Foundation & Soil Terms

A community irrigation ditch system with roots in Spanish colonial New Mexico. Acequias introduce seasonal moisture into soils along their corridors, creating cyclical wet-dry patterns that drive foundation movement in adjacent properties. Homes near acequias in the Rio Grande Valley, Española Basin, and Mesilla Valley may experience seasonal heave or settlement tied directly to irrigation cycles rather than weather.

The depth of soil that experiences significant moisture change — and therefore significant volume change — in response to seasonal and long-term surface moisture conditions. Above the active zone, the soil wets and dries with the seasons. Below it, moisture content is relatively stable year-round.

The depth of the active zone is a critical design parameter for any deep foundation repair in expansive clay country. A pier that bears within the active zone is still subject to the uplift forces generated by the surrounding clay when it swells.

A foundation system using adobe brick or rammed earth, common in historic New Mexico construction. Behaves differently from concrete — more susceptible to moisture intrusion, erosion at the base, and differential movement. Repair approaches that work on conventional concrete foundations often do not apply directly. Evaluation requires understanding the original construction method and current condition of the adobe itself.

A fan-shaped deposit of sediment laid down where a stream or wash exits a mountain canyon and spreads across a flatter surface. In New Mexico, alluvial fans extend from every mountain range onto the adjacent basin floors.

Foundation implications vary by position on the fan: upper fans are typically granular and potentially collapsible; lower fans are finer-grained and more likely to contain clay.

Ground settlement caused by the removal of groundwater from an aquifer. When water is pumped from fine-grained sediments, the water pressure that was partly supporting those sediments is reduced and they consolidate.

In the Deming area of the Mimbres Basin, decades of agricultural pumping have produced measurable subsidence. Unlike most foundation movement, this is a regional process — it cannot be reversed by foundation repair.

The ability of soil or rock to support the load placed on it without failing or compressing excessively. Bearing capacity depends on soil type, density, moisture content, and load geometry.

In New Mexico, finding competent bearing often means getting through caliche, loose alluvial material, and active clay zones to reach stable material. The depth to competent bearing varies by location and is established by investigation.

A hole drilled into the ground to collect soil samples and measure soil properties at depth. Borings reveal what is actually in the ground below the surface.

Multiple borings are necessary in laterally variable environments where a single boring characterizes only one location in what may be a complex soil profile.

A hardened calcium carbonate layer found throughout New Mexico soils, formed over thousands of years as mineral-rich water evaporated near the surface. Caliche depth, thickness, and hardness vary significantly across the state — block by block in some Albuquerque neighborhoods. Often misread as reliable bearing material; a thin caliche layer over loose soil below is not a stable foundation. Drilling through caliche for pier installation requires equipment and experience specific to New Mexico conditions.

Soil that carries load adequately under dry conditions but consolidates — loses volume — when moisture infiltrates it. The open particle structure collapses when water dissolves the bonds between particles.

Collapsible soil is common across most developed basin floors and alluvial fan surfaces in New Mexico. A foundation stable for decades can begin moving within a season if moisture conditions change.

A ground improvement technique where low-slump grout is injected under pressure into the soil, compacting the surrounding material and filling voids. The grout forms a bulb that displaces and densifies the adjacent material.

Used when the problem is loose, poorly consolidated soil rather than a condition requiring piers to transfer load to deeper bearing.

A grading practice where soil is cut from high areas of a site and used to fill low areas before construction. The filled portion is often less compacted than undisturbed native soil, creating differential settlement risk as the fill consolidates over time. Common in New Mexico's hilly terrain and a frequent contributor to foundation movement in tract developments built on graded lots.

The permanent, static weight of a structure — the weight of framing, roofing, concrete, and all fixed components. Does not include variable weight of occupants, furniture, or snow.

Push piers use dead load to drive themselves to bearing. This is why push piers are problematic for most New Mexico residential construction: wood-frame homes do not have enough dead load to drive piers to adequate depth.

Settlement that occurs unevenly across a foundation — one part moves down more than another. The structural damage associated with foundation problems is almost always the result of differential settlement.

Diagonal cracking at door and window corners is the classic indicator. The crack geometry indicates which part of the foundation dropped.

Modifications to the grading, gutters, downspouts, or surface drainage around a structure to direct water away from the foundation. In New Mexico, where the majority of foundation movement is moisture-driven, drainage correction is often the most effective first intervention — and sometimes the only one needed. Not a structural repair, but frequently more useful than one.

The gradual dissolving of soluble underground minerals — primarily gypsum and halite (salt) — by groundwater movement. Common in eastern and southern New Mexico. As the mineral mass dissolves, voids form beneath the surface that can cause sudden settlement or sinkhole-like collapse. Not detectable by visual inspection; requires subsurface investigation.

A mineral deposited when a body of water evaporated and left its dissolved minerals behind. Common evaporite minerals include gypsum, anhydrite, and halite (rock salt).

Evaporites are soluble. Groundwater that contacts these formations dissolves them over time, creating subsurface voids — the primary foundation hazard in the Pecos Valley.

