Soil Sample Collection and Analysis

INTRODUCTION

Accurately collecting, observing, analyzing, and recording soil samples is an important part of any fieldwork related to geology, whether it is simply recording data about a physical location or to assess a piece of land’s worthiness to host projects, such as engineering or agricultural. This experiment employed basic observation techniques and the use of content vocabulary to provide a basic but scientifically accurate description of a soil sample taken on Tuesday, October 1, 2013. The objectives of the experiment were as follows:

1. Use sensory observations and specific terminology to classify soil samples taken.

2. Reflect upon the soil analysis method to gain a greater understanding of the scientific method, particularly in how it relates to practical geology and fieldwork.

EXPERIMENTAL PROCEDURE

The procedure for the experiment was carried out in accordance with the principles set forth by the class and the particular assignment.

1. Materials—clean garden shovel; 8 oz. and 16 oz. cups for soil samples; water and clean, transparent plastic bottle for performing the “jar test;” gloves; hand lens; trowel; hammer. These instruments were used to collect and analyze the samples.

2. Procedure—A suitable spot for collecting a sample was located on Tuesday, October 1. The shovel was used to break through the subsurface layers of dirt in order to collect a sample in accordance with the guidelines of the assignment. Once the shovel had reached a depth of roughly 10,” the 16 oz. cup was filled with soil. It was emptied by half into the 8 oz. cup, and both were evaluated for uniformity to one another. Once it had been determined the sample was representative of the soil in the area, the water, bottle, and some of the soil sample were used to perform the jar test. Afterward, remaining samples were examined using the hand lens to determine properties and criteria reported below and as outlined in the lab assignment.

RESULTS

The sampled soil was silty sand (SM) with organic fines—10% fine, hard, subangular gravel; 65% coarse to medium hard subrounded sand; and 25% organic and silt dark brown to black nonplastic fines with low dry strength and slow dilatancy; moist; maximum size coarse sand. No cobbles or boulders were found in the sample, and the jar test gave the percentage of gravel, sand, and fines. Upon inspection after the shovel had been removed, the soil was observed to be laminated and consist of two layers, a very thin, roughly 2 mm layer of gravel and sand, followed by a layer of sand and fines.

Using the hand lens and the unaided eye, particle size ranges were determined to be fine gravel, fine to medium sand with the largest but smallest percentage amount being coarse. Gravel angularity was subangular and through the use of the hand lens, sand was determined to be subangular and subrounded. Particle shape was not relevant, as the largest gravel was still less than 3” in any dimension. The maximum particle size were gravel pieces that were less than ½” in diameter. Hardness of coarse sand and gravel was medium to strong. Gravel fractured when struck and the sand fractured and powdered. The plasticity of fines were nonplastic to low. The dry strength was low to medium, as moderate pressure was needed to cause the soil to break and crumble into pieces and some powder. The dilatancy was determined to be none to slow after squeezing the sample and slapping the sample between the palms created an increased sensation of dampness on the skin but visible water was difficult to discern. The toughness was low to medium, as it took somewhere between light and medium pressure to roll the thread to its plastic limit, and there was not much stiffness to the thread or lump. The color of the soil was brown and dark brown and reddish brown. Gravel was mostly white, and the sand was brown and reddish brown. The odor had some organic and earthy smell to it but was not as pungently fecund as garden soil - indicating possible chemical contaminants rooted in the soil. The moisture content was moist, with some liquid noticeable, especially upon squeezing.

DISCUSSION

Having found vegetation in the area where soil was collected, it was expected that the soil sample would have some organic fines in it, and the topsoil indicated the presence of sand and gravel in the substrata. Thus, initial expectations about what the soil sample would yield were confirmed. The geological formation of the area observed suggests that the soil samples in other nearby test sites would likely be similar to what was found here.

CONCLUSIONS

The experiment yielded the following conclusions:

1. The soil in the test area is predominantly silty sand with organic fines.

2. Physical observations using sensory data including touch, smell, and sight can yield significantly detailed reports about soil; however, calculations for composition is rudimentary and estimated.