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Pages 66-86

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From page 66...
... 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.
From page 67...
... Case Examples 67   a flexible pavement (no approach slab) ; however, this can only be done if abutment embankment settlement is not critical, as indicated in the survey.
From page 68...
... 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.
From page 69...
... 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.
From page 70...
... 70 Practices for Bridge Approach Systems • Design of backfill material: Bridge designer. • Design of drainage control: Bridge designer.
From page 71...
... Figure 43. Section views of the approach slabs from the Iowa DOT standard (Iowa DOT Standard Road Plans)
From page 72...
... 72 Practices for Bridge Approach Systems • Ground Improvement. No ground improvement is typically carried out in Iowa.
From page 73...
... Case Examples 73   • Failed Sealant in Joints. This is an occasional issue in Iowa.
From page 74...
... 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 specifications 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.
From page 75...
... Figure 44. Section views of bridge approach design in Massachusetts: Types I, II, and III.
From page 76...
... 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)
From page 77...
... 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 performance standpoint, buried approach slabs mitigate the bump at the end of the bridge, where the approach backfill settles immediately behind the abutment.
From page 78...
... 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.
From page 79...
... Case Examples 79   (b)
From page 80...
... 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.
From page 81...
... 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.
From page 82...
... 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.
From page 83...
... Case Examples 83   (a)
From page 84...
... 84 Practices for Bridge Approach Systems of select material for backfilling. As indicated in the survey, material conforming to gradation limits as determined by AASHTO T 27 is selected.
From page 85...
... 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.
From page 86...
... 86 Practices for Bridge Approach Systems • Design for rehabilitation of an existing approach: Either district design staff or central engineering division, in coordination with our geotechnical unit. • Design of backfill material: Standard details developed by central engineering division.

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