Practices for Bridge Approach Systems (2021)

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66 Case Examples Five state DOTs (Colorado, Iowa, Massachusetts, Texas, and West Virginia) were selected as case examples to further highlight differences between the design and construction practices of bridge approaches found across the DOTs. Information collected through the case examples includes • Typical design and construction practices for approach slabs; • Information related to backfill type and properties; • Methods to deal with water management; • Inspections, QC, and maintenance practices; • Overall assessment of performance of current design methods; and • Lessons learned. The case examples were completed through review of bridge-approach-standard specifi- cations and state-of-the-practice surveys, as well as telephone and e-mail interviews with the survey respondent from each of the selected DOTs. Some of the case examples that participants provided gave the team additional information regarding design documents, research reports, and presentations to assist with developing this chapter. Note that the information presented in this chapter is only a summary of typical practices of the selected DOTs and highlights some of the unique features of the DOTs’ design and construction practices for bridge approaches. 4.1 Case Example 1: Colorado Department of Transportation 4.1.1 Typical Design and Construction of Bridge Approach Systems in Colorado The Colorado DOT practice was selected as one of the case examples based on the survey responses which indicated some unique features used by the DOT, including a no-approach slab detail and the use of structural backfill (flowfill or Class 1) with mechanical (geotextile) reinforce- ment as their typical practice. The standard specifications and details for bridge approaches in Colorado were used in conjunction with the survey responses to provide a summary of the current practices employed to construct bridge approach systems as discussed as follows. • Bridge Abutments. The preferred abutment type in Colorado is integral abutments followed by stub and semi-integral abutments. As indicated in the survey, MSE abutments, full-height spill-through abutments, and full-height closed abutments are rarely used. • Approach Slabs. Colorado DOT typical practice for approach slabs consists of using reinforced slabs with 12-in. thickness and that are 20 ft in length. Three (3) in. of asphalt are typically placed on top of the approach slabs. A second approach is also possible that consists of using C H A P T E R   4

Case Examples 67   a flexible pavement (no approach slab); however, this can only be done if abutment embank- ment settlement is not critical, as indicated in the survey. Figure 42 shows section views of the typical bridge approach design in Colorado, with and without an approach slab. The minimum length of the two reinforced approach slabs after the bridge is 40 ft. • Sleeper Slabs. The standard specifications and drawings of Colorado DOT indicate that a sleeper slab is typically placed between the roadway and the approach slab. The main reason for this is that Colorado DOT places an expansion joint at the end of the approach slab. • Connection Between Abutment and Approach Slabs. All the approach slabs are connected to the abutments, regardless of the abutment type. This practice is followed as no expansion joint is placed between the abutment and approach slab. (a) (b) Figure 42. Section views of bridge approach design in Colorado: (a) mechanically stabilized backfill without approach slab, and (b) approach slab detail (with asphalt).

68 Practices for Bridge Approach Systems • Expansion Joint. As indicated previously, all expansion joints in the current Colorado practice are placed between the roadway and approach slab, above the sleeper slab location. • Backfill Materials. Colorado DOT specifies the use of structural backfill (flowfill or Class 1) with mechanical (geotextile) reinforcement as their typical practice. A series of requirements are used to ensure the quality of the backfill construction, including the following: – Moisture content at placement: ± 2% of the optimum moisture content – Required compaction: 95% – Gradation according to AASHTO or United Soil Classification System (USCS): AASHTO T 180 – Limit of fines (% passing No. 200 sieve): 5 to 20 • Ground Improvement. Colorado’s ground improvement practice consists of subexcavation of clay layers and replacing them with structural backfill (Class 1). • Water Management. Colorado DOT standard specifications and drawings indicate that a subdrain is typically included in the backfill. The subdrain is typically made from a 6-in. preformed pipe as indicated in the drawing in Colorado DOT Worksheet B-206-M2. For runoff water, the survey responses indicate that the water from both the bridge deck and approach is captured, and an open drainage system is generally specified. • Construction Acceptance Criteria. Colorado DOT uses the Smoothness Process Control Test as an acceptance criterion for the approach-slab ride quality after construction. This includes measuring bare concrete or asphalt overlay surface areas using a 10-ft straightedge, and high spots of more than 3⁄16 in. in 10 ft shall be marked and diamond ground until the high spot does not exceed 3⁄16 in. 4.1.2 Inspection and Maintenance Colorado DOT survey responses indicated that the DOT conducts periodic inspections of bridge approach components every 2 years, similar to the frequency of NBIS inspection of the bridge. This includes inspecting the approach for the following types of degradation: • Differential settlement (bump), frequency: 2-year routine inspection, • Joint seal failure, frequency: 2-year routine inspection, • Void formation or approach embankment erosion under slab; frequency: 2-year routine inspection, and • Lateral spread of the approach embankment; frequency: 2-year routine inspection. Note that the survey response indicated that the maintenance crew will make a note of any joint failure during daily highway drive-by in bridge areas. For differential settlement, Colorado DOT does not specify a quantitative test. Instead, a qualitative description of ride quality is used to assess settlement/bump. Ride quality is typi- cally not assessed through metrics for bridge approaches in Colorado. Repairs or rehabilitation to fix bump formation are initiated based on a smoothness/ride quality criterion. If maintenance or repair is required to restore ride quality across the bridge approach, replace- ment of the asphalt overlay can be completed. The frequency of this activity is every 2 to 3 years. 4.1.3 Performance Issues and Mitigation Practices The three most common bridge approach systems in Colorado have a typical life of 7 to 10 years before they need rehabilitation. These systems are as follows, presented in the order of most used: • Integral abutment with RC approach slab • Semi-integral abutment with RC approach slab • Stub abutment with RC approach slab

