Soft marine soil

Construction of highway embankment on soft marine soil at Kakinada Port, India... 

Ideally, if very soft soils are to be tested, shear strength, excess ambient pore pressure, and the bulk density (saturated density) all need to be measured in situ. If less easily disturbed marine soils are to be tested, it may be possible to both test in situ and obtain the bulk density from onboard ship measurements of good-quality cores. 

The three-storey shops in Shah Alam, Selangor, Malaysia were supported on piles but the 2 m wide walkway rested directly on a 3 m thick layer of poorly compacted residual soil fill, underlain by 5 m thick soft marine clay. 

Universiti Tun Hussein Onn Malaysia (UTHM) sits on deep deposit of soft marine clay with low strength and high compressibility. Pre-treatment of the soil by ground improvement is necessary before construction works can commence on these grounds. Various ground improvement techniques are available in the market, such as vertical drains with surcharge, stone columns, mass replacement, stabilisation, etc. 

Consolidation is another topic which students found hard to cope with. After explaining the concept and its applications in detail systematically and slowly, I gave them some real cases to think about. The Nicoll Highway incident (Ministry of Manpower, 2005) with the collapse of the retaining structure after 33 m of soil excavation in soft marine clay that occurred in Singapore in April 2004 was used an illustrative example. Towards the end of the consolidation topic coverage, students were asked to voluntarily submit their calculations on whether the 50-m thick soft marine clay has completed its consolidation settlement under a reclaimed sand fill placed about 50 years ago. 

One technique to improve the stability of breakwaters and containment dykes con-stmcted on soft foundations is to use geotextile reinforcement across the base of the stmcture (Fig. 20.19). This basal reinforcement technique has been used successfully for many years in the onshore construction of embankments on soft foundation soils, and is discussed in detail in chapter Geotextiles used in reinforcing foundations. Because of its cost—benefits, this technique has also been used in marine engineering structures over the past 20 years. 

The reinforced soil technique, such as basal-reinforced breakwater constmction, is an example of a land-based technique employed in a marine engineering environment to provide a cost-effective solution to improve the stability of stmctures constmcted on soft marine foundation soils. The presence of soft marine foundation soils close to coastlines in bays, harbours, estuaries and deltas makes for difficult conditions on which to constmct stable marine stmctures. Reinforced soil is one technique along with other associated foundation consolidation and strengthening technologies that is expected to be used more often in these locations. 

Surface water can be defined as any river, lake, stream, pond, marsh, or wetland as ice and snow and as transitional, coastal, and marine water naturally open to the atmosphere. Major matrix properties, distinguishing water types from each other, are hard and soft water, and saline and freshwater. Groundwater is typically defined as water that can be found in the saturated zone of the soil. Groundwater slowly moves from places with high elevation and pressure to places with low elevation and pressure, such as rivers and lakes. Partitioning interactions of the groundwater with the solid soil matrix is an important factor influencing the fate of toxicants. Physicochemical properties of water that may affect toxicity of chemicals in all water types are listed in Table 2.2. 

Comparison of dynamic shear modulus ratio (G/G versus strain ratio (y/fr) for various soil types and ranges of marine deposits. (Data from Fang, H.Y. et al.. Dynamic shear modulus of soft silt, Intermtioml Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, University of Missouri, RoUa, MO,... 

For pile embankment construction, usually driven piles are used. Lateral displacement and large deformation will occur in the subsoil especially if the soil is very sensitive. As this may cause problems of instability in nearby structures, precautions need to be taken. The technique of pile embankment has been successfully used in Malaysia especially for construction of high road embankments on soft soils such as alluvial and marine clays, and peat. 

In the area of east China, south China, Sichuan basin and the terrace area of main rivers, the sediments are fluviatile facies, lacustrine facie and marine facie deposit, and the soil of sand, silt and slime are widely distributed, which is very helpful for the disasters of sand liquefaction and seismic subsidence of soft soil. 

Table 1. Physical and mechanical properties of Lianyrmgang marine soft soil (Q4 ).

Hu Jun, et al (2008) have taken triaxial test for the marine soft soil in Lianyungang to attain tri-axial rheological parameters, the soil samples were analyzed by different depths, different confined pressures, different verticd stress level conditions of morphological characteristics of s-t curve. The study showed that the yield stress of the stress... 

In order to describe the nonlinear stress-strain relations of the marine soft soil, a single hidden layer BP model was setup with the use of neural network technology. For the model, the input values are bias stress, confining pressure and time, the output value is the strain. Therefore, nodes of the input layer is 3, the number of nodes of the output layer is 1. The number of hidden layer units ranging from 5 to 25, and it need to be determined based on the training and fitting results. The neurons in the hidden layer is a sigmoid transform function, the neurons of the... 

Chen Yinan, Pan Hualiang, Liu Songyu, et al. Characteristic of Marine Soft Soil in Lianyungang. Geotechnical Engineering Technique, 2001, (4) 212-216 (In Chinese). 

Zhang Junhui, Miao Linchang. Tests on Rheological Behavior of Lianyungang Marine Soft Clay and Two-yield-surface Rheological Model. Rock and Soil Mechanics, 2005, 26(1) 145-149 (In Chinese). 

FIGURE 7.2 Soil cores collected using Geobor system, (a) Glacial till and soft rock, (b) Dense marine sands. 

When a reclamation has to be realised on a natural soft soil (e.g. recent marine sediments), a stability analysis of the containment bunds and the fill front itself has to be made. The loading introduced by the bunds and the fill is considered to be a quick loading condition, compared to the rate of consolidation of the natural subsoil. As such, the soft cohesive material behaves undrained and the most critical situation is the undrained condition as illustrated in Figure 8.24. This figure demonstrates the effect of excess pore water pressure (positive or negative), dissipation and the increase/decrease of the shear strength with consolidation. 

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