Using micropile as settlement reducer: centrifuge and numerical investigations

Ahmed Alnuaim, Hany El Naggar, M.H. El Naggar

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Earth Walls and Foundations

ABSTRACT: In this paper, the concept of settlement reducer piles is adopted to examine the performance of micropiles as settlement reducers instead of a typical pile foundation. A centrifuge test was conducted in order to validate a 3D finite element model (3D FEM), which was used to evaluate the effect of different parameters such as the number of micropiles, spacing of micropiles and thickness of the raft on the overall performance of micropiles in terms of maximum settlement, bearing capacity, differential settlement and bending moment in sand. The 3D FEM is able to accurately simulate the volume increase of micropile type B during pressurizing the grout during the installation which is one of the most important features of micropiles type B. The results showed that 60% reduction in the settlement of MPR at the center of the raft, for micropiles spacing of 5. It was also found that uniformly distributed micropiles increased the load carrying capacity of the foundation, but may result in increases in differential settlement and bending moment of the raft. Therefore, additional micropiles should be strategically located in order to reduce the differential settlement and the raft bending moment. RÉSUMÉ Dans cet article, le concept de piles règlement réducteur est adoptée pour examiner la performance de micropieux comme réducteurs de règlement au lieu d'une fondation sur pieux typique. Un test de la centrifugeuse a été réalisée afin de valider un modèle 3D par éléments finis (3D FEM), qui a été utilisé pour évaluer l'effet de différents paramètres tels que le nombre de micropieux, espacement des micropieux et l'épaisseur du radeau sur la performance globale de micropieux en termes de règlement maximale, capacité portante, tassement différentiel et moment de flexion dans le sable. Le FEM 3D est capable de simuler avec précision l'augmentation de volume de type micropieux B pendant la pressurisation du coulis lors de l'installation qui est l'une des caractéristiques les plus importantes de type micropieux B. Les résultats ont montré que la réduction de 60% dans le règlement du MPR au centre du radeau, pour micropieux espacement de 5. On a également constaté que micropieux réparties uniformément augmenté la capacité de charge de la fondation, mais peut entraîner une augmentation des tassements différentiels et moment de flexion du radeau. Par conséquent, micropieux supplémentaires devraient être situés stratégiquement afin de réduire le tassement différentiel et le radeau moment de flexion. 1 INTRODUCTION When a raft foundation is subjected to high concentrated loads (i.e. column loads) near the center of the raft, both total and differential settlement can be high. The differential settlement may cause high tensile stress at the raft base, which will require large reinforcement. Also, the settlement underneath the column may damage the beam-column connections. In order to overcome these adverse effects, the raft thickness may be increased and consequently its flexural stiffness and hence reduce the settlement. Alternatively, piles can be used as total and differential settlement reducers while keeping the raft thickness unchanged (Burland et al., 1977). This method works by using as minimal number of piles as possible and allowing the piles to carry loads close to their full capacities to reduce the total settlement of the raft, which will consequently minimize the differential settlements. The piles should be installed right under or close to the concentrated loads. The use of piles to reduce the settlement and differential settlement of a raft foundation was investigated through a number of studies; for example, Randolph (1994), Clancy and Randolph (1996), Horikoshi and Randolph (1996 and 1998). In the mid 1980's, micropiles were introduced into North America and their use has been rapidly growing due to their numerous benefits. Micropile is a small diameter 'cast-in-place' pile. Micropiles The concept of underpinning foundation systems using micropiles, such as a micropiled raft foundation, is relatively new. Han and Ye (2006) performed one micropile load test in clay using a 1.5 m by 1.5 m square raft with four micropiles 150 mm in diameter and spaced at 5Dmp. It was found that the load transmitted by the micropiles was about 70% to 86% of the additional load which was applied to the raft after it was underpinned by the micropiles. However, the effect of flexibility of the raft on the interaction between the raft and soil, the load sharing between the raft and the micropiles,

RÉSUMÉ: micropile as settlement reducer: centrifuge

Access this article:
Canadian Geotechnical Society members can access to this article, along with all other Canadian Geotechnical Conference proceedings, in the Member Area. Conference proceedings are also available in many libraries.

Cite this article:
Ahmed Alnuaim; Hany El Naggar; M.H. El Naggar (2014) Using micropile as settlement reducer: centrifuge and numerical investigations in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper160,author = Ahmed Alnuaim; Hany El Naggar; M.H. El Naggar,title = Using micropile as settlement reducer: centrifuge and numerical investigations,year = 2014}