A Literal “Muddy Boots” Problem
Weeks Marine’s contract to build a new dock in Corpus Christi Bay required up to 10 feet of new fill placed in shallow water onto very soft Gulf Coast clays. Fill was trucked to the site, dumped at the leading edge of the fill, and then shoved waterward by light bulldozers. Right away, they learned that the trucks simply could not drive on the recently-placed fill. The underlying bay deposits were too soft to support the new fill, the truck tires would shove into the working grade, and the dozers were spending all of their time towing the trucks out of the mud.
Taking A Different Path
Weeks Marine hired us to engineer a better truck path. Upon arriving at the site we immediately realized that building a stable road over the very soft bay clays would be a Herculean task. We had solved a similar problem in Pascagoula several years before and knew that it could be accomplished with sand and geotextiles, but the cost and schedule impacts would be unbearable. A different solution was necessary—an intentional mudwave.
A mudwave usually happens by accident. When filling new embankment too quickly onto soft, saturated ground, it’s possible for the embankment weight to exceed the native soil’s strength and the whole mass slides waterward. It’s usually a huge setback for the project.
Mudwaves require tremendous effort to control once one starts. Whole textbook chapters are dedicated to designing embankments and improving drainage in order to prevent mudwaves. Intentional mudwaves are so rare as to be legendary. Old engineers talk about them wistfully, recalling megaprojects from the 1960’s and 70’s.
A Massive Squeegee
The key to this particular problem was that one of the last steps in wharf construction was to dredge the water in front of the dock from 2 feet deep to 30. An intentional mud wave established, and carefully controlled, out in front of the leading embankment edge would effectively squeegee the soft soils out from beneath the new embankment, improving the subgrade, allowing the new fill to densify, and effectively supporting the dump trucks. The slimy muck would end up on the waterward side of the site and could be removed with the already-planned dredging.
A Road To Success
The plan was an unqualified success. Trucking rates met and even exceeded the plan, the fill could be compacted to specifications without difficulty, and the project was back on track. We needed to pause and muck out the very-tall mud pile twice simply to maintain control of the work, but that was easily incorporated into the overall flow of the filling.