Lock 22 extension feasibility study

Project Summary

The U.S. Army Corps of Engineers, Rock Island District (USACE), selected Hanson to perform an engineering feasibility study, addressing navigation improvement planning for the Upper Mississippi River and Illinois Waterway System for the years 2000 to 2050.  The deliverable was a detailed report. 

The engineering feasibility study addressed the original design of Lock 22 and a lower guidewall extension.  Lock and Dam 22, located on the Mississippi River about nine miles downstream from Hannibal, Mo., was constructed from 1933 to 1938.

To obtain information for the study, Hanson investigated the subsurface conditions to document soil and rock engineering properties for the design of the lock extension from the existing 600-foot-long lock to a 1,200-foot-long lock.

Hanson’s team performed a geotechnical exploration program consisting of 31 geotechnical borings drilled from a barge on the river to depths ranging from 35 feet to 65 feet deep in soil and rock.  The typical geologic profile consisted of 15 feet of water, 7 feet of soil, and up to 40 feet of rock that was predominantly limestone but, in some circumstances, included some shale. 

Ten of the geotechnical borings obtained 4-inch-diameter rock core.  The team used the rock core to perform about 30 unconfined compression tests and about 90 triaxial tests at confining pressures up to 2,000 psi in accordance with ASTM D-2664.  Hanson’s team also performed 12 packer tests to determine the in situ hydraulic conductivity of the rock mass.

Working with the USACE, Hanson produced a geotechnical appendix to support the extension of Lock 22 and its lower guidewall.  The appendix addressed subsurface conditions and other engineering analyses – performed by Hanson – that were needed for inclusion in the report.

The detailed report included the following elements:

• analysis of seepage and uplift,
• guidelines for factors to be considered in the construction of the lock and guidewall extension,
• recommendations for applicable rock excavation methods,
• recommendations for soil and rock shear strength parameters, and
• discussion of any unusual conditions that might impact design or construction.

Using information from the report, the USACE plans to incorporate the following into the construction phase of the project:

• placing the lock and guidewall extension in the wet area,
• extending the existing intermediate wall with a concrete-filled pile structure,
• modifying the existing landslide guidewall for reuse as a lockwall, and
• using concrete beams spanning cells for the lower guidewall.