Search Content

Each year miles of utility trenches are cut, backfilled, and surfaced by utility companies, government agencies, and contractors. Improper repair of these trenches leads to bumps, settlements and pavement failure. Unfortunately, city and county governments are not always responsible for the repair and have little control over the construction methods used. To provide information regarding the methods of repairing utility trenches that are commonly used in Minnesota, the Local Road Research Board (LRRB) requested that this report be written The report outlines the results of a survey of Minnesota cities who were asked to detail their specifications and construction methods for backfill and surface repair.

Among the most promising and innovative concepts today for alleviating urban traffic congestion is the use of video imaging for vehicle detection, automatic surveillance, and advanced control strategies. Because of its conceptual appeal, research in this area was initiated in the mid 70's in the United States and abroad. A system for vehicle detection through video imaging was recently developed at the University of Minnesota and is being implemented on the 1-394 and l-35W freeways in Minneapolis, Minnesota for incident detection. The Minnesota system, called AUTOSCOPE (TM), emulates loop detectors, a large number of which can easily be placed within the field of the camera's view through interactive graphics. In recent tests its performance matched or exceeded that of loops in vehicle counting, speed measurements, and extraction of certain measures of effectiveness. Evaluation tests of the AUTOSCOPE (TM) were very encouraging, thus the system was installed at a traffic intersection to demonstrate the effectiveness of this new technology as a replacement for loop detectors.

This report presents a literature review of instrumentation practices for the measurement of stresses, strains, and deflections in pavement structures. Various types of instruments that are commonly employed in pavement instrumentation projects are discussed, as well as the factors that influence their performance. In a series of laboratory experiments, the performance of three different types of embedment strain gages, two LVDTs, and one soil stress cell are investigated. These experiments are designed to evaluate the accuracy and durability of commercially available transducers. For strain gages, the selection of an appropriate transducer must balance compliance and measurement sensitivity. All of the strain gages tested in concrete gave reasonable results. It was found that hermetically sealed LVDTs should be sufficient enough for robust installations. Experiments with soil stress cells embedded in sand indicate the variability that may be expected in the field due to installation procedures, and emphasize the need for in-soil calibrations. A set of recommendations are provided with respect tot the sensor procurement and installation specifications for Mn/ROAD.

This Soil Factor Design Method was written for counties, townships, and municipalities for use in designing aggregate roads. Although many design methods for aggregate roads exist, most require thorough soil identification and soil strength testing. Since most local agencies do not have the means to perform elaborate testing of soils and because they are familiar with soil factors, this design method should be helpful. This procedure requires soil identification, traffic counts and rational judgement. At present Mn/DOT does not have a design method for aggregate roads. It is not the intention of this manual to change the present legal load limits for gravel roads. For those who would like a more thorough design method, or more background information on aggregate roads, the method includes information on the use of the U.S. Forest Service Aggregate Surface Design Guide. Also included is information regarding compaction, drainage, frost action, geosynthetic use, lime stabilization, and an appendix with sample problems based on the Soil Factor and Forest Service design methods.

The need to reduce our states dependence on land fills resulted in a unique cooperative venture by three state agencies. A partnership was forged between the Minnesota Pollution Control Agency (MPCA), the Minnesota Department of Natural Resources (DNR) and the Minnesota Department of Transportation (Mn/DOT) to investigate the use of recycled tire rubber and processed asphalt shingle scrap. The result is a two mile section of the Willard Munger Recreational Trail in St. Paul, constructed with asphalt paving mixtures which contain varying percentages of recycled tire rubber and shingle scrap. Special bituminous mix designs were formulated using 3% rubber, 6% rubber, 3% rubber with 6% shingles and 9% shingles. The mixtures containing rubber did not exhibit acceptable mix characteristic values under present Mn/DOT bituminous specifications. The shingle-only mix met specifications and yielded an economic advantage of decreasing the asphalt cement demand of the mix. Conventional mixing and paving equipment was utilized for construction. This application appears to be a viable alternative containing rubber increased from 35% to 50% over the cost of the conventional mixture. Since the use of shingle scrap was negotiated by the private companies involved, no comparable cost data is available.

