Geomechanics Lab Report

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  • Topic: Particle size distribution, Atterberg limits, Soil tests
  • Pages : 10 (2403 words )
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  • Published : March 26, 2013
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The main intention of this investigation was to determine the various stages of the Atterberg Limits. These included the liquid limit test (LL), plastic limit test (PL), plastic index test (PI) and linear shrinkage (LS) of a soil sample provided by the administration. This was then followed by a sieve analysis to determine the particle size distribution of another soil sample so that a suitable classification in both situations could be made in accordance with the Australian Standards AS1726 - 1993.

Procedure (Sample preperation)
On commencement of the experiment, each group was provided with two parts of 500grams of soil retrieved from the field and then oven dried by the experiment supervisor. One part of the soil sample was coarse grain gravel for the particle size distribution chart and sieve analysis, whilst the remaining 500 grams of soil was of fine grained fraction.

* Preparation of Coarse Grained Fraction
During this procedure the mass of 500grams of soil was recorded and soaked in water for duration of 24 hours. This was then followed by placing the soil sample into a 0.075mm mesh sieve and the entire fine particle was washed away using running tap water and a small spray bottle until the water had started running clear. The sieved sample was then transferred in a tray which was again put into the oven at 100 degrees for 24 hours.

* Preparation of Fine Grained Fraction
The remainder of the 500 grams of the sample was then sieved through a 0.425 mm mesh sieve and the contents collected. This procedure was done until approximately 150 to 200grams of material was successfully passing sieve.

Procedure (Sieve Analysis)
This procedure involved the sieve analysis of the coarse fraction. This involved weighing the mass of the oven dried coarse grained fraction so that we are able to determine the particle size distribution. For this experiment the mass of coarse fraction used was 312.10 grams. This was then followed by arranging the sieves from top to bottom in order from larger gapped mesh in the sieve to the smaller one (i.e. 37.5mm to 0.075mm) and then pouring the sample in the top sieve whilst shaking it for approximately 10 minutes. This provided mechanical energy to the soil allowing for it to pass all the sieve layers.

The next procedure involved recording the soil mass that had accumulated on each sieve and the bottom pan. Furthermore the percentage of original mass retained and cumulative passing % vs. particle size plot has been constructed as shown in Appendix A. As shown in the plot it can be noted that the results obtained were not accurate enough for the effective size values of D_10 and D_30 to be calculated. Yet the effective size D_60 was able to be found and was shown to be 1.1 mm as shown in the particle size vs percentage passing table in appendix A.

Due to the fact that all effective size values have not been able to be attained from the graph, the uniformity coefficient C_u and the coefficient of curvature C_c were not able to be calculated. Yet if they could be then they would be calculated using these equations:

where CU=Coefficient of Curvature
Cc=Coefficient of Curvature

All values recorded have been further discussed in the results section of this report.

Procedure (Atterberg Limits determination)

* Liquid Limit (LL)
The liquid limit test west performed on the fine Sandy soil over the course of two sessions to determine the water content (percentage) at the point when the soil started to behave with liquid qualities. This test procedure involved gradually adding water to a round well created in two thirds of the soil sample on a glass plate. Then using two spatulas the sample was mixed until a smooth paste was formed. This was then followed by placing a small amount of the sample into the liquid limit device and leveling it horizontally using the spatula to create a smooth surface.

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