Costly Oversights in Geotechnical Practice: Fid-Bau Portal

Costly Oversights in Geotechnical Practice

Lukas, Robert G.

The author was engaged to review three projects where either settlement or instability had occurred thereby resulting in costly repair operations. The problems arose for a number of reasons including an oversight where geotechnical issues were not properly addressed or overlooked, extending the state of the practice beyond proven techniques without adequate confirmation, and less than acceptable monitoring during construction. Case 1 involved an attempt to achieve ground improvement of buried weak deposits below deep fill by dynamic compaction without consideration of the depth of improvement achieved and the compressibility of the underlying deposits. Another example includes the improper use of dynamic compaction to densify fill deposits containing large portions of lumber. Case 2 involves a residential structure supported upon compacted silty clay fill that is on the order of 4.6 m thick under one portion of the building with only a shallow fill under the other portion. Differential settlements resulted in cracking in the structure and the floor slab and the need for underpinning. Case 3 involves an excavation for a future landfill through over consolidated clayey glacial till soil with a compacted clay liner on the slope face. During construction, a number of shallow sliding surfaces developed resulting in the need for removal of the clay liner, providing adequate drainage discharge, and reconstruction of the slope face.