Transportation Research Record: Journal of the Transportation Research Board

Suitable performance models are needed for estimating medium- and long-term budgetary requirements to keep bituminous surfacing of the road network in serviceable condition. Long-term deterioration models are used for predicting both the proportions of the network that will require resurfacing and in what years. These predictions can then be used in estimating required budgets. Such models also can indicate the network level of service that can be achieved within various budget scenarios. The research reported here used subjective condition data to develop deterioration models for five types of pavement bituminous surfacing: chip seal, geotextile seal (chip seal with geotextile underlay), dense-graded asphalt, open-graded asphalt, and ultrathin asphalt. The condition data were collected through visual inspection surveys, which were conducted every 2 to 3 years by experienced personnel who followed detailed guidelines. Cracking, stone loss, texture loss, deformation, and patching data were collected for dense-graded, open-graded, and ultrathin asphalt. For chip seal and geotextile seal, binder condition and level data were also collected. The condition ratings of the distresses were then combined into a single measure, the surface inspection rating. Markov chains were used to develop deterioration models of surface inspection rating as a function of surface age for the five surfacing types. These models were validated, and the reasonableness of their predictions was assessed according to practical experience and engineering judgment. The models proved to be practicable because of ease of development and reasonableness of predictions.

Gravel roads are an important portion of the road network in western Argentina, and their maintenance requires a huge amount of economic and human resources. Recently, the use of alternative treatments based on the application of mineral salts such as hydrous magnesium chloride, also known as bischofite, has been introduced in this region. Such treatments are being applied for dust control and surface stabilization on unpaved roads. This paper presents the main results obtained during a research project carried out by the National University of San Juan, Argentina, along with local road agencies and companies. Test sections of gravel roads were treated with bischofite applied in two ways. Over 18 months, measurements of surface roughness and dust emission were made on those sections. The main results show that the use of bischofite contributed to a notable reduction in the evolution of roughness and dust emission as compared with untreated gravel sections. Bischofite appears to be appropriate not only for the environment but also for road agencies and road users; important cost savings were verified through economic assessments that compared treated and untreated gravel road sections.

Recently, use of pavement preservation technologies, such as bituminous seal treatments, has increased. Seal treatments are often used to rejuvenate aged asphalt pavements and can decrease permeability and retard oxidation, cracking, and raveling. Many factors affect rejuvenation, and current specifications governing how rejuvenation is characterized could be enhanced. Viscosity testing of asphalt binder extracted and recovered from a pavement's near surface is the predominant means of characterizing rejuvenation (e.g., a product must reduce viscosity by 40% to be classified as a rejuvenator). This paper presents data that suggest other rejuvenation approaches are worth considering because (a) extraction and recovery can adversely affect viscosity results, (b) viscosity testing cannot be conducted without forced and unrealistic blending of aged binder and rejuvenator, (c) high test temperatures may not be the most informative for distresses of interest (e.g., cracking), and (d) viscosity could not detect rejuvenation behaviors of some proprietary products. Alternatively, this paper suggests rejuvenation specifications be developed with bending beam rheometer (BBR) testing of mixture beams sawn from laboratory-compacted asphalt surfaces (e.g., a product must increase the m-value by 0.040 to be classified as a rejuvenator). This approach has shown promise for viscosity testing, and many concerns about viscosity testing are alleviated with BBR testing. A specification approach that uses BBR testing of laboratory-compacted asphalt is described and recommended for rejuvenation characterization.

Road condition affects the operations and costs of vehicles that use the infrastructure. Various models of vehicle operating cost provide an indication of the effects of road roughness on fuel consumption, additional damage to a vehicle, and tire wear. These models do not include the effect of road conditions on the condition of and potential damage to transported freight. Such potential damages are mitigated through the use of improved vehicle technologies or packaging. In agricultural transportation, packaging often is not a solution because the use of older vehicle technology on mostly rural roads with lower levels of riding quality is a main contributor to the problem. This paper evaluates quantified effects of the riding quality on low-volume roads on the level of damage to tomatoes in California. The paper is partly based on a study that focused on vehicle–pavement interaction and its effects on the broader California economy. Vehicle responses to road conditions were measured during operations on a range of rural routes. Laboratory experiments were developed to replicate the dominant vibrations of the trucks and to measure the stresses that tomatoes typically undergo at these vibration levels. The damage and failure levels for the tomatoes during transportation were determined, and these damage levels were used to calculate typical costs to agricultural suppliers that are due to road conditions. The problem thus could be quantified and input data provided for a cost–benefit evaluation of the potential maintenance and improvement of various routes used to transport tomatoes.

