CME 315 Lab 12

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Nov 24, 2024

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CME 315: SOIL MECHANICS AND LABORATORY Fall 2023 (Instructor: Professor Krishna Reddy) Laboratory 12: UNCONFINED COMPRESSION (UC) TEST Submitted by: Sammi Saba ID# 65405513 Department of Civil, Materials, and Environmental Engineering University of Illinois Chicago (UIC) November 15, 2023

Abstract The focus of this laboratory experiment, the Unconfined Compression (UC) Test, is to determine the unconfined compressive strength of cohesive soil, specifically clay. The primary objective is to calculate the unconsolidated undrained shear strength, a crucial parameter for assessing the bearing capacity of foundations and other engineering structures. Following the ASTM D2166 standard, the laboratory test involves preparing a cylindrical soil specimen, measuring its dimensions, and subjecting it to axial loading in a compression device. The resulting stress-strain relationship is used to determine the unconfined compressive strength and derive the undrained shear strength. The results obtained in this laboratory provide valuable insights into the mechanical behavior of cohesive soils under unconfined conditions. Introduction The unconfined compression (UC) Test, as outlined in ASTM D2166, serves as a crucial method for determining the unconfined compressive strength (q u ) of cohesive soils, particularly clay, under unconfined conditions. This experimental procedure is pivotal in geotechnical engineering as it provides essential data for calculating the undrained shear strength (s u ) of the soil. The undrained shear strength is a key parameter used in the assessment of foundation-bearing capacities for structures such as dams and foundations. The test helps engineers understand the soil's behavior under different loading conditions, aiding in the design and construction of structures. The procedure involves extracting a cylindrical soil specimen, measuring its dimensions, and subjecting it to axial loading while monitoring deformation and load. The resulting stress-strain curve obtained from this test enables the determination of critical parameters like unconfined compressive strength and cohesion, which are fundamental in evaluating soil stability and deformation characteristics over time. Methodology For this experiment: - We correctly followed ASTM D2166 in this experiment. The purpose, equipment, test procedure, and data analysis align with the ASTM guidelines. For this laboratory experiment, we used multiple trials at different points and as a result, our data had little to no room for error.

Results These were data results and calculations from the unconfined compression (UC) experiment: Diameter (d) =1.455 in = 3.696 cm Length (L 0 ) = 3.374 in = 8.57 cm Mass = 169.5 g Table 1: Moisture Content Determination Sample no. Moisture can number - Lid number 2B 8A/4-TL M C = Mass of empty, clean can + lid (grams) 11.6 g 11.0 g M CMS = Mass of can, lid, and moist soil (grams) 31.2 g 30.0 g M CDS = Mass of can, lid, and dry soil (grams) 28.2 g 27.4 g M S = Mass of soil solids (grams) 16.6 g 16.4 g M W = Mass of pore water (grams) 3 g 2.6 g W = Water content, w% 18.07 % 15.85 % Area (A 0 ) = 1.66 in 2 =10.71 cm 2 Volume = 91.78 cm 3 Wet density = =1.85 g/ cm 3 𝑀 𝑉 = 169.5 𝑔 91.78 𝑐𝑚 3 Water content (w%) = 15.85 % Dry density ( d ) = 1.597 g/ cm 3 ρ

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Table 2: Unconfined Compression Test Data Sample Deformation (mm) Strain (ε) Corrected Area (A’) Load (lb.) Stress (psi) 0 0 1.66 0 0 0.01 0.00296 1.665 12 7.21 0.02 0.00593 1.67 20.5 12.28 0.03 0.00889 1.675 28.5 16.84 0.04 0.0119 1.68 37.6 22.38 0.05 0.0148 1.685 48.5 28.78 0.06 0.0178 1.69 62.5 36.98 0.07 0.0207 1.695 79.8 47.08 0.08 0.0237 1.70 96.3 56.65 0.09 0.0267 1.705 112.5 65.98 0.10 0.0296 1.711 125.3 73.23 0.11 0.0326 1.716 141.5 82.46 0.12 0.0356 1.721 155.0 90.06 0.13 0.0385 1.726 167.7 97.16 0.14 0.0415 1.732 177.6 102.54 0.17 0.0504 1.748 193.9 110.93 0.18 0.0533 1.753 195.8 111.69 0.19 0.0563 1.759 198.9 113.08 0.20 0.0593 1.765 201.9 114.39 0.21 0.0622 1.77 203.7 115.08 0.22 0.0652 1.776 197.7 111.32 0.23 0.0682 1.781 185.2 103.99 0.24 0.0711 1.787 141.1 78.96

Using this graph we can obtain: Unconfined compressive strength (q u ) = 115.08 psi Undrained shear strength (s u ) = Cohesion (c) = = = 57.54 psi ? 𝑢 2 115.08 ?𝑠𝑖 2 Discussion The obtained results from the unconfined compression (UC) Test offer valuable insights into the mechanical properties of the cohesive soil under investigation, specifically clay. The stress-strain relationship derived from the experiment allows for the determination of critical parameters, notably the unconfined compressive strength (q u ) and undrained shear strength (s u ). In the data obtained, the unconfined compressive strength is found to be 115.08 psi. This parameter represents the maximum stress the soil can withstand in unconfined conditions, providing essential information for assessing its load-bearing capacity. Furthermore, the undrained shear strength (s u ) or cohesion (c), is calculated to be 57.54 psi. This parameter is crucial for understanding the soil's behavior under undrained conditions immediately after construction, providing engineers with essential data for designing foundations and structures that rely on the

soil's stability and load-bearing capacity. The data obtained through the UC test contribute to a comprehensive understanding of the soil's mechanical behavior, aiding in informed decision-making in geotechnical engineering applications. Conclusion In conclusion, the unconfined compression laboratory, conducted in accordance with ASTM D2166 standards, has provided essential data for understanding the mechanical properties of cohesive soils. The calculated unconfined compressive strength and undrained shear strength are crucial in assessing the soil's capacity to bear loads and resist deformation. The obtained results contribute to the body of knowledge in geotechnical engineering, aiding in the design and construction of foundations and structures. Overall, this laboratory experiment offers valuable insights into the behavior of cohesive soils under unconfined conditions, facilitating informed decision-making in engineering applications. Reference ● ASTM D 2166 - Standard Test Method for Unconfined Compressive Strength of Cohesive Soil

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