Page 1 FOUNDATION ANALYSIS AND DESIGN Module 1 (Lecture 2) GEOTECHNICAL PROPERTIES OF SOIL AND OF REINFORCED SOIL Topics 1.1 SOIL CLASSIFICATION SYSTEMS 1.2 AASHTO System ? Unified System ? Examples and Solutions 1.3 HYDRAULIC CONDUCTIVITY OF SOIL 1.4 STEADY-STATE SEEPAGE 1.5 FILTER DESIGN CRITERIA 1.6 EFFECTIVE STRESS CONCEPT Page 2 FOUNDATION ANALYSIS AND DESIGN Module 1 (Lecture 2) GEOTECHNICAL PROPERTIES OF SOIL AND OF REINFORCED SOIL Topics 1.1 SOIL CLASSIFICATION SYSTEMS 1.2 AASHTO System ? Unified System ? Examples and Solutions 1.3 HYDRAULIC CONDUCTIVITY OF SOIL 1.4 STEADY-STATE SEEPAGE 1.5 FILTER DESIGN CRITERIA 1.6 EFFECTIVE STRESS CONCEPT FOUNDATION ANALYSIS AND DESIGN SOIL CLASSIFICATION SYSTEMS Soil classification systems divide soils into groups and subgroups based on common engineering properties such as grain-size distribution, liquid limit, and plastic limit. The two major classification systems presently in use are (1) the AASHTO (American Association of State Highway and Transportation Officials) Systems and (2) the Unified Soil Classification System (also ASTM), the AASHTO classification system is used mainly for classification of highway subgrades. It is not used in foundation construction. AASHTO System The AASHTO Soil Classification System was originally proposed by the Highway Research Boardâ€™s Committee on Classification of Materials for Subgrades and Granular Type Roads (1945). According to the present form of this system, soils can be classified according to eight major groups, A-1 through A-8, based on their grain- size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are fine-grained materials. Peat, muck, and other highly organic soils are classified under A-8. They are identified by visual inspection. The AASHTO classification system (for soils A-1 through A-7) is presented in table 8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, the plasticity index is greater than the liquid limit minus 30. For qualitative evaluation of the desirability of a soil as a highway subgrade material, a number referred to as the group index has also been developed. The higher the value of the group index for a given soil, the weaker will be the soilâ€™s performance as a subgrade. A group index of 20 or more indicates a very poor subgrade material. The formula for group index, ???????? , is ???????? = ( ???? 200 - 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200 - 15)( ???????? - 10) [1.23] Where ???? 200 = percent passing no 200 sieve, expressed as a whole number ???????? = liquid limit ???????? = plasticity index Page 3 FOUNDATION ANALYSIS AND DESIGN Module 1 (Lecture 2) GEOTECHNICAL PROPERTIES OF SOIL AND OF REINFORCED SOIL Topics 1.1 SOIL CLASSIFICATION SYSTEMS 1.2 AASHTO System ? Unified System ? Examples and Solutions 1.3 HYDRAULIC CONDUCTIVITY OF SOIL 1.4 STEADY-STATE SEEPAGE 1.5 FILTER DESIGN CRITERIA 1.6 EFFECTIVE STRESS CONCEPT FOUNDATION ANALYSIS AND DESIGN SOIL CLASSIFICATION SYSTEMS Soil classification systems divide soils into groups and subgroups based on common engineering properties such as grain-size distribution, liquid limit, and plastic limit. The two major classification systems presently in use are (1) the AASHTO (American Association of State Highway and Transportation Officials) Systems and (2) the Unified Soil Classification System (also ASTM), the AASHTO classification system is used mainly for classification of highway subgrades. It is not used in foundation construction. AASHTO System The AASHTO Soil Classification System was originally proposed by the Highway Research Boardâ€™s Committee on Classification of Materials for Subgrades and Granular Type Roads (1945). According to the present form of this system, soils can be classified according to eight major groups, A-1 through A-8, based on their grain- size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are fine-grained materials. Peat, muck, and other highly organic soils are classified under A-8. They are identified by visual inspection. The AASHTO classification system (for soils A-1 through A-7) is presented in table 8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, the plasticity index is greater than the liquid limit minus 30. For qualitative evaluation of the desirability of a soil as a highway subgrade material, a number referred to as the group index has also been developed. The higher the value of the group index for a given soil, the weaker will be the soilâ€™s performance as a subgrade. A group index of 20 or more indicates a very poor subgrade material. The formula for group index, ???????? , is ???????? = ( ???? 200 - 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200 - 15)( ???????? - 10) [1.23] Where ???? 