Weathered basalts are polygonal fragments of various dimensions generally spread in a wide grading envelope. They are found in high-volume portions of basaltic spills where the rock is extremely fractured and where degradation processes prevail over decomposition. This material was used as base and subbase layers of experimental pavement sections tested with a heavy traffic simulator. The same material was used as the base and subbase of a pavement on a low-volume road in Rio Grande do Sul state, Brazil, that was monitored for 10 years. The main conclusion from the study is that the low-volume road pavement presented different forms of surface degradation in comparison with the experimental road tested with the traffic simulator. The design model obtained in the traffic simulator study was used to identify the point at which the pavement started to deteriorate and thereby identify when a maintenance program was needed rather than to predict when the pavement had already fully deteriorated.

Application of appropriate preventive maintenance treatments, at the right time, extends the service life of pavements, resulting in benefits to road users through increased ride comfort and safety and to road agencies through the reduction of future maintenance costs and improvement of the network condition. Preventive maintenance treatments usually have been applied on the highly trafficked sections of the Serbian national road network, but they have not been applied on the low-volume part of the network. This study used the Serbian low-volume roads network as a case study to identify appropriate preventive maintenance treatments for low-volume roads, model these into a pavement management system, and assess the potential benefits of their application compared with the current practice. The World Bank's RONET (road network evaluation tools) model, designed to assess the current characteristics of road networks and their future performance according to various levels of interventions (and budgets), was selected for this study. The model was modified for the study to incorporate use of preventive maintenance treatments. Modifications included adjustment of the pavement deterioration curves to incorporate a slower deterioration rate resulting from the application of crack sealing and pothole patching and surface dressings or thin overlays while the pavement was still in good condition. The results indicate that the use of preventive maintenance treatments would result in increased net benefits and a substantial reduction in future road agency costs compared with the maintenance scenario without preventive maintenance.

Unpaved roads play a crucial role in the economic and social development of societies, linking rural communities to education, health services, and markets. The asset value of unpaved roads is low compared with national and provincial road networks, because agencies responsible for rural roads management lack the resources to assess and maintain the network properly. Lack of resources is especially critical in developing countries, where the majority of the population lives in rural areas and where few tools are available for sustainable management of the unpaved network. The main objective for this study was to develop and validate cost-effective maintenance standards for unpaved rural roads. The study was directed at improving the management process of unpaved road networks that serve rural populations. The scope was to develop maintenance standards that can be used by agencies in charge of network management, given available resources and technical skills. The developed four-step methodology evaluates an unpaved road network for 4 years, identifies the effects of maintenance treatments on the condition of roads from field data analysis, defines maintenance strategies, and develops optimal maintenance standards. The study was part of a 4-year project conducted at the University of Waterloo, in Ontario, Canada, that resulted in the development of a sustainable management system for rural road networks in developing countries. The proposed standards were applied and successfully validated and were demonstrated to be adaptable to varying climates, budgets, traffic, and road structures.

Bituminous ash produced by the oil industry is used in landfill in large quantities. Recycling ashes coming from the oil industry can have signifi-cant benefits for the environment and is an attractive option for highway construction because it saves material acquisition and disposal costs. An experimental study was undertaken to investigate the use of these ashes as a replacement for mineral filler in hot-mix asphalt concrete. Physical tests were performed on the bituminous ash to determine its gradation, specific gravity, and chemical composition. Two cases were considered for determining the ash proportion. To evaluate the effect of a reduction in asphalt binder, ash with a maximum particle size of 0.074 mm [i.e., passing the Number (No.) 200 sieve] was used as a replacement for the asphalt cement content at percentages of 0 (i.e., control mix), 5, 10, and 15 by total asphalt weight. Also, ash was used as a replacement of the fine aggregate at percentages of 0, 30, 50, and 70 by total aggregate weight. In both cases, the ash came from thermal desorption in the hydrocarbon processes. Mix design was accomplished according to the Marshall mix design method (ASTM D1559). The results of these studies showed that use of ash passing the No. 4 sieve improved asphalt concrete characteristics while it reduced the use of aggregates when the asphalt proportion was 4.5%. Likewise, use of 0.8% fine ash (i.e., finer than the No. 200 sieve) to reduce the asphalt content in the hot dense mixture also improved the performance of asphalt concrete.

