Static and dynamic characteristics of peat with macro and micro structure perspective

Peat soils occur in many countries but are often described differently both from qualitative and quantitative perspective. It is primarily derived from the anaerobic decomposition of plant and animal matter. Due to this composition, the structure and fabric of this soil is very different from inorganic soils like clay, sand and gravel. Peat soils normally regarded with apprehension by geotechnical engineer due to the lack of understanding for its geotechnical properties. However the rapid pace of urban infrastructure development and diminishing land resources for such development and the abundance of peat soil deposits in the marginal areas demand an urgent need for a through geotechnical characterisation of peat soils. According to Von Post classification, peat can be classified as Fibrous; soil materials contain three fourths or more (by volume) fibres after rubbing, Hemic; intermediate in their degree of decomposition and Sapric; more decomposed amorphous materials. This research is primarily focused on the static and dynamic properties of two classes of peat; Hemic and Fibrous obtained from different location where Holme Fibrous Peat 1 (HFP1) and Holme Fibrous Peat 2 (HFP2) in Holme Fen Post (Cambridgeshire, United Kingdom); Solway Hemic Peat (SHP) in Solway Post (Carlisle, United Kingdom) and Malaysia Hemic Peat (MHP) in Western Johore (Malaysia). There is an estimated 1.6 million hectares (minimum) of peat land available in United Kingdom and meanwhile Malaysian peat was approximately 2.6 million hectares, respectively. The behaviour and composition of these peats are different from each other, accentuating the need for a useful engineering geological classification of peat soils. The understanding of the static and dynamic behaviour of peat is still embryonic in the field of geotechnics and need to be fully understood. Additionally, the effects fibre in the peat soils accentuate the dearth of knowledge and therefore a clear understanding of the overall static and dynamic properties of peat soil is very necessary. Experimental results for undrained cyclic triaxial tests using VJ Tech Cyclic Triaxial Testing Apparatus are presented. Soils are subjected to dynamic loading of various forms. Some of these forms, which are those from sources such as earthquakes, traffic loads and wave. To assess the level of the consequent ground motion of the soil, two parameters those are vital in dynamic analysis; shear modulus (G) and damping ratio (D) properties. Results show distinct differences in the parameters for the hemic and fibrous peat. The significant of peat type, microstructure, loading frequency, confining pressure and index properties are also discussed. The interpretation of soil genesis based on fabric analysis is essential to ascertain its influence on the analysis of its engineering behaviour. Aydemir et al. (2004) suggested the use of image analysis in research to identify more clearly the composition and structure of the fabric in a soil. Literature shows its usage to be focused more on inorganic soils. The imaging technique that was used in the laboratory to analyse different types of peat soils are explained. Comparing the techniques, the author found that the image analyses of a digital image were more representative as the analysis was carried out on the whole sample. However the preparation of sample for image analysis need to be done carefully as explained in this research in order to minimize the disturbance to the sample particle. The author also initiates that for classification of peat; it is important to include image analysis for fabric and not based on the laboratory tests only. Some thought provoking concepts of fabric and micro structural studies of the tested peat soils are discussed with a view to initiating a peat classification that will prove useful in ground investigation and subsequent geotechnical design. This helps geotechnical engineers to appreciate the various techniques available in image processing to investigate the particle arrangement and facilitate to classify the peat soils more appropriately. This research is contributing to provide a further useful classification as to the current classification for different classes of peat