Case Examples 69   To better understand the performance of the bridge approach systems used in Colorado, the survey responses for common performance issues experienced are summarized in the following list. The survey used a qualitative scale for the frequency of the common issues with a three-tier rating system: rarely, occasionally, and often. • Bump Formation and Ride Quality. This is an occasional issue where a bump is formed between the bridge deck and the approach or the roadway and the approach. Colorado’s practice consists of using a 3-in. asphalt overlay placed on the bridge deck and approach slab to match the main pavement, which is considered a design practice to limit bump formation. For ride quality across the approach slab itself, this is rare to occur but can be fixed by milling/ filling the asphalt overlay. • Failed Sealant in Joints. This is an occasional issue in Colorado. The typical solution for failed sealant in an expansion joint is replacement of the sealant. This can also be done for other types of joints. • Transverse and Longitudinal Cracking. This is a rare issue in Colorado. Repair is typically accomplished by grouting cracks with epoxy grout material. • Failed Paving Notch or Seat at Abutment. This is a rare issue in Colorado and is repaired by replacing the damaged notch or seat at the abutment with new concrete. • Erosion of Backfill. This is an occasional issue in Colorado. The repair consists of opening voids and using flowfill or shotcrete to grout voids. • Blockage of Subdrain. This is a rare issue in Colorado and can be repaired by replacing the drainage pipe. • Differential Settlement. This is a rare issue in Colorado. The mitigation practice for this is replacing the slab with a new concrete slab and also replacing the backfill material. 4.1.4 Lessons Learned A list of questions was submitted to Colorado DOT for input and to identify what can be considered as lessons learned by the DOT. A summary of the responses is provided in the following list. • Hot mixed asphalt is always used on approach slabs as a design practice to limit bump formation. • The main benefit of using structural backfill (flowfill or Class 1) with mechanical (geotextile) reinforcement as typical practice is the quality of compaction and favorable performance of the soil-and-geotextile composite. • Regarding selection of abutment type, semi-integral abutments are selected because of cost and keeping surface runoff past the bridge; however, the thermal analysis is laborious. • Without concrete approach slab centered at abutment back-face, a 10-ft band of heat-resistant geogrids is sandwiched in the bottom with hot-asphalt-filled, saw-cut grooves at the top for minor movement and waterproofing. When a concrete approach slab is used, the end of the approach slab is built with a 2- to 3-in. precamber (grade raised) in the roadway vertical alignment to counteract future settlement of the embankment. 4.1.5 DOT Bureaus: Roles and Responsibilities for Bridge Approaches As design, maintenance, and rehabilitation of approach slabs is multidisciplinary, a follow-up question was sent to DOTs selected for case examples to identify different roles within the DOT with respect to bridge approaches. In Colorado, bureau responsibility varies depending on the district involved and on the specific projects. A summary of the roles and responsibilities of the different bureaus, offices, or units follows. • Design of approach for a new structure: Structure, geotechnical, and maintenance. • Design for rehabilitation of an existing approach: Designer and regional maintenance.

70 Practices for Bridge Approach Systems • Design of backfill material: Bridge designer. • Design of drainage control: Bridge designer. • Routine inspection of approaches: Inspection unit and follow-up by design unit. • Maintenance of ride quality: Regional maintenance and design unit. • Repair of approach settlement or damage: Regional maintenance and design unit. 4.2 Case Example 2: Iowa Department of Transportation 4.2.1 Typical Design and Construction of Bridge Approach Systems in Iowa The Iowa DOT current standard specifications and details for bridge approaches are largely based on the results of a recent study funded by Iowa DOT between 2002 and 2005 to study approach slab performance (White et al. 2005). The findings of this research led to revisions in Iowa DOT standard specifications for approach slabs, which started being incorporated in bridges built in 2006. A summary of the current practices employed by Iowa for bridge approach systems follows. • Bridge Abutments. The preferred abutment type in Iowa by the order of usage is integral abutments followed by stub and semi-integral abutments, with the use of semi-integral abutments increasing in the recent years. As indicated in the survey, MSE abutments and full-height spill-through abutments are never used in Iowa, while full-height closed abutments are rarely used. • Approach Slabs. Iowa DOT uses a unique approach slab system that consists of using three approach slabs after the bridge as follows: two reinforced approach slabs immediately after the bridge, one with double reinforcement and one single-reinforced, followed by an unreinforced approach slab to connect to the roadway. Figure 43 shows section views of the typical approach slab design in Iowa. Typical thickness of the slabs is 12 in. The minimum length of the two reinforced approach slabs after the bridge is 40 ft combined. • Sleeper Slabs. The standard specifications and drawings of Iowa DOT include sleeper slabs in one of the details (standard detail BR-205). Historically, sleeper slabs had limited use in bridge approach construction. However, for the past 5 years, sleeper slabs use has increased as they are a recent adoption for Iowa DOT continuous concrete slab (CCS) bridges on the primary system, which use a tied approach. • Connection Between Abutment and Approach Slabs. The connection between the abut- ment and approach slabs varies in Iowa by the type of abutment. For integral abutments, the approach slabs move independently from the abutment (with the exception of CCS bridges on the primary system, which use a tied approach and sleeper slab), while for other types the approach slabs are rigidly connected to the abutment (with a pinned, not a moment, connection). • Expansion Joint. The location of the expansion joint varies by abutment type. For integral abutments, the expansion joint is placed between the bridge deck and the approach slab (except for CCS on primary systems, which used a tied approach), while for other types the joint is placed between the approach slab and the roadway. For a stub abutment the expan- sion joint is between the bridge deck and backwall and consists of a strip seal (common), modular joint (rare), or finger joint. • Backfill Materials. Iowa DOT specifies the use of granular or porous backfill materials behind the abutments. The DOT has a construction specification for placing backfill behind abutments that includes flooding granular material for compaction. Geosynthetic materials are also used to contain the flooded backfill.

