Geotech Lab 2 report cody

Georgia Institute of Technology School of Civil and Environmental Engineering Soil Mechanics Laboratory MEMORANDUM To: Date:2/1/2024 From: , Lab Partners: Subject: Grain Size Sample(s) Description (developed in Lab 1 – include in all reports) : Name: Piedmont Soil Source: Bulk Condition: Dry Fine-grained Visual Classification and Unified Symbol: ML, Red Remarks: No Odor Test Procedure (10 points) Due to the fine-grained nature of the sample, it was determined that a sieve analysis would be an ineffective method of classification so the a hydrometer analysis was run on the sample. A ~50 g sample of piedmont soil was measured and recorded while two 1000 cm³ cylinders were prepared. Before introducing the sample to the cylinders, two deflocculating solution were created, each using 5 g of sodium hexametaphosphate as a dispersing agent with 125 ml of deionized water, measured using a volumetric flask, and added to each cylinder. Cylinder 1, which will be referred to as the control cylinder was then filled with water till the water line met the 1000 ml line and using a stopper, the cylinder was inverted for at least 1 minute and the temperature was taken right after mixing and the hydrometer was placed in the cylinder to calculate the hydrometer reading ( R zero ) , which was used to find the meniscus correction ( R mc ) . After observing and recording the control values, the ~50 mg of soil was mixed with the dispersing agent in a mixing cup with water to fill 2/3 of the cup and placed in a mixer for 3 minutes. The well mixed mixture was transferred to the remaining 1000 cm³ cylinder and mixed by inversion using the rubber stopper for an additional minute. The hydrometer was added immediately after and the readings were recorded at times 30 seconds, 1 minute, and 2 minutes without disruptions to the configuration. Following the 2-minute reading, the hydrometer was taken out and stored in the control cylinder and placed back in 30 seconds before each additional reading at 4 minutes, 8 minutes, 15 minutes, 30 minutes, and 1 hour and each reading was recorded. After which, following the ASTM D422 table 1 and 2, specific gravity was calculated as well as effective depth, L, using the data from the hydrometer. Test Results (20 points)

The lab started with calibrating the data in order to ensure accuracy, thus the zero correction, R zero , and was found and the meniscus correction R mc was found, 3.5, and 0.5 respectively. R mc was found using the height of the meniscus subtracted from R zero . This data was then applied to the hydrometer reading, R, to find the R temp and the corrected reading using equation 1 and equation 2, which was then applied to equation 3 to find the actual reading of the hydrometer. From there, enough data was present to find percentage finer of the particles, equation 4, as well as particle diameter, equation 3. The data acquired from the 4 equations were recorded into table 1 and the distribution curve was plotted in figure 1 with diameter, mm, plotted on a log scale in the x- axis, and percent finer, %, in the y-axis. Equation 1: Hydrometer reading of temperature R temp = 1000 ( 0.99823 − ρ w − 0.000025 ( T − 20 ) ) 0.41 = 1000(0.99823 – 0.99777- 0.000025 ( 22 − 20 ) ¿ * ρ w data is in appendix table 1. Equation 2: Hydrometer correction equation R corr = ( R + R mc ) − R zero + R temp 44.9= (45+3) - 3.5 + 0.41 Equation 3: Actual Reading R a = R + R mc 48=45+3 Equation 4: Percent Finer P = R corr α w ∗ 100 89.8 = (44.91*1)/50 * 100 * W = weight of soil = 50 g * α data, appendix equation 1 Equation 4: Stokes’ Law: Particle Diameter D = K √ L / t 0.0546 = 0.01332 √ 8.4 / .5 *L values, appendix table 2 Table 1: Hydrometer Test Data Time (min) Hydrometer Reading R Temp (° C) Corrected Reading R corr Actual Reading R a K [Table 1] L (cm) [Table 2] P (%) D (mm) 0.5 45 22 44.91 48 0.01332 8.4 89.82 0.054596 1 43 22 42.91 46 0.01332 8.8 85.82 0.039514 2 40 22 39.91 43 0.01332 9.6 79.82 0.029183 4 34 22 33.91 37 0.01332 10.2 67.82 0.02127 8 29 22 28.91 32 0.01332 11.1 57.82 0.01569 15 24.5 22 24.41 27.5 0.01332 11.8 48.82 0.011814 30 21 22 20.91 24 0.01332 12.4 41.82 0.008564 60 18 22 17.91 21 0.01332 12.9 35.82 0.006176

hydrometer sampling may introduce an error because of prolonged reading time” (Brown et al. 1998). The article highlights a large issue that was also observed in the experiment, where during the times between recording, after placing the hydrometer into the sample cylinder, the hydrometer would bounce up and down for a period of time, sometimes past the times that were recorded, thus resulting in inaccurate, possibly lower or higher R, data. Additionally, a longer reading time could mimic the effect of a diminishing sedimentation velocity, thus resulting in lower R values. The experiment was conducted under the assumption that the soil was a fine-grained soil, and knowing the particle distribution is an important factor when it comes to understanding the properties of fine-grained soils. For example, for the data from the hydrometer test, it is possible to determine the percentage of silt and clay particles, which can affect many decision factors in an engineering and construction perspective, with silts being slightly larger, ranging from 0.002 to 0.05 mm, and clays being smaller than 0.002 mm. Knowing whether a soil is silt dominated or clay dominated allows engineers to determine the water permeability of the soil as well as the retention ability, which would in turn allow for them to determine if the soil can support structures. And as addressed above, knowing which soil type dominates the sample could allow for predictions on soil movement as well as structural support from the soil. The idea of water retention ability of soil and water permeability also relates to why the mixture had to be introduced to a dispersing or deflocculating agent. Due to the heavier clay nature of the sample, this indicates that there are higher natural attractive forces between the particles that require being broken up. Thus, in order to ensure accurate data where the particles are not condensed into clumps, the use of a deflocculation agent is crucial to break up the bonds that hold the particles together and allow for an accurate data set of grain size distribution. Additionally, during the experiment, it was crucial that the hydrometer was removed between long periods of data observation due to the disruption of particle settling in the cylinder. If the hydrometer had stayed in the test cylinder, particles would have settled onto the hydrometer or would not have settled to the bottom in accurate time due to the blockage caused by the hydrometer and led to inaccurate data, which would have depicted a much higher rate of clay particles in the solution. Concluding Remarks (10 points) Overall, the experiment visualized how varying particles sizes affected density and buoyancy and how the data could be applied to real world classifications. Furthermore, the experiment highlighted the importance of understanding the different properties of clays and silts and how they react especially due to their natural bonds with water. The experiment focusing on soil particles smaller than 75 microns, emphasized the necessity of the hydrometer test over traditional sieve analysis for precise results, as well as Stokes' Law and specific gravity in calculating particle distribution and density, leading to the conclusion of a higher clay content in the soil sample. References (10 points) Brown, Dan A. et al. “Comparison of strength and stiffness parameters for a Piedmont residual soil.” (1998). F. G. Bell & C. A. Jermy (1994) Building on Clay Soils which Undergo Volume Changes, Architectural Science Review, 37:1, 35-43, DOI: 10.1080/00038628.1994.9697327 A.S.T.M. Standard D422-63, 1998 “Standard Test Method for Particle-Size Analysis of

Soils,” ASTM International, West Conshohocken, PA. Appendix (10 points) Table 1:Density of Water Table Table 2: Effective Depth based on Hydrometer

Equation 1: G s = 2.65 α = 1.65 G s 2.65 ( G s − 1 )