Geosynthetic in Road Pavement and associated Works

Typical Problem of Low Bearing Capacity

FAILURE CRITERIA FUNCTIONAL STRUCTURAL SERVICEABILITY RUTTING FATIGUE DRAINAGE/ MOISTURE RUTTING FATIGUE REFLECTIVE AND LONGITUDINAL CRACKING CONTAMINATION SERVICEABILITY LOW TEMPERATURE CRACKING

Increase in traffic volume Contamination of road material WHAT CAUSES ROAD PAVEMENTS TO FAIL? Poor drainage Increase in traffic volume Contamination of road material Short term design Increase in traffic loads Insufficient strength of road material Poor existing soil properties Defects in construction method and quality control

Pavement – Typical components Typical Asphalt Pavements WEARING COURSE BINDER BASE FOUNDATION SUBGRADE Main structural element (durable) BOUND MATERIAL Pavement foundation GRANULAR MATERIAL OVER SOIL Existing soil BOUND MATERIAL: high stiffness, crack and deformation resistant GRANULAR MATERIAL OVER SOIL: adequate platform to place layer above 2

Geosynthetics in Pavements - Today More common and well known, well established solution Used as an alternative to conventional system Considered as cost-effective solution Basic Application includes: 1. Subgrade Separation and Stabilization 2. Base reinforcement 3. Overlay stress absorption and reinforcement 4. Drainage arrangement

1. Subgrade Separation and Stabilization

Subgrade Separation The placements of a flexible porous textile between dissimilar materials so that the integrity and functioning of both materials can be remain intact or are improved. Nonwoven Geotextile is used between subgrade and base course to prevent the intermixing of subgrade and base course aggregate Adopted when subgrade is strong enough (CBR > 3.0) If CBR is weak then subgrade stabilization is also required by providing high strength geotextile or geogrid

Concept of geotextile separation in roadways (after Rankilor, 1981) Subgrade Separation Concept of geotextile separation in roadways (after Rankilor, 1981)

Without Separation – Base Stone Fouling Occurs Fouling of the base aggregate gradually reduces the quality and strength of the base aggregate. Rigid Pavement Flexible Pavement

Intermixing problem of aggregate and subsoil “If you combine 10 kg of stone and 10 kg of mud, you have 20 kg of mud” . . . and the associated loss of support!

SUBGRADE STABILIZATION For larger rut depths, more strain is induced in the geosynthetic. In this case, considerable reduction in aggregate thickness is possible by the use of a stronger geosynthetic. If subgrade CBR is very weak (CBR<1.5) proper stabilization is required by providing high strength geotextile or geogrid. It provides lateral restraint to the subgrade which increases the allowable bearing capacity of the subgrade

SUBGRADE STABILIZATION A stabilization geotextile/geogrid facilitates ease of construction over weak subgrade A geogrid is effective in reducing the required fill over a weak subgrade

Summary for Separation and Stabilization The following general conclusions can be drawn relating to a typical road base: A geosynthetic that functions primarily as a separator (typically when the subgrade CBR  3) will increase the allowable bearing capacity of the subgrade by 40-50% (separation geotextiles) A geosynthetic that functions primarily to provide confinement of the aggregate and lateral restraint to the subgrade (typically when the subgrade CBR < 3) will both increase the allowable bearing capacity of the subgrade and provide an improved load distribution ratio in the aggregate. The combined benefits can enhance load carrying capacity of the road by well over 50% (stabilization geogrids or geotextiles) With very weak subgrade (CBR<1.5), it is often beneficial to combine the benefits of both separation and stabilization

2. Base reinforcement

BASE REINFORCEMENT Permanent roads carry larger traffic volumes and typically have asphalt or portland cement concrete surfacing over a base layer of aggregate. With the addition of an appropriate geosynthetic, the Soil-Geosynthetic-Aggregate (SGA) system gains stiffness via “confinement” of the aggregate.

Geogrid base reinforcement, confines and stiffens the aggregate base layer providing long-term support for the paved surface by: A. Preventing lateral spreading of the base B. Increasing confinement and thus stiffness of the base C. Improving vertical stress distribution on the subgrade

The unique structure allows the grid to get a good “grip” on the aggregate particles and results in effective mechanical interlock. The unique shape of the geogrid ribs confines aggregate particles due to its high stiffness and the strength at the corners (junctions), just like a rack confines billiard balls.