Figure 43. Section views of the approach slabs from the Iowa DOT standard (Iowa DOT Standard Road Plans).

72 Practices for Bridge Approach Systems • Ground Improvement. No ground improvement is typically carried out in Iowa. • Water Management. Iowa DOT standard specifications and drawings indicate that a sub- drain is usually included in the backfill. The subdrain is typically made from polyethylene corrugated tubing. For runoff water, the survey responses indicate that the water from both the bridge deck and approach is captured and released openly onto the surface of the embankment slope and channeled in a rock flume. • Construction Acceptance Criteria. No construction acceptance criteria for bridge approaches are currently used in Iowa. 4.2.2 Inspection and Maintenance Iowa DOT survey responses indicated that the DOT conducts periodic inspections of bridge approach components every 2 years, during NBIS inspection of the bridge. This includes inspecting the approach for the following types of degradation: • Differential settlement (bump), frequency: 24 months. • Joint seal failure, frequency: 24 months. • Void formation or approach embankment erosion under slab, frequency: 24 months; Iowa DOT standards include installation of a port in the wingwalls to allow for borescope (snake) camera inspections below the approach slabs. For differential settlement, Iowa DOT uses the IRI to assess the severity of settlement or bump formations. Ride quality is typically not assessed quantitatively for bridge approaches in Iowa. Repairs or rehabilitation to fix approach settlement are initiated based on the following types of criteria: • User complaint • Safety • NBIS inspections If maintenance or repair is required to restore ride quality across the bridge approach, leveling using asphalt courses is a common strategy. Injection of expanded polyurethane underneath approach slab/pavement may be done or replacement of the approach slab/pavement can be completed, as necessary. 4.2.3 Performance Issues and Mitigation Practices The three most common bridge approach systems in Iowa have a typical life of 30 years. These systems are as follows, presented in the order of most used: • Integral abutment with RC approach slab • Stub abutment with RC approach slab • Semi-integral abutment with RC approach slab To better understand the performance of the bridge approach systems used in Iowa, the survey responses for common performance issues experienced are summarized in the list that follows. The survey used a qualitative scale for the frequency of the common issues with a three-tier rating system: rarely, occasionally, and often. • Bump Formation and Ride Quality. This is an occasional issue where a bump is formed between the bridge deck and the approach or the roadway and the approach. In such cases, milling and filling with hot-mix asphalt (HMA) can be completed to replace the ride quality. If the issue is ride quality across the approach slab itself, which is a rare issue in Iowa, slab replacement or pressure injection can be completed.

Case Examples 73   • Failed Sealant in Joints. This is an occasional issue in Iowa. The typical solution for failed sealant in an expansion joint is replacement of the sealant with a bonded compression seal, while resealing is used for other types of joints. • Transverse and Longitudinal Cracking. This is an occasional issue in Iowa. Repair is typically replacement of the approach slab panel if the cracking is severe. • Failed Paving Notch or Seat at Abutment. This is an occasional issue in Iowa. Paving notch replacement or backwall replacement is typically completed to repair this condition, depending on the details. • Erosion of Backfill. This is an occasional issue in Iowa. Nothing is done in most cases. For severe erosion, replacement of the approach and repair of fill is typically performed. • Blockage of Subdrain. This is a rare issue in Iowa. Typically, nothing is done as this condition may be unknown because of the location of the subdrain inside the backfill. The design has redundancy, as the subdrain has two outlets. • Differential Settlement. This is a rare issue in Iowa. Bridge approach replacement is required if differential settlement is detected between the bridge approach and bridge deck. 4.2.4 Lessons Learned A list of questions was submitted to Iowa DOT for input and to identify what can be considered as lessons learned by the DOT. A summary of the responses is provided in the following list. • Regarding abutment type, Iowa DOT’s current first preference is always to use an integral abutment for long-term durability purposes followed by a semi-integral abutment and lastly a stub abutment. Constraints on the use of the different abutment types are related to the thermal expansion and contraction of the bridge that must be accommodated, and the constraints are listed in the Iowa DOT Bridges and Structures Bureau LRFD Bridge Design Manual. • With regard to geosynthetic materials use, Iowa DOT typically does not use GRS. One pilot project was done for a GRS-IBS berm. Geosynthetic materials are typically used to contain the flooded backfill during construction. • To elaborate on the use of a “safety” criterion as a factor to initiate repairs or rehabilita- tion to fix bump formation, observation from highway maintenance crews, bridge crews, or snowplow operators leads to reporting and addressing significant bumps that could damage vehicles. • Void formation beneath approach slabs is typically found during NBIS inspections and addressed as necessary. 4.2.5 DOT Bureaus: Roles and Responsibilities for Bridge Approaches Similar to other DOTs, bureau responsibility varies with respect to bridge approaches. A summary of the roles/responsibilities of the different bureaus, offices, or units in Iowa follows. • Design of approach for a new structure: Bridges and Structures Bureau • Design for rehabilitation of an existing approach: Bridges and Structures Bureau • Design of backfill material: Soils Section—Design Bureau • Design of drainage control: Bridges and Structures Bureau • Routine inspection of approaches: Bridges and Structures Bureau • Maintenance of ride quality: district bridge crew or highway maintenance crew • Repair of approach settlement or damage: district bridge crew or highway maintenance crew

