Design and Construction of a Highway Interchange over Abandoned Lead and Zinc Mines - Route 249 - Joplin, Missouri

摘要

V The Missouri Department of Transportation is completing the Route 249 - US 171 interchange on an abandoned underground lead-zinc mining site near Joplin, Missouri. The interchange required the construction of 5 major bridges connecting massive earth embankments and involved the construction of 23 bents, 3 culverts and 3 MSE walls. The geotechnical characteristics of the project site are the product of the original limestone and chert bedrock geology, the tectonic processes leading to brecciation, folding and paleo karst, and the anthropogenic (manmade) activities associated with mining. These processes resulted in a site that exhibited critical geotechnical attributes: 1. Highly variable rock parameters (strength, deformability and hydraulic conductivity) 2. Very low level of predictability or correlation between subsurface explorations 3. Locally modified hydrologic regime due to the mining disturbance 4. Presence of residual mining voids in both the upper "confused" zone and the lower "sheet" zone 5. Potential for ground loss beneath foundation elements 6. Presence of heterogeneous mine fillings including compressible clay 7. Presence of vertical shafts with random and partial filling These attributes led the design team to the selection of a foundation design concept that required bent specific geologic characterization based on subsurface exploration and geotechnical testing; pre design utilizing stress analyses and other analytical approaches to predict the interaction of ground quality, voids and imposed loading; systematic confirmatory exploration during construction; and ground treatment and foundation design modifications as required by the confirmatory construction site engineering and inspection work. The basic premise of this approach was that there were no foreseeable ground conditions at the project site that could not be adequately improved to provide foundation support for the proposed structures. Discussions during the pre bid phase emphasized ground conditions would be evaluated on a continuous basis in the field, reducing or eliminating any delays. This paper describes the historical research, site investigation, design methodologies and construction of spread footings at 7 of the bents and the 220 micropiles used to provide deep foundations for 16 of the bents. Pregrouting of the rock mass involved 8698 yds~3 (6,650 m~3) of LMG and 504 yds~3 (385 m~3 ) HMG and was conducted to confirm design assumptions at all bents and as a site preparation for those bents to, be micropiled. A separate program of mine shaft location and treatment was also required.