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Questions and Answers
What is the classification criterion for granular materials in the AASHTO system?
What is the classification criterion for granular materials in the AASHTO system?
Which plasticity index indicates that a soil is classified as clayey?
Which plasticity index indicates that a soil is classified as clayey?
In the AASHTO soil classification, what is the classification for soils in which more than 35% of particles pass through the No. 200 sieve?
In the AASHTO soil classification, what is the classification for soils in which more than 35% of particles pass through the No. 200 sieve?
Which grain size classification describes the fraction that passes through the No. 200 U.S. sieve?
Which grain size classification describes the fraction that passes through the No. 200 U.S. sieve?
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What is the significance of the coefficient of uniformity (Cu) in soil classification?
What is the significance of the coefficient of uniformity (Cu) in soil classification?
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What is the primary basis for the USDA soil classification system?
What is the primary basis for the USDA soil classification system?
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Which of the following particle sizes characterizes sand in the USDA classification?
Which of the following particle sizes characterizes sand in the USDA classification?
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What is the group symbol for inorganic clay in the USCS classification system?
What is the group symbol for inorganic clay in the USCS classification system?
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In the USCS classification system, soils with 50% or more passing through the No. 200 sieve are classified as:
In the USCS classification system, soils with 50% or more passing through the No. 200 sieve are classified as:
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Which symbol represents poorly graded soil in the USCS classification?
Which symbol represents poorly graded soil in the USCS classification?
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What information is NOT required for classifying soil according to the USCS?
What information is NOT required for classifying soil according to the USCS?
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What does the prefix G signify in the USCS soil classification system?
What does the prefix G signify in the USCS soil classification system?
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In the USDA soil classification, how many total classes are there?
In the USDA soil classification, how many total classes are there?
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What was the earliest method of soil classification based on?
What was the earliest method of soil classification based on?
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Why was the triangular classification diagram method found to be less suitable for geo technical engineering?
Why was the triangular classification diagram method found to be less suitable for geo technical engineering?
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Who developed a classification system considering soil size distribution and particle consistency?
Who developed a classification system considering soil size distribution and particle consistency?
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Which soil classification system is widely used by geotechnical engineers?
Which soil classification system is widely used by geotechnical engineers?
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What is a common feature of the USDA soil classification system?
What is a common feature of the USDA soil classification system?
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Which classification system is primarily used by state and county highway departments?
Which classification system is primarily used by state and county highway departments?
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What was a key development in soil classification by Arthur Casagrande?
What was a key development in soil classification by Arthur Casagrande?
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How are the soil classification systems grouped?
How are the soil classification systems grouped?
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What was C.F. Marbut's main emphasis regarding soil classification?
What was C.F. Marbut's main emphasis regarding soil classification?
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What was a criticism of the early soil classification systems developed by Marbut and the USDA?
What was a criticism of the early soil classification systems developed by Marbut and the USDA?
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What was the primary issue with the soil classification system in relation to its application by different scientists?
What was the primary issue with the soil classification system in relation to its application by different scientists?
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Which concept heavily influenced Marbut's classification of soils in 1935?
Which concept heavily influenced Marbut's classification of soils in 1935?
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What was the outcome of modifying the 1938 USDA classification system in 1949?
What was the outcome of modifying the 1938 USDA classification system in 1949?
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What was a continuing problem faced by scientists in soil classification?
What was a continuing problem faced by scientists in soil classification?
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How did the classes in both early soil classification systems relate to genetic concepts?
How did the classes in both early soil classification systems relate to genetic concepts?
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What was Marbut's perspective on the relationship between soil characteristics and examination?
What was Marbut's perspective on the relationship between soil characteristics and examination?
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Study Notes
Early Development of Soil Classification
- C.F. Marbut emphasized that soil classification should focus on morphology, not theories of soil genesis, because theories are constantly evolving.
- Marbut's classification from 1935 relied heavily on the concept of a "normal soil," which is a product of equilibrium where downward erosion keeps pace with soil formation.
- The USDA released a new soil classification system in the 1938 Yearbook of Agriculture.
- Both early classifications, Marbut's and USDA's, were qualitative, leading to ambiguity and inconsistencies in application.
- Neither system clearly linked the higher categories to mapping units like soil series and their subdivisions.
- Both systems reflected the qualitative soil genesis concepts of that time.
- The 1949 modification of the 1938 system highlighted the need for a new classification system that could be consistently applied by a wider range of soil scientists.
Soil Classification Methods
- Soil classification can be divided into two groups: one for engineering and one for soil science.
- The most common engineering classification systems are the USDA, USCS and AASHTO systems.
USDA Soil Classification
- The USDA system, adopted in 1938, is based on grain size distribution.
- The primary classifications are sand, silt, and clay.
- The system is further refined into 12 classes often displayed on a triangle diagram.
USCS Soil Classification
- This system, developed by Casagrande in 1948, categorizes soils into two broad groups: coarse-grained and fine-grained.
- Coarse-grained soils are gravelly and sandy with less than 50% passing a No. 200 sieve. They are labeled G (gravel) or S (sand).
- Fine-grained soils are 50% or more passing a No. 200 sieve and labeled M (inorganic silt), C (inorganic clay), or O (organic silt and clay). Peat, muck, and highly organic soils are labeled Pt.
- Other symbols are W (well-graded), P (poorly graded), L (low plasticity), and H (high plasticity).
- The system requires information about percentages of gravel, sand, silt and clay, uniformity coefficient (Cu), coefficient of gradation (Cc), liquid limit, and plasticity index.
AASHTO Soil Classification
- This system is mainly used by highway departments.
- It categorizes soils into seven major groups: A-1 to A-7.
- Groups A-1, A-2, and A-3 are granular materials with 35% or less passing the No. 200 sieve.
- Groups A-4, A-5, A-6, and A-7 are silt and clay-type materials with more than 35% passing the No. 200 sieve.
- The classification is based on grain size (gravel, sand, silt, and clay) and plasticity.
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Description
Explore the evolution of soil classification practices, focusing on the contributions from C.F. Marbut and the USDA. This quiz covers key concepts from different classification systems and their impacts on soil science. Test your knowledge on historical methods and the challenges faced in achieving consistency.