74 Practices for Bridge Approach Systems 4.3 Case Example 3: Massachusetts Department of Transportation 4.3.1 Typical Design and Construction of Bridge Approach Systems in Massachusetts The Massachusetts DOT practice was selected as one of the case examples based on the unique buried approach-slab design used in the DOT for about 80 years. The standard specifica- tions and details for bridge approaches used by Massachusetts DOT were used in conjunction with the survey responses, and a recent presentation by the Massachusetts DOT respondent provides a summary of the current practices employed to construct bridge approach systems. The practices are discussed in the following list. • Bridge Abutments. The preferred abutment types for Massachusetts DOT are stub abutments and full-height closed abutments followed by integral abutments. As indicated in the survey, semi-integral abutments and GRS-IBS abutments are used occasionally, while MSE abut- ments and full-height spill-through abutments are never used. • Approach Slabs. Massachusetts DOT typical practice for approach slabs consists of using buried RC approach slabs, which are RC approach slabs that are buried under 14 in. of backfill and asphalt pavement. Figure 44 shows section views of the typical bridge approach design by Massachusetts DOT. Typical thickness of the slab is 10 in. and the typical length is 15 ft. The DOT also has details for precast approach slabs that are also buried. These systems are installed so that there is a gap between the soil and the bottom of the slab, which is filled with nonexcavatable, flowable fill to provide full bearing contact. • Sleeper Slabs. The standard specifications and drawings of Massachusetts DOT do not include the use of sleeper slabs, since the approach slab is buried. • Connection Between Abutment and Approach Slabs. The connection between abutments and approach slabs varies by the type of abutment in Massachusetts. For integral abutments and semi-integral abutments, the approach slabs move independently from the abutment, while for stub abutments and full-height closed abutments the approach slabs are rigidly connected to the abutment. • Expansion Joint. All expansion joints in the current Massachusetts DOT practice are placed between the bridge deck and approach pavement, since the approach slab is buried immediately after the abutment. No expansion joint is used with GRS-IBS abutments. • Backfill Materials. Massachusetts DOT specifies the use of granular or porous granular materials for the backfill behind abutments. A series of requirements are used to ensure the quality of the backfill construction, including the following: – Required compaction: 95% – Limit of fines (% passing No. 200 sieve): 0–10 – Specific gradation is also required as follows: ½-in. sieve, 50%–85%; No. 4, 40%–75%; No. 50, 8%–28%; No. 200, 0%–10%. • Ground Improvement. No ground improvement is typically done in Massachusetts. • Water Management. Massachusetts DOT survey responses indicated that a pipe is typically used in the backfill to collect and drain water. For full-height abutments, a drainpipe is run through the abutment stem. For integral abutments, a perforated PVC drainpipe is placed at the base of the abutment stem and parallel to the abutment and drains out the sides. In both cases, crushed stone is used around the pipe openings to help drain the backfill. For runoff water, the survey responses indicate that the water from both the bridge deck and approach is captured and released openly onto the surface of a slope. Sometimes, closed systems are specified and in such cases a culvert, storm drain, or other closed system is used. • Construction Acceptance Criteria. No construction acceptance criteria for bridge approaches are currently used in Massachusetts.

Figure 44. Section views of bridge approach design in Massachusetts: Types I, II, and III.

76 Practices for Bridge Approach Systems 4.3.2 Inspection and Maintenance Massachusetts DOT survey responses indicated that the DOT conducts periodic inspections of bridge approach components during NBIS inspection of the bridge. This includes inspecting the approach for the following types of degradation: • Differential settlement (bump); frequency: during NBIS inspections • Joint seal failure; frequency: during NBIS inspections For differential settlement, Massachusetts DOT does not specify a quantitative test for severity of the bump. The respondent indicated that differential settlement and bump formation are not a major issue in Massachusetts because of the use of buried approach slabs. Ride quality is also typically not assessed through metrics. Repairs or rehabilitation to fix bump formation are initiated based on a smoothness/ride quality criterion. Note that ride quality is also not consid- ered a major issue by the respondent because of the use of buried approaches. If a bump occurs the depression can be filled with asphaltic concrete. 4.3.3 Performance Issues and Mitigation Practices The three most common bridge approach systems in Massachusetts have a typical life of 20 to 30 years before they need rehabilitation. These systems are as follows, presented in the order of most used: • Full-height closed abutment with buried RC approach slab and flexible pavement • Integral abutment with buried RC approach slab and flexible pavement • Stub abutment with buried RC approach slab and flexible pavement To better understand the performance of the bridge approach systems used by Massachusetts DOT, the survey responses for common performance issues experienced are summarized in the following list. The survey used a qualitative scale for the frequency of the common issues with a three-tier rating system: rarely, occasionally, and often. • Bump Formation and Ride Quality. The survey responses indicated that poor ride quality and bump formation are rare issues in Massachusetts. This is attributed to the unique design philosophy of approach slabs employed by the DOT, which consists of burying an RC approach slab under backfill and flexible pavement. Therefore, the approach pavement is the main pavement and it extends to the bridge. Any issue with ride quality becomes a pavement issue and repaving is performed. • Failed Sealant in Joints. This issue occurs often in Massachusetts. Typical solution for failed sealant in an expansion joint is replacement of the sealant or joint, depending on severity. • Transverse and Longitudinal Cracking. This is an occasional issue in Massachusetts. However, it is a pavement issue, since buried approach slabs are used. The typical repair for transverse and longitudinal cracking is repaving. • Failed Paving Notch or Seat at Abutment. This is a rare issue in Massachusetts and no mitigation practice was specified in the responses. • Erosion of Backfill. This is a rare issue in Massachusetts and no mitigation practice was specified in the responses. • Blockage of Subdrain, This is a rare issue in Massachusetts and no mitigation practice was specified in the responses. • Differential Settlement. This is also a rare issue in Massachusetts. The mitigation practice for this is patching depressions with asphaltic concrete. 4.3.4 Lessons Learned A list of questions was submitted to Massachusetts DOT for input and to identify what can be considered as lessons learned by the DOT. A summary of the responses is provided in the following list.

