Ernest T. Selig

Fundamental Nonlinear Track Load-Deflection Behavior for Condition Evaluation

Locations of rapid track condition deterioration are typically well known to railway track engineers, although the cause and methods of improvement may be unclear. The rapid deterioration of these locations can be due to many factors such as poor conditions of the components (rail, tie, and ballast) or failure of any of the components or subgrade. The exact cause of the problem is generally unknown as attempts to maintain the track in acceptable condition (by surfacing or undercutting) are implemented. In conjunction with track geometry measurements, which help to identify poorly performing track locations, track load-deflection behavior can contribute to the knowledge of the cause of the problem, with an ultimate goal being identification of a cost-effective, long-term solution to improving the performance of the track. Fundamentals of track load-deflection behavior, how track behavior relates to performance, indices that can be used to determine suitable maintenance strategies, and the relation of these indices to actual track performance all contribute to the evaluation. As indications of the track load-deflection behavior, several track stiffness measurement techniques that have been proposed and tested are described. The goal is to clarify the need to measure track stiffness and to identify rational means of relating the data to track condition and, ultimately, to ensure maintenance, renewal, and safety.

Railway track condition indicators from ground penetrating radar

Two embankments with track performance problems related to embankment instability were investigated. Both sites demonstrated potential for GPR to identify substructure instability resulting in track settlement. The capability to non-destructively evaluate track condition and diagnose the problem cause will ensure that ensuing maintenance addresses the root problem cause, thereby enhancing safety and maintenance efficiency. Two characteristics of the GPR data from these two track performance problem locations were identified as potential track condition indicators. These characteristics were applied to GPR data from a third location with observed performance problems. The application of the condition indicators demonstrates potential for simplifying data interpretation.

Development of material properties for railway application of ground-penetrating radar

A research project is being conducted to identify methods of using ground penetrating radar (GPR) to improve railway track condition assessment and enhance track inspections and safety. The safety of passing traffic can be improved if better indicators of problematic track conditions can be developed and utilized to better inspect the track for safety and to guide maintenance. The research effort has included evaluation of data collection techniques including testing a variety of GPR systems, identification of data interpretation techniques, and comparison of GPR data to track condition information. One limitation that has been identified is a lack of information on the electrical properties of track materials. Although data from geologic materials is well documented, the specific characteristics of railway track materials are different. For example, granite is documented widely as an intact rock mass and is used as ballast for track. However, in the railway ballast application, granite is used as crushed stone. During this research, tests were conducted to measure the dielectric permittivity of a variety of track materials to verify and supplement field measurements and to provide reference data for data interpretation. This paper describes the research project and the results of the testing and analysis.

Field Tests of a Large-Span Metal Culvert

Full-scale field tests were conducted on a 9.5-m (31-ft 2-in.) span low-profile arch culvert to provide input for development of improved large-span culvert load and resistance factor design specifications. The test structure was constructed of 5.5-mm (0.215-in.) thick black steel plate with 152 × 51 mm (6 × 2 in.) corrugations. No supplemental circumferential or longitudinal stiffeners were added. Two tests were conducted with SW backfill material, one each compacted to 87 and 92 percent of maximum standard Proctor density. Live-load tests were conducted with a truck with tandem axles loaded to 156 kN (35,000 lb) per axle at depths of fill of 0.3, 0.6, and 0.9 m (1, 2, and 3 ft). Measurements were made of culvert deformation, culvert strain, culvert-soil interface pressure, soil density, soil strain, foundation movement, and temperature. Thrusts and moments were determined from the culvert strain.

EVALUATION OF DYNAMIC EARTH PRESSURE CELLS FOR SUBGRADE

Two types of commercially available dynamic earth pressure cells were tested to determine their suitability for measuring traffic-induced stresses in subgrade. The main consideration was how well the gauges could be calibrated for accurate representation of soil stresses. Tests were conducted with fluid pressure applied directly to the cells and with cells buried at various depths in a soil test chamber. The effects of soil type, proximity of adjacent cells, major principal stress direction, and temperature were investigated. Results indicate linearity, hysteresis, sensitivity, conformance, and accuracy. The two cells performed differently, but one was much more accurate than the other.

