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Every year, ODOT undertakes numerous pavement patching/resurfacing projects to repair pavement distress and structural failure due to soft and/or organic soils constituting the subgrade. Other than the temporary solution of patching/resurfacing, removal of weak soils and replacement with new suitable engineered fill can be used for permanent remediation. However, when problem soils are relatively deep this method can be too costly. There are various vertical column support methods used for civil engineering structures when soils are not strong enough to support the structure. Although some of these methods are utilized by several state DOTs to remediate settlement problems of existing roadways, they were not used in Ohio for this purpose. This study investigated the applicability of various vertical column support systems to improve subgrade and reduce settlements for existing roadways in Ohio. A decision matrix has been developed to identify the feasible methods. Two sites with ongoing subgrade settlements have been investigated through detailed subsurface investigations for possible implementation. Several technically feasible vertical column support methods have been identified for these sites. Lifetime cost-benefit analysis performed show that although there are some upfront costs associated with these remediation methods, the vertical column support ground improvement methods are significantly more cost effective compared to the current practice of patching/resurfacing temporary alternative during the project's lifetime, and can result in significant cost savings to ODOT and roadway users.

The objectives of this study were to determine how to incorporate the increase in stiffness of stabilized subgrade in the design of (Flexible?) pavement, and to examine the longevity of subgrade stabilization. Pavement sites that included stabilized subgrade across the state of Ohio were selected for field measurements. The field work included measurements made with portable seismic properties analyzer (PSPA), falling weight deflectometer (FWD), core collection, and dynamic cone penetrometer (DCP) at multiple locations at each site. Original construction records, soil logs, and soil classification data were consulted as well. The FWD and DCP data were used to determine the resilient moduli and layer coefficients of aggregate base and stabilized subgrade and the resilient modulus of the unstabilized subgrade. Several methods of data analysis were used, including back calculation using finite element modeling from the FWD data and estimation of modulus from the DCP data and soil classification using procedures given in the 1993 AASHTO Guide for Design of Pavement Structures, ODOT's Pavement Design Manual, and a report for ODOT written by Eddie Chou [2004]. As borne out by FWD and DCP measurements, both cement stabilization and lime stabilization resulted in significant long term increases in the modulus of the stabilized subgrade relative to the unstabilized subgrade. The modulus and stiffness of the base is also increased because it is confined by the stabilized soil underneath and the pavement on top. The significant increase in the modulus of the base and stabilized subgrade has an impact on the thickness design of pavement.

The overall goal of WHRP Study #0092-08-07 was to collect information and data on the use of intelligent compaction (IC) technology to allow the Wisconsin DOT to make an informed decision on any useful application of this technology. Three objectives were identified to meet the overall goal of the study: (1) identify the advantages and limitations of the IC technology; (2) determine the material types and conditions that might cause inaccurate decisions or output from the IC roller (e.g., the accuracy of the outputs regarding layer stiffness), and (3) provide recommendations to the Wisconsin DOT on the use and implementation of IC technology for pavement construction. Field demonstration projects were planned and executed to collect data and information related to the use of IC rollers in Wisconsin. The demonstration projects confirmed that IC for soils is more advanced than for hot mix asphalt (HMA) layers. Level 2 and Level 3 soil IC rollers can be used almost immediately in Wisconsin. Unfortunately, there are many more issues or unanswered questions for compacting HMA layers than for unbound layers. The two areas where IC rollers can have immediate positive benefits, especially for unbound materials, are: (1) as a testing device to continually map the stiffness of an area prior to placing both unbound and HMA materials to identify areas with weak supporting layers and, after the layer has been compacted, and (2) to develop stiffness-growth relationships to determine the rolling pattern and number of passes to achieve a specific stiffness level. The key technical issues include lift thickness, bridging localized construction defects, and the fact that the IC roller output is a composite value influenced by the supporting layers. Additional pilot projects are recommended to increase contractor and agency personnel's confidence in using this technology.

