Vertical Expansion of an Existing Lime Mud Storage Pond, 1993 Environmental Conference Proceedings

An existing lime mud storage pond at a pulp and paper mill in southeastern North Carolina had reached its capacity and needed to be expanded. Because of real estate constraints, the only option for expansion was vertical. The plan was to construct a new dike on top of the lime mud surface within the perimeter of the existing pond while maintaining operation of the pond during construction.

Subsurface investigations were conducted on the stored lime mud to assess the material’s physical characteristics. In order to acquire satisfactory samples, access to the lime mud surface was required. Preliminary design concepts were utilized to build “peninsula” dikes projecting toward the center of the pond to allow access for drilling and sampling. These “peninsulas” were constructed using two to four feet of sand fill on a geogrid base.

Test results indicated that the lime mud had low shear strength, high compressibility, and high water content. Due to these factors, significant difficulties were anticipated with settlement and material displacement during construction. A phased plan was developed which incorporated the anticipated settlement into the construction sequence.

Expansion of the facility was designed utilizing geogrid for uniform support of construction materials. Foundation

stability was significantly improved through the consolidation of lime mud beneath the new dikes. Other geosynthetics were specified for use in seepage control structures and erosion controls for the project. Procedures were specified to monitor lime mud response to the applied loads during construction and to assess the performance of the installed geosynthetics.