A microscopic, stochastic model for intersection design and traffic flow analysis is presented in this report. A simulation program, INTERSIM, based on this modeling, is developed. The INTERSIM program can be used to evaluate alternative control schemes and geometric configurations. INTERIM can also assist in solving traffic operation and management problems, e.g., determining optimum signal phasing and timing of intersections via an iterative process. The most common situations encountered in practice are examined. These include: four-way and T-intersections with up to three lanes on each approach; stop sign control; signal control (fixed time or vehicle actuated) with various phasing schemes; detector placement and functions, multi-use lanes; protected and permissive left-turn movements; and right turns on red, among others. The proposed modeling applies to both over-saturated and under-saturated traffic conditions. INTERSIM is superior to the other intersection simulation programs due to its ease of operation and fast execution speed.

When a culvert is placed under a road, the presence of air at freezing temperatures in the culvert may induce differential frost conditions in pavements. Also, a differential frost heave pattern can appear when the culvert is placed in a frost-susceptible soil. In this project, computer simulations of temperature distributions and frost heave patterns around culverts were carried out, and the effects of various insulation techniques were analyzed under weather conditions representative of Minnesota winters. The pavement slope variance, which is a commonly used variable describing the roughness (or loss of serviceability) of a given pavement section profile, proved to be a valuable indicator under frost heave conditions. Results indicate that culvert insulation reduces the value of the pavement slope variance throughout the freezing period: the higher the insulation thickness, the lower the resulting slope variance (or loss of serviceability).

One of the most common maintenance activities performed on bituminous pavements by local governmental agencies relates to crack treatment. Crack treatments include .crack sealing, crack filling, and crack repair. Crack sealing is the method of placing material in a crack to create a water tight barrier, while crack filling involves coating the sides or edges of a crack in an attempt to reduce the rate of deterioration. Crack repair is more extensive than both sealing or filling and can involve fine mix' patching, tight blading, mill and repair, and overlays. Generally, rubberized materials, due to their ductile properties are considered to be crack sealants while asphalt based materials are considered fillers. This report discusses the most commonly used materials and practices used by local engineers in Minnesota to seal and fill cracks on bituminous pavements. The report is based on the results of a survey conducted by the authors in 1991. The report presents the results in several ways and summarizes the findings.

The Minnesota Department of Transportation is continually investigating ways to improve the cold temperature performance of its asphalt concrete pavements. One reported method is to modify the asphalt binder with ground reclaimed automobile and truck tire rubber. In 1984, a project on TH 7 (State Project 4703-17) was selected for the field trial of an asphalt-rubber cement dense graded concrete utilizing a product produced by Arizona Refining of Phoenix Arizona. Construction of the asphalt-rubber cement dense graded asphalt concrete required some special effort and specialized equipment to maintain adequate mixing and placing temperatures. Evaluations included crack counting, resilient modulus, inplace air voids rutting, roughness, recovered penetration and cost considerations. Interesting results regarding the resilient modulus of the asphalt rubber samples were found. However, the formulation used provided little or no perceived benefits to the roadway at much higher costs. The high costs were due in part to the nature of the project. However, this appears to be a cumbersome and expensive procedure with the primary benefit being waste tire utilization.

The Minnesota Department of Transportation is investigating alternative means of culvert renewal in lieu of removal and replacement. Several state of the art renewal techniques were selected for trial on 1-35 near Hinckley, Minnesota in an effort to find an inexpensive and less disruptive alternative to removal and replacement of deteriorated culverts. Seven different reliners were placed in concrete and metal pipe, and five joint repair options were placed in concrete pipe. These reliners and repairs were compared using costs, skills and resources required, time, culvert preparation, traffic disruption, work area requirements, placement problems, and grouting procedures. Field performance of the reliners and joint repairs was checked visually after one year to evaluate the short term effects of climate. At this point in time all reliners appeared to be performing adequately. Relining and joint repair should be considered as an inexpensive, time saving, and minimally disruptive alternative to removal and replacement of deteriorated culverts. Smooth reliners are inexpensive, flexible, easy to install and perform better hydraulically than corrugated or ribbed reliners. Savings can be significant in both money and time with very little disruption to the driving public.