Soil containing clay minerals that swell when they absorb water and shrink when they dry out — repeating that cycle indefinitely. Volume change can be ten to fifteen percent between dry and saturated states.

A foundation bearing on expansive soil is pushed upward in wet conditions and drops back in dry conditions. The only reliable way to know if clay is present is to get into the ground at the specific site.

The initial and often most dramatic settlement that occurs when dry, loose soil receives significant moisture for the first time. Collapsible soils can maintain their structure for decades in arid conditions, then consolidate rapidly on first wetting from a plumbing leak, irrigation change, or heavy rain event. Common across the West Mesa, Estancia Valley, and Jornada del Muerto.

A systematic program of field and laboratory work to characterize the soil and groundwater conditions at a specific site — including what materials are present, how deep they extend, and how they behave under load and moisture.

A geotechnical investigation produces data, not a sales proposal. The repair decision follows from that understanding.

Upward movement of a foundation driven by expanding soil beneath it. The most common cause in New Mexico is expansive clay swelling as it absorbs moisture. Frost heave is also significant at higher elevations.

Heave is consistently misdiagnosed as settlement. Installing settlement piers on a heaving foundation pins the structure while the surrounding soil continues to push up, making the problem worse.

A steel shaft with one or more helical plates, installed by rotating it into the ground using hydraulic torque equipment. The helical plates advance the pier like a screw, allowing it to reach bearing depth without requiring the structure's dead load.

Helical piers are the correct residential pier solution for most New Mexico foundation work. Installation torque is monitored in real time and correlates directly to bearing capacity.

Settlement caused by the sudden collapse of loose, dry soil structure when moisture is introduced. The soil grains, held in an open arrangement by capillary tension when dry, lose that tension when wet and consolidate into a denser state. Distinct from gradual settlement — hydrocompaction can occur quickly and produce significant elevation change.

The lateral force exerted by water-saturated soil against foundation walls, basement walls, or crawlspace walls. In New Mexico, most relevant in areas with high water tables or poor drainage. Can cause wall bowing, cracking, and water intrusion independent of foundation settlement or heave.

The process of collecting soil samples, surveying the foundation, and analyzing movement to determine the appropriate response. In New Mexico, investigation is not optional — the soil varies too much to guess.

A desert basin in south-central New Mexico running roughly from Socorro to Las Cruces. Characterized by collapsible soils — fine-grained deposits that maintain structure when dry but consolidate rapidly when water is introduced. One of the higher-risk zones in the state for sudden settlement triggered by plumbing leaks, irrigation changes, or first-time wetting events.

Fine-grained sediment deposited at the bottom of an ancient lake. New Mexico's closed basins — the Estancia, the Mimbres, the Tularosa — held lakes during wetter periods of the Pleistocene.

Lacustrine clays tend to be highly expansive. They are often buried beneath younger, drier surface soils, meaning a foundation may have expansive clay at depth without any surface indication.

Significant changes in soil type, density, or bearing capacity over short horizontal distances — sometimes within a single foundation footprint. Common in river floodplains and alluvial fan margins.

In practice, lateral variability means a single boring does not characterize the site. The Hatch–Rincon Corridor is an example where lateral variability within a single lot is the rule.

A dark, clay-rich shale formation underlying much of northwest New Mexico, particularly the San Juan Basin and Four Corners region. Expands significantly when it absorbs moisture and shrinks when dry, producing some of the most pronounced foundation heave in the state. Frequently misdiagnosed as settlement because surface symptoms look identical — a critical distinction because the repairs are opposite.

A small-diameter drilled and grouted deep foundation element, typically 3 to 12 inches in diameter. Micropiles are drilled rather than driven, allowing them to penetrate hard rock, cobbles, and dense caliche.

Used when the soil profile requires reaching bearing at significant depth through materials that would prevent helical pier installation.

The movement of water through soil via capillary action, lateral flow, or vapor transmission. In foundation contexts, moisture migration can introduce water to soils that were dry at the time of construction, triggering expansion in clays or collapse in collapsible soils. Sources include irrigation, plumbing leaks, ponding surface water, and seasonal groundwater fluctuation.

The specific source of moisture that initiated or is sustaining foundation movement. Identifying the moisture trigger is the starting point for repair design in moisture-driven foundation problems.

Common triggers: landscape irrigation on previously dry soil, broken supply lines, roof drainage directed toward the foundation, and changes in surface grade that concentrate runoff.

A clay mineral with a layered atomic structure that absorbs water between its molecular layers, causing the mineral — and the soil containing it — to swell. Sodium montmorillonite is the most expansive form.

It is present in the Mancos Shale of the San Juan Basin, in basalt-derived soils on the Taos Plateau, and as a component of clay assemblages throughout New Mexico.

The horizontal wood member that sits on top of the foundation wall and anchors the structural framing. The transition point between concrete or masonry and wood framing.

In elevated-moisture environments, if water consistently reaches the mudsill, it will rot. A rotting mudsill produces the same visible symptoms as foundation settlement.

