Behavior of Granular Materials Under Triaxial Compression with Pulsating Deviator Stress, HR-131, Special Report

Behavior of granular material subjected to repeated load triaxial compression tests is characterized by a model based on rate process theory. Starting with the Arrhenius equation from chemical kinetics, the relationship of temperature, shear stress, normal stress and volume change to deformation rate is developed. The proposed model equation includes these factors as a product of exponential terms. An empirical relationship between deformation and the cube root of the number of stress applications at constant temperature and normal stress is combined with the rate equation to yield an integrated relationship of temperature, deviator stress, confining pressure and number of deviator stress applications to axial strain. The experimental program consists of 64 repeated load triaxial compression tests, 52 on untreated crushed stone and 12 on the same crushed stone material treated with 4% asphalt cement. Results were analyzed with multiple linear regression techniques and show substantial agreement with the model equations. Experimental results fit the rate equation somewhat better than the integrated equation when all variable quantities are considered. The coefficient of shear temperature gives the activation enthalpy, which is about 4.7 kilocalories/mole for untreated material and 39.4 kilocalories/mole for asphalt-treated material. This indicates the activation enthalpy is about that of the pore fluid. The proportionality coefficient of deviator stress may be used to measure flow unit volume. The volumes thus determined for untreated and asphalt-treated material are not substantially different. This may be coincidental since comparison with flow unit volumes reported by others indicates flow unit volume is related to gradation of untreated material. The flow unit volume of asphalt-treated material may relate to asphalt cement content. The proposed model equations provide a more rational basis for further studies of factors affecting deformation of granular materials under stress similar to that in pavement subjected to transient traffic loads.

Preventing Cracking at Diaphragm/Plate Girder Connections in Steel Bridges, HR-393, 1998

Some of the Iowa Department of Transportation (Iowa DOT) continuous, steel, welded plate girder bridges have developed web cracking in the negative moment regions at the diaphragm connection plates. The cracks are due to out-of-plane bending of the web near the top flange of the girder. The out-of-plane bending occurs in the "web-gap", which is the portion of the girder web between (1) the top of the fillet welds attaching the diaphragm connection plate to the web and (2) the fillet welds attaching the flange to the web. A literature search indicated that four retrofit techniques have been suggested by other researchers to prevent or control this type of cracking. To eliminate the problem in new bridges, AASHTO specifications require a positive attachment between the connection plate and the top (tension) flange. Applying this requirement to existing bridges is expensive and difficult. The Iowa DOT has relied primarily on the hole-drilling technique to prevent crack extension once cracking has occurred; however, the literature indicates that hole-drilling alone may not be entirely effective in preventing crack extension. The objective of this research was to investigate experimentally a method proposed by the Iowa DOT to prevent cracking at the diaphragm/plate girder connection in steel bridges with X-type or K-type diaphragms. The method consists of loosening the bolts at some connections between the diaphragm diagonals and the connection plates. The investigation included selecting and testing five bridges: three with X-type diaphragms and two with K-type diaphragms. During 1996 and 1997, these bridges were instrumented using strain gages and displacement transducers to obtain the response at various locations before and after implementing the method. Bridges were subjected to loaded test trucks traveling in different lanes with speeds varying from crawl speed to 65 mph (104 km/h) to determine the effectiveness of the proposed method. The results of the study show that the effect of out-of-plane loading was confined to widths of approximately 4 in. (100 mm) on either side of the connection plates. Further, they demonstrate that the stresses in gaps with drilled holes were higher than those in gaps without cracks, implying that the drilling hole technique is not sufficient to prevent crack extension. The behavior of the web gaps in X-type diaphragm bridges was greatly enhanced by the proposed method as the stress range and out-of-plane distortion were reduced by at least 42% at the exterior girders. For bridges with K-type diaphragms, a similar trend was obtained. However, the stress range increased in one of the web gaps after implementing the proposed method. Other design aspects (wind, stability of compression flange, and lateral distribution of loads) must be considered when deciding whether to adopt the proposed method. Considering the results of this investigation, the proposed method can be implemented for X-type diaphragm bridges. Further research is recommended for K-type diaphragm bridges.

Fatigue and Residual Stress Investigation of Composite Prestressed Steel Beams, HR-74, 1963

Two composite, prestressed, steel beams, fabricated by slightly different methods, were fatigue tested to destruction. Stresses and deflections were measured at regular intervals, and the behavior of each beam as failure progressed was recorded. Residual stresses were then evaluated by testing segments of each beam. An attempt was made to assess the effects of the residual stresses on fatigue strength.

Void Ratio and Shear Strength of Two Compacted Crushed Stones, Progress Report, HR-99

Triaxial compression tests of two crushed limestones of differing highway service records indicate a fundamental difference in their shear strength -- void ratio relationship. Analyses were based on stress parameters at minimum sample volume, i.e., before there was significant sample dilation due to shear. The better service record sample compacted to higher density, and had a high effective angle of internal friction and zero effective cohesion. The other sample compacted to lower density and had a lower friction angle, but gained significant stability from effective cohesion. Repeated loading-unloading cycles reduced the cohesion, apparently due to modification of the sample structure. Extrapolations of the results to zero void ratio agree with sliding friction data reported on calcite, or with triaxial parameters reported on carbonate rocks.