Case Examples 77   • The main benefits of using buried approach slabs from a structural standpoint is that applying a live load surcharge to the back of the abutment for design is not needed. From a perfor- mance standpoint, buried approach slabs mitigate the bump at the end of the bridge, where the approach backfill settles immediately behind the abutment. A buried approach slab settles with the backfill but because it is still attached to the abutment, it forms a ramp that gradually brings vehicles up to the level of the abutment without a sudden bump point as a result of the difference in elevation of the settled backfill and the back of the abutment. The material used above the buried approach slab is roadway subbase gravel, then the layers of the pavement structure. • For GRS-IBS abutments, the main benefit is that they don’t require heavy equipment to construct. They can be constructed with human labor and small pieces of equipment to cut the blocks as needed, to place the geomesh, and then to backfill and compact. No major performance issues were observed with this type of abutment in Massachusetts, although the sample size is limited. • Abutment types are selected based on the site constraints and project parameters. Typically, integral abutments and stub abutments are considered to be equal. Integral abutments are preferred if the geological aspects are conducive; for example, bedrock is low enough so that the piles can be driven below point of fixity and stub abutments where they cannot. Since most Massachusetts DOT bridge projects involve replacement of existing bridges, the aim is to span over and leave the existing abutments in place. As a result, integral or stub abut- ments are typically considered for such situations, since the amount of excavation is reduced, facilitating construction and its duration. Full-height abutments are selected where the clearance over the feature is high and the site constraints make abutments close to the feature. The disadvantage is construction time and excavation for the larger footings. In these cases, if the abutment is not subject to scour, an integral abutment may be used with an MSE wall in front to reduce construction time and cost. If the site allows for a longer bridge, a multispan bridge is constructed with piers next to the feature and a stub or integral abutment further up on the slope. The advantage is a lower construction cost. 4.3.5 DOT Bureaus: Roles and Responsibilities for Bridge Approaches Similar to other DOTs, bureau responsibility varies with respect to bridge approaches. A summary of the roles/responsibilities of the different bureaus, offices, or units in Massachusetts follows. • Design of approach for a new structure: Approaches are designed by the highway designers. Since most of the designs are by consultants, this is all by one company. In the case of in-house- designed bridges, this would be the Highway Design Section. • Design for rehabilitation of an existing approach: Highway Design or the Maintenance Section. • Design of backfill material: Unless it requires special considerations, such as geofoam, the backfill material is standard material from standard specifications. • Design of drainage control: Highway designers. • Routine inspection of approaches: Within the immediate vicinity of the bridge, the bridge inspectors perform their routine inspections. Further back, pavement crews use an auto- matic roadway-analyzer vehicle that rides around and measures pavement roughness. This is only for pavements owned by Massachusetts DOT, however. • Maintenance of ride quality: Specific problems are dealt with by the Maintenance Section. All of Massachusetts DOT’s maintenance is performed by contractors. Resurfacing is done as a project by the Maintenance Section. • Repair of approach settlement or damage: Specific problems are dealt with by the Maintenance Section. All of Massachusetts DOT’s maintenance is performed by contractors.

