Rigid inclusions for ground improvement
Soil displacement induced when installing controlled modulus columns (CMC) as ground reinforcement could affect the columns installed close by. Realising numerical analyses may provide useful insights, this paper describes a numerical approach to investigate how groups of CMC installed in different sequences could affect columns installed previously. Coupled consolidation analyses in large strain mode and incorporating soil-CMC interaction were carried out using the three-dimensional finite difference software package FLAC3D. The CMCs were modelled using advanced non-linear Hoek-Brown material with a tensile yield criterion while soils with a typical profile were characterised using the modified Cam Clay and the elastic-perfectly plastic material with a Mohr-Coulomb yield criterion. Where possible, the predicted responses of ground surrounding the CMCs were compared to a number of existing analytical methods. Predictions revealed that lateral soil movement and soil heave near existing CMCs induced by installing new CMCs towards the existing CMCs were approximately 15% and 25% greater than corresponding predictions when a reverse installation sequence was adopted. The maximum excess pore water pressures, induced near existing columns due to installing new columns towards the existing ones, were almost twice more than those caused by the reverse sequence of installation. Moreover, the predicted bending moments generated in the existing columns induced by installing new columns towards the existing CMCs were almost 22% greater than the corresponding values when the reverse installation sequence was adopted. This shows the importance of selecting an appropriate installation sequence in the CMC construction process as well as considering the initial stress field and bending moments in the surrounding soil and CMCs, respectively when designing embankments on improved soft soils.
Nguyen, HH, Khabbaz, H, Fatahi, B & Kelly, R 2016, 'Bridge Pile Response to Lateral Soil Movement Induced by Installation of Controlled Modulus Columns', Procedia Engineering, vol. 143, pp. 475-482.View/Download from: UTS OPUS or Publisher's site
© 2016 The Authors. Published by Elsevier B.V.Controlled modulus columns (CMC) for ground improvement are installed using a hollow stem displacement auger to induce lateral soil displacement effect, followed by grout injection. While the method reduces spoils, the excessive lateral soil displacement may damage adjacent structures. Although there has been growing interest in quantifying such effects, only a handful of studies have been attempted. This paper presents the results of a numerical investigation on the CMC installation effect on an existing bridge pile using the three-dimensional finite difference software package FLAC3D. It has been found that when the CMC is long and the existing bridge pile is slender, the pile bending moment and pile lateral movement, induced by the CMC installation effect, can be significant.
Nguyen, H, Khabbaz, H, Fatahi, B & Hsi, J 2017, 'Effects of installing controlled modulus columns on previously installed columns', proceeding of the International Conferences on Soil Mechanics and Geotechnical Engineering, the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul, South Korea.View/Download from: UTS OPUS
Controlled modulus columns (CMC) ground improvement technique is an attractive geotechnical solution for
modification of soft soils. This technique uses a displacement auger during column installation, aiming to reduce the construction cost
and disposal of excavated materials. However, lateral and vertical soil movement induced by the installation process may pose
potential risks to the adjacent previously installed columns. Only a handful of studies have been attempted in quantifying such effects.
This paper presents the results of a numerical investigation on the effects of CMC installation sequence on the already installed
columns using the three-dimensional finite difference software package FLAC3D . The results indicate that the installation sequence
should be taken into account in the design process to minimise any adverse effects of installing new CMCs on the existing columns.
Nguyen, HH, Khabbaz, H, Fatahi, B, Santos, R, Marix-Evans, M & Vincent, P 2016, 'Installation Effect of Controlled Modulus Columns on Nearby Existing Structures', Geotechnical Special Publication Proceedings, GeoChina International Conference, ASCE, Shandong, China, pp. 125-133.View/Download from: UTS OPUS or Publisher's site
© 2016 ASCE.Controlled modulus columns (CMC) ground improvement technique is a novel approach to reduce ground settlement. To install CMC, a rotary displacement auger is used to form a vertical cylindrical cavity, by displacing the surrounding soils laterally, followed by grout injection. While the method reduces spoil generation, excessive lateral soil displacement may damage the adjacent structures and freshly-grouted CMCs. Although there has been growing interest in quantifying such effects, only a handful of studies have been attempted. This paper presents results of a numerical investigation on the CMC installation effect on an existing bridge pile using the three-dimensional finite difference software package FLAC3D. The bridge pile response to the lateral soil movement induced by the CMC installation are presented and discussed.
Nguyen, HH, Fatahi, B & Khabbaz, H 2014, 'Challenges In Assessing The Installation Effects Of Controlled Modulus Columns On Behaviour Of Surrounding Soils', Proceedings Of Fourth International Conference – Geomate 2014 Geotechnique, Construction Materials And Environment, International Conference on Geotechnique, Construction Materials and Environment, The GEOMATE International Society, Brisbane, Australia, pp. 44-49.View/Download from: UTS OPUS
Ground improvement technique using controlled modulus columns (CMC) has become increasingly popular in recent years. A rotary displacement auger is screwed and pushed into the ground during installation, to create a vertical cylindrical cavity before concrete is injected to form a CMC. This process causes disturbance of the surrounding soils and results in lateral displacement. In certain circumstances, such displacement may cause damage to freshly grouted neighbouring columns or nearby structures.
This paper integrates the existing methods in assessing the lateral displacement of the surrounding soils due to CMC installation. Analytical, numerical and physical modelling techniques are discussed. The study aims to provide recommendations on novel techniques as well as important parameters for simulating CMC installation process and assessing the effect of this process on nearby freshly grouted CMCs and bridge piles.
Nguyen, HH, Khabbaz, H, Fatahi, B, Vincent, P & Marix-Evans, M 2014, 'Sustainability considerations for ground improvement techniques using controlled modulus columns', PROCEEDINGS OF THE 2014 AGS SYMPOSIUM, AGS Symposium on Resilient Geotechnics, The Australian Geomechanics Society, AUSTRALIAN NATIONAL MARITIME MUSEUM, DARLING HARBOUR, NSW AUSTRALIA, pp. 170-170.View/Download from: UTS OPUS
Sustainability is becoming an ever more important consideration for the selection of ground improvement methods on construction projects around the world. When considering this criterion, the controlled modulus column (CMC) technology emerges as one of the relatively novel technologies that are capable to deliver valuable and sustainable outcomes. CMC installation is a vibration free process and produces very limited soil cuttings, making CMC suitable for improvement of soft ground, contaminated sites and ones adjacent to sensitive structures. Besides, CMC uses grout only without the use of steel reinforcement; hence carbon footprint estimated for CMC is generally lower than those for traditional piling techniques. Besides these valuable aspects, it is believed that this technology can still be advanced to contribute more to the sustainable development, owing to ongoing research works and practical experience. This paper summarises the key sustainability aspects of using CMC technology and highlights some potential aspects for further development. Future research directions are discussed to enhance sustainable design practice. These include general discussions on the issues of economic design with trial field tests, the use of recycled industrial by-products for grout mix, improved design, maximising the resiliency of structures and the energy consumption. The CMC installation effects on the surrounding soils and environment are also discussed sensibly in this paper.