Penetrometer: Lab Report
Group Number/Members:
Group 4: Milad Shafii, Mohammed Abdur Rahman, Rory Richardson, Ioulia Mantelian
Module Code/Name
CE1203 – Geotechnical Properties
Programme:
Civil Engineering BEng – Year 1
Lecturer(s):
Richard Freeman/Mike Hurst
Contents
1. Introduction..................................................................................................................2
2. Apparatus....................................................................................................................3
3. Procedure.................................................................................................................3/4
4. Data/Readings/Results/Observations.......................................................................5/6
5. Calculations.................................................................................................................6
6. Results.........................................................................................................................7
7. Discussion................................................................................................................7/8
8. Conclusion...................................................................................................................8
9. Recommendation for Further Work.............................................................................8

List of Figures
Figure 1.............................................................................................................................3
Figure 2.............................................................................................................................3
Figure 3.............................................................................................................................3
Figure 4.............................................................................................................................3
List of Tables
Table 1..............................................................................................................................5
Table 2..............................................................................................................................5
Table 3..............................................................................................................................5
List of Equations
Equation [1.1]....................................................................................................................6
Equation [1.2]....................................................................................................................6
Equation [1.3]....................................................................................................................6

1. Introduction:
During the experiment there was both a liquid limit and a plastic limit test. The idea of the plastic limit test was to take relatively moist clay at its plastic limit and weigh it before and after being in an oven for 24 hours. As for the liquid limit test the idea was to observe how deep a penetrometer could penetrate c sample of clay of a variety of moisture contents.

2. Apparatus:
Figure 2 Spatula
Figure 1 Pot

Figure 3 Scales Figure 4 Penetrometer
3. Procedure:
The experiment was split into two tests: * Plastic Limit test * Liquid Limit test
Plastic Limit Test
From the 4 samples of clay, the sample containing the lowest moisture content was used for the plastic limit test. A sample was extracted and rolled into a ball. This sample of clay was then separated into a number of pieces and individually each piece was rolled into a cylinder of approximately 3mm in diameter against a glass plate, at which point cracks became clear on the surface. The cracked cylindrical samples of clay were then placed in a previously weighed tin, which was weighed once again (with the weight noted down) with the clay inside. The tin was then placed inside an oven for approximately 24 hours to give time for all the water present in the clay to evaporate. Once removed from the oven the tin was weighed once again and the weight was noted down.
Liquid Limit Test
Beginning with the moistest sample of clay, using the spatula, clay was removed from the initial beaker it was present in and smothered into a small pot, firstly across the inside sides of the, to ensure no air gaps were present. After being filled the pot was placed under the penetrometer and the penetration test cone was lowered so it just barely touched the clay. The dial on the penetrometer was then read and recorded at which point the penetration test cone was released into the clay for exactly 5 seconds. The dial was then lowered to touch the top of the penetration cone and the figure shown was read once again and subtracted from the previous reading giving a distance of the penetration of the cone. This process was then repeated to minimise error. After the second test the top of the clay which had been penetrated was then extracted and placed in a weighed tin, which was weighed once again with the sample of clay inside. This test was repeated for all 4 samples of clay and once the test had been completed all 4 tins of clay were placed into the oven for 24 hours (the tins were all numbered so they would not get mixed up). Once the 24 hours had passed the weight of the tins were measured once more.

4. Data/Readings/Results/Observations:
- Plastic Limit Test Results Tin Number | Mass of empty tin (g) | Mass of tin plus “wet” soil (g) | Mass of tin plus “dry” soil (g) | 22 | 16.8 | 26.2 | 24.5 |
Table 1

- Liquid Limit Test Results Test Number | Penetration Reading 1 (mm) | Penetration Reading 2 (mm) | Average Penetration (mm) | Tin Number | Mass of empty tin (g) | Mass of tin plus “wet” soil (g) | Mass of tin plus “dry” soil (g) | 1 | 23.70 | 23.20 | 23.45 | 52 | 5.3 | 18.3 | 13.3 | 2 | 20.20 | 19.90 | 20.05 | 94 | 16.6 | 33.7 | 27.2 | 3 | 18.60 | 19.20 | 18.90 | 68 | 5.4 | 10.1 | 8.4 | 4 | 13.90 | 13.60 | 13.75 | 76 | 5.3 | 12.3 | 9.9 |
Table 2

