Design Risks Of Ground Improvement Methods Including Rigid Inclusions

Abstract

After an introductory presentation of design approaches the risks involved are investigated. Considered are different ground improvement methods, like soil mixing, vibro compaction and vibro stone columns, as well as pile-like supporting elements, including vibro concrete columns and full displacement columns named rigid inclusions. The difference in stiffness of the inserted material and the soil determines the design and the risks involved. Three categories with increasing risk are proposed. Ground improvement methods, ductile in compliance with EN 1997-1 and DIN 1054, proved to be extraordinary robust and present only a small risk with regard to a possible variation of soil and material parameters and loads. The design is usually determined by the serviceability limit state. Risks increase with the application of non-ductile methods with small column diameter, like rigid inclusions, because the ultimate limit state is controlling the behaviour. Namely, in order to mobilize high skin friction, the lower and upper end of the column have to fail during punching in the soil below and the load transfer platform above. Even a small variation in material parameters, system geometry or loads may lead to a complete loss of bearing capacity and progressive failure, resulting in expensive damages of civil engineering structures and time consuming repair works.

Analysis of deformations of road embankments founded on displacement columns improving soft subsoil

“…The risk of failure with respect to particular soil improvements methods is analysed in [24,25]. Due to the ductile/brittle behaviour of the systems, the authors differentiate the technologies into three groups.…”

Design methods for geogrid reinforced foundation systems on weak subsoil

“…Total replacement of local soil is usually not worth the extra cost, instead, the emphasis is on reinforcing the existing soil when possible. [1] Every construction is preceded by preliminary investigations with the aim of determining if the structure can or cannot be safely built without altering subsoil conditions. [2] Several E3S Web of Conferences 368, 02023 (2023) https://doi.org/10.1051/e3sconf/202336802023 GeoAfrica 2023 possibilities are available for designers to do that in a safe way, including but not limited to: soil replacement, dynamic soil compaction, soil injection, horizontal geosynthetic reinforcement, gravel piles and vibro-stone columns, prefabricated vertical drains, rigid inclusion technique, jet grouting and lightweight structural materials.…”