3. Overlay stress absorption and reinforcement

Reflective Cracking in Pavements Many pavements, which are considered to be structurally sound after the construction of an overlay, prematurely exhibit a cracking pattern similar to that which existed in the underlying pavement – Reflection Cracking Reflective cracks A. destroy surface continuity B. decrease structural strength C. allow water to enter sub-layers. Thus, the problems that weakened the old pavement are extended up into the new overlay.

Solution for Reflecting Cracking Overlay reinforcement by: Glass Grid Geogrid made of glass fibers

Crack Reflection Solutions APPLICATIONS Geogrids Crack Reflection Solutions

Surface Rutting Solution APPLICATIONS Geogrids Surface Rutting Solution

Fatigue Cracking Problem APPLICATIONS Geogrids Fatigue Cracking Problem

Fatigue Cracking Problem APPLICATIONS Geogrids Fatigue Cracking Problem

APPLICATIONS Geogrids Road Widening Works

GS against Reflective Cracking 0 Not reinforced 1A Nonwoven GT without emulsion 1B Nonwoven GT with emulsion 1C Nonwoven GT impregnated with elastomeric bitumen 2 Polyester geogrids 3 Fiberglass geogrid 4 SAMI 5 Woven GT 5 10 15 20 25 30 35 40 45 3 2 1 4 7 8 1A 1B 1C Crack propagation (cm) GS against Reflective Cracking Loads number (x1000)

4. Drainage arrangement

Importance of proper & effective drainage Undesired water can lead to damage to pavements The pore water pressure built-up in subgrade may lead to pavement permanent failure Loss of subgrade support Reduction of granular layer stiffness

Conventional method of drainage Side trenches are constructed in pavements along the length to drain away the subgrade water Trenched are filled with gravel

Drawbacks of Conventional method Costlier solution Difficult to install As the time pass, the efficiency of drainage reduces due to the clogging of gravel layer Consumption of natural resources

Solution with Geosynthetics Edge Drain: by Drainage Composite

Quantifying the Geosynthetic Benefit Traffic Benefit Ratio (TBR) (also known as Traffic Improvement Factor or TIF) is a ratio comparing the performance of a pavement cross-section with a geogrid-reinforced base course to a similar cross-section without geogrid reinforcement, based on the number of cycles to failure, with failure defined as a selected depth of rut. In general, geosynthetics have been found to provide a TBR in the range of 1.5 to 20, depending on the type of geosynthetic, its location in the road, and the testing scenario.

Advantages of Geosynthetics in Pavements Improved service life, lower maintenance Better drainage arrangement Improved load carrying capacity Better load distribution by pavement section Cost effective if compared to conventional solution Possible to construct over very weak soil Reduction on rut depth and cracking Considerable saving in design thickness Chemically inactive, non biodegradable material hence high durability

INSTALLATION GUIDELINE

Installation of Geosynthetics For Separation, Stabilization & Base Reinforcement 1. Subgrade Preparation - Roadway subgrade preparation typically involves removal of all vegetation, roots, and topsoil. - Localized soft soil or otherwise unsuitable subgrade areas may be require to be excavated and backfilled with selected materials.

2. Geotextile Placement - The geotextile is usually laid in the direction of construction traffic - On very soft subgrade (CBR < 1.0) the fabric layout and aggregate placement should begin on firm soil on the site perimeter. - The geotextile should not be dragged across the subgrade. - Wrinkles and folds in the fabric shall be removed by stretching and staking as required.

3. Geotextile Overlap Rolls of geotextiles must be overlapped, sewn, or jointed as required Overlap as per FHWA

4. Aggregate Placement - Construction vehicles should not drive on fabric - First lift should be placed at minimum 300 mm thick - Rut depths should be less than 75 mm - Initial lift should be compacted by tracking-additional lifts with smooth drum vibratory

5. Aggregate Spreading & Compaction

INSTALLATION PHASES

Effective depth of Road Mesh placement 3 to 6 inches HMA HMA BASE SUBGRADE

Method of deployment for full scale placement ROADMESH DEPLOYMENT

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