Installation Effect of Controlled Modulus Columns on Nearby Existing Structures

© 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

Sustainability considerations for ground improvement techniques using controlled modulus columns

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

Three-Dimensional Simulation of a Load Transfer Mechanism for Frictional and End Bearing CMC Supported Embankments on Soft Soil

© ASCE. Recently, the use of controlled modulus columns (CMC) has gained popularity in the support of rail and road bridge approach embankments on soft soils. If the columns are extended into a competent firm soil, and designed to take nearly all the vertical loads, they become rigid inclusions. The advantage of this design approach is that settlement will be controlled, but the drawback is that the columns will attract greater load, including bending moment and shear force in situations where non-uniform loading or ground conditions exist. The load on the composite soil-CMC is uniformly distributed by the upper layer of granular load transfer platform (LTP). In this paper, the effect of CMC length on the load transfer mechanism is numerically investigated. Coupled flow-deformation analysis has been performed for a long period to understand the system response in the long term, while interface elements capable of simulating gapping and sliding between CMC and the surrounding soil are considered. A geosynthetic reinforcement layer has been simulated using the inbuilt FLAC3D geogrid element. The force in the reinforcement layer has been evaluated, and in particular, a clear comparison is made between the stresses in CMC and the ground settlement with floating and end-bearing columns