Resilient Modulus of MnROAD Subgrade Soil

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Date Created
2002
Description
Laboratory remolded subgrade soil samples have been widely used to study subgrade resilient modulus. But physical conditions, such as moisture content and density, of such specimens may not represent in-situ conditions very well. Therefore, AASHTO and the Long-Term Pavement Performance program (LTPP) have recommended that undisturbed thin-walled tube samples should be used to study subgrade resilient behavior. The Minnesota Department of Transportation (Mn/DOT) is developing mechanistic-empirical pavement design approaches through the Minnesota Road Research project and has realized the importance of resilient modulus in the design approaches. Currently, the Mn/DOT is making an effort to study resilient modulus of unbound pavement materials through laboratory experiments. Under a research project at the Mn/DOT, several thin-walled tube samples of subgrade soil were obtained from six different pavement sections at the Minnesota Road Research project. Repeated loading triaxial tests were conducted on the soil specimens to determine resilient modulus at the Mn/DOT laboratory. Also, some soil properties, such as resistance R-value and plasticity index were obtained. R-value is an indicative value of performance when soil is placed in the subgrade of a road subjected to traffic. Two constitutive models (Uzan-Witczak universal model and the deviator stress model) were applied to describe the resilient modulus. The objective of the research was to compare these two well-known constitutive models in describing subgrade soil resilient behavior and to study effects of material properties on the resilient modulus. From the specimens tested, the experimental results showed that the universal model described the subgrade resilient modulus slightly better than the deviator stress model and the coefficients in these two constitutive models were found to have correlation to material properties. Also, no well-defined relationships between R-value and the coefficients in the constitutive models were observed from the results of the tested specimens. Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 1786, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/1786-03.

Field trial of the calcium carbide gas pressure method of determining moisture content

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Date Created
1963
Description
On highway construction projects it is necessary to determine moisture contents of soils and aggregates in connection with earthwork, subbase, base, concrete, and bituminous construction. This determination by the present conventional methods is time consuming, and there has been increasing criticism by contractors that tests of this type are causing delays in the progress of their work. Consequently more rapid methods have been sought for making reliable moisture control tests particularly on base materials and embankment soils. The purpose of this investigation was to determine the accuracy and time saving possibilities of the Calcium Carbide Gas Pressure (CCGP) Moisture Tester when used as a field testing device in comparison with conventional field methods for moisture content determination. This report presents the results of extensive field tests with the instrument. A previous study (Investigation No. 122) had established that moisture contents can be accurately determined with this device under the ideal working conditions of the laboratory. Moisture testers were placed on 14 field projects selected so that the widest possible range of soil types could be tested. Some base and subbase materials were also tested.

Resistance R-values of typical soils and aggregates

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Date Created
1961-02
Description
The results of this investigation to date indicate that the stabilometer may be a very useful tool in the evaluation of Minnesota soils and aggregates. However, the method of applying the results of the test to the design of flexible pavements still has to be established. This remaining problem is undoubtedly the most difficult and will be the third phase of Investigation No. 176

Field Evaluation of Trench Backfilling Procedures: Interim Report

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Date Created
1968
Description
This study was originated in 1960 at the request of the Minnesota Local Road Research Board. Its basic objective is to determine a means of backfilling slit-type trenches so that little or no settlement results. In the first four years personnel from the Research Section, Office of Materials, Minnesota Highway Department, collected data by observing trench backfilling during regular construction operations and then measuring the subsequent settlements. In 1964, 1965, and 1966 dummy trenches were excavated and backfilled under more controlled conditions. This work was done by the City of St. Paul and Minnesota Highway Department maintenance forces. All testing was done by Research Section personnel. In 1963, a progress report titled BACKFILLING TRENCH EXCAVATIONS was published by the Materials and Research Section, Minnesota Department of Highways. Included were general recommendations for street preparation, backfilling, and patching. Also, the effectiveness of various types of compactors was discussed and specific compaction procedures for given soils and traffic conditions were recommended. The results of the controlled backfill studies reported herein have confirmed certain of those recommendations for compaction procedures but have contradicted others. The investigation to date has not satisfied its objective and is being continued.

Backfilling Trench Excavations: Final Report

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Date Created
1971-06
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In the summer of 1969, seventeen dummy trenches were excavated and backfilled using the original A-6 day loam soil. The backfill was compacted to densities from 95.2 to 103.5 percent of AASHO T-99 maximum density. Surface settlements and settlements at depths of 0.7, 2.0, 4.0 and 6.0 ft were measured over a period of 21 months. The settlements were mostly in the 0.04- to 0.08-ft range. Only four settled less than 1/2 in. Seventy percent of the settlement occurred during the first fall and spring after construction. Observed settlement was dominantly in the upper 2 feet of the 6-ft backfill. There was essentially no movement at the bottom of the trench. It is concluded that settlements of approximately 1/2 to 1 in. must be anticipated for trenches with plastic soils even when compacted in relatively thin layers to relatively high densities.