78 Practices for Bridge Approach Systems 4.4 Case Example 4: Texas Department of Transportation 4.4.1 Typical Design and Construction of Bridge Approach Systems in Texas The Texas DOT practice was selected as one of the case examples, primarily because of their use of cement-stabilized backfill as standard practice in Texas and avoidance of integral abutments. The standard specifications and details for bridge approaches in Texas were used in conjunction with the survey responses and follow-up questions to the DOT to provide a summary of the current practices employed to construct bridge approach systems, as discussed as follows. • Bridge Abutments. The preferred abutment type in Texas DOT is stub abutments. Semi- integral abutments are also used but rarely. As indicated in the survey, integral and full-height closed abutments were previously used by the DOT but they are not currently used, while full- height spill-through abutments are never used. The DOT responses to follow-up questions indicated that MSE walls are sometimes used around abutments on independent foundations, where select backfill and/or cement-stabilized abutment backfill (CSAB) may be the backfill material. • Approach Slabs. Texas DOT typical practice for approach slabs consists of using an RC approach slab or a pavement with no approach slab. Figure 45 shows section views of the typical bridge approach design in Texas DOT. Typical thickness of the slab is 13 in. and the typical length is 20 ft. For flexible and rigid pavements, the thickness of the pavement varies. The follow-up question responses indicate that some districts often use the wide-flange pave- ment terminal details on high-volume roads as an intermediate transition between approach slabs and roadway. • Sleeper Slabs. Texas DOT’s standard specifications and drawings show that sleeper slabs are used when the roadway pavement is concrete. • Connection Between Abutment and Approach Slabs. Both types of abutments used in Texas (stub and semi-integral) are rigidly tied to the approach slabs. The response to the survey indicated that for semi-integral designs, the abutment and approach slab are tied together with a system that allows rotation. • Expansion Joint. The location of expansion joints varies by the type of abutment. For stub abutments, expansion joints are placed between the approach slab and bridge deck as well as between the roadway and approach slab. For semi-integral abutments, only one joint is used between the roadway and the approach slab. • Backfill Materials. Texas DOT allows the use of several backfill materials, including granular or porous backfill, controlled-density fill material, crushed rock, and cement-stabilized and flowable backfill. The survey responses indicated that this varies by district and availability of material. A series of requirements are used to ensure the quality of the granular or rock backfill construction, including – Moisture content at placement, – Required compaction, – Gradation according to AASHTO or USCS, – Limit of fines (% passing No. 200 sieve): 0–10, and – Material requirements specific to the material used. • Ground Improvement. No ground improvement is typically done in Texas. However, the survey indicated that cement or lime treatment was used more than 15 years ago. • Water Management. Texas DOT survey responses indicated that no drainage pipe is used in the backfill underneath the approach slab in Texas. However, as stated in the DOT follow-up responses, recent experimental semi-integral abutments have a specific granular backfill assigned with pipe underdrains, as well as two layers of polyethylene sheeting between

Case Examples 79   (b) (c) (a) Figure 45. Section views of bridge approach design in Texas: (a) section showing backfill and abutment with and without approach slab, (b) approach slab section with asphalt pavement, and (c) approach slab section with concrete pavement.

80 Practices for Bridge Approach Systems the approach slab and this backfill. Texas DOT has an active research project that is advancing efforts for semi-integral abutments, which includes monitoring of experimental bridges. For runoff water, the water from both the bridge deck and approach may or may not be captured depending on the project. If captured, the water can be drained openly onto the surface of a slope, openly at the bottom of a slope, openly into the underlying backfill or embankment fill, or openly into a culvert, storm drain, or other closed system. These options depend on district preference and project specifics. • Construction Acceptance Criteria. Acceptance criteria is included in Item 422 in the standard specifications, which specifies that “[t]he engineer will use a 10-ft straightedge (1⁄8 in. in 10 ft) to verify ride quality and determine locations where corrections are needed.” 4.4.2 Inspection and Maintenance Texas DOT survey responses indicated that the DOT conducts periodic inspections of bridge approach components at least annually or biannually when the bridge is inspected. This includes inspecting the approach for the following types of degradation: • Differential settlement (bump), • Joint seal failure, • Void formation or approach embankment erosion under slab, and • Lateral spread of the approach embankment. For differential settlement, Texas DOT does not specify a quantitative test for severity of the bump, as only qualitative description is used. Ride quality is typically assessed using IRI or the pavement management information system (PMIS). Repairs or rehabilitation to fix bump formation are initiated based on user complaints and safety criteria. These repairs are done on an as-needed basis and may include one of the following techniques: • Injection of a portland cement grout underneath approach slab/pavement • Injection of expanded polyurethane underneath approach slab/pavement • Replacement of approach slab/pavement • Leveling with HMA 4.4.3 Performance Issues and Mitigation Practices The most common bridge approach systems in Texas based on the survey responses are as follows, presented in the order of most used: stub abutment with RC approach slab and stub abutment with rigid pavement. To better understand the performance of the bridge approach systems used by Texas DOT, the survey responses for common performance issues experienced are summarized in the following list. The survey used a qualitative scale for the frequency of the common issues with a three-tier rating system: rarely, occasionally, and often. Note that mitigation practices were not entered in the survey but were provided during the follow-up interview. • Bump Formation and Ride Quality. This issue occurs occasionally in Texas. • Failed Sealant in Joints. This issue occurs often in Texas. • Transverse and Longitudinal Cracking. This issue occurs rarely in Texas. • Failed Paving Notch or Seat at Abutment. This issue occurs rarely in Texas. • Erosion of Backfill. This issue occurs occasionally in Texas. • Blockage of Subdrain. This issue occurs rarely in Texas. • Differential Settlement. This issue occurs occasionally in Texas.

