|TO:||All Design Section Staff|
|DATE:||April 20, 1998|
|SUBJECT:||Mechanically Stabilized Earth (MSE) Supported Abutments|
We have received a recommendation from the WSDOT Geotechnical Branch to initiate use of MSE systems to support bridge abutments (see attached memo of 4/1/98). During the recent California and Kobe, Japan earthquakes, this type structural abutment support systems performed very well, with no observed bridge damage.
The use of MSE supported bridge abutments should be considered for use on upcoming projects. In general, this type of abutment support system can be considered if the MSE wall height (beneath the superstructure) does not exceed 20 feet. Until we have a little more experience with the design and construction of this type of structural system, I am requesting that preliminary bridge plan be used as the "approval document". BDM changes will follow after some use of this approach. Based on the Geotechnical Branch recommendations, the following design/approval elements must be included when this concept is utilized.
This MSE "bridge abutment support" application is non-standard. Each proposed use must be approved by the Bridge Engineer and the Geotechnical Branch. The preliminary bridge plan will be used for this purpose. This Bridge Engineer will sign the preliminary bridge plan, and the Geotechnical Branch will respond with a memo (prior to the Bridge Engineer signing the preliminary bridge plan) approving the concept.
The allowable (Service Load) bearing pressure is 290 kPa (3TSF) for the bridge abutment foundation resting on the MSE support.
The front edge of the bridge abutment footing shall be at least 2 feet behind the back face of the MSE wall.
There shall be a minimum of 5 vertical clearance from the bottom of the superstructure to the top of the MSE will fill in front of the abutment. There shall also be at least 5 feet of horizontal clearance between the face of the bridge abutment and the back face of the MSE wall. The top of the MSE wall shall be constructed with fall protection/arrest (noted on preliminary bridge plan).
This interim Bridge and Structures Office policy is effective immediately.
cc: M. M. Lwin, Bridge and Structures, 47340
R. George, Bridge Preservation, 47341
T. Allen, Materials Laboratory, 47365
J. Weigel, Construction, 47354