Geosynthetics for Ground Performance Improvement: Matching Product to Problem

Geosynthetics improve ground performance by doing one of five jobs: keeping two soils apart, letting water out while holding soil back, carrying tension the soil cannot, confining loose fill, or stopping water passing through. Picking the right product starts with naming the problem in the ground. This guide works from the problem to the product, for Indian sites with soft clay, black cotton soil, loose sand and high monsoon water tables, and points to the IRC and MoRTH documents that govern the design.

Start with the ground, not the catalogue

Most ground performance problems on Indian sites fall into six groups:

A site can have several of these at once. A road on black cotton soil, for example, often needs separation, stabilisation and drainage together.

Separation: keeping the stone clean

When stone aggregate is placed directly on wet clay, traffic pushes the stone down and the clay squeezes up between the particles. The granular layer slowly turns into a clay-stone mix with a fraction of its design strength. A nonwoven geotextile laid on the subgrade keeps the two apart for the life of the road while letting water through.

What to check: grab and CBR puncture strength (ASTM D4632 and D6241) for survival during construction, apparent opening size (ASTM D4751) against the subgrade grain size, and permittivity (ASTM D4491) so water can pass. Heavier GSM is chosen where the stone is angular and the construction traffic is heavy. IRC SP:59-2019, *Guidelines for Use of Geosynthetics in Road Pavements and Associated Works*, and MoRTH’s *Specifications for Road and Bridge Works* (Section 700, Geosynthetics) cover selection and installation for road work.

Stabilisation: making a thinner layer stiffer

A biaxial geogrid placed at the base of, or within, a granular layer locks the particles into its apertures. That stops the layer spreading sideways under each wheel, so it stays dense and spreads load over a wider area of subgrade. The usual gains are less rutting and, where the design supports it, a thinner granular layer for the same performance.

Two points decide whether a grid will work:

• Aperture against aggregate size. The stone must be large enough to lock into the openings. A grid with apertures much larger or much smaller than the aggregate gives little interlock.
• Stiffness at low strain. Compare tensile strength at 2% and 5% strain (ASTM D6637 / EN ISO 10319), not only the peak rating.

On very soft, wet subgrades a geogrid is often combined with a geotextile beneath it, since the grid does not separate fines. Our post on geocells and geogrids compared covers when to choose each.

Confinement: giving loose sand a structure

Clean sand and fine fill cannot interlock with a flat grid. A geocell holds the whole thickness of the fill inside a honeycomb of HDPE strips. Under load, the fill pushes outwards, the cell walls push back, and the confined layer behaves like a stiff mat. Geocells are used for access roads over sand, platforms, slope surfaces and channel linings. Cell size and depth are chosen by load: smaller, deeper cells for heavier concentrated loads, larger, shallower cells for surface protection over wide areas.

Basal reinforcement: building over soft clay

An embankment on soft clay can fail by sliding through the foundation soil or by spreading laterally. A high-strength geogrid or woven geotextile at the base of the embankment carries tension that resists both. IRC:113-2013, *Guidelines for the Design and Construction of Geosynthetic Reinforced Embankments on Soft Subsoils*, sets out the stability, bearing capacity, lateral sliding and settlement checks, along with construction practice and monitoring.

Basal reinforcement controls stability. It does not make the clay consolidate faster. On thick soft deposits, the settlement still has to be managed by staged filling, surcharging or vertical drains, and the time that takes belongs in the programme from day one. Our post on geosynthetics on the Ganga Expressway’s alluvial soil describes this soft-ground treatment.

Drainage and filtration: getting water out

Soil loses strength when water cannot escape. A geotextile wrapped around a gravel trench or laid behind a wall lets water into the drain and keeps the soil out, so the drain does not clog. Where a thicker flow path is needed, a drainage geocomposite, a core bonded to geotextile filters, carries water in the plane of the layer under a slab, behind a retaining wall or within a landfill cap.

Filter design matters more than brand. The geotextile’s opening size has to hold back the finer fractions of the soil while staying permeable over time; on fine silts, a filter that is too tight can blind.

Barrier: stopping seepage

For ponds, canals, tanks and landfill cells, the soil itself is the problem: it lets water or leachate through. An HDPE or LDPE geomembrane, or a geosynthetic clay liner, forms the barrier. This is a different job from ground improvement in the structural sense, but it often appears on the same site, for example a lined pond on a stabilised platform.

A worked example (illustrative)

The numbers below are invented to show how the comparison is built. A real design comes from site investigation and the relevant IRC method.

A factory yard of 5,000 sq m sits on clayey subgrade with a soaked CBR of about 2%. The conventional option is to dig out 600 mm of clay and replace it with granular fill. The alternative being considered is a nonwoven geotextile on the subgrade with one layer of biaxial geogrid, and a granular layer 400 mm thick, subject to design checks and a trial section.

• Excavation avoided: 5,000 × 0.2 m = 1,000 m³ of clay that does not have to be dug, carted and disposed of.
• Granular fill avoided: also 1,000 m³ of material not bought, hauled, placed and compacted.
• Geosynthetic supply: about 5,000 sq m of geotextile and 5,000 sq m of geogrid, plus lap allowance.

The decision rests on local rates for excavation, disposal and fill against geosynthetic supply and laying, and on time. On a site where fill comes from far away, the saving in trucks is often the deciding factor.

Installation basics that apply to all of these

• Clear roots, stumps and sharp debris; fill soft spots before laying.
• Lay the product flat and taut, in the direction the design shows, with the specified laps.
• Do not drive tracked plant directly on any geosynthetic. Push fill forward over it from material already placed.
• Compact in layers to the specified density.
• Keep rolls out of prolonged sun before use.

Projects on this site

Ocean products have been used for ground stabilisation on industrial and defence sites. Examples include Ocean geotextile 3 MM for industrial ground stabilisation at the Reliance project in Vijayawada, geocell for industrial park ground stabilisation in Hosur, Tamil Nadu, and Ocean HDPE geocell 330 × 100 mm at the Air Force project in Gwalior.

Frequently asked questions