200 = percent passing no 200 sieve, expressed as a whole number ???????? = liquid limit ???????? = plasticity index FOUNDATION ANALYSIS AND DESIGN Table 8 AASHTO Soil Classification System General classification Granular materials (35% or less of total samples passing no. 200 sieve) A-1 A-2 Group classification A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 Sieve analysis (%) passing) No. 10 sieve 50 max No. 40 sieve 30 max 50 max 51 max No. 200 sieve 15 max 25 max 10 max 35 max 35 max 35 max For fraction passing No. 40 sieve Liquid limit (LL) 40 max 41 min 40 max Plasticity index (PI) 6 max Nonplastic 10 max 10 max 11 min Usual type of material Stone fragments, gravel, and sand Fine sand Silty or clayey gravel and sand Subgrade rating Excellent to good General classification Silt-clay materials (More than 35% of total sample passing no. 200 sieve) Group classification A-4 A-5 A-6 A-7 A-7-5 a A-7 b Page 4 FOUNDATION ANALYSIS AND DESIGN Module 1 (Lecture 2) GEOTECHNICAL PROPERTIES OF SOIL AND OF REINFORCED SOIL Topics 1.1 SOIL CLASSIFICATION SYSTEMS 1.2 AASHTO System ? Unified System ? Examples and Solutions 1.3 HYDRAULIC CONDUCTIVITY OF SOIL 1.4 STEADY-STATE SEEPAGE 1.5 FILTER DESIGN CRITERIA 1.6 EFFECTIVE STRESS CONCEPT FOUNDATION ANALYSIS AND DESIGN SOIL CLASSIFICATION SYSTEMS Soil classification systems divide soils into groups and subgroups based on common engineering properties such as grain-size distribution, liquid limit, and plastic limit. The two major classification systems presently in use are (1) the AASHTO (American Association of State Highway and Transportation Officials) Systems and (2) the Unified Soil Classification System (also ASTM), the AASHTO classification system is used mainly for classification of highway subgrades. It is not used in foundation construction. AASHTO System The AASHTO Soil Classification System was originally proposed by the Highway Research Boardâ€™s Committee on Classification of Materials for Subgrades and Granular Type Roads (1945). According to the present form of this system, soils can be classified according to eight major groups, A-1 through A-8, based on their grain- size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are fine-grained materials. Peat, muck, and other highly organic soils are classified under A-8. They are identified by visual inspection. The AASHTO classification system (for soils A-1 through A-7) is presented in table 8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, the plasticity index is greater than the liquid limit minus 30. For qualitative evaluation of the desirability of a soil as a highway subgrade material, a number referred to as the group index has also been developed. The higher the value of the group index for a given soil, the weaker will be the soilâ€™s performance as a subgrade. A group index of 20 or more indicates a very poor subgrade material. The formula for group index, ???????? , is ???????? = ( ???? 200 - 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200 - 15)( ???????? - 10) [1.23] Where ???? 200 = percent passing no 200 sieve, expressed as a whole number ???????? = liquid limit ???????? = plasticity index FOUNDATION ANALYSIS AND DESIGN Table 8 AASHTO Soil Classification System General classification Granular materials (35% or less of total samples passing no. 200 sieve) A-1 A-2 Group classification A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 Sieve analysis (%) passing) No. 10 sieve 50 max No. 40 sieve 30 max 50 max 51 max No. 200 sieve 15 max 25 max 10 max 35 max 35 max 35 max For fraction passing No. 40 sieve Liquid limit (LL) 40 max 41 min 40 max Plasticity index (PI) 6 max Nonplastic 10 max 10 max 11 min Usual type of material Stone fragments, gravel, and sand Fine sand Silty or clayey gravel and sand Subgrade rating Excellent to good General classification Silt-clay materials (More than 35% of total sample passing no. 200 sieve) Group classification A-4 A-5 A-6 A-7 A-7-5 a A-7 b FOUNDATION ANALYSIS AND DESIGN Sieve analysis (% passing) No. 10 sieve No. 40 sieve No. 200 sieve 36 min 36 min 36 min 36 min For fraction passing No. 40 sieve Liquid limit (LL) 40 max 41 min 40 max 41 min Plasticity index (PI) 10 max 10 max 11 min 11 min Usual types of material Mostly silty soils Mostly clayey soils Subgrade rating Fair to poor a If PI =LL-30, it is A-7-5. b If PI>LL-30, it is A-7-6. When calculating the group index for a soil belonging to groups A-2-6 or A-2-7, us only the partial group index equation relating to the plasticity index: ???????? = 0.01( ???? 