--- title: "Retaining Wall with Geotextile and Geogrid Reinforcement: How to Design One" date: 2022-09-15 author: "Pawan Khatri" url: https://oceangeosynthetics.com/retaining-wall-with-geotextile-and-geogrid-reinforcement/ --- September 15, 2022 | [Geogrids](https://oceangeosynthetics.com/category/geogrids/), [Geotextile](https://oceangeosynthetics.com/category/geotextile/), [Insights](https://oceangeosynthetics.com/category/insights/) # Retaining Wall with Geotextile and Geogrid Reinforcement: How to Design One A retaining wall with geotextile and geogrid reinforcement is a block of compacted fill held together by horizontal layers of geosynthetic, with a thin facing on the front. The facing only stops the soil spilling out. The stability comes from geogrid soil reinforcement inside the fill, which turns a wedge of loose backfill into a wide, heavy mass that resists the ground behind it. This article covers the design side: what each geosynthetic does in the wall, how the reinforced block is sized, and what Indian guidance asks for. For the site sequence, see our step-by-step guide on [how to install geogrid in a retaining wall](https://oceangeosynthetics.com/how-do-you-install-geogrid-on-a-retaining-wall/). ## The parts of a geosynthetic reinforced wall Working from front to back, a typical wall on an Indian road or industrial project has: 1. **Facing.** IRC:SP:102-2014 lists precast concrete panels, precast concrete blocks or hollow blocks, gabions, geosynthetic wrap-around, metallic facings and other proven proprietary systems. 2. **Levelling pad.** SP:102 calls for a pad of at least M15 plain cement concrete, 150 mm thick, under the first row of facing. 3. **Drainage bay.** A strip of free-draining aggregate at least 600 mm wide behind the facing, or a drainage geocomposite in its place. 4. **Reinforced fill.** Select granular soil, compacted in layers, with geogrid or geotextile at the designed levels. 5. **Retained fill.** The natural ground or embankment behind the reinforced zone. 6. **Separation and filter layers.** A non-woven geotextile wherever drainage aggregate touches finer fill. ## What each geosynthetic does The two materials in the title do different jobs, and swapping one for the other is a common design mistake. | Material | Role in the wall | Typical position | | --- | --- | --- | | Uniaxial geogrid | Primary reinforcement: carries tension perpendicular to the face | Horizontal layers through the reinforced fill | | Biaxial geogrid | Strength in two directions; used for foundation layers, secondary reinforcement and base works | Under the levelling pad on weak ground, or at the face between primary layers | | High-strength woven geotextile | Sheet reinforcement; also forms wrap-around faces | Horizontal layers, folded back at the face | | Non-woven geotextile | Filter and separator, not reinforcement | Between drainage bay and fill, around drain pipes | | Drainage geocomposite | Replaces or supplements the aggregate drainage bay | Against the back of the facing or the retained cut | Ocean’s [geogrid range](https://oceangeosynthetics.com/products/geogrid-manufacturers/) includes uniaxial and biaxial grades, and its [geotextiles](https://oceangeosynthetics.com/products/geotextile-manufacturers/) cover both woven and non-woven types. A non-woven geotextile drains water within its plane and filters soil; a woven one has far higher strength but little in-plane flow. That is why a wall with marginal backfill often needs both. ## Sizing the reinforced block Design follows two families of checks. **External stability** treats the reinforced block as a gravity wall: sliding along its base, overturning (kept in check by holding eccentricity under L/6), bearing pressure on the foundation and overall slope stability. SP:102 asks for a bearing factor of safety of at least 1.4 at the limit state and ignores passive resistance in front of the toe. **Internal stability** checks each reinforcement layer: will it rupture under the tension it carries, and is it long enough beyond the failure plane to resist pullout? SP:102 sets the pullout factor of safety at 1.5 or more and also checks the connection between reinforcement and facing. The guideline also fixes some geometry regardless of the calculation: - **Length:** at least 0.7H or 3 m, whichever is more, where H is the design height including embedment. - **Embedment:** at least 600 mm or H/20, whichever is more (relaxable to 400 mm on existing roads with precautions). - **Vertical spacing:** primary reinforcement no more than 800 mm apart in any wall; no more than twice the block width