Case Examples 81   Mitigation strategies for common issues as indicated by Texas DOT responses for follow-up questions are as follows: 1. Improvement of the embankment foundation soil—if the foundation soils are too weak to support the embankment, they can be improved by a. Excavation and replacement, b. Preloading or precompression, c. Dynamic compaction, and d. Stone columns, compaction piles, auger cast piles, or deep soil mixing. 2. Improvement of approach embankment/backfill material a. High-quality fill—limit the percentage of fines and needs to be properly compacted. Compaction of fill adjacent to the backwall and wingwalls can be problematic. b. CSAB or flowable fill—solves the compaction problems and is resistant to moisture gain and loss of material. 3. Effective drainage and erosion control methods a. Create design for drainage of the bridge and where it is going once off the bridge. b. Use surface drains and/or gutter system. c. Reduce the amount of fines in the backfill and use a more porous material or CSAB. 4. Design of approach slabs 4.4.4 Lessons Learned A list of questions was submitted to Texas DOT for input and to identify what can be considered as lessons learned by the DOT. A summary of the responses is provided in the following list. • Use of CSAB is beneficial in regard to limiting compaction problems, as well as resisting moisture gain and loss of the material. However, CSAB is not appropriate for semi-integral abutments. Flowable fill has been used instead in accelerated construction situations and to fill voids associated with precast connection access. • Flowable fill to fill voids, injection of expanding foam, and mudjacking are typical mitigation strategies in addition to the strategies mentioned before. • Granular and porous backfill/crushed rock is a necessity for semi-integral abutments, and naturally matches up with cases involving MSE walls. It is also likely better for free drainage. Flowable backfill can be used for reliable filling of voids. Both CSAB and flowable fill have risks for piping of material because of the speed of runoff in small voids. • Some districts have their own preferences on approach slabs because of maintenance or other considerations. – Some districts do not like approach slabs since maintenance actions to restore approach slabs because of settlement are perceived to be difficult and addition of asphalt by in-house forces is more manageable. – Some districts perceive harder-to-address scour voids under approach slabs. – While the report notes a typical free-to-rotate detail on approach slabs, some specific districts modify details to have three edges of support in the form of two wingwalls and the abutment backwall. • Full-height closed abutments are avoided because of construction costs and general prefer- ence to “header banks” at bridge ends. • Texas DOT is actively pursuing semi-integral abutments both with and without approach slabs. Implementation is slow as a result of the large amount of standardized practice and the need to gain insight from trial installations.

82 Practices for Bridge Approach Systems 4.4.5 DOT Bureaus: Roles and Responsibilities for Bridge Approaches Similar to other DOTs, bureau responsibility varies with respect to bridge approaches. A summary of the roles/responsibilities of the different bureaus, offices, or units in Texas follows. • Design of approach for a new structure: The approach slab is constructed using a standard. The standard is designed by the Bridge Division or the district that issues the standard if the approach slab detail used is done by the district. • Design for rehabilitation of an existing approach: Varies • Design of backfill material and drainage control: Backfill material is selected based on the standard specifications for construction and maintenance and what has historically worked for a district. • Routine inspection of approaches, maintenance of ride quality, and repair of approach settlement or damage: These aspects are managed at the district or area office, usually by the maintenance sections. Repairs can be done by in-house forces or contracted out. 4.5 Case Example 5: West Virginia Department of Transportation 4.5.1 Typical Design and Construction of Bridge Approach Systems in West Virginia The West Virginia DOT practice was selected as one of the case examples as a result of their use of reinforced-soil mass backfill with geotextile layers in their practice. This includes the use of Class 1 aggregate in the backfill along with woven geotextile reinforcement with maximum spacing of 18 in. as indicated in the West Virginia DOT Standard Bridge Plans. The standard specifications and details for bridge approaches in West Virginia were used in conjunction with the survey responses to provide a summary of the current practices employed to construct these bridge approach systems, as discussed in the following list: • Bridge Abutments. The preferred abutment types in West Virginia are integral and semi- integral abutments. These are followed by stub abutments, MSE abutments, and full-height closed abutments. Full-height spill-through abutments were previously used by West Virginia DOT but not currently. • Approach Slabs. West Virginia DOT typical practice for approach slabs consists of using RC approach slabs. Flexible pavement is permitted on bridges on state local service roads with ADT less than 500 vehicles per day (vpd) and average daily truck traffic less than 100 vpd. All integral abutments with total anticipated thermal movement greater than 0.5 in. require RC approach slabs regardless of the route. Figure 46 shows section views of the typical bridge approach design in West Virginia DOT. Typical thickness of the slab is 12 in. and the typical length is 20 ft. For flexible pavements, the thickness is 6.5 in. and the length is 50 ft. • Sleeper Slabs. West Virginia DOT’s standard specifications and drawings show that sleeper slabs are typically used in approach slab construction. • Connection Between Abutment and Approach Slabs. All the approach slabs are rigidly connected to the abutments, regardless of the abutment type. • Expansion Joint. The location of expansion joints varies by the type of abutment. For integral, semi-integral, and MSE abutments, the joint is placed between the roadway and the approach slab. For stub abutments and full-height closed abutments, the joint is placed between the approach slab and bridge deck. • Backfill Materials. West Virginia DOT uses granular or porous granular material in the backfill with geosynthetic reinforcement with engineered filter fabric along the perimeter

Case Examples 83   (a) (b) Figure 46. Section views of bridge approach design in West Virginia: (a) approach slab section and (b) sleeper slab detail.

