Dirt Conclusion

The soil collected at the beginning of the semester was used as a semester long project. When the soil was first collected I would have initially classified it as a "sugar sand", which is a common name for sand in the area. The soil looked consistent in nature, light in color, and non organic. As the semester progressed, certain tests were performed to further classify the soil for what it was. A grain size distribution curve (Figure 1G) was created for that soil which verified that the soil was indeed mostly sandy in nature. This classification was later strengthened during the compaction test, the soil had a dry unit weight of 15.63 kN/M^3 which falls between the range of a typical sand soil type.

When the soil was initially described by visual inspection it was vague, not until the soil was inspected under a microscope was the true nature of the soil relieved. The soil was initially thought to be greyish brown, but was later determined to be a transparent version of that color. Organic matter seen in the soil was observed in the beginning of the semester, and was later verified under a microscope, although in a greater quantity than initially thought. A rough estimate of the percentages of particle sizes was determined during the visual classification portion of the testing which coincides with the values obtained from the grain size distribution curve. Further inspection of the soil under a microscope revealed that the particles had a very angular shape, something that was not noticed during the initial description of the soil when it was collected.

Both a hydrometer test and a stopper tube test showed that the larger particles (sand) settled out very quickly, followed by the fines, and organic matter floating on top of the water. These test showed a simple percentages of the particles making up the soil that could be compared to the grain sized distribution curve.

Overall the sand was determined to be mostly quartz, this seems reasonable due to the crystalline shape of the particles and the transparent characteristic. I just under four months, my definition of the soil has changed from  "sugar sand" at the beginning of the semester to a more refined definition of a quartz sand at the conclusion of the semester.

Visual Classification and Microscopic Analysis

For the visual classification portion of the lab several tests were performed to determine the type of soil being tested using the naked eye. The soil seemed to have a rounded (smoothly curves sides and no edges) shape, a slight organic odor, a light grey/brown color consistency, and depending on the area of the container a dry or moist condition. A stoppered tube test was preformed to gage the range of the particle sizes. It was noted that the soil was mostly sand because the particles immediately settled out during the test. Some fines were noticed during the testing and very few particles of organic matter were floating on the top of the water. The soil had a high dispersibility because it settled in under 4 seconds and was roughly 97% sand, 2.5% fines and .5% organic. Further testing also revealed that the hardness of the soil in question was low because it took little effort to break. Overall the soil was believed to be quarts due to the characteristics tested above.The soil being tested also had no dry strength, specimen crumbled when handled. From a toughness perspective the soil had none and a 3mm thick thread could not be rolled from the soil, making the soil nonplastic in nature.

During the microscopic analysis portion of this lab a microscope with magnification levels of 10X, 60X, and 200X were used to inspect the soil sample.At 10X (Figure 1M) magnification the soil appears to be a light brown in nature having a rounded particle shape, with particle sizes all relatively the same size. As the magnification was increased to 60X (Figure 2M) the color of the particles began to look more transparent, the edges of the particles became more angular, and the fines particles became visible. At this level of magnification organic particles could be seen and particles of various colors were observed. Finally at the 200X (Figure 3M) level the soil clearly had a distinct angular edge, the individual particles looked almost clear and the fines particles could clearly be seen between the sand particles.

The USCS classification of this soil would be a uniformly graded sand, this is made apparent in the lab due to the uniform size of the particles and the low content of fines and gravels. When comparing the USCS classification to the visual classification the soil being tested falls into the sand category based on the grain size distribution.

Figure 1M: 10X Magnification

Figure 2M: 60X Magnification

Figure 3M: 200X Magnification

Compaction of Soil

The experimental dry unit weight of the soil was determined to be 15.63 kN/M^3 (Figure 1C). This data was then compared to the know range of 14.7-22.6 kN/M^3 for sands and gravels from Table 1. This information corresponds to the assumption that the soil was mostly sand with an estimated Gs of 2.70 which shows that the accuracy and reasonableness of the values obtained in the lab are correct.

Figure 1C: Proctor Compaction Curve with Polynomial Trend line

 

Figure 2C: Original Lab Data Sheet
 

                                                                           Figure 4C: Sample Calculations

 

Grain Size Distribution

       After creating a particle size distribution curve (Figure 1G) and hand calculations (Figure 2G) from the data it was possible to determine that the soil being tested was mostly sandy in nature. The data showed that 0.09% of the soil was gravel, 99.3% was sand and 0.61% was considered fines. This coincides with the visual inspection during the hydrometer test. The larger bottom portion of the soil column was light colored sand and the smaller upper layer was made up of smaller particles with a darker color. The data calculated for the hydrometer curve (Figure 3G) was paced into the grain size distribution curve and shows that the soil is mostly in the sand category between the #4 and #200 sieves. Based on this grain size distribution curve the USCS would classify this soil as Sand.

 

         Figure 1G: Grain Size Distribution Curve With Hydrometer Curve

        Figure 2G: Sample calculations for Grain Size Distribution Curve.

Figure 3G: Sample Calculations for Hydrometer