for friction-connected blocks; no more than 500 mm for wrap-around faces. ## Worked example (illustrative) Take an illustrative 5.4 m exposed wall with 0.6 m embedment, so H = 6.0 m, built with hollow concrete blocks 300 mm deep, on a site with select fill of 18 kN/cu m and friction angle 32 degrees. - Reinforcement length: 0.7 × 6.0 = 4.2 m, which beats the 3 m minimum, so 4.2 m. - Embedment: H/20 = 0.3 m, below the 600 mm minimum, so 0.6 m governs. - Spacing: twice the block width is 600 mm, tighter than 800 mm, so layers at 600 mm or less: about ten layers over 6 m. - Load on the bottom layer: Ka = 0.31, horizontal stress about 0.31 × 18 × 6 = 33 kPa, so about 20 kN per metre of wall from the soil alone, before traffic surcharge and partial factors. The designer then picks a geogrid whose long-term design strength, after creep, installation damage and durability reduction factors, exceeds the factored load. Lower layers usually get a stronger grade than upper ones. Real designs add surcharge, seismic load and the facing connection test (ASTM D6638 for block walls), and must be done by a qualified engineer. ## Fill and drainage: where walls actually fail SP:102 gives a desirable gradation for reinforced fill: 100% passing 75 mm, 85–100% passing 4.75 mm, 60–90% passing 425 micron and less than 15% passing 75 micron, with plasticity index below 6. Where that soil is not available locally, clayey or silty sandy gravel (GC, GM) can be used if fines stay within 20% and drainage is improved. It also recommends limiting particle size to 19 mm with geosynthetics unless installation damage has been tested with the actual fill. Drainage gets the same weight. RS walls are not normally designed for water pressure, so the drainage bay, perforated pipes and outlets have to keep water out. On hill-side walls, SP:102 asks for a drainage bay between the retained cut and the reinforced block, continued below the toe to a drain. Our article on [geosynthetics for retaining wall drainage](https://oceangeosynthetics.com/geosynthetics-for-retaining-wall-drainage/) covers the options. A [drainage geocomposite](https://oceangeosynthetics.com/products/geo-composites/) can replace the aggregate bay where good stone is scarce; Ocean supplied and installed 1,000 sq m of geocomposite for [retaining wall and landscaping works in Rewari](https://oceangeosynthetics.com/retaining-wall-landscaping-with-geocomposite-in-rewari/). ## Facing options - **Precast panels:** standard for flyover and ROB approaches. Reinforcement connects to inserts cast into each panel. - **Segmental blocks:** common for industrial sites and boundary walls; the grid is clamped between courses. - **Gabion facing:** tolerates settlement and drains freely, which suits hill roads. See our post on [gabion walls](https://oceangeosynthetics.com/gabion-walls/). - **Wrap-around geotextile or geogrid:** cheapest face, often vegetated or later covered with shotcrete or a block skin. If you are still deciding whether a wall needs reinforcement at all, read [when to use geogrid in a retaining wall](https://oceangeosynthetics.com/when-to-use-geogrid-in-retaining-wall/). ## Frequently asked questions ### Can a non-woven geotextile be used as the main reinforcement? Not for a wall of any real height. Non-woven geotextiles have low tensile strength and stretch a lot under load. They belong in the wall as filters and separators. Primary reinforcement should be geogrid or high-strength woven geotextile. ### How long should geogrid be behind a retaining wall? IRC:SP:102-2014 sets a minimum of 0.7 times the design height or 3 m, whichever is greater. Surcharge, sloping backfill or seismic load can make the design length longer. ### Which tests should the geogrid supplier provide? Wide-width tensile strength (ISO 10319 or ASTM D6637), creep data of at least 10,000 hours, installation damage and durability results, and for block walls the block-to-grid connection test (ASTM D6638). SP:102 asks for tests from an independent accredited laboratory. ### Is a geogrid wall cheaper than an RCC retaining wall? Often, for tall walls with space behind them, because the facing is thin and site fill does most of the work. It needs room for reinforcement 0.7H long, so on tight sites an RCC wall may still be the practical choice. ## Plan your reinforced wall with Ocean Share your wall height, facing type and fill source with our team through the [contact page](https://oceangeosynthetics.com/contact/), and we will suggest geogrid, geotextile and drainage products to match the design. 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