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E-mail: judith_lcc@hotmail.com Abstract Good quality soils are always preferred in development projects, where the bearing capacity of the grounds is sufficiently high and the resulting subsidence is non-excessive. However these sites may not be as readily available with increased population and land use, making it inevitable to construct on less favourable soils, like soft organic materials. To ensure long term stability of structures erected on such soft soils, elaborate and extensive foundation systems are generally required. Alternatively, pre-treatment with ground improvement techniques is necessary. Both these methods tend to incur high costs and labour as well as require prolonged construction period, while making a rather negative impact on the environment in terms of raw material sourcing, heavy machinery mobilization and exposure to the risk of groundwater contamination. This paper describes an exploratory study on a simple shallow foundation system for construction on soft soils, which can be a potentially cheaper and more sustainable approach. The foundation system, termed the “Akar Foundation”, literally translates as “Root Foundation”, is essentially a lightweight platform supported by a group of hollow stumps (i.e. PVC pipes). The ‘root’ base served dual functions: 1. to collectively assert a stronger grip of the soft soils, hence giving higher bearing capacity; 2. to spread the imposed structural load evenly into the subsoil, thus avoiding excessive and non-uniform settlements. 50961
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The effects of the end condition of the pipes (i.e. open or close) as well as the spacing between the pipes on the foundation settlement mechanism were examined, with static load tests conducted using a lab-scale simulation chamber. The findings showed that the effectiveness of the “Akar Foundation” depends on the compatibility of the pipe spacing and inpidual pipe lengths, highlighting the inter-relationship between the mobilisation of end resistance, skin friction and formation of soil plug in the open-end system. In a promising light, the reduced subsidence suggest the potential of the “Akar Foundation” as an economical yet effective foundation system in economically challenged soft soil areas. Keywords: Shallow foundation, Soft soils, Subsidence 1. Background: Problems and Current Practice Construction on soft soils, such as organic and peat soils, has always been considered a challenging task by the civil engineering community. Low strength and high compressibility are typical characteristics of such soils, making them inadequate to support the additional load of infrastructure built on them. Some additional considerations are required to provide a sufficiently strong foundation to support the development above ground. The foundation has to not only bear the dead and live loads without collapse, but also to undergo limited and uniform settlement with time. Organic soils are commonly found as extremely soft, unconsolidated superficial deposits that are an integral part of the wetland system (E.P.M. Jarret, 1995). They are recognized as problematic materials for their notoriously low shear strength, high compressibility and permeability as well as considerable secondary compression or creep characteristics (P. Kallioglou et.al, 2009). A main constituent of these soils is the organic matter, which encompasses any organic compound contained in the soil, with the exception of living biomass. The organic matter consists of humus, dead vegetable and animal biomass, water-soluble organic compounds, and other non-living organic substances or organo-mineral components (C. Siewert, 2002). In Malaysia, peat and organic soils are considerably extensive, making development on such areas a challenging endeavour for civil engineers. A.A. Mutallib et al. (1991) reported that these deposits represent some 8 % of the total land area of the country, which is equivalent to approximately 2.6 million hectares of land area. Organic soils in particular, have an inhomogeneous and anisotropic structure that differs greatly from inorganic soils, resulting in their peculiar engineering properties (P. Kallioglou et al., 2009), which are usually not condusive for load-bearing. These soils are commonly water-logged and contain high percentage of organic matters at different decomposed stages. The Malaysian peat, for instance, is usually found at sites with high water levels all year round, thus providing very limited resistance against loading and settlement in short or long term (C-M Chan and Z. Abu Talib, 2008), where even a moderate load can lead to a large change in volume in these soils (Huat, 2002).