Arizona Automotive Institute Transportation Officials Soil Classification Questions

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Arizona Automotive Institute

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1. Classify your soil based on the USCS system (see attached figures). Using the data from lab 3 Sieve # 20 30 40 50 60 80 100 120 200 pan d (mm) 0.85 0.6 0.425 0.3 0.25 0.18 0.15 0.125 0.075 mass of sieve (gm) 368.98 425.06 375.86 389.22 437.96 351.09 343.05 346.89 330.68 371.97 mass of soil sieve + soil (gm) 508.9 492.72 437.36 445.72 458.9 375.6 351.9 352.58 339.3 376.82 total mass= mass of soil (gm) 139.92 67.66 61.5 56.5 20.94 24.51 8.85 5.69 8.62 4.85 399.04 cumulative mass retained (gm) 139.92 207.58 269.08 325.58 346.52 371.03 379.88 385.57 394.19 399.04 cumulative percent retained (gm) 35.06 52.02 67.43 81.60 86.84 92.98 95.20 96.62 98.78 100 cumulative percent passing (gm) 64.94 47.98 32.57 18.41 13.16 7.02 4.80 3.38 1.22 0 We can see that the fines content is 1.22. Since 1.22 < 50%, we can conclude that the soil is not a fines soil. Therefore by looking at the graph we can determine the coarse content or CC and determine whether the soil is gravel or sand. However, since the GSD graph ends before the 4.75mm diameter, we can conclude that 98.78% of the soil is comprised of sand. Using the liquid limit that was found from lab 5, (LL=49.46%) and the Plastic limit given to us (PL=20%) we can find the plastic index which is (PI=29.46). The plastic index may be needed in the USCS flow chart. Using this USCS flow chart for sand, classify our soil. Since our fines content is less than 5%, we go up the top route and Calculate our coefficient of uniformity or Cu. According to our calculations, our Cu = 4.45 < 6. Thus we take the bottom route. This means that our soil is poorly graded and since we have no gravel content, our soil is poorly graded sand. 2. Classify your soil based on the AASHTO system (research required). We can also classify our soil using the AASHTO system with this chart by using our data for the % passing from the sieve analysis and with the Liquid Limit and Plasticity Index. AASHTO Soil Classification System Chart General Classification Group Classification Granular Materials (35% or less passing Silt-Clay Materials (>35% the 0.075 mm sieve) passing the 0.075 mm sieve) A-1 A-3 A-1-a A-1-b A-2 A-4 A-5 A-6 A-7 A-2-4 A-2-5 A-2-6 A-2-7 A-7-5 A-7-6 50 max 30 max 15 max … Sieve Analysis, % passing 2.00 mm (No. 10) (0%) 0.425 (No. 40) (32.57%) 0.075 (No. 200) (1.22%) … … … … … … … … … 50 max 25 max 51 … … … … … … … … min 10 35 35 35 35 36 36 36 36 min max max max max max min min min Characteristics of fraction passing 0.425 mm (No. 40) Liquid Limit (49.46) … Plasticity Index (29.46) 6 max Usual types of significant constituent materials stone fragments, gravel and sand General rating as a subgrade … 40 41 40 41 max min max min N.P. 10 10 11 11 max max min min fine silty or clayey gravel sand and sand excellent to good 40 41 40 41 min max min max 10 10 11 11 min max max min silty soils clayey soils fair to poor We first start off with the A-1 section, working our way down from the No. 10 Sieve all the way to the plasticity index. If our data meets the requirement, then we classify the soil there. If not, we move on to the right and redo the same process. For example, for A-1-a, our No. 10 sieve is 0% 41; Plasticity Index is 29.46 > 11. This means that our usual types of significant constituent materials are silty or clayey gravel and sand and that our general rating as a subgrade is good. Since the general rating as a subgrade of the AASHTO system of our soil is good and the USCS classification of our soil is poorly graded sand, this must mean that we have an error, most likely from our recorded observations of the GSD table from lab 3. Though the error may be small as Cu is almost greater or equal to 6 which may put or soil to well-graded sand which would match closer to the AASHTO rating, provided that our Cc is between 1 and 3. 3. Provide a table for each system detailing what values were needed for classification. USCS (Unified Soil Classification System) Fines content (F) 1.22% Sand content (S) 98.78% Gravel content (G) 0% Liquid limit (LL) 49.46% Plastic limit (PL) 20% Plastic index (PI) 29.46% Coefficient of uniformity (Cu) 4% ● Used for general geotechnical work ● 2-Symbol designation (e.g., SP, ML) ● Sieve analysis and Atterberg limits AASHTO System No. 200 sieve 1.22% No. 10 sieve 0% No.40 sieve 32.57% Liquid limit (LL) 49.46% Plastic limit (PL) 20% Plastic index (PI) 29.46% ● Used for roadways (subgrade) ● Designation: A1-A8 with subgroups ● Sieve analysis and Atterbergs 4. Discuss your soil classification and what it may mean for your “site.” 5. Discuss the differences between the two classification systems. As mentioned earlier, the main distinction between the UCSC and the AASHTO is that the USCS deals with general geotechnical work and has a two symbol classification. For example, soil that is well-graded sand will have the symbol SW. The initial letter is for the general soil type whereas the second is describing the soil. This is the gradation which is for coarse-grain soils which can be either well-graded or poorly graded depending on our coefficient of uniformity (Cu). As for fine-grained soils, we look at the atterberg limits in order to determine the plasticity. As for the AASHTO classification system, this is used for roadways and has A1-A8 classification with subdivisions. The two major divisions are broken up between the Granual materials and the Silty-clay materials. Once we take a look at the sieve analysis, it takes us to the types of constituent materials and the general grating as a subgrade. Going back to the sieve analysis, this is ultimately the similarities between the two classifications and how both deal with sieve analysis and atterberg limits. In summary, the USCS system uses the particle size analysis and plasticity characteristics of soils. In this system, the soils are classified into 15 groups. As for the AASHTO system, the soil classification system is based on particle size and plasticity characteristics. Soils are then classified into eight groups A-1 to A-8. Soils within each group are evaluated according to the group index (GI). 6. Calculations Calculations for Cu: d60 = sqrt(6*7) = 6.48 mm sqrt(1*2) = 1.41 d10 = sqrt(1*1.41) = 1.19 mm Cu = d60/d10 = 5.45 mm References ● AASHTO classification guides AASHTO Soil Classification - Video Lecture ● “Comparison: AASHTO & Unifical Soil Classification System: Soil Engineering.” Engineering Notes India, 16 May 2018, n-aashto-unifical-soil-classification-system-soil-engineering/44954.
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4. Discuss your soil classification and what it may mean for your “site”.
The soil is classified as poorly graded sand as per the unified soil classification system
(USCS). This means the soil is coarse grained in nature and the fraction of particles passing
through the 4.75 mm sieve opening and retained on 0.075 mm sieve opening is the highest.
This is more importantly the textural classification of soil as it is based on the particle size
distribution. The soil is also found to be poorly graded which implies that it has an uneven
distribution of particle size within 0.075-4.75 mm range. Poorly graded soils can imply that

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