Investigation of Steel-Stringer Bridges: Superstructures and Substructures, Volume I, TR-522, 2007

There are hundreds of structurally deficient or functionally obsolete bridges in the state of Iowa. With the majority of these bridges located on rural county roads where there is limited funding available to replace the bridges, diagnostic load testing can be utilized to determine the actual load carrying capacity of the bridge. One particular family or fleet of bridges that has been determined to be desirable for load testing consists of single-span bridges with non-composite, cast-in-place concrete decks, steel stringers, and timber substructures. Six bridges with poor performing superstructure and substructure from the aforementioned family of bridges were selected to be load tested. The six bridges were located on rural roads in five different counties in Iowa: Boone, Carroll, Humboldt, Mahaska, and Marshall. Volume I of this report focuses on evaluating the superstructure for this family of bridges. This volume discusses the behavior characteristics that influence the load carrying capacity of this fleet of bridges. In particular, the live load distribution, partial composite action, and bearing restraint were investigated as potential factors that could influence the bridge ratings. Implementing fleet management practices, the bridges were analyzed to determine if the load test results could be predicted to better analyze previously untested bridges. For this family of bridges it was found that the ratings increased as a result of the load testing demonstrating a greater capacity than determined analytically. Volume II of this report focuses on evaluating the timber substructure for this family of bridges. In this volume, procedures for detecting pile internal decay using nondestructive ultrasonic stress wave techniques, correlating nondestructive ultrasonic stress wave techniques to axial compression tests to estimate deteriorated pile residual strength, and evaluating load distribution through poor performing timber substructure elements by instrumenting and load testing the abutments of the six selected bridges are discussed. Also, in this volume pile repair methods for restoring axial and bending capacities of pile are developed and evaluated.

Highway Applications for Rammed Aggregate Piers in Iowa Soils, TR-443, 2003

This report describes a study to evaluate Geopier® soil reinforcement technology in transportation construction. Three projects requiring settlement control were chosen for evaluation—an embankment foundation, a box culvert, and a bridge approach fill. For each project, construction observations, in situ soil testing, laboratory material characterization, and performance monitoring were carried out. For the embankment foundation project, Geopier elements were installed within and around an abutment footprint for the new I-35 overpass at the US Highway 5/Interstate 35 interchange in Des Moines, Iowa. Although the main focus of this investigation was to evaluate embankment foundation reinforcement using Geopier elements, a stone column reinforced soil provided an opportunity to compare systems. In situ testing included cone penetration tests (CPTs), pressuremeter tests (PMTs), Ko stepped blade tests, and borehole shear tests (BSTs), as well as laboratory material testing. Comparative stiffness and densities of Geopier elements and stone columns were evaluated based on full-scale modulus load tests and standard penetration tests. Vibrating wire settlement cells and total stress cells were installed to monitor settlement and stress concentration on the reinforcing elements and matrix soil. Settlement plates were also monitored by conventional optical survey methods. Results show that the Geopier system and the stone columns performed their intended functions. The second project involved settlement monitoring of a 4.2 m wide x 3.6 m high x 50 m long box culvert constructed beneath a bridge on Iowa Highway 191 south of Neola, Iowa. Geopier elements were installed to reduce total and differential settlement while ensuring the stability of the existing bridge pier foundations. Benefits of the box culvert and embankment fill included (1) ease of future roadway expansion and (2) continual service of the roadway throughout construction. Site investigations consisted of in situ testing including CPTs, PMTs, BSTs, and dilatometer tests. Consolidated drained triaxial compression tests, unconsolidated undrained triaxial compression test, oedometer tests, and Atterberg limit tests were conducted to define strength and consolidation parameters and soil index properties for classification. Vibrating wire settlement cells, total stress cells, and piezometers were installed for continuous monitoring during and after box culvert construction and fill placement. This project was successful at controlling settlement of the box culvert and preventing downdrag of the bridge foundations, but could have been enhanced by reducing the length of Geopier elements at the ends of the box culvert. This would have increased localized settlement while reducing overall differential settlement. The third project involved settlement monitoring of bridge approach fill sections reinforced with Geopier elements. Thirty Geopier elements, spaced 1.8 m apart in six rows of varying length, were installed on both sides of a new bridge on US Highway 18/218 near Charles City, Iowa. Based on the results of this project, it was determined that future applications of Geopier soil reinforcement should consider extending the elements deeper into the embankment foundation fill, not just the fill itself.

Preformed Phoenix Ethylene Propylene Diene Monomer (EPDM) Compression Joint Seals, MLR-93-02, 1999

There is an ongoing drive towards improvements and achieving success in effective and long term sealing of portland cement concrete pavement contraction joints. A variety of joint sealing products and procedures have been applied in Iowa in search of improvements in seal performance. Hot poured rubberized asphalt products were mainly used for sealing all joints in earlier years for highways. In the 1980s, silicone sealant products were becoming popular, especially for the major highways. As a high level of sealant performance was not achieved from silicones in Iowa conditions, other sealing products were tried. Preformed neoprene compression seals are being tried as a substitution for silicone sealants. Due to high costs of materials and installation with neoprene seals, the search for improvements through other joint sealing products and procedures continued. An agreement was made with Phoenix, North America, Inc., to provide and install preformed Ethylene Propylene Diene Monomer (EPDM) compression joint seals. The research site was a 600 ft (183 m) test section of northbound I-29 in Pottawattamie County, Iowa. Seal installation was done August 20, 1992. Seal performance has been good over the past seven years and the seals are still showing no significant signs of decreasing performance.