Laboratory Evaluation of Soil-Lime Mixtures: 1961-1962 Progress Report

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Date Created
1962
Description
A limited supply of high quality base aggregates in several parts of Minnesota has resulted in a search for a means of improving the physical and strength characteristics of locally available soils and poor quality granular materials. Other states faced with a similar problem have attempted to use soil stabilization as a solution. Common stabilization agents include cement, bituminous materials, sodium and calcium chloride, and sulfite liquor. More recently, several southern states have successfully used lime for stabilization of roadbed materials. The purpose of this study is to determine the effect of hydrated lime on the physical and strength properties of typical Minnesota soils and aggregates. This first progress report presents the findings of tests conducted during 1961 using hydrated lime and five secondary chemical additives with five fine grained soils

Laboratory Evaluation of Lime Treatment of Typical Minnesota Soils: Final Report

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Date Created
1964
Description
This investigation was included in the research program of the Minnesota Local Road Research Board as a project of special interest to County and Municipal Engineers as well as to Engineers of the Minnesota Highway Department. The project was conducted as a part of the Highway Planning Research Program financed jointly with Federal-Aid funds provided through the United States Department of Commerce, Bureau of Public Roads together with State funds and County and Municipal State-Aid funds. A laboratory study such as this generally does not provide all the information necessary to determine whether a particular method will prove satisfactory as a construction procedure or to accurately predict field performance. This laboratory study does show that lime has some possibilities as an effective treatment for certain Minnesota soils. However, an experimental field project is needed to establish the suitability of the various laboratory tests as a means for evaluating the adequacy of the soil-lime mixtures for use in road structures.

Backfilling Trench Excavations: Progress Report 1962

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Date Created
1962
Description
Engineers who are associated with trenching in public thoroughfares have been striving for many years to find better construction methods and procedures for backfilling these trenches. We cannot expect the public to tolerate detrimental settlement if it can be avoided with a reasonable expenditure of funds. In this study the presently used procedures of backfilling and compaction were observed. It was found that these procedures can definitely be improved. The major conclusions which can be drawn from the study are listed below. The layered system is the most reliable compaction procedure for limiting settlement to a minimum. With one compactor type, the Hydra-Hammer, the entire trench backfill can be compacted in one lift irrespective of soil type or traffic volume on the street. Adequate stability, to prevent detrimental settlement, can be attained with many compactor types if the lift height is adjusted to soil type and condition, and the trench loading conditions. All vibratory type trench compactors should be used strictly on the granular soils and the lift height must be chosen with respect to the particular compactor and the traffic volume. The Pneumatic Button Head compactor can effectively compact all soil types in lifts up to 0.5 feet in thickness. The Plate Tampers are excellent compactors for all soil types and they are capable of compacting soil lifts between 1.0 and 1.5 feet depending upon the traffic load. Heavy construction equipment should be used to compact only the upper lift in a trench and this lift should be restricted to the range of 1.0 to 2.5 feet in thickness depending upon the soil type and the traffic load. Further research under more controlled field conditions is planned for 1963.

Climate Research at MnROAD: MnROAD Lessons Learned

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Date Created
2006
Description
From the beginning, MnROAD was imagined by its planners as a cold-regions research facility for pavements. In its first decade of operation, MnROAD was the site of numerous experiments whose main aim was to observe the effects of a Minnesota winter (or more than one winter) on the pavement system, from the materials in the surface course to the soils in subgrade. In holding to its goals as a cold-regions research facility, MnROAD engineers developed an extensive knowledge of pavement construction, design, and maintenance in cold-regions climates. In many areas, MnROAD engineers were pioneers in their particular cold-regions study: for instance, MnROAD engineers were some of the first in the United States to closely observe low-temperature cracking in pavements. Furthermore, MnROAD has gathered a significant amount of environmental data and data related to cold-regions phenomena such as low-temperature cracking. This brief details some of the MnROAD products dealing with MnROAD’s experience in cold-regions pavements.

2000 Spring Load Restrictions Legislative Task Force Report

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Date Created
2001-02
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Spring is a critical period for Minnesota's roads because the roadbed soils and aggregate base materials are in a weakened state during and after the thawing process. Spring load restrictions (SLR) are used as a preservation strategy to reduce damage, thereby protecting Minnesota's investment in the infrastructure. However, the imposition of spring load restrictions impacts industry, both in their operations, and financially. While it is clear that spring load restrictions benefit the infrastructure, there are two issues of which little is known: (1) the economic impacts that result when access to the transportation system is restricted and (2) extent of enforcement efforts. The development of the Spring Load Restrictions Task Force was in response to 1999 legislation requiring the Commissioner of Transportation to establish a task force to study spring load restrictions and report to the legislature its findings and any recommendations for legislative action by February 1, 2000. The legislation also calls for task force members that represent many interests including aggregate and readymix producers, agriculture, waste haulers, construction, and logging. Other members representing local agencies, associations, and enforcement have also been included.