# How Retaining Walls Work > How retaining walls work: soil pushes sideways with lateral earth pressure, and walls resist through mass, structure, reinforced soil, anchors and drainage. URL: https://ridgelineoutdoorliving.com/blog/how-retaining-walls-work/ Last-Modified: 2026-10-14 Guide # How Retaining Walls Work A retaining wall holds back soil that would otherwise creep, slump or slide downhill. This guide explains lateral earth pressure, how walls resist sliding and overturning, how gravity, cantilever, geogrid and anchored systems differ, and why drainage and site conditions decide the design. 8 min read Published October 14, 2026 ![Engineered stone-faced retaining wall holding back soil on a terraced hillside](/images/featured/engineered-stone-faced-retaining-wall-terracing-a-.webp) A retaining wall holds back soil that would otherwise creep, slump or slide downhill. That soil does not sit quietly in place. Its weight pushes sideways against whatever confines it, and the wall’s entire job is to resist that push for decades. Every retaining wall that stays standing works the same way in principle: it provides enough resistance to keep the soil behind it stable. What differs from wall to wall is where that resistance comes from. ![Segmental retaining wall terracing a sloped yard and holding back soil](/images/features/segmental-retaining-wall-terracing-a-sloped-yard-w.webp) ## The Force Every Retaining Wall Has to Resist Soil is heavy. A cubic yard of it commonly weighs on the order of 2,000 to 3,000 pounds, and that weight does not only press downward. Because soil is made of loose particles rather than a solid mass, the weight also spreads sideways, pressing against anything that confines it. Engineers call this lateral earth pressure: lateral meaning sideways, earth meaning the retained soil. The soil the wall holds back is the retained soil, and the sideways force it applies is the load the wall must carry. Lateral earth pressure behaves much like water pressure in one important way: it increases with depth. The push against the wall is modest near the surface and greatest at the base. Because the pressure itself grows with depth and it acts over a taller face, the total force grows much faster than the wall height. Under the standard equivalent-fluid model engineers use, doubling the retained height roughly quadruples the total push on the wall. This is why a six-foot wall is not a slightly bigger version of a three-foot wall; it is a fundamentally different structural problem. Several site conditions raise the pressure further. Loose or soft soils push more than dense, free-draining granular soils. Heavy clay retains water and presses harder. Soil that was compacted against the wall during construction can leave residual pressure locked in. A slope rising above the wall adds weight to the retained mass. And anything sitting on the ground behind or above the wall, such as a driveway, parked vehicles, a patio, a pool or a building, adds what engineers call a surcharge load: extra weight pressing down on the soil, which the soil converts into extra sideways push against the wall. ## How a Wall Stays Stable: Sliding, Overturning and Bearing A retaining wall can lose its fight with lateral earth pressure in three basic ways. It can slide, pushed bodily forward along its base. It can overturn, rotating outward around its bottom front edge, the way a heavy bookcase tips. Or it can sink or tilt because the ground beneath it cannot carry the load, a failure of bearing. Every sound retaining wall design is, at its core, a check that the wall has enough resistance against all three. ![Cross-section diagram of retaining wall sliding, overturning and bearing failure modes](/images/content/cross-section-diagram-showing-the-three-failure-mo.webp) Resistance starts with weight. Gravity pulls the wall straight down, and friction between the base and the soil below converts that weight into resistance to sliding. Weight and width together resist overturning: the heavier the wall and the wider its base, the harder it is for soil pressure to rotate it forward. The base or footing spreads the load onto the ground, and it must sit on firm, stable, well-compacted soil, because a wall founded on soft or settling ground will move no matter how strong the wall itself is. The buried portion of the wall at its base, called the embedment, also helps, because the soil in front of the wall resists being pushed aside. Different wall systems arrange these elements differently. A poured concrete wall typically stands on a concrete footing; a dry-stacked block wall usually sits on a compacted gravel base. What they share is the requirement for stable support beneath the wall. ## How Different Retaining Wall Systems Create Resistance All retaining walls solve the same problem, but they generate their resistance in distinctly different ways. ### Gravity walls A gravity wall resists purely through mass and geometry. Built from stone, mass concrete, gabion baskets or stacked segmental blocks, it is simply heavy enough and wide enough that its own weight defeats sliding and overturning. Many gravity walls lean slightly back into the hill, letting the retained soil’s weight bear down on the wall itself, which adds stability. The physics is simple: heavy, wide things are hard to push over. ### Cantilever walls A reinforced concrete cantilever wall uses structural strength instead of bulk. Its cross-section is shaped like an inverted T or L: a vertical stem that holds back the soil, and a horizontal footing beneath. Steel reinforcement inside the concrete lets the relatively thin stem resist the bending that soil pressure creates. The clever part is the heel, the rear portion of the footing buried under the retained soil. The soil resting on the heel weighs the footing down, so the wall recruits the weight of the very soil it retains to resist overturning. ### Geogrid-reinforced walls ![Cross-section diagrams comparing gravity, cantilever and reinforced retaining wall systems](/images/content/cross-section-diagrams-of-four-retaining-wall-syst.webp) Segmental block walls above modest heights usually work as reinforced-soil systems, formally called mechanically stabilized earth. Layers of geogrid, a stiff polymer mesh, extend horizontally back from the block face into the compacted fill. Friction and mechanical interlock between the grid and the soil knit the fill into a single reinforced soil mass that behaves like one large, heavy gravity structure. The visible blocks are mostly