Case Study: Design and performance of a 46m High MSE Wall
Location and Purpose for Retaining wall measurement
The Seattle – Tacoma International Airport (STIA) is located in SeaTac, Washington. This airport required an expansion because of the limitations to the distances between the existing runways due to the inclement weather conditions. So a third runway was constructed to the west of the two existing runways. The third runway embankment construction included the three MSE wall.
The following are the three MSE walls:
• Single tier 58ft high south MSE wall
• Vertical two-tier 85ft high north wall
• Vertical four-tier 150 ft high west MSE wall
In this study, the third runway was constructed on a significant volume of the compacted earth fill that was required to raise the grade to a maximum of about 165 ft to meet the level of the existing runway. The west MSE wall was constructed to avoid the relocation of the creek and a wetland enhancements were required elsewhere to compensate for the impacted wetland area. The west MSE wall which forms part of the western boundary of the third runway embankment. This wall construction required approximately 1,430 ft (436 m)long, four-tier MSE wall up to 150 ft (45.7m) tall. The total area of the wall face was approximately 130,200 ft2 (12,100 m2). The exposed height of the MSE wall is 137.5ft (41.9m). Prior to construction of the MSE wall the soil consisted of soft peat interlayered with loose to medium dense silty sand and sandy peat. Figure 1: Perspective aerial photo of the new third runway at STIA viewed from the northwest and showing the north and west MSE walls
Instrumentation and Measurements
The objective of the monitoring program was to evaluate the wall performance during and at the end of construction. The west wall performance was observed by monitoring the displacements of the wall face, foundation soils and retained soils, tensile strains and inferred stresses in reinforcing strips, and piezometric levels.. The red flag criteria, was defined to identify the performance data that appeared potentially problematic, unanticipated or erroneous. When a data is red flagged, it triggers an action by determining the cause, effect, and by provide a basis for remedial action as necessary. The fig. 2 illustrates all the types of instrumentations used to monitor the wall during the construction.
Figure 2: West MSE wall cross section with typical instrumentation
Data Acquisition Methods:
The automatic data acquisition system (ADAS) was a modular Campbell Scientific Inc (CSI) CR10X environmental data logger system. The ADAS consisted of a 12 channel CR10X data logger, 16-channel multiplexer/terminal modules, vibrating wire interfaces, internal battery pack and charging controller, a Redwing CDMA digital cell-modem, a Yagi antenna, a 100-AHR marine, deep cycle battery and a 75 W solar panel. The strain gage cables were terminated at the
multiplexers and the piezometer cables were wired to one of...