Project Objective:

Study applicable theories, choose the theory that most closely answers the question on the pressure distribution and magnitude of integral abutments and check the theory with our data.

• Separate the different mechanisms responsible for the pressure built-up. We have data that will help us quantify the different affects on the development of the pressure. For example, data at the beginning of the measurements does not show the accumulated plastic strain. Data right after a freeze period shows very high pressures that dissipate with higher temperatures. (Note that one would expect the passive pressure to be the greatest at the highest temperatures).
• Identify the role of skew in the development of pressure. Data taken at the East and West part of the abutment can be used to quantify the effect of skew.
• Recommend design parameters for the safe evaluation of pressure behind integral abutments.

Project Abstract:

In an on-going research project with the NJDOT, we have instrumented an integral bridge and have been gathering data every two hours for the past two years. We found that there is a significant pressure built-up in the soil behind the abutment. We have reported the built-up to the NJDOT, however our project does not allow for an in-depth analysis of the mechanics that are responsible for the development of the high pressures.

We have identified at least four mechanisms responsible for the increase in the pressure: 1) strain ratcheting (or the plastic accumulation of strain) due to the cyclic loading of the soil; 2) a flow of the sand particles during the daily and seasonal cyclic loading; 3) the presence of frozen ground; and 4) possible failure of a soil wedge during the active pressure periods of the winter months which may be shifting the equilibrium position during every season.

In order to recommend design parameters for the correct pressure distribution and magnitude, we must understand the pressure development mechanisms. This is of vast and immediate importance to the design community, considering that the construction of integral abutments is becoming widespread.