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PKWATCGS
Geotechnical
- Apr 21, 2006
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Someone posted a question back in 2004 (thread 822-104369) essentially asking: "what is the tolerable post-construction settlement for road pavements on embankments constructed over soft ground?"
Recent experience in Australia indicate that jointed Plain Concrete Pavements (PCP)continue to perform adequately after total post-construction settlements of up to 300mm.
Of course, it is differential settlement that causes damage rather than total settlement. For rigid pavements, the general guide is that D/T^2 should be less than 2.5E-4/m where D is the depth of differential settlement and T is the half wave length of settlement. For example, in the longitudinal direction of the road, a maximum settlement of 300mm at the centre of a settlement bowl having a half wave length of 35m would satisfy this guide. In the transverse direction, the corresponding maximum differential settlement would be approximately 42mm over a half wave length of 13m.
The maximum differential settlement that a concrete pavement can tolerate may also be expressed in terms of the allowable strain in the concrete. The maximum strain in a pavement due to curvature may be assessed using the simple relationship (strain = t/R) where t = thickness of pavement and R = radius of curvature. R will be a function of the lateral variability of the soft soil properties and thickness, embankment thickness and stiffness, and the stiffness of the pavement, which need to be assessed on a case by case basis.
However, in selecting the appropriate design tolerable settlement and differential settlement of road embankments, the designer must also consider road safety base on the speed limit of the road, ride comfort, flood and drainage criteria.
Recent experience in Australia indicate that jointed Plain Concrete Pavements (PCP)continue to perform adequately after total post-construction settlements of up to 300mm.
Of course, it is differential settlement that causes damage rather than total settlement. For rigid pavements, the general guide is that D/T^2 should be less than 2.5E-4/m where D is the depth of differential settlement and T is the half wave length of settlement. For example, in the longitudinal direction of the road, a maximum settlement of 300mm at the centre of a settlement bowl having a half wave length of 35m would satisfy this guide. In the transverse direction, the corresponding maximum differential settlement would be approximately 42mm over a half wave length of 13m.
The maximum differential settlement that a concrete pavement can tolerate may also be expressed in terms of the allowable strain in the concrete. The maximum strain in a pavement due to curvature may be assessed using the simple relationship (strain = t/R) where t = thickness of pavement and R = radius of curvature. R will be a function of the lateral variability of the soft soil properties and thickness, embankment thickness and stiffness, and the stiffness of the pavement, which need to be assessed on a case by case basis.
However, in selecting the appropriate design tolerable settlement and differential settlement of road embankments, the designer must also consider road safety base on the speed limit of the road, ride comfort, flood and drainage criteria.