State departments of transportation implement risk-based transportation asset management systems to standardize risk-oriented procedures and to help decision makers allocate available funds. These procedures can help agencies effectively allocate funding to repair, replace, or maintain their assets in a way that provides the highest overall value to all stakeholders. Because reliable tools with which to measure and compare the socioeconomic impact of distribution of bridge maintenance funds are lacking, decisions are driven by annual average daily traffic (AADT) and the experience of decision makers. Although AADT measures the number of users that would benefit if funding were allocated for a given bridge project, it fails to account for the impact that a given bridge has on the state's or region's economic growth. A reliance on AADT puts low-volume bridges on farm-to-market roads at a disadvantage in competition for scarce funding, as shown by the many structurally deficient low-volume bridges located in croplands of Iowa, a state whose economy is based on agriculture. This paper proposes a method for integrating the socioeconomic impact of funds allocated to maintenance and repair with AADT and for considering the consequences of this decision. The paper demonstrates a stochastic two-way sensitivity analysis social return on investment as the primary metric on two typical Iowa bridges and finds that adding social return on investment to the decision-making process provides a mechanism for more efficiently allocating available resources.

In rural areas, thin asphalt surface pavement structures have been constructed for low-volume road networks. For this type of road, a light weight deflectometer (LWD) may be useful for evaluating the responses of a pavement structure. Of the responses, the mobilized horizontal tensile strain at the bottom of asphalt pavement indicates the fatigue cracking potential, while the mobilized vertical compressive strain at the top of the base layer indicates the rutting potential. A series of linear elastic analyses was performed on a thin asphalt surface pavement structure. Correlations between the two mobilized strains and deflection basin parameters were found. A model thin asphalt surface pavement structure was constructed in the field. Many sensors were installed for measuring the mobilized stresses and strains during an LWD test. The test results generally were in agreement with the linear elastic analyses. The mobilized strains in the thin asphalt surface pavement structure could be predicted with the correlations with deflection basin parameters obtained from the LWD test.

Low-volume roads constitute a major portion of the world's transportation infrastructure and hence require an economical and effective pavement design. When constructed on unstable and soft subgrades, these roads are susceptible to premature pavement failures and require subgrade stabilization. The presented research focuses on mechanical stabilization of soft clay with graded sand that has been adopted as a base course for pavements. For this study, a local soft clayey soil from Dallas was mixed with various fractions of a graded sandy soil, and the stiffness behavior of the compounded material was studied. The soil mixtures were then studied for their basic soil characterization, including standard Proctor compaction studies. Statically compressed soil specimens were prepared and then evaluated for their unconfined compressive strength and resilient moduli. Resilient moduli results were used in the design of low-volume roads, both with aggregate base and with no aggregate base. Results show that the variation of sand content in soft soil considerably affects the strength and stiffness properties of the subgrade. The effects of improved subgrade performance on the aggregate base and surface layers of the low-volume pavement are highlighted.

This research proposes the development of a method of localization and prediction of AASHTO soil classification that can contribute to the decision-making process in projects for low-traffic-volume roads in the metropolitan area of Fortaleza, Ceará, Brazil. Geoprocessing and artificial neural networks were used as modeling techniques, and biophysical and spatial variables were used to explain the modeled phenomenon. The characteristics investigated (pedology, geology, geomorphology, vegetation, altimetry, and position) were correlated with the AASHTO classification. The soil AASHTO classification data were taken from projects and preexisting studies and totaled 876 points. In the development of this geotechnical estimates generation model, artificial neural network topologies were calibrated, validated, and tested so as to find a model that could best fit the set of tests. The model had an accuracy rate of 92.6% for the generation of estimates of AASHTO soil classification in the Fortaleza region, on the basis of the biophysical variables studied. The tested model was used to construct neural geotechnical maps that can be used to predict the AASHTO classification of soils not yet characterized in the lab and to predict the type of subgrade of a region not yet explored. Results show that the artificial neural networks technique is promising for geotechnical studies of low-traffic-volume roads.

