The term soil reinforcement is conventional since decades ago for the stabilization of soft ground such as of clay and peat. Numerous research has arisen in the utilization of natural fibres as the reinforcement materials. Cost reduction, increment of sustainability awareness and eco-friendly environment are some of the advantages when using natural fibres to stabilize soft ground. A research study was carried out to evaluate the strength of the soft soil when unreinforced and reinforced using natural fibres. The findings on the experimental investigation of the study will be presented in this paper. Crushed coir fibres were used to reinforce an intermediate plasticity soft clay where both materials were collected locally in Brunei Darussalam. The crushed coir fibres were added at 0.5%, 1.0%, 1.5% and 2.0% to the dry weight of the sample. A series of an unconsolidated undrained Tri-axial test was conducted on the unreinforced and reinforced samples where the behaviour of the samples were observed and compared. The results indicated that inclusion of fibres affects the soil’s undrained shear strength. It was observed that increasing the percentage inclusion increases the undrained shear strength of the soil, up to a certain amount. Further increment of fibres, however, does not show further improvement in the undrained shear strength.

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Settlement often occurs on weak soil due to its inability to support heavy loads which is not safe to the structures and the surroundings. In order to enhance the engineering properties of weak soil, a ground improvement technique called soil reinforcement was introduced. Soil reinforcement can be considered as economical because the reinforcement materials can be of natural fibres, hence eco-friendly. Fibres from coconut, rice husks and rhumbia are some of the natural fibres that can be found in abundance in Brunei Darussalam. In this paper, comparative study on the consolidation characteristics of soft soil reinforced with coconut husks or coir fibres at different inclusion of lengths and crushed forms were carried out on an intermediate plasticity clay obtained locally from the site of a RIPAS bridge at Sungai Kebun in Bandar Seri Begawan. The sample was first compacted to its maximum dry density in accordance to BS 1377: Part 4 to obtain its optimum moisture content for the samples preparation of consolidation tests series. The coir fibres used were in two different forms: (i) strands of 10, 20 and 30 mm length, and (ii) crushed form. The percentage inclusion of fibres was kept at an increment of 0.5% with a maximum of 2.0%. The consolidation behaviour of these reinforced samples were observed and compared with the unreinforced sample. The results indicated that different percentage inclusion of coir fibres affects the soils' consolidation behaviour in terms of the coefficient of consolidation, cv and coefficient of permeability, k. The fibres inclusion also affected the soil's compression index, Cc and coefficient of volume compressibility, mv. From the conducted experimental investigation, it can be concluded that the soil samples reinforced with 20 mm length of coir fibres give the most significant effect to the soil's consolidation behaviour when it was added at 1.0%.

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