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Performance characteristics of embankment on soft ground.

Kasim, Fauziah and Marto, Aminaton (2003) Performance characteristics of embankment on soft ground. Project Report. Universiti Teknologi Malaysia. (Unpublished)

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Abstract

Soft clay deposits are available along the west coast and some parts of the east coast of Peninsular Malaysia. Due to the increase in population and good economic growth, a lot of projects are implemented in these areas. Constructions on soft clays are often affected by stability and settlement problems. In order to counter these problems, one has to know the engineering properties of the soft clay. Therefore, the first objective of this study is to determine the engineering characteristics of soft clay. Samples of soft clay for this study are taken at certain depth from construction sites being carried out along Peninsular Malaysia. This study is carried out to identify the engineering properties of soft clay such as soil index, consolidation characteristics, shear strength parameters, mineralogy and microstructure of the soil. Correlations and brief catalogues are produced to assist in the preliminary design process. X-rays diffraction (XRD) and X-rays fluorescence (XRF) are used to determine the mineralogy of soft clay. Scanning electron microscopy (SEM) is used to study the microstructure of clay. From this study, it can be concluded that the soft clays in the research area have high moisture content which reaches 139%. Whereas, the specific gravity (Gs) is between 2.42 – 2.65, compressibility index (Cc) is between 0.09 – 1.36, coefficient of consolidation (cv) is between 1.24 – 8.72 m2/years and coefficient of volume compressibility (mv) is between 0.056 – 2.084 m2/MN. The effective cohesion (c’) values are in the range of 0 – 2 kN/m2, while the effective friction angle (φ’) are in the range of 17º – 31º. Tests using XRD concludes that the primary mineral in soft clay is quartz and the secondary mineral is kaolinite. On the other hand, XRF tests shows that the quantity of silica oxide and aluminium oxide are quite high in soft clay, which are due to the presence of kaolinite mineral. Test using SEM verified the presence of kaolinite mineral and pyrite in soft clay. From the correlation derived, it shows that the compressibility index increases with natural moisture content, Atterberg limit, initial void ratio and organic content. On the other hand, the effective friction angle is found to be influenced by the natural moisture content and plasticity index. Then correlation obtained shows that the effective friction angle decreases with increasing natural moisture content and plasticity. Soft clay is a sediment which can be found in abundance along the coastal areas of Peninsular Malaysia. The soft clay has created a challenge in construction industry, particularly in the road construction. In such circumstances, settlement is very important because it governs the serviceability of the overlying structure i.e. roadways, because low shear strength, excess pore water pressures and lateral deflections affected stability of an embankment. In order to understand the behaviour of soft clay beneath the embankment, Malaysian Highway Authority had led constructions of 14 trial embankments in Muar Flat site in 1986 – 1988 by using various methods for determining the most effective method in terms of cost and time beside knowing the suitable prediction methods for simulation of the actual condition behaviour. The main objective for this research is to determine the soft clay behaviour beneath the Muar Trial Embankment via laboratory testing and simulation of consolidation and slope stability using finite element method. Three embankments selected for the study were Embankment Built to Failure (Scheme 3/5), 3 m Control Embankment (Scheme 3/2) and 6 m Control Embankment (Scheme 6/6). Laboratory works conducted were tests for basic characteristics, compressibility and shear strength of soils. Comparisons between the current laboratory results and the previous results show that there are reductions in moisture content up to 49 %. For compressibility parameters, pre-consolidation pressure (pc) increased up to 160 % while initial void ratio (eo) and vertical consolidation coefficient (cv), decreased above 44 % and 74 %, respectively. On the other hand, the undrained shear strength increases up to 160 % for upper clay layer and 116 % for lower clay layer. Three soil constitutive model such as Linear Elastic, Elastic Plastic and Modified Cam Clay Model were used in simulation of consolidation analysis. The comparison of simulation results from analysis of SIGMA/W, SEEP/W and SLOPE/Ws software showed a small variation between previous works and current findings. Analysis of slope stability simulation showed that the prediction of failure thickness and slip surface depth for Scheme 3/5 are 5.25 m and 7.9 m, respectively. The values are much closer to the actual measurement compared to previous predictions by other researchers. The safety factor for the 3 m embankment obtained is much smaller compared to the safety factor of the 6 m embankment. This is due to the construction of berms for the 6 m embankment. From the simulation analysis consolidation, it can be seen that the result of excess pore water pressure using the Modified Cam Clay Model over estimated the actual readings in the range of 20 % to 80 % for all embankments. Hence, a good prediction shown by this model was on the settlement behaviour and lateral deflection, where the differences with the actual measurements are about 10 % to 30 % and 20 % to 40 %, respectively. For Elastic Plastic and Linear Elastic Models, the result of simulation analysis showed the excess pore water pressure and settlement behaviour were under estimated about 80 % and 70 % respectively.

Item Type:Monograph (Project Report)
Uncontrolled Keywords:soft ground, embankment, consolidation, geotechnical instrumentation, pore water pressure
Subjects:T Technology > TE Highway engineering. Roads and pavements
T Technology > TA Engineering (General). Civil engineering (General)
Divisions:Civil Engineering
ID Code:2811
Deposited By: Rashidah Abdul Shukor
Deposited On:21 May 2007 06:58
Last Modified:08 Jun 2012 08:41

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