Major winter storms occasionally remove portions of the steep mountainous roads within the Siuslaw and Willamette National Forests of western Oregon. On average, at least one flexible welded wire reinforced wall is built a year in these forests to reestablish the failed roadway. This paper summarizes the procedures used for foundation investigation, analysis and design, and construction administration of welded wire reinforced retaining walls in these forests. Since 2005, the U.S. Department of Agriculture Forest Service has designed the walls according to the current AASHTO LRFD Bridge Design Specifications. The two forests follow AASHTO procedures with some modifications. These modifications include a narrower bench width at the toe of the wall, less conservative global stability resistance factors, no performance of settlement analysis, and stricter fill requirements for reinforced walls.

The Siuslaw and Willamette National Forests in western Oregon have approximately 8,000 mi (12,900 km) of aggregate- and native-surfaced roads. These forest roads provide access for the general public (mainly recreation) and allow timber to be hauled to local lumber mills. The forests have developed a procedure for assessing whether an existing aggregate-surfaced road has the capacity to support this traffic. The procedure notes any existing surface distress, determines aggregate depths and material quality, ascertains the subgrade characteristics along the road segment, and then segments the road into like sections according to these observations. Next, the surfacing thickness program of the U.S. Department of Agriculture Forest Service is used to determine aggregate requirements for supporting traffic without excessive surface deterioration. Options for mitigating typical surface distress are addressed. The Siuslaw and Willamette National Forests have found that this procedure provides a reasonable and cost-effective means with which to determine where to apply aggregate on forest roads and how much, conserving the limited rock resources in national forest lands.

The resilient modulus of subgrade soil is used to design a pavement structure that is adequate for the expected traffic and environmental loading. Both mechanistic and empirical design procedures use this property. The resilient modulus test is a complex test that requires significant resources, including a high level of technical ability on the part of the operator. For smaller or less critical projects with a low volume of traffic where costly and complex resilient modulus testing is not justified, a correlation with other, simpler tests could be used. In this study, a correlation with the results of an unconfined compression (UC) test is explored for estimation of the resilient modulus of fine-grained soils. This paper presents several models with which to estimate the resilient modulus of fine-grained soil from the results of UC tests considering two sample preparation techniques: static and impact compaction. The simplest model considers only unconfined compressive strength to predict the resilient modulus with a fair correlation. The more detailed models also consider the plasticity index, percentage of material passing the Number 200 sieve, and modulus of the stress–strain curve from the UC test. The sample preparation technique had a significant influence on the UC test results.

Over the years, and under traffic loading and wetting and drying cycles, unpaved roads achieve a significant degree of compaction. Sustainable upgrading of these roads to a paved standard is best accomplished by making use of in situ conditions to provide a sound foundation for the new road. This usually reduces the need to import large quantities of virgin material. The dynamic cone penetrometer (DCP) device can be used to quickly and cheaply assess the in situ conditions, including material quality and moisture regimes at selected test positions, as well as to determine the suitability of imported materials for incorporation into the new road pavement. The information obtained from the in situ testing can then be used to identify uniform sections along the road alignment. By comparing the in situ layer strength profiles of each of these uniform sections with the required design strength profiles for a particular design loading, the required layer needs for the new pavement can be determined. The paper describes the use of the DCP for the environmentally optimized design of low-volume roads, including the manner of characterizing the in situ road conditions and the selection and specification of borrow pit materials. The use of the DCP for compaction quality control is outlined. Data from various road sections in several countries in southern Africa are used to support the approach.