Test Number | Average Penetration (mm) | Mass of “wet” soil (g) | Mass of “dry” soil (g) | Water Content (%) | 1 | 23.45 | 13 | 8 | 62.50 | 2 | 20.05 | 17.1 | 10.6 | 61.32 | 3 | 18.90 | 4.7 | 3 | 56.67 | 4 | 13.75 | 7 | 4.6 | 52.17 |
Table 3

The average penetration reading was figured out using the following equation:
Average Penetration= (Penetration 1+Penetration 2)2
[1.1]
The water content was figured out by using the following formula:
Water Content=(wet mass-dry mass)dry mass×100
[1.2]
To figure out the plasticity index the following formula is used:
Plasticity Index=Liquid Limit-Plastic Limit
[1.3]
5. Calculations
For each of the average penetration results the first and second penetration reading were added to one another and then divided by 2. So for instance with “Test Number 1” the first reading “23.70” and the second reading “23.30” were added up giving “46.90” and then divided by 2 giving an average reading of “23.45”.
The liquid limit of the clay is figured out by looking at the graph drawn and figuring out what the water content is when the penetration is 20mm. At 20mm the water content is 60%.
To figure out the plastic limit for the sample of clay used in Table 1 equation [1.2] has to be used where the plastic limit = water content. So the plastic limit is (9.4-7.7)/7.7x100.
The plasticity index is 60-22.08=37.92%.

6. Results:
By referring to the graph drawn we can establish that the liquid limit is 60%, as previously mentioned. Also by looking at the soil classification graph it comes to our attention that the soil used in the experiment was clay of a high plasticity.
7. Discussion:
The results extracted from the experiment indicate that the water content was not as varied between the soil samples as initially believed. This could be due to a number of reasons including the fact that the soil samples may have slowly dried as the experiment went on, or the fact that the water content was not consistent within the soil samples. On the other hand the penetration values differed which contradicts the initial suggestion made. Nevertheless there are other possibilities that can have caused this issue to arise such as the soil samples being placed in the oven for an inappropriate amount of time (they were only in for approximately 24 hours rather than the preferred but arguably unnecessarily 48 hours) or that when the test cone was released into the soil sample the pressure applied to the button that released the cone varied from one soil sample to the next, even though the task was carried out by the same individual. Or possible when the test cone was placed just barely above the soil sample, close enough so that it was touching, there could have been a slight difference in position from one sample to the next. Also the readings on the penetrometer may not have been precise. What however does seem the most strange is how the experiment was repeated to minimise human error, and as such indicates that the equipment/soil itself may not have been prepared or the equipment may have been incorrectly used. The expected results were rather a straight line of best fit through the origin. To confirm that the results were certainly incorrect they would have to be compared to that of other individuals experiments, in which if found that the graph is incorrect the experiment may have to be repeated. In terms of precision the apparatus could have been more precise, and some of the tasks given, such as lowering the test cone of the penetrometer so it barely touches the coil sample, could have been done by a qualified teacher rather than a student. However the plastic limit test seemed to provide results that were as expected, low. This indicates that the cause of the odd results can not be traced easily and if required the experiment will have to be repeated.
8. Conclusion:
As a whole the experiment did not provide any clear results on the given soil samples as the results and graph were not as expected.
9. Recommendation for Further Work:
Should this experiment be repeated it would be ideal to follow these steps to ensure better results: * A different piece of apparatus is used * The soil samples have moisture added to them directly before being used in the experiment, rather than being previously prepared (which was done to save time) * The tests should be repeated more than 2 times (3-5 times) to completely eradicate any form of human error * Greater care must be taken when the apparatus is use. * Soil samples should be placed into the oven within a very short while of having water added to them * Soil samples must be in the oven for longer than 24 hours, 48 hours is the preferable time