Paper Example on Soil Sampling

Introduction

From the experiment, the test can be inferred to be a stress-controlled test. The specimen is loaded gradually as the shearing force is applied in equal increments until the (Geocities.ws, n.d.) sample fails. Dry sand is used for this experiment as the direct stress of different magnitudes are used to analyze the behaviour under different loads. According to the standard tests carried out with the same samples, it is expected that the resisting shear stresses exhibited by the soil in all the four stresses be uniform and the shear stress increases with shear displacement until a failure shear stress value is reached.

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Similarly, in our results, the specimen's shear stress resistance forces increase with a corresponding increase in the horizontal displacement. This is true as signified by the graphs. Within the loading capacity, all vertical stresses put on the soil show similar results throughout the test. The shear resistance remains approximately constant for any further increase in the shear displacement (Anon, 2018). For the combined graph, the higher the weight of the normal stresses applied the higher the horizontal displacement experienced.

Within the graph of the normal stress versus the shear strain, the loose sand exhibits similar behavior to what is expected. An increase in the normal stresses results to a corresponding increase in the shear stresses. This behavior is shown throughout all the different normal stresses, and when a line of best fit is drawn, it has a positive gradient. This behavior is however not affected by soil type since all loose soil may show the same characteristics. The situation is mainly influenced by the soil state and, primarily the increased soil density is responsible for this behavior. The more the weight is added to the soil, the more the decrease in volume. A reduction in volume results to a corresponding increase in the density rapidly as the stress is increased.

A change in volume then implies that the strength of the material will increase due to an increase in intergranular contact forces hence commendable particle strength. For the strain versus the height properties, the samples exhibit similar behavior as that in theory. For the 200Kpa loading is exceptional and the soil state could be blamed for this occurrence. Shear strength parameters are essential since the soil, and the foundation could be communally tested together by placing one on top of the other. However, the test contains various limitations in that the soil is not allowed to fail on its own, but only along the restrained plane of split of the shear box (Anon, 2018). Apart from this, the shear stress distribution over the shear surface of the specimen (Anon, 2018) may not be uniform.

For the triaxial test, although the data is majorly scattered, there still can result a pattern that holds for all the specimens used. An increase in the axial strain that causes failure of the specimen results in a corresponding rise in the deviator stress up to an absolute limit which then becomes constant. This is the general pattern all through the experiment as is expected for the soil sample. This behavior can be majorly accrued to the fact that upon the increase in the axial strain, the pore water pressure increases with the increase in strain up to a certain limit. The limit varies depending on the amount of strain applied on the particular case.

Continued loading past the limit the value of the change in deviator stress will decrease and will further become negative. This is due to the tendency of the soil to dilate. Since the test is a consolidated undrained test, the pore water at failure is (Anon, 2018) not measured hence the limit is not actually recorded during the trial. Also, the drained angle of friction of the clay decreases due to its decrease in plasticity under shearing. In general, it can be said that the residual shear strength of the clay (Anon, 2018) is defined.

During the shearing process, the behavior of the soil to increase the deviator stress could also be explained as the net loss in volume of the specimen under stress. Apart from this, the soil could initially be in a solid state or otherwise, in loose concentration. This discrepancies in the nature of the specimen cause the graphs to be irregular. The other reasons that may cause a substantial amount of errors experienced during the experiment is the parallax error involved in the measurement of the appropriate box size for the specimen by the researcher. The specimen holder in both tests could have experienced gradual changes in their dimensions over the years leading to inaccuracy during measurement.

The data collected from this test in however very useful regarding practical applications. The data could be used I the prediction of how the soil within a slope will react when submitted to shear forces by a building. This will enable various civil engineers to know where a building should be located on a given slope. Apart from this, the data will be used to determine the stability of the soil in a particular slope as to whether it is suitable for settlement. The soil samples taken from the various places could be used to develop a substantial knowledge about an area or region as to whether the soil could sustain the shear stresses from the adjacent slope.

Conclusion

In both scenarios, the direct shear stress and the triaxial tests are essential and have vast applications in the civil and structural engineering world. It is through the soil analysis that people can be able to determine whether the building can be brought up to a precise location. The stresses and strengths information of the soil can only be determined through these methods. The methods are simple to understand, and the reliability of their data is high. However, they do not allow the soil specimens to exhibit their extensive cracking and shearing behaviors since the shearing is only limited to specific dimensions. Other discoveries should be made to make the results entirely reliable.

References

Terzaghi, K., Peck, R.B. and Mesri, G., 1996. Soil mechanics in engineering practice. John Wiley & Sons.

Wan, C.F. and Fell, R., 2004. Laboratory tests on the rate of piping erosion of soils in embankment dams. Geotechnical Testing Journal, 27(3), pp.295-303.

Anon, (2018). [online] Available at: https://www.slideshare.net/asimayaz1/principles-of-geotechnical-engineering [Accessed 1 May 2018].

Geocities.ws. (n.d.). Dominic Trani - Soil Shear Strength Tests. [online] Available at: http://www.geocities.ws/dominic_trani/paper4.html [Accessed 1 May 2018].