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1  Bridge approach systems are used by state departments of transportation (DOTs) to form a smooth transition between the roadway and bridges. Adequate performance of bridge approaches is of extreme importance to transportation agencies as they affect both safety and the public perception of ride quality if the transition is not smooth. However, as a result of several factors, differential settlement or bumps are often present at the end of bridges. Assessing the behavior of bridge approach systems requires a holistic understand- ing of the different components that form the approach, which include approach slabs and their wearing surfaces; abutments and their foundations; connections between the deck, abutment, and approach slab; expansion joints; approach slab supports (such as sleeper slabs); backfill materials and reinforcement; and subsurface and surface drainage systems, and how the configuration of the components affects the performance of the bridge approach system. The objective of this synthesis was to document the current state of the practice for designing, constructing, and maintaining bridge approach systems, with particular focus on approach slabs and their supporting elements; the types of connections between the approach slab and the abutment; performance criteria for the approach such as ride quality and joint performance; settlement and compaction of backfill; and water management and drainage. The synthesis included a literature review of state design guides, standard specifica- tions, and research studies. The literature review was mainly compiled from the design and inspection guides and standard specifications, details, and drawings of 33 state DOTs, as shown in Appendix A, and includes different components of the bridge approach system and performance criteria for bridge approach systems. A state-of-the-practice survey was also conducted to collect information related to design and construction practices, water and joint management, operation and maintenance, and performance issues and mitigation practices related to bridge approach systems. The survey was sent to the voting members of the AASHTO Committee on Bridges and Structures and had an 86% response rate (44 respondents out of 51 agencies from 50 states plus the District of Columbia). Based on the information gathered from the literature review and survey, the synthesis results indicated that state DOTs have a variety of different options for the design and specification of each bridge approach component, and they may be arranged into a large range of different configurations to provide a serviceable bridge approach. In general, systems using an integral or otherwise jointless design, a reinforced concrete (RC) approach slab, and a granular or porous granular backfill material are the most favored designs by the DOTs. Approach slabs are most often designed as one-way slabs in accordance with AASHTO Load and Resistance Factor Design (LRFD) 4.6.2.3 and it is often assumed that S U M M A R Y Practices for Bridge Approach Systems
2 Practices for Bridge Approach Systems the underlying backfill settles and provides no support for some fraction of their length. When the site conditions and bridge configuration allow, the RC approach slab may be omitted and a more cost-effective flexible pavement can be used to carry traffic directly to the bridge. Expansion systems for accommodating expansion and contraction of the bridge super- structure vary widely. The current preferred practice is to eliminate joints or move joints away from the bridge. The types of joints used by the state DOTs include pressure relief joints, which are primarily for bridges with small thermal movements; strip seal joints and compression seal joints, which are the most commonly used joint types; and modular expansion joints and finger joints, which are used only when thermal movements are large. Multiple expansion joints may be used, either at both ends of the approach slab or on the roadway end of the approach between different approach elements. A sleeper slab is commonly placed at the roadway end of the approach to support the approach slab and an expansion joint, if one is present. The drainage systems used to capture and direct water runoff from the bridge and approach are considered separately from the structural approach system but are crucial to the approachâs performance. The majority of DOTs capture the runoff from the bridge and/or the approach using surface drainage systems with inlets and catch basins, gutters, or flumes. Subsurface drainage systems consisting of weep holes or subdrains help water drain from the backfill and embankment fill and prevent large hydrostatic pressures from building. The surface and subsurface systems selected typically depend on the site and project requirements. Current state of the practice for assessing construction quality includes testing the smoothness of the approach riding surface and quality control (QC) testing of the backfill material and approach installation. Smoothness may be measured using a straightedge to evaluate localized roughness or by automated methods using inertial profilers or profilo- graphs. Automated methods facilitate the calculation of indices such as the international roughness index (IRI), which quantitatively reflect the smoothness of the riding surface. Many state DOTs specify acceptance criteria for both localized roughness and the IRI or a comparable index to ensure the ride quality of the as-built bridge approach system. To ensure quality installation of the backfill, the majority of DOTs specify a minimum compacted density between 90% and 100% of the maximum dry density. Additionally, some of the DOTs specify moisture content of the fill at placement despite the propensity of the backfill to experience bulking at specific water contents and to settle during service. Inspections of bridge approach systems are generally conducted every 2Â years in con- junction with biennial bridge inspections. Joint sealant failure, differential settlement, and erosion of the backfill are the most common types of deterioration noted. Even though differential settlement is monitored, few DOTs evaluate differential settlement quantita- tively. Federal law requires at least a qualitative assessment of ride quality and element- level inspection of select elements within the bridge approach system such as the approach slabs for material degradation and damage, and some state DOTs have developed their own inspection guides that address state-specific concerns and performance issues related to bridge approach systems. While DOTs deliberately include preventive strategies in their designs, retroactive repairs including joint repair and replacement, approach slab jacking, profile corrections by grinding or filling, and application of asphalt overlays are still commonly required. A total of five DOTs (Colorado, Iowa, Massachusetts, Texas, and West Virginia) were selected for case examples and interviewed to discuss which practices they have found
Summary 3  to be effective in providing durable bridge approach systems. The examples included a summary of each DOTâs practice as well as lessons learned and suggested practices. Because of the multidisciplinary nature of this topic, a question inquiring about the roles of different DOTâs departments regarding design, repair, and inspections of bridge approach systems was included in the interview, which appeared to vary for the different components. In general, the information collected in this synthesis shows that design considerations for bridge approach components vary across the DOTs. This is illustrated by the differences observed in the reviewed DOT standard specifications, as well as by the survey responses. As a result of this synthesis, the following areas have been identified as knowledge gaps that could be addressed through future research: ⢠Identification and characterization of correlations between design choices and long-term ride quality and other performance metrics for bridge approach systems with the overall goal of identifying the optimum design configurations for bridge approach systems, which requires a multidisciplinary approach to cover all the components of such systems. ⢠Determination of the types and frequency of QC testing that are most beneficial to long-term serviceability of bridge approaches. ⢠Assessment of the effectiveness of unique design details used by some of the state DOTs that have achieved good performance for potential wide implementation across other DOTs. ⢠Sponsored research to develop and evaluate innovative solutions to improve the long- term serviceability of bridge approaches. ⢠Set criteria and metrics for which repair of joints and ride quality is required and below which deferred repair is appropriate.
