lab 3

Andrew Chapman – asc2172Soil Mechanics - Wednesday Group

Soil Mechanics Laboratory ReportLab #2 – Atterberg Limits

I. INTRODUCTION:

The purpose of the Constant Head Permeability Test experiment is to determine the coefficient of permeability for an unknown sample of sand. The coefficient of permeability is a coefficient which helps describe the flow of water through soil. The coefficient of permeability was determined experimentally as well as analytically; these values were then compared.

II. DISCUSSION:

The constant head permeability test is a rather simple procedure. A cylinder of soil is soaked until fully saturated. Then it is attached to an apparatus such that tubing is coming out both ends of the cylinder, one for inflow and one for outflow. Water is then poured into the inflow tube at such a rate that the water height and therefore head pressure remains constant. As water flows out of the outflow tube it is collected while time is simultaneously measured. The height between the maintained height of the water in the inflow tube and the height of the outflow tube is then measured to determine the head difference. These variables can then be used to calculate the coefficient of permeability.

III. RESULTS:

The dry density of the unknown sample was determined to be 1.556 g/cm3. The void ratio of the unknown sample was determined to be 0.7035. The coefficient of permeability (standardized to 20 oC) was experimentally determined to be 0.0165135 cm/s. The data leading to this result is summarized in [Appendix A]. Using the Chaupis method, the coefficient of permeability was found to be 0.08119cm/s. Using the U.S. Department of Navy method, the coefficient of permeability was found to be 0.1 cm/s. Calculations are summarized in [Appendix B].


IV. QUALITATIVE ERROR ANALYSIS:

There were several sources of potential error in this laboratory experiment. The first source of error was in the maintenance of a constant head difference. It is very possible that the experimenters failed to pour water into the funnel at a rate that would have maintained a perfectly constant head pressure. This source of error could have been mitigated with a more complex apparatus including a constantly running water source and an overflow route. A second source of error was in the measuring of the flow. The same graduated cylinder was used for each test without being completely dried between trials. This would have led to inaccurate volume measurements. A third source of error can likely be found in the limitations of measuring the head difference with a human eye and a measuring tape, an imprecise combination.

V. SUMMARY:

The constant head permeability test experiment successfully yielded a value for the coefficient of permeability. However, this experimental value, 0.0165135 cm/s was rather different than the analytical values determined by the Chaupis and U.S. Department of Navy methods, 0.08119cm/s and 0.1 cm/s, respectively. The wide difference between the experimental and analytical values suggests that the possible sources of error mentioned in section IV of this report manifested themselves and affected the results.


[Appendix A]

Date Tested: 3/35/15Tested By: Andrew ChapmanSoil Description: Sand

Item Test 1-1 Test 1-2 Test 1-3Average Flow, Q (cc) 13 12 10Time of Collection, t (s) 40.49 40.25 30.03Temperature, T (deg. Celsius) 25 25 25Head Difference, h (cm) 12 12 12Area of specimen, A (cm) 26.42079422 26.42079422 26.42079422Permeability (cm/s) 0.020253424 0.018806944 0.021006203

Item Test 2-1 Test 2-2 Test 2-3Average Flow, Q (cc) 19 21 17Time of Collection, t (s) 35.2 40.08 32.75Temperature, T (deg. Celsius) 25 25 25Head Difference, h (cm) 22.5 22.5 22.5Area of specimen, A (cm) 26.42079422 26.42079422 26.42079422Permeability (cm/s) 0.018159862 0.0176276 0.017463819

Item Test 3-1 Test 3-2 Test 3-3Average Flow, Q (cc) 28 27 27Time of Collection, t (s) 32.53 30.14 30.82Temperature, T (deg. Celsius) 25 25 25Head Difference, h (cm) 37 37 37Area of specimen, A (cm) 26.42079422 26.42079422 26.42079422Permeability (cm/s) 0.017609879 0.018327487 0.017923117

Dry Density1.55564967

7

Void Ratio0.70346835

7

k0.01857537

1

k200.01651350

4

Chaupis k0.08118712

3U.S. Navy k 0.1


[Appendix B]

k = QL/Ahtk20 = k (nT/n20)kchaupis = 2.4622(D10

2 (e3/(1+e)))^.7825

lab 3

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