SUSTAINABILITY CONSIDERATIONS FOR GROUND IMPROVEMENT TECHNIQUE USING CONTROLLED MODULUS COLUMNS

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The sustainability concept has been increasingly accepted to be a key aspect in engineering design and construction, most noticeably in government supported projects. Since geotechnical engineering is one of the key parts of construction, geotechnical engineers have opportunities with the power to deliver project outcomes that are not only economical and safe but also sustainable. Ground improvement techniques, aim to increase ground bearing capacity, improve stability, and reduce short and long term ground settlements. These techniques have an impact on the environment, local ecological systems and ground conditions. Appropriate techniques are increasingly demanded due to decreasing available and favourable land for construction and redevelopment of urban areas. Nowadays, a large number of ground improvement methods exist in the industry, with each serving a limited number of purposes. Selection of one or a combination of two or more methods requires deep understanding of various ground treatment methods. Decision making should rely on trials, design requirement, project budget and time restraint, ground and site conditions. Alongside with the control of quality, durability, cost and safety, authorities also require design and construction of infrastructure to consider environmental outcomes, forming important aspects of sustainable development.

Although sustainability in geotechnical engineering has been addressed by a number of authors (Abreu et al., 2008; Holt et al., 2010; Jefferson et al., 2007), little attention on sustainable development has been placed during the process of geotechnical engineering design and implementation. Instead, the geotechnical community should set out clearly specified sustainability outcomes with tangible results to be achieved within a set time frame. At this stage it will be very likely that any sustainability policies/requirements attached to the contract works may receive mixed responses from businesses.

To target sustainability outcomes in geotechnical engineering and ground improvement works, three major “triple bottom line” Economic, Environment and Social impact proposed by Elkington (1997) should be followed in combination with “financial, social, human, natural and produced” factors. Economic benefits and social reactions should not be considered as barriers for sustainable development. In fact, adoption of sustainable solutions should be considered to enhance the competiveness in bidding and winning projects. Today sustainability in geotechnical engineering targets (i) reduction in energy consumption, (ii) lower carbon emission during implementation and (iii) decrease in material usage. This should be accompanied with increased use of reused, recycled or green materials and locally available materials instead of importing (Mitchell and Kelly, 2013). Geotechnical engineers should be aware of and equipped with methods of sustainability assessment (e.g. how carbon footprint is estimated).

One way to achieve those outcomes would be through technological innovations. One of the relatively new innovative ground improvement methods is the controlled modulus column (CMC) ground improvement technique. This technology was first developed in France and now has become a method of choice for many projects having tight construction schedule or with concerns related to soft soils and contaminated ground. CMC possesses several features that are distinct from those of more traditional methods such as prefabricated vertical drains, stone columns, deep soil mixing or piled embankment foundation. CMC has been used considerably in Europe with increasing popularity in the US. The technique has recently been used in a number of projects in Australia, mainly involving construction of bridge approach embankments, port development and warehouse foundation with the aim to reduce both total and differential settlement and to accelerate construction sequence (Fok et al., 2012; Wong and Muttuvel, 2012).

This paper summarises the key sustainability aspects of using CMC technology and highlights some aspects that are potential for development. Future research directions are discussed to further enhance sustainable design practices. These include fuel consumption during operations, economic design with trial field tests, the use of recycled industrial by-products for grout mix, improved design, and maximising the resiliency of structures. The remainder of the paper will discuss the current state of art in assessing installation-induced displacement of the surrounding soils.

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