Grameen Sampark Final April 0... - pmgsy
Grameen Sampark Final April 0... - pmgsy Grameen Sampark Final April 0... - pmgsy
18 Subgrade Failure Criterion The basic design thickness in the case of low-volume roads is the thickness of unbound granular material, which will limit the vertical compressive strain on top of the subgrade to an acceptable level. The strain induced in the subgrade by moving wheel load is mostly elastic (recoverable). However, the accumulation of the irrecoverable part of strain leads to permanent deformation in subgrade. The permanent deformation manifests at the surface of the pavement as rutting in the wheel paths, although due to inherent variability of the subgrade and pavement materials and the construction techniques, surface roughness develops along with rutting. Performance Criteria Addopted By Different Organizations AustRoads Design for granular pavements with thin bituminous surfacing [2 3] The limiting strain criterion for the subgrade is given by Eq. 1. It was derived by applying mechanistic procedure to a range of pavements. Where, 7.14 N = [8511/ µ ] (1) µ Grameen Sampark = vertical compressive strain (microstrain) at the top of the subgrade N = allowable number of repetitions of the strain before unacceptable level of rutting develops. Implicit in the design procedure for granular pavements with thin bituminous surfacing, is a terminal condition which is considered to be unacceptable and hence signifies the end of life of the pavement. The terminal condition is considered to be an average rut depth of about 20mm, and terminal roughness about three times the initial roughness. AASHTO Low Volume Road Design Procedure [1] The low-volume road design procedure used by AASHTO is based on lower level of reliability (50%) because of their low usage and associated low level of risk. Predicted future traffic, seasonal resilient moduli of roadbed soil, elastic modulus of aggregate base and subbase layer, design serviceability loss, allowable rutting and aggregate loss (GL) of surface course are the main input for the design of low volume roads. Common values for terminal serviceability index are Pt=2.0. For minor highways like aggregate surfaced roads, where funds or economy is the main factor, the design is done by reducing the traffic or design life rather than reducing the terminal serviceability to a number lower than 2.00. Aggregate loss due to traffic and erosion should be considered in the design and this may be calculated using any of the following equations 2, 3 and 4. According to a study by University of Texas at Austin: Where, GL = 0.12 + 0.1223 (LT) (2) GL = Total Aggregate loss in inches; LT = Number of loaded trucks in thousands Another study in Brazil formulated the following equation: GL = (B/25.4)/ (0.0045LADT + 3380.6/R + 0.467G) (3)
Where, GL = Total Aggregate loss in inches during the period of time being considered; B = Number of blading during the period of time being considered; LADT = Avg. daily traffic in the design lane; R = Avg. radius of curve, in feet, and; G = Absolute value of grade, in percent British study done in Kenya is more applicable to areas with little truck activity and is given below: Where, AGL = 2 2 2 [T /(T + 50] * f (4.2 +0.092T +0.889R + 1.88VC) (4) AGL = Annual aggregate loss, in inches; T = Annual traffic volume in both directions, in thousands of vehicles; R = Annual rainfall, in inches; Pradhan Mantri Gram Sadak Yojana VC = Average percentage gradient of the road, and f = 0.037 for lateritic gravels; 0.043 for quartzite gravels, 0.028 for volcanic gravels, and 0.059 for coral gravels. Rutting is bound to occur in average surfaced roads, and is considered as performance criteria for these roads. The typical value of allowable rut depth for designing an aggregate surfaced road falls between 1.00 and 2.00 inches. Design charts are available to estimate the required thickness of aggregate surfaced roads for low volume roads. Vermont Agency of Transportation [4] procedure for the design of low-volume pavement structures is based on the 1993 AASHTO Guide for Design of Pavement Structures. The following performance indicators in terms of PSI were used: For paved roads, initial PSI = 4.0 and terminal PSI = 2.0 and for unpaved roads, initial PSI = 4.0 and terminal PSI = 1.0 Grameen Sampark 19
- Page 2 and 3: In this Issue Editorial 3 Potential
- Page 4 and 5: 4 Potential Applications of Interlo
- Page 6 and 7: 6 Interlocking Concrete Block Pavem
- Page 8 and 9: 8 materials used for production of
- Page 10 and 11: 10 Construction of Sub grade This i
- Page 12 and 13: 12 Typical Pavement Compositions Ty
- Page 14 and 15: 14 Guidelines for the use of In
- Page 16 and 17: 16 layers due to repeated applicati
- Page 20 and 21: 20 A maximum of 50mm rut depth was
- Page 22 and 23: 22 Stabilization of Soil Subgrade w
- Page 24 and 25: 24 Changes in Cohesion and Direct
- Page 26 and 27: 26 Increase in the C.B.R. value is
- Page 28 and 29: 28 Laboratory Test (Under Vertical
- Page 30 and 31: 30 Apart from the above, both faces
- Page 32: News in Brief General Body Meeting
Where,<br />
GL = Total Aggregate loss in inches during the<br />
period of time being considered;<br />
B = Number of blading during the period of<br />
time being considered;<br />
LADT = Avg. daily traffic in the design lane;<br />
R = Avg. radius of curve, in feet, and;<br />
G = Absolute value of grade, in percent<br />
British study done in Kenya is more applicable to areas<br />
with little truck activity and is given below:<br />
Where,<br />
AGL =<br />
2 2 2<br />
[T /(T + 50] * f (4.2 +<strong>0.</strong>092T +<strong>0.</strong>889R +<br />
1.88VC) (4)<br />
AGL = Annual aggregate loss, in inches;<br />
T = Annual traffic volume in both directions,<br />
in thousands of vehicles;<br />
R = Annual rainfall, in inches;<br />
Pradhan Mantri Gram Sadak Yojana<br />
VC = Average percentage gradient of the road,<br />
and<br />
f = <strong>0.</strong>037 for lateritic gravels; <strong>0.</strong>043 for<br />
quartzite gravels, <strong>0.</strong>028 for volcanic<br />
gravels, and <strong>0.</strong>059 for coral gravels.<br />
Rutting is bound to occur in average surfaced roads, and<br />
is considered as performance criteria for these roads.<br />
The typical value of allowable rut depth for designing an<br />
aggregate surfaced road falls between 1.00 and 2.00<br />
inches.<br />
Design charts are available to estimate the required<br />
thickness of aggregate surfaced roads for low volume<br />
roads.<br />
Vermont Agency of Transportation [4] procedure for the<br />
design of low-volume pavement structures is based on<br />
the 1993 AASHTO Guide for Design of Pavement<br />
Structures. The following performance indicators in<br />
terms of PSI were used:<br />
For paved roads, initial PSI = 4.0 and terminal PSI = 2.0<br />
and for unpaved roads, initial PSI = 4.0 and terminal PSI<br />
= 1.0<br />
<strong>Grameen</strong> <strong>Sampark</strong> 19
Change language