84 Practices for Bridge Approach Systems of select material for backfilling. As indicated in the survey, material conforming to grada- tion limits as determined by AASHTO T 27 is selected. Bottom/fly ash and steel slag are not considered as select granular backfill. The following properties shall be used: plasticity index not to exceed 6 (AASHTO T 90), angle of internal friction no less than 34°, substantially free of shale or other soft poor durable particles, resistivity greater than 3,000 ohm-centimeters (AASHTO T 288), pH between 5 and 10 (AASHTO T 289), chlorides less than 100 parts per million (AASHTO T 291), sulfates less than 200 parts per million (AASHTO T 290), and 1% maximum organic content (AASHTO T 267). The main requirement used to ensure the quality of the backfill construction is – Required compaction: Compacted in layers not to exceed 4 in. after compaction. • Ground Improvement. Ground improvement is typically done in West Virginia only in rare occasions for deep fill sections or when MSE walls are being used. A specified depth of subgrade will be removed and replaced with select material. • Water Management. West Virginia DOT survey responses indicated that a drainage pipe is used in the backfill underneath the approach slab. The system consists of perforated pipe included within select material for backfilling and engineered filter fabric, unless weep drains are used in the abutment. For runoff water, only water from the bridge deck is captured and redirected. The runoff water is then released openly onto the surface or at the bottom of slope. • Construction Acceptance Criteria. Based on the survey response, the only requirement of the West Virginia DOT is that approach slabs be in reasonably close conformity with the lines, grades, and dimensions specified in the plans or established by the engineer. 4.5.2 Inspection and Maintenance West Virginia DOT survey responses indicated that the DOT conducts periodic inspections of bridge approach components every 2 years, during NBIS inspection of the bridge. This includes inspecting the approach for the following types of degradation: • Differential settlement (bump); frequency: 2 years (as part of NBIS inspection) • Joint seal failure; frequency: 2 years (as part of NBIS inspection) • Void formation or approach embankment erosion under slab; frequency: 2 years (as part of NBIS inspection) For differential settlement, West Virginia DOT uses a qualitative description of ride quality. The respondent indicated that “ride quality is described in NBIS bridge safety inspection narrative (i.e., acceptable transitions, abrupt transition, 1” height transition differential, etc.).” For ride quality metrics, at the approach slab and bridge deck, straightedge testing is used to assess the ride quality, with a surface not to exceed 0.125 in. of deviation using a 10-ft rolling straightedge. Repairs or rehabilitation to fix bump formation are initiated based on user com- plaints and safety criteria. These repairs are done using different frequency intervals and may include one of the following techniques: • Injection of expanded polyurethane underneath approach slab/pavement; frequency: 5 years (only recently utilized) • Replacement of approach slab/pavement; frequency: unknown • Additional asphalt wearing surface; frequency: 2 to 3 years. 4.5.3 Performance Issues and Mitigation Practices The three most common bridge approach systems in West Virginia based on the survey responses and their expected service lives are as follows, presented in the order of most used:

Case Examples 85   • Integral abutment with RC approach slab: Typical life until rehabilitation is 10 years. • Semi-integral abutment with RC approach slab: Typical life until rehabilitation is 15 years. • Stub abutment with flexible pavement: Typical life until rehabilitation is 2 to 5 years. To better understand the performance of the bridge approach systems used by West Virginia DOT, the survey responses for common performance issues experienced are summarized in the following list. The survey used a qualitative scale for the frequency of the common issues with a three-tier rating system: rarely, occasionally, and often. • Bump Formation and Ride Quality. The issue of poor ride quality between the approach slab and bridge deck and across the approach slab occurs rarely in West Virginia. The mitigation practice for this is the new use of reinforced soil mass backfill with geotextile layers. Poor ride quality between the approach slab and main roadway occurs often, and the mitigation practice for this was the introduction 5 years ago of an RC sleeper slab at the end of the approach slab in the design. • Failed Sealant in Joints. This issue occurs occasionally in West Virginia. The respondent did not indicate a mitigation practice. • Transverse and Longitudinal Cracking. This issue occurs occasionally in West Virginia. The respondent did not indicate a mitigation practice. • Failed Paving Notch or Seat at Abutment. This issue occurs rarely in West Virginia. The respondent did not indicate a mitigation practice. • Erosion of Backfill. This issue occurs often in West Virginia. The mitigation practice for this is the new use of reinforced-soil mass backfill with geotextile layers. • Blockage of Subdrain. This issue occurs occasionally in West Virginia. The respondent did not indicate a mitigation practice. • Differential Settlement. This issue occurs rarely in West Virginia. The mitigation practice for this is the new use of reinforced-soil mass backfill with geotextile layers. 4.5.4 Lessons Learned A list of questions was submitted to West Virginia DOT for input and to identify what can be considered as lessons learned by the agency. A summary of the responses is provided in the following list. • Current practice includes using reinforced-soil mass backfill where approach slabs are used. The main benefit of this from the DOT’s point of view is that it results in less settlement of the approach fill. • To elaborate on the “safety” criteria as a factor to initiate repairs or rehabilitation to fix bump formation, safety is evaluated during NBI inspection, with any critical finding properly documented and submitted to engineering staff for consideration of further action. • Regarding abutment type, West Virginia DOT prefers either integral or semi-integral abut- ments to eliminate expansion joints on the bridge unless skew or thermal movement prohibits their use. In cases where integral or semi-integral abutments cannot be used, site conditions for a particular structure indicate whether a full-height or stub abutment is chosen. 4.5.5 DOT Bureaus: Roles and Responsibilities for Bridge Approaches Similar to other DOTs, bureau responsibility varies with respect to bridge approaches. A summary of the roles and responsibilities of the different bureaus, offices, or units in West Virginia follows. • Design of approach for a new structure: Either district design staff or central engineering divi- sion, in coordination with our geotechnical unit.

86 Practices for Bridge Approach Systems • Design for rehabilitation of an existing approach: Either district design staff or central engi- neering division, in coordination with our geotechnical unit. • Design of backfill material: Standard details developed by central engineering division. • Design of drainage control: Either district design staff or central engineering division. • Routine inspection of approaches: District bridge safety inspection staff. • Maintenance of ride quality: District maintenance forces. • Repair of approach settlement or damage: District maintenance forces or, at times, private contractor if grouting is required.