Remote Sensing Techniques for Highway Retaining Walls

Detroit, Michigan, USA

Retaining walls are a critical component of highway systems with most states having thousands of miles of walls in their networks. Structural monitoring using remote sensing techniques can quantitatively assess the performance of retaining walls in service and can offer the data needed to perform risk assessments and prioritize infrastructure investments.

Infrastructure Theme

Funding Source

MDOT

About the Project

Highways consists of a large number of civil engineered structures that are vital to their safe and efficient operations including bridges, culverts, retaining walls, among others.

In particular, retaining walls are an important part of highway systems with most states having thousands of miles of walls in their networks. For instance, earth and service road retaining structures were popularly constructed along many freeway corridors in the metropolitan Detroit region in Michigan since the early 1960’s. To date, highway managers have focused on the health and upkeep of bridges in their networks but recent federal directives is requiring the adoption of risk management strategies for all highway structures including retaining walls. In this regard, many highway managers are struggling with how to make asset management decisions regarding retaining walls given their large inventories of walls and their complex soil-structure behavior. Structural monitoring offers one possible approach to quantitatively assessing the performance of retaining walls in service and offering the data needed to perform risk assessment decisions.

 

In Michigan, the major types of retaining walls employed to support service roads, overpasses and earth structures along major highway corridors include: cantilever reinforced concrete walls, concrete walls supported by caisson tiebacks, mechanically stabilized earth (MSE) walls, sheet pile walls and soldier pile walls. Ten site visits (selected from a list of 74 potential retaining wall sites presented by MDOT) were conducted May through October 2017. Of the ten selected locations, two of the ten walls have been identified as potentially showing some structural distress to warrant instrumentation. The two walls identified include a caisson supported RC wall along M-10 near Schaefer Highway and a cantilever RC wall along I-696 at Central Park Boulevard supporting W Eleven Mile Road on the south side of I-696.

 

In this study, two retaining wall structures in the metropolitan Detroit region are studied using a wireless monitoring system permanently installed.  One wall is a traditional cantilever retaining wall while the second is a tie-back wall type. The monitoring systems consist of three major types of sensing transducer: inclinometers, strain gauges and thermistors. These transducers were interfaced to a wireless sensing node termed Urbano which has been designed for long-term unattended operations in infrastructure monitoring applications. It is designed with a cellular modem which utilizes cellular communication to push data to the Internet. Long-term tilt and strain response of the wall is used to identify soil loads on the backwall and to validate performance features of the walls.  Using the measured performance of the walls, wall demand and capacity are estimated to assess the risk of failure of each wall monitored.  The monitoring strategies for both walls considered sensing transducer types to assess the mechanical behavior of the wall and environmental factors driving wall behavior. The intention of the sensors selected is to provide valuable data from which the load demand and structural capacity of the walls can be evaluated or estimated for risk assessment.