200 - 15)( ???????? - 10) [1.24] The group index is rounded to the nearest whole number and written next to the soil group in parentheses; for example, ???? - 4 ? ? ? | Soil group (5) ? Group index Page 5 FOUNDATION ANALYSIS AND DESIGN Module 1 (Lecture 2) GEOTECHNICAL PROPERTIES OF SOIL AND OF REINFORCED SOIL Topics 1.1 SOIL CLASSIFICATION SYSTEMS 1.2 AASHTO System ? Unified System ? Examples and Solutions 1.3 HYDRAULIC CONDUCTIVITY OF SOIL 1.4 STEADY-STATE SEEPAGE 1.5 FILTER DESIGN CRITERIA 1.6 EFFECTIVE STRESS CONCEPT FOUNDATION ANALYSIS AND DESIGN SOIL CLASSIFICATION SYSTEMS Soil classification systems divide soils into groups and subgroups based on common engineering properties such as grain-size distribution, liquid limit, and plastic limit. The two major classification systems presently in use are (1) the AASHTO (American Association of State Highway and Transportation Officials) Systems and (2) the Unified Soil Classification System (also ASTM), the AASHTO classification system is used mainly for classification of highway subgrades. It is not used in foundation construction. AASHTO System The AASHTO Soil Classification System was originally proposed by the Highway Research Boardâ€™s Committee on Classification of Materials for Subgrades and Granular Type Roads (1945). According to the present form of this system, soils can be classified according to eight major groups, A-1 through A-8, based on their grain- size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are fine-grained materials. Peat, muck, and other highly organic soils are classified under A-8. They are identified by visual inspection. The AASHTO classification system (for soils A-1 through A-7) is presented in table 8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, the plasticity index is greater than the liquid limit minus 30. For qualitative evaluation of the desirability of a soil as a highway subgrade material, a number referred to as the group index has also been developed. The higher the value of the group index for a given soil, the weaker will be the soilâ€™s performance as a subgrade. A group index of 20 or more indicates a very poor subgrade material. The formula for group index, ???????? , is ???????? = ( ???? 200 - 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200 - 15)( ???????? - 10) [1.23] Where ???? 200 = percent passing no 200 sieve, expressed as a whole number ???????? = liquid limit ???????? = plasticity index FOUNDATION ANALYSIS AND DESIGN Table 8 AASHTO Soil Classification System General classification Granular materials (35% or less of total samples passing no. 200 sieve) A-1 A-2 Group classification A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 Sieve analysis (%) passing) No. 10 sieve 50 max No. 40 sieve 30 max 50 max 51 max No. 200 sieve 15 max 25 max 10 max 35 max 35 max 35 max For fraction passing No. 40 sieve Liquid limit (LL) 40 max 41 min 40 max Plasticity index (PI) 6 max Nonplastic 10 max 10 max 11 min Usual type of material Stone fragments, gravel, and sand Fine sand Silty or clayey gravel and sand Subgrade rating Excellent to good General classification Silt-clay materials (More than 35% of total sample passing no. 200 sieve) Group classification A-4 A-5 A-6 A-7 A-7-5 a A-7 b FOUNDATION ANALYSIS AND DESIGN Sieve analysis (% passing) No. 10 sieve No. 40 sieve No. 200 sieve 36 min 36 min 36 min 36 min For fraction passing No. 40 sieve Liquid limit (LL) 40 max 41 min 40 max 41 min Plasticity index (PI) 10 max 10 max 11 min 11 min Usual types of material Mostly silty soils Mostly clayey soils Subgrade rating Fair to poor a If PI =LL-30, it is A-7-5. b If PI>LL-30, it is A-7-6. When calculating the group index for a soil belonging to groups A-2-6 or A-2-7, us only the partial group index equation relating to the plasticity index: ???????? = 0.01( ???? 200 - 15)( ???????? - 10) [1.24] The group index is rounded to the nearest whole number and written next to the soil group in parentheses; for example, ???? - 4 ? ? ? | Soil group (5) ? Group index FOUNDATION ANALYSIS AND DESIGN Unified System The Unified Soil Classification System was originally proposed by A. Casagrande in 1942 and was later revised and adopted by the United States Bureau of Reclamation and the Corps of Engineers. This system is presently used in practically all geotechnical work. In the Unified System, the following symbols are used for identification. Symbol ???? ???? ???? ???? ???? ???????? ???? ???? ???? ???? Descripti on Grav el San d Sil t Cla y Organ ic silts and clay Peat and highl y organ ic soils High plastici ty Low plastici ty Well grad ed Poorl y grad ed The plasticity chart (figure 1.7) and table 9 shows the procedure for determining the group symbols for various types of soil. When classifying a soil be sure to provide the group name that generally describes the soil, along with the group symbol. Tables 10, 11 and 12, respectively, give the criteria for obtaining the group names for coarse- grained soil, inorganic fine-grained soil, and organic fine-grained soil. These tables are based on ASTM Designation D-2487. Table 9 Group Symbol for Soil According to the Unified Classification System [Based on Material Passing 3-in. (75-mm) Sieve] Major division Criteria Group symbol Coarse-grained soil ???? 200 < 5, ???? ???? = 4, 1 = ???? ???? = 3 GW ???? 200 > 50 ???? 200 < 5, ???? ???? < 4, and /or ???? ???? not between 1 and 3 GP Gravelly soil ???? 4 > 0.5 ???? 200 ???? 200 > 12, ???????? < 4, or Atterberg limits plot be low A line (figure 1.7) GM ???? 200 > 12, ???????? < 7, and Atterberg limits plot on or above A line (figure 1.7) GCRead More

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