Geotechnical Engineering Portfolio

Location Description

Location

Location of the sample was taken at a residential area off of Carolina Ave. in Fort Myers, Fl. At this location the sample came from the back yard of the house where a 3-4 inch-deep hole was extracted. The day prior to the collection of the sample at this location rain was observed around late afternoon. As for the day of the collection it was a clear sunny day as the sample was collected around 5:20 pm.

Sample Description

The soil sample that was extracted from the location stated above was retrieved by digging approximately 3-4 inches beneath the surface level. The soil that was obtained in the process consisted of some organic soil matter such as grass blades, roots, and leaves. Other inorganic materials such as rocks and gravel were present throughout the soil. For testing purposes, the organic and inorganic matter in the soil would not be needed therefore by using a screen and allowing the soil to sieve through produced a consistent texture of soil without any unwanted particles.To be noted since the soil was sifted prior to testing, lab results may differ to the soil characteristics at that location. When analyzing the sample visually the distinct color of the sample was to be medium to dark brown which would be expected when extracting soil only a few inches below the surface. When touching the soil a few observations could be made such as the grain size of the soil and as for this particular sample it could be classified as a coarse grained. The reasoning to classify it as coarse grained is because when touching the soil, it does not leave a dust residue on your fingers as might a fine-grained soil would. The moisture content of the sample was moderate as it would feel damp and cold to the touch but not overly filled with water to where it would be sticking to its surroundings or on to its self.

Sample

Figure 2 : Bulk sample of our soil

Pictures

Figure 1: Sieving out the roots/grass

Figure 3: Top view of soil

Raw Data

Figure 4: Raw data taken during SG test

Compiled Data

Water Content

Table 1: Water content data

Specific Gravity

Data & Sample Calculations

Table 2 : SG data

Discussion of Results

Validity of Results

When analyzing the specific gravity value that was obtained after performing lab and calculations show that the value falls outside the typical range of 2.65-2.80 for many common soils. A specific gravity of 2.46 is outside the range but that value can be justified by a few circumstances such as the specific type of soil and were it was extracted from before testing and also how accurate the test in the lab was performed. The test soil that was used could be categorized as a more organic soil since organic manner was found mixed in the sample when in the process of collecting the sample. The soil was taken from only about 2-4 inches below from the ground surface so that layer is typically known to be composed of organic soil.During the execution of the lab a sample size of 51.76 g was taken to conduct the procedure, during the steps some mass was lost during the transfer of the soil from the dish to the pycnometer. Lost soil mass was swept up and transferred back into the pycnometer though not all of the soil was able to be retrieved. Specific gravity indicates how much heavier a substance is compared to water and with the combination of organic soil and loss of mass due to transfer is a strong possibility for the specific gravity value to fall outside the accepted range of 2.65-2.80.

Pictures

Figure 9: Soil Mixed with water

Figure 8: Soil being transferred from dish pycnometer

Comments

Comments

As stated before the typical Specific gravity range for soils is to be around 2.65-2.80, however our soil produced a value that was lower then the typical range. Going into the lab it was to be expected to see a value out of the range since our soil is considered to be organic as it was sourced from 2-4 inches from the ground surface. With a starting mass of 51.76 g we cant guarantee that this was the actual amount during testing as we experienced difficulties when transferring soil from the dish to the pyconometer. Soil that had spilled out was swept up and placed back into pyconometer but not every particle could haven retrieved. under these circumstances we understand that the final value could be skewed but not to the point to where it would greatly effect any other laboratory test that required the use of specific gravity.