Field Tests of Buried Pipe Installation Procedures

Full-scale field tests to evaluate pipe-soil interaction during backfilling were conducted on the campus of the University of Massachusetts at Amherst. The program consisted of 14 tests, with each test including concrete, plastic, and metal sections. In addition to pipe type, installation variables included in situ soil conditions, trench width, backfill material including controlled low-strength flowable material, haunching effort, and compaction methods. Test trenches were excavated under undisturbed in situ soil conditions. Eleven installations were conducted with 900-mm (inside diameter) pipe, and three installations were conducted with 1500-mm (inside diameter) pipe. Pipe and soil behavior was monitored during backfilling. Measurements included pipe shape, pipe strains, pipe-soil interface pressures, soil density, soil stresses, and soil strains. The pipes were buried to a cover depth of 1.2 m and were then excavated to inspect the pipe bedding and haunches. The results indicated significant variations in pipe behavior caused by installation practices. The rammer compactor produced greater backfill density than did the vibratory plate compactor with the same number of coverages and produced higher residual lateral soil stresses that contributed to better overall pipe performance during backfilling. The silty sand backfill tripled the peaking deflection during sidefill compaction compared with that with angular crushed rock backfill, but the former was more sensitive to deviations from good installation practice. Backfill compaction in the region from the spring line to 30 degrees below the spring line has a significant positive effect in mitigating poor bedding and haunching conditions. Pipe tests with controlled low-strength material for backfill performed very well.

INSTRUMENTATION FOR MONITORING LARGE-SPAN CULVERTS

This paper describes experience gained from an extensive instrumentation plan devised to monitor the behavior of 2 large-span culverts, soil behavior, and culvert-soil interaction during backfilling and live load testing. The aims of the plan were to help control construction deformations, including ensuring safe working conditions, and to gather sufficient data to advance the state of the art in the design and construction of large-span culverts. The instrumentation plan and sample results from the test program are included and discussed.

Structural Behavior of Three-Sided Arch Span Bridge

A study was undertaken to evaluate the methodology used for the structural design of three-sided culverts with arched top slabs. An 11 -m span by 3.4-m rise bridge was instrumented and monitored during installation, under an HS-25 + 30 percent live load and at 6-month intervals for 2 years after installation. The bridge consisted of ten 1.6-m-wide precast segments. Three of the interior segments were instrumented with soil stress cells mounted on the legs of the bridge and with anchor pins for use with a tape extensometer to determine change in shape of the bridge. Survey data were taken on the same three segments and the two adjacent segments. Visual observations were also made to monitor cracking. The live load test was conducted with 0.3 m of cover. Final cover was 0.9 m. The bridge showed less movement under the live load than under the 0.9 m of earth load. The 2-year data show that the shape of the bridge and the soil stresses at the sides of the bridge cycle on an annual basis and that the spans hav...

Resilient Modulus Backcalculation Techniques for Track

The layer moduli of track substructure components are important factors in the evaluation of track condition and estimation of maintenance costs. Layer moduli can be estimated from in-situ tests such as the cone penetration test (CPT); however, for layers of open graded aggregate, such as railway ballast with large individual particles, the results of the CPT are significantly influenced by individual particles and may not reflect the behavior of the mass. A method of evaluating layer properties using downhole measurement of layer deformation is presented in this paper. Tests were conducted on track using downhole measurements of layer deformation under both quasi-static test loads and passing traffic. The applied loads were measured by instrumenting the track superstructure. The top of rail load and substructure deformation data were used with a geotechnical model of track to backcalculate the moduli of individual layers. The process is similar to the procedure for processing data from the falling weight deflectometer; however, data from actual traffic can be evaluated. The results are compared to the CPT results from the same site and also to expected results for similar materials.

Laboratory Tests of Buried Pipe Installation Procedures

Laboratory testing of buried pipe was conducted to evaluate the pipe-soil interactions that take place as pipes are backfilled. The program consisted of 25 tests with metal, plastic, or concrete pipe. In addition to pipe type, test variables included trench conditions, backfill material, compaction method, haunching effort, and bedding condition. The tests were conducted in an indoor test facility designed to allow for the installation of pipe in a realistic manner. Pipe and soil behavior were monitored during installation, and measurements included pipe deflections, pipe strain, pipe-soil interface pressures, soil density, soil strength, and horizontal soil stresses. Backfill was placed to at least 150 mm above the spring line to observe the effects in the important haunch zone. Ten of the tests were continued until the backfill was at least 300 mm over the pipe. The results indicated significant variations in pipe behavior because of installation practices. The wider trench produced greater upward deflections during sidefill compaction. The rammer compactor was the most effective means of achieving high backfill density and stiffness, forcing backfill into the haunch zone, and developing beneficial lateral soil stresses at the sides of the pipe. Installation in trenches with walls of soft materials results in lower lateral pressures and higher invert pressures on the pipe. The coarser-grained backfill material achieved suitable soil unit weight and stiffness with less compactive energy than the finer-grained material. The haunching effort provided improved pipe support in the lower haunch zone.