Priyantha W. Jayawickrama

Survey of state practices to control skid resistance on hot-mix asphalt concrete pavements

A nationwide survey on design methods for achieving adequate skid resistance on hot-mix asphalt concrete pavements was conducted. Information was collected on the design practices used by 48 state departments of transportation (DOTs) in the contiguous United States. Survey findings show that the emphasis placed on the skid resistance aspects in various state DOT design procedures vary considerably. Based on the data collected, 21 out of 48 state highway agencies either do not have any design guidelines specifically addressing pavement skid behavior or assume that adequate skid resistance may be ensured through proper mix design. The general approach used by these agencies involves frequent monitoring of pavements to identify pavements with skid-related problems so that appropriate action may be taken. Survey findings indicated that state DOTs that consider skid resistance in their design procedures emphasize controlling the quality of coarse aggregates used in pavement surface course construction. The procedures used for aggregate qualification, however, vary significantly from one state agency to another. Some state DOTs rely on simple aggregate classification methods based on aggregate type, whereas others perform detailed laboratory evaluation. The laboratory test procedures that are most commonly used in evaluating aggregate frictional properties are the polish value test, acid insoluble residue test, and petrographic analysis. In addition to laboratory testing, Florida, Kentucky, Pennsylvania, and Texas use alternative procedures to qualify aggregates based on their field skid performance.

USE OF DYNAMIC CONE PENETROMETER TO CONTROL COMPACTION OF GRANULAR FILL

Granular material is commonly used as backfill and embedment material for buried structures, including thermoplastic pipe. Proper compaction of this material is crucial to the successful performance of the pipe. However, the commonly used Proctor density approach cannot be used for the field compaction control of these materials because it does not provide a well-defined moisture-density relationship. An alternative method used by the authors for compaction control of such materials is described. This method involves a device known as the dynamic cone penetrometer (DCP). Findings are presented from a series of DCP tests conducted on a range of granular backfill materials that belong to ASTM D 2321 Classes I and II. These materials were compacted using (a) an impact rammer and (b) a vibratory plate compactor. The level of compaction energy was varied by changing the number of passes. The data obtained from these tests are presented in the form of DCP blow count profiles, which are then used as the basis for comparison between different materials, compaction equipment, and levels of compaction energy. A series of full-scale load tests conducted on high-density polyethylene (HDPE) pipe installations is also described. An overview is provided of how the DCP data may be combined with load-deflection data from full-scale load tests to establish guidelines for compaction control of pipe backfill.

Evaluation of Production Models for Load Rating Reinforced Concrete Box Culverts

Analyses of two production-oriented culvert load-rating demand models were performed using live-load test data from three instrumented RC box culverts under four cover soil depths. The demand models were a two-dimensional (2D) structural-frame model and a 2D soil-structure interaction model. As expected, increased sophistication in the soil-structure model compared with the structural-frame model resulted in higher precision and accuracy for predicted moments. The impact of modeling accuracy for sections in a culvert where the demand moments approach zero was deemed practically insignificant. When evaluating model accuracy, it is of first importance that the models predict meaningful load magnitudes. Variations in predicted moment accuracy and precision were not uniform but were a function of the location of the critical section in the culvert structure. Improvements in modeling prediction associated with increased modeling sophistication were seen only when the structural-frame model was very imprecise.

Influence of Cover Soil Depth on the Load Rating of Reinforced Concrete Box Culverts

This paper describes the influence of cover soil depth on the load rating of the designs of multibarrel, cast-in-place (CIP) reinforced concrete (RC) box culverts and highlights implications for the load rating and design of culvert structures. The basics of culvert load rating are discussed and are followed by a history of culvert design policy and the challenges created by the use of culvert standard designs. A population of Texas Department of Transportation CIP RC standard culvert designs developed between 1930 and 1980 was load rated by using AASHTO policy guidance and a two-dimensional model of direct stiffness structural demand for a full range of cover soil depths. This analysis resulted in a set of 1,081 relationships of load rating versus cover soil depth. Three typical relationships of rating versus depth are illustrated and described in detail. The distribution of characteristic relationships of rating versus depth on the basis of culvert geometry, design cover soil depth, and design era is explored. Cover soil depth is shown to be a critical parameter that must be explicitly considered for the intelligent load rating and design of RC box culverts.

Pullout Resistance Factors for Steel MSE Reinforcements Embedded in Gravelly Backfill

Abstract This paper presents results from a laboratory program of 287 pullout tests of galvanized steel reinforcements used in the construction of mechanically stabilized earth (MSE) walls. Results focus on the evaluation of pullout resistance factors for ribbed steel strip and welded steel grid reinforcement embedded in gravelly backfill. This project used Texas Tech University’s large-scale MSE test box with dimensions of 3.6 × 3.6 × 1.2 m and an applied overburden capacity equivalent to 12 m of soil fill. The research design evaluated pullout resistance factors for both ribbed strip and welded grid reinforcements for a variety of independent variables, including overburden pressure, reinforcement length, grid bar size, and grid geometry including both transverse and longitudinal bar spacing. Appropriate statistical analyses were used to interpret the data within the context of published design guidance for inextensible MSE reinforcements. The results show that pullout resistance factors for both ribb...