a facing; the real structure is the reinforced soil behind them. This is how relatively light block walls safely reach heights that would otherwise demand massive concrete. ### Anchored walls Where space is tight or loads are high, an anchored wall transfers the force somewhere else entirely: deeper ground. Steel tendons called tiebacks or ground anchors are drilled through the wall face, past the soil that could potentially slide, and grouted into stable soil or rock beyond it. The anchors are then tensioned, actively pulling the wall face back against the retained earth. Instead of resisting pressure with weight, the wall ties itself to ground that is not moving. ## Why Water Changes Everything Water is the single biggest reason retaining walls are called on to resist more than their designers intended. Soil that is saturated behaves far worse than the same soil dry: research on cantilever retaining walls has found that saturated soil exerts roughly twice the pressure of dry soil. Water also adds its own weight to the retained mass, and if it has no escape route, it presses directly on the wall with hydrostatic pressure, the same pressure that pushes against a dam. Finally, water softens the ground beneath the wall, undermining bearing at exactly the moment the load is highest. ![Retaining wall drainage with gravel backfill and weep holes behind the wall face](/images/features/hillside-sub-surface-drainage-with-weep-holes-behi.webp) This is why drainage is a structural feature, not a finishing touch. Gravel zones, drain pipes and weep holes exist to move water out of the retained soil so that pressures stay close to the dry-soil values the wall was designed around. A wall with blocked drainage is a wall being asked to carry a load it may never have been designed for. ## Why Site Conditions Decide the Design Because height, soil type, slope, water and surcharge loads all change the force a wall must resist, there is no universal wall design. A low garden wall on flat, well-drained ground carries modest loads and can rely on simple mass. A tall wall below a driveway, on clay soil, on a hillside lot carries several loads at once and needs engineering that accounts for each of them. This is also why experienced contractors treat tall walls, walls with structures or slopes above them, and walls on steep ground, such as the hillside properties common around Pasadena [/locations/pasadena/ →](/locations/pasadena/), as engineered projects rather than landscape features. Understanding how retaining walls work comes down to one exchange: soil pushes, and the wall system resists, using mass, structure, reinforced soil or anchors, on a stable base, with water managed so the push stays within what the wall was built to handle. ## Frequently Asked Questions ### What is the difference between active and passive earth pressure? Active earth pressure is the sideways push the retained soil applies to the back of the wall; it is the load the wall must resist. Passive earth pressure is the opposite: the resistance mobilized in the soil in front of the wall when the wall presses into it. The buried base of a wall, called the embedment, takes advantage of passive resistance, because the soil in front must be compressed and pushed aside before the wall can slide forward. ### What role does groundwater play in how a retaining wall works? Rain is not the only water a wall may face. Where the groundwater table rises into the retained soil, the wall carries continuously saturated ground rather than occasional wetting, and seepage can keep water moving toward the wall indefinitely. Drainage for such sites has to manage a steady flow, not just storms, which is one reason walls near known groundwater or springs need site-specific design rather than a standard detail. ### Why do some retaining walls lean backward into the slope? That backward lean is called batter, and it is deliberate geometry. Tilting the face toward the retained soil aims the wall’s own weight into the hill rather than letting it sit directly over the toe, which improves resistance to overturning. Segmental block walls achieve the same effect through setback, stepping each course slightly back from the one below. A slight backward lean is a sign of intentional design, not poor construction. ### Why does backfill compaction matter behind a retaining wall? Compaction gives the fill behind the wall its strength and stiffness, and in a geogrid-reinforced system the compacted soil is itself part of the structure: the reinforced mass only behaves as one heavy unit if the soil is dense and uniform. Loosely placed fill settles later and shifts the load. There is a counterpoint, though: compacting aggressively right against the wall face can lock extra pressure into the wall, so builders compact in controlled lifts. ### How does a retaining wall help prevent soil erosion? The same resistance that keeps a slope from sliding also keeps rainfall from carrying its soil away: the wall fixes the ground’s geometry so the soil stays put, and its drainage collects water and releases it in a controlled way instead of letting it sheet down the face. A wall cannot manage water arriving from upslope on its own, however, so erosion control still depends on how the surrounding ground sheds water. Previous article How Much Slope Should a Yard Have? Yard Grading for Drainage [/blog/how-much-slope-should-a-yard-have/ →](/blog/how-much-slope-should-a-yard-have/)Next article How High Should a Retaining Wall Be? [/blog/how-high-should-a-retaining-wall-be/ →](/blog/how-high-should-a-retaining-wall-be/) On this page * The Force Every Retaining Wall Has to Resist * How a Wall Stays Stable: Sliding, Overturning and Bearing * How Different Retaining Wall Systems Create Resistance * Why Water Changes Everything * Why Site Conditions Decide the Design * Frequently Asked Questions Talk to a Designer Free on-site consultation across Greater Los Angeles. Same-week availability. Schedule a Consultation [/contact/ →](/contact/) (626) 469-5822 [tel:+1-626-469-5822 →](tel:+1-626-469-5822) Talk to a Designer Free on-site consultation across Greater Los Angeles. Same-week availability. Schedule a Consultation [/contact/ →](/contact/) (626) 469-5822 [tel:+1-626-469-5822 →](tel:+1-626-469-5822) Have questions about a project of your own? A free on-site consultation, a phased budget tier, and a master plan that fits your property and your goals. Schedule a Consultation [/contact/ →](/contact/) Call (626) 469-5822 [tel:+1-626-469-5822 →](tel:+1-626-469-5822)