Soils

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.

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.

This technical note describes how to assemble and install the frost resistivity gages used to collect data for the report "Resistivity Probes, Installation and Readout Techniques."

Resistivity gages discussed in this manual rely on the measurement of electrical resistance between conductors mounted along a cylindrical probe (see Figure 1) to determine where the soil is frozen and where it is thawed. This determination is based on the wide difference between the volume resistivity of frozen soil (from 500,000 up to several million ohms) and thawed soil (20,000 to 50,000 ohms normally). Frost penetration is determined by making sequential resistance measurements between adjacent pairs of electrodes down the resistivity probe and documenting at what depth the resistance goes from a high to a low value. It is not even necessary to actually read the resistance since a readout circuit may be used in which voltage measurements for each probe section may be ratioed to a fixed one megohm resistor located in the output circuit. This arrangement will work just as well as the actual resistance measurement since it is the shape of the curve that contains the frost depth information, not the absolute value of the measurements. Figure 1 is a sample resistivity installation. Typical curves are shown in Figure 2. For comparison, two curves of temperature vs depth are also shown, one at mid-winter conditions and one during spring thaw. The resistivity gage measurements were made by reading the resistance (or voltage drop) between solid copper rings spaced evenly on a buried PVC rod using an alternating current (ac) voltage source.

A three-month research project was conducted on the frost heaving patterns of a culvert. Problems are typically encountered when such a culvert is placed under a road in a frost-susceptible soil. Major differential frost heaving is produced and has a negative effect on the structure of the road itself while creating a rough ride and reducing safety for road users. This project analyzes the performance over the winter period of several potential remedial designs. The goal is to find a design that will minimize the differential frost heave for the broadest possible conditions in terms of frost-susceptibility and of freezing pattern.

The French conducted a thorough research program from 1969 to 1977 to produce design standards for building durable and non-frost susceptible roads. Based on this research, a frost heave simulation program was developed by "Laboratorie Central des Ponts et Chaussees" in France. The intent of this research has been to investigate the possible use of this computer program as well as acquiring information and data concerning French soils that have been tested for frost heave.

This innovation update relates to Report 2009-12, "Using the Dynamic Cone Penetrometer and Light Weight Deflectometer for Construction Quality Assurance," published in February of 2009.

This report presents the findings of the second phase of an exploratory project to assess the potential of nonvibratory methods of compaction for utility-related compaction needs. Proposed refinements and additions to existing compaction procedures are based on the use of an alternating flooding and vacuum procedure introduced through a pipe or series of pipes embedded in the soil. This process had been demonstrated in early Phase I laboratory tests to give better results than flooding alone for granular soils. Phase II laboratory and field tests produced compaction results ranging from an acceptable level of compaction to an unacceptable level. The flood/vacuum method appeared to work best in well-graded granular materials including some, but not an excessive amount of, fine particles. The cycle times for flooding and vacuum removal of the water appeared to be too long for practical use. The flood/vacuum technique by itself, or without reasonable levels of static compaction, does not appear to be a viable technique for field use. It appears that results from the technique could be significantly approved by adding mechanical disturbance of the backfill material or vibration energy to the flooding cycle.

An extensive pavement material sampling and testing program was devised and carried out during construction of the Minnesota Road Research Project (Mn/ROAD). This guide provides comprehensive information regarding the type and location of soil and base material samples collected from the Mn/ROAD project. Information regarding nondestructive soil testing is provided which includes Dynamic Cone Penetrometer (DCP) and Falling Weight Deflectometer (FWD) testing. Material sample information provided is divided into sample types, then into proposed research applications. Sample locations and proposed laboratory tests are shown. Testing locations for the nondestructive tests conducted on the project are provided. Information listed in a "Mn/ROAD ID#" column provides a unique identification to each sample. This sample identification can be used to request samples or obtain test result data contained in the Mn/ROAD database. During construction of the Mn/ROAD project, approximately one third of the samples collected were immediately tested to characterize the subgrade layers of the project. The remaining samples were put into storage for future research needs. Appendices A, B and C contain descriptions of Mn/ROAD database tables related to soil samples and nondestructive tests. Test cell profile diagrams are provided in Appendix D.

Intelligent compaction (IC) is a roller-based innovative technology that provides real-time compaction monitoring and control. IC can monitor roller passes, vibration frequencies/amplitudes, and stiffness-related values of compacted materials or intelligent compaction measurement Values (ICMV). Various ICMVs have been introduced since 1978. Based on the five levels of ICMV in the 2017 FHWA IC Road Map, the current implementation of ICMV in the United States has been limited to Levels 1 and 2. However, Level 1 and 2 ICMVs fail to meet the FHWA IC Road Map criteria. To achieve the full potential of IC technology, Level 3 and above ICMVs are needed to gain the confidence of agencies and industry and the adoption of IC to soil and base compaction. This project aims to (1) evaluate Level 3-4 ICMV systems against Level 1 ICMV systems for soils, subbase, and base compaction and (2) develop a blueprint for future certification procedures of IC as an acceptance tool. This study also aligns with the goals of the ongoing HWA IC for foundation study and the TPF-5(478) pooled fund study. This final report details the ICMV background, field test efforts, analysis results, and an IC specification framework for compaction acceptance.