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The state and many counties throughout Minnesota are using a variety of subgrade stabilization techniques for various materials used in road construction. Such methods appear to improve constructability and lead to increased performance and reduced maintenance. While a number of studies have investigated such stabilization efforts (including materials and techniques, relative increases in strength and/or stiffness, etc.) no overall quantification and summary of the effects of material stabilization have been brought forward with recommendations of parameters to be used for design purposes. Although these techniques and materials are commonly used, minimal information has been obtained relating to the Mechanistic-Empirical (ME) properties of these improved materials such that the more cost-effective designs can be implemented. Not having recommendations for the ME properties of the improved materials, the designer is forced to use values for the non-stabilized material. While this does likely lead to extended road life, costs could be greatly reduced by taking advantage of the improved properties of the stabilized roadway materials. This project has involved determining which types of subgrade stabilization are being used, identifying which of these stabilization techniques/materials are of interest to the Minnesota Department of Transportation (MnDOT), compiling the results of past research relating to these stabilization techniques, summarizing the results of past research and proposing a mix design procedure that obtains material properties for use in design. This proposed mix design procedure will allow the designer to account for improved stiffness due to stabilization, reducing costs and improving the efficiency of the design.

The current test rolling program as used by Mn/DOT is in need of an update and/or supplement to existing equipment, procedures and specifications. The traditional roller is very heavy and cumbersome and the current construction specification is not technically based. Due to the heavy weight, the roller is only appropriate in approving lifts that are three to four feet thick. While this is ideal for large projects where thick lifts are to be evaluated, most projects do not need this magnitude of loading. This implementation project has developed a more adaptable test roller system and an appropriate construction specification for this modified system. The new test roller and construction specification allow for variation in the weight applied, which will allow varying site conditions to be tested. Such a system would be especially appropriate for roadways that are designed for less than 10 ton loads. This system is easily transported, such that mobilization will be more efficient, and data are continuously recorded during test rolling. The modified test roller is an instrumented system mounted on a standard dump truck. A new test specification has been proposed for the new system and deflection criteria have been established for several combinations of subgrade types and roller weights. The results of the project have also provided a method for comparing pavement structures and layer properties as constructed to their intended design, linking roller deflections to pavement performance. The new system has been utilized on several regional projects and has been shown to work effectively.

Aggregate base materials are becoming increasingly expensive in many parts of Minnesota because gravel mines and rock quarries are being lost to other land uses. These aggregate materials are classified for use and placed in quantities based on design procedures and testing techniques that are several decades old. To optimize material use and reduce waste, new mechanistic-based design procedures and testing techniques need to be implemented to achieve better value during road construction. This research study is aimed at evaluating pavement base/subbase performances of locally available aggregate materials (with gradations still falling within the MnDOT specified gradation bands) in Minnesota through mechanistic pavement analysis and design. The main objective of this study is to demonstrate that locally available aggregate materials can be economically efficient in the implementation of the available mechanisticbased design procedures in Minnesota through the MnPAVE mechanistic-empirical flexible pavement design method. The goal is to develop the components of a new granular material best value software module to be added to the MnPAVE program. This report summarizes the detailed research findings from which the following conclusions can be drawn: (1) locally available aggregate materials with varying levels of quality can still properly serve traffic-level and environment-related loading from a mechanistic-empirical pavement design perspective provided that important aggregate properties, such as gradation and particle shape, are optimized; (2) potential shear failure in base and especially subbase need to be properly addressed as non-unique modulus-strength relationships were observed; and (3) the proper use of local materials can be quite cost-effective.

The purpose of this investigation is to evaluate the practicality and accuracy of using nuclear devices for determining moisture and density of materials used in highway subgrades and base courses and the density of bituminous paving courses. In Minnesota the sand cone method of density determination is presently used for control of embankments and granular base materials, In the last two years the burner dry moisture content has been supplemented with the "quickie" moisture method using the carbide pressure meter. It was felt that the nuclear method showed enough promise to make a study on it to compare the performance of devices using this method to that of the presently used methods in terms of accuracy and of time requirements in obtaining the results.

