APPLIED APPROACH SLAB SETTLEMENT RESEARCH, DESIGN/CONSTRUCTION (FHWA-OK-13-09 2227)

Abstract

Approach embankment settlement is a pervasive problem in Oklahoma and many other states. The bump and/or abrupt slope change poses a danger to traffic and can cause increased dynamic loads on the bridge. Frequent and costly maintenance may be needed or extensive repair and reconstruction may be required in extreme cases. Research critically investigated the design and construction methods in Oklahoma to reveal causes and solutions to the bridge approach settlement problem. The major objectives of the research were: 1) Investigate causes of, and solutions to the approach slab settlement problem in available literature. 2) By direct investigation, determine primary causes of approach slab settlement for selected bridges in Oklahoma. Bridge configurations studied included those commonly used by ODOT and representing different embankment and foundation soil conditions typically encountered in Oklahoma. 3) Recommend solutions to minimize or eliminate approach slab settlement problems associated with Oklahoma bridges. 4) Recommend construction solutions to minimize potential for approach settlement problems. The major tasks completed included: 1) A review of available published literature related to the bridge approach settlement problem. 2) A survey of ODOT Field Divisions to solicit information about bridge sites experiencing settlement problems. In addition, potential sites were identified through discussions with key persons in the ODOT Materials Division. 3) Of the potential test sites, field reconnaissance investigations were conducted for 30 bridges at 22 separate locations in Oklahoma. These sites were identified as having moderate to severe problems and were representative of different bridge types, different geology, and different ages. To the extent possible, design, construction and maintenance records were obtained for these bridges. 4) At five of the test sites, subsurface investigation was conducted including: drilling and sampling, cone penetrometer testing, laboratory classification testing and oedometer testing to determine settlement parameters. 5) Statistically analyzed data to determine if there were relationships observed between bridge / embankment / foundation features and observed distresses. 6) Analyzed settlement of foundation soils and wettinginduced collapse settlement in embankment soils. 7) Developed recommendations for design and construction methods for addressing the approach slab settlement problem. The investigation revealed that erosion under the approach slab and under the abutment is a serious problem for many Oklahoma bridges. Consolidation of foundation soils was also found to be an important contributor to the approach slab settlement problem.