As the pavement design process moves toward mechanistic-empirical techniques, knowledge of seasonal changes in pavement structural characteristics becomes critical. Specifically, frost penetration information is necessary for determining the effect of freeze and thaw on pavement structural responses. This report describes a methodology for determining frost penetration in unbound pavement layers and subgrade soil using temperature, electrical resistivity, and moisture data collected for instrumented Long Term Pavement Performance (LTPP) Seasonal Monitoring Program (SMP) sites. The report also contains a summary of LTPP frost depth estimates and a detailed description of the LTPP computed parameter tables containing frost penetration information for 41 LTPP SMP sites. The frost penetration analysis methodology and the accompanying E-FROST program is used in-situ soil temperature as a primary source of data to predict frost depth in unbound pavement layers. In addition to temperature data, electrical resistivity and moisture data were used as supplemental data sources for the analysis when temperatures were close to the freezing isotherm. The Enhanced Integrated Climatic Model (EICM) was used to fill intermediate gaps in the measured soil temperature data.

This report introduced the research begun in 1999 at the University of Wisconsin-Madison to further understand aspects of geosynthetic-reinforced subbases in a pavement system. To learn more about how the performance of highway pavement is improved with geosynthetics, a field demonstration was conducted using a 21-m section along a Wisconsin highway (USH 45) near Antigo, Wisconsin, that incorporated three test sub-sections. Three different geosynthetics including a woven geotextile and two different types of geogrids were evaluated for stabilization. The same pavement structure was used for all test sections except for the geosynthetics. Observations made during and after construction indicate that all sections provided adequate support for the construction equipment and that no distress is evident in any part of the highway. Much has been learned about instrumentation of geosynthetics with foil-type strain gages. The installation procedures and weatherization techniques used during this demonstration project appeared to be a success. Additionally, better strain gage results are possible for a geotextile when a longer (25 mm) strain gage is used. The falling weight deflectometer did not provide sufficient resolution to differentiate between different types of geosynthetic test sections especially in a field environment where there's heterogeneity of natural soils. However, a greater seasonal variability of the subgrade was noted. A control section without reinforcement was not constructed at this time that would have allowed for comparison and assessment of the geosynthetic addition.

This study was conducted to develop a methodology to incorporate the structural contribution of working platforms, including those constructed with industrial by-products, into the design of flexible pavements. Structural contribution of the working platform was quantified in terms of a structural number or an effective roadbed modulus. Resilient modulus obtained from large-scale model experiments(LSME) conducted on several working platform materials (i.e., crushed stone (referred to as "breaker run", Grade 2 granular backfill (referred to as Grade 2), foundry slag, foundry sand, and bottom ash) were used in the analysis. Design charts are presented that show the structural number or the roadbed modulus as a function of type of material and thickness of the working platform. Another study was conducted to evaluate the structural contribution of geosynthetic-reinforced granular layers that are used as working platforms to the pavement structure. Based on the LSME and from the field Falling Weight Deflectometer (FWD) tests, the relationship between back-calculated elastic modulus and bulk stress was obtained. The improvement in layer coefficients is rather small for the nonwoven geotextile and drainage geocomposite (10%) and somewhat higher for the geogrid (40%) and for the woven geotextile (18%) in a 0.30-m thick granular working platform layer (treated as a subbase). The contribution of geosynthetics would be even less having a thicker subbase layer.

A study was conducted to define an equivalency criterion for five materials used for working platforms during pavement construction on a poor subgrade: conventional crushed rock (referred to as "breaker run") and four alternatives [i.e. Grade 2 granular backfill (referred to as "Grade 2"), foundry slag, bottom ash, and foundry sand]. Total deflection data for the equivalency assessment were obtained from a large-scale model experiment (LSME) simulating a prototype-scale pavement structure and in the field using a rolling wheel deflectometer (RWD). Design charts were developed for selecting the equivalent thickness of alternative working platform materials so that the alternative provides equal deflection as a layer of breaker run. Another phase of the study was conducted to determine the equivalency of geosynthetic-reinforced aggregate working platforms in providing support during pavement construction over soft subgrade. Four reinforcing geosynthetics (a geogrid, a woven geotextile, a non-woven geotextile, and drainage geocomposite) incorporated into two granular materials: Grade 2 and breaker run were used in this study. Design charts were developed for selecting the equivalent thickness of an alternative geosynthetic-reinforced working platform material so that the alternative provides equal deflection as a layer of breaker run.