Use of Hydrated Fly Ash as a Flexible Base Material

Common uses for fly ash, such as soil stabilization and cement replacement, account for less than 20 percent of the fly ash produced in the United States. Therefore, finding other bulk uses for fly ash is important. One such potential application is hydrated fly ash as a base material. The Texas Department of Transportation (TxDOT) is working to produce specifications to incorporate hydrated fly ash as a flexible base material. High-calcium Class C fly ash has a self-hydrating capability in the presence of moisture. Class C fly ash produced from coal power plants using lignite and subbituminous coal is mixed with water, dumped in large pits, and left to hydrate for a period of 3 to 6 weeks. The result is a hard, homogeneous mass of hydrated fly ash that can be mined to produce a construction aggregate much like limestone. TxDOT has used this material on several test projects. It has a desirable compressive strength, but in some instances its adhesion to seal coats has been a problem. Laboratory studies in...

Improved Load Rating of Reinforced-Concrete Box Culverts Using Depth-Calibrated Live-Load Attenuation

AbstractThis paper describes depth-calibrated live-load attenuation for the load rating of reinforced-concrete box culverts using production-simplified models. In-plane depth calibration is accomplished using a production-simplified, two-dimensional, linear-elastic, finite-element, soil-structure interaction model with results compared with those from the recommended direct-stiffness, structural-frame model. Out-of-plane live-load attenuation considers each potential critical section depth rather than the cover soil depth only. The effectiveness of depth calibration is assessed by comparing predicted live-load moments obtained from the models versus measured live-load moments obtained from full-scale culvert load tests. A load rating case study illustrates the potential for improved alignment between load rating and observed performance. Findings show that depth calibration improves current load rating practice by increasing the accuracy and precision of live-load demand predictions, particularly in culve...

Pullout Resistance Factors for Steel Reinforcements Used in TxDOT MSE Walls

This paper presents results from an extensive laboratory program of pullout testing of steel reinforcements used for Mechanically Stabilized Earth (MSE) walls constructed in Texas. Results focus on evaluation of pullout resistance factors for sandy backfill and MSE reinforcement combinations used by the Texas Department of Transportation (TxDOT). A unique aspect of this study is that this project uses Texas Tech Universitys large-scale MSE Test Box, one of the largest such devices in the world, with dimensions of 3.7m x by 3.7m x 1.2m (12ft x 12ft x 4ft) and an applied overburden capacity of 12.2m (40ft) of backfill. This test box facilitates pullout testing at a scale not unlike typical field construction. Results consist of pullout resistance factors for both ribbed strip and welded grid reinforcements for a variety of test variables including overburden pressure, reinforcement length, level of compaction, grid wire size, and grid geometry. We evaluate the data within the context of published AASHTO design guidance for inextensible MSE reinforcements.

Pullout Resistance Factors for Inextensible Mechanically Stabilized Earth Reinforcements in Sandy Backfill

This paper presents results from a laboratory program of 402 pullout tests of inextensible reinforcements used for walls of mechanically stabilized earth (MSE). Results focus on the evaluation of pullout resistance factors for ribbed-steel strip and welded-steel grid reinforcements embedded in sandy backfill that marginally met AASHTO requirements for select granular fill. This project used Texas Tech Universitys large-scale MSE test box with dimensions of 12 3 12 3 4 ft and an applied overburden capacity of 40 ft of backfill. This test box facilitated pullout testing at a scale not unlike typical field construction. The research design evaluated pullout resistance factors for both ribbed-strip and welded-grid reinforcements for a variety of independent variables, including overburden pressure, reinforcement length, level of compaction, grid wire size, and grid geometry, such as transverse and longitudinal wire spacing. Appropriate statistical analyses were used to interpret the data within the context of published AASHTO design guidance for inextensible MSE reinforcements. The results show that pullout behaviors of both ribbed strips and welded grids in properly compacted sandy backfill are conservative compared with the default pullout resistance factors provided by AASHTO. The data also suggest that the current AASHTO equations for pullout resistance factors for grid reinforcement do not accurately capture the influence of transverse and longitudinal bar spacings.

Instrumentation and Monitoring of an MSE/Soil Nail Hybrid Retaining Wall

MSE/soil nail hybrid earth retaining walls provide a more economical design for applications in cut/fill situations than the traditionally used full height MSE and drilled shaft retaining walls. MSE/soil nail hybrid earth retaining walls use a soil nailed wall in the cut section and an MSE wall in the fill section. In spite of the significant cost savings they offer, hybrid walls have not seen widespread use primarily because of lack of understanding on wall design and performance. This paper describes an instrumentation and monitoring effort that was undertaken with the objective of improving our understanding of hybrid wall design and performance. In this project, two separate panels of a hybrid wall constructed in San Antonio, Texas were selected for instrumentation and monitoring. The first wall panel consisted of a 4.0m soil nail wall and a 5.4m MSE wall while the second wall panel consisted of 5.0m soil nail wall and a 4.4m MSE Wall. The instrumentation scheme for the wall included vibrating wire strain gages, vertical inclinometers, horizontal inclinometers, and tiltmeters. The data collected from these two instrumented wall sections provide valuable insight to the mechanisms controlling the performance of MSE/Soil Nail Hybrid Wall systems.