No. 7 of 19 Soil Stabilization and Base Reinforcement by Ryan 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 Properties Defined 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 Stabilisation Example 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 Reinforcement Economics (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