Low-volume roads are often constructed with untreated or lightly treated gravels as the surface or base, and these materials are sensitive to moisture variation. The proper design of low-volume roads requires determining the effects of moisture variation on soil behaviors. A soil–water characteristic curve (SWCC) that characterizes the relationship between the degree of saturation and suction is an important tool for quantifying the mechanical properties of unsaturated soils. The increased use of additives to improve the engineering properties of marginal soils in pavement design has necessitated the need for rapid methods to quantify the SWCC of stabilized soils. This study used the dewpoint method for quick measurement of suction values at various water contents for silt and clay soils stabilized with Class C fly ash. The results indicate that significant suction could exist in soils stabilized with fly ash and that the suction values are greatly affected by the degree of saturation. The suction and degree of saturation in stabilized soils play a significant role in the strength of the stabilized material. The material stabilized with fly ash exhibited hysteresis on the SWCC. The data were also used to compare the suitability and efficiency of five predictive models. It was found that the Fredlund and Xing and van Genuchten models fit the curves for stabilized soils very well as compared with the simplified van Genuchten, Campbell, and Brutsaert models. It is recommended that the Fredlund and Xing and van Genuchten models be included in the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures.

Hygroscopy is the main stabilization mechanism that explains the good performance of magnesium chloride hexahydrate (6H₂O_•MgCl₂ or simply MgCl) roads, as it absorbs and retains relative humidity (RH), reducing erosion and increasing durability. However, road users have observed that the skid resistance of MgCl roads decreases with increased RH. To study the skid resistance of MgCl roads, the study calculated the drag factor or friction coefficient of the road surface with a braking test, in which an accelerometer was installed in a vehicle and deceleration was recorded during braking. The braking test was used to calculate the effect of RH and surface condition on skid resistance in 30 road sections located in the northern region of Chile. The testing was designed with a factorial experiment that took the following into consideration: surface condition (well-graded, sealed, and loose aggregate), whether water was artificially added to the surface (normal or wet), and a wide range of RH (between 10% and 70%). The results showed that when RH was greater than 35% to 40%, the friction of MgCl roads decreased as RH increased. In environments in which the air humidity was lower than 60%, the friction coefficient was higher than 0.55, a value that provides suitable friction conditions for most geometric designs for low-volume roads. The study showed that a braking test is a simple and consistent tool for assessing braking performance on MgCl roads. In addition, the study concluded that special attention should be given to surface characteristics and geometric design where MgCl road sections are exposed to RH greater than 60%.

Significant regions of the United States are covered with unstable sands that present traction and maintenance problems on unsurfaced, low-volume roads. Gravel for road surfacing is often unavailable or expensive because of the lack of local gravel deposits. The majority of these sandy areas occur in forested lands with thriving timber and paper industries. The objectives of this study were to review the various wood products and byproducts that are available and carry out a qualitative evaluation of their potential for stabilizing low-volume roads in unstable sands. Wood-related materials may provide cost-effective and environmentally beneficial alternatives for road stabilization materials in areas where gravel is not available or economical for use. The results of a literature search and market survey of wood products, byproducts, and paper mill byproducts are presented along with grain-size distribution test results for unstable sands and some materials. The performance of U.S. Forest Service roads previously stabilized with wood chips, chunkwood, and paper mill sludge was evaluated by site observation. Most of the materials were found to be at least marginally effective in some environments. Paper mill boiler ash shows particular promise as a recycled material for road stabilization and is recommended for further study.

Secondary compression is a major concern for road construction situated on marine clayey soil conditions in the eastern and southeastern provinces in China. Marine clay characterization in the field is hence an important step in the design of low-volume roads. Piezocone penetration tests (CPTu) were conducted for site investigation of a low-volume road situated in Lianyungang, Jiangsu Province, China. The compressibility of relatively homogeneous marine clay at the site was analyzed, with a focus on the postsurcharge secondary compressibility. The primary compression index (C_CL) was obtained from odometer tests on undisturbed samples. The postsurcharge secondary compression index (C_αε) was backcalculated from the settlement curves and defined with the time-dependent strain response. The ratio of C_αε/C_CL fell in the range of 0.05 ± 0.01, indicating that high secondary compressibility is associated with the clay deposits. Finally, regression analysis was performed to correlate the C_αε to the CPTu normalized cone tip resistance (Q_tn). A modified empirical correlation between C_αε and Q_tn was further developed on the basis of comprehensive evaluation of data from Lianyungang marine clay and the literature.

