modelling the responses in the subbase and subgrade layers. The strain in the HMA layer shows a lag when compared to the fitted model. The HMA tensile strains matched well with the predicted strains at lower time of loading and lower temperatures. Subbase stresses were greater than predicted values. The subbase strains matched well with the predicted ones. The measured subgrade stresses were greater than predicted stress values.