Practices for Bridge Approach Systems (2021) / Chapter Skim
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From page 41... ...
41 State of the Practice To develop a better understanding of the design, maintenance, and performance of bridge approach systems throughout the United States, a survey was sent to all of the 50 state DOTs and to the District DOT. The survey link was sent to the voting member of the AASHTO Committee on Bridges and Structures (COBS)
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From page 42... ...
42 Practices for Bridge Approach Systems 3.1.2 Approach Pavement or Slab Agencies' responses related to the type of approach slab or pavement used in bridge approach systems are presented in Figure 24. All of the state DOTs with the exception of Maryland reported using structural RC approach slabs.
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From page 43... ...
State of the Practice 43 • Bridge skew, • Abutment depth, • Soil type, and • Distance to unexcavated embankment. Flexible pavement is the second-most-common roadway used for the bridge approach, with 25% of the responding state DOTs (11 of 44)
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From page 44... ...
44 Practices for Bridge Approach Systems 3.1.4 Type of Connection Between Approach and Bridge Agencies were asked if the approach slab/pavement, as applicable, is typically rigidly connected to the abutment or bridge deck by steel ties or if the approach slab/pavement is permitted to move independently of the bridge structure. A summary of the results is presented in Figure 25.
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State of the Practice 45 3.1.5.2 Specified Properties of Backfill Figure 27 presents the number of responding agencies with specified requirements for compaction, gradation, percent fines (defined as percent passing a No. 200 sieve)
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46 Practices for Bridge Approach Systems 3.1.6 Additional Materials or Systems Behind Abutments State DOTs were asked if there were any additional materials behind the abutments, such as drainage systems, waterproofing systems, and elastic inclusions. Waterproofing and drainage systems are commonly composed of geosynthetics and these vertical systems are distinct from the horizontal geosynthetic reinforcement that may otherwise be found in the backfill.
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From page 47... ...
State of the Practice 47 listed include geotextiles, geofoams, subdrain systems, preformed cellular polystyrene, and honeycomb cardboard. There is no common practice that the majority of the responding DOTs follow.
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48 Practices for Bridge Approach Systems settlement including test rolling, monitoring settlement as a result of consolidation, and phasing construction. Both Oregon and South Carolina use ground improvement methods to mitigate seismic loads, including stone columns and wick drains as listed in Table 5, as well as jet or compaction grouting, precast concrete piles, earthquake drains, and soil mixing columns.
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From page 49... ...
State of the Practice 49 fill materials. Texas, Illinois, and Florida reported using this option.
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50 Practices for Bridge Approach Systems 3.2.2 Subdrains in Backfill The survey included questions regarding the use of subdrains in the backfill underneath the approach and to describe the subdrain configuration, if applicable. Approximately 55% of the responding agencies (24 of 44)
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From page 51... ...
State of the Practice 51 Four DOTs (Arkansas, Maine, North Carolina, and Wisconsin) reported using no expansion joint with integral, semi-integral, or MSE abutments, while three DOTs (Hawaii, Louisiana, and Texas)
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From page 52... ...
52 Practices for Bridge Approach Systems 3.2.3.3 Expansion Joint Seal Replacement Frequency The replacement frequencies reported for strip seals, compression seals, and backer rods and sealants are presented in Table 7, and the replacement frequencies reported for less commonly used joints are reported in Table 8. In general, DOTs commented that joint repairs were reactive rather than proactive, and several agencies stated that joint seals were replaced upon failure or on an as-needed basis when asked about frequency.
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From page 53... ...
State of the Practice 53 3.3 Operation and Maintenance The third section of the survey included questions about inspection frequency of bridge approaches and their elements; metrics used to assess approach performance, including ride quality; and repair techniques and criteria to initiate repair. 3.3.1 Periodic Inspection of Elements The current state of the practice includes periodic inspection of approach slabs and elements throughout their life.
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From page 54... ...
54 Practices for Bridge Approach Systems The majority of responses indicated that these types of distress are monitored every 2 years during NBI inspections. The NBI inspection data is federally required to be collected and reported at least biennially, although longer inspection intervals can be approved.
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State of the Practice 55 3.3.3 Measurement of Ride Quality DOTs were asked if they measure ride quality of the approaches and what methods they use, if applicable. This question was divided into ride quality of the main roadway, of the approach slab/pavement, of the bridge deck, and of the joints.
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From page 56... ...
56 Practices for Bridge Approach Systems 34% 32% 39% 18% 0 5 10 15 20 25 30 35 40 45 Roadway Approach slab/pavement Bridge deck Joints N o. o f R es po nd in g D O Ts Area Where Ride Quality Is Assessed Figure 36.
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State of the Practice 57 3.3.5 Repair Methods for Restoring Ride Quality DOTs were asked which methods they use to restore ride quality and how frequently they are applied. The responses are summarized in Figure 39.
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58 Practices for Bridge Approach Systems In general, these repair actions are conducted rarely or on an as-needed basis. Nebraska and Wyoming were the only respondents to report using portland cement grout injection, expanded polyurethane (EPU)
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From page 59... ...
State of the Practice 59 Placing the expansion joint between the approach and the roadway or between the approach and the bridge were both common joint configurations. Only six DOTs (Hawaii, Maine, Missouri, North Carolina, South Carolina, and Washington)
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60 Practices for Bridge Approach Systems 3.4.2 Performance Issues DOTs were asked to identify how often they experience different types of performance issues pertaining to ride quality, joint integrity, concrete cracking, drainage, and erosion. The responses of 38 agencies are shown in Figure 40; six agencies did not respond to the question.
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From page 61... ...
State of the Practice 61 3.4.3.1 Expansion Joint Sealant Failure The responses describing strategies to prevent or repair sealant failures in expansion joints are summarized in Table 13. The majority of responding DOTs reported that the sealant or joint would be replaced.
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From page 62... ...
62 Practices for Bridge Approach Systems 3.4.3.3 Erosion of Backfill The responses describing strategies to prevent, mitigate, or repair erosion of backfill are categorized in Table 15. These categories are not mutually exclusive, as some DOTs listed multiple options to choose from or indicated they conduct a combination of activities from the different categories.
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From page 63... ...
State of the Practice 63 sleeper slabs with a geotextile system underneath. Alaska uses a special structural fill placed for 50 ft from the abutments and compacted to 98% of the maximum dry density.
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64 Practices for Bridge Approach Systems Strategy Blocked Subdrain Drainage Infiltration Replacement/repair 3 4 Maintenance 3 0 Design and quality 2 3 Table 21. Strategies to address blocked subdrains and drainage infiltration.
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From page 65... ...
State of the Practice 65 In general, there is a shift toward using integral and/or semi-integral abutments and moving the expansion joint from the bridge side of the approach to the roadway side. Several DOTs commented that they added sleeper slabs to their designs when they moved the expansion joint to the roadway side.
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