This report summarizes the results of a literature research effort to assist the Minnesota Department of Transportation (Mn/DOT) in (1) evaluating methods and devices for reliably determining in-situ drainage characteristics of base and subgrade materials and (2) evaluating the specifics of the most promising options that are best suited to Mn/DOT's needs. This research effort is limited to existing information and studies. The primary goal of this effort is to identify a device or method that would be used by field inspectors to ensure that base and subgrade materials are capable of removing infiltrated water from pavement systems in order to prevent accelerated pavement deterioration. The device or method must be durable and easy to use by field personnel. The device or method must also be economical so that it can be distributed for state-wide use. The research effort is being performed in two phases. Phase I (summarized in this report) is a comprehensive survey and review of existing literature to identify methods and devices for measuring in-situ drainage characteristics of aggregate base and granular subgrade materials and to summarize salient characteristics of these methods and/or devices. Phase II will focus on a more detailed evaluation and· analysis of the most promising methods and/or devices identified in Phase I. The selection of the methods and/or devices for the Phase II study will be performed in conjunction with Mn/DOT's review of the Phase I findings.

This report summarizes the devices from Phase I of this study, as well as Phase II results. In Phase II, researchers evaluated the inverse auger hole test, open single-ring infiltrometer test, and the direct velocity technique for measuring the in-situ drainage characteristics of aggregate base and granular sub grade materials. According to research findings, the referenced methods of calculating hydraulic conductivity from the test measurements appear to be incorrect. The devices will have to be modified and the method of calculating hydraulic conductivity from the test measurements revised to obtain an appropriate value for hydraulic conductivity. The appropriate value for hydraulic conductivity calculated from modified tests can be used to estimate the drainage of the aggregate base and subgrade materials. Another important finding from Phase II involves the characterization of flow within the aggregate base and granular subgrade material. As designed, the flow is primarily horizontal. Based on this finding flow normally will be in an unconfined flow regime. As such, it is critical that enough discharge capacity and storage capacity be provided within the aggregate base and granular subgrade material to prevent saturated confined conditions beneath the pavements during infiltration. The study also recommends continuing the investigation of drainage characteristics beneath pavements.

The primary objective of this study was to determine whether concrete lug anchors retarded pavement movement on steep grades. Minnesota Department of Transportation's policy is that grades in the 3 to 5 percent and greater range are steep and may require lug anchors. Standard lug anchor spacing varies from 150 feet, center to center, for 3 percent grades to 75 feet, center to center, for 5 percent and greater grades. During the initial study of lug anchors on State Project 0702-49 it was observed that pavement settlement was occurring at these lug anchor locations. Settlement of up to 1 1/2 inches was observed. It was felt that this settlement was being caused by surface water entering the pavement structure, flowing in a down hill direction via the base aggregates, being trapped at the lug anchors and finally, due to traffic loads, being pumped out, thereby causing loss of base fines and some subgrade soil fines. End result was pavement settlement. Therefore, a second phase of this study, utilizing 2 inch perforated pipe to control surface water was initiated on S.P. 0702-51 This report covers both studies. Conclusions based on this study are: 1) that lug anchors do prevent the downhill movement of the concrete pavement; 2) that when lug anchors are used a perforated pipe system also be built to collect the surface water that enters the pavement structure thus eliminating the anticipated base pumping and pavement settlement.

This Technical Summary pertains to Report 2012-18, “Subgrade Stabilization ME Properties Evaluation and Implementation,” published June 2012.

This Technical Summary pertains to Report 2011-15, “Development of New Test Roller Equipment and Construction Specifications for Subgrade Compaction Acceptance,” published June 2011. The research being implemented via this project can be found mainly in the LRRB-produced Report 2008-08, “Development of Improved Test Rolling Methods for Roadway Embankment Construction,” published February 2008.

This Technical Summary pertains to Report 2012-01, “Best Value Granular Material for Road Foundations,” published January 2012.