STRUCTURAL DESIGN OF FLEXIBLE PAVEMENT Introduction Flexible pavement

STRUCTURAL DESIGN OF FLEXIBLE PAVEMENT

Introduction • Flexible pavement consist several layers of material placed on a subgrade. • Each received loads from above, spread and distribute then pass on the layer below. • The lower the layer the less load carry. • The aim is to ensure transmitted stresses are sufficiently reduced and do not exceed the capacity of underlying subgrade.

Introduction

Element of a Flexible Pavement Structure Material layers arranged within a pavement in order of descending load bearing capacity. Highest load bearing capacity at top. Typical flexible pavement structure consist of: • Surface course: wearing course and binder course. Wearing course provides a uniform running surface with characteristic such as skid resistance, smoothness. Wearing course normally pervious. Binder course provides a smooth platform for wearing course. Provide riding quality and structural strength of pavement.

Element of a Flexible Pavement Structure • Road Base: distribute traffic loads so that transmitted stresses within capacity of lower layer. • Subbase: load distributing layer. Minimize the intrusion of fines from subgrade to pavement structure. Provide drainage. Normally used crused agg. The overall thickness of pavement depends on the traffic load, climate, mechanical properties of material and subgrade strength.

Factors to be Considered in The Design Failure mechanism • Two failure mechanism; permanent deformation of whole structure and cracking of bituminous layer • Accumulate of permanent strain from all layers leads to surface cracking. • Cracking is a fracture failure results from fatigue in bituminous material. Traffic loading • Tire loads and pressure • Axle and wheel configuration • Load repetition • Traffic distribution • Vehicle speed • Equivalent Standard Axle (ESA).

Factors to be Considered in The Design Environment Effect • Environment variations affect pavement material, subgrade soil. • Important environment factor; temperature and moisture. • Temperature rise will deteriorates a bituminous pavement. Affects rheology and cause expansion and contraction in the asphalt pavement. • Moisture can cause certain type of soil to expand. • Placing HMA in wet condition will damage the mix (stripping). Rainfall reduce skid resistance.

Method of Design for New Pavements • The objectives of pavement design is to determine the number, material composition and thickness of the different layers in the pavement that will be able to sustain the anticipated traffic load and environment condition. • Method of pavement: – Method based on precedent. – Empirical Design Method – Theoretical Method

Method of Design for New Pavements Method Based on Precedent • Design procedure by rule of thumb. • Rely upon standard thickness of pavement for a particular classification of road. Empirical Design Method • Based on either soil classification (group index), or soil strength (CBR value). Use an empirical approach which the input and pavement failure were determined using experience, experiment or combination of both.

Method of Design for New Pavements Theoretical Method • Theoretical (analytical or mechanistic). Use mechanical models with practical verification. • Semi-theoretical (mechanistic-empirical). Relate pavement parameter to physical causes. • Advantages of mechanistic-empirical method: – Suitable for new pavement and rehabilitation works. – Accommodates various type of load. – Material properties reflect the actual pavement providing reliable performance predictions. – Accommodates environmental and aging effects.

General Design Process

Malaysia Design Methods Arahan Teknik Jalan 05/85 • Introduce in 1985. • Suitable for medium and heavy traffic. • Thickness design based on CBR of the subgrade and total number of 8160 kg standard axle application for a specific design period.

Malaysia Design Methods Arahan Teknik Jalan 05/85

Malaysia Design Methods Arahan Teknik Jalan 05/85 Carriageway width = 7. 5 m Shoulder width = 2. 0 m Layer materials: Surfacing = asphaltic concrete Road base = wet mix macadam Sub-base = sand

Malaysia Design Methods Arahan Teknik Jalan 05/85

Malaysia Design Methods Arahan Teknik Jalan 05/85 1000 per direction

Malaysia Design Methods Arahan Teknik Jalan 05/85

Malaysia Design Methods Arahan Teknik Jalan 05/85

Malaysia Design Methods Arahan Teknik Jalan 05/85 (pindaan 2013) • Improved design development data and mechanistic method of analysis into single tool that is presented in the form of catalogue of predesign pavement strurture.

Malaysia Design Methods Input for Pavement Design.

Malaysia Design Methods Pavement Design Methodology • Vertical strain on top of the subgrade. Control the accumulation of permanents deformation of the subgrade. • Horizontal strain at the bottom of the lowest bound pavement course. Control fatigue damage due to repeated traffic load.

Malaysia Design Methods Determination of Design Traffic • Traffic data required are: – – Number of CV during year 1 of design period. Vehicle class and axle load distribution Directional and lane distribution factors Traffic growth factors.

Malaysia Design Methods Traffic Category

Malaysia Design Methods Subgrade Properties and Category

Malaysia Design Methods Properties of Paving Material

Malaysia Design Methods Environmental Effects

Malaysia Design Methods Design Period and Reliability

Malaysia Design Methods Types of Standardized Pavement Structure

Malaysia Design Methods Catalogue of pavement structure

Malaysia Design Methods

Malaysia Design Methods Overseas Road Note • Based on research conducted in 30 tropical and sub-tropical countries. • Suitable for traffic up to 30 million cumulative equivalent standard axle in one direction. • Consider the variability in material properties and construction control, the uncertainty in traffic forecast, the effects of climate and high axle loads and the overall statistical variable in road performance. Heavy vehicle = 3000 kg unladen weight.