Most concrete problems people call us about are not really concrete problems. They are ground problems that show up in concrete. A slab is a thin, stiff plate resting on soil. When the soil stays put, the slab stays put. When the soil settles, swells, or washes away, the slab follows.
The Albuquerque metro sits on a surprisingly varied mix of soils, from the mesas on the west side to the Rio Grande valley floor to the alluvial fans below the Sandias. Soil can also change from lot to lot, so treat the generalizations below as a starting point for a conversation, not a diagnosis of your property.
Caliche
Caliche is a layer of soil cemented by calcium carbonate, formed over long periods in arid climates. It can range from a crumbly, chalky layer to something closer to rock. Caliche is common on the mesas and higher terraces, including much of the West Mesa and Rio Rancho, and it shows up in parts of Paradise Hills as well.
Why it matters
- Excavation can be slow and may require heavier equipment or breaking.
- A hard layer can perch water above it, keeping the soil over it wetter than you would expect.
- Uneven bearing is a risk when part of a slab or footing sits on hardpan and part sits on softer soil or fill.
- It can complicate trenching for utilities, footings, and drainage.
Good preparation typically aims for uniform support: excavating to a consistent level, removing pockets of soft soil, and making sure water has a way out rather than sitting on top of the hardpan.
Collapsible soils
Collapsible, or hydrocompactive, soils are dry, low-density sands and silts that can hold a surprising amount of load while dry. When they get wet, the bonds between grains weaken and the soil can compact suddenly, sometimes significantly. These soils are commonly associated with the West Mesa, Rio Rancho, and other areas built on windblown and alluvial deposits.
The trigger is almost always water: a new lawn or planter bed against the house, a leaking irrigation line, roof runoff dumping beside a slab, or monsoon water ponding along a foundation. The damage often shows up as a section of slab or foundation that drops, sometimes years after construction, when the water situation changes.
Expansive clay
Clay-rich soils swell when they absorb water and shrink when they dry. Expansive clay is not uniform across the metro; it tends to appear in pockets, sometimes within otherwise sandy areas. Because it moves in both directions, it can lift a slab in one season and let it drop in another, producing cracks, raised joints, and stress on walls and doors.
Common responses include removing and replacing expansive soil beneath the slab with non-expansive fill, moisture-conditioning the soil before placement, using foundation systems designed for movement, and, above all, keeping moisture around the slab as consistent as possible.
Rio Grande valley alluvium
Along the valley floor, in places like the North Valley, Los Ranchos de Albuquerque, and Corrales, soils are generally river-deposited sandy and silty loams. Groundwater can be shallower here than on the mesas, and acequias and irrigation ditches are part of the landscape. Compaction can vary considerably, especially where old fields, ditch alignments, or fill have been reworked over the years.
Practical considerations include softer or variable bearing, seasonally wetter soils near irrigation, and the need for careful compaction and drainage. Flood-irrigated properties in particular benefit from planning around where water goes when the ditch runs.
Sandia foothill alluvial fans
Closer to the mountains, in areas like Tanoan and Albuquerque Acres, soils are often coarse alluvial fan deposits: decomposed granite, gravel, cobbles, and sometimes boulders. These soils often drain well and can provide good bearing, but they bring their own challenges.
- Excavation can turn up boulders that need to be removed and the voids backfilled and compacted.
- Lots are frequently sloped, which can mean cut-and-fill sites, where the fill side needs careful compaction.
- Arroyos and runoff paths can carry significant water during monsoon storms, eroding slab edges and undermining base.
- Slopes often call for retaining walls designed for the soil and drainage conditions.
Geotechnical reports: what they tell you
For foundation installation and structural slab foundations, a geotechnical report is often required, and it is valuable even when it is not. A geotechnical engineer samples and tests the soil and provides recommendations, which commonly address bearing capacity, collapse or swell potential, over-excavation depth, compaction requirements, moisture conditioning, and drainage.
The report is only useful if it is followed. When we review one, we are looking for those specific recommendations so they can be built into the scope. If you are comparing bids on foundation work, ask each contractor how they will address the report. Our contractor vetting guide has more on that.
Over-excavation and recompaction
One of the most common soil recommendations in the metro is over-excavation: digging below the bottom of the planned slab or footing, then replacing the soil in compacted lifts, often with moisture added to bring it to a target condition. The goal is to remove or neutralize soil that could collapse or swell, and to give the concrete a uniform, predictable base. The depth and extent are site-specific and should come from the engineer when one is involved.
Moisture management and irrigation discipline
Whatever is under your slab, water is usually what turns a stable situation into a problem. A few habits go a long way:
- Grade soil to slope away from foundations and slab edges.
- Extend downspouts and canales so roof water lands well away from concrete.
- Keep drip emitters and spray heads off slab edges; xeriscape plantings near the house help.
- Check irrigation for leaks, especially after winter and before the monsoon.
- Do not let water pond along driveways, patios, or foundation walls after storms.
When something has already moved
If a slab has already settled, concrete leveling can often lift it back toward grade and fill voids underneath, provided the slab is intact and the water source is corrected. Our guide to why concrete cracks helps you sort cosmetic cracks from movement that needs attention. And if you are planning new work, a site visit is the best way to understand what your ground will ask of it.