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Geotechnical Engineering

Essay by   •  May 8, 2019  •  Lab Report  •  883 Words (4 Pages)  •  26 Views

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  1. Equipment Schematics[pic 1]

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  1. [pic 18][pic 19]

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The value of t50 can be obtained by plotting d50 on the graph in figure 5

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Hence, Cv can be calculated

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  1. [pic 31]

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Figure 6 visually compares the coefficient of volume consolidation between measurements that were recorded during the laboratory and the data collected by the soil technician. The trends for both set of data are similar whereby a significant proportion of the deformation occurs early on and reduces as time passes. However, the values collected from the laboratory are significantly smaller than the ones from the soil technician. This could be due to various reasons including systematic errors from the machine and human errors such as setting up the equipment in the wrong way.

Section B: Design Component

  1. A piezometer is used for measuring pressures in ground. When the instrument is placed in the ground, the liquid inside the piezometer will rise due to the pressure differences inside and outside the pipe. The height of the liquid determines the pressure at that depth. To monitor groundwater pressures in the field, the piezometer should be placed in a borehole where the groundwater pressure at the deepest point of the borehole will be recorded by the instrument.

  1. The coefficient of compressibility is the ratio of volumetric strain over change in effective stress and can be measured by applying the oedometer test on a saturated soil sample. The test measures the deformation of the specimen as it is subjected to incremental loading. The deformation would then be plotted against the elapsed time which will allow for the analysis of the pore water pressure dissipation, giving us the change in vertical effecting stress. The coefficient of compressibility can then be found in the slope of the graph of the vertical deformation versus the change of effective vertical strength.
  1. The coefficient of consolidation can be estimated by calculating the slope of the graph of time versus the rate of dissipation. This graph is obtained by conducting a full-scale loading trial which involves applying incremental loading to saturated soil. This will case the water to drain out of the sample, dissipating pore water pressure. The dissipation of pore water pressure is then plotted against the elapsed time.

Values obtained from field tests are typically more accurate than values from the laboratory. This is largely due to the fact that the dissipation of pore water pressure is highly dependent on the permeability of the soil which is a sensitive parameter. This means that it is difficult to maintain the condition of the soil while it is being transported to the lab, producing less accurate results to the field tests.

 

  1. The pore water pressure is given by the equation:  

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        Upper Piezometer where h = 2m

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        Lower Piezometer where h = 6.5m

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