ODOT has recently developed guidelines for subgrade treatments to be used during plan development and construction. This study evaluates these guidelines by comparing them with existing guidelines developed elsewhere and validating them through comparison of the actual treatment methods and quantities used with those suggested by the guidelines. Soil boring data and construction record from 7 reconstruction and 2 new construction projects were obtained. Actual treatment methods and quantities were obtained from the project field offices. Dynaflect deflection data, when available, were analyzed to determine their usefulness in subsurface assessments. GB1 criteria for excess moisture content predicted the undercut quantity reasonable well, but the criteria for acceptable moisture content tend to under predict the undercut quantity in many cases, likely due to increased soil moisture content after removal of existing pavement. For reconstruction projects, the average undercut depths (i.e., the overall undercut quantities) versus the corresponding SPT NL values seem to fall reasonably well within the upper bound provided in the Section 204 guidelines. However, the actual undercut depths vary significantly even for soils with similar or same NL values. Actual undercut depth and quantity are somewhat correlated with the average SPT NL value, Dynaflect W5 deflection, and soil moisture content. The regression equation developed has a coefficient of determination (or R-square value) as high as 0.71.

The performance of asphalt concrete pavements is in part affected by the seasonal variations of the resilient modulus of the AC layer and of the subgrade soil. To determine the variation of these parameters throughout Ohio, seven moisture-temperature-rainfall recording stations, previously installed during an Ohio Department of Transportation-funded project, and two additional ones installed during this project, were monitored for an additional period of 2-1/2 years, These stations, located to include various climatic zones and the four most common soil types within the state, recorded air, asphalt concrete and subgrade soil temperature, rainfall and moisture content (or degree of saturation) of the subgrade soil on a two-hour basis. Recorded data led to the development of polynomial equations to calculate the average asphalt concrete pavement temperature from the air temperature and to the division of the state into three temperature zones: Northern, Central and Southern. Recorded depths of frost penetration indicated average depths of 45 to 61 cm. within the southern zone and of 70 to 52 cm. within the northern zone. Similarly, the northern and the southern zones experience an average of 7 to 12 and 4 to 5 freeze-thaw cycles, respectively. The degree of saturation calculated from moisture and temperature sensor readings varied form about 90% to 100% throughout the monitoring period. The late spring to early summer consistently led to a higher degree of saturation at all depths. Finally, a method to back calculate the resilient modulus of subgrade soils (Eri) at the break point from measured FWD deflections was developed. Seasonal averages of this modulus were obtained at each of six station locations where FWD testing was conducted. Seasons were ranked in terms of expected higher resilient modulus. The designated "fall" testing period (early fall) showed the highest followed by "summer," "winter" and "spring" in decreasing order. Determined monthly and seasonal variation of material properties will find immediate application as inputs in mechanistic-empirical pavement design procedures

The objective of this study was to develop a method to predict the timing of weight limits on secondary highways in Wisconsin. Two types of weight limits are of interest: overloads when the pavement is frozen and weight restrictions during thawing and post-thawing recovery period. To meet this objective, three sections of secondary highways with flexible pavements were instrumented and monitored to determine how freezing, thawing, and post-thaw recovery affect pavement stiffness. Data collected from these sites were used to develop a computer model (UWFrost) that can be used to predict seasonal changes in the support capacity of pavements.

Seasonal variations in climatic conditions have long been recognized to have a significant impact on the structural response of flexible pavements. Of particular significance is the effect of subgrade moisture content on subgrade support values and potential roadway damage. The Montana Department of Transportation is conducting a project to evaluate the response of subgrade resilient modulus to seasonal changes in subgrade moisture content. Moisture content is being measured through permanent subsurface instrumentation while deflection tests are periodically being conducted to establish subgrade resilient modulus values. This report describes work performed in support of this project. The purpose of this study was to provide laboratory data on subgrade support values for the instrumented sites. These data will illustrate the variation in subgrade support with changes in moisture content and sample dry density. This information will be used to verify the accuracy of the data generated in the field and might also be used to help guide the backcalcuation procedure. Laboratory testing has consisted of resilient modulus, triaxial compression, CBR and R Value tests. Results have been generated for various combinations of sample dry density and degree of saturation. These results have been related to resilient modulus whenever possible. The results tend to show that ultimate strength related parameters are most sensitive to changes in dry density and moisture content for the cohesive subgrade soils and that deformation related parameters are most sensitive for the more non cohesive subgrade soils.