Raw Data

Figure 10: Raw data taken during grain size distribution

Compiled Data

Sieve Analysis

Data & Sample Calculations

Table 4: Complied sieve analysis data

Hydrometer Analysis

Table 5: Complied Hydrometer Analysis

Grain Size & Hydrometer Curve

Figure 13: Combined Sieve and Hydrometer curve

Cu & Cc Values

Cu & Cc Values for Soil

Figure 16: Combined sieve and hydrometer curve displaying particle diameter sizes

D10 = 0.21 mm

D30 = 0.34 mm

D60 = 0.52 mm

USCS Soil Classification

Figure 18: USCS Soil classification path

Figure 19: soil being placed into sieves to begin sieve analysis

Pictures

Figure 22: Agitating the solution

Figure 20: soil being mixed with sodium hexametaphosphate

Figure 21: pouring solution into hydrometer

Comments

Comments

The data that was collected and analyzed during the sieve analysis was the most accurate data within the grain size distribution lab. Hydrometer findings may not truly reflect the characteristics of the soil as the calculation that were performed were dependent on two tables that did not provide the specific gravity value that was needed and the actual hydrometer reading values did not satisfy everyone point needed therefore linear interpolation was need to be preformed to find the actual hydrometer readings.

Raw Data

Figure 23: Raw data recorded during compaction lab

Compaction Curve

Figure 24: Compaction Curve with degrees of saturation

Compaction

Table 8: Compiled data for compaction

Sample Calculations

Table 10: Sample calculations for compaction

Table 9: Data points used on compaction curve

Degree of Saturation

After sieve analysis and using the USCS classification chart a final classification of poorly graded sand was achieved. With knowing this information prior to compaction it allowed us to set some expectations before testing. One of them was that the soil should have a dry unit weight within the range of sands and gravels of about 14.7- 22.6 kN/m3. After compaction we did just that and had recorded a maximum dry unit weight of about 16.25 kN/m3 with a corresponding optimum water content of 15%. This had resulted in a degree of saturation of about 76.1% which holds up nicely to our compaction curve.

Degree of Saturation

Figure 25: Sample Calculations for Degree of saturation

Field Specifications

Field Specifications

Figure 26:Compaction curve displaying field specifications at 97 % gamma d max

Represented by the orange arrows on the compaction curve is this particular soil under field specification of 97% of max dry unit weight, thus would produce a of 15.67 kN/m2 with minimum and maximum range of water content at 13 and 17 percent respectively.

Comments

Comments

The soil compacted very well and provided a great looking compaction curve. Compaction effort was minimal as the soil had just enough moisture to allow the soil to begin to stick to itself and become more dense. The soil seemed to hold the moisture well as it didn't become soupy with the addition of water that was being mixed into the soil after each compaction test.

Figure 27: Compacted soil in mold

Figure 28: Weighing the compacted soil in the mold

Pictures

Figure 29: Hammer used for compaction

Visual Description

Results

The soil in Figure 30. can be classified primarily angular with some particles considered to be sub angular. Soil that did pass through the #200 sieve can be visually classified as round and were significantly smaller in diameter.

The soil is primarily a darker brown in color to the naked eye but with the help of a microscope small white sand particles become noticeable throughout the mixture of the soil. The soil had a distinct smell which is to be expected when studying a soil that is rich in organics, with the addition of water the aroma became stronger and almost to a point to where it wasn't an enjoyable smell. using the test tube test, in Figure 33 and 34 shows the process or particle settlement in the water. the cloudiness of the test tube is caused by all the fine particles still in suspension as all the coarse particle have settled to the bottom. within several minutes the test tube had cleared up and all soil particles had settled

Fine Grain Soil Classification

USCS Classification

Even though a plastic limit test was not conducted for this particular sample after considering the physical properties of the soil it was agreed upon to consider the soil to be silt and clays with a liquid limit less than 50 for this particular classification. The crushing characteristics or dry strength was considered to be low as it did require some applied pressure to break up chunks of dry soil. The reaction that the soil had after opening our hands and tapping the back resulted in a quick dilatancy. Without a proper liquid limit test being performed a decision on toughness couldn't be determined. When water was introduced to the soil it seemed like the soil rejected the water therefore required more force during mixing. By observing this we feel as though creating rolling snakes would have been a challenge so therefore none was selected for the toughness classification.

Discussion

Discussion

When considering the soil as a whole it was classified as a poorly graded sand. However, when studying just the fine grains it could be classified as silts and clays according to USCS. The findings from this lab follows the grain size distribution results. With the visual confirmation that was provided under the microscope shows why this particular soil is considered to be poorly graded sand as on size is noticeably dominate throughout the mixture. Observing the white particles was a surprising find since they are not noticeable from a standard viewing position.