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Geotechnical Challenges in Weak Rock and Karst Conditions
A large aggregate and concrete supplier has constructed, using the design/build process, a $90 million cement plant in north central Florida, in an area of active karst conditions. The construction includes three large heavily-loaded silo groupings, with an applied base pressure of 476 KPa, and other tall heavy structures with large overturning moments. Both shallow mat and drilled shaft foundations were used. The geotechnical exploration indicated the presence of highly plastic clay overburden soils, with an underlying highly dissolutioned limestone formation. Depth to limestone varied from zero to 12.2 m due to past dissolutioning. Geophysical surveys, standard penetration test borings, pit excavations, dilatometer tests, pressuremeter tests, and 100 mm diameter rock coring were performed at the site to characterize the subsurface profile and limestone quality. Due to the limestone porosity, which included voids, a grouting program was performed in heavily-loaded and settlement-sensitive structure areas to reduce the risk of settlement and sinkholerelated distress. Drilled shaft design parameters were confirmed by Osterberg load test methods. The settlement prediction of shallow mat foundations was complicated by the unknown elastic stiffness of the highly dissolutioned limestone formation, a lack of historical foundation performance data in the area, and adjacent foundation interaction effects. Shallow foundation preparation consisted of plastic clay removal in rock cavities, air jet cleaning, and backfilling with high slump Controlled Low Strength Material (CLSM) to restore limestone competency. On-site excavated limestone was also used as fill/backfill, where appropriate, to further reduce costs. This paper discusses the geotechnical issues and challenges which occurred on this fast-track design/build project, and how they were solved by the contractor/designer/geotechnical consultant team.
Geotechnical Challenges in Weak Rock and Karst Conditions
A large aggregate and concrete supplier has constructed, using the design/build process, a $90 million cement plant in north central Florida, in an area of active karst conditions. The construction includes three large heavily-loaded silo groupings, with an applied base pressure of 476 KPa, and other tall heavy structures with large overturning moments. Both shallow mat and drilled shaft foundations were used. The geotechnical exploration indicated the presence of highly plastic clay overburden soils, with an underlying highly dissolutioned limestone formation. Depth to limestone varied from zero to 12.2 m due to past dissolutioning. Geophysical surveys, standard penetration test borings, pit excavations, dilatometer tests, pressuremeter tests, and 100 mm diameter rock coring were performed at the site to characterize the subsurface profile and limestone quality. Due to the limestone porosity, which included voids, a grouting program was performed in heavily-loaded and settlement-sensitive structure areas to reduce the risk of settlement and sinkholerelated distress. Drilled shaft design parameters were confirmed by Osterberg load test methods. The settlement prediction of shallow mat foundations was complicated by the unknown elastic stiffness of the highly dissolutioned limestone formation, a lack of historical foundation performance data in the area, and adjacent foundation interaction effects. Shallow foundation preparation consisted of plastic clay removal in rock cavities, air jet cleaning, and backfilling with high slump Controlled Low Strength Material (CLSM) to restore limestone competency. On-site excavated limestone was also used as fill/backfill, where appropriate, to further reduce costs. This paper discusses the geotechnical issues and challenges which occurred on this fast-track design/build project, and how they were solved by the contractor/designer/geotechnical consultant team.
Geotechnical Challenges in Weak Rock and Karst Conditions
McIntosh, Kirk A. (author) / Knott, Randy A. (author)
Geo-Denver 2000 ; 2000 ; Denver, Colorado, United States
2000-07-17
Conference paper
Electronic Resource
English
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