Soil Bearing Capacity and Techniques to Improve the Bearing Capacity of Soil

Soil at a construction site may not always be totally suitable for supporting structures in its natural state. In such a case, the soil needs to be improved to increase its bearing capacity and decrease the expected settlement. This paper gives an overview of techniques that are commonly used to improve the performance of saturated clayey soil in situ, its functions, methods of installation. Then, this study concluded that there is an urgent need to study the technique of removal and replacement for improving soil behaviour taking into consideration geotechnical requirements (i.e.bearing capacity and settlement) and cost to achieve the optimum thickness of replacement layers and the most suitable material corresponding to minimum total cost of foundation works. Keywords: Bearing capacity failure, Preloading, drains, stone column, Dynamic compaction, Grouting methods of soil improvement

Experimental study of an innovative driven and grouted soil nail (x-Nail)

This paper describes an experimental investigation of a newly developed driven and grouted soil nail (x-Nail), which combines the capabilities of a purely frictional driven nail and a compaction-grouted nail. The innovative design allows the x-Nail to be driven into the ground with a latex balloon attached that is used subsequently for compaction grouting. A grout bulb is thus formed at the driven end of the nail to improve its pull-out resistance. For compaction grouting, a special type of additive-mixed cement grout was used in this investigation because of its zero bleeding and high bond strength. A series of pullout model tests was conducted to examine the performance of the x-Nail compared to a purely frictional soil nail. It was found that more than 90% of the pullout force of the x-Nail was resisted by the expanded grout bulb and the end bearing resistance of the grout bulb increased with the increment of the injected grout volumes. The experimental results revealed that the pullout force of the x-Nail increased approximately 1800%, 1550%, 1200% and 900% compared to the purely frictional soil nail for the injected grout volumes of about 350 ml, 270 ml, 220 ml, and 170 ml, respectively.

Compactage Horizontal Statique : retours d’expérience

Le procédé de Compactage Horizontal Statique, mis en œuvre pour la première fois aux États-Unis dans les années 1950 par les ingénieurs d’Hayward Baker Inc. (Groupe KELLER), a été développé considérablement par la suite, de telle sorte que depuis le début des années 1990, il trouve également une diffusion croissante en Europe (Warner J. 1982. “Compaction grouting-the first thirty years”. Gr Geotech Eng, ASCE, 1982: P694–707). Alors qu’à l’origine, les applications du procédé étaient limitées à la consolidation sous les fondations d’ouvrages susceptibles de subir des tassements, il en existe maintenant beaucoup d’autres. Aujourd’hui, les domaines d’application du Compactage Horizontal Statique sont multiples : amélioration et renforcement de sol pour des ouvrages neufs ou des reprises en sous-œuvre mais également pour des traitements de vides karstiques. Un exemple de chantier vient illustrer une application de ce procédé sous des éoliennes en mettant en évidence les avantages de ce procédé dans un contexte géotechnique difficile de zones décomprimées et de vides dans la craie jusqu’à des profondeurs de 20 à 45 m. Il a également été associé à un autre procédé de renforcement de sol par inclusions rigides pour traiter les sols superficiels. La détection et la délimitation des zones d’anomalies par des sondages destructifs avec enregistrements de paramètres n’ont pas été possibles en phase projet et ont été très compliquées en phase travaux pour garder un délai d’exécution court. Le retour d’expérience de cette opération montre que dans un tel contexte, il y a lieu de prévoir plusieurs mailles : une maille primaire lâche sur l’ensemble de l’emprise de l’ouvrage de manière à délimiter grossièrement les zones à injecter, et une maille secondaire voire tertiaire en intermaille, pour circonscrire précisément la zone d’anomalies.

Insights Into Compaction Grouting for Offshore Pile Foundations

The authors are currently investigating the possibility to apply compaction grouting for offshore pile foundations (Jacket piles as well as monopiles) as a possible retrofitting technique for an optimised foundation concept. In this research project, we are developing a design approach aiming to predict the ideal amount and properties of a grout for a specific soil situation and desired improvement of pile bearing capacity after installation and during service time. Both numerical and experimental tests have been carried out to investigate the injection process during which a highly viscous grout is injected into the soil under high pressure to displace and compact the surrounding soil without fracturing it. The implicit Material Point Method (MPM) based on a mixed formulation is the numerical technique chosen to deal with the expected large deformations and the arbitrary shape of the developing grout bulb. The usage of MPM prevents both the need of remeshing and the numerical instability induced by extensive mesh distortion. For validation with experimental results, we have constructed a testing chamber with one transparent sidewall. This chamber enables us to observe the injection process directly at the transparent vertical window and to measure the in-plane soil displacements and strains by means of the Digital Image Correlation (DIC) technique. The results already reveal the interrelation of soil and grout properties for a successful usage of this common ground improvement technique.