Sustainability and resiliency issues need to be considered for the selection of the stabilizer(s) for a given type of soil because of inherent environmental and societal impacts. Soils in southern Italy can exhibit high compressibility and low strength properties. As a result, stabilization techniques are often needed to improve subsoils and thereby optimize pavement performance. To investigate the sustainability issues, a model was formulated in which user and environmental costs were considered to assess the overall sustainability and resiliency of a transportation infrastructure for low-volume roads. An experimental plan was designed and implemented in real field conditions. Several soils and stabilizer-related variables were considered in the experimental design. Laboratory strength tests, including the California bearing ratio, unconfined compressive strength (UCS), and indirect tensile strength (ITS), were conducted on control and treated soils. The results led to conclusions pertaining to lime stabilization potential for improving the performance of weak soils, correlations between ITS and UCS properties, and the potential of combined treatments as a strategy for achieving the target performance in a short period of time. Life-cycle cost analyses were used to evaluate benefits and address the sustainability and resiliency of lime and cement treatments for the present soils for low-volume road conditions. The outcomes of this research should benefit practitioners and researchers working in this field.

There is increasing interest in the use of chemical treatments to reduce maintenance and gravel replacement on gravel roads. However, selecting the most appropriate chemical treatment is difficult because of the proprietary nature of many of the chemical treatments available and limitations by many agencies in procuring such proprietary products. Of the approximately 200 chemical treatment products available in the United States, only calcium chloride and asphalt emulsion carry formal ASTM and AASHTO specifications. Some federal and county road agencies have additional, very basic product specifications for some other categories of products; however, these are generally not linked to ASTM and AASHTO testing criteria. This situation has led to limited use of many chemical treatments. This paper provides sample provisional specification language that road agencies and road owners can use to procure and apply chemical treatments on unpaved roads. This provisional specification language was developed in conjunction with federal road agencies and chemical treatment suppliers as part of a new selection procedure for chemical treatments for unpaved roads.

In Australia, the mechanical and chemical stabilization of pavement materials has been under way for more than 30 years. Recently, new polymeric-based additives have been shown to provide superior sustain-ability advantages for the construction and maintenance of low-volume roads (particularly unsealed roads) over traditional cement-blended additives. However, little quantifiable information has been published on the improved geotechnical characteristics resulting from the use of such polymeric-based additives. This paper reports on a series of uncon-fined compressive strength tests that were performed on three typical pavement material types, which were all treated with a single type of polyacrylamide additive. The compaction effort was varied at three levels (i.e., 25, 35, and 45 blows per layer with modified compaction effort). All samples were cured for 14 days prior to testing. The results of this study confirmed an increase in dry density and unconfined compressive strength for the three soils treated with the polyacrylamide additive.

This paper presents the results of a laboratory study of three expansive soil samples collected on the SC-112, an unpaved state road that connects the city of Rio Negrinho to Vila Volta Grande in Santa Catarina State, Brazil. The road's lack of pavement inhibits the development of the region by obstructing traffic during the rainy season. The study estimated the percentage of lime that would need to be added to the soil to minimize expansion of the soil and evaluated changes in the physical and mechanical characteristics of the soil. The study used the miniature, compacted, tropical (MCT) classification, which was developed in Brazil to study the properties and behavior of tropical soils. The following tests were used to study the physical and mechanical characteristics of the soil samples, soil–lime mixtures, and lime: Atterberg limits, grain size, compaction, California bearing ratio, MCT soil disk method, and chemical analysis of the lime. Lime requirements were estimated with the lime fixation point, pH, and MCT soil disk methods. The results of plasticity limit tests showed that the base exchange reactions of lime with the soil occur immediately after the addition of water to the soil–lime mixture. Use of the MCT methodology tests showed that the natural soil samples with the addition of lime changed their behavior from nonlateritic to lateritic. The addition of 3% lime to two soils and 2% to the third soil caused physical and mechanical changes in the soils that allow their use as subgrade of low-volume road pavement.