An honest assessment that no structural repair is warranted — sometimes the correct answer after evaluation. TLS Foundations recommends this when the evidence shows movement has stabilized or can be managed with drainage correction alone.

Settlement caused by buried vegetation or stumps decomposing over time, creating voids beneath foundations. Common on lots where trees were cleared and stumps buried rather than removed.

A structural element installed beneath a foundation to transfer load from a shallow footing to deeper, more competent bearing material. Piers are the primary structural repair tool in foundation work.

Piers solve a load-transfer problem — they do not address soil conditions causing movement unless those are specifically accounted for in the design.

A method of injecting expanding polyurethane foam beneath slabs, into soil voids, or along foundation perimeters to fill gaps, stabilize loose material, and restore elevation. Applied through small drilled ports with minimal excavation. Sometimes used for slab leveling, void filling, compaction trench remediation, and perimeter soil stabilization.

A steel pier installed by hydraulically jacking it into the ground using the weight of the structure as a reaction force. The pier is driven until the resistance at depth equals the capacity of the hydraulic ram.

Push piers are not appropriate for most New Mexico residential foundation work. Wood-frame homes do not generate enough dead load to drive piers to the depths required in our soil profiles.

A laboratory measurement that quantifies how much the water content of a soil can change while the soil remains plastic. A high plasticity index indicates a soil with high swell potential.

Plasticity index is a key parameter in swell potential assessment. In Mancos Shale evaluation, plasticity index testing is part of the standard investigation sequence.

A shallow, flat-floored depression in arid terrain that collects water after rain events and drains by evaporation rather than outflow. Common across eastern New Mexico and the High Plains.

Playas concentrate the most expansive material in the formation. A structure on or near a playa margin consistently sees more moisture-driven foundation movement.

The point at which a drill or pier cannot be advanced further due to encountering hard material like caliche or bedrock. Caliche refusal does not necessarily mean competent bearing has been reached — the hard layer may be thin.

A zone of active crustal extension running the length of New Mexico, where the earth's crust is pulling apart along a series of faults. The pulling-apart process dropped elongated basins while adjacent mountain ranges rose.

Those basins have been filling with sediment for millions of years, creating the thick sequences of alluvial fan deposits, river sediments, and lake beds that now underlie most of New Mexico's developed areas.

Downward movement of a foundation caused by compression or consolidation of the soil beneath it. Settlement can be uniform or differential.

The critical diagnostic distinction in New Mexico is between settlement and heave — both produce visible distress, but the correct repair for each is different. The wrong repair produces a worse outcome than the original condition.

A foundation system consisting of a concrete slab poured directly on the prepared ground surface, without a basement or crawlspace. The slab bears directly on the soil below it and is the dominant foundation type for residential construction in New Mexico.

When the soil swells, the slab heaves. When the soil consolidates, the slab settles. Differential movement across the slab produces cracking, floor tilt, and door problems.

Upward foundation movement caused by the formation of ettringite, a mineral that expands significantly when sulfate-bearing soils react with calcium in concrete. Common in areas with gypsum-rich soils and Mancos Shale. Distinct from standard expansive clay heave — the mechanism is chemical, not moisture-driven swelling — and requires different evaluation and repair approach.

The tendency of a soil to increase in volume when moisture is added, expressed as a percentage volume change or as the pressure the expanding soil can generate. Measured in the laboratory on undisturbed samples.

Swell potential drives helical pier design in expansive clay environments. A pier specified without accounting for uplift forces will be inadequate in high-swell-potential soil.

A laterally variable sedimentary formation in the Española Basin, with interbedded expansive clays and non‑expansive sands. Foundations in this formation often experience differential movement between adjacent areas of the same site.

The practice of continuously measuring the rotational resistance encountered during helical pier installation, and using that measurement to infer bearing capacity in real time.

Torque monitoring is the primary quality control method for helical pier installation and is essential in variable soil profiles where bearing conditions change significantly with depth.

The process of extending a foundation's support to deeper, more stable soil or bedrock. Accomplished through various pier systems — helical piers, push piers, micropiles — driven or drilled past unstable near-surface soils to reach material with adequate bearing capacity. The appropriate depth depends on local soil conditions and cannot be determined without investigation.

A soil sample collected in a way that preserves the natural structure, density, and moisture content of the in-place material — as opposed to a disturbed sample that has been remolded during collection.

Undisturbed samples are required for laboratory tests that depend on natural soil structure: consolidation testing, swell potential testing, and shear strength testing.

An open space in the subsurface created by the dissolution of soluble rock or soil, the decomposition of organic material, or the deterioration of mine workings. Voids represent the complete absence of bearing material at a given depth.

Dissolution voids have no surface expression while forming. A void growing beneath a foundation produces no visible indication until it is large enough to cause movement — or until its roof collapses suddenly.

Attempting to control soil moisture around a foundation. This is only appropriate for certain soil types; doing it on collapsible soil can cause settlement.