No. 7 of 19Soil Stabilization and Base Reinforcement

byRyan R. Berg, P.E.

The information presented in this document has been reviewed by the Education Committee of the International Geosynthetics Society and is believed to fairly represent the current state of practice.

However, the International Geosynthetics Society does not accept any liability arising in any way from use of the information presented.

Lecture Outline

• Definitions

• Applications

• Materials

• Design

• Specifications

• Economics

• Installation

• Summary

Soil Stabilization

Definition:

• when a geosynthetic is placed at the subgrade/fill interface to increase the support of construction equipment over a weak or soft subgrade

Base Reinforcement

Definition:

• When a geosynthetic is placed as a tensile element at the bottom or within a flexible pavement base (or sub-base) course to:

(i) improve the service life;(ii) obtain equivalent performance with a

reduced structural section; or(iii) combination of (i) and (ii)

Soil Stabilization

Applications:

• Temporary roadways• Initial construction lift of permanent roads• Area construction platforms

Base Reinforcement

Applications:

• Permanent roads

• Parking lots

• Airport taxiways

• Container loading facilities

• Railway tracks

Materials

Soil Stabilisation and Basal Reinforcement

• Geotextiles- Woven- Nonwoven

• Geogrids- Extruded- Knitted or Woven

• Geogrid-Geotextile Composites

Design

• Design parameters

• Survivability

• Durability

Required Geosynthetic PropertiesDefined by Examining:

Soil Stabilisation and Basal Reinforcement

Design Parameters

• Minimum acceptable rut depth• Traffic expected to use road

- wheel load/axle load- number of axles- number of passes

• Foundation soil properties - shear strength- soil type

Design Parameters include:

Soil Stabilisation and Basal Reinforcement

• Lateral restraint

• Bearing capacity increase

• Membrane tension support

Possible reinforcement mechanisms provided by geosynthetics:

Design

Soil Stabilisation and Basal Reinforcement

Lateral Restraint

Bearing Capacity Increase

Membrane Tension Support

Placing Fill on Geotextile

Over Careful Placing

Subgrade Stabilisation

Design

• Several design methods are available

• Design techniques mainly rely on: - membrane tension, and

- bearing capacity increase

• Check filtration

• Most methods are generic; some are empirical-

based, upon specific geosynthetic product

• Stewart et al., 1977

• Barenburg, 1980

• Giroud and Noiray, 1981

• FHWA Geosynthetics Manual,

• Holtz et al., 1998

and others

Subgrade StabilisationExample Design Methods

Specifications

Design may be:

(i) generic, or (ii) product-specific.

Specification must follow design. Therefore, SPECIFICATION with

(i) generic properties or (ii) Approved Products List

may be appropriate.

Subgrade Stabilisation

Base Reinforcement

Design

• Several design methods exist• Design techniques mainly rely on:

- Lateral restraint (or confinement), and- Bearing capacity increase

• Check filtration• Most methods are empirical-based, upon

specific geosynthetic product

Base Reinforcement Example Design Methods

• Penner et al., 1985• Burd and Houlsby,

1986 • Barksdale et al., 1989• Burd and

Brocklehurst, 1990• Davies and Bridle,

1990• Miura et al., 1990• Sellmeijer, 1990

• Webster, 1993• Dondi, 1994• Tensar, 1996• Wathugala et al., 1996• Akzo-Nobel, 1998• Zhao and Foxworthy,

1999

•Designs are usually empirical-based, upon product-specific performance.

•Specification must follow design. Therefore, SPECIFICATION with an Approved Products List is usually appropriate.

Base Reinforcement

Specifications

Subgrade Stabilisation

Economics

• Geosynthetics provide cost savings in construction and maintenance of pavement structures• Savings are realized with decreased over-

excavation and decreased required granular fill• Cost savings are often demonstrated by simply

examining initial construction costs but, life cycle cost analysis may show additional, maintenance cost savings

• For some projects, cost savings may be demonstrated by simply examining initial construction cost

• Will not be cost effective for all projects

Base ReinforcementEconomics (Continued)

Installation

• Prepare the ground

• Unroll the geosynthetic

• Back dump aggregate

• Spread the aggregate

• Compact the aggregate

Prepare the Ground • remove the stumps, boulders, etc.;

fill in low spots.

Unroll the Geosythetic

Directly over the ground to be stabilized.If more than one roll is required, overlap rolls.

Rolling out on Prepared Formation

Forming a Curve Using Folds

Forming a Curve Using Cut Pieces

Back Dump Aggregate

• onto previously placed aggregate.

Do not drive on the geosynthetic. Maintain 150 mm to 300 mm cover between truck tires and geosynthetic.

Back Dumping Aggregate

Spread the Aggregate

• over the geosynthetic to the design thickness.

Spreading Aggregate

Compact the Aggregate

• using suitable compaction equipment.

Compaction of Aggregate

Repair of Rutted Section

Subgrade Restraint

• Fill in any excessive ruts formed during construction.

• In no case should ruts be bladed down, as this would decrease the amount of aggregate cover between ruts.

Repair of Rutting with Additional Material

Summary

Subgrade

Geosynthetics are cost-effective, as

subgrade restraint, to support

construction equipment over soft soils

Base Reinforcement

Geosynthetics can be cost-effective for base reinforcement of flexible pavements to:

- improve service life

- obtain equivalent performance with a reduced structural section or combination of the two

Summary