Low-volume roads constructed in steep hillside terrain by cut and cast techniques may experience instability in the form of excessive subsidence that leads to large cracks and differential movement along the roadway bench. The technique of deep patch embankment repair with geosynthetics (DPERG) has been employed in the western United States; DPERG generally involves a 1- to 2-m-deep excavation that is backfilled with compacted granular soils and one or more layers of geosynthetic reinforcement. The design goal of a DPERG is not necessarily to eliminate future slope movement but to confine potential failure surfaces to a region of the slope well below the roadway bench and extending out to the slope face such that a failure surface does not extend up onto the roadway bench. This design results in movement along the roadway bench that is more uniform and less disruptive to traffic. This paper describes the results of a study to evaluate the DPERG technique by analytical methods supported by field observations for the purpose of determining the required depth of the DPERG and the optimum layer spacing of the reinforcement. The study showed that for a given slope geometry and set of soil properties that had led to failure in an unreinforced slope, there were several combinations of DPERG depth and number of reinforcement layers that satisfied the design goal. The study showed that more tightly spaced reinforcement layers were beneficial and that for widely spaced layers, the design goal of a DPERG could not be met, even for a thick DPERG depth.

Deep patch embankment repair with geosynthetics (DPERG) is a cost-effective and sustainable method of mitigating roadway embankment damage associated with shallow slumping of the outside shoulder. DPERG is a shallow embankment repair that consists of subexcavating 3 to 6 ft (1 to 2 m) and backfilling with granular material and layers of geosynthetic reinforcement that are vertically spaced 6 to 24 in. (150 to 600 mm). DPERG is constructed either half width or full width, depending on the extent of roadway distress. Use of the deep patch on federally owned roads in the Pacific Northwest dates back to the 1980s. Recent research has improved understanding of soil–geosynthetic interaction, and this knowledge has led to improved DPERG performance and a reduction in DPERG costs. This paper summarizes design and construction recommendations gained from this recent research and experiences with hundreds of DPERGs constructed on Western Federal Lands Highway Division projects in the Pacific Northwest.

The load equivalency method is widely used to consider the effect of traffic loading on pavement design, and the equivalent axle load factor (EALF) for paved roads has been studied often. For unpaved roads, however, EALF is not well understood because it is not necessarily the same as it is for paved roads. In this study, cyclic plate load tests were conducted on unpaved road sections (six base-over-subgrade sections and four subgrade-only sections) constructed in a geotechnical box (2 m × 2.2 m × 2 m) to investigate the load equivalency for unpaved roads. The base-over-subgrade sections were constructed as unstabilized, T1 geogrid–stabilized, and T2 geogrid–stabilized base courses of 15% California bearing ratio (CBR) with thicknesses of 0.23 m and 0.30 m over weak subgrade of 2% CBR. The subgrade-only sections were constructed with CBR values of 6.2%, 7.4%, 9.5%, and 11.0%. The intensities of the cyclic loads were increased from 5 kN to 65 kN, at increments of 5 kN. For each load intensity, 100 cycles were applied on one test section. The EALFs were analyzed in terms of permanent deformation. The results showed that the regression powers of the ratios of axle loads for unpaved roads with aggregate bases over weak subgrade ranged from 1.9 to 2.9, which were lower than a power of 4, the typical value used for paved roads. The powers for subgrade-only sections had an even wider range, from 1.1 to 3.4. The increase of base thickness, the presence of geogrid, and the use of a higher-grade geogrid increased the power.

Geosynthetics have been used in a wide range of applications on forest roads over the past 40 years. Some of the earliest uses involved reinforcement in simple walls, drainage or filtration in geocomposite underdrains, and subgrade stabilization. These early efforts were typically experimental. Geosynthetic application over time became better defined by function, and use was specified for drainage, filtration, separation, or reinforcement. Road uses were typically in underdrains to keep a granular filter material clean, for separation over soft subgrade soils to keep aggregate from becoming contaminated, as reinforcement layers within a mechanically stabilized earth retaining wall or reinforced fill, and as interlayers within a pavement. Today geosynthetic use is more sophisticated and better defined: materials for each function have specific strength and durability properties appropriate for their use. New combinations of materials have resulted in drainage geocomposites, multilayer filters, geogrids with geotextiles, geofoam, and geocells. Many applications in erosion control, as well as other creative uses, have also been developed. Today, more attention is given to quality control and properties testing to better characterize the materials. Although use of geosynthetics has gained wide acceptance in many sectors of civil engineering and highway construction, it is still limited on forest roads. This paper documents the evolution of geosynthetics' use on forest roads, highlights current creative and cost-effective applications of geosynthetics, and promotes geosynthetics in the construction of low-volume roads.