The document discusses different methods of pavement design, focusing on the Group Index method. This empirical method involves determining the Group Index value of soil through properties like particle size, liquid limit, and plasticity index. This value is used along with traffic volume on design charts to find the required pavement thickness and layer thicknesses. An example is provided to demonstrate determining the Group Index for a given soil and using the design chart to identify pavement structure for heavy traffic conditions.
The document discusses different methods of pavement design, focusing on the Group Index method. This empirical method involves determining the Group Index value of soil through properties like particle size, liquid limit, and plasticity index. This value is used along with traffic volume on design charts to find the required pavement thickness and layer thicknesses. An example is provided to demonstrate determining the Group Index for a given soil and using the design chart to identify pavement structure for heavy traffic conditions.
The document discusses different methods of pavement design, focusing on the Group Index method. This empirical method involves determining the Group Index value of soil through properties like particle size, liquid limit, and plasticity index. This value is used along with traffic volume on design charts to find the required pavement thickness and layer thicknesses. An example is provided to demonstrate determining the Group Index for a given soil and using the design chart to identify pavement structure for heavy traffic conditions.
The document discusses different methods of pavement design, focusing on the Group Index method. This empirical method involves determining the Group Index value of soil through properties like particle size, liquid limit, and plasticity index. This value is used along with traffic volume on design charts to find the required pavement thickness and layer thicknesses. An example is provided to demonstrate determining the Group Index for a given soil and using the design chart to identify pavement structure for heavy traffic conditions.
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METHODS OF PAVEMENT DESIGN
• 1 . GROUP INDEX METHOD (EMPIRICAL)
• 2. C- VALUE METHOD (EMPIRICAL) • 3. CALIFORNIA BEARING RATIO METHOD (EMPIRICAL) • 4. TRIAXIAL TEST METHOD (SEMI- THEORETICAL) • 5. McLEOD METHOD (EMPIRICAL) • 6. BURMISTER METHOD (THEORETICAL) A.)GI METHOD OF PAVEMENT DESIGN • Group Index method of flexible pavement design is an empirical method which is based on the physical properties of the soil sub- grade. • To design the thickness of the pavement you have to go through the following steps: Find out the Group Index Value(GI) of the soil. Use the design charts to find out the thickness of the pavement and layers. Finding GI Value • Group Index is a number assigned to the soil based on its physical properties like particle size, Liquid limit and plastic limit. It varies from a value of 0 to 20, lower the value higher is the quality of the sub-grade and greater the value, poor is the sub-grade. • To find out the value of GI we, can either use the following equation, GI = 0.2a + 0.005 a.c. + 0.01b.d where, • a= percentage of soil passing 0.074 mm sieve in excess of 35 percent, not exceeding 75. • b= percentage of soil passing 0.074 mm sieve in excess of 15 percent, not exceeding 55. • c= Liquid limit in percent in excess of 40. • d= Plasticity index in excess of 10. Using design charts to find the thickness • Once the GI value is found next we can use the design charts given by IRC(Indian Roads Congress) to find out the thickness of the pavement and its thickness of various layers. • Charts are prepared based on the GI value and one can find the thickness of the pavement to be designed for different traffic volume. • Traffic volume is classified in three categories as Light, Medium and Heavy. When nos. of vehicles per day is less than 50, this is light traffic, greater then 50 and less than 300 is medium and greater than 300 is classified as heavy traffic. Group index value ranges of different soil:- • For good soil – 0 to 1 • For fair soil – 2 to 4 • For poor soil – 5 to 9 • For very poor soil – 10 to 20 DESIGN CHART PROBLEM:- • A sub-grade soil has the following peoperties: Soil passing 75 micron sieve = 60 percent Liquid limit = 65 percent Plastic limit = 45 percent Design the pavement section bt group index method for heavy traffic with over 400 commercial vehicles per day. Solution: Group Index = 0.2a+0.005ac+0.01bd here, a = 60 – 35 = 25 b = 55 – 15 = 40 c = 60 – 40 = 20 d = 30 – 10 = 20 G.I. = 0.2x25 + 0.005x25x20 + 0.01x40x20 = 5 + 2.5 + 8 = 15.5. Say 16 By using Design Chart Thickness of sub-base >Combined thickness of surface, base and sub-base courses = 57 cm For heavy traffic, Therefore, Thickness of surface and base courses = 57 – 27 = 30cm