Pavement Thickness Design (Group Index Method)

Pavement thickness kan tih hian Kan kawng neih te chhah zawng sawina a ni mai a, Kan kawng te hi a then a chhah em em laiin a then pan te te a siam a ni thung. Mi nawlpui chuan kawng that zawng chu a chhah dan a zirah ten kan ngai a, a dik na chen a awm rualin, kan mithiam zawk engineer te chuan heng kawng chhah zawng hi mumal takin an lo design thin a ni. Kawng chhah zawng (Pavement thickness) hi design dan hrang hrang a awm a, tunah erawh chuan Group Index Method in han zir chiang chhin phawt teh ang

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.

 Group Index kan tih hian kan sawi tum ber chu lei that zawng leh chhiat zawng kan teh na ti mai i la kan sawi sual awm lo e. AASHTO Soil Classification system tihian a sawi Range A-1(best soil) to A-8 (worst soil). Tin Group Index a zirin tihian a then hrang leh a ni “Group index values near 0 indicate good soils, while values of 20 or more indicate very poor soils. However, a soil that may be "good" for use as a highway subgrade might be "very poor" for other purposes, and vice versa”. Tin, IRC(Indian Roads Congress) an in nawlpui a vangin kan hriat pawlh loh turah ngai ang.

Awle, Group Index leh a tlangpui chu kan sawi tawh a, tunah a mainpoint ah i lut tawh ang hmiang..

Khing a chung a kan sawi zawng zawng khi ti chiang tur leh an design dan kan hriatfiah theih zawk nan example nen ka sawi dawn a ni

Pavement(kawng) kan design reng reng hian, kan kawng design a kal tur zawng zawng kan hriat hmasat ber a ngai a, chung zingah chuan a common leh hmang nasa ber motor(vehicle) kan hmang dawn a ni. 

"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"

Nitin a commercial vehicle 300 chuang kalna kawng i han design dawn teh ang hmiang. He kawng design tur a i mawmawh ber chu kawng i design na hmun tur a lei kha a ni, kha lei kha i la a nga, chung lei te chu a properties chiang tak a i hriat hnuah, a hnuai a reading kan neih  soil kan test atang khan a lo chhuak dawn a ni.

Soil portion passing 0.074mm seive, percent=50

Liquid Limit, percent =40

Plastic Limit, percent =20

Khing value pathum kan neih te khi Group Index Formula ah khan dahlut ta i la

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.

Kan value hmuh chhuah chu 6.57 a ni (G.I.= 6.57)

Kan value hmuh hi 6.75 a ni a AASHTO dan ah chuan soil chhe tak chu a ni lo a ni

  

Group Index value leh Graph kan neih atang Pavement thickness chu awlsam te in kan zawng thei tawh dawn ni.

A hnuai a Photo a ka dah graph hi ngun takin en ta i la

Group Index of Subgrade= 6.57,  Combine Thickness =47cm (For Heavy Vehicle)

Chutiang zelin Surface Thickness= 4 cm

Base= 26 cm

Sub base =17 cm kan nei thei ta a ni.

A chung a kan thil tih neuh neuh a zir leh soil properties a zir in Pavement thickness te hi an lo design zawk thin a ni.

Group Index Method hi empirical method pakhat ve mai a ni a, next ah chuan CBR( California Bearing Ratio) hmang a design dan kan zir leh dawn nia.

I hlawkpui ngei ka beisei..

Group Index 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:

1. Find out the Group Index Value(GI) of the soil.

1. Use the design charts to find out the thickness of the pavement and layers.

Finding GI Value : Now let's discuss Group Index(GI) first. 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, or we can use the charts

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.

The second method to find out the GI value is to use two charts whose numerical values added together to get the GI value.

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. 

You have follow the corresponding curve for the given traffic and for the one among the three different curves you can find the total value of the thickness of the pavement. Then there are two other curves, one to find out the thickness of the sub-base and one to find the thickness of the base course.

Limitation of Group Index method: Limitation of this method is that this is based only on the physical properties of the soil and does not consider the strength parameters.